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-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

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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



Fiaure 3.5. Page 34



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


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


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



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


Current Density

135 140 345 1 50 155 160 Time in minutes


Electnc Fumace Slag Power, Temperature, and Rate of Reduction AC Experiments


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


- 600 3 O

Cunent Density - 300




Diameter = 0.62 cm, 30 V, 5 cm depth, 9.76 cm2 , 50

205 21 0 21 5 220 225 230 Time in minutes


- Slag Temperature

205 21 O 21 5 220 225 230 .Tirne in minutes


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 /


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


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



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


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, 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


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


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


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


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

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converting process in the Thompson smelter", The 1 4 ~ ~

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N. Stubina, J. Chao and C. Tan, "Recent electric

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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

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A. Warczok and T.A. Utigard, "Fayalite slag reduction

by solid carbon", Can. Metal. Quart, Vol. 37, 1998,

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iron oxide by solid carbon", Metal. Trans., O 88,

1977, pp. 189-190

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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


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


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

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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

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



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


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


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



. 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


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!


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


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


Diameter = 0.78 cm, 10 V, 4.5 cm degth, Il cm2


l3primecit 12 Appendii D, Page 3 01 July l99û

Eledric Fumace Slag Power, Temperature, and Rate of Redudion DC Experîments


245 250 255 260 265 270

Time in minutes


Rate of Reduction

245 250 255 260 265 270 time in minutes


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


Dlameter = 0.70 cm, 18 V, 4.5 cm depth, 9.8 cm2

Rate of Reduction


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


l Slag Temperature, R* = 0.84

m 0

C

Rate of Reduction, R~ = 0.83


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 - - - - * - - - - - - - * - * - . . . - - - - * * - - - - - - - - - * - - * - - - - - - - * * - - - - - - -


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


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


[ 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


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


Appendix F, Page 7

Electrïc F umace Slag Power, Temperature, and Rate of Redudion Anode Electmde Separation


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


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 - ......... .................-... - ................... ................... - ......... - . . . . . . . . . . ....- - -....

!


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

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