INFORMATION TO USERS
This manuscript has been reproduced from the microfilm master. UMI films the
tex- directly from the original or copy submitted. Thus, some thesis and
dissertation copies are in typewriter face, h i l e others may be from any type of
cornputer printer.
The quality of mis reproduction is dependent upon the quality of the copy
submitted. Broken or indistinct print, colored or poor quality illustrations and
photographs, @nt bleedthrough, substandard margins, and improper alignment
can adversel y affect reprodudion.
In the unlikely event that the author did not send UMI a cornplete manuscript and
there are missing pages, these will be noted. Also, if unauaiotized copyright
material had to be rernoved, a note will indicate the deletion.
Oversize materials (e.g., maps, drawings, charts) are reproduœd by sedioning
the original, beginning at the upper left-hand m e r and continuing from left to
right in equal sections with small overlaps. Each original is also photographeci in
one exposure and is induded in reduced fom at the back of the book.
Photographs included in the original manuscript have been reproduced
xerographically in this copy. Higher quality 6" x 9" black and white photognphic
prints are available for any photographs or illustrations appearing in this copy for
an additional charge. Contact UMI d i r d y to order.
Bell & Hawell Information and Leamino 300 North Zeeô R d , Ann A M , MI 481061W USA
-521-
Electric Furnace Slag Reduction,
Kamal Philippe EL-RASSI
December 1998
A thesis submitted in conformity w i t h the requirements for the
D e g r e m o f MASTER OF APPLSED SCIENCE
Graduate Depatbnent of Metallutgy and Materials Science in the University o f Toronto
@ Copyright by Kaaal Philippe EL-RASSI 1998
National Library of Canada
Bibliothèque nationale du Canada
Acquisitions and Acquisitions et Bibliographk SeMces services bibliographiques
395 Wellington Street 395. rue Wellington Otrawa ON K1A ON4 Ottawa ON KIA ON4 Caneda Canada
The author has granted a non- exclusive licence aliowing the National Library of Canada to reproduce, loan, distn'bute or sel1 copies of this thesis in rnicroform, paper or electronic formats.
The author retains ownership of the copyright in this thesis. Neither the thesis nor substantial extracts fiom it may be printed or otherwise reproduced without the author's permission.
Your ti& votre rëfwnce
Our 1Sle Narre réfdrenw
L'auteur a accordé une licence non exclusive permettant à la Bibliothèque nationale du Canada de reproduire, prêter, distribuer ou vendre des copies de cette thèse sous la forme de microfiche/fih, de reproduction sur papier ou sur format électronique.
L'auteur conserve la propriété du droit d'auteur qui protège cette thèse. Ni la thèse ni des extraits substantiels de celle-ci ne doivent être imprimés ou autrement reproduits sans son autorisation.
Electric Furnace Slag Reduction, AC versus DC
M.A.Sc. 1998 Kamal Philippe EL-RASSI
Department of Metallurgy and Materials Science University of Toronto
Abs tract
The production of nickel, copper, and cobalt is of great
importance to the Canadian economy. Hence, the recovery of these
valuable metals from discarded slags has a great economic
incentive. By improving the reduction of these slags, it will be
possible to increase the recovery of these valuable metals.
The objective of the present investigation was to measure
the rate of slag reduction during electric furnace smelting and
slag cleaning operations. Specifically, the reduction rate was
measured by direct CO,,, and COz,,, measurements with a gas
i n f rared analyzer.
The parameters investigated were slag temperature and
composition, current density, AC versus OC, electrode depth and
diameter, electrode separation, and electrode tip temperature
measurement for AC and DC currents. From the rate of slag
reduction and electrode consumption, a better understanding of
the reduction process was established.
ACKNOWLEDGMENTS
The a u t h o r t h a n k s D r . T o r s t e i n Ut igard for h i s advice,
s u p p o r t , and guidance th roughout t h e course o f t h i s
p ro j ect .
Spec ia l thanks is extended t o D r . Andrew Warczok f o r
h i s experimental and t e c h n i c a l support. Thanks a s well to
Mr. R.A . Bergman, and David Powell from t h e machine shop.
1 would a l s o like t o t h a n k my p a r e n t s P h i l i p and Adla
EL-RASSI and my b r o t h e r s f o r helping and s u p p o r t i n g me
through t h i s p r o j e c t .
The f i n a n c i a l s u p p o r t provided by t h e Center for
Chernical Process Metallurgy (CCPM) and the U n i v e r s i t y of
Toron to is g r e a t l y appreciated.
Table of Contents
TITLE PAGE
ABSTRACT
TABLE OF CONTENTS
LIST OF DATA TABLES
LIST OF FTGURES
LIST OF APPENDICES
NOMENCLATURE
1 INTRODUCTION
NICKEL ORE SMELTING
INCO THOMPSON SMELTER
ELECTRIC FURNACE OPERATION
ii
iii
iv
ELECTRIC FURNACE HEAT AND SLAG F u N c T ~ O N
2 LITERATURE REVIEW
vi
vii
X
xi
2.1 BOUDOUARD REACTION
2 . 2 OTHER RATE LIMITING MECHANISMS
2.3 FEO-CAO+ 102 AND F E O - C A O - S I O ~ - A L ~ O ~ SYSTEMS
2 . 4 MECHANISMS AND KINETICS OF FEO ~ D U C T I O N
2.5 AC VERSUS DC FURNACES
2 - 6 REDUCTION OF FEO SLAG WITH C tsl AS S A R M A ~ ~ PROPOSED
2 . 7 FEO REDUCTION MECHANISM ACCORDING TO FUN^^
2 . 8 RESULTS OF DAL, LI , AND G R I M S E Y ~ ~
3 EXPERIMENTAL TECHNIQUE
4 RESULTS
4 - 1 AC POWER AND TEMPERATORE IN ELECTRIC FURNACE SLAG
4 - 2 ELECTRIC FURNACE SLAG, AC EXPERIMENTS 4 ,7 , AND 8
4 . 3 CONVERTER SLAG, AC EXPERIMENTS 5,6, AND 9
4 - 4 ELECTRIC FURNACE SLAG, DC EXPERIMENTS 10-14, AND 20
4 . 5 CONVERTER SLAG, DC EXPERIMENTS 15-19
4 . 6 CONVERTER AND ELECTRIC FURNACE SLAG ELECTRODE SEPARATION
EXPERIMENTS 2 1-2 5
4 . 7 ELECTRODE TIP TEMPERATURE MEASURMENTS, AC AND DC
4 . 8 EXPERIMENTAL AND THEORETICAL CARBON CONSUMPTION
5 DISCUSSION
6 CONCLUSIONS AND RECOMMENDATIONS
7 REFERENCES
List of Data Tables
Table Number Title Page
Table 4.2
Table 4.3
Table 4.4
Table 4.5
Table 4.6
Table 4.7
Table 4.8
Table 4.9
Table 4.10
Table 4.11
Table 4.1 INCO slag samples and experimental reduction
sample analysis 38
AC power and temperature steady state data
in electric furnace slag 3 9
AC experimental steady state data in
electric furnace slag
AC experimental steady state data in
converter slag
DC experimental steady state data in
electric furnace slag
DC experimental steady state data in
converter slag
Electrode separation DC steady state
data in electric f u r n a c e slag
Electrode separation DC steady state
data in converter slag
Electrode tip temperature experiments
steady state data summary
Experimental and theoretical graphite
consumption
Experimental and electrolysis rates of
reduct ion 101
Table A2
Table B1
Table B2
Table Al Experimental slag samples, Thompson Smelter,
INCO Limited
Calibration data for the Omega N2 FlowMeter
AC current data sample, 04 May T E F l EXP3
Data sample reduct ion calculation analysis
List of Figures
Figure Number T i t l e Page Number
Figure 1.1
F i g u r e 1 . 2
Figure 1 .3
Figure 2.1
Figure 3 .1
Figure 3.2
Figure 3.3
Figure 3 . 4
Figure 3 .5
Figure 3 .6
Figure 4 . 1
F i g u r e 4 .2
F i g u r e 4.3-9
F i g u r e 4.10-11
F i g u r e 4.12-14
Figure 4.15
INCO Thompson Smel te r Flowsheet 3
Roast Smelting Process 1 0
E l e c t r i c Furnace Cross S e c t i o n 11
Schematic of F e 0 Reduction with Carbon 22
Experimental Setup Apparatus 30
Elec t rode Tip and Thermocouple 31
Elec t rode Sepa ra t ion Apparatus 32
Cooling Cap Design, Part 1 33
Cooling Cap Design, Part 2 34
Cooling Cap Design, P a r t 3 35
AC, E l e c t r i c Furnace S l a g Steady State
Data 4 0
AC, Increas ing Voltage S e t p o i n t 4 1
AC, E l e c t r i c Furnace S l ag , Power, %CO,
%COz, Current Density, Slag Temperature,
and Rate of Slag Reduction 45-51
AC, Electric Furnace Slag , Slag
Temperature, and Rate v e r s u s Power,
and Arrhenius P l o t 52-53
AC, Converter Slag, Power, %CO, %CO2,
Curren t Density, S l a g Temperature, and
Rate of S l ag Reduction 57-59
AC, Converter Slag, Slag Temperature and
Rate versus Power 60
Figure 4.16 AC, Converter Slag, Arrhenius Plot 61
Figure 4.17 No Electrode P o w e r , Furnace and Electric
Furnace s l a g Temperature Profile 65
F i g u r e 4.18-1 9
Figu re 4.20-22
F i g u r e 4.23-24
F i g u r e 4 .25
F i g u r e 4 . 2 6-28
F i g u r e 4.29-30
F i g u r e 4.31
F i g u r e 4.32-33
F i g u r e 4 . 3 4
F i g u r e 4 .35
F igure 4.36
F i g u r e 4.37
F i g u r e 4 . 3 8
DC, Electric Furnace S lag , Power, %CO,
%COz, C u r r e n t Densi ty , S l a g Temperature,
and Rate o f S l a g Reduction 66-67
DC, E l e c t r i c Furnace S l ag , S l a g
Temperature and Rate versus Power,
and Ar rhen iu s P l o t 68-70
DC, Conve r t e r S l ag , Cu r r en t , Vol tage ,
Power, %CO, %CO2, S l a g Temperature, and
Rate of S l a g Reduct ion 73-74
DC, Conve r t e r S lag , S l a g Temperature and
Rate versus Power, and A r r h e n i u s P l o t 7 5
C o n v e r t e r S l a g , Anode / Cathode S e p a r a t i o n ,
%CO, %COz, Cu r r en t , Vol tage , Ra te o f
Reduct ion, and S l a g Temperature 80-82
Electric Furnace S l ag , Anode / Cathode
S e p a r a t i o n , %CO, %CO2, Cu r r en t , Vol tage , Rate
o f Reduct ion, and S l a g Temperature 83-84
Conve r t e r S l a g , DC E l e c t r o d e S e p a r a t i o n ,
Rate, Power, C. D . , and Slag Temperature 85
Electric Furnace S lag , DC E l e c t r o d e
S e p a r a t i o n , Rate, Power, C.D., and S l a g
Temperature 86-87
AC, E l e c t r o d e T i p Temperature, Electric
Furnace Slag 92
AC, E l e c t r o d e T ip Temperature and S l a g
Temperature f o r Conve r t e r S l a g 93
DC, E l e c t r o d e T i p Temperature for Anode
and Cathode, S l a g Temperature for Electric
Furnace Slag 94
AC / DC, G r a p h i t e Consumption Cornparison 99
AC / DC, Composit ion % versus N i , Cu, C o and
P e r c e n t N i and Co versus Fe3Q4 for AC 100
vüi
Figure 4 .39 DC, Electrolysis contribution for the
Rate of Reduction in Converter and Elec t r i c
Furnace Slags 102
Slag Reduction Rate Wnder Di f f e ren t
Conditions, Slag Temperature = 1250 OC,
C u r r e n t D e n s i t y = 2 . 5 ~crn-*
DC and AC Reduction Rates versus Slag
Temperature
No Power, Reduction R a t e versus Slag
Temperature
F i g u r e 5.1
F i g u r e 5.2
F i g u r e 5 . 3
Appendices
Appendix Number T i t l e of Sections Page
Appendix A: Experimental slag samples analysis
from INCO Limited, Thornpson Smelter
Slag graphite contact-area calculations
Fun's reduction mode1 development
Some important definitions
Nitrogen flow calibration procedure
Othe r calibration graphs
Electric furnace circuit diagram
Experiments detail calculations
Appendix 5:
Appendix C:
Appendix D:
Appendix E:
Appendix F:
AC current data sample
Data sample reduction caiculation
AC, Electric furnace experimental graphs
Converter slag experirnental graphs
DC, Electric f u r n a c e experimental graphs 1
DC, Converter slag experimental graphs
DC, Anode / Cathode separation graphs for
electric furnace and converter slags
Appendix G: AC, Electrode Tip Temperature graphs 1
Pictures : Experimental and apparatus pictures
Nomenclature
a t m
I . D .
min
m o l
O.D.
R
ROR
Meaning
slag
equivalent to, explanations, units
area in m2 or Ampere
atmosphere
current density (~crn-*)
activation energy
exponential
gas
height
c u r r e n t , Ampere
inside diameter
joules
kelvin degrees
kilo j ou le s
liquid or liter
meter
metal
minute
mole
outside diameter
resistance (ohm), or gas constant
rate of reduction (mol Oz / min c m 2 )
second
s o l i d
converter slag (INCO, Thompson)
electric f u r n a c e slag (INCO, Thompson)
thickness
weight
INTRODUCTION
1.1 N i c k e l Ore Smelting
Nickel i s p re sen t i n p y r r h o t i t e (FeS) , Cha lcopyr i t e
(CuFeS*) , and Pen t l and i t e ( (Fe.Ni) +Sa) o r e s . Ore smelting
s t a r t s by adding water t o t h e o r e and c r u s h i n g i t wi th
s teel rods o r b a l l s t o l i b e r a t e t h e s u l f i d e m i n e r a l s from
the rock. The second s t e p is s e p a r a t i n g t h e pu lp mix ture
of rock, Fe, Cu , and N i s u l f i d e p a r t i c l e s . P y r r h o t i t e
p a r t i c l e s w i l l respond t o t h e p o l e s o f t h e magnetic drums,
and t h e n f l o t a t i o n is used t o sort o u t t h e remaining
mixture o f p e n t l a n d i t e , c h a l c o p y r i t e , and rock p a r t i c l e s .
Through f l o t a t i o n , c h a l c o p y r i t e w i l l f l o a t f i rs t ,
p e n t l a n d i t e nex t , and w a s t e rock is l e f t i n t h e tank.
A f t e r f l o t a t i o n , p e n t l a n d i t e c o n c e n t r a t e is d r i e d and t h e
c o n c e n t r a t e i s now 6 t o 10 wt% N i . Within t h e p a r t i c l e s ,
t h e chernical bond of t h e l a t t i c e p a r t i c l e s i s s t i l l i n t a c t ,
unbreakable w i t h mechanical means.
Roas t ing of t h e p y r r h o t i t e t o Fe0 is t h e lSt s t e p i n
t h e s m e l t i n g process . ~ ~ r r h o t i t e is oxidized in t h e
r o a s t e r , and FeS w i l l p rov ide fuel f o r the c o n c e n t r a t e t o
roast i t s e l f ; by t h e end, much of t h e Fe w i l l have changed
t o FeO. T h e r o a s t e d c o n c e n t r a t e is smelted i n t h e electric
fu rnace and i r o n ox ide combines with t h e Si02 f l u x and rises
with the unwanted s l a g . The dense s u l f i d e phase sinks and
t h e mol ten s lag rises t o t h e top. Removing t he remaining
i r o n from t h e va luab le molten s u l f i d e s is t h e r o l e o f t h e
c o n v e r t e r s . I n t h e converters, oxygen in the blast
Chapter 1, Page 1
o x i d i z e s t h e FeS and the çnergy of t h i s r e a c t i o n keeps t h e
bath mol ten .
The o x i d i z e d i r o n combined w i t h t h e added f l u x i n g
agent forms s l a g . The molten s o l u t i o n of N i , Cu, S, and
p r e c i o u s m e t a l s i s poured i n molds t o c r y s t a l l i z e . A s t h e
m a t t e c o o l s , t h e lst c r y s t a l s that beg in t o form are CuS,
slow cooling a l l o w s more Cu and S t o m i g r a t e and t h e s e
c r y s t a l s i n c r e a s e in size. F i n a l l y , the rnatte c o o l s t o a
s t a t e where t h e NiS c r y s t a l l i z e s locking i n CuS and
metallic c r y s t a l s .
The r e s u l t is a s t r u c t u r e wi th we l l - de f i ned g r a i n s
large enough t o be r n e c h a n i c a l l y separated. M e t a l l i c
c r y s t a l s can be magnetically removed, CuS most r e s p o n s i v e
t o f l o t a t i o n c a n be skimrned from t h e t o p , and wha t remains
is t h e NiS. The NiS i s r o a s t e d t o rernove t h e s u l f u r . From
h e r e on, N i is r e ady for some commercial p r o c e s s e s . I f
more p u r e N i i s r e q u i r e d , t h e n ' f u r t h e r r e f i n i n g i s
required, and e l e c t r o l y s i s i s employed.
1.2 INCO Thompson Smelter
Nickel and o t h e r products a r e e x t r a c t e d a t t h e INCO
Thompson Smelter l o c a t e d north o f Winnipeg, Manitoba,
Canada. The smelter c o n s i s t s of fluid bed r o a s t e r s , and
e l e c t r i c f u r n a c e s for treating t h e n i c k e l s u l f i d e
c o n c e n t r a t e s as shown in Figure 1.1. The metallurgy of t h e
c o n v e r t i n g process i n t h e Thompson Smelter is documented
f u l l y by ~ i a k o w ' et al.
Some typical n i c k e l matte smelting reactions:
Chapter 1, Page 2
2 FeS + 3 O2 + S i 0 2 + Fe2Si04 + 2 S02(gl (1-1)
Ni,Cu,Co-(su l f ides ) + O2 + Ni,Cu,Co-(oxides) + SOÎlg l ( 1 . 2 )
3 FeS + 5 O2 + Fe304 + 3 S02(g) ( 1 - 3 )
3 Fe304 + FeS + 5 SiO2 + 5 Fe2Si04 + S021g) ( 1 . 4 )
Ni,Cu,Co- ( o x i d e s ) + FeS + S i 0 2 + N i , Cu, Co- ( s u l f i d e s ) + FezSi04 + SOz (1.5)
The r o a s t e r s desulfurize the c o n c e n t r a t e s by o x i d a t i o n
of h a l f the i r o n s u l f i d e t o iron oxide. The smel ted
s u l f i d e s o f N i , Cu, Co, and F e are t h e n removed a s fu rnace
matte and transferred t o the Peirce-Smith air blown
c o n v e r t e r s . T h e c o n v e r t e r s remove t h e i r o n by s e l e c t i v e
o x i d a t i o n t o produce t h e f i n a l smelter produc t , a 75%
n i c k e l c o n t e n t matte. Al1 t h e s l a g samples used f o r t h e
p r e s e n t i n v e s t i g a t i o n are from t h e INCO Thompson Smel te r .
1.3 Electric Furnace Operation
Electr ic fu rnaces a r e widely used t o srnelt o r e s and t o
r ecove r v a l u a b l e m e t a l s from n icke l and copper c o n c e n t r a t e s
and produce molten mat te , molten s l ag , CO(,), CO219) and S02(,I
gaçes . Fa lconbr idge ~ i r n i t e d ~ and JNCO Limited c u r r e n t l y
p r a c t i c e electric fu rnace sme l t i ng in Canada.
I n t h e e l e c t r i c furnace submerged e l e c t r o d e process ,
heat i s generated by t h e passage of electric c u r r e n t
through the mol ten slag between t h e submerged carbon
e l e c t r o d e s . I t offers a h i g h throughput capacity and a
srna11 p r o d u c t i o n o f off-gases3 with a low SOr(,,
c o n c e n t r a t i o n i n the off-gas. The calcine reduct ion and
Chapter 1, Page 4
smelting in an electric furnace yields a sulphur deficient
matte. Sulphur deficient matte4 is defined with respect to
the stoichiometric amount of s u l p h u r required for cornbining
al1 of t h e iron, nickel, copper, and cobalt in the matte as
their respective sulphides, FeS, N i 3 S 2 , Cu2Sr and COS.
Slag from smelting of nickel concentrate contains
rnainly fayalite (2FeO. SiOÎ) , magnetite (Fe i04) , lime (Cao) , rnagnesia (MgO) , metal sulphides, and alumina. Depending on
the smelting conditions, slag composition varies
s i g n i f icantly. Thompson smelter nickel slags typically
contain about 37% FeO, 38"ai02, 8% Fe304, 0.24% Ni, 0.05%
Cu, 0.07% Co, 7.3% A1203, 2.6% Cao, and 2% MgO.
Figure 1.2 shows a simplified flow s h e e t of the roast
smelting process, while Figure 1.3 is an i m m e r s e d g r a ~ h i t e
electrode process, w h e r e roasted concentrates are added on
the top of the calcine banks. Electrodes tips are immersed
in the slag bath, and resistance heating of the molten slag
liberates electrical energy4.
When the electrodes are immersed in the molten slag
layer, and a current is passed, the temperature of the slag
increases and smelts the charge. Energy is absorbed in
superheating the molten slag surrounding the electrode
tips, and the slag superheat is utilized in smelting the
charge-. Therefore, a d j u s t i n g the electrodes position and
the power density controls slag and matte temperatures.
T h e refractories in some smelters are protected by water
cooling the side-walls where f r o z e n slag layer forms.
Chapter 1, Page 5
S i n c e carbon from t h e e l e c t r o d e s react with oxygen in
the slag to from CO and COz gases, t h e r e f o r e t h e electrodes
are p r o v i d i n g a mean t o r e d u c e t h e s l a g . However, t h i s is
an expens ive source o f ca rbon and ideally, most o f the
r e d u c t i o n shou ld be due t o any added coke powder.
Cornmonly used reducing agen t s5 a r e carbon, carbon monoxide,
CO,,,-hydrogen mix tu re , hydrogen, and some m e t a l s such a s
p ig - i r on , ferro s i l i c o n , a n d aluminum.
1.4 Electric Furnace Boat and Slag Function
An e l e c t r i c furnace5 is a r e s i s t a n c e f u r n a c e w i t h t h e
e l e c t r o d e s dipped i n t o t h e slag that forms the resistance . Heat i s p roduced i n t h e s l a g by t h e e lec t r i c c u r r e n t
accord ing t o t h e power formula I ~ R . Heat t r a n s f e r iç from
t h e slag, t o t h e charge , t o t h e gas, and it is p a r t l y by
direct c o n t a c t b u t m o s t l y by convec t ion .
Near t h e e l e c t r o d e s t h e s l a g moves upwards because o f
t h e mic ro a r c s and t h e f o rma t ion of CO from t h e r e d u c t i o n
of i r o n oxides by t h e ca rbon from t h e e l e c t r o d e s . A t t h e
surface, this h o t slag moves towards t h e c o o l e r w a l l s ,
t r a n s f e r r i n g p a r t of i t s h e a t by convec t i on t o t h e cha rge .
I n a n electric f u rnace , t h e s l ag f u n c t i o n s are t o f l u x
t h e gangue, and t o ca r ry the c u r r e n t . The s l a g fluxes t h e
gangue (main ly i r o n ) by forming f a y a l i t e (2Fe0.Si02) and it
i s t h e chief r e s i s t a n c e t o the f low o f electric c u r r e n t .
L iqu id silicates d i s s o c i a t e i n t o c a t i o n s ~ e ' + and silicate
a n i o n s . Anions have large i o n i c radi i , and t e n d t o form
c h a i n s which i n c r e a s e s t h e viscosity of t h e s l a g with
Chapter 1, Page 6
increasing a c i d i t y . Whereas cations with small radii,
mainly ~ e " , conduct the current (ionic conductivity), and
large cations like ca2+ a l t e r t h e conductivity.
1.5 Electric Furnace Pexformance
The overall heat efficiency of an electric furnace
depends on many factors. Most importantly, current
density, distance between the electrodes, distance between
the electrodes and the matte surface, and specific
resistance of the slag. Specific resistance is determined
by the composition of the slag and the raw rnaterials.
Also, the performance of the electric furnace depends
g r e a t l y on the amount and type of reductant used.
Efficient reduction is required to maintain high
r e c o v e r i e s . Increased coke additions are beneficial to
control slag losses of Ni, Cu, and Co, but this is limited
in relation to fu rnace temperature, and matte saturation to
metallic form. If the sulphur content of matte falls4 below
25%, an iron-nickel rich alloy precipitates at 1050 OC, and
this causes a metallic buildup on the furnace hearth.
Excessive buildup may lead to disturbances in the
operation, by decreasing the working* volume of the electric
furnace. Recent electric furnaces2 are rectangular with six
equally spaced self-baking carbon electrodes. Usual ly it
c o n s i s t s of two matte water-cooled tap h o l e s . The
electrodes are consumed in the furnace; the power and
current are approximately 30 MVA and 50 kilo-amperes2 per
phase respectively.
Chapter 1, Page 7
1.6 Coke Addltion
In order to obtain high metal recoveries, coke
additions should be made to the fumace. The addition of
coke to the charge provides a reductant for ferric and
f e r rous iron. This leads to metal saturation4, and a solid
Fe-Ni-Cu-Co alloy precipitates from the rnelt.
The alloy composition in equilibrium with liquid
matte, is a function of the oxygen potential that decreases
with coke additions. It is desirable to operate as close
as possible to the metallic saturation boundary. This
boundary represents a condition of low oxygen potential, at
which slag losses of dissolved cobalt and nickel are at
their lowest levels.
1.7 Izon Oxide Reduction Pxocess
The degree of iron oxide reduction in molten slag is
related to the amount of valuable metal recovery. Hence,
the reduction mechanism of iron oxide by carbon is of great
importance and will be discussed in detail. From the
amount of Iiterature available, and the continuous research
from the steel-making industry, one can readily see the
importance of the molten slag reduction mechanism.
The controlling stage(s) of the overall reduction
process of Fe0 from various slags using graphite or
saturated iron is currently s t i l l being discussed. Mass
transfer in the slag, the Boudouard reaction, chemical
diffusion in the slag phase, interfacial adsorption and
Chapter 1, Page 8
desorption reactions, nucleation of gaseous and metal
products, have al1 been suggested as rate limitations. In
general, reduction reactions follow the generalized scherne
outlined below:
1.8 This Investigation
Tests have been carxied out to measure the reduction
rate of both oxidizing (>25% Fe304) and reducing (<IO% Fe304)
nickel slags from the Thompson smelter, a property of INCO
limited. Available slag samples were electric furnace slag
and converter slag. The slag reduction rate was rneasured
and compared under various conditions.
AC
d e p t h ,
cathode
c u r r e n t , DC current, slag temperature, electrode
and electrode diameter were varied. The anode and
electrodes were separated, and an infrared gas
analyzer rneasured the-CO and CO2 gases generated. This was
accomplished with the aid of an alumina tube ( I . D . = 2.5
cm, length = 250 cm) around the electrode. In addition,
the temperature at the tip of the submerged electrode(s)
was successfully measured.
Chapter 1, Page 9
Roast Smelting Process
Flux (SiO,) 1 O f f Gas so,, CO,, CO
Flux ( S i O , )
CONVERTER
Off Gao, SO,
Calcine
O f f Cas, SO,
Figure 1.2, Page 1 O
Electric Furnace Cross Section
ELECTRODE Calcine
' Fe304 or metal build-up I
Figure 1.3, Page 11
2 -1 Boudouard Reaction
Various authors6-9 have concluded that the Boudouard
reaction is the rate-limiting step in the reduction of
liquid iron oxide from slags.
Warczok and u t iga rd7 reduced synthetic f ayalite
(2Fe0.SiOz) slags from 1250 to 1450 OC, and deduced that the
rate of reduction increased with increasing temperature,
and increasing magnetite ( % Fe304) content. Fayalite slag
reduction rate was reported as a rate of oxygen removal
based on nitrogen f lowrate, CO(,, , and CO2(,, concentration.
~ote(+) = 5.39 XI 06exp[ - 29600 kJ
] ; EA ~246129- m-.s T,K, mol
This activation energy compares weli with previously
reported values.
Soma and sasakis reduced liquid i r o n oxide
submerged block of graphite. Krainer et a l 9 reduced
SiO2-Ca0 and FeO-SiO2
thermobalance. The
conclusion was made
generated was close
calcuLati~ns(~*~'.
slags in graphite crucibles kept
Boudouard reaction rate limiting
because the CO;CO~ ratio of the
by a
FeO-
in a
step
gases
to that predicted by thermodynamic
Chapter 2, Page 12
2.2 O t h e r Rate Limiting Mechanisms
Shalimov e t alIo s t u d i e d t h e r e a c t i o n k i n e t i c s of FeO-
S i02 melts w i t h s o l i d carbon, by mon i to r i ng t h e weight l o s s
w i t h t i m e . The i n f l u e n c e of temperature (1300-1450 OC),
pressure (0.1-2 a tm) , and c o n c e n t r a t i o n dependence o f F e 0
(60-100%) were i n v e s t i g a t e d .
I t was conc luded that CO and CO2 d i f f u s i o n in the gas
does n o t c o n t r o l t h e o v e r a l l process. I n a d d i t i o n , the
increase i n the r e d u c t i o n r a t e with ove ra l l p r e s s u r e does
n o t suppo r t t h e idea that d i f f u s i o n i n gas c o n t r o l s t h e
p r o c e s s . The a c t i v a t i o n energy f o r r e d u c t i o n was 190
kJ/mol, and t h e adsorpt ion-chernica l s t e p a t t h e slag-gas
boundary was t h e c o n t r o l l i n g stage.
Yerçhov and ~ o ~ o v a " reduced FeO-Si02 s l a g s w i t h 10-mm
diameter g r a p h i t e r ods . The r a t e s o f r e a c t i o n s 2 . 5 and 2 . 6
were determined by a r o t a t i n g specimen t e chn ique . I t was
shown that t h e i r o n o x i d e r e d u c t i o n i n mol ten s l ag , obeys
mass t r a n s p o r t laws a t high F e 0 c o n t e n t 40-60%, and obeys
d i f f u s i o n laws a t low Fe0 c o n t e n t 10-20%.
Pazdnikov e t al1* determined t h e ra te o f r e d u c t i o n of
i r o n ox ide by carbon monoxide i n CuzS-FeS-Fe0 m e l t s .
Chapter 2, Page 13
Samples were prepared from pure s u l p h i d e s o f copper and
i r o n w i t h additions of w u s t i t e . It was demons t ra ted t h a t
the r e a c t i o n p roceeds by d i f f u s i o n , where t h e rate o f
reduct ion o f iron ox ide increased w i t h i n c r e a s i n g Cu2S and
F e 0 c o n c e n t r a t i o n s i n t h e m e l t .
2.3 Fe0-Cao-Si02 and Fe0-Cao-Si02-A1203 Sys tems
un'^ reduced Fe0-Cao-Si02 slags i n a magnesia c r u c i b l e
a t 1650" 35 OC wi th a g r a p h i t e rod as the r e d u c t a n t . The
r e d u c t i o n rates span three p o s s i b l e stages. F i r s t o r d e r ,
second o r d e r , and f i n a l l y 1.77'" o r d e r w i t h r e s p e c t t o 1.5%,
15%, a n d 40% Fe0 c o n t e n t respectively. The observed rates
were between t h e rates o f the chemically limited g r a p h i t e
g a s i f i c a t i o n , and t h e rates p r e d i c t e d from molecular
d i f f u s i o n .
Reduc t i on r a t e of Fe0 from Ca0-SiO2-A1203 s l a g s , i n
g r a p h i t e crucible with less than 5% Fe0 at 1430 O C was
rneasured by ~ h i l b r o o k and ~ i r k b r i d e ' ~ . The r a t e was
p r o p o r t i o n a l t o t h e second o r d e r of Fe0 c o n c e n t r a t i o n i n
the slag, s i r n i l a r to Funr s13 f i n d i n g . Ozawa e t al1',
de t e rmined the rate of r e d u c t i o n o f Fe0 w i t h d i f f e r e n t
rates and types of coke a d d i t i o n s . For cokes o f h i g h e r
v o l a t i l e c o n t e n t (Hz, N2), t h e reduction was c o n t r o l l e d by a
chernical r e ac t i on . For coke of lower v o l a t i l e c o n t e n t , the
reduction was c o n t r o l l e d by Fe0 t r a n s p o r t . I n a d d i t i o n ,
t h e r educ t ion ra te in.creased as t h e basicity (CaO/Si02) of
molten slag increased.
Chapter 2, Page 14
Sarama et a116 reduced Fe0-Cao-SiO2-A1203 s l a g s by
graphite, coke, and c o a l . A gas film ( s e p a r a t e d the solid
carbon £rom the molten slag) was observed by a n X-ray
f l uo roscopy technique. Because the r e a c t i o n r a t e i n c r e a s e d
with e x t e r n a l stirring, they concluded that d i f f u s i o n of
Fe0 ( ~ e ~ + and 02- i o n s ) frorn the s l a g t o t h e s lag-gas
i n t e r f a c e , was one of t h e rate l i m i t i n g s t e p s f o r the
o v e r a l l reduction r e a c t i o n .
Utigard et al" reduced commercial copper slags us ing
carbon monoxide. T h e r e s u l t s show t h a t the r e d u c t i o n r a t e
i n c r e a s e s w i t h increasing i n j e c t i o n dep th and s l a g
t empera tu re . The rate was determined as a f u n c t i o n of
temperature and CO(,I pressure, and the activation energy
was estimated.
2 . 4 Mechanisms and Kinetics of Fe0 Reduction
~ o r ~ i a n n i " reduced rnolten slags rich i n iron oxide
( 8 0 % ) b y coke. A g r a p h i t e c r u c i b l e was used and the weight
loss was recorded cont inuous ly . The growth of iron n u c l e i
was shown t o be either chemical ( r e a c t i o n s 2.3-2.41, o r
e l e c t r o c h e m i c a l ,
T h e r a t e -de t e rmin ing s t e p was related t o t h e n u c l e a t i o n o f
i r o n and t o t h e chemical reaction, u n t i l free oxygen i o n s
are present i n the slag.
Chapter 2, Page 15
Sommervi l le e t a1'19'20' s t u d i e d t h e k i n e t i c s of i r o n
o x i d e (< 5%) r e d u c t i o n by c a r b o n i n s l a g , a n d c o n c l u d e d
t h a t o n l y t h e gas -ca rbon r e a c t i o n was r a t e c o n t r o l l i n g .
The c o n c e p t of t h e e x i s t e n c e o f g a s bubbles a t t h e slag-
m e t a l i n t e r f a c e was d e v e l o p e d . They deduced t h a t t h e rate
c o n t r o l l i n g r e a c t i o n i s t h e gaseous d e c a r b u r i z a t i o n of
i r o n . The proposed mechanism was t h e same a s Shal imov e t
al'' w i t h t h e slag-gas in te r face d iv ided i n t o two steps:
where +,la, represents a vacant s i t e a v a i l a b l e for the
a d s o r p t i o n o f oxygen on t h e s l a g s u r f a c e . Reaction 2 . 4 ,
t h e g a s - g r a p h i t e i n t e r f a c e , is a l s o t h e sum of two s t e p s :
where r e p r e s e n t s a vacant s i t e a v a i l a b l e for the
a d s o r p t i o n of oxygen on t h e metal s u r f a c e , t h e a c t u a l t e r m
u s e d was d i s s o c i a t i v e che rn i so rp t ion .
Channon e t al2' s t u d i e d t h e mode o f current t r a n s f e r
be tween e l e c t r o d e s and s l a g i n a submerged arc f u r n a c e .
The current f low f rom the graph i t e e l e c t r o d e t o t h e m o l t e n
s l a g obeyed ohrnrs law for c u r r e n t d e n s i t i e s < 12 ~ / c r n ~ . A t
h i g h e r c u r r e n t d e n s i t i e s , w i t h t h e g r a p h i t e e l e c t r o d e s
immersed i n t h e molten slag, arcing o c c u r r e d c a u s i n g a n
imbalance i n t h e rate o f h e a t i n g i n t h e furnace.
Chapter 2, Page 16
O
Arcing occurred due t o extreme l o c a l i z e d hea t ing a t
the t i p of t h e e l ec t rodes , l ead ing t o an increase i n t h e
r e a c t i o n r a t e , r e s u l t i n g i n t h e formation of gaseous
products , CO and S i O . Arcing is not d e s i r a b l e i n large
sme l t ing furnaces designed f o r r e s i s t a n c e heat ing. A s
a r c i n g occurs a t a cons tan t v o l t a g e supply, t h e r e s i s t a n c e
of t h e system i n c r e a s e s r e s u l t i n g i n a lower c u r e n t , hence
t h e t o t a l power d i s s i p a t e d i n the c i r c u i t will decrease.
2 . 5 AC Versus DC Furnaces
The comparison update by ~ o w r n a n ~ ~ for AC and DC
f u r n a c e s stated t h a t the e l e c t r i c a l o p e r a t i o n of a DC
furnace i s cons iderably e a s i e r t h a n AC. With DC f urnaces,
e l e c t r i c a l l o s s e s were higher bu t not by much, and
e l e c t r o d e consumption was much less. It was not p o s s i b l e
t o compare t h e energy consumption d u e t o t h e v a r i a t i o n i n
the d a t a from d i f f e r e n t furnaces .
Da1 e t reduced n icke l s l a g by g r a p h i t e e l e c t r o d e s
w i t h AC and DC c u r r e n t s . Reduction with DC was more
effective and enhanced the recovery of pay metals. I t was
proposed t h a t reduct ion under AC occurred with t h e
format ion of a s o l i d iron a l l o y a t t h e s lag-gas i n t e r f a c e ,
fol lowed by a secondary reduct ion of the b u l k s l a g by i r o n .
Under DC cond i t ions , e l ec t ro -depos i t ion of pay meta ls
seemed t o be t h e dominant process , e s p e c i a l l y a t h i g h power
i n p u t s .
Chapter 2, Page 17
2 .6 Reduction of Fe0 Slag w i t h Ci., as sarma16 Proposed
FeO(il i s d i s so lved i n the s l ag and [Fe-C,] means carbon
is dissolved in the iron product. Reaction (2.12) consists
of four phase s where the gas film separates the molten s l ag
from s o l i d ca rbon , and the reaction proceeds w i t h the aid
of gaseous i n t e r m e d i a t e s .
E'eO(l, + (1 + x ) C I s I = [Fe-C,) + CO(,, (2.13)
Fe(,] + x CI,, = [Fe-C,] ; iwon-carbon alloy ( 2 . 1 4 )
The overall reduct ion p r o c e s s can be schematically
represented by F igure 2.1 where equations 2.3, 2.4, and
2.13 resurnes as follows:
Diffusion of Fe0 [ ~ e ~ ' and 02- i o n s ] from t h e b u l k of the
s l a g t o the slag-gas interface
Chemical r e a c t i o n at the slag-gas interface
Diffusion of carbon into iron t o form a liquid iron
carbon alloy
Diffusion of away from slag-gas interface toward
the gas-graphite interface
Chemical r e a c t i o n at t h e gas-graphite interface
Diffusion of CO away from the gas-graphite interface t o
the slag-gas i n t e r f a c e
The slowest process o r combination i n the previous sequence
will be t h e rate-limiting step.
~ r a b k e ~ ' proposed a mechanism for the oxidation of
ca rbon in CO2-CO mixtures. It was stated that oxygen
transfers from CO2 to the carbon surface, which i s then
reduced to CO.
Chapter 2, Page 1 8
Co2 (CJ) -) CO ( g ) + O(adsorbed) (2.15)
0 + C(dissolved) + CO (9) ; chemical reaction ( 2 . 1 6 )
C(dissolved) + C02(g) = 2 COlg) ; g a s i f i c a t i o n r e a c t i o n ( 2 . 1 7 )
2 . 7 Fe0 Reduction Mechanian According to Fud3
Reaction ( 2 . 5 ) i s a heterogeneous r e a c t i o n , where t h e
gaseous produc t s escape from t h e reaction site i n the form
of bubbles and grow as the r e a c t i o n proceeds . T h i s ha s
been observed by X-ray photography. The bubble w i l l reach
a c e r t a i n size and floats away from the s o l i d surface where
then, molten s l a g w i l l c o n t a c t the g r a p h i t e surface.
Overall, Fe0 i s being consumed from t h e b u l k slag, CO(,, is
gene ra t ed , and CO2&) is consumed at the gas -g raph i t e
i n t e r f ace . The r e a c t i o n rate is a combination of t h e s e
cyclic events.
T h e Reduction mechanism o f Fe0 was c o n t r o l l e d by :
Mass t r a n s f e r of Fe0 i n s l ag , and chemical r e a c t i o n a t
the gas -g raph i t e interface for Fe0 < 5% i n s l ags
Chernical reaction a t gas-graphite i n t e r f a c e , and a t gas-
slag i n t e r face f o r Fe0 > 40% in slags
By al1 three s t e p s for 5% < Fe0 < 40%
~ a r c z o k ' and Utigard obtained s i m i l a r results a s E'unf s13
f o r s lags over 40% FeO, where t h e Boudouard' r e a c t i o n
controls. According t o Paul et a l6 , CO gas bubbles form
c o n t i n u o u s l y a t t h e gas-graphite interface as observed
experimentally. Therefore , t h e i r transport i n the gas
Chapter 2, Page 19
phase can be neglec ted a s t h e r a t e - c o n t r o l l i n g s t ep , and
t h e mass t r a n s p o r t of carbon i n a carbon-saturated i r o n
m e l t can be neglected as the ra te - l i rn i t ing . The
c o n t r o l l i n g steps are s i m i l a r t o Funr s13 conclusions.
2 .8 Results of D a l , Li, and ~ r i m s e ~ * ~
The use of d i r e c t c u r r e n t is b e n e f i c i a l due
e f f e c t of e l e c t r o l y s i s and t h e e l e c t r o c a p i l l a r y
t h a t i s t h e r ap id migrat ion of d r o p l e t s i n a
e l e c t r o l y t e . The rnovement helps p a r t i c l e growth
t o t h e
motion,
l i q u i d
through
c o l l i s i o n , t h u s i n c r e a s i n g coalescence and s e t t l i n g . Wi th
DC c u r r e n t s , e l ec t ro -depos i t ion is t h e dominant r educ t ion
mechanism.
With zero c u r r e n t , reduct ion occurs through t h e
existence of a gaseous l a y e r of
t h e s o l i d carbon s u r f a c e from
d i f f u s i o n , rnetal i o n s t r a n s f e r
where t h e y are reduced w i t h CO
T h e CO2 d i f f u s e s bac'k t o the
Boudouard r e a c t i o n occuxs.
CO and CO2, which separates
the l i q u i d s l a g . Through
t o the slag-gas i n t e r f a c e ,
according t o r e a c t i o n 2 . 3 .
carbon su r face , where t h e
G a s i f i c a t i o n was dismissed a s r a t e c o n t r o l l i n g because
of t h e rapid i n c r e a s e of t h e r a t e with temperature . The
d i f f u s i o n l a y e r a t t h e slag-gas i n t e r f a c e dec reases due t o
the convect ion formed by r e s i s t a n c e hea t ing adj acent t o t h e
e l e c t x o d e s .
Chapter 2, Page 20
Since increase in AC power had little effect on the
reduction rate, the process i s most likely dominated by
chernical reactions of the type:
This mechanism represents the dominant rate control for the
reduction of iron rich non-ferrous slags in which,
diffusion of ferrous and ferric oxide is unlikely to be
rate controlling.
Increase in DC power enhanced the reduction rate
significantly. This is due to electro-deposition of metal
ions on the cathode (copper and matte drops migrate towards
the cathode through a diffusion boundary) with the
formation of at the anode.
From this review, it is seen that the existence of
several stages in the reduction of Fe0 in various slags has
been documented. Some researchers claim that Fe0 reduction
is controlled by the rate of graphite gasification, while
others claim that the reduction isg limited by diffusion.
Chernical reactions, surface absorption, gaseous mass
transfer, and mass transfer in the slag are al1 involved in
the rate-limiting step. Hence, the rate-limiting step may
easily change as the actual physical condition(s) change,
and various parameters are required for a complete kinetic
mode1 .
Chapter 2, Page 21
Schematic of Fe0 Reduction with Carbon
Below is a diagram of a carbon molecule reacting with the gas and slag
SLAG
Coke - -
Figure 2.1. Page 22
Measuring the reduction rate of nickel and copper
slags is based on the continuous maasurement of CO and CO2
gases formed by reactions of the graphite electrodes with
oxygen in the slag. A NOVA i n f r a r e d gas a n a l y z e r was
employed for COI,, and measurements (maximum 20% by
volume) , Industrial nickel s l a g s from INCO Limited
(Thompson Smelter) were reduced with* AC and DC currents. A
Fluke data acquisition system was used to monitor and log
the progress of the reduction with time.
3.1 Variables and Parametets Investigated
The various parameters investigated were:
1. Slag temperature [1200 to 1450 O C ]
2. Electrode current density [O. 1 to 12 ~/cm']
3. Fe304 content 8-30 weight percent, [electric furnace and
converting slags, INCO Thompson Smelter]
4.AC current and DC current
5. Electrode depth [O.S-5 cm] and diameter [0.62-1.32 cm]
6. Gases generated by the anode and cathode separately
7. Electrode tip temperature for AC and DC currents
The material cost for each experiment was above $400
dollars and each experiment took over 36 hours to complete.
Therefore, some experiments were repeated only twice.
Chapter 3, Page 23
3.2 Power Supplies
Alternating current (AC) and Direct current (DC) power
sources were used for the reduction of reducing and
oxidizing slags. The AC current was supplied by a 6.1 KVA
step-down Power-Stat Variable Auto-Transf ormer (Variac) . The input voltage to the auto-transformer was 110 AC volts,
60 Hz, and the output voltage (0-135 V, 45 A) was varied as
required. An auto-transformer has one winding that serves
as both the primary and the secondary.
The DC power source supply was a 3 . 0 KVA, 120 VAC
input, 50/60 Hz - 1 Ph, 0-140 V output, and 22 amps
supplied by The Superior Electric Co., Bristol, Conn,
U.S.A.
3.3 Data Acquisition
The use of a data acquisition (DAQ) system to monitor
the experiments enhanced the capabilities of capturing the
required data at high rates. A F l u k e HYDRA 2620A DAQ unit
was used for al1 data logging. The unit can log 20 mixed
s i g n a l s simultaneously and is controlled via a bi-
directional RS-232 cable. The analog circuitry is isolated
from the digital circuitry, which enables the rneasurernent
of high voltages directly up to 300 V AC rms. A HYDRA
logger for windows9sm software package was used to scan,
signal condition, and advanced trend plotting. T h i s
enabled the monitoring of the reaction rate and al1 signals
instantaneously as the experiment progressed.
Chapter 3, Page 24
3 . 4 Experimental Equipment Used
The experimental apparatus is illustrated in Figure
3.1 page 30. The electric furnace is an in-house built 3
phase, 220 volts, 10 glowbars heating elements - (each £ive series) surrounded with the following instruments:
OMEGA CN9000A temperature controller (f 1 OC)
4 R-type (Pt&13%Rh vs. Pt) thermocouples. One
thermocouple was protected by an alumina sheath and
dipped 2-5 cm in the molten slag, another for the
furnace temperature, and the third and fourth
thermocouples are for the electrodes tip temperature
t w o graphite electrodes (0.62, 1.0, and 1.32 cm O. D. )
and a potentiometer level controller
two dryrite colurnns to dry the gas before r e a c h i n g the
CO, CO2 gas analyzer
nitrogen OMEGA MN-5610 high precision digital mass
f lowmeter (0-10 lmin-')
zero to 150 units OMEGA rotameter
NZ gas input alumina tube (1. D. = 4 mm)
CO and COz output alumina and copper tube (1. D. = 4 mm)
Power-Stat voltage source (6.1 KVA, 0-135 volts AC),
and a 3.0 KVA, 22 amps AC to DC power source
20 signal Fluke HYDRA Mode1 2620A data acquisition
unit and a program was Witten for data logging
magnesia c r u c i b l e (I.D. = 7.0 cm, H = 1 4 . 3 cm, th =
0.3 cm)
alumina/rnullite reaction tube (I.D. = 9.3 cm, H = 50.5
cm, th = 0.5 cm)
water manometer colurnn was used to monitor and i n s u r e
an over-pressure i n s i d e the system at al1 times
Chapter 3, Page 25
14 specially designed water-cooled brass cap that sealed
the a l u m i n a / m u l l i t e reaction tube w i t h a viton gasket
15 AC/DC Current sensor 0-100 amps (Met raby te Company)
that works on the c u r r e n t hall effect p r i n c i p l e
16 DC current shun t r e s i s t o r 0-50 amps (Electrosonic) to
measure DC current. Both current sensors have a 1 %
error
several AC and DC ohmmeter and voltmeter display
panels
two channel digital real t i m e (60 MHz, 1 G S / s )
Tektroniks TDS210 oscilloscope was used with a
Wavestar signal acquisition software, and a TDSCM
communication module f o r cornputer i n t e r f a c e and s i g n a l
acquisition
two (200 MMX, 16 'MB RAM) IBM compatible cornputers
Epson p r i n t e r
two N2 gas cylinders
stainless steel hollow tubes, 1.32 cm in dia rne te r and
approximately 60 cm i n length
alurnina electrode separation tube (I.D. = 2.85 cm, H =
60 cm, th = 0.30 cm)
3.5 Experimentrl Ptoceduie
650 g of t h e i n d u s t r i a l s l a g w a s p l aced in a magnesia
crucible 1 = 7.0 cm, H = 1 4 . 3 cm), and t h e n inside a
closed alumina/mullite reaction tube ( I D = 9.3 cm, H =
50.5 cm, th = 0.5 cm) in the middle of the fu rnace . The
sample site was found appropriate since it resulted in 5-cm
depth of slag inside the magnesia crucible. The fu rnace
Chapter 3, Page 26
temperature was raised by 100 degrees every 30 minutes to
reach its set p o i n t (1205-1400 OC).
High purity nitrogen was used during h e a t i n g 0-0.25
lmin-' to prevent pre-oxidation. 'Nitrogen flowrate was
increased up to 4.0 lmin-' during the experiment to dilute
t h e CO and COt gases formed by reactions between the
g r a p h i t e electrodes and t h e s l a g . Also, to transport the
gases to the NOVA CO and COz infrared analyzer . The input
flowrate of the nitrogcn was measured by the Omega high
precision mass flowmeter.
An R-type thermocouple protected by an alumina sheath
was dipped 2-5 cm in the s l a g . After temperature
stabilization of the molten slag, the graphite electrodes
were immersed into the liquid slag to a spec i f i ed depth and
t h e input power was varied (0-50 volts, 0-75 amps) AC or DC
current . The electrodes were dipped u n d e r dif f erent
settings for approximately 20 minutes, or until CO and CO2
gases and
electrodes
g a s levels
elect rodes
the temperature stabilized. Thereafter, the
were raised for 5 to 10 minutes until CO and CO2
were back to zero. For some experiments, the
were kept immersed in slag and only the power
was turned on and off, which resulted in faster
stabilization of the molten slag temperature and output
gases.
The sarne apparatus was used for the experiments of the
tip of the electrodes temperature. To determine the
electrode tip temperature, the electrodes were threaded and
a stainless steel hollow tube was used as an extension of
Chapter 3, Page 27
the electrodes. A thermocouple was placed in the middle of
the stainless steel tube touching the electrode tip, Figure
3.2. For the electrode separation experiments, one of t h e
electrodes was separated with a grooved end alumina tube
( I . D . = 2.85 cm, H = 60 cm, th = 0.30 cm). This alumina
tube was closed with a rubber gasket through which an input
tube for nitrogen and an output tube for the gas were
added, Figure 3.3. A brick cap was u s e d instead of t h e
brass cooling cap, Figures 3 . 3 - 3 . 6 . The alumina tube w i t h
the grooved end below the slag surface allowed circulation
and homogeneous mixing of t h e slag.
The current, voltage, slag temperature, furnace
temperature, CO and CO2 gases, N2 flowrate, frequency, and
electrodes depth were measured and logged continuously with
the HYDRA Fluke data acquisition system. From the
continuous analysis of t h e CO and COz gases, the reaction
rate was calculated as shown below. At the end of the
experiment, the graphite electrodes were cooled and weighed
to determine t h e graphite consumption.
The rate of slag reduction defined as the rate of
oxygen removal, was calculated f rom the nitrogen f lowrate,
and the CO and CO2 gases concentration using the following
equation (derived in Appendix A) :
Available oxygen was calculated from the oxygen in NiO,
CoO, Fe304, and FeO.
Chapter 3, Page 28
Units Check:
P Pa mol
m3 - min - - mol 4 Rate = m3 minm2
m2 x mol 4
Where A i s t h e surface area of the immersed graphite
m3 e l e c t r o d e s i n m2, VNZ is the n i t r o g e n flowrate i n - , and
min
%CO and %CO2 a r e t h e c o n t e n t s in t h e off gas from the
r e a c t i o n t u b e .
The degree of reduction is t h e sum of t h e rate of
reduction over the amount reducible oxygen i n grarns for the
whole r e d u c t i o n period. The amount of reducible oxygen is
t h e oxygen present i n t h e s l a g mainly i n Fe304, FeO, NiO,
and CoO.
Rate of Reduction x Area Degree of reduct ion = Oox,(, . .. . d2
T h e t h e o r e t i c a l amount of used
reduci ble oxygen coke is equal to:
CO keUsed = Atime,~n, %CO, %CO Imol l2gofC
+-)x- X x v ~ z ( r _ ) X ( ~ min 100 24.L mol
For a complete de ta i l of the calculations performed, see
Appendix A.
Chaptcr 3, Page 29
EXPERIMENTAL SETUP APPARATUS
Electrode Level Control - -. . - - - - -- . - - - . .
R Type pp Thermocouple a - . - . - - . . . - - --
: SIGNAL READINGS - 1--
I
/ iTrmpt T m 2 coco? . -..- -
I
i ' Cornputer Interface
- -- Gra p h iteeE1eect~od~sS
R Type Thermocouple l
Brass Cooling Cap l --
Furnace Inside :
Furnace Wall A _ - - a -
-. . . Magnesia-Crucible--_
Alumina/Mullite Tube
Heating Elements
Not to Scale
Figure 3.1, Page 30
Electrode Tip and Thermocouple
MullitelAlumina Tub
Live R-Themiocoupie Ground R-fhemimuple
Brick Capsule
Hollow Stainless Steel Tube
Live Electrode Ground Electrode i
Niand Cu Slag I
Fiaure 3.2. Paae 31
Electrode Separation Apparatus
Live Elsdmde
MullitefAlumina Tuba
N2 Input -- - .L Alumina Tube
Brick Capwle
Ni and Cu SI-
Cooling Cap Design, Part 1
BRASS Material, Dimensions in mm
Figure 3.4, Page 33
Cooling Cap Design, Part 2
BRASS Material, Dimensions in mm
Fiaure 3.5. Page 34
Cooling Cap Design, Part 3
BRASS Material, Dimensions in mm
Figure 3.6, Page 35
RESULTS
Table 4.1 gives the chernical composition of the
starting slags and the final slags from al1 the reduction
experiments. Appendix A includes the calibration of the
experirnental equipment used, a circuit diagram of the in-
house built furnace, and a list of al1 the equations used
to determine the reduction rate. The other Appendices
include various experimental graphs and sample experimental
data.
4.1 AC Power and T-erature in E l e c t r i c Furnace Slag
To equilibrate the system and to check the
conductivity of the slag and examine the power source
available, three experiments were performed. Table 4.2
presents the experimental data including i) power, ii)
current density, and iii) temperature as the voltage was
varied. By adjusting the voltage (AC Variac) to a certain
set point, and using graphite electrodes with 0.62-cm
diameter, the depth (0.5-6.0 cm) was varied with the
electrode level controller to change the current density,
which changed the slag temperature, al1 this while keeping
the furnace temperature constant. Figure 4.1 is a graph of
the steady state values obtained . a f t e r changes in the
system.
To investigate f u r t h e r the effect of the electrodes
depth, three levels were chosen (0.5, 1.5, and 2.55 cm) . The voltage was varied from 0-25 V and slag temperature,
current, power, and current density are plotted versus the
Cbapter 4, Page 36
voltage in Figure 4.2. See o t h e r f i g u r e s i n Appendix B for
other depths . The s lag temperature started at
approximately 1210 O C and as t h e power was increased,
current density and slag temperature increased and the
maximum values reached were 1270 OC,' 300 watts, 15 amperes,
and 5 ~cm".
From these experiments, a better understanding of the
conductivity of the slag was obtained. Other converter
slag experiments showed higher c u r r e n t values (> 30 A) with
low voltage input (< 5 V), and this is due to the high
total iron content ( 5 1 . 4 % Fetotal) compared to (34.4% Fetotal)
in electric furnace s l a g .
Chaptcr 4, Page 37
Table 4.1 INCO Slag Samples and Experimental Reduction Sample Analysis
TCS 1 = Thompson Coverter Slag TEF 1 = Thompson Electrlc Furnace SIog
Sample Type and Date 1 Cu Ni Co Fe Cr Ca Al Mg Si S Fe4* Fe@, Vol.Sl
'original S m p b ~
)6 Mar TEF1 EXP 1 û6 MÎr TEFI EXP 1, Middle 12 hlCDr TEFl EXP 2 MMay7Efl EXP3 18 May TEF 1 EXP 4 28 May TEFI EXP 7 29 May TEF1 U(P 7, Middle 11 Jun TEF1 €W 8 11 Jun TEF1 EXP 8. Middle
26MayTCSlEXPS 28MayTCS1 W 6 12 Jun TCSl EXP 9
24 Jun TEF1 EXP 10 29 Jun TEF1 W 11 01 Jul TEF1 EXP 12 01 Jul TEF1 W 12, Middle 02 Jul TEFl EXP 13 03 Jul TEF 1 WP t 4 24 Jul TEP1 EXP 20
Slag TCS 1 TEF 1
Cu Ni Co Pa Cr ca AI ng si Q FeO Peso, SiO, cao Al$, crao, 0.05 3.24 0.77 51.4 0.05 0 . 2 5 1.14 0.17 0 . 9 0.87 38.2 29.9 20.2 0.46 2 . 2 7 0.01 0 .05 0.24 0.07 34.4 0.05 1.76 3.82 1.81 10.3 1.17 37.2 7.6 38.6 2.59 7 . 2 6 0 . 0 5 7
1 DC 110 Aua TEF1 EXP 24 1 <.O5 0.14 0.069 30.9 *.O5 1.85 4.61 3.39 17.5 0.71 1.83 4.9 0.27 1
06 Jul TCSl EXP 15 17 Jul TCS1 EXP 16 18 Jul TCS1 EXP 17 22 Jul TCSI EXP 18 23 Jul TCS1 EX? 19 23 Jul TCS1 EXP 19,Middle
0.12 0.39 0.54 51.9 0.097 0.4 1.58 2.02 10.1 0.7 5.88 12.7 0.064 0.16 0.85 0.69 51.3 <.O5 ??? 1.6t 3.13 10.2 0.8 6.22 12.7 0.064 0.16 1.04 0.79 51.2 <.O5 0.41 1.67 2.43 9.8 1.1 5.88 13,7 0.095 0.15 1.7 0.83 51.7 <.O5 0.37 1.37 1.76 10.1 0.87 6.43 14.0 0.064 0.56 2.02 0.83 50.7 <.O5 0.52 1.42 1.89 9.81 0.91 6.88 14.3 0.220
, 0.13 1.63 0.63 51.8 <.O5 0.35 1.29 1.91 9.82 0.8 6.77 14.3 0.095
1 ELECTRODE
Summary Chapter 4, Page 38
SEPARATION
All Experiments, 1998
11 Aug TEF1 EXP 25 -
*.O5 <.O5 *.O5 20.3 <.O5 1.28 20.6 1.97 11.7 0.55 0.56 2.2 0.32
31 Jul TCSI EXP 21 04 Aug f CS1 f XP 22 06 Aug TCS1 EXP 23
0.14 1.94 0.76 49.7 <.O5 0.39 1.79 1.17 10.3 0.57 11.70 24.7 O.ûô4 0.16 1.61 0.66 49.5 0.2 0.43 2.08 1.74 O 0.77 20.30 43.1 0.095 0.33 0.62 0.62 49.5 0.07 0.45 2.11 1.53 10.8 0.43 17.80 39.5 0.064.
Table 4.2 AC Power and Temperature Steady State Data in Electric Fumace Slag
I Dota cm cm cm2 V A W A cm*' O C OC 1 min" Q Anode, g Cathode, g
h
6-Mar TEFl EXP 1
12-Mar TEFl Ex? 2
4-May TEFI EXP 3
TYPE
AC Enperiments Chapter 4, Page 39
Ewperirnent
Enperiments 1 - 3 06 March - 04 May 1998
Electrode "ltage Denrity Diameter Current 'Ower Temperature
Surface Temperature
Current Flow
Furnace Used
Slag Electrode
N2 Electrode
Graphite Left Rig ht
AC Power and Temperature Profile Steady State Com parison
AC, Electric Furnace Slag Steady State Data
L
Slag Temperature, OC 1200 - l 1 1 1 l
1 2 3 4 5 6
SET 1 - 6
AC, Uectric Furnace Slag Steady State Data
- 4
Current Density, ~ c m "
- 1
1 2 3 4 5 6
SET 1 - 6
Fiiure 4.1, Page 40
AC Power and Temperature Increasing Voltage Setpoint AC Experiments
Experiment 2
TLurnace = 1255 =C Figure 4.2, Page 41 O6 March 1998
4 . 2 Electric Fumace Slag, AC Experïmeatr 4 , 7 , and 8
In Appendix B there are two .sample tables of data
acquired from t h e data acquisition system. Table 4.3 lists
the steady s t a t e results for some AC experirnents u s i n g
electric furnace slags. Electrode depth and voltage were
varied and the rate of slag reduction, defined as the r a t e
of oxygen rernoval, was calculated from the nitrogen
flowrate, and t h e percent CO and COz off-gas concen t ra t ions .
The degree of reduction, which is t h e percent of
available oxygen consumed, is also shown. The graphite
used is the mass difference of the electrodes before and
after t h e experiment, and t h e calculated graphite is the
theoretical amount of graphite required based on CO and CO2
off-gas concentrations, see Appendix A for the calculation
procedure.
Figure 4.3 shows the % CO and CO2 off-gas, power, slag
temperature, and the rate of slag reduction as the voltage
was increased from 10 to 20 volts AC. The %CO and %CO2 in
off-gas, rate of reduction, slag temperature, power, and
current density al1 increased approaching steady state in
less than 20 minutes. Other figures in Appendix B show
similar experimental results at various electrode (0.62-cm
diameter) depths and d i f f e r e n t power inputs.
In Figures 4.4-4.9, the electrode depth was f ixed at
5-cm and the voltage varied by 5 volts step from 5-30
volts. As seen in these figures, the slag temperature and
the rate of slag reduction approach steady state often
Chapter 4, Page 42
about 15 minutes after the electrode power is applied. The
steady state values of the voltage, current, power, current
density, electrode depth, rate of reduction, CO/C02 ratio,
and slag temperature are listed in Table 4.3. As the power
was increased from 20-1200 watts, slag temperature
increased from 1200-1450 O C , and the rate of reduction
increased from 0.3 to 4.1 (mol O2 / min m2) .
Figures 4.10 and 4.11, show the steady state rate of
reduction (mol O2 / min m2) and the slag temperature ( O C )
versus power (W). As the power increased by increasing
voltage set-point, the current density increased and the
temperature of the slag increased, through which the rate
of slag reduction linearly increased with a least square
line fit R~ value greater than 0.85. AC power was 1400
watts when the rate of slag reduction was 8 (mol O2 / min
m2) .
To check the behavior of the rate of slag reduction
with temperature, an Arrhenius plot was determined
resulting in activation energy value between 200-320
kJ/mol. This value compares very well ( -250 kJ/mol) with
previous authors 7,8, là The calculated standard deviation
was found to be 86 kJ/mol. This large value is due to the
temperature difference between the bulk of the slag and the
electrodes t i p where the Boudouard reaction takes place.
In the sections to follow, this temperature difference will
b e shown and further explanation will be provided.
Chapter 4, Page 43
Table 4.3 AC Experimental Steady State Data in Electric Fumace Slag
I Cm Cm Cm2 V A W Am'' O C OC I min" % % ratio mole Op min" me2 %
!-y 'EF 1 w 7
r WERIMENT ~ ~ e c t r o d .
Chapter 4, Page 44
surface TYPE
Expwiwnis 4,7, and 8 18May - 11 June 1998
Nu* Voitage
h p t h Cuvent Powr
Current Density
Furnau Tenperaîure
Sr00 Temperature
W~ now CO C@ ûegree of ' Reduction COI CR ~ ~ ~ u ~ o n
Electric Furnace Slag Power, Temperature, and Rate of Reduetion AC Experiments
AC,Electric Fumace Slag Diameter = 0.62 cm, 3.5 cm depth, 6.84 cm2
s r
4 -
n
140 150
Time in minutes
Diameter = 0.62 cm, 3.5 cm depth, 6.84 cm2 1
Slag Temperature
Rate of Reduction -
-4
1 t I I I 1 t
1 50
fime in minutes
Figure 4.3, Page 45 18 May 1998
Electric Fumace Slag Power, Temperature, and Rate of Reduction AC Experiments
Diameter = 0.62,s V, 5 cm depth, 9.76 cm2
68 70 72 74 76 78 80 Time in minutes
Diameter = 0.62 cm, S V, 5 cm depth, 9.76 cm2 1210
68 70 72 74 76 78 80 Time in minutes
Diameter = 0.62 cm, 5 V, 5 cm depth, 9.76 cm2
-
Current Density
68 70 72 74 76 78 80 Time in minutes
Figure 4.4, Page 46 1 1 June 1998
Power, Temperature. and Rate of Reduction AC Experiments
Diameter = 0.62 cm, 10 V, 5 cm depth, 9.76 cm2
92 94 96 98 100 102 1 04 Time in minutes
Diameter = 0.62 cm, 10 V, 5 cm depth, 9.76 cm2 1
L ' . l i L t i I ' I
I I I I J i L 1
92 94 98 1 O0 1 O2 1 04 96 Time in minutes
Oiameter = 0.62 cm, 10 V, 5 cm depth, 9.76 cm2
98 100 96 ~ i m a in minutes
Expriment 8 Figure 4.5. Page 47 11 June 1998
Electric Furnace Slag Power, Temperature, and Rate of Reduction AC Experiments
Diameter = 0.62 cm, 15 V, 5 cm depth, 9.76 cm2
110 115 120 125 1 30 Time in minutes
Diameter = 0.62 cm, 15 V, 5 cm depth, 9.76 cm2 I
Slag Temperature
7
Rate of Rec
110 115 120 125 130 Time in minutes
Diameter = 0.62 cm, 15 V, 5 cm depth, 9.76 cm2 300
zoo f aa
1 3 ; 100 g
1 0
11 5 120 125 Time in minutes
Figure 4.6, Page 48
Electric Fumace Slag Power, Temperature, and Rate of Reduction AC Experiments
Diameter = 0.62 cm, 20 V, 5 cm depth, 9.76 cm2
10 Current
Voltage v 135 140 145 150
Tirne in minutes
Diametei = 0.62 cm, 20 V, 5 cm depth, 9.76 cm2 -
Rate of Reduction
Slag Temperature
l
135 140 145 150 155 160 Time in minutes
Diameter = 0.62 cm, 20 V, 5 cm depth, 9.76 cm2
Current Density
135 140 345 1 50 155 160 Time in minutes
Figure 4.7, Page 49 1 1 June 1998
Electnc Fumace Slag Power, Temperature, and Rate of Reduction AC Experiments
Diameter = 0.62 cm, 25 V, 5 cm depth, 9.76 cm2
Current
Voltage
1 70 175 Time in minutes
Diameter = 0.62 cm, 25 V, 5 cm depth, 9.76 cm2 1 1350
Slag Temperature
165 170 175 180 lime in minutes
Diameter = 0.62 cm, 25 V, 5 cm depth, 9.76 cm2
- 600 3 O
Cunent Density - 300
165 170 175 180 Time in minutes
Figure 4.8, Page 50 1 1 June 1998
Electric Fumace Slag Power, Temperature, and Rate of Reduction AC Experiments
Diameter = 0.62 cm, 30 V, 5 cm depth, 9.76 cm2 , 50
205 21 0 21 5 220 225 230 Time in minutes
Diameter = 0.62 cm, 30 V, 5 cm depth, 9.76 cm2
- Slag Temperature
205 21 O 21 5 220 225 230 .Tirne in minutes
Diameter = 0.62 cm, 30 V, 5 cm depth, 9.76 cm2
Figure 4.9, Page 51
AC, Rate, and Activation Energy Steady State Calculation
1 AC, Electric Furnace Slag, 0.5-4.5 cm Depth
500 1000 Power, Watts
AC, Arrhenius Plot, Electric Furnace Slag
-1 . 1 1 1 I 1 L 1 1 1 t 1 I 1 I : O
5.9 6.1 6.3 6.5 6.7
(1 1 Temperature, K ) x 104
Experiment 7 Figure 4.1 0, Page 52 29 May 1998
AC, Rate, and Activation Energy Steady State Calculation AC Experiments
AC, Electric Furnace Slag, 5 cm Depth
1 Slag Temperature, R~ = 0.97 /
500 750 Power, Watts
AC, Arrhenius Plot, Electric Fumace Slag
6.0 6.2 6.4 6.6 (1 1 Temperature, K ) x IO'
Experiment 8 Figure 4.1 1, Page 53 1 1 June 1998
4 . 3 Convetter Slag, AC Experiments 5 , 6 , and 9
Figu re s 4.12-4.14 show t h e %CO and %CO2 i n o f f -ga s ,
c u r r e n t , v o l t a g e , s l a g temperature, rate of s l a g r e d u c t i o n ,
c u r r e n t density, power, and CO/C02 r a t i o for c o n v e r t e r slag
under d i f f e r e n t electrode depths, d i a m e t e r s and d i f f e r e n t
AC power i n p u t . The measured p e r c e n t CO and COt i n o f f -ga s ,
slag t empe ra tu r e , and t h e rate + of reduction graphs
approached steady state f a i r l y q u i c k l y (< 20 minutes).
Figu re s 4.12 and 4.13 have t h e same voltage b u t d i f f e r e n t
e l e c t r o d e depth, 3.5-cm and 4.0-cm respectively. For t h e
4.0-cm d e p t h case, t h e r a t e o f r e d u c t i o n , t h e s l a g
t empe ra tu r e , t h e power, and t h e current density were al1
h i g h e r . Other graphs of t h e same nature a r e shown i n
Appendix C.
The c u r r e n t during the c o n v e r t e r slag ( 2 9 % Fe304)
expe r imen t s was much h i g h e r t h a n w i t h t h e electric f u r n a c e
s l a g (8% Le30s) experiments due t o t h e h igh magne t i t e
c o n t e n t of t h e converter s l ag . The i r o n content enhances
t h e i o n i c c o n d u c t i v i t y and t h e c u r e n t t r a n s f e r is much
easier with the presence of iron i o n s . This preven ted t h e
v o l t a g e from i n c r e a s i n g t o higher values because t h e limit
of the power sou rce was reached. These h igh c u r r e n t
values, r e s u l t e d i n higher r e d u c t i o n rates f o r c o n v e r t e r
slag.
Table 4.4 is a summary of the converter slag AC
experiments at steady state. Figu re 4.15 shows the r a t e o f
reduction and slag t empera tu r e v e r s u s power for converter
slag a t 5.0-cm e l e c t r o d e depth. The slopes of both lines
Chapter 4, Page 54
a r e similar to the electric furnace experimental results in
the previous section. The rate of s l a g r e d u c t i o n was 1
(mol O2 / min m2) at zero watt power input, and increased to
5 ( m o l / min m2) at 1250 watts.
From the steady state data obtained, the a c t i v a t i o n
energy was found to be 616 and 850 kJ/mol with an R~ value
of 0.99 and 0.75 respectively and 166 kJ/mol standard
deviation, Figure 4.16. These results are much higher than
the electric furnace slag values and t h e literature
reported results as well. This rnay be because t h e actual
electrode-slag interface temperature is much higher than
the bulk slag temperature. If we knew this interface
temperature, the rate should have been p l o t t e d versus t h i s
temperature. These high activation energies may a l s o be
due to the narrow temperature range (30 O C ) o v e r which the
activation energy was calculated.
Figure 4.12 shows a rapid increase in the rate of slag
reduction as power is applied. This shows that it is n o t
the bulk slag temperature that controls the rate. The bulk
slag temperature takes approximately 20 minutes to increase
and stabilize. Hence, measuring the electrode tip
temperature is very important and this will be presented in
section 4.7.
Chaptcl4, Page 55
Table 4.4 AC Experimental Steadv State Data in Converter Slaa
I cm cm cm2 v A w A m * ' OC OC 1 min-' n % ratio mo* O, min*' m- % 1 &May TCS1 EXP 5
20-May TCS1 EXP 6
12-Jun TCS1 EXP 9
EXPERIMENT Numkr
Chapter 4, Page 56
Voltage
Ewpcrimetns 5,6, and 9 26 May - 12 June 1998
Electrode Depth
Cwrent Area Power Cwent
y Furnace Temperature
Slag Temperature
N2 Flow
CO CO> CO /CO* Degree of ,,,."
:onverter Slag Power, Temperature, and Rate of Reduction AC Experiments
Diameter = 0.62 cm, 3.5 cm depth, 6.84 cm2
153 159 162 165 168 171 Time in minutes
Diameter = 0.62 cm, 3.5 cm depth, 6.84 cm2 3 1 1 1260
Rate of b R e d u h A
153 156 159 162 165 168 171 Time in minutes
Diameter = 0.62 cm, 3.5 cm dep.th, 6.84 cm2
Curent Density
153 1 56 159 162 165 168 Time in minutes
Figure 4A2, Page 57 26 May 1998
Conuerter Slag Power, Temperature, and Rate of Reduction
Diameter = 0.62 cm, 4.0 cm depth, 7.81 cm2
100 tO5 110 Time in minutes
4 r Diametei = 0.62 cm, 4.0 cm depth, 7.81 cm2
Rate of Reduction
303 110 Tirne rn minutes
8 1 Diameter = 0.62 cm, 4.0 cm depth, 7.81 cm2
i --- Power 4
Current Den*
-
CO r CO,
100 1 O 5 110 Time in minutes
Figure 4.1 3, Page 58 28 May 1998
Converter Sfag Power, Ternperature, and Rate of Reduction
Diameter = 0.62 cm, 10 V, 5 cm depth, 9.76 cm2 1.5 30
Current
155 160 Time in minutes
Diameter = 0.62 cm. 10 V, S cm depth, 9.76 cm2 I - Çlag Ternperature
145 155 160 Time ln minutes
Diameter = 0.62 cm, 10 V, 5 cm depth, 9.76 cm2
150 155 160 Time in minutes
Figure 4.1 4, Page 59
AC, Rate and Temperature Profiles Steady State Calculation
AC, Arrhenius Plot, Converter Slag, 5 cm Depth
y = -1 0 . 2 ~ + 67.2
E = - Slope*R*10~ = 851 kJ 1 mol
l
-0.5 I I 1 I I I I 1 I I
6.42 6.46 6.50 6.54 6.58
(1 I Temperature, K ) x 10'
AC, Arrhenius Plot, Converter ~ l a g , 1-4 cm Depth
6.55 . 6.60 (1 1 Temperature, K ) x 1 O'
Expenments 9 and 6 Figure 4.16, Page 61 28 May 1998 12 June 1998
4 . 4 Electric Ririwrce Slag, DC Experhnts 10-14, and 20
The DC power source used was a 3.0 KVA, 120 VAC input,
50/60 Hz -1 Ph, 0-140 V output, and 22 A maximum current.
Table 4.5 lists t h e experirnental DC current steady state
electr ic fu rnace data. A s for previous experiments, the
slag sample was placed in t h e furnace from the s t a r t with
purified nitrogen flushing the surface of the slag. The
f u r n a c e temperature was raised by 10'0 OC steps every thirty
minutes to reach set point (1270 OC). Figure 4 .17 shows the
s l a g and furnace temperature without imrners ing the
electrodes, t h e slag thermocouple was imrnersed in slag
-3cm. The slag temperature was below furnace temperature
by 10-40 OC usually, and this was observed during al1
experirnents.
Figures 4.18 and 4.19 show the power, temperature, and
rate of slag reduction for the same electrode depth (4.5-
cm) with varying OC voltage input. In Figure 4.19, as the
voltage was raised from 12 to 15 V DC, t h e c u r r e n t
increased from 13 to 19 A, power increased, slag
temperature increased from 1300 to 1350 OC, and the rate of
slag reduction increased from 2.2 to 3.5 (mol Oz / min m2).
The voltage was reduced to zero when steady state was
reached, usually in less than 20 minutes, and another step
was started. More experimental data can be viewed in
Appendix D.
To examine the voltage source signal and to check if
arc ing is occurring, an oscilloscope with an image
capturing software was used t o view and capture the signal.
Chapter 4, Page 62
The s i g n a l from t h e power s o u r c e by i t se l f was a smooth
s t r a i g h t l i n e for DC. When t h e power was connec ted t o t h e
e l e c t r o d e s , a r c i n g was observed f o r s h o r t p e r i o d s o f tirne,
every 10-20 seconds for t h e complete period of e l e c t r o d e
immersion, and t h e effect of t h i s a r c i n g on t h e reduction
is n e g l e c t e d .
F i gu re s 4.20-4.23 d i s p l a y the steady state graphs for
t h e DC electric furnace s l a g exper iments . E l e c t r o d e depth
was f ixed at 4 .5 c m but t h e d i a m e t e r was changed from 0.62
t o 1 . 0 cm. Th i s r e s u l t e d i n different s u r f a c e areas and
hence the c u r r e n t d e n s i t y changed. Furnace t e m p e r a t u r e was
changed from 1270 t o 1300 OC for some expe r imen t s . The r a t e
of r e d u c t i o n , and s l a g temperature r e s u l t s are s i m i l a r t o
p r e v i o u s AC exper iments excep t for t h e power i n p u t . Wi th
DC exper iments , much less power (400 watts) was r e q u i r e d t o
a c h i e v e t h e same r e d u c t i o n rates a s AC (1250 w a t t ) . The
reason f o r t h i s is b e l i e v e d t o be the e l e c t r o l y s i s
c o n t r i b u t i o n t o t h e r e d u c t i o n and the h igh temperatures
reached a t the t i p of t h e anode e l e c t r o d e .
The exper i rnen ta l a c t i v a t i o n energy values are between
300-500 k J / m o l . During sorne experiments, t h e r a te of s l ag
r e d u c t i o n changed e r r a t i c a l l y due t o e l e c t r o d e breaking and
f a l l i n g i n the slag.
Chapter 4, Page 63
Table 4.5 DC Experimental Steady Stîte Data in Electric Furnace Slag
Expenmrnm 10.14, and 20 24 Junr - 24 July 1998
Electric Furnace Slag Furnace and Slag Temperature Profile DC Experiments
Furnace and Electric Furnace Slag Temperature Profile, No Electrode Power
Furnace Temperature
,/ Slag Temperature
Time, Hour
Figure 4.1 7, Page 65
Electric Fumace Slag Power, Temperature, and Rate of Reduction OC Experirnents
Diameter = 0.78 cm, 13 V, 4.5 cm depth, 11 cm2
195 200
Time in minutes
Diameter = 0.78 cm, 13 V, 4.5 cm depth, 11 cm2 3 1 1 1375
195 200 205
Time in minutes
Diameter = 0.78 cm, 13 V, 4.5 cm depth, 11 cm2
Current Density
195 200
Time in minutes
Experiment 12 Figure 4.1 8, Page 66 O1 July 1998
Electric Fumace Slag Power, Temperature, and Rate of Reduction
Diameter = 0.75 cm, 11&15 V, 4.5 cm depth, 10.6 cm2
385
Time in minutes
Time in minutes
Figure 4.1 9, Page 67 24 July t 998
DC, Rate, Power, and Temperature Steady State Calculation DC Expenments TEF
DC, Electtic Furnace Slag, 4.5 cm Depth
Slag Temperature, R' = 0.95 . , - , - , , , , , - - - ----------------a----- / ------a--------------- 1 1
Rate of Reduction, R*= 0.99
200 300
Power, Watts
DC, Arrhenius Plot, Electric Furnace Slag
E = -Siope x R x 1 o4 = 495 kJ I mol
6. .4 6.6
(1 1 Temperature, K) x 10'
Figure 4.20, Page 68
DC, Rate, Power, and Temperature Steady State Calculation DC Expenments TEF
DC, Electric Furnace Slag, 4.5 cm Depth
1 Slag Temperature, R1 = 0.99
1 rn Rate of Reduction, R~
200 300 400 Power, Watts
DC, Arrhenius Plot, Electtic Furnace Slag
6.0 6.2 6.4 (1 1 Temperature, K) x 10'
Figure 4.21, Page 69 01 July 1998
DC, Rate, Power, and Temperature Steady State Calculation DC Experirnents TEF
DC, Electric Furnace Slag, 4.5 cm Depth
DC, Arrhenius Plot, Electric Furnace Slag
(1 1 Temperature, K ) x lo4
Expriment 20 Figure 4.22, Page 70 24 July 1998
4 .5 Convetter Slag, DC Experiments 15-19
The electrode diameter, voltage, and depth of the
electrode in slag are al1 listed with the title of each
graph. Figures 4.23-4.24 and others in Appendix E show t h e
experimental power, t e m p e r a t u r e , and rate of r e d u c t i o n of
slag for DC experiments. With h i g h e r vo l t ages , the percent
CO and CO2 in off-gas were higher and higher slag reduction
rates were achieved.
With DC power i n p u t , t h e % COz gas output was h i g h e r
t han the AC experiments almost for al1 cases. Appendix E
l i s t s t h e results of other DC converter slag experirnents
w i t h v a r i o u s electrode depth and power input. Table 4.6 is
a summary of the steady state DC experimental converter
slag experiments.
Figure 4.25 shows the rate of reduction and bulk slag
temperature versus power input as the voltage was varied.
The r e s u l t s are similar to previous observations, that is
the rate of reduction and slag temperature increases as t h e
power increased, except that for these DC experiments. The
highest power i n p u t was 500 watt (power source limit) and
the same rate of reduction was obtained a s d u r i n g AC power
i n p u t . An A r r h e n i u s plot was determined and an activation
energy value of 614 kJ/mol was obtained. This value is
higher than reported literature and the reason could be
because of the temperature readings. High-localized
temperature was measured around the electrode and this
apparent activation energy shows how the r a t e of s l a g
reduction is strongly related to temperature.
Chapt-4, Page 71
Conterter Slag Power, Temperature, and Rate of Redudion
Diameter = 0.70 cm, 7.5 V, 3.8 cm depth, 8.2 cm2
Time in minutes -
I Diarneter = 0.70 cm, 7.5 V, 3.8 cm depth, 4.1 cm2
1
Rate of Reduction
Slag Temperature
95 05 115 Time in minutes
Fiiure 4.23, Page 73 06 July 1998
Converter Slag Power, Temperature, and Rate of Reduction DC Eaperiments
Diameter = 0.60 cm, 6.2 V, 4.0 cm depth, 7.6 cm2
150 170
nme in minutes
Diameter = 0.60 cm, 6.2 V, AOcm depth, 7.6 cm2 1270
1 Rate of Reduction
Time in minutes
. Figure 4.24, Page 74 22 July 1998
DC, Rate, Power, and Temperature Steady Staie Calculation DC Experiments TCS
DC, Converter Slag, 4.1 cm Depth
Power, Watts I
DC, Arrhenius Plot, Converter Slag
Figure 4.25, Page 75 23 Joly 1998
4 . 6 Convertel: and Electric Furnace Slag Electrode Separation DC Exparimonts 21-25
For d i r e c t c u r r e n t (DC) experlments, t h e consumption
of t h e anode and t h e cathode e l e c t r o d e s were d i f f e r e n t , s o
separation o f each e l e c t r o d e was necessary t o de t e rmine t h e
amount of gases gene ra t ed by each. The experiments were
s u c c e s s f u l and t h e r e s u l t s from the CO and CO2 graphs show
v e r y c l e a r l y t h a t more gas i s gene ra t ed a t t h e anode, hence
it is consumed more. T h i s i m p l i e s t h a t t h e r e i s b o t h
r e d u c t i o n and e l e c t r o l y s i s o c c u r r i n g a t t h e anode.
F o r some experiments, t h e percen tage of CO and CO2 was
above 20 % and t h a t i s due t o t h e appa ra tus volume size and
l i t t l e d i l u t i o n . The f low of t h e n i t r o g e n on t o p o f t h e
s l a g was sometimes high and it prevented the gas bubbles
from r i s i n g up t o t h e t o p through t h e alumina t u b e t o t h e
gas a n a l y z e r . T h e r e f o r e , t h e gas bubbles went o u t from
below t h e grooved end alumina tube (gas runaway), this was
confirmed by h e a r i n g t h e gas bubbles pop. So a s the
n i t r o g e n f l o w r a t e was reduced, gas d i l u t i o n d e c r e a s e d and
t h e CO and CO2 c o n c e n t r a t i o n s reached above analyzer lirnits
( 2 0 % ) . T h i s cou ld have been f i x e d by having a l a r g e r
a l u m i n a tube around t h e e l e c t r o d e under study, which will
also require a new coo l ing cap des ign o r by u s i n g t h e
a n a l y z e r pump.
F igu res 4.26-4.30 show the r e s u l t s f o r both types of
slags for anode and cathode electrode s e p a r a t i o n . From the
graphs, t h e r e is a d i f f e r e n c e w i t h t h e % CO and COz g a s e s
g e n e r a t e d a t t h e anode and cathode f o r e lec t r ic f u r n a c e
s l a g and for converter slag.
Chapta 4, Page 76
The first three figures for the converter slag anode
and cathode separation experiments, show that the rate of
reduction at the cathode was (2 mol O2 / min mZ) lower than
at the anode (2.5 mol 02 / min m2). Figures 4.29 and 4.30
show the electric furnace s l a g reduction results. There is
a large difference between the amount of gases generated at
the cathode and the anode and hence the rate of reduction
at the cathode (0.5 mol Oz / min m2) is much lower than at
the anode (1.5 rnol Oz / min m2) .
Tables 4.7 and 4.8 list all the electrode separation
steady state experimental data for both converter and
electric furnace slag. One column in each table states if
the anode or cathode was separated o r not. Appendix F
contains more results from other anode/cathode separation
experiments.
Figures 4 . 3 1 - 4 . 3 3 show a plot of the slag temperature,
power, rate of slag reduction, and current density versus
experiment number, both for converter and electric furnace
slag electrode separation experiments. The top graph in
each figure shows the slag temperature and the power a r e i n
abou t the same range 1200-1325 O C and 0-225 wat ts f o r a l l
experiments. The furnace temperature was set to 1270 OC for
all these experiments. The electrode depth was set a t 3 .25
o r 3 . 4 cm.
The rate of reduction and slag temperature increased
as usual as the power was increased. The cathode rate of
reduction was lower than the anode rate of reduction as
expected and this is shown clearly in the graphs; the
Chapter 4, Page 77
ca thode r a t e of r e d u c t i o n d id not change much with
increasing power. T h i s is complernented later with data on
t h e e l e c t r o d e consumption and you can see how the cathode
electrode was not consumed as much as t h e anode.
Chaprcr 4, Page 78
t t t t t t w r 1
Converter Slag Power, Temperature, and Rate of Redudion Anode 1 Cathode Separation
Anode Separaüon, Converter Slag Diameter = 0.90 cm, 2 4 V, 3.4 cm depth, 9.7 cm2
Time in minutes
Cathode Separation, Converter Slag Diameter = 0.90 cm, 2-5 V, 3.4 cm depth, 9.7 cm2
145 155 Time in minutes
Experiment 23 Figure 4.26, Page 80 06 August 1998
Converter Slag Power, Temperature, and Rate of Reduction Anode / Cathode Separation
Anode Separation, Converter Slag Diameter = 0.90 cm, 2-4 V, 3.4 cm depth, 9.7 cm2
110 120 ,
Time in minutes
Cathode Separation, Converter Slag Diameter = 0.90 cm, 2-5 V, 3.4 cm depth, 9.7 cm2
Rate of Reduction
145 155 Time in minutes
Experiment 23 Figure 4.27, Page 81 06 August 1998
Converîer Slag Power, Temperature, and Rate of Reduction Anode Electrode Separation
Anode, Diameter = 0.90 cm, 4 V, 3.4 cm Depth, 9.7 cm2
Current
8
; Voltage * Time in minutes
Anode, Diameter = 0.90 cm, 4 V, 3.4 cm Depth, 9.7 cm2
O t 1 1
240 250 260 270 Time in minutes
Experiment 23 Figure 4.28, Page 82
Electric Fumace Slag Power, Temperature, and Rate of Reduction Anode Electrode Separation
Anode Separation, Electric f urnace Slag
180 190 200 210
T ime in minutes '
Cathode Separation, Electric Furnace Slag Diameter = 0.82 cm, 12-15 V, 3.25 cm depth, 8.4 cm2
Figure 4.29, Page 83 1 1 August 1998
Electric Fumace Slag Power. Temperature. and Rate of Reduction Cathode Eledmde Separation
Anode Separation, Electric Furnace Slag Diameter = 0.82 cm, 17-20 V, 3.25 cm depth, 8.4 cm2
1 1320
0.0 ' 1 , 1 I I t I I 1 1 1 1 1 1 1 1200
170 180 1 90 200 23 O Tirne in minutes
Cathode Separation, Electric Fumace Slag
O 290 O
fi-
Time in minutes
Figure 4.30, Page 84 11 August 1998
Rate, Power, and Temperature Steady State Calculation DC Electrode Separation
DC, Converter Slag, 3.4 cm Depai I+~node Slag Temperature + ~ o w e r ]
1
1 3 5 7 9 11 13
1 - Anode Cathode Anode
OC, Converter Slag, 3.4 cm Depth 1 -a- Rate of Reduction + Current Density 1
1 3 5 7 9 11 13 - Anode Cathode Anode
Experiment 23 Figure 4.31, Page 85 O6 August 1998
Rate, Power, and Temperature Steady State Calculation DC Electrocle Separation
DC, Electric Fumace Slag, 3.25 cm Depth I+~node Slag Temperature + Power 1
Anode Cathode
ai- - 2 O S
0.0
DC, Electric Fumace Slag, 3.25 cm Depth - X e of Reduction t Cuvent Density 1
1 3 5 7 9 11 - Anode Cathode
Figure 4.33, Page 87 1 1 August 1998
4 . 7 Electrode Tip Temperature Measurements, AC and DC
The furnace temperature was set to 1270 OC for the
electrode t i p temperature (ETT) measurements and a 1-cm
diameter electxode was used. The electrode was hollow from
inside and threaded, in which the thermocouple sits
p r o t e c t e d with a SS hollow tube. The steady s t a t e slag
temperature was approximately 1250 OC. The e l ec t rode t i p
temperature provides further evidence of the importance of
the reactions occurring at the electrode slag interface.
The graphite electrodes were submerged in slag around
which a gas layer was formed.
Reaction 4.1 occurs on the slag-gas interface and produces
COz<<lI , w h i l e reaction 4.2 occurs on the electrode-gas
interface conçuming CO2(,) and forming C O I q I . Reaction 4 - 2 is
endothermic and as the temperature at the tip of the
electrode is increasing, the r eac t ion is pushed to t he
right further and more COI,) is generated which further
r e a c t s with Fe304tsias). T h i s process occurs cyclically for
both alternating and direct cufrent and if there is a large
temperature difference between the electrode tip and the
slag bulk, then the rate of reduction at the interface w i l l
be much higher.
Table 4.9 lists the experimental steady state
electrode tip temperature data for both types of slag. The
Chapter 4, Page 88
temperature and the power profile for the AC electrode slag
interface temperature experiments are shown in Figures
4.37-4.40 for both types of slag. The electrode with the
thermocouple inside it was placed on top of the slag at the
beginning of the experirnent to heat up slowly, and t h e n it
was immersed approximately 3.9-cm in the s l a g . The
electrode t i p ternperature took about 30 minutes t o reach
t h e s l a g bulk temperature a f t e r immersion. The voltage was
t h e n varied systematically and steady state ternperature was
achieved with each step,
In Figures 4.34 and 4.35
temperature difference (10-50 O C )
the s l a g increased.
17 V AC, w i t h 35
experimental setup,
used. Temperature
power on and off
The voltage
as power increased, the
between the electrode and
increased t o a maximum of
amps, and 590 w a t t s . With the same
electric furnace and converter slag was
readings were very good and turning the
for 10-15 seconds did n o t
electrode thermocouple output. The temperature
course as the power was turned off b u t no
temperature readings were recorded.
a f f e c t t h e
dropped
s p i kes
After 115 minutes in
was fluctuating because
completely consumed. The
was immediately attacked
readings became e r r a t i c .
Figure 4.34, the current reading
the electrode was be ing a lmos t
thermocouple inside the e l e c t r o d e
with slag and the temperature
With low AC power input [< 300
watts) to the system, the temperature dif ference between
the slag and t h e electrode was about 10 OC, see Appendix G
for further experiments.
Chapter 4, Page 89
With d i r e c t current power, t h e reaction occurring a t
the surface of the electrodes is not the same for the
cathode and the anode. Hence, measuring the temperature of
both electrodes will help us in understanding the
electrolysis process and to provide further evidence on why
the anode is consumed faster than t h e cathode.
The anode (+ve) electrode, cathode (-ve) electrode,
converter slag, and fu rnace temperatures were recorded
simultaneously and the power was varied. The experimental
results are shown in Figures 4.36. Note the slag-starting
temperature was close to 1210 OC, which is lower than the
previous experiments by 40 OC. With zero power input, the
anode, cathode and slag temperatures were about the same ( f 5
O C ) . As the voltage was increased (0-3 V DC), the
temperature difference between the anode and cathode was (+
2-32 OC), ( + 0-22 O C ) between cathode and slag, and f i n a l l y
(+ 0-40 O C ) between anode and slag. With this low voltage
(< 3.0 V) , the power was 135 watts and the current reached
61 amps, above system limit.
The anode electrode temperature was above the cathode
electrode temperature and above the slag temperature. With
this temperature difference, the reaction rate at the anode
slag interface is h i g h e r than expected which explains the
high gas liberation at the anode, and that the mass loss of
the anode is greater than at the cathode. The next section
will discuss the electrolysis contribution to the rate of
slag reduction.
Chapter 4, Page 90
Table 4.9 Etecboda Tip Temperature Experlments Steady Stak Data Summary
I -- - -
Data 8 Numbe cm cm cm' V A W ~ c m " OC 'C I min" *c
TYPE
13-Aug rcs i w26
13h~ tcs 1 EXP 26
WAug rcs 1 EXP 29
Electrode Tip Twnprature ds Expenments 26.28 13 18Augurt 1998
Expenment E'ecvode Mpth
Diameter :Fe VotUge P-r Curronl ~ ~ ~ ~ 2 1 h i r e y;/penture Na F,w
E I W o d e Temperature
4 . 8 ExperiP.ntal and Theoretical Catbon Consirnption
Table 4.10 lists the carbon consumption for the AC and
DC experiments. The experimental carbon consumption was
measured by weighing t h e electrodes before and after each
experiment. The theoretical carbon consumption was
calculated from the %CO and %CO2 in off-gas with the g a s .
infra red analyzes and from nitrogen flow rate integrated
with t i m e as follows:
%CO, %CO lm01 l2gofC Co keused = Atimq,,, ,c v& x +-)x-x
mn 100 24.1 L moi
Experimental and theoretical values are very close to each
other in most cases. For a few experiments, the
experimental values are high; meaning that the electrode
must have broken off and fallen in the slag.
During the AC experiments, the left and right
electrode consumption's were very close to each other while
for the DC experiments, the anode was consumed up to five
times more than the cathode for electric furnace slag.
This was a l s o visible where the tip of the anode electrode
was much thinner than the cathode electrode, Figure 4.37.
During converter s lag OC experiments, the anode was
consumed more than the cathode but the difference is not as
high as for the electric furnace slag experiments. It 1s
not clear why, but it is probably because of the high
magnetite content in converter s l a g and also due to the
degree of reduction. For the converter slag experiments,
t h e magne t i t e c o n t e n t was decreased from 29 t o 1 0 %, w h i l e
during electr ic furnace slag exper iments ; t h e magnetite
c o n t e n t was decreased from 8 t o 3 % . For t h e e l e c t r o d e
s e p a r a t i o n exper iments , the non-separated e l e c t r o d e
consumption was high due t o poor p r o t e c t i o n w i t h n i t r o g e n .
F igu re 4 . 3 8 shows t h e Ni, Cu, and Co c o n t e n t s i n t h e
final s l a g b e f o r e and a f t e r r e d u c t i p n wi th AC o r DC. For
t h e electric fu rnace s l a g , t h e N i composi t ion was reduced
more w i t h DC t h a n AC, whi le f o r Cu it is t h e same r educ t ion
and t h i s is because t h e Cu con ten t is 0.05 o r lower, w h i c h
i s below d e t e c t i o n l i m i t . Whereas for c o b a l t , t h e same
results were obtained f o r AC and DC.
F o r c o n v e r t e r slag, t h e DC experirnents were much
better t han AC since t h e N i and Co c o n t e n t s o f the s l a g
were lowered s i g n i f i c a n t l y below the s t a r t i n g slag c o n t e n t
v a l u e s . So, i t seems t h a t with DC, w e are a b l e t o reduce
t h e s l a g more and g e t h i g h e r pay m e t a l s recovery . Although
we have high e l e c t r o d e consumption (2-3 times more) w i t h OC
exper iments , w e do have a b e t t e r r e d u c t i o n average, so it
al1 depends on what you want t o do. The lower p a r t of
Figure 4.38 shows how t h e N i and Co c o n t e n t s d e c r e a s e w i t h
decreasing magne t i t e c o n t e n t in electric f u r n a c e slag AC
r e d u c t i o n . The area on the graph below 0 .05 %, is below
the d e t e c t i o n l i m i t .
E l e c t r o l y s i s c o n t r i b u t i o n d u r i n g the c o n v e r t e r s l a g
r e d u c t i o n exper iments is higher t h a n d u r i n g electric
f u r n a c e slag, and t h i s is due t o t h e h igh c u r r e n t s reached.
Based on Faraday's Law, the e l e c t r o l y s i s c a l c u l a t i o n i s a
function of t h e c u r e n t .
' Chaptcr 4, Page %
C S 1 - ~ 6 0 -
min 1 C
96500.- x 4 ë ~ r e a , r n ~ mol
Table 4-11 lists the experimental reduction rate and the
rate calculated by electrolysis only. From the values
presented, it seems that the electric furnace slag rates
are close to each other while for converter slag, the
electrolysis contribution is higher and this is due to
higher currents as mentioned before. These electrolysis
calculations assume 100% current efficiency.
F i g u r e 4 . 3 9 is a crude graph of these results and it
shows that electrolysis contribution during reduction is
rather important and significant. For now, electrolysis
contribution seems to be over 50% of the total reduction.
Chaptcr 4, Page 97
Table 4.10 Experimental and T heoretkal Gtaphtie Consumption
Activation Energy Sampk Type and Date Ni F e '
A C
c u R
Theorctccal Expefimerital Leil Electiode Riaht Electrade kJ 1 moi R~ , Graphite Consumptlon, grams
06MuTEFlMPl 06 My TEFI W 1. Middh 12 Mar TEFI EXP 2 04MayTEFlMP3 18 May TEFI W 4 29 May f EFl W 7 19 May TEFl MP 7, Middh 11 Jun TEFl EXP 8
R E N T
06 Jul TCSl MP 15 17 Jul TCSl W 16 18 Jul TCSI W 17 n JUI TCSI EXP 18 23 Jul TCSl W 19 n JUI TCSI EXP ts, MU~I.
11 Jun TEFI W 8. Middle
24 Jun TEFI MP 10 29 Jun T F 1 W 11 O1 Jul TEFI EXP 12 01JuITEFl W12.Middh û2 Jul TEFI W 13 03 Jul T E 1 MP 14 24 Jul TEF 1 €XP 20
0.39 12.7 6.6 nia nia Na 0.85 12.7 11.2 14.7 8.3 6.4 1.04 13.7 13.3 13.3 5.8 7 4 1.7 14.0 9.3 t 2 0 5.9 6.1
2.02 14.3 11.9 12.0 5.2 6.8
<.OS 6.8
26 May TCSl M P 5 28 My TCSl MP 6 12 Jun TCS~ EXP 9
0.069 2.5 26 12.6 12.0 0.5 0.099 2.3 3.2 3.7 3.1 O. 6 <.O5 3.1 6.4 8.8 6.3 2.5
0.073 3.1 0.054 4.3 5.2 13.6 8.7 5.0 <.O5 4.2 6.6 7. O 5.8 1 2
0.081 3.7 8.3 11.6 6.1 5 6
1.06 17.1 3.3 3.6 1.9 1.7 1.06 17.9 2.6 2.8 1.5 1 3 1.59 15.5 3.4 2.7 1.4 1 2
1 O Aug TEF t W 24 11 Aug TEFI EXPS
All Exptrimeni8.1998
n/a 616 1 .O as1 0.8
0.14 4.9 0.7 2.1 2.1 n/a <,O5 2.2 1.3 1.5 1.5 nla
31 Jul TCS1 W 21 U4 Aug TCSl W 22 06 Aw TCS1 MP 23
1.94 24.7 2 4 824 3.9 78 7 1.61 43.1 7.2 57.2 12.4 45.3 0.62 39.5 5.7 41.3 5 0 36.3
Graphite Consurnption Compaflson
AC Electrode Consumption Comparison Electric Furnace Slag and Converter Slag
i Electric Fumace, Left Electrode
Electric Fumace, Right Electmde - - - - - - - -
Cl Converter, Left Electrode - - - - - - - -
R Converter, Right Electrode - - - - - - - -
1 2 . 3 4 5 6 7 8 9
Experiment Number
DC Electrode Consumption Comparison Electric Furnace Slag and Converter Slag
1 OConverter, Anode
1 - - - - - 1 O Converter, Cathode
Expriment Number
AC and DC Experiments Figure 4.37, Page 99
Reduction Experiments
Maximum % Reduction
Element L 1
i
AC Power, Fe304, Ni, and Co Percent, Originally Electric Furnace Slag Contained 8% Fe304
AC and DC Gcpen'ments Figure 4.38, Page 100
Table 4.1 ExperYnental and Electrolysis Rates of Reduction
1 Electric Furnace Slag 1 Converter Slag 1 Rate of Reduction in mole 4 min' m"
r 1 1 1 1 1 1
( EXP # 1 Experimental 1 Electrolysis 1 €XP # 1 Ewpenmental ( Electrolysis ]
Efectrolysis Contribution Chapter 4, Page 101
DC, Reduction Comparison Electric Fumace Slag 6 .
-c Rate of Reduction - - 0 - - ~lectrol~sis 1
I O 20 30 40 50
Experiment Number
DC, Reduction Comparison Converter Slag
Expewiment Number
Electrotysis Contribution Figure 4.39, Page 102
DISCUSSION
The expe r imen t s w i t h AC and DC c u r r e n t r e s u l t e d i n
similar r e d u c t i o n r a t e s with a few key d i f f e r e n c e s . With AC
c u r r e n t , t h e r a t e o f slag r e d u c t i o n was 4-5 mole O2 / min m2
a t 1250-1500 watts power i n p u t w i t h both e l e c t r o d e s consumed
e q u a l l y . With DC c u r r e n t , similar rates of r e d u c t i o n were
achieved with 400-500 watts power input and t h e anode was
consumed 2-5 times more than t h e ca thode .
With DC c u r r e n t r e d u c t i o n it i s c l e a r t h a t more
r e d u c t i o n was achieved resulting i n h i g h e r pay metals
r e cove ry t h a n w i t h AC c u r r e n t . The chemical compos i t i ons of
t h e e x p e r i m e n t a l s l a g samples are l i s t e d i n Tab l e 4 . 1 for AC
and DC c u r e n t . The magne t i t e c o n t e n t was relatively
d e c r e a s e d more w i t h DC t h a n AC c u r r e n t .
With DC
because o f the
( h i g h e r t h a n
power i n p u t , t h e anode was consumed more
high t empe ra tu r e a t the tip o f t h e e l e c t r o d e
c a t h o d e by -25 OC) . and also because
e l e c t r o l y s i s ( o x i d a t i o n on t h e anode). Note t h e rate
s l a g r e d u c t i o n as it i n c r e a s e s compared t o the increase
s l a g b u l k t e m p e r a t u r e and t h e e l e c t r o d e t i p t e m p e r a t u r e .
seems t h a t t h e r a t e of s l a g r e d u c t i o n i n c r e a s e s
a cco rdance w i t h i n c r e a s e of e l e c t r o d e t e m p e r a t u r e . This
complements t h e s u g g e s t i o n t h a t the t e m p e r a t u r e of t h e
e l e c t r o d e is wha t controls t h e rate of s l a g r e d u c t i o n . This
a l s o a f f e c t s t h e c a l c u l a t i o n s of t h e a p p a r e n t a c t i v a t i o n
energy . I n a d d i t i o n , the temperature range u s e d t o
c a l c u l a t e these E,'s i s rather narrow and t h i s could be why
some o f the values o b t a i n e d were high and f a i r l y scattered.
Chapicr 5, Page f O3
Figu re 5 . 1 shows the rate of slag r e d u c t i o n i n mol O2 /
min m2 f o r electr ic f u r n a c e and c o n v e r t e r s l a g under v a r i o u s
c o n d i t i o n s o f power input. The s l a g t empe ra tu r e f o r F igu re
5 . 1 is about 1260 OC f o r al1 t h e cases excep t for t h e no
power case where t h e s l a g t empe ra tu r e is 1220 OC. The
c u r r e n t density i s 2.5 ~crn-*. I n a l 1 cases, t h e c o n v e r t e r
s l a g r e d u c t i o n r a t e s are h i g h e r t h a n t h e electr ic f u r n a c e
rates. Note a l s o t h e l a rge d i f f e r e n c e between t h e rates f o r
t h e anode and ca thode for elect r ic f u r n a c e s l ag , w h i l e f o r
c o n v e r t e r s l a g t h e y a r e abou t t h e same.
F i g u r e s 5 . 2 and 5 .3 show t h e r a t e o f reduction v e r s u s
t empe ra tu r e f o r DC power, AC power, and for No power. The
d a t a plotted was picked f o r c o n s t a n t c u r r e n t d e n s i t y .
Although t h e r e i s some s c a t t e r i n t h e d a t a , t h e c o n v e r t e r
s l a g r a t e is h i g h e r than electr ic f u r n a c e s l a g i n a l 1 cases.
I t is presumed t h a t t h i s h i g h e r r e d u c t i o n and pay
m e t a l s recovery w i t h DC c u r r e n t i s more v a l u a b l e t h a n t h e
e x t r a cost o f t h e e l e c t r o d e consumption. Ope ra t i ng p l a n t s
w i l l choose t h e method of r e d u c t i o n f o r t h e i r s l a g s
depending on t h e i r needs. If t h e l e v e l of r e d u c t i o n with AC
is enough to meet c e r t a i n p r o f i t margin and env i ronmenta l
r e g u l a t i o n s , t h e n AC power s h a l l be used. If t h e i n t e n t i s
t o reduce t h e s l a g as rnuch as p o s s i b l e and r e c o v e r most of
t h e pay metals from t h e s l a g , t hen DC power i n p u t should be
t h e c h o i c e .
Special Case
- - . _ _ . -- .. - . - -- _ .. - - - - - -- - __
Ni Slag Reduction Rates Under Different Conditions
Slag Temperature = 1260 OC, CDD = 2.5 ~crn - *
Discussion Figure 5.1, Page 105
DC Power, 2-3.4 Acrn" l
l
1
...............*.............. ...; 1
t
i l
I
................. -.--*......----*., 1 1
I l
I
Slag Temperature, O C , i 4
4 t
AC Power, 2.6 ~crn'* 2.5
I
/ Electric Furnace Slag 1
t b
i 0.01. l . l fi
I . , 1 . ! i i . i i . i , , , I
I 1220 t 230 1240 1250 1260 1270 1280 1 t
l
I
1 ?
j Slag Temperature, O C i
Discussion Figure 5.2, Page 106
6 . 1 Conclusions
Consider the graphite surface as a wall where COZrg) is
consumed and CO4,) is generated. The slag bulk contains al1
the i r o n as magnetite and wustite. The Boudouard reaction
happens on the graphite-gas interface. This reaction is
endothermic and it will react quite fast at temperatures
above 1200 to 1250 OC. The magnetite will t hen react with
the CO formed and gets reduced forming CO2(,). This occurs
at the gas-slag interface. The rate lirniting step or the
slowest step is believed to be at the gas-slag interface.
From the basic slag reduction experiments with AC and
üC power input, slag reduction rates were successfully
measured as the reduction progressed. The rate of
reduction increased with increasing electrode depth and
increasing slag temperature. With DC power input, the
reduction yielded more pay metals than with AC power input
for approximately the same reduction tirne. The rate of
slag reduction with DC was higher than that of AC, and
about 2-3 times less power was required.
With AC reduction, it was observed that both
electrodes lost the same amount of graphite, while during
DC reduction, the anode lost about 2-5 times more of its
mass than the cathode. This observation complernented with
the electrode separation experiments explained and showed
more feedback on why we are getting more reduction with DC
power. The electrode separation experiments performed
Chapta 6, Page 108
showed h i g h e r gas g e n e r a t i o n and higher r educ t ion r a t e s a t
t h e anode t h a n a t t h e ca thode .
T h e e l e c t r o d e t i p experiments w i t h AC power showed
h i g h e r t empera ture a t t h e t i p (10-50 O C ) depending on t h e
amount of power i n p u t . With DC power input , t h e ca thode
e l e c t r o d e t i p was about -25 O C higher than t h e b u l k s l a g ,
whi le t h e anode was -50 OC h ighe r . T h i s e x p l a i n s why t h e
anode i s be ing consumed more than t h e cathode. Also ,
e l e c t r o l y s i s i s h e l p i n g t h e reduc t ion process and speeding
t h e r e d u c t i o n c l o s e t o t h e anode.
Cons ider ing prev ious r e sea rch f ind ings , pay m e t a l s a re
depoç i t ed on t h e cathode, whi le ox ida t ion is o c c u r r i n g on
t h e anode. Also from t h e e l e c t r o l y s i s c a l c u l a t i o n
performed, it seerns t h a t t h e e l e c t r o l y s i s c o n t r i b u t i o n t o
t h e r a t e of r e d u c t i o n cou ld be more than 5 0 % . Th i s
conf i rms t h a t DC o p e r a t i o n seems t o be a better o p t i o n than
AC and that e l e c t r o l y s i s c o n t r i b u t e s t o t h e r e d u c t i o n i n
electric fu rnace s l a g and c o n v e r t e r s lag .
A s for t h e a c t i v a t i o n e n e r g i e s calculated, t h e v a l u e s
compare r ea sonab ly w e l l t o p rev ious ly r epo r t ed va lues .
However, s i n c e t h e e l e c t r o d e t i p temperature is h i g h e r than
t h e s l a g bu lk , i t is n o t obvious which temperature s h a l l be
cons ide red for t h e a c t i v a t i o n energy c a l c u l a t i o n s . This
may e x p l a i n some of t h e h igh a c t i v a t i o n energy v a l u e s
c a l c u l a t e d . These a c t i v a t i o n energy numbers s h a l l be
cons ide red as apparent a c t i v a t i o n ene rg i e s .
Chaptcr 6, Page 109
Finally, considering these higher rates of reduction
as well as improved metal recoveries with DC, a DC slag
reduction operation seems a better choice than an AC.
6 . 2 Recommendations
The author recommends the continuation of this
research especially with DC current. From an experimental
point of view, the cooling brass cap on top of the
alumina/mullite tube should be re-designed to fit better
the input and output streams. Addition of coke and coal on
top of the slag surface to examine the effect on the rate
of reduction. More DC electrode tip temperature
experiments should be performed using an 8 KVA DC power
source. The pay metals s i z e , composition, and distribution
if examined will shed more light on-how the pay metals are
collecting at the bottom of the crucible.
F i n a l l y , from an industrial point of view, it is the
%reduction that counts and how much does it cost to achieve
a certain level of pay metals recovery; hence, an economic
analysis of a DC slag reduction operation would be h e l p f u l .
Chaptcr 6, Page 1 10
REFERENCES
J. Diakow, Y. Mak, and R. Orr, "Metallurgy of the
converting process in the Thompson smelter", The 1 4 ~ ~
Annual Conference of Metallurgists, Edmonton, Alberta,
August, 1975
N. Stubina, J. Chao and C. Tan, "Recent electric
f u r n a c e developments at Falconbridge", Non-ferrous
pyrometallurgy, Trace metals, Furnace practices and
energy efficiency, Proc. of the Int. Symp., CIM,
Edmonton, 1992, pp. 245-257
W.G. Davenport, and A.K. Biswas, "Extractive
Metallurgy of Copper", 3rd edition, Pergamon, 1994
V. M. Zamalloa, "Mechanisms of *roas t ing , reduction and
smelting of Ni-Cu concentrates", Ph.D. thesis,
University of Toronto, Department of Metallurgy and
Materials Science, 1995
Fathi Habshi, " Principles of EXTRACTIVE METALLURGY",
Vol. 3, Pyrometallurgy, Gordon and Breach Science
Publishers, 1986
A. Paul, B. Deo, and N. Sathyarnurthy, "Kinetic mode1
for reduction of iron oxide in molten slags by iron-
carbon melt", Steel Research, Vol. 10, 65, 1994, pp.
414-420
A. Warczok and T.A. Utigard, "Fayalite slag reduction
by solid carbon", Can. Metal. Quart, Vol. 37, 1998,
No. 1, pp. 27-39
T. Soma, Y. Sasaki, "Reduction mechanism of molten
iron oxide by solid carbon", Metal. Trans., O 88,
1977, pp. 189-190
References, Page 1 1 1
H. Kra ine r , H.P. Beer, and H. Brandl , "Investigation
on t h e r e a c t i o n between s o l i d ca rbon and l i q u i d , h igh
i r o n o x i d e ( I I ) c o n t a i n i n g slags", Tech. M i t t e i l u n g
Krupp Forschungsberg. Vol. 2 4 , 1966, pp. 136-146
M. P . Shalimov,
"Mechanism and
with carbon",
31-34
V.N. Boronenkov, and S .A . Lyamkin,
k i n e t i c s of r e a c t i o n of FeO-Si02 m e l t s
Russian Metallurgy, Vol. 6 , 1980 , pp.
G.S. Yershov, and E.A. Popva, "Reduction of iron o x i d e
and silica i n molten slags by carbon", Russ ian
Me t l l u rgy and Mining, 1964 , p. 13
I.P. Pazdnikov, V.I. Deyev, and V.I. Srnirnov,
" K i n e t i c s of i r o n oxide r e d u c t i o n by ca rbon monoxide
i n CuZS-FeS-Fe0 melts", Russ ian Me ta l l u rgy and Mining,
Vol. 1 6 , 1967, pp. 22-26
F. Fun, "Rates and mechanisms of Fe0 r e d u c t i o n from
s l ags " , Meta l . Tranç. , Vol. 1, 1970, pp. 2537-2554
W.O. Ph i lb rook , and L.D. Ki rkb r ide , "Rate of Fe0
r e d u c t i o n from a Cao-Si02-A1203 slag b y ca rbon
saturated i ron" , J. of Metals, T r a n s a c t i o n s AIME,
1956, pp. 351-356
M. Ozawa, S. Kitagawa, S. Nakayama, and Y . Takesono,
"Reduct ion of F e 0 i n molten slags by s o l i d carbon i n
the electric arc furnace operation", Transactions
I S I J , Vol. 26, 1986, pp. 621-628
B. Sarnia, A.W. Cramb, and R. J. Fruehan, "Reduct ion of
Fe0 i n smelting slagç by s o l i d carbon: Exper i rnenta l
r e s u l t s " , M e t a l l u r g i c a l and Materials T r a n s a c t i o n s ,
Vol. 278, 1996, pp. 717-730
T.A. Utigard, G. Sanchez,
C. Diaz, D. Cordero, and
k i n e t i c s o f l i q u i d i r o n
J. Manriquez, A. Luraschi,
E. Almendras, "Reduct ion
oxide-containing slags by
References, Page 1 12
ca rbon monoxide", M e t a l l u r g i c a l and M a t e r i a l s
T r a n s a c t i o n s , Vol. 288, 1997 , pp. 1-6
C . Borg iann i , 'K ine t i c s o f coke r e d u c t i o n of mol ten
s l ag r i c h i n iron oxide", I r o n and S tee lmaking , Vol.
2, 1978 , pp. 61-66
1. Sommervil le , P . Grieveson, and J. Tay lo r , " K i n e t i c s
o f r e d u c t i o n o f i r o n o x i d e i n slag by ca rbon i n i r o n :
Part 1 effect of oxide concen t r a t i on" , Ironmaking and
S tee lmaking , Vol. 1, 1980, pp. 25-32
K . Upadhya, 1. Sommervil le , and P . Grieveson,
" K i n e t i c s o f r e d u c t i o n o f i r o n oxide i n s l a g by carbon
i n i r o n : P a r t 2 e f f e c t o f carbon c o n t e n t of i r o n and
s i l i c a c o n t e n t of s l a g " , Ironmaking and Steelrnaking,
Vol. 1, 1980, pp. 33-36
W. Channon, R. Urquhart, and D. Howat, "The mode o f
c u r r e n t t r a n s f e r between e l e c t r o d e and s l a g i n t h e
submerged-arc furnace" , J o u r n a l of t h e Sou th A f r i c a n
I n s t i t u t e of Mining and Meta l lu rgy , 1974, pp. 4-7
B . Bowman, "Performance comparison u p d a t e AC v s . DC
fu rnaces" , I r o n and S t e e l ~ n ~ i n e e r , J u n e , 1 9 9 5 , pp.
26-29
1. Dal, N. L i , and E. Grimsey, "The r e d u c t i o n of
n i c k e l s l a g by g r a p h i t e e l e c t r o d e s with AC and DC
c u r r e n t s " , P y r o m e t a l l u r g i c a l fundamentals and p r o c e s s
development , CIM, Sudbury, Vol. II, 1997, pp. 77-92
H. J. Grabke, "Oxygen t r a n s f e r and carbon g a s i f k a t ion
i n t h e r e a c t i o n of different carbons w i t h CO2", Carbon,
Vol. 1 0 , 1972, pp. 587-599
A. Sa to , G . Aragane, K. Kamihira, and S. Yoshimatsu,
"Reducing Rate of Molten Iron Oxide by S o l i d Carbon o r
Carbon i n Molten Iron", T r a n s a c t i o n s I S I J , Vol. 27,
1987, pp. 789-796
References, Page 1 13
26. 0. Barth, "Electric smelting o f sulfide ores", The
Royal Institute of Technology, Stockholm, Sweden, pp.
241-262, 1960
27. A. Dymnich, N. Semenov, D. Gerchikov, A. Paukov, and
D. Khazan, "Kinetics of carbon oxidation in an iron
alloy i n a n oxidiçing slag", Russian Metallurgy, 22,
IV, 1974, pp. 30-33
28. A. Warczok, and T. Utigard, "The effects of
alternating and direct c u r r e n t ç on the rate of slag
c l e a n i n g " , Non-Ferrous Pyrometallurgy: Trace Metal,
Furnace Practices and Energy Efficiency, CIM,
Edmonton, 1992, pp. 403-419
29. P . P o p e l a r , " C u r r e n t - v o l t a g e behavior during anode
effect in c r y o l i t e melts", M.A.Sc. t h e s i s , U n i v e r s i t y
of Toronto, Department of Metallurgy and Materials
Science, 1995
References, Page 1 14
APPENDICES
A - G
Appendix A: Experirnental s l ag samples a n a l y s i s
£rom INCO Limited, Thornpson Smel te r
Slag graphite c o n t a c t a r e a c a l c u l a t i o n s 2
Fun' s reduc t ion mode1 development 3
Some important definitions 5
Nitrogen flow c a l i b r a t i o n procedure 7
Other calibration graphs 9
Electr ic furnace c i r c u i t diagram 1 2
Experiments d e t a i l c a l c u l a t i o n s 13
Table Al: Expetimental Slag Samples, Thompson INCO Limited
, Molecular weight) Electric Furnace Slag 1 Converter Slag
L I g moï1 1 w t % m o ~ % mol 1 ut% mol% mol
Total 1
Electric Furnace Slag = TEFl Converter Slag = TCSl
Mass Balance Appendix A, Page 1
Slag-Graphite Contact Area Calculations
Area o f base circle = x . r2 2 0 . 5 Area o f cone = x . r. s = x . r . . ( h 2 + r )
Pythagorous theorem: s2 = h2 + r2
Volume of cone = (1/3) n . r 2 . h
Diameter = d = 2.r
For a c y l i n d r i c a l g r a p h i t e rod dipped i n liquid metal:
Sur face area = 2nr. i~ + n. r2
A f t e r few initial experirnents, the cone area was found t o
be t h e correct one t o measure t h e ' c u r r e n t density. The
r e a s o n i s t h a t t h e reduction i n i t i a l l y p r o g r e s s e s rapidly
and t h e e l e c t r o d e s shape changes from c y l i n d r i c a l t o a
c o n i c a l shape.
Appcndix A, Page 2
Fun's Reduction Model Developatent
Fun's kinetic modell3 consideers the Fe0 r e d u c t i o n i n
three p a r t s . Up t o 5% FeO, between 5 and 40 % FeO, and
over 40 % FeO, (mass pe rcen t ) .
(BI. 1)
(BI. 2)
(BI. 3)
(Bl. 4)
(BI. 5)
(BI. 6)
FeO, A l - ln[-] = -[
1 1; a = PCDY F d
FeO, V - 1 I 1 +-+- nrur
1 - \\te= 1" r ep resen t s t h e gas-slag chernical r eac t ion a.k,
1 "term 2" r ep resen t s the gas-graphi te r e a c t i o n a.K.k,
1 "te- 3n r e p r e s e n t s the rnass transfer of Fe0 in slag
k m
For low mass contents of Fe0 (< 5 % ) ' terms 2 and 3
dominate.
For intermediate rnass con ten t s of FeO, al1 terms are
important.
For high mass contents of Fe0 (> 4 0 % ) , terms 1 and 2
dominate.
Appendix A, Page 3
The regular s o l u t i o n model was used t o determine the
activity c o e f f i c i e n t s needed. The r e g u l a r s o l u t i o n model
uses t h e i n t e r a c t i o n energy paramete r s be tween c a t i o n s .
T h e e q u i l i b r i u m constant K f o r r e a c t i o n 81.3 , was
calculated from AGO = -49.705 + 47.50xT i n J o u l e s .
FeOt [= ] c o n c e n t r a t i o n of Fe0 i n s lag a f t e r t i m e t , rnass %
FeO, [=] i n i t i a l c o n c e n t r a t i o n of F e 0 i n s l a g , mass %
A [ = ] gas-graphite and gas-slag reaction a r e a , m2
V [= ] volume of slag, mJ
nt,, [ = ] t o t a l number of moles of s l ag
k2 [= ] r a t e c o n s t a n t of forward 81.3
k3 [ = ] r e a c t i o n rate c o n s t a n t f o r t h e Boudouard r e a c t i o n ,
mol m-* s-'bar-'
k [ = ] e q u i l i b r i u r n constant of B 1 . 3
Pco [= ] p a r t i a l pressure of CO in gas p h a s e , bar
yre0 [=] activity c o e f f i c i e n t o f Fe0 i n s l ag
kFeO [= ] mass t r a n s f e r coefficient of Fe0 in slag, m.s" - E
i is t h e excess p a r t i a l rnolar f r e e energy
AH^ is t h e r e l a t i v e partial molar e n t h a l p y
Xj and Xr [=] fractions of cation s p e c i e s j and k
aij [=] interaction energy parameter between cations
Appendix A, Page 4
Activation Energy
I n order for any reaction to occur, the colliding
molecules must have a t o t a l kinetic energy equal to or
g r e a t e r than the activation energy, which is the minimum
arnount of energy required to initiate a chernical reaction.
Lacking this energy, the molecules rernain intact, and no
change results from the collision.
E, is the a c t i v a t i o n e n e r g y [kJ/mol], R is the gas
c o n s t a n t [8.314 J/K.mol], T is the absolute temperature,
and e is the base of the n a t u r a l logarithm. The q u a n t i t y A
represents the collision frequency, and is called the
frequency factor.
I A p l o t of ln k v e r s u s - gives a straight line whose slope rn
T
E a , and whose intercept b with the o r d i n a t e is equal t o - - R
[ t h e y axis] is In A.
Appendix A, Pagc 5
Metal Loss
Meta1 losses in slags are dissolved or mechanically
entrained. When dissolved, Cu, Ni, and Co are uniforrnly
distributed in a single homogeneous phase. When physically
entrained, this is due to incomplete phase separation.
Nickel seems to be present in the slag both in the form of
matte inclusions and dissolved nickel oxide, Cobalt main1 y
a s dissolved CoO, and Copper is entrained as Cu$.
3 Definitaon of Terms
Voltage is the potential difference in electrical terms ond
is expressed as energy (W) per unit charge (Q).
Elec t r i ca l current is the movement of free electrons from
the negative end of the material to the positive end ( C h ) .
Resistance of the slag is the opposition to current.
Diodes conduct current in only one direction and h e n c e are
used i n rectifier circuits.
Rectification is the process of converting AC to pulsating DC .
Appendix A, Page 6
N f t t o g e n Flow Calibration Procedure
A typical see through cylindrical glass tube equipped
with a soap bubble pump a t t h e bottom of it was used to
determine the accuracy of t h e nitrogen flow meter.
The cylindrical glass tube dimensions were taken and
the nitrogen gas was allowed to enter from the bottom and
bubbles were pushed up the cylinder by the gas through a
30-cm distance. The time was measured repeatedly over O to
5 l i t e r s per minute.
The following is an example to illustrate the procedure:
Volume = Area. h = 1.089 x 1oV4 m3
Liter m3 One - nitrogen flow rate = 1.6667 x IO-' -
minute s
Volume - 1 .089x 104 m' - = 6.53 seconds Flowrate m3
1.6667 x 10-' - S
T h i s ca lcula ted t i m e was compared to t h e actual time
it took for t h e b u b b l e s t o pass t h e 30 c m c y l i n d e r , see
Table A2, From table A2 it was determined that the actual
f l o w is 10% more than t h e digital reading. Hence al1 flow
rate data were multiplied by 110%.
N o t e : the nitrogen flowmeter is ca l ibra ted from t h e manufacturer a t room temperature and 1 atm.
Appendix A, Page 7
1 Table A2 Calibration Data for the OMEGA N2 FlowMeter 1
Diameter = 2.1 cm Distance = 27.5 cm Area = 3.46 cm2 Volume = 95.25 cm3
= 9.52E-05 m3
Flowmeter = 1 .O0 lrnin*' 0,001 00 m'min-' 1.67E-05 m3sed
Time = Mass Flow meter
Flow lmin-' 0.10
firne sec
CONCLUSION
Whatever you read from the flowrneter must be multiplied by 11 0%. Note that the range of calibration was between 0.1 - 2.0 ~rnin-'
Actual Time Actual AVG 36 Differ
16.0 17.4
11.6
8.3
0.6
8.8
l l . 7
12.2
Appendix A, Page 8
Slag Reduction Apparatus Calibration Graphs
Type R Thermocouple
- - 1 I
- Temperature = 71.9 mV + 248, R* k 1 *
1
I I
I l
I
1
1
l
I
1
I
1
I
I
I 1
I
l
1
I I
1
1 I
I
Voltage, DC
Calibration Appendix A, Page 9
Slag Reduction Apparatus Calibration Graphs
Potentiometer, Electrode Level
AC Transformer Calibration
Voltage, AC
Calibration Appendix A, Page 11
Electric Furnace Circuit Diagram
Two Way switch, electrode level
- + Temperature Controll
Rad
R ig h t elect rode I 1 F
Tnnsfomer 0-150 VAC ~ V O C
Diegram Ai , Page 12
Expetiments Detail Calculations and Special Comments
Data was sampled every 5 seconds. The N2 flowrate was aâjusted by + 10% der calibrating the flowmeter with the bubble apparatus. Voltage reading was d by the Fluke DAQ, no adjusbnent was required. Current was measured by the Hollow current sensor box and DC current shunt, both correspond very well with the hand clamp. Slag temperature was m e a s d by an R type thennocouple dipped 2-4 cm in the slag protected
with an almina sheath. Electrode depth was controlled manually. The surfixe iuea of the electrodes was considered to be a cone head. This was obsenred on several occasions by just pulling out the electroâes shortly after immersion in îhe slag. Surface a m of a Cone = Pi Radius S lant = Pi Radius * ( depth2 + radius' f 5
C u m t Density = Cumat mcvurrd in Amp
&Ca d - "'O ratio is just the prcentage read hom the infrared analyzcr SC@ Volume of 1 mol at 20 degrees Celcius, PV = nRT
fiaIeofRe&cfJon*Atta d , Dcgree of Reduaion (%] = 100 Co
n Reducible oxygen = Oxygen containeâ in Fe304, Feû, NiO, and Co0 Frorn the sarnple analysis we have %Fe304 and %Fe, so we can determine how much Fe we have and then how much Fe304 and the difference will result in the amount of Feû. Ni is present as Ni3& and NiO, so we will considet half the % given for N i 0 Co is mainly present as Co0 Cu is present as Cu2S mainly 100 g sample Exarnple: Analysis of iNCO slag sample : 3.24 % Ni ,0.77 % Co,
28.9 % Fe304, and 51.4 % Fe total
3.24 16of O x . in Ni0 = +* 100 g , . ,,,,,?Fa = 0.694
Prinred by Matkmic4 for Shicirnts Appendix A, Page 13
In Fe3 o4 we have3 moles o f F e , therefore: 3 @0.1284 mol ofFe= 0.3744 mol ofFe contained in Fe3 O4
The rest of the moles are in Fe0 : thaî is = 0.9203 mol - 0.3744 mol = 0.5459 mol Fe0
Oxygeri in Fe3 O4 = 4 0.1248 mol 16 g = 7.9872 g Oxygen in Feû = 0.5459 16 = 8.7344 g Total oxygen = 0,694 + 0.164 + 7.9872 + 8.7344 = 17.58 g
14 Amount of Used Coke in grams: 12 orc =Atime(min)*(& Flow $ ) r ( s + * ) * 21.irktlt t
S 5 How fast Fe3 O4 is king reduced: initial amount is given in %:
initial = 100 g = 28.9g '" *oh[=]BrBmS 28.9 g - (e + w) * lV2 Flow & * Atime (min) * to have it in percent, just Divide by the initial sarnple m a s and multiply by a 100
Printed by Mctlhcmatica for S&nw Appendix A, Page 14
Appendix B: AC c u r r e n t data sample 1
Data sample reduction calculation 3
AC, Electric furnace experimental graphs 5
AC Power and Temperature Profile Increasing Voltage Setpoint AC Experiments
Experiment 2 Tfurnace = 1255 oc Appendix 8, Page 1 06 March 1998
AC Power and Temperature Profile Increasing Voltage Setpaint
Expriment 2 Tfurnace = 1255 OC Appendix 8, Page 2 O6 March 1998
AC ~owcr and Tempentum Pmnk uata sample c o ~ k c ~ o n
Table B1 AC Curtent D a t a Sample, 04 May TEFl EXP3
Time VoLtage urrent C.D. Temperature Power Depth Area Nz
Time V o l t a g e urrent C.DI Temperature Power Depth Area Nz 4 : ? 5 15 10 1 . 7 1213 156 2.3 3-62 4.0 4 :27 15 11 2 . 8 1215 160 4 . 0 4:30 1 5 11 2.8 1220 162 4.0 4:33 15 10 2.7 1223 157 4.0 4:36 1 5 10 2.6 1225 154 4 - 0 3 4:38 15 10 3.6 1227 150 4.03 4 :40 I5 I 0 2.7 I228 L55 4 . 0 3
Decrease voltage t o zero and d ip the electrodes, then increase voltage t o 15 V
Time Volsaqe urrent C.D. Temperature Power Depth Area Nz 4 : 45 15 16.7 2.6 1235 254 3.9 6.44 4.03 4:49 15 16.8 2.6 124 1 2 54 4 .04 4:51 15 16.7 2 .6 1246 2 52 4 .04 4:53 15 16.7 2.6 1246 252 4.04 4:55 15 16.6 2.6 1246 24 9 4.05 4:58 15 16 .3 2.5 1246 245 4 - 0 5 5:OO 15 16 .1 9 .5 12 4 6 2 4 3 4 .05 5 : 02 15 16 .3 2 .5 12 4 6 2 4 6 4 .flS
rime Volsaqe urrenr C.D. Temperature Power Depth Area Nz 5:05 1 5 . 3 19.6 3 .O 1245 300 5.8 9.55 4.05 5 : 07 15.3 19.8 2.1 1249 303 4.06 5:09 15.3 19.8 2.1 1258 303 4.06 5:lO 15 .3 19 .6 2.0 1261 300 3 -06 i: 12 15.3 20 .1 2.1 1264 308 4 - 0 6 5 : 1 4 15 .1 2 0 . 1 2 .1 i271 306 4.07 5:16 15.2 20.2 2 .1 1275 307 4.07 5:18 15.2 20 .3 2.1 1278 309 4.07 5:20 15.2 20.1 2 .1 1270 306 4.07 5:22 15.3 19.9 2.1 1264 304 4 - 0 8 j:tR 15.2 20 .3 2 .1 1272 309 4.08
Vol tage was decreased s o T O V since temp was too high
rime Voltage tlrrent C.D. Temperature Pawer Depth Area Nt i:29 10.2 12.8 1.3 1273 1 3 1 5.0 9-56 4.08 i:32 10.2 12.6 1 . 3 1262 1 3 1 4.06 j;33 10 .2 12.8 1 .3 1254 1 3 1 4.08 i;35 10.2 12.6 1.3 1249 129 4.09 i : 36 10.3 12 .7 1.3 124 3 131 4 -09 j:40 10.2 12 .7 1.3 1241 130 4.09 !:43 10.2 12.5 1.3 1240 128 4 . 1 J:45 10.2 1 2 - 0 1.3 1239 122 4 .1
Voltage was decreased to 5 V keeping same depth
: i m e Voltage urrent C.D. Temperature Power Depth Area Nz i:47 5.1 6 .9 0.7 1235 35 5.8 9.56 4 .1 i:49 5.2 6 . 4 0.7 1226 3 3 4 . 1 i r50 4.9 6.2 0.6 1223 3 1 4 . 1 i:53 5.1 6.2 0.6 1220 32 4.1 i:55 5 .1 7.2 0.8 1216 3 7 4.1 i:57 5.0 7 . 1 0.7 1214 3 6 4 - 11 i: 59 5.1 7.0 0.7 1213 3 6 4.11
N2 Elcrctrode Surface Cunent Rate of Oegree of Rate of U d CQ CO Flow T-Sfag TJum Voltage Current Powr Depth Areta ûendîy CO col Reduction Redudion R d u d i o n Fe@, % % lrnin*' O C OC V A W cm cm2 ratio milimd Q min" % mol O2 min" rn" g O min
17 97 -25 97,s 97.75 w 38.25 38,s w.75 3B 38.25
105,s 105.75 106 106.25 108.5 108.75 1 O7 107,25 107,5 107.75
145.5 145.75 1 48 140.25 148,s 146.75 1 47 l47,2S 147.5 liiil
0.5 0.5 0.6 0.6 O .6 0.6 O.? 0.7 0.7 0.7 0.8
Summry Appendix 8, Page 4 €MC F umaco Slag, 18 My 1998
Electric Fumace Slag Power, Temperature, and Rate of Reduction AC Experimts
No Power, Diametei = 0.62 cm. 3.0 cm depth. 5.87 cm2
Voltage and Cunent = O
1 73 175 1 77 179 181 1 83 Time in minutes
No Power, Diametei = 0.62 cm, 3.0 cm depth, 5.87 cm2 6 1 1 300
t Power & Current Density = O 1
ïime in minutes
No Power, Diameter = 0.62 cm, 3.0 cm depth, 5.87 cm2 t 1 200
O - 1195 6 - s
73 175 177 179 181 183
Tirne in minutes
4 Appendi B. Page 5 18 May 1998
Appendix C: AC, Conver te r slag experimental graphs
E RI-
Converter Shg Power, Temperature, and Rate of Reduction AC Ewrnents
Diameter = 0.62 cm. 2.5 cm depth, 4.91 cm2
147 1 48 1 49 Time in minutes
a Diameter = 0.62 cm, 2.5 cm depth, 4.91 cm2 1256
147 148 149 Time in minutes
147 148 149 Time in minutes
Appendn C, Page 2 28 May 1998
Converter Slag Power. Temperature. and Rate of Reducüon AC Experiments
Diameter = 0.62 cm, 1 cm depth, 2-04 cm2
Diameter = 0.62 cm, 1 cm depth, 2.04 cm2
Rate of Reduction
75 80 85 90 95 100 Time in minutes
Diameter = 0.62 cm, 1 cm depth. 2.04 cm2 I
75 80 85 90 95 100 Time in minutes
Expriment 5 Appendbr C, Page 3 26 May 1998
Converter Slag Power, Temperature, and Rate of Redudion AC Experirnents
l
Diameter = 0.62 cm, 2.5 cm depth, 4.91 cm2 1
123 129 1 32 1 35 138 Time in minutes
4 1
Dbmeter = 0.62 cm, 2.5 cm depth, 4.91 cm2 , 1260 I Rate of Reductio
O L I rn I p 1 1245
123 126 129 1 32 135 138 Time in minutes
Dbmeter = 0.62 cm, 2.5 cm depth, 4.91 cm2 400
6 - 9 O
1 ab .O 4 - 3 a d ' O 0 2 - O
l
O * 1 . I 1 1 1 1 f
1 23 126 129 132 135 I Time in minutes
Appendn C. Page 4 26 May 1998
Converter Slag Power, Temperature, and Rate of Reduction AC Em-ments
Diameter = 0.62 cm, 4.0 cm depth, 7.81 cm2
Current
C
Voltage I
-C%-,-,,--
1 L 1 1 t
200 Ume in minutes
Diameter = 0.62 cm. 4.0 cm depth, 7.81 cm2 3 , 1 1270
185 190 195 200 205 210 21 5 Time in minutes
Dbmeter = 0.62 cm, 4.0 cm depth, 7.81 cm2
-
Current Density
200 lg5 Time in minutes 205
Appendi C, Page 5 26 May 1998
Converter Shg Power, Temperature, and Rate of Reducüon AC ExperWnents
Diamter = 0.62 cm, 10 V, 5 cm depth. 9.76 cm2 1.5 1
35 37 39 41 43 45
Tîm in minutes
Diameter = 0.62 cm, 10 V, 5 cm depth, 9.76 cm2
Degree of Reduction -
C
Rate of Reduction
35 37 39 41 43 45 Time in minutes
Dbmetei = 0.62 cm, 10 V, 5 cm depth, 9.76 cm2
Expriment 9 Aqpendhc C. Page 6 12 June 1998
Cariverter Slag Power, Temperatue. and Rate of Redaiam AC Enperknents
Dismeter = 0.62 cm, 15 V, 5 cm depth, 9.76 cm2
55 60 65
Time in minutes
Diametei = 0.62 cm, 15 V, 5 cm depth, 9.76 cm2 12 i 1 1270
55 60 65 Time in minutes
Diameter = 0.62 cm, 15 V, 5 cm depth, 9.76 cm2
. l . l * * ~ b r t . . . I I i O 55 60 6s 70
Time in minutes
Expefïmnt9 riippendi C, Page 7 12 June 1998
Conveiter Slag Power, Temperature, and Rate of Redudion AC l3piments
Diameter = 0.62 cm, 20 V, 5 cm depth, 9.76 cm2
70 75 80 85 90 Tlme in minutes
1 Diameter = 0.62 cm, 20 V, 5 cm depth, 9.76 cm2
El6 -
Rate of Reduction
70 75 80 85 90 Time in minutes
I
1 Dismetet s 0.62 cm, 20 V, 5 cm akpth, 9.76 cm2
70 75 80 85 90 95 Time in m i n m
Appendix D: OC, Electric f u r n a c e experimental graphs 1
Eledric Fumace Slag Power, Temperature, and Rate of Reduction
Diarnetei = 1 cm, 28 V, 4.5 cm depth, 14.2 cm2
Voltage A
22s Time in minutes
Diameter = 1 cm, 28 V, 4.5 cm depth, 14.2 cm2 - 1255
.................. . . . . . . . - . . . . . . . . . ... . . . . . . . . . - -- . . - . . - -
Slag Temperature
Rate of Reduction
d a - ti E
ins f!
21 5 225 235 Time in minutes
Appendix D, Page 1 29 June 1998
Elednc Fumace Slag Power, Temperature, and Rate of Reduction
Diameter = 1 cm, 20 V, 4.5 cm depth, 14.2 cm2
260 270 280
Time in minutes
Diameter = 1 cm, 20 V, 4.5 cm depth, 14.2 cm2 - 1235
1 Slag Temperahire
- -. - -. -. -. ..... . . . . . .. . . . . . . . . . . . . . . . . . . . .
............................................... -_ .. . .- . .__I._.___ ...... -_ .... ..... .- ....... .... -
1 I i
260 270 Time in minutes
Appendix O, Page 2
Electric Fumace Slag Power, Temperature, and Rate of Reduction DC Experiments
Diamter = 0.78 cm, 10 V, 4.5 cm depth, 11 cm2
232 236
Tirne in minutes
3 Diameter = 0.78 cm, 10 V, 4.5 cm depth, 11 cm2 4
1
232 236 Time in minutes
Diameter = 0.78 cm, 10 V, 4.5 cm degth, Il cm2
232 236 Time in minutes
l3primecit 12 Appendii D, Page 3 01 July l99û
Eledric Fumace Slag Power, Temperature, and Rate of Redudion DC Experîments
Diameter = 0.78 cm, 14 V, 4.5 cm depth, 11 cm2
245 250 255 260 265 270
Time in minutes
Diameter = 0.78 cm, 14 V, 4.5 cm depth, 11 cm2
Rate of Reduction
245 250 255 260 265 270 time in minutes
Diameter = 0.78 cm, 14 V, 4.5 cm depth, 11 cm2
245 250 255 260 265 270 Time in minutes
Experiment 12 Appendix O, Page 4 01 July 1998
Electric Fumace Slag Power, Temperature, and Rate of Reducîion DC Experiments
Diameter = 0.70 cm, 18 V, 4 5 cm W h , 9.8 cm2
290 295 Time in minutes
Dlameter = 0.70 cm, 18 V, 4.5 cm depth, 9.8 cm2
Rate of Reduction
290 295 300 305 Time in minutes
Diameter = 0.70 cm, 18 V, 4.5 cm W h , 9.8 cm2
Appendir O, Page 5 M July 1 998
Efectric furnace Slag Power, Temperature, and Rate of Redudion DC Expenments
Diameter = 0.75 cm, 1281 5 V, 4.5 cm depth, 10.6 cm2
16 ,
\ voltage
Time in minutes
Diameter = 0.75 cm, 12&15 V, 4.5 cm depth, 10.6 cm2
Rate of Reduction
190 230
Time in minutes
Appendn D, Page 6
DC, Rate, Power, and Temperature Steady Sîate Calculation OC Experiments TEF
DC, Electric Furnace Slag, 4.5 cm Depth
l Slag Temperature, R* = 0.84
m 0
C
Rate of Reduction, R~ = 0.83
200 300 Power, Watts
6.3 6.5
(1 1 Temperature, K) x 10'
Appendix D, Page 7 O2 July 1998
Appendix E: DC, Conve r t e r slag experimental graphs
Conveiter Slag Power, Temperature, and Rate of Recution DC Experiments
150 160
Time in minutes
Diameter = 0.70 cm, 8 V, 3.8 cm ckpM, 8.2 cm2
C * * - - - - - . - - - - - - - -
Rate of Reduction
150 time in minutes
Appendix E. Page 1
Converter Slag Power, Temperature, and Rate of Redmon DC Gperiments
Diametet = 0.70 cm, 5 V, 3.8 cm -th, 8.2 cm2
Rate of Reduction
-ment 16 Apnd'i E, Page 2 06 Juîy 1998
Converter Slag Power, Temperature, and Rate of Reduction DC Experiments
Diameter = 0.60 cm, 2 V, 3.8 cm depth, 7.1 cm2 d
I- - Voltage V
195 205
Time in minutes
Diameter = 0.60 cm, 2 V, 3.8 cm depth, 7.1 cm2
2 Rate of Reduction
4 a 1 - - - - * - - - - - - - * - * - . . . - - - - * * - - - - - - - - - * - - * - - - - - - - * * - - - - - - -
1 95 205 Time in minutes
Appenai E, Page 3
ConverterSlag Power, Temperature. and Rate of Reduction DC Experiments
Time in minutes
Diameter = 0.60 cm, 5 V, 3.8 cm depth, 7.1 cm2
Rate of Reduction
Slag Temperature
Appendii E, Page 4 18 July 1998
Converter Slag Power, Temperature. and Rate of Reduction DC Experiments
Diametei = 0.60 cm, 5 V, 4.0 cm depth, 7.6 cm2
21 O 230 250
tirne in minutes
I
Diamter = 0.60 cm, 5 V, 4.0cm -th, 7.6 cm2 1260
- 1255
O L . I 1240
190 21 0 230 250
Time in minutes
Appendix E. Page 5 22 July 1998
Converter Slag Power, Temperature, and Rate of Reduciton DC Experiments
Diameter t 0.60 cm, 7 V, 4.0 cm -th, 7.6 cm2
255 265 275 285 295 305
Tfme in minutes
-
Dlameter = 0.60 cm, 7 V, 4.0cm depth, 7.6 cm2 4
Rate of Reduction
.
O L I I L 1 L 1 . 255 275 295 31
The in minutes
Experiment 18 Appendbt E, Page 6 22 Juty 1998
Converter Slag Power, Temperature, and Rate of Reduction OC Experiments
Diameter = 0.64 cm, Sa7 V, 4.1 cm depth, 8.2 cm2 12 ,
Time in minutes
Diameter = 0.64 cm, 5&7 V, 4.1 cm depth, 8.2 cm2 5 ,
Appendix E, Page 7 23 July 1998
Converter Slag Power, Temperature, and Rate of Reducbon DC Experhents
Time in minutes
I
160 180 200 Time in minutes
Appendk E, Page 8 23 July 1998
Converter Shg Power, Temperature, and Rate d Reduction OC Expeiiments
305 325
Time in minutes
Experiment 19 Appendii E, Page 9 23 Juîy 1998
Appendix F: DC, Anode / Cathode separation graphs f o r
e lec t r ic f u r n a c e and conver t e r slags 1
Converter Slag Power, Temperature, and Rate of Redudion Anode Eledrode Separation
Anode, Diameter = 0.90 cm, 4-5 V, 3.25 cm Depth, 9.3 cm2
Time in minutes
Anode, Diameter = 0.90 cm, 4-5 V, 3.25 cm Depth, 9.3 cm2
[ The irregular behavior in the rate of 1 reduction is due to the gas .................................... below the slag ....... surface, .... . . . gas,pnj t 4 - .- - - ---. -
Time in minutes
Appendix F, Page 1 01 August 1998
Converter Slag Power, Temperature, and Rate of Reduction Anode Eledrode Separation
Anode, Oiameter = 0.90 cm, 4-2 V, 3.25 cm Depth, 9.3 cm2
Voltage CO2 , ,-, - - O
265 275 285 295 305 31 5
Time in minutes
Anode, Diameter = 0.90 cm, 4-2 V, 3.25 cm Depth, 9.3 cm2 3 1265
Slag Temperature O O
--.-A-. - - - 1280 f . ....................... . . . . .
a Ci
1 O C jumps in temperature, probably thermocouples got !i
E e 1255 ,a
V)
1250 285 275 285 295 305 315
Time in minutes
Apperidix F, Page 2
Converter Stag Power, Temperature, and Rate of Redudion Cathode Eledrode Saparation
Cathode, Diameter = 0.90 cm, 1.6&4.3 V, 3.25 cm Depth, 9.3 cm2
320 330 340 350
Time in minutes
Cathode, Diameter = 0.90 cm, 1.6a4.3 V, 3.25 cm Oepth, 9.3 cm2 3 1 1270
31 O 320 330 340 350 360 fime in minutes
Appendix F, Page 3
Converter Sl8g Power, Temperature, and Rate of Redudion Cathode Eledrode Separation
Cathode, Diameter = 0.90 cm, 1.5a4.2 V, 3.25 cm Depth, 9.3 cm2
................................ .............. -..--..-- ..-...-.. Current
20 -- ---- ....---A..
a 8
a': ,\ *- y 1
n 8 .
: ; ;';
Time in minutes
Cathode, Diameter = 0.90 cm, 1.5lk4.2 V, 3.25 cm Depth, 9.3 cm2 3 1300
L
Slag Temperature
Rate of Reduction
O 1 I I 1 t 1200
355 365 375 385 395 405
Time in minutes
Electric Fumace Slag Power, Temperature, and Rate of Redudion Cathode Eledrode Separation
Cathode, Diameter = 0.84 cm, 13-18 V, 3.4 cm Depth, 8.7 cm2 1.5 1 , 20
Time in minutes
Cathode, Diameter = 0.84 cm, 13-18 V, 3.4 cm Depth, 8.7 cm2 0.3 - 1 320
I
160 170 180 190 200 Time in minutes
Appendix F, Page 5 10 August 1998
Eledric Fumace Slag Power, Temperature, and Rate of Redudion Cathode Electrode Sepration
Cathode, Diameter = 0.84 cm, 4-8 V, 3.4 cm Depth, 8.7 cm2 1.25 r 1 10
Voltage
...... ---... ........... .................. *-+ .... . - - - . -- 8
CO ,-. a I-#
# I
# #
#
a-' I I rn ....... .-.--.-. .... ; ..............-.. - . b. ......-.... ..... ...-.--. ........................... .---
I m a Fm
6 # '? i'
8
I #
8 * w # ":
I
-;. ..... -. ............ .- -. - .. . *-
... .-- .......-.-.a.....-.............
?
CO2 I #
? I . 1 d . d I - . -
* O
115 125 135 145 155 165
Time in minutes
Cathode, Diameter = 0.84 cm, 4-8 V, 3.4 cm Depth, 8.7 cm2
Slag Temperature
i20 130 f 40 150 160 Time in minutes
Expriment 24 Appendk F, Page 6
Electric Fumace Slag Power, Temperature, and Rate of Redudion Anode Electrade Separation
Anode, Diameter = 0.84 cm, 11 -1 6 V, 3.4 cm Depth, 8.7 cm2
Time in minutes
Anode, Diameter = 0.84 cm, 11 -16 V, 3.4 cm Depth, 8.7 cm2
60 70 80 Time in minutes
Appendix F, Page 7
Electrïc F umace Slag Power, Temperature, and Rate of Redudion Anode Electmde Separation
Anode, Diameter = 0.84 cm, 5-11 V, 3.4 cm Depth, 8.7 cm2
PL-: J ,.. - ............. .. ... " ..........
O
/* u 8 8
205 21 5 225 235
1 ime in minutes
Anode, Diameter = 0.W cm, 5-1 1 V, 3.4 cm Depth, 8.7 cm2
1 1 Furnace Temperature, "alurnina sheath btoken
205 21 5 225 235 245 255
Time in minutes
Appendix F, Page 8 10 August 1998
Electric Fumaœ Slag Power, Temperature, and Rate of Redudion Anode Eledrode Separation
Anode, Diameter = 0.84 cm, f6-21 V, 3.4 cm Depth, 8.7 cm2
Time in minutes
Anode, Diameter = 0.84 cm, 16-21 V, 3.4 cm ûepth, 8.7cm2
Slag Temperature - ......... .................-... - ................... ................... - ......... - . . . . . . . . . . ....- - -....
!
260 265 Time in minutes
Appendix F, Page 9
Appendix G: AC, Electrode Tip Temperature graphs
- 1270 OC, Experiment 26 AC, Converter Slag, TF",, - 1 320
1 O0 150 200 Power. W
- 1270 O C , Experiment 29 AC, Converter Slag, TF,,, -
Electrode Temperature, R* = 0.9
Slag Temperature, FI2 = 0.9
Eqmrhmîs 26 and 29 Appendir G. Page 4 13 August 1998 1 8 August 1998
Eledroda Tip Temperature Experiments
AC, Electric Furnace Slag, = 1270 OC, Expriment 27 1500
- 1270 OC, Experiment 26 DC, Convetter Slag, TF"- -
1 Anode Temoerahire Slag Temwrature O Cathode Temmrature 1
Exptiments 26 and 27 AppendU G, Page 5
Experimental and apparatus p i c t u r e s
Picture 1 : Top view of electrode clamps
Inside v i e w of alumina tube and M g 0 crucible
Picture 2 : B o t t o m of brass cooling cap with
input/output N2 ahmina tubes and a
thennocouple protected with alumina sheath
Picnues, Page 1
Picture 3 : TOP Figure is the in-house bu i l t furnace
Bottorn Figure is a close up v i e w , Dials, Na
flow, Variac, Brass Cap, cooling water,
input/ouput tubes
Picture 4 : Top Figure is the furnace
B o t t o m Figure is the gas analyzer, cornputer,
and data acquisition system
Pictuces, Page 3
Picture 5: Top left , electrode separation setup
Top right, alumina separation tube, l e f t
electrode and r ight electrode
Bottom Figure, electrode separation setup
with a brick cap on top of an alumina tube
Rctures, Page 4
Pic ture 6: Electrode consumption comparison
Picmes, Page 5
Picture 7 : Converter slag reduction
Mg0 crucible side and top view
Top Figure, AC power
Middle Figure, DC power
B o t t o m Figure, DC power
Pictures, Page 6
Pic ture 8 : E l e c t r i c furnace slag reduction
Mg0 crucible, side and top v i e w
Top F i g u r e , DC power
Bottom F i g u r e , DC power
Pictures, Page 7