THE TOOLS OF POWER POWER:

The Bond Work Index, A Tool To Measure Grinding Efficiency

C. A. Rowland, Jr. Senior Process-Project Engineer /-. -

Yining Systems Division , IJ

Allis-Chalmers Corporation - - Milwaukee, Wisconsin

. , - - ... ,

For presentation at the 1976 SME-AIME Fall Meeting & Exhibit Denver, Colorado - September 1-3, 1976

PREPRINT NUMBER

76-B-311 .mi . A1 , ? E m - % 4c

-1-

~ D U ~ ~

With the rapidly rising cost for electrical energy and the long range pre-

dictions for continued rising costs and ewn possible energy shortages, operation

of rod, b d l , autogenous and partial autogauxls grinding circuits to efficiently

u t i l i ze the pwer delivered to the mills w i l l be a d e d . This calls for a wthod

to evaluate grinding circuit: p e r f o m c e that is accurate, reliable and readily

usable as an operating tool by supervisory, technical and operating personnel.

Neither the Rittinger a d Kick theories of camhution, which preceded

the Bond Theory by m r e than 50 years, had a mthematical mans that could be

used to predict and evaluate the perfonrwce of crushers and grinding mills used

to comninute ores and rocks. This severly Limitd the practical use of these two

theories, whichmre confzadictory to each other. They have been superseded by

the Bond Third Theory of ccminution. (1)

DISCUSSION

In addition to the Third Theory of 'kminution, better known as the Bond

Theory, Red Bond mde three significant contributions to ass is t in the efforts

t o change the art of cominut ih into a science.

1) The Bond rod milling and ba l l milling closed circuit grindability tests.

2) The Bond impact crusher tes ts .

3) The Bond equation, the mathematical statemnt for applying Bond Theory

of Comminution. (1)

Where W = Wk hrs. per short ton (907.44 kilograms).

wi = iyrork Index

P = Product size in m i m e t e r s which 80;L passes

F = Feed size in m i c m t e r s which 8VL passes

Power per metric tome (1000 k i l o g r m ) can be obtained by multiplying W by 1.102.

Grinding power calculated, h e n using work indices obtained from Bond

- 2- (2)

grindability tests in the Band Equation, is for the follu~iTlg specific conditions:

1) Rod Ni.lling - wet, open cikcuit grin- in a 2.44 lrrter (8') dianrter

inside liners rod m i l l .

2) Bdll Nilling - wet closed circuit grinding in a 2.44 naeter (8') W t e r

, inside liners bal l m i l l .

3) P a ~ e r calculated is the p w e r required a t the pinion sha£t of the mill ,

which includes m i l l bearings and gear and pinion losses, but does not

include m t o r losses o r losses in any other drive cmpments, such as

reducers and clutches.

There are eight efficiency factors that are applied to the calculated grind-

ing p u m to a l l m for variations fram the specified conditions as related to the

grinding circuit and equipznt used. The background and reasons for these have

been published ( I ) , (2), (3) and are not part of the discussion. The factors are:

EF1 Dry Grinding

EF2 Open Circuit Bdll Milling

EF3 Di-ter Efficiency Factor

EFq Oversized Feed

EFj Fine grinding in bal l mills to product sizes finer than 8U77 passing 200

msh (75 microueters)

EX6 High or IWJ ra t i o or reduction rod milling

EX7 LorJ Ratio or reduction bal l milling

EF8 Rod Hilling

When accurate, Mill Feed Rate, M i l l Parer , Feed and Product Size Analysis

data are available, using the Bond Equation as shown, m r k indices can be calcula-

ted. To distinguish these fnrm ~mrk indices (ITi) obtained from grindability tes ts

~urk indices calculated frm operating &ta are designated as !.Jio.

In using this equation, the feed is the feed to the grinding circuit and the

76-B-311

-3-

product is the product fran the circuit. In a closed circuit operation, do not

use the f e d into and the discharge from the mill as is done with an open circuit

mill. Work index is a ueasure of grindability for the work to be done o r dune in

grinding the circuit feed t o the circuit product.

Operating rark index has the sane definition as ' tmk index1'(') which states

that "wrk in& is the required to break a hnmgenous material from a

theoretically infinite feed size to 8W0 pass- 100 micrmters". Thus, by defi-

nition, wrk indices calculated fran operating data always relate the operating

Qta fram which Wio is calculated, to the s a m feed size and product size as

giwn in the Mini t ion ; n a ~ l y , f rom a theoretically infinite feed s ize to 80??

passing 100 m i c m t e r s .

Thus, operating rmk hdex can be used for in-plant grinding mill reporting

and grinding studies such as :

I) Record m i l l p e r f o m c e on an hourly, daily, weekly or m t h l y basis,

whichever is desired.

2) Ccqare current p e r f o m c e with past p e r f m c e .

3) Cornpare c'kcuits in a d t i - c i r c u i t plant.

4) In plants ~$-ith two or mre grindjng circuits, one or m r e circuits can be

used as a standard, with others as tes t circuits for testing the effect

of such variables as:

a) dl1 spee&

b) size of grinding media

C) feed size

d) product size

e) ~ n x r n t of grinding mdia in m i l l

f ) liner designs

g) liner wear

h) changes in ore .

5) ikasure grinding efficiency.

GRINDING EFFLCIENCJ

As calculated, operating work indices include mto r , drive knd grinding m i l l

efficiencies and inefficiencies, therefore, are not directly comparable t o mrk

indices obtained from grindability tes ts performed on the same m i l l feed, without

the application of correction factors.,

M i l l parer as m u r e d in many p lmts is m t o r input pmer, that i s , electri-

cal energy going into the w t o r . It has to be converted to power a t the m i l l

pinionshaft. This is done by applying the m t o r efficiency factor (electrical and

mchanical losses) to obtain w t o r output pwer. I f the plant does not have the

w t o r efficiency data, it can be obtained £ran the m t o r mmfacturer. When the

mto r i s coupled direct t o the pinionshaft, notor output pmer is m i l l pinionshaft

power. I f a speed reducer or other drive element i s used between the m t o r and the

pinion shaft, then the efficiency of the units used must be applied t o the mtor

output power to obtain pwer a t the m i l l pinion shaft.

The grin- efficiency factors should be 'applied as required t o place the

operating work i n d e ~ a t the same level as the results from grindability tests. The

operating work index so calculated is referfed to as Wioc. This operating work ,

index divided by the mrk index fran the grindability tes t gives a reasme of ,

grinding efficiency as a d t i p l i e r of grindability tes t results.

f ~ ) = Efficiency Factor

The efficiency of the grinding circui t is

100 [L) = -ding efficiency in percent wioc

The multipliers for the efficiency factors can be determined from the f01lm-k~:

EF1 - Dry grinding - for the same range of work as wet grinding, dry grinding

requires 1.3 tines as m h pmer as wet grinding.

EF2 - Open Circuit Grinding - when grinding in open circuit bal l mills, the

amunt of extra power required, compared to closed circuit bal l milling,

76-B-311

-5-

is a function of the degree of control required on the product produced

The inefficiency factors for open circuit grinding are given in Table I.

EF3 - D b ~ ~ t e r Efficiency Factor - using the base m i l l h t e r of 2.44 mters

(8') inside liners, the W t e r efficiency factor can be calculated

fran the following:

(4)

Table I1 gives a tabulation of EF'3 factors for some of the m r e comrpn m i l l

m t e r s in both the imperial and mtric measuring systems. This table S ~ J S

that when the m i l l d i a ~ t e r inside liners is larger than 3.81 ~ t e r s (12.5 ') that

the d.izmxer efficiency factor does not change and remains 0.914.

EFq - Oversized Feed - when the grinding m i l l is fed a coarser than optirrnrm

feed, this factor applies to rod milling and ba l l milling. The wst

frequent use is with single stage ba l l milling. This is the one

efficiency factor that is directly related to work index as is s h m in

the following equation:

Where Rr - Ratio of reduction = F H

(6)

Fo = Optiwrm feed size (7) Rod milling: 16,000

When available, use the mrk index fran a grindability tes t a t the desired

grind for Wi in equation 5. For equation 7 , if available, use either the work .

index from an impact t e s t o r a rod m i l l grindability test , xhich ever is higher

and for equation 8, use the work index from a rod mill grindability tes t , since

these m e represent: the coarse faction of the feed which is the portion of the

f&d coarser than optiuium. Tf not available, then use the grindability tes t re-

76-8-311

-6-

sults , available.

Without grindability tes t results, finding the proper work index figure to use

in equation 5 i s a trial and error calculation which can be p r o g r m d for a am-

puter. Using this approach, the nark index used in equation 5 should equal the

Wioc obtained, after applying EFq and al l other correction .factors t o the mrk

index calculated from operating data.

EF5 - Fineness of Grind Factor - chis applies to fine grinding when the 8VL pas-

size of the product (P) is finer than 75 miaomters (200 msh). The equa-

tion to determine this is:

EF6 - High or Low Ratio of Reduction Rod f i l l ing - the equation t o be used, un-

less :

L = Rod Length

This factor generally applies to low ratios of reduction, but its applica-

tion to high rat ios of reduction does not always apply and should be used

only if the Wioc i W i grinding efficiency factor indicates that it should be

used.

EF7 - Low Ratio of Reduction Ball M i l l - the need t o use this factor does not

occur very often as it only applies t o bal l milling when the Ratio of Re-

duccion is less than 6. This sham up p&ticularly in regrinding concen-

t rates and tailings. The equation for this i s :

EF8 - Rod Milling - a study of rod m i l l operations shows that rod m i l l perf-ce

is affected by the attention given to feeding a uniform feed size t o the

m i l l and the care given t o maintaining the rod charge. This efficiency

factor cannot be definitely determined. In selecting rod mills based upon

pmer calculated from grindability t e s t s , the following procedure has been

recomnmded (2) :

1) Idhen calculating rod m i l l power for a rod-ailling-only application, use

an inefficiency factor of 1.4 when the feed is to be prepared w i t h open

ci rcui t crushing, and use 1.2 h e n the feed .. is to be prepared with

closed c i rcui t crushing. The other milling efficiency factors also

rmst be applied t o the calculated. grin- power.

2) !hen calculating rod m i l l power for a rod mill-ball m i l l c i rcui t , do not

allm for i m p r m w t in the ba l l mill performance. I f the rod m i l l

feed is produced w i t h open ci rcui t crushing, apply a 1 .2 inefficiency

factor t o the pier calculated for the rod milling stage only. If the

rod m i l l feed w i l l consistently be 80"/. passing 1/2" o r finer, such as

produced with closed c i rcui t crushing, do not apply a rod m i l l ineffi-

ciency factor. The other milling efficiency factors also m t be

applied t o the calculated grinding p-.

While this factor i s used in selecting rod mills, the inabili ty to ma-

sure and define i t accurately reduces i t s value and significance in

calculating Wioc and therefore, should probably not be used in deter-

mining the efficiency of rod m i l l performance, However, hcwledge of

its existence can be helpful in analyzing rod m i l l p e r f o m c e .

MAMPLES

The f i r s t ~ W O exanples are given to show haw to calculate W i o and Wioc for

single stage ba l l mills. Figure 1. The f i r s t example is a couparisun of bm

parallel mills frcan a daily operating report. P i i l l s ize 5.03111 x 6. lm (16.5' x

KwHfi4tric tonne

W i l l 1 M i l l 2

10.8 11.3

Feed s ize (8W7 passing) nicraneters 7500 8600

Product Size (80'77 passing) micrometers 220 195

Calculated Work Index Wio (Equation 2) 19.33 18.58

Correct t o Pinionshaft Power Wtor 18.56 17.84 Efficiency 0.96

Convert t o Short Tons Nil t ip ly by 0.9074 16.83 16.18

D i i m e t e r Efficiency Divide by 0.914 (m3)

Ball mi l l grindabili ty t e s t a t 65 resh gave a W i - 14.5. Using this t o

calculate oversized feed factor:

E q = (See Equation 5) =

Divide by EFq

Wioc

Efficiency Factor = & =

W i

Efficiency in % 96 99

This example shows that M i l l 2 is sl ight ly m r e eff ic ient than M i l l 1 even I

though it has a higher pawer consumption per tome. This shows the use of the

mrk index equation taking into account the differences in feed and product sizes.

The calculation is only pa r t of the t o t a l plant performance study and must be I tied into the to ta l plant operation.

The next sample covers an in-plant study on the effect of mi l l speed on

m i l l performance. The two speeds being studied a re 68"/, and 73% of c r i t i c a l speed I in 5.03111 (16.5' d i e t e r inside she l l 16' inside liners) b a l l mills. This study I was over a period of four m t h s . Grindability t e s t s were nm on m t h l y coqxsite

samples of the feed t o each m i l l . The operating data, t e s t data and calculations

are given in Table T I I .

The data given in Table I1 can be campared in several ways. A cmparison

based upon pawer per ton cons~led is given in Table IIIA. This shows the differ-

ence in p e r per ton of mi l l circuit feed cormm~d without taking into account

the variations in mi l l c i rcu i t feed, mil l c i rcu i t product and grindabili t ies as

shown in data tabulated i n Table 111.

E l k b a t i n g variations in mill c i rcu i t feed and product, Table IIIB shows

the comparison based upon the w r k index calculated fkom the operating data (Wio).

The next comparison eliminates the variations caused by differences in the

grindability of the ore. This i s the unre accurate comparison as it compares

grinding circuit p e r f o m c e as referred t o a comrpn base or reference. Table

I I I C gives the comparison based upon Wioc. - W i

The next two exarples a r e fo r rod m i l l ba l l mi l l circuits. Figure 2 shars a

conventional rod mill-ball m i l l circuit. The data fo r this circuit and \Jio calcu-

lations are:

Rod mil l s ize 3 . h x 4.88m (11.5' x 16' diarneter inside shel l 3 . 3 5 ~ 1 1 '

4.72111 15.5' rods)

Ball m i l l s ize 4.7211 x 4.88m (15.5' x 16' cLim~ter inside she l l 4 . 5 7 ~ 1 5 ' )

Rod m i l l feed produced by closed c i rcu i t crushing mimanzters 14,500

Rod m i 1 1 product micro~z~ters 1300

Ratio of reduction 11. I5

Rod length t o mil l d k w t e r r a t i o 1.409

Optirmnn r a t i o of reduction L5.05

P m per mtiric tonne m t o r input Kw 4.2

m t o r efficiency % 95.6

Calculated operating mrk indeu W i o 21.62

On basis m t o r output x 0.956 20.67

On basis s b r t ton x 0.9074 18.76

Dianaeter factor + 0.939 (EF3)

Low r a t i o of reduction EF6

1 + (11.15 - ~ 5 . 0 5 ) ~ = 1.101 (divide) 18.15 1X)

'ioc

Rod mil l grindability test resul ts W i

Efficiency factor Wioc t W i 1.21

Grinding Efficiency in % 82.6

Ball mil l feed m i c r a t e r s 1300

Bdll mil l product m i c r m t e r s 115

Ball mi l l r a t i o of reduction 11.3

Power ~ e r mtric tonnemtor input Kw 9.2

Calculated operating work index TJio 15.75

On basis m t o r output

On basis s b r t ton x 0.9074

Diameter Factor .t EF3

Rod m i l l low r a t i o of reduction

Wioc

Ball mil l grindability t e s t resul ts W i

Ball mil l grindability test results W i

M i n e d 15.0 x 4.2 + 14.3 x 9.2 TI-4 27T4

Efficiency factor Wioc t W i

Grinding efficiency in %

This shms the rod mil l is inefficient while the b a l l mill is perfomring

efficiently bet ter than indicated from the grindability t e s t resul ts , with the

76-B-311

-u- overall circuit operating in l ine with grindability t e s t resul ts .

Figure 3 shows a rod mill-ball m i l l c i r cu i t with a concentration step be-

tween the rod mill and the ball 11611 with the tailings being ren~ved from the

c i rcui t . There is also a concentration s tep between the ba311 m i l l and the

c lass i f ier . In det- grinding efficiency, each stage is considered as a

single stage. The power per tonne for rod milling is determined fran the rod

mi l l feed r a t e and the pier per tonne for b a l l milling is &tennined £ram the

b a l l mi l l feed r a t e .

Pod mill size 4.27 x 6 .lm (14' x 20' diameter inside she l l 4 . I .h - 13.5'

5.94~1 19.5' rods).

Ball m i l l size 5.03m x 7.62111 (16.5' x 25' diameter, inside shel l 4.88111 16.0')

Rod m i l l feed produced by closed c i r cu i t crushing micr~~l~ters 19,000

Rod m i l l product m i c r m t e r s 1300

Ratio of reduction 14.62

Rod length to mill a t e r r a t i o 1.44

O p t k r a t i o of reduction L5.22

Power per short ton m t o r input Kw

l%tor efficiency %

Calculated operating work index Wio 25.59

On basis m t o r output x 0.952

Diameter factor + 0.914 (EF3)

Rod mil l grindabil i ty t e s t results Wi 16.5

Oversized feed factor EFq -P-

Divide 24.65 by 1.22

'ioc

Efficiency factor Wioc + W i

Grinding Efficiency in %

Note the efficiency factor of 1.22 lines up with the 1.2 factor recomtx=nded for

selecting rod mills for rod milling circuit when feed is produced with closed cir-

cuit crushing.

B a l l mill feed micrmters 1450

B a l l mill product A-2nd concentration stage tailings size micrmters 90

Bdll m i l l product B-classifier fines size micrmters

Combined ba l l mill products microwters

Power per short ton mto r input Kw 13.8

bbtor efficiency %

Calculated Operating Work Index W i o

On basis nutor output x 0.952

D i a w t e r factor + 0.914 (EF3)

Fineness of grind factor E3'5

Divide 11.86 by 1.07 11.08

Ball mill grindability tes t results W i 11.43

Efficiency factor Wioc 5 Wi

Grinding effiency in %

The four matqles were given to show how the Bond mrk index equation can

be used to evaluate grinding m i l l p e r f o m c e , report m i l l operating data and

evaluate in-plant grinding studies.

It has been determined that kvrk indices obtained from standard Bond

Grindability Tests cannot be used to determine the p m e r required for grinding in

primary autogenous and partial autogenous grinding circuits. (4) However, cal-

culating ~mrk indices £rm operating data i s satisfactory for dusting the

performnce of such circuits. When compared with the work indices obtained from

corresponding grindability and %act tes t s , the perfomace of autogenous

and part ial autogenous circxits can be rated.

Table IV is a copy of a -one m t h conrputer runoff sheet on which daily

operating data and the mrk indices cdculated from the operating data for an

autogenuus m i l l are tabulated. This is a typical sheet showing what can be done.

The feed size is generally not used in this calculation for primvy autogenous

and part ial autogenous mills, in that the feed (10 +*) factor bec-s insigni-

ficant because of the large size of the feed.

(5) Bassarear and Horst, in t h e e paper on evaluating plant performme,

i l lus t ra te how work index data can be used t o evaluate process p e r f o m c e and

mdifications. They particularly discussed the semi-autogenous-ball mill grind-

ing circuits a t Cyprus Pima and the use of computer based controls. The simpli-

fied grindability t e s t procedure employed for the Pina ore types vm developed to

give work index as defined by Band and includes periodic chedcingwith standard

Bond Grindability tests. Tests such as this can be used for specific ores whcxe

there is not a wide variation in suecific gravity and in breakage patterns.

For secondary autogenous grinding (pebble milling) Bond Grindability Tests

can be used to determine grinding power to this add the power required to wear the

ore ~ d i a from media size t o mill feed size. PEll performance can be measured

using the s a procedure for evaluating ba l l m i l l performance in a rod mill-ball

mill circuit .

EWUEMZD CkWXATIONS AND ANDmL CSRCUrrS

Relative to its use in computer programs for controlling a grinding circuit

or reporting grinding circuit performme, a correct understanding of the Bond

Equation and the term ' k r k indextt is required. The Band Equation measures mrk

done or to be done. Wark index as defied is power. Since there is no factor in

the equation that takes into account the classification function, the Bond Equa-

tion is not a math mdel for a closed grinding circuit. Being a masure of

- 14-

grindability, work index can be used in m t h rrodels when a grindability £unction

is called for.

To use the Bond Work Index equation in c-uterized programs for mea&5ng

m i l l performance and controlling grinding circuits in addition to power and feed

ra te data either on-line size masming equi-t or k t h mdels that w i l l

ma tha t i ca l l y determine the 80% passing size in micrmeters of the feed and pro-

duce size are required. Unless it is a widely fluctuating variable it i s possible

to use a constant value for the feed size which should be checked periodically.

However, with computer control and ~ ~ ~ a s u r e t r m t , the product s ize has to be con-

stantly k t o r e d .

CONCLUSION

Work indices calculated from operating data, either m u a l l y or by computer, with

or without comparison t o work indices obtained fran grindability tes ts , can be

used t o indicate grinding circuits that are operating inefficiently. Work indices

however, do not indicate the cause for the inefficient use of grinding power, nor

do they indicate the acceptability of the product produced by the grinding c i rcu i t

~upenrisory, technical and operating personnel studying the operating data

and chec !g the operation of the plant can determine the cause for any ineffi-

cient use of p m and the acceptability of the product produced.

The Bond equation util izing knxk index as the measure of grindability i s an

accurate, reliable &~d readily usable rnethod to obtain a consistent measuremnt

of grinding circui t performance. It takes into account variations in feed size

and product size with the work index calculated fran the operating data reflecting

either changes in the grihdability or changes in efficiency. Work indices cal-

culated fr& operating data, hen compared to work indices obtained from Bond

Grindability tests for the same m i l l feed, give a direct measure of grinding

efficiency. The Bond Equation and the equations for the associated efficiency

factors can be used by plant supervisory and technical personnel and can also be

used in corcputer prograns for reporting and/or process control. The Band Equa-

tion and work index are useful tools in evaluating grinding circuit performance to

help m x k k e the use of the pmer delivked to g r i n d k g circuits in minerals Dro-

cessing plants.

PmERENCES *

(1) Bond, F. C. "Crushing & Grinding Calculations", British Chemical Engine-,

June 1960, pp. 378-385 and 543-548. (Revised January 1961, Allis-Chalmers

publicaticm OX-9235B).

(2) Rowland, C. A., Jr. "Grinding Calculations Related to the Application of

. Large Rod and Ball Mills", Canadian Journal, Vol. 93, No. 6, June 1972 I

(3) Rowland, C. A. Jr. , "Comparison of Work W c e s Calculated Ram Operating

I Data with Those From Laboratory Test Data", Proceedings Tenth Internationdl

Minerals Processing Congress 1973, pp. 47-61.

(4) Rowland, C.A. , Jr. and Kjos , D. M. , "htogmous and Semi-Autogenous Mill

Selection and Design", presented to SME Meeting, Acapdco, Mexico, Sept.

TABU I

OPEN C n z c u r r TNEFFlcmCY MUL-

Product Size Control Reference % Pass-

Inefficiency Multiplier

M i l l IxaEter M i l l I>iameter Eamter Efficiency Inside Shell Inside Liners M t i p l i e r

Feet Meters Feet Meters

3.0 0.914 2.6 0.79 1.25 3.281 1 .0 2.88 0.88 1.23 4.0 1.22 3.6 1.10 1.17 5.0 1.52 4.6 1.40 1.12 6.0 1.83 5.6 1.71 1.075 6.562 2.0 5.96 1.82 1.06 7.0 2.13 6.5 1.98 1.042 8.0 2.44 7.5 2.29 1.014 3.5 2.59 8.0 2.44 1.000 Base 9.0 2.74 0.992 9.5 2.90 2 :::: . 0.977 9.843 3.0 9.34 2.85 0.970

0 3.05 9 .5 2.90 0.966 10.5 3.20 10.0 3.05 0.956 11.0 3.35 10.5 3.20 0.948 11.5 3.51 11.0 3.35 0.939 12.0 3.66 11.5 3.51 0.931 12.5 3.81 12.0 3.66 0.923 13.0 3.96 12.5 3.81 0.914 13.124 4.00 12.62 3.85 0.914

TABL

E I1

1

(CO

NTI

NU

ED)

IN-P

LAN

T GRINDING S

TUDY

DES

CRIP

TIO

N

Feed

Siz

e 80

% P

assi

ng

Pro

duct

Siz

e 80

% P

assi

ng

Feed

Rat

e TPH

Ave

rage

Pay

er K

w

Red

ucti

on R

atio

KwH/T

&to

r In

put

(Eff

icie

ncy

: 93

%)

KwH/T

at

Mil

l P

inio

nsh

aft

Wio

(O

pera

tigg

Wor

k In

dex)

M

i11

Dia

met

er E

ffic

ien

cy E

D

Ove

rsiz

ed F

eed

Fac

tor

EF4

Wio

c:

Gri

nd

abil

ity

Tes

t E

quiv

alen

t G

rin

dab

ilit

y T

est

Res

ult

s Wi

Rod

Mil

lin

g @

118

0 um

(14

Mes

h)

Bal

l M

illi

ng

@ 2

12 u

m

(65

Mes

h)

Bal

l M

illi

ng

@ u

rn

(100

Mes

h)

Eff

icie

ncy

Fac

tor

Wio

c t. Wi

(Wi

used

was

at

212

urn)

G

rind

ing

Eff

icie

ncy

in %

Ap

ril,

191

5 I

68%

14

i.11

A

1697

6 25

8 23

8 22

83

65

.8

9.59

8.9

2

16.3

4 0.

914

1.3

6

13.1

5

13

.8

14

.0

13

.4

0.9

4

103.

6

CS M

ill

B

1648

9 24

3 24

5 23

30

67.9

9.

51

8.84

15

.68

0.91

4 1

.33

12

.90

16

.3

13

.2

15

.3

0.9

8

10

2.3

Mil

C 15

779

236

278

2548

6

6.9

9.

17

8.52

1

4.9

3

0.91

4 1

.30

12

.57

15

.8

13

.0

13

.1

0.9

7

10

3.4

Mil

l D

1

1524

2 25

1 25

8 24

45

60.7

9

.48

8.8

1

16

.01

0.

914

1.3

9

12

.60

16

.1

14

.3

13

.3

0.88

1

13

.5

TABLE I11 A C'LEQAFCLSON BY PER TON (KwH/T)

6877 CS 7% CS 14mth - Nil1 A M i l l B Average Mill C Mill D Average

Januar~ 10.68 10.15' 10.4l-5 10.13 ---- 10.U

February 10.42 9.68 10.14 9.43 ---- 9.43

March 10.42 10.10 10.26 9.79 10.52 10.155

4 r i l 9.59 9.51 9.55 9.17 9.48 9.325

' TABLE I11 B ahCIPARIS(3N BY OPEXTJX TXIE INI?EX Wio)

68% CS 7% CS b t h - fill A W l B Average Mill C Mill D Average

Januar~ 16.51 16.21 16.36 16.48 ---- 16.48

February 16.53 15.72 16.12 15.54 ---- 15.54

Elarch 16.94 15.69 16.31 14.97 16.51 15.74

April 16.34 15.68 16.01 14.93 16.01 15.47

TABI;E I11 C 'io, COMPARISON BY EFFICIENCY FACrOR - 68% CS 73% CS

bpm Mill A Mill B Average Mill C Mill D Average

Jrnuar~ 1.04 1.22 1.13 1.01 --- 1.01

February 0.97 0.91 0.94 0.91 --- 0.91

April 0.94 0.98 0.96 0.97 0.88 0.925

TABLE IV

Gross HP-HR

Crude Gross Feed HPWTX LTPH

4738. 14.9 254.7 5432. 13.8 249.2 5487. 14.3 252.9 6076. 15.4 259.7 5451. 15.5 234.0 4713. 17.6 266.3 5711. 17.5 275.9 5308. 16.9 252.8 5601. 15.6 245.7 4705. 14.6 217.8 5975. 15.8 250.0 5350. 13.5 223.9

4534. 14.3 188.9

M i l l HR HP

%-500 P80 Mesh

752. 35.5 701. 33.5

1116. 23.0 664. 31.5

15L5. 10.5 818. 35.5 136. 59.5

1086. 33.4 1142. 29.5 961. 16.0

1121. 30.0 818. 26.0

775. 21.5

Date s/lm-

8/2/75 8/3/75

Weighted Average

FEEDER $7

BALL MILL 1

SUMP .1

PUMP

CIRCUIT PRODUCT CL4SSIFIER OVERSIZE

SINGLE STAGE BALL MILL CIRCUIT

FIGURE 1

FEEDER 4-

ROD I'lILL -1

SUMP I <-q, -&

PUMP &

CIRCUIT PRODUCT CLASSIFIER

0.~~9 BALL MILL

ROD l l ILL - BALL MILL CIRCUIT

FIGURE 2

FEEDER I

ROD MILL I 4 ROD MILL PRODUCT

TO MASTE-; ST CONCENTRATIOt4 STAGE

CONCENTRATES BALL MILL FEED

TO WASTE~-----------~ND CONCENTRATIOPI STAGE BALL MILL t

PRODUCT A I CONCENTRATES

\L PUMP

FINES BALL MILL PRODUCT CLASS I F I ER

ROD NILL - COMCEfiTRATION - BALL T.IILL C I R C U I T

FIGURE 3