testing for autogenous and semi-autogenous grinding

8/13/2019 Testing for Autogenous and Semi-Autogenous Grinding

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NUM ER85 407

b

TESTING FOR AUTOGEMOUS AND

SEMI-AUTOGENOUS GRINDING

A DESIGNER S POINT OF VIEW

For presentation at the SME-AIME Fall Meetin

D. J. Barratt

Wright Engineers Limited

Vancouver, British Columbia

Permission is hereby given to publish with appropriate acknowledgmentsexcerpts or summaries not to exceed one-fourth of the entire text of the paper.Permission to print i n more extended form subsequent to publication by the Institutemust be obtained from the Executive Director of the Society of Mining Engineers

If and when this paper is published by the Society of Mining Engineers of AIME itmay embody certain changes made by agreement between the Technical PublicationsCommittee and the author so that the form in which it appears here is not necessarilythat in which i t may be published later.

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The application of autogenous and s e mi-autogenousgrinding circuits in recent years has contributed to-ward subs tantial savings in c apit al and operating cos ts

compared to conventional cir cui b, particularly for

larg e sca le copper and molybdenum operations. Such

savings have been realized from the deletion of oper-

ating, maintenance, equipment purchase and substan-tial civll/s tructur al cost s associated with secondary-

/tertiary crushing and screening, fine ore storage and

conveying. In spite of the downturn in the copper-

moly industr y i n North America, t he re is still anin te re st in autogenous and semi-autogenous grincting

fo r copper-zinc, gold and silver ores and in t he over-

sea s market.

Both single-stage and two-stage circldts are in

operatton. Primary circ uit s oper ate autogenously or

semi-autogenously in either open or closed4rcuit.

Crltlcalsizes are extract ed and crushed for recycle insome cases (e.g. ABC circ ldt ). Secondary grinding is

conduc ted using b a i l l s or pebble m i l l s .

In view of these potenti al concepts, which result in

dirfer ing operating schedu les and possible opera ting

co st savings compared t o conven tional grinding c;rcuits, what is the basis for a te ch dc al evaluation ofautogenous or semi-autogenous grinding in terms of

power require ment and equipment selection a t thepre-design stag e? The answer lie s in established

t sting methods, empirical calculations and the

amount of tim e and money available for study. Most

importantly, an unbiased approach toward the proble m

and an objectivity which recogrdses the properties of

the orebody in question are indispensable attributesrequbed of the m etallu@cal enginee r and his col lea-

gues.Basis For valuation

Selectton of a m p l e s

The principal objecti ve fo r the metallurgLcal en@-neer is to dete rmi ne th e spe-c power requ ire men tand mesh of grind necessary f or subsequent processing.

Normally, thi sin volv es a study with th e mine geologist

and mine production engineer of the following p a n -

meters before testwork begins:- Ore zones and or e types.

M h e r a l o ~ jnd liberation analyses.

D i a m ond drill core and logs.

- Accessible workings (e.g. trenche s, pits, adits,

drircs, etc.).Proposed mine plan and production sequence.

- Ore hardness (e.g. presenc e of chert s, clays, friable

minerats or rocks).- Fracturing (e.g. fau lt or joint planes, presenc e of

gouge material).

- Types and degrees of mineral. alte rat ion.

ll this inform ation should be used to se lec t

samples for eit her batch o r continuous testing.

The decision as to how much grinding teat wor k is

reqtdred Is more complex for autogenous or semi-

autogenous (collec tively rea d AS A G for econo m y)

grinding than fo r convent ional grinding. Firstly, con-

ventional crushing and grinding circuib can be design-ed conf ldenuy on th e basis of small-scale. batch o r

locked-cycle t es ts requiring only 35 kg sample pe r

test. Secondly, ASA G circuits can be designed us ng

various methods each of which ca n h s an element of

rlsk c o n mensurate wit3 th e experience of th e en@-

neem involved and the amoun t of sample teste d. The

magnitude of risk can be tabulated as in Table 1

Traditionally, continuous testing has been used to

develop engineering design criteria. The higher cost

for continuous testing and t he attend ant leas t contin-gency and risk associated with testin g bulk samples

can be justified if the total cost, including sample

acquisition and transportation, is less than the present

value of potenti dl savings in cap itdl and operating

costs presented by the higher contingencies associated

with t he altern atives outlined in Table1

Incontrast,

fo r conventi onal crushing and grinding it is unneces-

s ry to test bulk samples unless a contingent process

route requires piloting. Ik should be emphasized a t

this point th at each ore type, which is s i g M c an t L e .

more than 10 in terms of its rank or consistency inm i l l throughput, should be teste d f or eit he r ASAG o r

conventional zche m es.

Bond Work Index and Hinerdlorn

Prior t o testLng fo r autogenous or se mi-autogenousgrinding, t is important to have an understanding of

th e spe df lc energy requirements for crushlng and

grinding as w e l l a s mineralogy.

The Bond Work Index is the generally accepted

parame ter f or gauging specific energy requirem

ents inconvent ional crushing and grinding. The res ults ar e

highly reliable if these tests are conducted on repre-

sent ati ve samples, usually of dril l core, and follow the

prescribed Bond method and te s t equip m e n t ( l )

Analysis of Bond Work Index te st r esu lt s fo r crush-ing, rod milling and ball milling w i l l indicate unSorm-

it y or other of breakage characteristics in diffew

ent size ranges. Very often one is much higher (or

lower) than the others and such variations can governthe power CfistribuUon between primary and secondary

st age s of grinding. Also, these obsemati ons d i l l givean indication of the potentidl e m e n c e of a critical

s h e relative to autogenous or se mi-autogenous grind-

ing For ins tanc e in grinding a masslve sulphide ore,

rod m131 Bond Work Index w a s found t o be 7.0 in

contrast to a ball m i l l Bond Work Index of 13.4. TheW e r e n c e was indicaz ve of the mineralogLcal struc-ture which showed that the rod m i l l was breaking

sulphide gr ins relatively easily away from harder

sil iceous mine* and the baJl m i l l w a s breaking these

sulphide gr ins across boundaries in order t o preparefeed fo r dW fe re nb l flotation of copper from zinc.

The crushing Bond Work Index w a s higher than the rod

m i l l Bond Work Index. Prediminary analysi s concluded

tha t this ore would be amenable t o ASA G and that the

chances of a c ri ti ca l size bldld-up would be l o w . In

another exa m ple, the rod m i l l Bond Work Index of asiliceo us copper-silver ore w a s found to be 21.0 v ersus

a ball m i l l Bond Work Index of 12.8. The fene

dissemination of sulphide minerah showed that energy

had to be expended in breakage across siliceous grain

boundaries before liberation of sulphides w a s posziblein t he ball milling stage. The chances of a bldld-up incrit ica l size were considered to be high and so an C

circ uit would be r e c o a mended f or inclusion in a tes t

programThe det erm inat ion of Bond WorJx Indices fo r rod

milling and ball milling requires about 25 kg of samplecrushed to minus 13 m m some of which (about 5 kg)

can be used to determ ine Abrasion Index f or th e

prediction of m eta 1 wear in grinding m i l l s . In addition,

Bond Work Index fo r crushing can be d eter min ed f o r a

range of samp les drawn from 100 lumps each 32 cm

cube in sFze and weighing 100 grams using the highenergy t w i n pendulum testC2) or 20 pieces each 90 cm

cube in th e standard test.



ASA G C i rc u i b

It is considered that the determination of power

requi remen t f or an ASAG m i l l reqldres the same

understanding of break age characLteristics and Bond

Work Index dev elope d f o r con ven tio nal gt-lnding intesting parti cular ore samples. In addition, however,

it is necessary t o know how compe ten t mn-of-mine o r

primary crushed ore is i n t he c oa rser sh e s a nd in what

b generally ter med the critical size range (75,000 to13,000 microns) when operating in th e presence of a

reduced ball charge (up to 125 by volume) or when

&ding autogenously. Variations in the competency

of these sh e s and feed s ize di s t rbut lon k determine

not only th e ba l l ch=ge level required but a l so the

power dr2w of the m i l l product sizin and ra te of

production and hence ldowatt-hours per tonne.

Whereas with convenfonal grinding in which power is

t ransmit ted to the ore through contact uiL\ a higin

lev el of media and power draw s relat ively cons'ant

with variations in production rate related to Bond

Work Index, pow er in an ASAG m i l l is t ransmit ted less

efficiently. Autogenous m i l l s are usual ly less e Mci ent

than SAG m i U s . Bowever, th e introduction of a

crush er in closed-circuit with an autogenous m i l l i s anzlternat ive which can improve power eM d en cy and

offer savings Ln ter ms of operat ing co st compared toSAG (Le. no bai l consu mption an d probably less h e r

wear). Whereas th e crusher se rJ es th e sa me purpose

as a ball load doe s in controlling th e build-up of

cri tica l sizes, a co arser circui t product usually resultswith reduced s p e d l o power consumption. Ifs e c o n d a r y p h d i n g is nec esa ry, more power and

cap ita l would have to be applied in this area with

coarser feed sizes and s alternative studies would be

necessary t o determine the most economical option.

if a cri tic al size d oes bldld-up in a SAG m i l l

conversion to A B C SABC o r SAC susually th e result.

Eow can t he metallurgical engineer predict the

bebav 'lour of o x types in SAG or ABC & c u b a t

reasonable cost ? The following st ep s ar e suggested i ncoxidera t ion of th e r i sk indicated in T a b h :

tep One: V k i t the property, exalcine d r X core,

review rock qu&t'j det erm ina zon R 9D analyses

(which are a measwe of fracturing or weakness),

watch for ore types which exhibi t a G h or low

~ s k ' a n c e to break age v hen being mined,

de tern ine presence of cher t or other forms of hard

rn o ~ h o u silica, conduct d e l d drop testa on rock

types.

tep Two: Se le c t s a ~ p l e s o r de t e rn iqa t i on o f

aond Work hd e x f or crdshing, rod milling and ball

ni l l ing to fin l product size (com m emurate with

liberation analyses and subsequent pmcess test

require rnen&) and Abrasion Index.

tep Three: Perform empir ical cak uia tio ns to size

a n ASAG circuit and prepare pre l iminry capi ta l

and op erating co st estim ates.

tep Four: If development ore or 150 m m dr 2.l

core is available, conduct batch min ing tests (see

Table 1). To date, these can only be done in t h e

United States. D r i l l COP can ah o be used for

small scale continuous tests.

tep Five: If the ore value warrants a grea t e r

degree of confidence h e . less contingency) in m i l l

sidng, conduct continuous testa on bulk samples.To date, these can be performed in Canada, the

United S'cztes, Chile and in th e fu tu re , Peru. Tes t

f a d i t i e s also e a t n Japan , Australia, Europ? and

South Africa.

These calculations are based on refer ence to

d m l l a r ores. Caution should be exercised with regar d

to the assumption t ha t breakage characterisUcs and

ball loading will be s i m i l a r to those of the referen ce

ores. The experience of th e m etalh@cal engineer is

cr l t i ca l i n this regard and th e contingency which s

indLuded in t he m i l l horsepower has to be judged in

th at l ight .

~ a r r a t t ( 3 )has suggested and has developed the

following formulae based on aond 'rloric Index d e t e ~

minations fo r a pow er -e md en t conventional scheme.

Fo ra t wos t a ge SAG circuit:

E M

Where:

i =

P =

F =

K r =

Kb =

PSAG =

ESAG

EB M =

Work Lqdex (metric)

C = crushing

R = r o d m i l l

B = b a l l m i l l

K80 product f or eac h stag e (microns)

K80 feed f or each stage (microns)

Composite of correct ion fa cto m fo r rod

milling(4) including those fo r ov ersize feed,

but exc luding tha t fo r m i l l diameter.

ComposLte o r correct ion factor s f or bal l

milling(4) including tho se f o r fine grinding,

but exc luding tha t for m i l l d i m eter.

K80 product selected for SAG stage

(microns)k Wh/tonne a t the m i l l w o n o r SAG m i l L

(before contingen cy fo r power swings)

kWh/tonne a t the m i l l pidon for secondary

st ag e ba ll mFU.

The m ost cri t ic al parameter governing ESAG is t he '

80 percen t pa&g s h e of the primary circui t product ,

PSAG. In u i h g t h k formula, lower values of ESAGc a n be e xpe ct ed fo r c o m e r p roduc t sk ns and thesein turn depend upon bal l loading and tine productlon o f

nat ur al fines. The usual relationships found i n t e s b g

c ompe t en t o res , i e . t hose in which breakage Fs

predomlnan'cly across @ boundaries, a e of t he

types shown i n Figures 1 2, 3, and 4. If avaUztble f o r a

reference ore , they can serve a3 a guide in select ing

SAG and s for de te rm inhg t he power spl it be tween

p r l n r y and s e c o n d a ~tages.

For those ores which break up more easily i n t he

coars er siz es (conglomerates and sandstbnes) or which

have a high clay component , th e fac tor 1 25 in

Equation 1) sstill used bu t t he p p h i c a l r el at ionsh ips

can change. Prod uct sLzLng and sp ed fi c power

consumption have been known to be independent o f

bal l loading with such o res dn ce reduction to a na tura l

h e appeared to be the governing factor.

Single-stage dr cu it s ar e m ore co m q on fn such cases,

ex cep t where 'Ine grinding is a requirement.

Once t he specFfic power con sunp tion ESAG, has

be en de te rmine d fo r ea c h ore t ype usi ng E q u a t i o n 3



a judgement has to be made regarding the safety

fac tor applicable t o account f or expected power

swings. In th e absence of t est results , it is usual to

add 25 to the most representative value of ESAG and

size tine m i l l from Equation (3) and manufacturers'

reco m m endations(5)

Where:

e s ne t grinding power per metre length of a 3

metre diameter m i l l with a grinding charge

having a bulk densi ty of 2.5 72 k W 2 k W .

g bulk density of th e mill charge in tonnes per

cubic metre.

m i l l diamet er inside l iners in m etres.

m il ll en gt h W d e i n e n in meters.

Net grinding power, e, is a function of m i l l speed

and m i l l charge volume. The figures given ar e fo r m i l l

speeds in the normal range of 72 75 percent of

cri t ica l and m i l l charse volumes of 30 to 35 and ar e

suitable fo r use in preliminary sizing.

~ o . v e d a y ( ~ )efe rs to a pow er number, p, which is

equiva lmt to:

and varies with mm charge volume for a &ven speed.

He has prepared'a p lot of dat a from pilot and produc-

t ion m i l l s and has re la ted it to a standard ball m i l l

curve for a cri t ical speed of 73%. He suggests th at

bal l m i l l curves for different speeds can be used t o

predic t power numbers f or ASAG m i l l s . These power

numbers do not appear t o account for expected power

swi ngs in a n ASAG m i l l .

Most SAG miUs of North Ameri can design hav e

been built using a m i l l diamete r 2 to 4 t imes the m i l l

length. Choice of ratio involves pra cti cal considera-tions such a s transportation, economics of manufac-

turing and retent ion time. In a single-stage circuit,

more emphasis s l ikely to be placed on length t o

guarantee sufflc ient re tention t ime fo r the production

of final product. In two-stage circuits, the primary

m i l l dimensions will usually be sel ecte d t o provide

impac t and a shor t retent ion t ime ra th e r than a t t r i -

tion, so th at a coarser product can be ground more

efficiently in a ball m i U . The sp li t between E s ~ ~ a n d

EBM for two-stage circd w i l l have been selected to

achieve the Pighest power efficiency and m i l l dimen-

sions fo r both stag es will &o be selected with thi3

objective it mind.

m a l l Scale Continuous Tests

One laboratory, Polysius Aerofall, n the United

Sta tes is currently offering autogenous grindability

t e s t s in a 450 m m (18 inch) diameter m i l l . a mple

requirement s betwee n 136 and 227 kg per test. This

materia l is crushed to minus 32 m m in preparat ion for

the test which is performed on dry material with an

18.12 kg ball charge, or about 10 of m i l l volume.

The m i l l is supple m ented by a draft fan and product

collect ion system Plus 14 mesh mat eri al is recycled.

The m i l l is a p eepher dl discharge n i i l fed by a

vibrating fee der and controlled by sound le vel tom a b a r m i l l loading. The m i l l is usually operated

with the peripheral par ts closed. The ball charg e

consis ts of a graded charg e ranging in siz e from 64

m m to 13 m m . The m i l l is operated fo r a sufflc ient

time (unspecified in the results) to establish balanced

conditions. ce these conditions ar e established, th e

m i l l is operated fo r one t two hours during which

time samples ar e taken. After this , the m i l l load is

removed f or volu m e t r k measurement and size analysis

dlong with th e feed and produ ct samples. Net m i l l

poweris

calculatedfrom

th e fo* wing form ula:

Net M i l l Power 0.682 (3.2 3 Lf) x Lf x g

Where Lf fract ional fi ll ing of the m i l l

g density of total m i l l load, lb/ft3

Ushg ne t mill power and 80 % passing sizes of feed and

pm du ct a n Autogenous Work Indexw (A Wi) a s deffi ed

by Mac~herson(7)s calclulated using Bond's formula.

This Autogenous Work Index s then used to esti-

mate th e ful l scal e pla nt Operating Work Index, Wio,

using a plot of A W i versus Wio from a library of

test ing and operat ing informati0n(7,~). The Operating

Work Indices apply to single-stage or two-stage

circui ts to fin al product size and th e objectiv. ' is t o

re la te A W i to t he Wio fo r a s i m i l a r ore. This

correlation s proprietary information which is n o t

g e n e r a y available to the en&teering fra terni ty.

MacPherson shows th at A W i is directly proportional toWio fo r values of A iJ i of less than and ores i n this

cate gor f should grind effici ently on a fully autogen-

ous ba d . Further, he shows, this proport iondity

f& off inversely as A ' rli increa ses above and th at

ores ir this range should require the addition of a ball

charge to t he primary m i l l or t he rem oval of pebbles

to enhance power efficiency. The method, apparently,

cannot be used to assess the ef fec t of variable circul-

ating loads resulting from changing clasii iicatio n or

bal l charge volume nor can it be used to fi-mly pre dic t

th e cho ice of an ABC cir cui t over semi-autogenous.

The advantages of such a method are th at re hti vsl y

s m a l l sample w dghts a re required, tha t results can be

obtained in a sho rte r tim e span compared with fullscale pi lot plant and t ha t choices for f ll scale pi lot

p lant t e st ing can be ident f led w i t h regard to c ircuit

type and different ore types.

With reference to the power distribution between

primary and secondary grinding stages(8), the relation-

ships Dust ra ted in F i g r e 4 de mons tra te Ynat M h a r

power efficiencies can be obtained with a coarser

primary product sent to ball milling. There ar e som e

exceptions (see the Section on Empki cal Calculations),

but generally indus trial practice has been to utilize

secondary ball m i l l i n g c ap ac it y to t h e P A s t a nd , i fnecessarj , inst ll more. B a l l m U t g c a pac it j. c a n be

justified if the inc rementa l dec rease in specific power

consumption for the primarf m i l l for example be-

tween 500 and 100 0 microns fo r primary m i l l circuit

pmduc t in FQuro 4 is greater than the correspondingincrease n specific power consumption required for

ball mil ling the coarser product . This a p p ~ a c h ould

be followed in the interest of minimizing capit a l cost

and operat ing cost through th e corre ct choice of

primary m i l l produ ct size, circnuit bjpe and po wer split.

With regard to contingency placed on result s pre-

dicted fmm determination of A W i no information has

been published. However, Hac Pherson claims good

correlation between thr oughputs calculated from A W i

and those experienced in indus t r id p lants prodded the

sample for A W i determination is crushed n a manner

( u n s p e d e d ) which simulates tlne method of ore break-

age h m miling bulk samples(7). Reader s have to



make t he accurnption t ha t the indu strial plants towhich he r efe rs a re power-efficient.

Batch ests

These tests are proprietary in that only one m i l l

manufacturer MPm is equipped to conduct the tests

and scale-up te st results. Observation of th e te sts is

mandatory with represe ntativ es of both the mine

owner and an ind eaen den t consu1t;ing metallur gical

engineer being present to note characterist ics of ore

breakage.The basic te st requires a 227 kg sample to be

ground for a spe-&ied ti me period (Le. power inp ut) in

a 1.83 m dia x 0.30 m m i l l with a specified ball

charge. The m i l l charge is then sized and a specif'lc

pnwer consumption is calculated in ter ms of kwh per

tonne of s o u n d product which passes a s et screen

mesh. Alternate test conditions can be designed for

which t he siz e distribution o f th e feed, b all charge

volum a, b all sk e s and ball charge composition can be

varied. It s very important that an independent

m etal lxgical engineer part icipates in designing th ese

test conditions based on is knowledge of all t he

properties of t he samp les which he has selected and

is background k nowledge of th e orebody.Up to f our tests, 1000 kg, can be completed each

day. For each ore type it is necessary to t e s t a t e as tthr ee levels of b all addition and one variation of feed

size distribution fo r a to tal of s x tests (1500 kg).

Samples should be selected from development rounds,

pit benches or 150 m m dri l core with over she crushed

to pass 200 m m . Each sample should be screened in to

p s 100 m m minus 38 m m and the inte rmedia te

fract ion so t ha t the tes t feed samples can be com-

podted with a b is toward coarser or f iner f rac t ions a s

well a s th e natur al size dist bution. Mixtures of ore

types in varying rati os can also be tested. in t h i s way,

any variations i n s p e d i c power consumption w i l l be

observed and used as a tool i n sizing the m i l l . Thistest faci l i ty w i l l sca le up te s t resul t s to give an

expected specific power consu m ption for continuousoperation. The method of scale-up s proprietary

information but t he independent observer can assess

th e .resat on th e basis of h i s experience.

Sizing of the n f l w l l follow th e sam e principles

discussed i n th e previous sectio n on Empirical Calcu-

h t i ons , usin Eq ua ti ~n 3). Cve should be taken in

applying a contingency. Firstly, it should not be

applied t the ba tcn tes t resul t s but only to t he

prediction for continuous operation which is the most

rep res enh tiv e of expected plant feed. Secondly, th eempi cal calculations should also be done as a check

based upon Bond Work Index data. Generally, a

contingency Of between 15 t o 20 has been found tobe adequate@) but ther e have been exceptions.

Examha tion of th e size distribution of th e m i l l

charge w i l l indicate any signs of bum-up of cri t ic al

sh es . The size distribution of th e minus 13 m m

(expected tro m m el undersize) fract ion of the charge

will indica te t he 80 p passing size of tine expected SAG

m i l l product. This should be used s a guide in sizing a

secondary grinding stage.

It is important therefore th at a metallurgical

engineer's judgement should be obtained in su ch

circumstances, which is independent from any given by

m i l l manufacturers, regarding the power required f or a

part icular operation. The d e e n of the tes t program,

the nature of the samples tested , and the interpreta-

tion of t he r esults should benef it from such indepen-

dent expertke .

The media comp etency t es ts outlined by

~owlan d(lO) r e conducted in a similar s i z e t e s t m i l l

but no a t t e mpt s made to measure power o r predict

specific power requirements Whereas the individual

cost of such a test is s imi la r to the s m a l l sca le

Aerofall con'inuous o r the MPSI batcn test, th e

information obtained s still preliminary and should be

used t o plan continuous tes ting programs. The

decision to utilize media competency tes ts in any

investigation is one of economics. Since information

from continuous pilot plant testing is much cheaper

than it used t o be, th e alternativ e of proceeding

d i r ~ c t l ywith piLOt pla nt test w ork more at tr act iv e i f

s m ples are available.

Continuous ests

The requi rement s fo r continuous pilot testin of

or es have been adeq uately described by WyslouzilTll).However, a summa ry of th e flowsh eet options which .ar e avai lable and a discussion of some of the t es t

pzmmet ers and the ir importance t o the plant desiqner

is given here to complete this com m entary on tes t

options.

Recognized com mer cial t e s t f acil itie s in Nortin

Americaare

located a t CSMR I

Lakefield, MPSIPolysius-Aerofall and Witteck. In South A m erica,

CIM M in Chile has been operating for two years and

there is a possibility o f an in sh lh ti on becomirrg

available in Peru. Other te st m i l l s are loca ted in

Australia, France, Japan, Portugdl, South Africa and

Sweden. The University of British Columbia is

currently experimenting with a 0.61 m diameter m i l l

which shows promise as a too l for simulat ion of

process variables with th e potent- of gen era tilg

infor mation f or equipment sizing.

The principal factor governing the cost of a test

program is the length of t ime required to achieve

stable conditions under which the circuit can be

sampled. Until recantl y, sev era l days of operation

witin periodic ch eck s of load lev el and successive

sample campaigns were required to ensure confidencei n results The application of load cells to the suppo rt

Pa m e of the te s t m i l l has in most cases considerably

reduced th e tim e taken to achieve stability. Use of

thi s tool w i Y enable three o r four tes t condi t ions to be

inves tba ted during a 2 4 hour period. Exceptions ar e

usually very hard ores for which crit ical size s have t o

be crushed and recycled.

The flowsheet options which should be available inany te st faci l i ty a re as follows:

- Full ] Autogenous i n closed-circuit with a scre en

and/o r dlassifier. Screen undersine can be fi na l

pro duc t or may requk-2 secon dary grinding in a ball

m i l l .

- Fully Autogenous with extr acti on of pebbles,

optio nal crushing of pebbles for re cycle and/o r

secondary grinding in a bal l or pebble m i l l .

- Semi-Autogenous i n closed-circuit with a scr een

and/or classifier. Screen undersize can be fin al

product o r may require secondary grinding in a bal l

m i l l .- Semi-Autogenous with extra ctio n of pebbles, op-

tional crushing of pebbles for recycle and/or secon-

dary grinding in a ball m i l l o r pebble m i l l .

The ease with which any of these circuit options

can be assembled and operated is another factor which

wil lbf lue nce tes t program cost and selection of a te st

facility.



For single-stage ci rcu ih in which th e primary m i l l

is operated autogenously, test parameters to be

investiqated are feed rates, specific power consump-

tion and, if necessary, the effect of pebble crushing invarying quantities on feed rate and specific power

consumption (kWh/tonne) to produce a fi na l product&zing. Where th e primary m i l l is semi-autogenous,

the principal variables are ball charse volume and bal l

si ze dlztribution.For two-stage circuits the test parameters which

should be investigated in order to establish the most

power-efficient d e a n cr i teria for the primary m i l l

and the overall circuit are:

Screen or trom me1 mesh opening on th e primarym i l l since this can influence feed rate and soecific

power consumption. The coarser th e product pre-

pared for secondary ball milling th e more efficie nt

w i l l become the overall circuit as discussed

previously. In the case of pebble milling the

maximum rate of pebble consumption which can be

tolerated w i l l influence the proportion of power

applied to pebble milling. Mesh openings can vary

from 35 mesh to 10 m m , providing measures are

taken to protect the primary m i l l discharge pump

in the case of coarser openings.Circulating load of scre en oversize which is return-

ed to the primary m i l l . ir the case of seni-

autogenous grinding where t oad, in percentage

terms, increases with increase in feed ra te reallzed

from increasing ball charge volu m es (and coarser

product sizing), this is one indication th at autogen-

ous grinding w i t crushing of pebbles should be

tested (the others being limitatio ns on feed ra te

and specifc power consumption).

Ball charge volume with a gLven bal l size distribu-

tion: a t le as t three ball charge volumes should be

tested 3, 6, 9 and possibly 12 in order to pre-

pare curves fo r product si ze vs specific power con-

sumption (Figure I), product size vs percentagesteelload by volume (Figure 2) and product size vs

feed ra te (Figure 3 . These relationships are typi-

ca l of the majority of ores but there ar e significant

exceptions (see co m m ents Empirical Calcula

tions).

Maximum ball size since this can influe nce the si ze

distribution within the primary m i l l , product sizing

and specif ic power consumption.

Pebble crushing since this can improve tkne power

effici encies of both autogenous and s e mi-autogen-

ous m i l l s through the extraction and crushing of a

cri tic al size which s limiting feed rate. In either

case, all or a portion of t he pebbles can be crushed

and recycled to the primary m i l l feed depending

upon whetiner pebble m i l l s are being used. If ll

the pebbles are being crushed, it is conceivableth at a portion could be recycled and the res t

tra nsf emd to secondary b l l milling or the total

amount could be reground in the secondary stage.

It is important th at equipment is available which is

capable of crushing pebbles to 100 % passing the

no mi nd gra te opening in the case of 100 recycl eto an autogenous m i l l and that such recycling s

continuous.

Pebble consumption and maintenance of a constant

pebble charge level when pebble m m g : early

recognition of any changes in charge level w i l l

avaid tim e wasted in andysin g spurious results.

For any of the circuib discussed, the following

observatLons ar e imperative vhich deserve th e at ten -

tion of the desiqn/evahation engineer:

Description of t es t equipment so th at he can

compare the capabilities of different test

laboratories. Pebble port and grate openingsshould be specified so tha t they conform ~ i t h

operational practice for maxiinurn power

efficiency.

reparation of test samples, circuit sampling

procedures, screen analysis procedures for bulk

samples, processing of te st d a b and report

content.

Method for recording and rnessure m en t of gross

and no-load power on th e t es t m i l l s and the

consistency o r reasons f or vw ht io n of no-laad

power.

Specific power consumption reported from a

pilot milk th is w i l l be calculated fro m the net

power a t the speed reducer output shaft. An

. inefficiency of the remaining drive components

mu s t be assumed or stated to a rr iv e a t a f i g r e

which is equivalent to that a t a m i l l pinioz (Le.

does not include losses i m i l l bearings and

sprock et drive).Method of m i l l load easdre m ent: in addition

to measurement by load cell, visual chec ks

should be made befo re, during and following a

test of m i l l charge leveL T:.ljs should bemaintained a t a lev el just below cri tic al to

ensure that specific power consu m ptions reflect

the most effici ent operation of the test m i l l

which is practically attainable. A level of

between 23 and 27% is generall-I considered to

be optimum depending upon ore char ac te rk ti cs .

M i l l charge sizing this can be done a t the end

of each test or group of tests and should be

examined for signs of any bd3-up n critical

size.

Variationsn

feed size distribution since feedrate, product siziflg and specific power

consumption can be mfi len ced by an increas e/-

decrease in the proportion of very coarse or

ff ie materiaL However, o&j sucn variat ions as

ar e expected in run-of-mine or 2rimary cmshed

ore should be tested.

Variations in ore ktqrpes since unexpected condi-

tions have m a t a w e d in co m mercial plants

because certain important ore hypes have not

been included in a conOLnuous test pmgram.

The mine production schedu le should be r e d e w-

ed for any such variations and the siyniilcant

ore types, i.e. those represen ting more than

10% of the to ta l during an e s t ~ b b h e d ime

uterval, should be included in bulk samples

which, in turn, shouU be selected so thatharder, sof ter and expected composites of

varying hardness can be tested separately.

Variations in the meed of the primary m i l l and

the ~ f f e c t f sucn variations on feed rate,

specitrc power consumption and product sizing:

these observakions are import ant for projectsfor which the m i l l feed rate is to be controllel

to a specific tar get on harder or softer ores for

subsequent processing.

The resdt.3 of properly conducted Pall. s c d e 2ont.L~-

uous test3 are the most accurat e of the methods

discussed fo r scale-up purposes. The provlso proper l.~

conducted does not just apply to indi-itdull testprocedures; it applies also to the planning of the



T.hb pla nt began com missioning in April 1985.

Operating resul% are not y et available.

The Es ca hn te Pro ject (750 mtpd) w a s desianed

foliowing tw o st ag es of study. FirsQy, a comparison

of ca pi tal and operat ing costs was conducted based on

empi ri ca l scale-u p .Porn Bond Work Index dat a.

Product fo r cyanidation was s e t a t 80 passing 44microns and various dri l l core sect ions were tested f or

gri nda bat y. Scale-up para meters were developed as

shown in Table 3.

Next, once ;nine deveb pm en t permitted, a 2 tonne

blJlk sample was selecte d fo r batch testing. Besults

ar e shown i Table 4.

It can be seen that i q Test No. 1, which featured a

sample having the natcal s h e distribi lt ion as re cd ve d

by the laboratory, the Q h e s t spe&Tc power reading

was ObC&ed with an 8 ball charge by volu m e. This

result was 636, of tha t cdc uh te d by the empir ica l

method for the sa n e product s ize (%a 0800 microns).

It w a s decided to e rr on the side of the empirica l

method in specifying the m u or purchase.

Current operational resu lts show t ha t th e SAG m i l l

is oparath'ung a t 5 bdL charge leve l by volume and isdelivering a K80 800 micron prod uct as predicted.

?eve* drawn a t th e pi?ion is 448 kU, 13.617

icXh/tonne (SAC; niiU and 570 k W 17.325 kWh/'anne

ball zi lU when proce-g 32.9 mtph, for a total of

30.942 kk'h /tonn e or 14.6; above th e conve ntion al

estimzte. f i charge volume ilhich is lower than

those Ssted has been selected b~ order to minimize

ve w . 0 bviously, th e SAG m i l l k consu nirig no re and

t h e 5 d l mill hsi power Vnan w a s predicted by the

empirical method, but the oversl l to ta l is 99.5 of th e

pre dic ted tot-aL

The primary m i is t c n f i ~ gowards the au:ogenol;s

mode by drawing more pover for the design tnwugh-

?ut. The en@eer was co rr ec t in select ing the next

size of m i l l (4.89 netre dh.) over t ac o r n a y

yo po se d by th e to st fi-ty (4.27 metre Cia. Lr the

aasence of conCriuous tes t resul ts. L? this case, the

i?cre n ent al cost iqcrease was s m a l l and the increased

n i i l volu ne ennbled the operator to sel ect more

fzi.ourable opera'hg conditions by reducini; th e bal l

chargn. These resul ts do, hovever, indicate th at

caution should be exercised ir t he b t e r p r e t a t i ~ n f

Satcn te st re su lk on very hard siliceous ores. For

por2hj . r~copper wp e or es (e.6. Quintanal, bat,zh tes t

re s :d b have been obtained which ar e closer t o operat-y , ~5s ,d33 .

Key Lake

Continuous tesL5ng f or a uranium ore a t Key Lake

as necessary t o con*n specCic power requ iremen tsfo r grinding and pr oduct sking for t ine subsequent

Isaching process. Pre lim ina q irdica tions from m i l l

manuf actur ers based on examin ation of drill cor e had

exhibited a wide varhtion in specific power reqdre-

entS and i , as decided t ha t the ore value jus LIe d a

n ore extaxsLve t es t program.

Two or e type s, o.ri@tating fr3m open pits , coc'ai?

hird quartzite, bouiders, clays and sand wMch are

f.r zen in winter and sticky a t oth er times. Sa ples of

each ore ty?e, 25 - 30 tonnes each, were piioted to

produce a coarse, minus 500 micron, pmdu ct in a

&?g?e-stase cbcllit. Sp ep Xc poiler consumption and

product siziriq were found to be iridependent of each

oth er. The only rpdationship which could be drawn was

invesf5&%tlon which should be d e a n e d to facilitateanalysis of resulta The irdiv idual para m et em outlinedhere should each be investiqated in an orderly manner

with certain changes made according to the behaviour

of the ore. For instance, trom q el slzs opening (and

circulat ing load) should be i7v es Qa ted for a given ball

charge volume so tha t th e optimum opening in term s

of power efficiency can be selected before studying

the ef fects of variat ion i n ball char ge volume. If such

changes ar e made a t raddom, t he chan ces of missing

th e most power efficien t condition are increased. It

shoulri also be re membered that the defFnitive selec-

tion of an ABC ci-cuit can only be made by rundqg

continuous tes cs.

Results fro m a hill rang e of t es ts should be evalu-

ated t o determine th e most pouer-2fficient circuit(s)

consistent with equip m e n t m g podbil i t ies .

Normally, t he sp-lected r esu lt f or th e primar y m i l l

speci?c power consam ption Is scaled-up &ectly to

the production rat ed horsepower a t the pinion with

1 0 % contingency. Siz qg of the m i l l then follows the

principles outl ined in the sect ion c on ce rm g Empirical

Calcula5ons using Equation 3).It is important , also, to ensure th at sufficient bal l

m i l l power is available for efficient secondary grind-

ing. Secondary ball m i l l s should be &zed on the baskof Bond Work L?dex applied to the ore fo r bal l mil l iig

with ch eck s on t h e ASAG m i l l pro du ct ob-ed durir,g

contiiiuous testin g. The reaso ning behind k t a te -

ment is that micro-fractures in a test product could

and very often do, give a lower pi lot plant operafig

Work Index f or ba ll milling c o op ar ed t o aond Work

Index and com mercial-scale pla nt operating Work

Lrdex de te r rnilations(l2).

It is evident, theref ore, t ha t a consulting metallur-

gic al engineer should participate in th e conduct of th e

tests on the Owner's behalf. H i s opLnion regardhg

circu it adjustments, deali rg with unexpected condit-

io cs and s?ecifying te st in fo rm ae on wbich should be

reported, w i l l ensure that design triter*? fo r m i l l

sel ecd on meets the objectives of aower efficiency and

capacity for t reat ing expected variat ions in ore types.

Teck-Corona

The tiemlo gold pn j e c t of Teck-Comna (1000

ntpd) provides an example of m i l l sizin3 ?g t he

e n pirica l calcul ation method alone. The sitilation

facing Teck-Corona was the ir inability to obtain

samples for batch o r conti iuous kst ing . Underground

access was not possible in sufficient t ime to provide

bulk samples. A t ight construct ion schedule dictated

th at engineering proceed on the basis of informatLon

obtai nabl5 only from drill core. This meant th at Bond

'rlork Indices had to be used for m i l l d d n g which w s sr e d e wed with m i l l manufacturers and other consul-

tants. two sta ge S A G m i W b a l l mFU circ -x it was

chosen after a co m pa r ii n with a rod mill/bd.l aillci-cuit showed appreciable capita l cos t szvings Motor

horsepower selecti ons followed Equations (1) nd (2) to

give a two-stage circlli t designed to produce K80 54

micron fee d fo r cyanidation. Dee& of the calcula-

tion ar e found in Table 2.

The SAG m i l l va s sized with 746 kW to @re a 25

contiqgency f or power swings on t he calculated power.

The bail mill was sized a t 1120 k W . Tota l i x t a l l e d

power for c on minution exceeded th at required fo r

conv ention al grinding by a f ac to r of 1.163 (including

secondary crushing).



For larg er scale projects, it has been demonstratedth at preliminary esti mates of sp ed % power require-ments using e mpiri cal calcu latio ns based upon BondWork Index can be verified by continuous scaletesting. Since resu lts fo r sof ter ores do not exhibit

the same degree of agreement, it appears th at lowerscale-up fac tor s can be used in such cases.

The impor tance of a thorough understanding of t he

mineralogy of o re types , var iat ion of Bond Work Index

and the use of refer ence ores in predicting P S G I O rthe 80 pas ing size of the primary u roduct, whenus ng empiriod calculations or batch scale tests is

stressed. P S G can only be deter mined experimental-ly by conducting continuous scale tests Further,

P S G is a singularly important parameter in thedesign of po wer-e mcien t autogenous o r semi-autogen-ous grinding drcuitz It appears to be a function of

ore hardness i n the case of crystalline rock, takLnginto account factors such as supergene alteration of

sulphides, hydrothermd alteration of siliceous rockand compre&ve strength. For ore types in which

crystal g n s or ore values ar e more loosely

cemented, PS G is limited by the natural grain sizeand a single-stage grinding ci rcui t is usually selectedwhere this su its downstream processes.

The power split between primary and secondarygrinding sta ges in a two-stage circuit is a function of

P S G fo r maximum power e-ency. Since ba llmilling involves a more eMc ie nt transmission ofenergy fo r comminution compared t o autogenous o rs e mi-autogenous grinding, the selection of P S G fo r

ball m i l l feed s made a t the point where it begins tocost less to grind y baJl milling than it does to

produce a f ine r product by primary grinding.The agreement in the examples between specific

power require m ents fore cast by e m pirical calculationsand either continuous pilot plant tests or operatingresul ts demonst rates the validity of t e scale-upfa ct or 1.25 i n Equation (1) fo r compete nt crystalline

ores. There is some evidence in the bxamples tosuggest that the contingencies outlined in Table 1 are

valid fo r the e mpk kal . calculation method and contin-uous pilot plant testwork. However, contingencies

applied to batch scale testwork can vary widelydepending upon the amount of testvork performed,

partLcularly with reg ard to variation i n ball chargevolume.

Comparison of industrial plant operating Work

Indices and Bond Work Indices on pilot plant secondary

m i l l feed with pilot plant operating Work Indices forball milling suggests that the dedgner should use a

Bond Work Index f o r ba ll milVqg in designing the

secondary stage,

In sum mary, t h e pl ant desiqner ha s a choice oftesting methods for a given ore. The ch ok e must be

made based on the degree of risk accep tabl e and the

costs willing to be paid to minimFze the mk goodunderstandfneS of mineralok~as w e I L as a thoroughinvestigation of rock types is reqlrired of the designer.Supervision of pre-design testwork by an indep enden tm etaIh$cal engineer is strongly reco m mended. H i s

input a t an early s tage in any project's life is impor-

tant so that comparative concepts can be estimatedand =alysed oft en before bulk samples are available

fo r testing.

Acknowledgement

The authors wish to thank the test facilities and

companies mentioned in the examples for suppkf~g

the data included in this paper. Also, th e management

fo r feed rat e and pilot m i l l ne t power (k W), shown inMgure 5, fo r each ore type. Specitto power consump-tion decreased with incre ase in ball charge volume forclay ore but increased in th e cas e of cobble ore. With

a ball charge volum e of 128 both ore types and blends

could be processed with a spec ific power consumptionin the range 3.0 3.8 kWh/tonne. This compares to

7.71 kWh/tonne derived f2 . o ~ he em pi ri cd formula.The tendency of sandstone and clays to comminute

easily to grain size is considered t o be the primecontributor to nis power eMciency, with grinding

power requi red mainly to break up the harderquartzite and basement materiaL

The production size m i l l w a s rated to draw 300 hPwith a contingency of 50% in the expectation thatwide power swings could occu r with mater ials ofdiffering hardnesses and tha t ball charges of up to 15by volume would be required in a to ta l m i l l volume of

up to 30%.

C e r r o Verde

re ce nt study involving ful l scale continuous pilotplant testing for dG and B C circuits on t i w e l l

known copper ore from P e r u w s preceded by prelim-

inary estimates of spedLfSc power requirements usingthe empirical calculation featured in this paper.Three ore composites were tested wtdch were eachmade up from mater ial drawn from ten ore type s

identifled in th e open pit. Each compos ite w a s repre-sentative of a particular production period in whichharde r or so fte r ores would be mined as w dl as ablend.

distinction between primary and secondarysulphides as w e l l as potassic and phyUlc alteration was

made i n deffning the ten ore types.The comparative data for preliminay and pilot

plant work is given in Table 5.t can be seen that there is good agreement

between t he pred ictb ns and pilot plant resultz for all

three types but the following points must bere m e m bered:The pilot pla nt drcuit had to be converted fro m

S G t o B C in order to reach a s i m i l a r

forec ast power efneiency.This con ved on w a s necessary a ft er ball charge

volumes of up to 12%had been tested, Le. the

critical. size w a s very hard and there w a s doubtwhether k t h e r ncreases in ball charge wouldhave had any beneficial effect.The product size from the primary m i l l in the

case of the soft er ore sample was muchcoars er and so t he power split between grinding

stages was very different from the oth er

composites and also fiom pr-diminary calcula-tions.

This paper ha s outlined th e proce sses by whichtes tin g fo r autogenous and semi-autogenous grinaing

clrcuita can be orga&ed a t reasonable c ost in prepar-atio n fo r equipment sizing and plan t design. Emphasishas been placed on disc usi ng the pa ramet ers which, if

investigated, w i l l result in a pow er- eff lci ent design.

Examples have been presented which dem ons tra tethe beneflts available to owners of smaller scale

properties through the use of empiricd calculations

and/or batch testing t o siz e equipment for a com m er-ci l installation. The benef lts and limitations offsredby s m a 3 l sc al e continuous +*sting have been oumed.



of Wr55ght Engineers Umlted s to be thanked forp e r m M o n to prepare and submit t ls paper to t?leSM E.

1. Bond, F.C., C ~ s ' h t ng and Grinding Cdl culatlons(Revised January 1961), AUls-Cham e n Publication07R9235B.

2. Flavel, M.D., Selection and U q g of Crushers,Chapter 21, Desk n and Instdllation ofCom minution Cbcuits, M - Jergensen, Editors.

3. Barrat t, D.J., Semi- Autogenous Grinding: A

Compa, on with t he C onventio nal Route, CIMBulletin, November 1979.

4. Rowland, C.A., Selec tion of Rod M i l l s , Ball M D ,

Pebble M i l l s and Regrind M U s , Chapter 23, Des knand In sta llat ion of Com minutlon Circuit s, Mular,Jergensen, Editors,

5. Dorr, A.A. and Basswear, J.H., Primary llLndingM i l l s : Selection, Slzing and Current Practices,Chapter 24 D e a n and Insta l la t ion ofCom minution Circuits, Mular, Jer gen sen, Editors.

6. Loveday, B.K., Predi ct ion of Autogenous Millingf'rom Pilot Pla nt Tests, =venth Com monwealthMining and Metalhrgical Congress, 5ong Kong,May 1978.

7. MacPherson, A.R., A Simple Method Pre dict th eAutogenous G b h g M i l l Require menta fo rProcessing Ore f r o m a New Deposit, Soci ety ofMining Engbeers, AIME Transactions, VoL 262,Septem ber 1977.

8. NacPherson, A. R., Power EMcient AutogenousGrinding Plants, pres ente d a t th e SM E-AIM E Fall.Meetinq, Denver, CO. November 1981.

9. Hood, M., Pena, F. Avelar, F.T. and Bailey, J.

Quintana Minerals Copper F l a t Project, presenteda t the SME-AIME A9nua.l Meeting, Atlanta, G A.,

March 1983.

10. Rowland, C.A., Pilot P lant Data fo r th e Design ofPrima ry Autogenous and Semi- Autogenous M i l l s ,

CIM Bulletin, Nove m be r 1981.

11 Wysloudl, D M. Standar d Laboratory-Pilot Pl antTests fo r Equipmen t Selectio n, Chap ter 15, De-nand Ins tdb ti on of Corn minution C i i d t s , Mular

Jergensen, Editors.

12. Fukuhara, R.S. and -I M.J., The HighmontGrinding Circuit Operatin g Ex perience with 5.0 m

(16 1/2 dia. aa l l M i l l s in an A-B-C circuitpresen ted a t the SME-AIME Fall Meeting, Salt

Lake City, U T, Oct ober 1983.



TABLE

COST AND R I S K ASSOCIATED WITH TESTY ORKDirect Laboratory Costs Only)

AUTOGENOUS ANDSEMI-AUTOGENOUS GRINDING

Primary j l l

Size of Sample Cost Hotor HPType of Testuor k Each r e Type Rbk Level Contingency :E mpir ical Calcula ions andScale-up from Bond +IrkIndices Crushhg, RodM i l l and B a l l M W 35 kg 2,0 00 High 25

Small Scale ContinuousTesting (45 c m dia m i l l 136 - 227 kg 1, 50 0 High t o Medium N / A

Batch Testing(1.8 m dia. mill) 2 tonnes 3, 00 Medium 15 20

Large Scale ContinuousTesting(1.8 m dia m i W 30 tonnes 20,000

W i Crushing (Metric)W i Rod M i l l (Xetric)W i Ball H i l l (Metric)Feed K a O CrusherFeed K80 Rod M i l l

Product K80 Rod M i l l

Product K80 B a l l M i l l

F ~ e d t phPower a t Pinion

CrusherRod M i l l

B a l l Y i l l

Total

Product KaO SAG M i l l

Power a t PinionBall xi l l

-SAG MSU

Ball H i l lTotat

Factor on Conventional

TABLE

SAG UILL 5 N GUSING THE EMPIRICAL CALCuLAnOH

FROM BOND W O R K INDICESTECK-CORONA PROJECT

CONVENTIONAL

17.617.622.1

127,000 Microns18,850 Micmns1,168 Microns

50 Microns

Low 10

SAG

17.617.622.1

127,000 Microns18,850 Microns1,168 Microns

110 Microns (fo r scale-

up)L 4

0.790 k W h/to nne 0.790 k U:?/tonne4.988 k h/tonne 4.988 k W h/tonne

24.497 kWh/tonne 14.572 k Wh/tonne30.275 k Wh/tonne 20.350 k Wh/tonne

X 1.25) 25.438 k W h/tonoe700 microns

(700 110 microns) 12.6 90 k Hh/tonne(t o 700 microns) 12.748 k W h/tonne

(700 50 micmns) 22.540 k Wh/tonne35.288 k h/tonne1.166



W i Crushing Metr ic)W i Rod MillCMetric)W i B a l l M i l l Metr ic)Feed K 80 CrusherFeed K80 Rod M i l l

Product K80 Rod M i l l

Product K 80 B a l l M i l l

Feed mtphPower a t Pinion

C m h e rRod M i l l

B a l l r nTota l

Product K80 S A G M i l l

Power a t P in ionB a l l M

S A G M i l l

B a l l M i l l

Tota lFactor on Conventional

1 0

T A B L E

S A G HIL L SlZLHG

U N G T H E E M P I RI C A L C A L C U L A T I O N

F R O H B O N D W O RK I N D I C E S

E S C A L A N T E P R O J E C T

C O N V E N T I O N A L S A G

20.1 20.118.2 18.216.4 16.4

88,900 Microns 88,900 Microns18,8 50 Microns 18 ,85 0 Microns

800 Microns 800 Microns44 Microns 11 0 Microns fo r scale-

up)32 32

0.788 k Wh/tonne 0.788 kV h/ton ne5.781 k Wh/tonne 5.781 k Wh/tonne

20.433 kWh/tonne 9.855 k Wh/tonne27.002 k U h/tonne 16.424 kWh/tonneV

X 1.25) 20.530 k Wh /tonne800 microns

800 1 10 microns) 9.855 kUh /tonneto 800 microns) 10.675 kWh/tonne800 44 microns) 20.433 kUh /tonne

31.108 W h/tonne1.152



est umber

Feed W t +4It

-4" + 1-1/21

-1 -1/2"

alls lbs: 4"

3"

2"

MUVolume:

U Product wt: + 411

-4" + 3"

-3" 2"

-2" + 1-1" + 1/2"

-1/2"

Total i l l ChargeMillvolume:

et k d h / t o ~ e f m i n u s800 Micron produc tScreen Analysis of Minus 1/2"

: cumulati ve retained on:nicmns

T A B L E

SAG ILL S I Z I N

B A T C H T E S T R E S U L T S E S C A L A N T E .

- 2-40.9 40.9

53.0 53.06.1 6.1

420 630

285 310

235 235

8.30 10.37

4.2 3.8

17.2 17.4

28.8 20.0

14.4 11.0

3.8 2.6

31.6 45.2



T A B L E 5

C E R R O V E R D E O R E

C O M P A R I S O N O F P R E L I M I N A R Y H I LL S LZ I NC W I T H P I L O T P L A N T R E S U L T S

P r e l imin a r y ( S A C ) Pilot P l a n t ( A B C ) Pilot P l a n t ( S A G )

U s i n g A-C B o n d 0 B o n d W o rk U s i n g B o n d W01

W o r k Indices for ndex P r o c e d u r e for ndex P r o c e du r e f o r

C r u s hi n g , R o d H i l l B a l l H i s t i n g Ball M m g

a n d Ball Hill r o m 1 m M h M m 0 H-h

S o f t e r O r e

P o w e r D r a v , k Wh/tonne a t M i l l Pinion- PrLmv t i I h- Seconda ry M i l l s 9.830- T o t a l 1 7 . 8 4 8

S e c o n d a ry C i r c u i t F e e d , ,Keg (Microns) 7 8 0Seconda r; r C i r cd t Produc t , K80 (Mic rons) 7 4

A v e r ag e O r e H i x

P o w e r rr w k Y h / to n n e a t i l l pinion

- ? r i m a r j M Us- ~ e c o n d i r , M i l l s- T o t a lS e c on d a ry C i r c d t F e ed , K ~ l nMicrons)

S e c on d a ry C i r c u t ~ r o d u z t ; 8 0 H ic ro ns ) 74

arder O r e

P o w e r D r a w , k k h / t o n n e a t : d i l l Pinion- P r i m a y M i l k- Seconda ry M i l l s 1 1 . 6 4 5- T o t a l 2 1 . 1 4 3Secondn-qr C i r : u i t Feed , K80 (Mic rons) 8 4 0Seconda r f C i rcu i t Produc t , K 8 0 H i c r s n s ) 74

UL r g S 5 V/V aall Zhhrge Volu m e



Figure 1

AUTOGENOUS PILOT TESTS

KWH PER TONNE V K8 PRODUCT

STEEL LOAD

W O ~ U m b W ~ m

PRODUCT K8 IIIICROHS)



mw 2

NTOGENOUS PILOT TESTS

S E E LO D BY YOL VS K8 PRODU T

m

DO

F -

NJTOGENEOUS PLOT TESTSPRODU rIONRATE Kg VS KBO PRODU T



igure

SEMI ALITOGENOUS GRINDING

EXAMPLE VARIATION O POWER DRAWN

vs PRIMARY MILL PRODUCT SIZING



Figure 5

P I L O T M lL L R E S U L T S

V R I T I O N S O F M l LL P O W E R V S F E E D R T E 6 B L L L O D

YEW IEE

VY

FIGURES REPRESENT

B LL CH RGE LEVEL

I I I I I I

4 6 7 D

VER GE NET MILL POWER k W

testing for autogenous and semi-autogenous grinding

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