factors which influence selection of comminution circuits

7/28/2019 Factors Which Influence Selection of Comminution Circuits

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Chapter 1

FACTORS WHICH INFLUENCE SELECTION OF COMMINUTION CIRCUITSD. J. B a r r a t t M. A. SochockyW r i g h t E n g i n e e r s L i m i t e dVancouver, B.C.Canada

INTRODUCTIONSummary of Fac tor s In f luenc ingComminut ion Ci r cu i t Des ign

The s e l e c t i o n o f a n a p p r o p r i a t ecom minution c i r c u i t f o r a s p e c i f i co r e i s o ne o f t h e m o st i m p o r t a n td e c is i o n s i n t h e d e s i g n o f ap r o c e s s i n g p l a n t . T he i m p o r t a n c e i sr e l a t e d t o t h e f a c t t h a t t h e c a p i t a lan d o p e r a t i n g c o s t s f o r c r u s h i n g a ndg r i n d in g p l a n t g e n e r a l l y r e p r e s e n t ,a s i s w e l l know n, t h e m a jo r p o r t i o no f t h e p l a n t c o s t s . T h i s c h a p t e rw i l l , t h e r e f o r e , i d e n t i f y a s many a sp o s s i b l e o f t h e f a c t o r s wh ic hi n fl u en c e t h e s e l e c t i o n o f ac o m m i n u t i o n c i r c u i t .

T he nu mber o f f a c t o r s w h i c h w i l lh av e t o be c o n s i d e r e d f o r an yc o m m i n u t i o n p r o j e c t w i l l d e p e n d ,among o t h e r t h i n g s , o n t h e t y p e o fp r o j e c t . I f , f o r e xa m pl e, t h ep r o j e c t i s a n e n t i r e l y n e w m i n i n gd e v e lo p m e n t, t h e n m o s t , if n o t a l l ,t h e f a c t o r s i d e n t i f i e d w i l l h av e t ob e a n a l y z e d . If t h e p r o j e c t i s a ne x p a n s i o n o f a d e v e l o p e d m i n i n go p e r a t i o n o r i f t h e n e w o r e b o d y i sa d j a c en t t o a v i a b l e o p e r a t i o n , t h e nt h e e x i s t i n g o p e ra t i o n w i l l i n f l u e n c et h e c ho ic e o f f a c t o r s o r d e s i g nc o n s t r a i n t s w hich n e e d t o b ec o n s id e r e d. The e x i s t i n g i n f r a s t r u c -

D r a v o E n g i n e e r sP i t t s b u r g h , PA .U.S.A.

t u r e o r s u p p o r t i n g s y st e m s may b eq u i t e a d e q u a t e t o a cco mm od ate t h er e q u i r e m e n t s o f a n y e x p a n s i o n o r newd e ve lo p m en t . H ence, t h o s e f a c t o r smay n o t h a v e t o b e c o n s i d e r e d . Toc o v e r , h ow e ve r, t h e w i d e s t s p e c t r u mo f p r o j e c t s , t h e f a c t o r s which h a veb e e n i d e n t i f i e d i n t h i s c h a p t e r a r et h o s e w h i c h w i l l h av e t o b ec o n s i d e r e d f o r t h e m o st c om ple x o fp r o j e c t s , t h a t o f d e v el o p i n g a ne n t i r e l y n ew m in i ng o p e r a t i o n .

The ra n g e o f f a c t o r s i s a s b ro ada s t h e r an g e o f d i f f e r e n t o r e t yp e s.T h u s , e a c h d e v e l o p m e n t m u s t b et r e a t e d w i t h i n d i v i d u a l i z e d c a r e .The m os t i m p o rt a n t s t e p i n t h ed e v e l o p m e n t i s t h e a n a l y s i s a n du n d er s t a nd i ng o f t h e o r e c h a r a c t e r i s -t i c s . The h a r d n es s o f t h e o r e , i t sa b r a s iv e n e s s , f r i a b i l i t y , m o i s t u rec o n t e n t , g r a d e , m i n e r a l i z a t i o ni n c l u d i n g g an gu e m i n e r a l i z a t i o n , l i b -e r a t i o n s i z e , c h em i s t ry , a nd o t h e rc h a r a c t e r i s t i c s s h ou ld b e t h e f i r s tt o b e an a l yz e d i n t h e i n v e s t i g a t i o n .The n e x t s h o u l d b e t h e d e t e r m i n a t i o nof f a c t o r s su ch a s p l a n t s i z e ,t h ro u g h p u t , l o c a t i o n , c l i m a t e ,a c c e s s i b i l i t y , a n d a v a i l a b i l i t y o fw a t e r .The s e l e c t i o n o f s a m p le s f o ri n i t i a l b en ch s c a l e w ork an d b u lks a m p l i n g (w hen n e ed e d) f o r f u r t h e r


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DESIGN, INSTALLATION OF COMMINUTION CIRCUITStesting, such as larger scalelaboratory investigations up to pilotplant scale, are very critical. Theimportance of careful sampling cannotbe over-emphasized.

With the development of thefirst metallurgical flowsheet thecomminution engineer will obtain thedesign criteria for liberation. Hewill determine the circuitconfiguration for stages of crushingand grinding and any intermediatebeneficiation steps. If mediacompetency tests show that autogenousgrinding is possible, variouscomminution circuits will have to betested and economically evaluated.In many cases it will be thecomminution engineer who will dictatethe grinding stages rather than themetallurgist. The advantages anddisadvantages of the variouscomminution circuits are many, butthe final analysis involves practicalconsiderations as well as economics.These considerations could be theavailability of items such as goodmedia, good straight rods, 10-12.7 cm(4-5in.) balls in a remotegeographical area, or trained peopleto run a sophisticated plant.

Finally, it is very important tohave a proper understanding ofcurrent practices in similar orrelated industries, to find out whyothers did what they did, and tolearn from their experience.Outline of Various ComminutionCircuits under Consideration

The variety of possible circuitsprovides greater challenges for thecomminution engineer. To simplifythe analyses in this chapter, onlythe most basic circuits predominantlyused and accepted by the miningindustry have been considered. Theseare as follows:- Crusher-Rod Mill-Ball Mill- Crusher-Ball Mill-Ball Mill- Crusher-Rod Mill-Pebble Mill- Crusher-Single Stage Ball Mill

- Single Stage Autogenous- Autogenous-Ball Mill- Autogenous-Pebble Mill- Single Stage Semi-Autogenous- Semi-Autogenous-Ball Mill- Autogenous-Ball Mill-CrusherEach circuit has its advantagesand disadvantages. However, for anyparticular ore, a specific evaluationhas to be made, and when it is shownthat the advantages outweigh thedisadvantages, that particularcircuit should be given additionalscrutiny. This does not mean that

each of the above circuits should betested. Needless to say, this wouldbe extremely time consuming andcostly. Relatively simple prelim-inary tests such as media competencytests and Bond crushing impact testsare available and can be used toeliminate a number of the abovepossibilities.Discussion of Project DevelopmentSequence as it affects the Choiceof Factors under Consideration

It is a pre-requisite for asuccessful plant design that acomminution engineer be specificallyassigned to a project to work rightfrom the beginning with themetallurgical staff. The process ofgathering design criteria and theevaluation of this data can be doneeither by the owner's staff or by anindependent consulting firm. Ineither case, the starting point isthe geologists8 report. This willdelineate the orebody and provide aguide to initial sample acquisition.The quantity of the ore sample isusually limited at this point andstudies are done on a bench scale todetermine basic starting parameters.These bench scale tests, togetherwith what one may call the"experience factor", will allow themetallurgist to propose a fewpreliminary flowschemes for treatingthe ore.

At this point a preliminaryeconomic viability study should be


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p r e p a r e d w h ic h w ou ld t a k e i n t oa cc ou nt some f a c t o r s r e l a t i v e t op l a n t l o c a t i o n , o r e t y p e , p r o d uc tt on n ag e an d q u a l i t y , e v en i f m anyf a c t o r s h av e t o b e o n l y a s s um p t io n so r e d u c a t e d g u e s s e s . W n ee d t oc on ce rn o u rs e lv e s w i t h t h i s c r i t e r i ao n l y i n a sm u ch a s i t a f f e c t s t h ecomminu t ion sys t em de s ig n . Them e t a l l u r g i c a l f l ow s h ee t w i l l s p e c i f yt h e f i n e n e s s o f g r i n d r e q u i r e d a ndp e r ha p s t h e n eed f o r m u l t i - s t a g eg r i n d i n g w i t h i n t e r m e d i a t e c o nc en -t r a t i o n s t e p s be tw ee n g r i n d i n gs t a g e s . B ased on t h i s i n f o r m a t i o n ,t h e c om m in ut io n e n g i n e e r s h o u l dc o n d uc t t h e a p p r o p r i a t e B ondg r i n d a b i l i t y tests. F o r t h e p u r p o seo f t h i s i n i t i a l f e a s i b i l i t y s t u d y , ac o n v e n t i o n a l , c r u sh i n g -r o d m i l l - b a l lm i l l c i r c u i t c an b e a ss um e d. T h i s i sa p r a c t i c a l f i r s t s t e p a n df a c i l i t a t e s t h e e v a l u a t i o n p r o c e s swhen c o n s i d e r i n g a l t e r n a t i v e s ch em e s.S am ple s s h ou ld a l s o b e s e n t a s s oo na s p o s s i b le t o a n a c c r e d i t e dl a b o r a t o r y f o r me di a c om p et en c y tes tsand a b r as i o n i n d e x t e s t i n g .Assuming, o f co u r s e , t h a t t h e i n i t i a le co no m ic e v a l u a t i o n was f a v o u r a b l e , amore d e t a i l e d f u l l s c a l e f e a s i b i l i t ys t u d y s h o u ld now be s t a r t e d .

T h i s s t u d y w i l l r e q u i r e atho ro ug h i n v e s t i g a t i o n o f a l l t h ef a c t o r s . D ep en din g u po n t h e l o c a t i o nan d s i z e o f t h e p r o j e c t an d t y p e o fd e p o s i t , t h e d e ve lo pm en t w i l l r e q u i r et h e a c q u i s i t io n o f a l a r g e rr e p r e s e n t a t i v e s a mp le , o r s e qu e n c e ofs a m p l e s , m o r e t h o r o u g h b e n c h s c a l ew ork , a n d p e r h a p s a p i l o tp l a n t - s c a l e i n v e s t i g a t i o n . Manyd e c i s i o n s w i l l h av e t o b e made a tt h i s p o i n t b y t h e c om m in utio ne n g i n e e r . He s h o u l d by t h e n h a v e t h er e s u l t s o f t h e me di a c om p et en cyt e s t s . The d e c i s i o n w i l l ha ve t o b er e a c h e d a s t o w h ic h c o m m in u ti onc i r c u i t s s h ou ld be t e s t e d an d a l s o a st o t h e l e v e l o f e f f o r t r e q u ir e d .Each c i r c u i t t e s t e d w i l l h av e t o b ee v a lu a t ed t a k i n g i n t o a c c o u n te co no m ic , m e t a l l u r g i c a l , a nd p r a c-t i c a l c o n s id e r a t i o n s w i t h r e g a rd t oe qu ip m en t s i z i n g . T he f i n a l

s e l e c t i o n s h ou l d b e t h e c o n se n su s o ft h e b e s t k no wle dg e a v a i l a b l e ( 1 , 2).

IDENTIFICATION OF FACTORSP r o p e r t i e s o f t h e O rebody o rS e l e c t e d C i r c u i t FeedG e o lo g ic a l I n t e r p r e t a t i o n o f D r i l lC o re a n d B u lk S am p le s. The i n i t i a li n f or m a t io n g a t h e r i n g p r o c e s s s h o u lds t a r t w i t h t h e g e o l o g i s t s 1 r e p o r t .S am pl in g m eth od s f o r f e a s i b i l i t ys t u d i e s depend o n g e o l o g i c a lc h a r a c t e r i s t i c s o f t h e d e p o s i t .

I n i t i a l sa m ple a c q u i s i t i o nm e t h o d s may v a r y an d s h o u l d b ea d ap t ed t o e ac h p a r t i c u l a r d e p o s i t ,b u t a t t h i s s t a g e o f t h e p r o j e c td e ve lo p m en t, t h e m e t a l l u r g i s t w o uldm os t l i k e l y h av e diam ond d r i l l c o r es a m pl es a nd p o s s i b l y s u r f a c e g r a bs a m pl es o r t r e n c h s am p le s t o t e s t f o rd e v e l o p m e n t o f d e s i g n p a r a m e t e r s ( 3 ,4 ) .The f a c t o r o f i n t e r e s t t o ac o m m in u ti on e n g i n e e r , f ro m t h eg e o l o g i s t s 1 r e p o r t , would b e t h ei d e n t i f i c a t i o n o f m i n e r a lc o n s t i t u e n t s p r e s e n t , t h e i r r e l a t i v eq u a n t i t y an d d e g re e o f d i s s e m i n a t i o n ,t h e num ber o f d i s t i n g u i s h a b l e o r ez o ne s an d t h e m ain c h a r a c t e r i s t i c s o fe a ch . T he f o l l o w i n g f a c t o r s s h o u l db e e v a l u a t e d t o p r o v i de t h e i n i t i a lb ac kg ro un d i n f o r m a t i o n f o r f u r t h e rd e c i s i o n m a k i n g .

M i n e r a l o ~ i c a l A n a ly s is . E x am i na ti ono f m i n e r a l s ~ e c i m e n s c an d e t e r m i n et h e i d e n t i t y , c h a r a c t e r , g r a i n s i z er a n g e an d m id d li ng a s s o c i a t i o n s o ft h e o r e m i n e r a l s an d c o n s t i t u e n t s ofg a n g u e r o c k ( 3 , 4 1. S u c h i n f o r m a t i o nw i l l p r o v id e l i b e r a t i o n s i z e a n a l y s e sf o r p r im a r y , i n t e r m e d i a te o r r e g r i n da p p l i c a t i o n s o f g r i n d i n g a nd t h ea p p r o p r i a t e c o n c e n tr a t io n s t e p s .T he e x a m i n a t i o n m eth od g e n e r a l l yu s e d is b as ed on r e f l e c t e d l i g h to p t i c a l m ic ro sc op y f o r p o l i s h e ds e c t i o n s o r s t er eo s c o p y f o r m i n e r a l


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DESIGN, INSTALLATION OF C O M M IN UT IO N CIRCUITS

g r a i n s . W here m i n e r a l s h a v e t o b em ore s p e c i f i c a l l y i d e n t i f i e d , X -rayd i f f r a c t i o n c a n b e us ed .O c c a s i o n a l l y t h e m i n e r a l s p r e s e n t i nt h e o r e a r e i n s u ch c om plexa s s o c i a t i o n s t h a t t h e y c an n o t b ei d e n t i f i e d b y s i m p l e o p t i c a l o r X-rayd i f f r a c t i o n t e c hn i q u es . I n t h e s ec a s e s , e l e c t r o n p r o b e a n a l y s i s c a n beu se d t o d e te rm i ne t h e m i n e r a lc h a r a c t e r i s t i c s a nd t h e o c c u rr e n c e o ft h e e l e m e n t ( s ) i n q u e s t i o n ( 5 ) .C h e m i c a l A n a l y s i s . A c o m p l e t ec h e m i c a l a n a l y s i s i s a l w a y s av a l u a b l e t o o l . W h ile i t i s morer e l e v a n t t o t h e d e s i gn o f t h eb e n e f i c i a t i o n f l o w s h e e t , i t m i g h tp r o v i d e t h e c om m in uti on e n g i n e e r w i t ht h e f i r s t c l u e s t o p o s s i b l e p ro ble m si n co mm in utio n c i r c u i t d e s i g n an d t ot h e n eed f o r a d d i t i o n a l c i r c u i td e s i g n p a r a m e t e r s .

I f , f o r i n s t a n c e , t h e r e i se v id e n c e o f a l k a l i e s o r s u l p h a t e s ,s l i m i n g may b e a p r o b l e m a n d s h o u l db e a n t i c i p a t e d . S u l p h a t e s may a l s op r o du c e a n a c i d i c s l u r r y w hich w o uldr e s u l t i n h ig h m ed ia w ear o ru n d e r l i n e t h e n ee d f o r a n o r e wa sh in gs t a g e i n t h e f l ow s h ee t .P h y s i c a l P r o p e r t i e s ( h a rd n e s s ,f r i a b i l i t y , g r a i n s i z e d i s t r i b u t i o n ) .The f i r s t v i s u a l o b s e r v a t io n s c a ni m m ed ia te ly g i v e a n i n d i c a t i o n o f t h eh a rd n e s s , b l o c k in e s s and f r i a b i l i t yo f t h e o r e an d o f t h e a m ou nt o fp r i m ar y f i n e s o r c l a y - t y p ec o n s t i t u e n t s , an d o t h e r p h y s i c a lp r o p e r t i e s . T he se o b s e r v a t i o n s c a np r o v id e c l u e s t o p o s s i b l e p ro b l em s i nc r u s h i n g , s c r e e n i n g a nd g r i n d i n g an dc a n i n f l u e n c e f l o w s h e e t d e s ig n .E xa mp le s a r e : t h e a v o i d a n c e o f s l i m eg e n e r a t i o n when p r o c e s s i n g t i n ,t u n g s t e n , l e a d , c h r o m i t e , o r t a n t a lu mo r e s ; t h e r e l e a s e o f m o ly b d e n i t e a t ac o a r s e g r i n d f rom f r a c t u r e p l a n e s i na b lo ck y g r a n o d i o r i t e ; t h ee l i m i n a t i o n of p r ob le m s i n a f i n ec r u s h i n g p l a n t b y u s e o f s e mi-a u t o g e n o u s g r i n d i n g when p r o c e s s i n g ac l a y e y o r e . H ow ev er, f u r t h e r t e s ts am p le s s h o u ld b e m ade a v a i l a b l e f o r

Bond g r i n d a b i l i t y t e s t s , a b ra s i o nt e s t s , a nd a u to g e n ou s m ed iac o m p e t e n c y t e s t s . I t s h o u l d b ee mp ha si z ed t h a t a l l t h ea f o re m e n t i o n ed t e s t s r e q u i r e a s m a l la mo un t o f s am p le . The r e s u l t s , w h i l eo b v io u s ly used a s t o o l s t o o b t a inf i n a l q u a n t i t a t i v e d e s i g n p a ra m e te r s ,a l s o e n a b l e t h e m e t a l l u r g i c a l s t a f ft o c h a r t a c o u r s e o f a c t i o n t h ro u gh ab e t t e r u n de r s ta n d i ng o f t h e o r ec h a r a c t e r i s t i c s . A n a ly s is o f t h i si n f o r m a t i o n s h o u ld e v e n t u a l l y n a rr owt h e num ber o f c i r c u i t o p t i o n sa v a i l a b l e .

I t s h o u l d b e em p ha si ze d t h a t i fa n o r e b o d y i s not homogenous ( andw ha t o r e i s ? ) t h e d i s t i n c t o r e t y p e ss h o u l d b e s am p le d s e p a r a t e l y . Bondg r i n d a b i l i t y t e s t s , a b r as io n testsand media compe tency tests s h o u l d b er u n o n e a c h o r e t y p e w hic h t h e m i n in gp l a n sh ow s co u l d b e , a t a n y t im e , am a jo r p o r t i o n o f t h e m i l l f e e d . I ti s recom mended t h a t e a c h t y p e o f o r eb e t e s t e d s e p a r a t e l y . T e s t i n g o fi n d i v i d u a l o r e t y p e s w i l l g i v e a ni n d i c a t i o n a s t o t h e d eg re e o ff l u c t u a t i o n t h a t c a n b e ex pe ct ed i nm i l l p e rf o rm a n c e. T e s t i n g o fc o m p o s i t e s s h o u l d b e d o ne i n t h ep i l o t t e s t i n g p ha s e ( 6 ) .D e s i g n R e q u i r e m e n t sR e vi ew o f C i r c u i t Fe ed P a r a m e t e r s( m i ne o u t p u t , p r o d u c t io n s c h e d u l e s ,t h ro u g h p u t and s i z e a n a l y s i s ) . I t i se s s e n t i a l t h a t t h e com minutione n g i n e e r h av e a c l e a r o v e r a l lu n d e r s t a n d i n g o f t h e p r o j e c t a nd i t sc o n c e p t i o n . He s h o u l d b e f a m i l i a rw i t h t h e m in in g p l a n s , s c h e d u l e s ,m i n i n g r a t e s , m i n j . n g m e t h o d s a n de q u ip m e n t s i z e s , e t c . T he se c a na f f e c t t h e s i z e an d /o r c h o i c e o fp r o c e s s i n g e q u ip m en t, p a r t i c u l a r l yf o r c r u s h i n g o r p r i ma ry m i l l i n g , a sw e l l a s o p e r a t i n g h o u rs i n p rim ary o rf i n e c ru s h in g , n e c e s s i t y f o r o r es t o r a g e , m a n p o w e r r e q u i r e m e n t s a n dt h e l o c a t i o n o f t h e c r us h in g o rg r i n d i n g p l a n t .

T h e p r i m a r y c r u s h e r i s n o r m a l l y


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SELECTIONOFCOMMINUTION CIRCUITS 5p a r t o f a n y p r op o se d p l a n t . I t i s i nm o st c a s e s a p r im a r y g y r a t o r y l o c a t e do n s u r f a c e o r , f o r u n de r gr o un d m i n es ,u s u a l l y a jaw c r u s h e r . The s i z e o ft h e s e c r u s h e r s w i l l b e d i c t a t e d n o to n l y by t h e m i ni ng r a t e an d t h e t o ps i z e o f t h e mined r o c k w hi ch w i l l b ed e l i v e r e d , b u t a l s o by t h e p r od u c ts i z e r e q u i r e d . F o r i n s t a n c e ,d ep en di ng upon t h e s i z e o f t h ea u t o g e n o u s m i l l s b e i n g c o n t e m p l a t e d ,a f e ed s i z e p a r am e t e r o f15.25-30.50 cm (6 -12 i n . ) may b ed e s i r a b l e .

A n oth er i m p o r t a n t f a c t o r w h ic ht h e c o mm in uti on e n a i n e e r h a s t o knowi n t h e e a r l y s t a g e s o f c i r c u i tp l a n n i n g i s t h e to n n a g e th r o u g h p u tr e q u i r e m e n t s . T h e s e a r e d e t e rm i n e di n d u e c o u rs e by e co no mic f e a s i b i l i t ys t u d i e s wh ic h a s c e r t a i n t h e q u a l i t yan d q u a n t i t y o f t h e p r o d u c t w h ic hw i l l b e n e e d e d f o r p r o j e c t v i a b i l i t y .T he se nu mb ers a r e a v a i l a b l e s o o n e r ,b u t p e r h a p s w i t h less a c c u r a c y , f r o mt h e h ea d a s s a y o f t h e o r e a nd f ro me x p e r ie n c e w hich c a n p r e d i c t t h ep r o d u c t s p e c i f i c a t i o n a n d t o n n a ger e q u i r e m e n t s .

r e q u i r e d t o o b t a i n Bond work i n d i c e sf o r r o d m i l l i n g an d b a l l m i l l i n g a n dlum p s am p l e s c a p a b l e o f g e n e r a t i n g7.7 cm ( 3 i n . ) c u b e s a r e n e c e s s a r yf o r c r u s h e r i m p ac t t e s t s . If a ne co no m ic o r e d e p o s i t h a s b e e ne s t a b l i s h e d a nd p r e l i m i n a r y b e nc hs c a l e w ork sh ow s p r om i s in g r e s u l t s ,f u r t h e r s a m p l in g w i l l b e n e e d e d .A l s o , i f p r e l i m i n a r y m e d ia c o m p et en cyt e s t s h av e in d i c a t e d t h a t t h e o r e h a sa u t o g e no u s o r s em i - au t og e no u sp o t e n t i a l , s am p le s h av e t o b eo b t a i n e d t o t e s t t h i s f u r t h e r . F o re i t h e r a n o pe n p i t o r u n de rg ro u n dm i n i ng o p e r a t i o n , p r e l i m i n a r y m i ned e ve l op m e n t w ork o f t e n c o n s i s t s o fd r i v i n g a d i t s o r s h a f t s i n t o t h ed e p o s i t . T y p i c a l ly f o r a u to g e n o u sm i l l t e s t i n g , 2 2 , 70 0 - 4 5 , 4 0 0 k g ( 2 5 -5 0 t o n s ) o f r e p r e s e n t a t i v e s a m p le f o re a c h o r e t y p e a r e r e q u i r e d f o rp r o c e s s i n g t h r o u g h a 1 .7 -1 .8 m ( 5 - 1 / 2o r 6 f t . ) d i a m e t e r p i l o t m i l l . T h es a m p l e s s h o u l d b e r u n - o f - m i n ep r e p a r e d i n t h e n or m al m a n ne r b yd r i l l i n g an d b l a s t i n g t o a b o u t a2 0 . 3 cm ( 8 i n . ) t o p s i z e .

T he r e l a t i v e c o s t s o f o b t a i n i n gs a m p l e s , t e s t i n g them a n d t h e timeReview Of Requirements for t a k e n a r e s i g n i f i c a n t f a c t o r s i n t h eTesting Various Circuits . The o f c i r c u i t t o b e i n v e s t i g a t e d .a nd q u a n t i t y o f s a m p l e may v a r y . I tc a nn o t b e s t r e s s e d - o f t e n -e no ug h t h a ta ny p r o c e s s f o r a n y g i v e n o r e b od y i so n ly a s r e l i a b l e a s t h e s am p l e u p o nwh ic h i t i s b a s e d . A company wouldb e w e l l a d v i s e d t o i n v e s t t h e t i m ea nd money t o o b t a i n p r o p e r s a m p l e s.The q u a n t i t y o f s a m p l e r e q u i r e dc a n n o t b e d e f i n e d . T he t y p e o rd e p o s i t an d t h e m i n e r a l i z a t i o n w i l ld i c t a t e t h e s a m p l i n g pro gram m e n e e ds .

A s h a s b e en a l r e a d y m e nt io ne d i na p r e v i o u s s e c t i o n , p r e l i m i n a r ys am p le s a r e u s u a l l y o b t a i n e d a sd r i l l i n g p r o g r e s s e s t o d e l i n e a t e t h eo re b od y. The c o r e s a r e s p l i t i n h a l fan d o ne h a l f g o e s f o r m e t a l l u r g i c a lt e s t i n g . S om etim es s u r f a c e g r a bs am p l i ng o r t r e n c h i n g i s a l s o u s e d a tt h i s p o i n t t o g e t m a t e r i a l f o rp r e l i m i n a r y t e s tw o r k . G e n e r a l l y ,2 2. 7 kg ( 5 0 l b . ) o f sa m p l e i s

I d e n t i f i c a t i o n o f C o n t ig u o u sP r o c e s s e s , t h e i r R e qu ir em e n ts a n dI n t e r - r e l a t i o n s h i p s w i t h I d e n t i f i e dC o m m in ut io n S t e p s . E ac h p i e c e o fc o m m i n u t io n e q u ip m e n t h a s i t si n h e r e n t c h a r a c t e r i s t i c s . T hu s, o n es a y s t h a t r o d m i l l s p r o d u c e fewerf i n e s t h a n b a l l m i l l s ; c l o s e d -c i r c u i t i n g r e d u c e s o v e r g r i n d i n g ;a u t o g e n o u s m i l l s b r e a k o r e a l o n gg r a i n b o u n d a r i e s a n d c o n s e q u e n t l y c a nl i b e r a t e v a l u e s a t c o a r s e r s i z e s .T h e se b a s i c t e n e t s , t o g e t h e r w i t h t h ep a r t i c u l a r p r o p e r t i e s o f t h e o r e ,i n f l u e n c e t h e c om m in ut io n e n g i n e e r ' st h i n k i n g w hen h e i s s e l e c t i n ge q u i p m e n t w h i ch m u st p r o d u c e ap r o d u c t t h a t h a s c h a r a c t e r i s t i c sc o m p a t i b le w i th t h o s e r e q u i r e d i n t h ef e e d f o r t h e s u b s e q u en t c o n c e n t r a t i o np r o c e s s . If a n o r e h a s t h e t e n d en c yt o sl ime, t h e c i r c u i t may i n c o r p o r a t e


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DESIGN, INSTALLATION OF COMMINUTIO N CIRCUITSh i g h - e f f i c i e n c y c l a s s i f i c a t i o n i nc l o s e d - c i r c u i t w i t h a g r i n d i n g m i l l .T h i s h i g h - e f f i c i e n c y c l a s s i f i c a t i o nmay c a l l f o r h ig h- sp ee d s c r e e n s o rt w o- st ag e c y c lo n e c l a s s i f i c a t i o n .Re mova l o f a t r o u b l e s o m e c l a yc o n s t i t u e n t may r e q u i r e d r y g r i n d i n ga nd p r e - c o n c e n tr a t io n b e f o r e t h e o r ec a n b e w e t t e d .

t h e p r i m a r y c r u s h e r r e q u ir e m e n t s . I nu n d er g ro u n d m i n es , e s p e c i a l l y if t h ep r i m a r y c r u s h e r is u n d e r g r o u n d , t h em i n e p r o d u c t may b e much f i n e r a sd i c t a t e d by t h e ha n d l in g c a p a b i l i t i e so f h a u l i n g o r h o i s t i n g e qu ip m en t.P r o c e s s d e ve lo p m e nt w ork m i g h t a l s ob e p r o v i d i n g t h e f i r s t i n d i c a t i o n s o ft h e g ro u nd p r o d u c t s p e c i f i c a t i o n .

C o n v e r s el y , t h e b e n e f i c i a t i o n M ost c om m in ut io n e qu ip m en t i sf l o w s h e e t m i g h t h a v e t o a c co m m o d at e a designed to work in a specifici z emesh Of grind that a piece Of r a n g e . H ow ev er, a s u s u a l , g r a y a r e a sc om m i nu ti on e q ui p m e nt n a t u r a l l y exis t a nd t h i s m ak e s l i f e f o r agr inds This is true wi th c om m i nu ti on e n g i n e e r b ot h c h a l l e n g i n ga u t o g e n o u s m i l l s . a n d i n t e r e s t i n g .T h i s c o n s i d e r a t i o n c a n b ei l l u s t r a t e d by a r e c e n t p l a n tf l o w s h e e t f o r a t a c o n i t e i r o n o r e .C om minution c i r c u i t s f o r a t a c o n i t eo r e w o ul d com m only b e d e s i g n e d a st w o -s ta g e s y s t e m s i n c o r p o r a t i n ge i t h e r a r o d m i l l - b a l l m i l l c i r c u i to r a ut o ge n o us g r i n d i n g f o l l o w e d byb a l l m i l l s . T he r e c e n t f l o w s h e e t ,h o we ve r , i n c o r p o r a t e d s i n g l e - s t a g ea u to g e n o us g r i n d i n g i n c l o s e d - c i r c u i tw i t h m a g ne t i c s e p a r a t o r s a ndc y c l o n e s . While t h e pow er e f f i c i e n c yo f t h e g r i n d i n g c i r c u i t wa s n o t a sf a v o u r a b l e a s t h a t o f t h e m ore commont w o -s ta ge p l a n t , t h e s i m p l i c i t y o ff l o w s h e e t o f f s e t t i n g t h e c a p i t a lc o s t s o f g r i n d i n g m i l l s m a d e o v e r a l le c o n o m i c s e n s e ( 7 ) .

Thus i t bec om es c l e a r t h a t t h ec om m in ut io n a s p e c t s o f t h e f l o w s h e e ta r e c l o s e l y i n t e r - r e l a t e d w i t h t h eb e n e f i c i a t i o n p r o c e s s e s a n d c l o s ec o o p e r a t io n i n d e s i g n i n g t h e s e i si n d i s p e n s a b l e .I d e n t i f i c a t i o n o f Fe ed a nd P r od u c tS p e c i f i c a t i o n s f o r E ac h C om m in ut io nS t e p i n t h e P r o ce s s . F eed a ndp r o d u c t s p e c i f i c a t i o n s b e g i n a t t h ee a r l i e s t s t a g e s o f f l o w s he e td ev el op m en t. S i z e a n a l y s i s o f t h ep l a n t f e e d o r m in e o u t p u t i s t h ef i r s t i t e m t o be d e t e r m in e d , s i n c et h e p r o p o r t i o n o f f i n e s c a n i n f l u e n c et h e n e c e s s i t y f o r s c r e e n i n g a f t e rp r i m a r y c r u s h i n g . Open p i t m i n e s c a na d j u s t t h e r u n -o f-m in e t o p s i z e t o

How f i n e t o c r u s h b e f o r eg r i n d i n g i s o n e o f t h o s e a r e a s .R e c e n t d e v e lo p m e n t s i n h i g h -e f f i c i e n c y c r u s h i n g c i r c u i t s m ake i tm o re a c c e p t a b l e t o d o aw ay w i t h r o dm i l l s and p ro ce ed d i r e c t l y t o b a l lm i l l s w h ic h d o n o t h a v e t h e s am ep r o d u c t a n d eq u ip m en t s i z el i m i t a t i o n s (8 , 9, 10). I f r o dm i l l i n g i s u s e d , i t i s p r e f e r a b l e t op r e p a r e t h e f e ed w i th c l o s e d - c i r c u i tc r u s h i n g i n o r d e r t o a v o id p ro bl em sc a us e d b y s e g r e g a t e d o v e r s i z e ( i . e .f o r c i n g r o d s a p a r t ) . I f c r u s h i n g i sd o n e u n d e rg r o u n d a n d t h e m i ne p r o d u c ts i z e i s t o o s m a l l f o r p r im a rya u t o g e no u s m i l l i n g , a s p ra c t i c e d i nN o r t h A m e r i c a , t h e m o re e v e n1 e n g t h :d i a m e t e r r a t i o t y p e o f m i l l ,a s u se d i n S o u t h A f r ic a n o rS c a n d i n a v i a n p r a c t i c e , may b e t h ea n s w e r .The I m po r ta nc e o f W ork I nde x a ndA b r a s i o n I n d e x . T h e B on d w o rk i n d e xme thod i s a v e r y u s e f u l a n dc o n v e n i e n t t o o l f o r a co mm in ut io ne n g i n e e r . A p p l i c a t i o n o f testr e s u l t s t o t h e Bond work i n de xf or m u la p r o v i d e s t h e i n i t i a li n d i c a t i o n o f t h e u n i t power r e q u i r e dt o g r i n d a n y p a r t i c u l a r o r e .A d d i t i o n a l l y , b e ca u se t h e m ethodr e q u i r e s a s m a l l am ou nt o f s am p le a ndc o s t s r e l a t i v e l y l i t t l e , u n i t pow err e q u i r e m e n t s f o r g r i n d i n g c an b ea s c e r t a i n e d q u i c k l y a n d a c c u r a t e l yf o r a num ber o f d i f f e r e n t o r e t y p e se a r l y i n t h e d e ve lo pm e nt o f a p r o j e c t


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SELECTION OF COMMINUTION CIRCUITS

by u t i l i z i n g d r i l l c o r e s a mp les .T h i s know ledge a t a n e a r l y s t a g e c a nb e ve r y u s e f u l i n a n y e co no m ica n a l y s i s . Work i n d e x s h o u l d b ed et er min ed f o r d i f f e r e n t a p p l i c a t i o n sof comminut ion, i .e. c r u s h i n g , r o dm i l l i n g an d b a l l m i l l i n g . It i so f t e n a f a l s e as su m p ti on t o e x p e c twork i n d ex t o b e u n if o rm f o r a l li n cr e m en t al s t a g e s o f s i z e r e d u c ti o ni n a p r oc e ss . I t i s i m p o r t a n t t or e c o g n i z e t h a t work i n d e x , W i , i s apa ramete r which i s u s ed t o d e te r m i n et h e u n i t po wer r e q u ir e m e n t. I n t h e s ed a y s o f m e t r i c a t i o n , w o rk i n d e x i ss t i l l r e po r te d on t h e b a s i s o f s h o r tt o n s an d c a n , if r e q u e s t e d , b ea d ju s te d t o r e f l e c t m e t r i c t on s .

A b r a s i o n tests s e r v e a s a ni n d i c a t i o n o f t h e m e t a l w ea r t h a t c a nb e e x pe c te d i n c r u s h i n g a nd g r i n d i n g .Once de te rm ined , th ey may be a f i r s ti n d i c a t i o n t h a t a u to g en o u s g r i n d i n gs ho ul d b e i n v e s t i g a t e d a s steel wearc an be a s i g n i f i c a n t c o s t item.Once a c o m p os it e o f t h e e n t i r e

o r e d e p o s i t i s e s t a b l i s h e d , B o n dg r i n d a b i l i t y work s h o u l d b e r u n t og e t t h e o v e r a l l u n i t powerr e q u i r e m e n t . M a t h e m a t i c a l a v e r a g i n go f B ond work i n d i c e s f o r a series o fo r e t y p e s n o rm a l l y d o e s n o t p r o d u c et h e c o r r e c t a v e r a ge u n i t powerr eq ui re m en t. D i f f e r e n t i a l g r i n d i n gc a u s es e ac h o r e t y p e t o b e g ro un d t oa d i f f e r e n t s i z e d i s t r i b u t i o n , somef i n e r a n d som e much c o a r s e r t h a n t h ea v e r a g e ( 11 ). I f p i l o t t e s t i n g i sn ee de d b e c a u s e o f t h e c o m p l e x i t y o ft h e f lo w sh ee t an d s i z e o f t h ed e p o s i t , B ond g r i n d a b i l i t i e s sh o u ldb e u se d d u r i n g t h e p r o c e s s o f t h i stest work t o c h ec k o n t h e g r i n d i n gd a t a p ro du ce d f ro m t h e p i l o t m i l l .F r e q u e n t l y , t h e s e m i l l s a r e o v e r s iz e di n r e s p e c t t o t h e p i l o t b e n e f i c i a t io nc i r c u i t and t h e r e f o r e r uni n t e r m i t t e n t l y and a r e c o n se q u en t lyn e v e r p r o p e r l y b a l an c e d . I n s m a l lmills i t i s d i f f i c u l t t o m ea su repow er c o nsu me d f o r g r i n d i n g b e c a u s eo f t h e hi g h p r o p o r t i o n o f p ow er w h ic hi s a bso rb ed i n d r i v e i n e f f i c i e n c i e sand f i x e d l o ad c h a r a c t e r i s t i c s . The

m a jo r re q u i re m e n t f o r a p i l o t m i l l i ng r i n d i n g t e s t w o r k i s t o e s t a b l i s h ar e l i a b l e r e l a t i o n s h i p b e tw eeng r i n d i n g p ow er a n d m e a su r e d p o w er .T h i s c a n b e d o n e i n t wo w a ys :- by u s i n g s o p h i s t i c a t e d i n s t r u -m e nt a ti o n t o t a r e t h e m i l l .- by g r i n d i n g a nu mb er o f o r e sw it h known power con sum ption ande s t a b l i s h i n g a n e m p i r i c a lr e l a t i o n s h i p b etw ee n p i l o t m i l lpow er a nd a c t u a l g r i n d i n g p o we r.I n c a s e s w here t h i s k in d o f p i l o tm i l l c a l i b r a t i o n i s n o t p o s s i b l e , t h eBond g r i n d a b i l i t y w ork i n d e x m e th odo f f e r s a n e x c e l l e n t pow er d e t e r m i n a n tf o r a n o r e .D e t e r m i n a t i o n o f P ow er R e q u i r e m e n t s .D e t e r m i n a t i o n o f po wer r e q u i r e m e n tmay c e a s e w i t h Bond g r i n d a b i l i t yw or k, a n d i n som e c a s e s w i t h s m a l l e ra n d m o r e h o m o g e n o u s o r e b o d i e s t h a tu t i l i z e t h e c o nv e n t i o n a l c r u s h i n g a ndg r i n d i n g f l o w s h e e t t h i s may b e t h eca se . The more common p r a c t i c e i s t or u n a p i l o t p l a n t and t o u s e o t h e rm ea ns t o v e r i f y t h e Bond n u m be rs .Many firms h a ve d e v e lo p e d l a b o r a t o r yt e c h n i q u e s t h a t h av e b ee n c o r r e l a t e dt o e x i s t i n g o p e r a t i o n s an d r e f i n e do v e r t h e y e a r s a s a n a l t e r n a t i v es u c c e s s f u l m ethod f o r d e t e r m i n i n g t h ep ow er r e q u i r e m e n t s . When p i l o t p l a n tm i l l s a r e us e d t o o b t a i n s p e c i f i cg r i n d i n g po we r, c a r e s h o u l d b ee x e rc i se d t h a t t h e m i l l i s i n b a la n cea nd t h a t t h e tests a r e r u ns p e c i f i c a l l y t o o b t a i n g r i n d i n g d a t a .F o r a u to g en o u s g r i n d i n g , e s p e c i a l l y ,a t h o r o u g h t e s t programme i s n e e d e d .M ost i n s t a l l a t i o n s now h a v e a 1.7-1.8 m (5-112-6 f t . ) d i a m e t e r t e s tm i l l a nd r e q u i r e 2 2 ,7 0 0 -4 5 ,4 0 0 k g( 25 -5 0 t o n s ) o f o r e f o r o n e t e s tprogramme. These tests c a n a l s o b ed on e a t t h e m ine s i t e a n d w i t h v e r yl a r g e an d v a r ie d d e p o s i t s t h i s maymake se ns e . However , i t i s p r o b a b l ym ore ec o no m i ca l t o s h i p t h e s a m p le t oa n e s t a b l i s h e d l a b o r a t o r y t h a t h a st h e p e o p l e a n d t h e m e t ho do lo gy


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DESIGN, INSTALLATION OF CO MMINUT ION CIRCUITSr e a d i l y a v a i l a b l e .

A m eth od e x i s t s t o d a y w h i chu t i l i z e s a s m a l l 450 mm m i l l t op r o v i d e p r e l i m i n a r y a u t o g e n o u s u n i tp o w er r e q u i r e m e n t s ( A u t o g e n o u s W orkI n d e x ) w hich c a n e s t a b l i s h t h er eq u i re m e n t f o r a f u l l s c a l e p i l o tt es t and e n s u r e t h a t t h e r e a r e n og r i n d i n g s u r p r i s e s i n t h e o re bo dy byp r o v i d i n g a n i n e x p e n s i v e way t o t es tt h e v a r i o u s o r e t y p e s ( 1 2 ) .

T h us , u n i t p ow er r e q u i r e m e n t sf o r many c o n v e n t i o n a l c i r c u i t s c a n b ed e t e r m i n e d by Bond g r i n d a b i l i yp r o c e d u r es , by v a r i o u s l a b o r a t o r ym i l l s w h i c h h a v e b e e n c a l i b r a t e d a n dr e l a t e d t o e x i s t i n g p r o d uc e rs a nd i fn eed b e by p i l o t p l a n t t e s t i n g . F o ra u to g e no u s a p p l i c a t i o n s p r e l i m i n a r ypow er may be ob t a i n ed f rom 450 mmm i l l t e s t s b u t a s a r u l e p i l o t p l a n tw o r k s h o u l d b e r u n .C i r c u i t S e l e c t i o nP ow e r , R e q u i r e m e n t v e r s u s A v a i l -a b i l i t y , Mode o f G e n e r a t i o n , C o s t a n dS p l i t b et we en C r u s h i n g a nd grind in^f o r V a ri ou s C i r c u i t s . N e e d le s s t os a y , w i t h t h e e x c e p t i o n o f a fewa r e a s i n t h e w o rl d , p ower i s t h e m o s tc r i t i c a l i t e m i n a ny g r i n d i n g c i r c u i te v a l u a t i o n . A s m e n ti o ne d b e f o r e , t h ec o m m i n u t i o n c i r c u i t i s p r o b a b l y t h em a j o r u s e r o f p ow er i n a n y m i n e r a lp r o c e s s i n g p l a n t . Whi l e c o s ta n a l y s i s may show t h a t a c i r c u i tw h i c h i s l e s s e f f i c i e n t i n t h e u s e o fp ow er c a n b e mo re e c o n o m i c a l o v e r a l l( 7 , 131 , t h e p o s s i b i l i t y o f f u t u r er a p i d e s c a l a t i o n o f pow er c o s t sr e q u i r e s a c a r e f u l e xa m in a t io n a s t ohow po we r c o n s u m p t i o n c o u l d b e k e p tt o a m in im um . T h i s i s r e a l l yi m p o r t a n t i f o ne c o n s i d e r s t h a t u n i tp ow e r c o n s u m p t io n c a n b e 2 5 % h i g h e rf o r s e m i- a ut o ge n ou s m i l l c i r c u i t s a ndp e rh a p s 100% h i g h e r f o r f u l l ya u t o g e n o u s m i l l c i r c u i t s com pared t oc o n v e n t i o n a l c r u s h i n g an d g r i n d i n gc i r c u i t s . M e t a l c o ns u mp ti on w i l ln a t u r a l l y b e less b u t w i t h p r i m a r ya u t o g e n ou s g r i n d i n g , o n l y a b o u t 60 %o f t h e t h e o r e t i c a l s a v i n g s c a n b e

r e a l i z e d b e c au se o f h i g h e r l i n e r a ndf e e d c h u t e w ea r i n c o m pa ri so n w i t h ac o n v e n t io n a l c i r c u i t ( 1 4 ) . A va il -a b i l i t y w i l l b e 90% o r l e s s f o r f u l l ya u t o g e n ou s g r i n d i n g a nd u p t o 9 2 % h a sb e en a c h i e v e d f o r s e m i- a ut o ge n ou sg r i n d i n g . J . H . B a s s a r e a r ( 1 5r e p o r t e d o n t h e e x p e r i e nc e o f C yp ru sP i ma Mi n i ng Co. w here co nv en t i o na la n d s e m i - a u t o g e n o u s m i l l s o p e r a t e o ni d e n t i c a l o r e . T he c om p ar is on i s f o ra f o u r - y e a r t i m e p e r i o d , 1 97 4- 19 77 .I t s ho we d t h a t l i n e r co n su m p ti on was6.7% more and media consum pt ion 14.5%m ore w i t h t o t a l s t e e l c on su mp tio nb e i n g 1 3.5 % h i g h e r f o r t h ec o n v e n t i o n a l c i r c u i t c om pared t o t h eSAG m i l l c i r c u i t ; h ow ev er, p o werc o n s u m p t i o n w a s 15.5% low er . Thus ,f o r t h i s co mp ar i so n, e x t r a s t e e lc o s t s i n c u r r e d by on e c i r c u i tb a la n c ed t h e e x t r a power c o s t f o r t h eo t h e r c i r c u i t .

U n i t p o w e r c o n s u m p t i o n f o rp e b bl e m i l l i n g c a n g e n e r a l l y b e a se f f i c i e n t a s b a l l m i l l i n g i f on ec o n s i d e r s t h e power t h a t i s u se d t og r i n d p e b b l e s a s w e l l ( 1 4 ) . H ow ever,i n r e a l t e r m s t h e maximum p ow er d r aw nb y a g i v e n m i l l s i z e u se d f o r pe bb lem i l l i n g i s o f t h e o r d e r o f 5 0% o f t h epow er u sed by t h e same m i l l i f i tw er e u se d a s a b a l l m i l l and hencet h e t o n n a g e p r o c e s s e d w ou ld b e h a l f .R o d m i l l - b a l l m i l l c i r c u i t s h av e t h eh i g h e s t u n i t pow er e f f i c i e n c y a ndo f f e r 95% o r g r e a t e r a v a i l a b i l i t y .T h i s i s a l i t t l e lo we r t h an a s i ng l e -s t a g e b a l l m i l l o r a b a l l m i l l - b a l lm i l l c i r c u i t (w hi ch o f f e r s 97 % )b e c a u s e o f d ow n- tim e f o r ro dc h a r g i n g . P ri ma ry b a l l m i l lc i r c u i t s , w hich a c c e pt c r u sh e rp r o d u c t a s f e e d , h av e an i n h e r e n t l yl o w e r u n i t p ow er e f f i c i e n c y c om pa redt o n o rm a l s e c on d a ry b a l l m i l li n s t a l l a t i o n s a nd a f a c t o r o f 10-205h a s t o b e a d de d t o t h e s t a n d a rd p owerc a l c u l a t i o n . G r a te d i s c h a rg e b a l lm i l l s , a r e c a p a b l e o f c o n su m in g 1 5%m ore p o we r t h a n o v e r f l o w b a l l millsf o r t h e sam e u n i t p ower e f f i c i e n c yb u t m a i n t e n a n c e c o s t s an da v a i l a b i l i t y would b e l e s s f av o u ra b le( 2 , 1 4 ) .


9/26

SELECTION OF COMMINUTION CIRCUITS 9

R ec en t a d v an c e s i n c r u s h e rc i r c u i t a u t o m a t i o n , i t i s c l a i m e d( 1 61 , h av e s h i f t e d t h e s i z e s p l i t t of a v o u r c r u s h i n g , p o s s i b l y e l i m i n a t i n gt h e n ee d f o r r o d m i l l i n g a ndp r o vi d in g a b e t t e r o v e r a l l o p e r a t i n gs y s te m . T h e t w i n p en du lu m t e s t h a sb ee n d es ig ne d t o e s t a b l i s h s i z ea n a l y s i s o f t h e c r u s h e r p r o d u c t a ndu n i t p ow er r e q u ir e m e n t s o t h a tc r u s h i n g a nd s c r e e n i n g f l o w s h e e t s c a nb e d e s ig n e d t o m in im iz e c a p i t a l an do p e r a t i n g c o s t a n d m a x i m i z e p o w e re f f i c i e n c y . C e r t a i n l y m or es o p h i s t i c a t e d c i r c u i t c o n t r o l s , w hic hmay i n c l u d e o n - l i n e c o m p u t e r s , h a v emade m i l l o p e r a t io n s m ore e f f i c i e n ta nd s h o u l d b e f u l l y e x p l o r e d .

I n s ummary t h e u n i t p ow er c o s t ,w h ic h d e p e n d s u p on t h e mo de o f p o w e rg e n e r a t i o n an d h e nc e l o c a t i o n o f t h ec o m m i n u t i o n p l a n t , i s p r o b a b l y t h em ost s i g n i f i c a n t f a c t o r wh ic h c a ni n f l u e n c e t h e s e l e c t i o n of e qu ip m en tand p l a n t d e s ig n i n o r d e r t o ke epo v e r a l l p ow er c o s t s t o a m inimum a n dt o a c h i e v e t h e m o st e c o no m i ca lc a p i t a l an d o p e r a t i n g c o s t . I n N o rt hAmerica t od a y, p u b l i c u t i l i t i e s s e l lpower a t p r i c e s r a n g i n g f ro m 1 .5 t o6 .5 c e n t s p e r kw-hr. a n d i n i s o l a t e da r e a s r e q u i r i n g d i e s e l g e n e r a t i o n ,t h e c o s t c o ul d be a s h i g h as 1 5 c e n t sp e r kw-hr. F o r p r o j e c t s f o r c e d t oa b s o r b a h i g h po we r c o s t , i t i su n l ik e l y t h a t p o t e n t i a l s a v i n g s i nl i n e r a nd m ed ia c o s t s t o b e r e a l i z e dby u s i n g a u t o g e n o u s g r i n d i n g c o u l do f f s e t t h e c o s t s a s s o c i a t e d w i t hh i g h e r u n i t po we r c o n s u m p t i o n s w henc o m p a r e d w i t h c o n v e n t i o n a l c r u s h i n ga n d g r i n d i n g .E f f e c t o f C i r c u i t S e l e c t i o n o nMetallurgical. W i t h t h es t an d a rd c on v en t i on a l c i r c u i t t h eq u e s t i o n i s how much t o g r i n d p e rs t a g e an d w h et he r t o c l o s e - c i r c u i t am i l l o r t o o p e r a t e i n o p en - c i r cu i t .Feed v a r i a t i o n t o t h e m i l l , a l t h o u g hn ev e r a d e s i r a b l e f e a t u r e , c o u l d b et o l e r a t e d a t l e a s t f r o m t h ep e r s p e c t i v e o f t h e c o mm in ut io nc i r c u i t d e s i g n. A uto ge no us g r i n d i n gh a s b r o u g h t n u m e r o u s n e w

c o m p l i c a t i o n s . Many o f t h e s e are ar e s u l t o f t h e r e s p o n s i v e n e s s o fa u t og e no u s m i l l i n g t o f e e d v a r i a t i o n .The o r e t e l l s t h e m i l l how i t w a n t st o b e g r o un d as t h e s a y i n g g o es . I ft h e o r e b r ea k s a l o n g g r a i n b o u n da r ie se a s i l y , t h e m i n e ra l v a l u e s c an b el i b e r a t e d a t a c o a r s e r g r i n d a nd w i t hh i g h e r e f f i c i e n c y t h a n w i t h med iag r i n d i n g . W ith o t h e r o r e s a l o t o fs l i m e s may b e g e n e r a t e d . A n o th e rt h i n g t h a t c a n b e ov e rl oo k ed i n t h ea u to g e no u s p l a n t d e s i g n i s t h a t f o r ag i v en p ro d u c t s p e c i f i c a t i o n t h e m i l lmay h a v e a 5 0% -1 00 % s w i n g i n f e e dr a t e d ep en di n g upon o r e s i z i n g ,h a rd n e s s , a nd o t h e r c h a r a c t e r i s t i c sw h ic h w i l l h a v e t o b e a c co m m od at ed b yt h e m e t a l l u r g i c a l c i r c u i t sd ow ns tr ea m. C e r t a i n l y t h e n e e d f o rb e t t e r b l e n d i n g f o r f e e d h om og en ei t yt o a u to g en o us m i l l s i s m o r e o b v i o u s ,a s w e l l a s t h e n ee d f o r c l o s em o n i t o r i n g o f c i r c u i t p er fo rm a nc e .

G e n e r a l l y w i t h a u t o g e no u s o rs em i -a u to g en o us g r i n d i n g t h e r e i s as ix -m o nt h t o tw o- ye ar l e a r n i n g c u r v eb e f o r e t h e o p e r a t i n g p r i n c i p l e s a n dc h a r a c t e r i s t i c s a r e w e l l u n de rs to od .A d d i t i o n a l l y s ome a d j u s t m e n t s t o t h ep r o c e s s f lo w s h ee t m i g h t h av e t o b em ade ( 1 4 ) . On t h e p l u s s i d e , i f a no r e i s wet a nd s t i c k y a nd a r e a lp ro b le m f o r c r u s h i n g an d s c r e e n i n ge x i s t s , a SAG m i l l may b e t h e a n s w e ra n d c a n o v e r r i d e a l l o t h e rc o n s i d e r a t i o n s ( 1 5 ) . T he c o s tb e n e f i t o f t i m e a nd r e l a t i v ep r o d uc t i o n l o s s e s o r g a i n s f o r s u c h ac h o i c e h a s t o b e worked o u t .

Rod m i l l s h a v e be e n c h o s e n i nmany c a s e s b e c au s e o f t h e i r i n h e r e n tf e a t u r e o f g r i n d i n g down t h e t o p s i z ep r e f e r e n t i a l l y a n d g e n e r a t i n g lessf i n e s t h a n p r im a r y b a l l m i l l s . T h i sc a n a f f e c t m a g n e t i c r e co v e r y a s i nt h e t a c o n i t e f l o w s h e e t s w h er e c o b be rw e t d ru m m a g n e t s f o l l o w t h e f i r s tg r i n d i n g s t e p . I t i s a m e t a l l u r g i c a lax iom t h a t v a l u a b l e m i n e r a l s s h o u ldb e r e c o v e re d f ro m t h e s t r e a m a s so o na s t h e y a r e l i b e r a t e d . I d e a l l ym u l t i p l e g r i n d i n g s t e p s , e ac hf o l lo w ed by a b e n e f i c i a t i o n s t e p ,


10/26

DESIGN, INSTALLATION OF CO MMINUT ION CIRCUITSw ou ld c o n s t i t u t e a more m e t a l l u r g -i c a l l y e f f i c i e n t f l o w s he e t t h a n on e -s t e p g r i n d i n g f o l l o w ed by o n e - s te pb e n e f i c i a t i o n . H ow ever, s u c h af l o w s he e t m i gh t n o t be c o s t - e f f i c i e n tb o t h f rom t h e c a p i t a l c o s t a ndo p e r a t i n g c o s t a s p e c t s a n d ,t h e r e f o r e , some m e t a l l u r g i c a l a n dg r i n d i n g power e f f i c i e n c y m i gh t h a vet o b e s a c r i f i c e d t o r e a c h a ne q u i t a b l e b a la n ce . F l o w s h ee t s f o rp r o c e s s i n g t i n , i r o n , t u n g s te n ,c h r o m i t e , l e a d an d ta n t a lu m o r e s a r et y p i c a l i n t h i s r e g ar d .

Wh e n c o mp a re d w i th a u to g e n o u sg r i n d i n g o r lump m i l l i n g , s y s t e m su s i n g c o n v e n t i on a l g r i n d i n g a n d s t e e lm e d ia t o m i l l c om pl ex s u l p h i d e o r e sc a n i m p a i r t h e r e c o v e r i e s o f c o p p er ,l e a d , a n d z i n c by f l o t a t i o n ( 17 , 1 8 ,1 9 ) . I t s h o u l d b e e m ph a si ze d t h a tt h i s ef fec t i s n o t a l w a y s o b s e r v e dw i t h t h e s e t y p e s o f o r e s . Thep h y s i c o - c h e m i c a l m e c h an i sm s w h i c hu n d e r l i e t h i s b e h a v i o u r a r e n o t f u l l yu n d e r s t o od . I n v e s t i g a t o r s s u g g e s tt h a t f a c t o r s w hich a l s o i n f l u e n c er e s u l t s a r e o r e t y p e and i r o nc o n t e n t , n a t u r e o f ga ng ue m i n e r a l s( w h e th e r a c i d i c o r b a s i c ) , t y p e s o ff l o t a t i o n c o l l e c t o r s a nd m o d i f i e r su s ed , d e g r e e o f o x i d a t i o n o f t h es u l p h i d e s an d t h e o xy ge n p o t e n t i a l o ft h e p u lp . The g e n e r a l c o n c l u s i o nseems t o b e t h a t i f s uc h o r e s a r ec o m p e te n t en ou gh t o g r i n da u to g en o u sl y t h e n s u c h a c i r c u i ts h o u ld b e u s ed , s u b j e c t o f c o u r s e t oe c o n o m i c a n a l y s i s .G e n e r a l C os t C o n s i d e r a t i o n s f o rV a r io u s C i r c u i t s . R ec en t p r a c t i c eh a s s e e n a n i n c r e a s e i n c om m in ut io ne q ui p m en t s i z e s t o l a r g e r a nd l a r g e ru n i t s w i t h t h e o b j e c t i v e o fd e c r e a s i n g c a p i t a l a n d o p e r a t i n gc o s t s . C e r t a i n l y a u to g en o us m i l l sa r e b e in g b u i l t i n l a r g e r s i z e s ,s u b j e c t t o c o n s t r a i n t s im posed b ys t r u c t u r a l d e s i g n r a t h e r t h a np r o c e s s . W it h c o n v e n t i o n a l m i l l s as i z e l i m i t seems t o h av e b e en r e a c h e df o r r od m i l l s a nd t h e d e b a t e i s nowc e n t e r e d o n t h e e f f i c i e n c y of l a r g e rd i a m e t e r b a l l m i l l s .

L a r g e r b a l l mills c an b e b u i l tf ro m t h e s t r u c t u r al / m e c h a n i c a 1s t a n d p o i n t , b u t t h e r e a r e i n d i c a t i o n st h a t c a p a c i t y ca n b e l i m i t e d t o b elowt h e m i l l ' s f u l l p o t e n t i a l i f maximumpow er e f f i c i e n c y a t t h e d e s i r e d g r i n di s t h e o b j e c t i v e . T h e r e f o r e , u nd erc e r t a i n c i r c u m s t a n c e s , i t may n o tm ake s e n s e t o d e s i g n a p l a n t w i t ht h e s e larger u n i t s . E x p e r i e n c ei n d i c a t e s t h a t t h e r e c o u ld be am a t e r i a l f l o w - t r a n s p o r t p ro ble mt h r o u g h t h e m i l l b e c a u s e s l u r r yf l o w r a t e i s r e l a t e d t o t h e a v a i l a b l em i l l c r o s s - s e c t i o n a l area, w h ic h i nt u r n i n c r e a s e s i n p r o p o r t io n t o t h es q u a r e o f t h e m i l l d i a m e t e r , w h e r e a st h e m i l l pow er d ra w i n c r e a s e s a s t h em i l l d i a m e t e r t o t h e p ow er 2.3-2.4( 9 , 1 4 ) . P o t e n t i a l m i l l c a p a c i t y i sa f u n c t i o n o f t h e m i l l d i a m e t e r t ot h e p o we r 2.6 ( 9 ) .

Rod m i l l s i z e i s c u r r e n t l yl i m i t e d b y t h e l e n g th o f t h e l o n g e s ts t r a i g h t r o d t h a t i s o b t a i n a b l e , 6 . 1m ( 2 0 f t . ) . To p r e v e n t r o d - t a n g l i n ga l e n g t h t o d ia m e te r r a t i o o f 1.3:l.Oi s r ec om m en de d. T he l a r g e s t r o dm i l l s i n e x i s t e n c e a r e 4.7 m d l a . x6 .2 5 m ( 15 -1 /2 f t . d i a . x 20-1/2 f t . )l o n g e f f e c t i v e cham ber l e n g t h (2 , 9 ,1 1 , 1 B a l l m i l l s c a n b e l a r g e ra nd s o f ew er p r o c e s s i n g l i n e s a r er e q u i r e d , w h i c h i s t h e c h i e fa t t r a c t i o n f o r c o n s i d e r i n g p r im aryb a l l m i l l i n g c i r c u i t s . The l a r g e s tb a l l m i l l d i a m e t e r r eco mm en de d f o rmaximum u n i t p o w er e f f i c i e n c y i s5 .0 m ( 1 6- 1 /2 f t . ) ( 1 4 ) . L a r g e rm i l l s e.g. 5.5 m ( 1 8 f t . ) d i a m e te rh av e b ee n s e l e c t e d f o r pr im a ry b a l lm i l l i n g a nd h av e e xp e r i e n c e d v a r y i n gd e g r e e s o f i n h e r e n t i n e f f i c i e n c i e si n v o l v i n g ch a r g e l e v e l , s p ee d , f e e ds i z i n g , m e d i a s ize, l i n e rc o n f i g u r a t i o n , m a t e r i a l r e s id e n c etime a n d mi x in g (2 0 ) . One 5 .5 m ( 18f t . ) d i a m et e r b a l l m i l l h a s r e c e n t l yb ee n i n s t a l l e d t o r eg r i n d pr od u c tf r o m a se m i - au t o ge n o us m i l l i n gc i r c u i t f o r a 1 3 ,6 0 0 m tpd ( 1 5 ,0 0 0s t p d ) c op per -m ol yb de nu m p r o j e c t a tH i l l s b o r o , New M e x ic o. T h i s i s as i n g l e - l i n e c i r c u i t a nd eq ui pm en t w asc h o s en t o m i n im i ze c a p i t a l an d


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o p e r a t i n g c o s t s . The o p e r a t i n ge f f i c i e n c y o f t h i s m i l l i s a w a i t e df o r c o m p a r i s o n w i t h o t h e r m i l l s o ft h e s a m e d i a m e t e r .O t h e r c o s t c o n s i d e r a t i o n s ,e v e r yt h in g e l s e b ei ng e q u a l , a r e :- P l a n t s wi th m u l t i - u n i t s i n g l e -s t a g e p r i m a r y m i l l s a r e m o r ec a p i t a l i n t e n s i v e th a n p l a n t sw i t h t w o- st ag e g r i n d i n g . T h i si s b e c a u s e p r i m a r y m i l l s r e q u i r ee x p e n s i v e f e e d i n g a n d o r es t o r a g e s y st em s , g e n e r a l l y w i t hmore l i n e s i n f i n e c r u s h i n g a nds c r e e n i n g . H ow ev er, s i n g l e -s t a g e c om minution c i r c u i t s c o s tl e s s t o o p e ra te as o p e r a t i n gl a b o u r i s l e s s a nd m a i n t en a n c eis l o w e r ( 2 1 ) .- S i n c e p e b b l e m i l l m e d i a h a sl ow e r d e n s i t y , p e b b l e m i l l s a r el a r g e r a nd m ore e x p e n s i v e f o rt h e sam e power a s b a l l m i l l s ,b u t t h e u n i t o p e r a t i n g c o s t s a r eu s ua l ly l e s s ( 2 1 ) .

- Semi-autogenous m i l l s draw morep ow er t h a n a u t o g e n o u s m i l l s o ft h e same s i z e an d t h e r e f o r e a r el e s s ex p e n s iv e t o i n s t a l l f o rt h e sam e t h r o u g h p u t . D. J.B a r r a t t ( 1 3 ) a t t e m p t e d t od e m o n s t r a t e c o m p a r a t i v e c a p i t a lc o s t , o p e r a t i n g c o s t a nd s p a c er e q u i r e m e n t s f o r s e m i - a u t o g e n o u sand c o n ve n ti on a l c i r c u i t s o v e r ar a n g e o f t h r o u g h p u t s up t o7 2 , 60 0 m tpd ( 8 0 , 0 0 0 s t p d ) u s i n gt y p i c a l c i r c u i t d e s ig n s an de q ui pm e n t s i z e s . W h i le t h i sp a pe r r e q u i r e s u p d a t in g t or e f l e c t t h e l a r g e r e q uip men ts i z e s c u r r e n t l y i n u s e a ndh i g h e r pow er c o s t s , i td e m on s tr a te s t h e d i f f e r e n c e s i nc o s t f o r g r i n d i n g e q ui pm e nt a n dt h e s p ac e a dv an ta ge a t h i g h e rt h r o u g h p u t s o f f e r e d b y semi-a uto ge no us c i r c u i t s . I n f a c t ,t h e s e m i - a u t o g e n o u s - b a l l m i l lc i r c u i t h a s p ro ved t o b e as u c c e s s f u l a nd p o p u l a r c h o i c e .It h a s a good t o l e r a n c e f o r f e e d

v a r i a t i o n . One o f t h ed i s a d v a n t a g e s i s t h a t t h e SAGm i l l m ust b e k e p t f u l l o f o r e ,o t he r w is e b a l l a nd l i n e rb r e a k a g e may r e s u l t . S u r g e s i nt hr o ug h p ut a s t h e o r e b ecom ess o f t e r o r f i n e r c a n r e s u l t andu n l e s s d o w ns tr ea m e q u i p m e n t i so v e r s i z e d , c o n t a i n m e n t p r o b l e m sa r e i n e v i t a b l e ( 15 ) .

W a te r S up p ly S o u r c e A v a i l a b i l i t y a ndC o s t v e r s u s P r o c e s s R e q u i r e m e n t s .Water i s t h e no rm a l m ed ia f o rp h y s i c a l b e n e f i c i a t i o n o f o r e s . V eryfew o r e s a r e up-g rad ed i n t h e d r ys t a t e . However, t h e r e a r e a r e a s i nt h e w o r ld w h e re w a t e r i s s c a r c e ,e xp en si ve , o r n o t a v a i l a b l e a t a l l .Some o f t h e s e o r e s a r e l o c a t e d n e a rt h e s e a c o a s t a nd s e a w a t e r ca n beu s ed . W ith o t h e r s , d r y p r e -c o n c e n t r a t i o n i s s o m e t i m e s p o s s i b l e .Dry p r im a r y g r i n d i n g , w i t h d r y i n g a sn e c e s s a r y , m i g h t be f o l l o w e d by d r ym a gn et ic c o b b in g , o r d r y g r a v i t yc o n c e n t r a t i o n . The p r e - c o n c e n t r a t ei s t h e n s h i pp e d t o a n a r e a w herew a t e r i s a v a i l a b l e f o r f i n a lp r o c e s s i n g .

Dry au togenous m i l l s , b a l lm i l l s , and rod m i l l s h a v e b e e n u s e d .T hey r e q u i r e m o re p o w er , n e e d c l o s et e m p e ra t u re a n d m o i s t u r e c o n t r o l an dr e q u i r e s o p h i s t i c a t e d d u s t c o n t r o le q u i p m e n t . Many d r y g r i n d i n gi n s t a l l a t i o n s a l s o e x i s t w here t h em a t e r i a l c a n no t b e w e t t ed , e .g .cem en t c l i n k e r , t a l c an d g o e t h i t i cd i r e c t s h i p p i n g i r o n o r e s w hic h a r eg ro und t o p e l l e t i z i n g f i n e n e s s a ndc ou ld n ev er b e f i l t e r e d i f t h e y wereg r o u n d w e t . T h e s e w o ul d b e p r o c e s s e dd r y e v en i f w a te r were p l e n t i f u l .F i n e grind in^ Co ncep ts . The amounto f r e g r in d i n g n e c es s a r y f o r a ni n t e r m e d i a te c o n c e n t r a t e o r a f i n a lc o n c e n tr a te t o g e n e r a t e a d d i t i o n a l" s u r f a c e a r e a " c a n o n l y b e d e v el o pe dw h e n t h e f l o w s h e e t i s e s t a b l i s h e d a n da n u p -g ra d ed p r o d u c t i s a v a i l a b l e f o rt e s t i n g . I t m i gh t seem t h a t t h i s i sa r e l a t i v e l y e a s y as s ig n m en t b ec a us er e a l l y o n ly a b a l l m i l l c a n b e u s e d .


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DESIGN, INSTALLATION OF COMMINUTIO N CIRCUITS( R e c e n t l y , i n a new c o p p e ri n s t a l l a t i o n i n t h e s o u t h w e s t e r nU n i te d S t a t e s , a t o w e r m i l l wass e l e c t e d f o r t h i s a p p l i c a t i o n . )H ow ev er, p ow er c a l c u l a t i o n c a n b em i s l ea d i n g . Bond g r i n d a b i l i t y i n d e xc a n b e u s e d , b u t e xt re m e c a r e s h o u ldb e t a k e n s i n c e Bond g r i n d a b i l i t yt e s t s r e q u i r e a r a t i o of r e d u c t i o n o fa b o u t 6 : l t o o b t a i n a c c u r a t e r e s u l t s( 1 1 ) . S p e c i a l t e s t s w i l l h av e t o b er u n a nd som e i n t e r p o l a t i o n s m ade. I nm a n y i n s t a n c e s ja r m i l l s o r A bbeym i l l s a r e u s e d a nd a t i m e / s u r f a c ec u r v e i s e s t a b l i s h e d . T h i s k i nd o ft e s t m i l l c a n b e c a l i b r a t e d w i t hknow n o r e s a n d a s p e c i f i c po we r c a nb e d e t er m i n e d . W h e th er t o r u n t h er e g r i n d m i l l i n o pe n - o r c l o s e d -c i r c u i t d e p e nd s o n t h e p r o d u c tc h a r a c t e r i s t i c s r e q u i r e d a nd o nc u r r e n t p r a c t i c e i n s i m i l a ra p p l i c a t i o n s .C o n s i d e r a t i o n s f o r B o th L a rg e an dSmall P l a n t s w i t h R eg a rd t o P l a n tL o c a t i o n , S i t e T o p og r ap h y a n d L a y ou t,A c c e s s i b i l i t y , C l im a t e a n d P r e c ip -i t a t i o n , M a t e r i a l s T r a n s p o r t a t i o n an dH a nd li ng , C a p i t a l a nd O p e r a t i n gC o s t s , E c o no m i ca l E v a l u a t i o n a n dP a r t s I n v e n to r y . P r o p e r f a m i l i a r i -z a t i o n w i t h t h e g e o g r a p h i c l o c a t i o n ,c l i m a t e , p h y s i c a l c h a r a c t e r i s t i c s o ft h e m ine s i t e , a c c e s s i b i l i t y a ndp r e c i p i t a t i o n i s p a r a m o u n t w h e nd e s i g n i n g a c om m i nu ti on p l a n t .W herea s t h e l o c a t i o n o f t h e o r e b o d yc a n n o t b e a l t e r e d , t h e p h y s i c a l l a y -o u t o f t h e p r o c e s s p l a n t a n d e q u ip -m en t s e l e c t i o n c a n b e a d a p t e d t oa l l o w a d v an t ag e t o b e t a k e n o f m o ree q u i t a b l e c o n d i t i o n s .

F o r i n s t a n c e u n de r a r c t i cc o n d i t i o n s a c om p a ct p l a n t d e s i g n i no n e b u i l d in g o f f e r s a n o p p o r t u n i t y t oc o n s e r v e e n e rg y a nd p r o v i d ec o m f o r t a b l e w o rk i ng c o n d i t i o n s , e .g .F ox M i n e a n d A r v i k . P r i m a r yc r u s h i n g , l o c a t e d c l o s e t o t h e m in ewhich may be a t a h i g h a l t i t u d e a n ds u b j e c t t o a v a l a n c h e s , c o u l d b es e p a r a t e d f ro m t h e f i n e c r u s h i n g an dg r i n d i n g p l a n t by u n de r gr o un dc o n v e y or t o a safer p o i n t a t a l o w e r

a l t i t u d e , e .g . C h i le a n c o p pe rp r o j e c t s . R ou g h ne ss o f t e r r a i n o ri n a c c e s s i b i l i t y may p r ec l u d e t h e u s eo f l a r g e r e q ui pm e nt , e .g . l i m i t -a t i o n s o f s p l i t t i n g c r u s h e r f r a me sa n d m i l l s h e l l s i n t o S m a ll e rc o m po n en ts t o p a s s r o a d b ed l o a d i n g so r r a i l t u n n e l d i m e n si o ns .P r e - co n c e n t r a t io n o r c r u s h i n gp r i o r t o s h ip m e n t t o a c o n c e n t r a to ro r re - p r o ce s s i n g p l a n t i s common i nt h e i r o n o r e i n d u s t r y w he re c r us h edo r e o r c o n c e n t r a t e i s r a i l e d a fe wh un dr ed m i l e s t o a f i n i s h i n g p l a n t o n

t i d e w a t e r . W ate r q u a l i t y o ra v a i l a b i l i t y m i g ht r e q u i r e t h a t a d r yg r i n d i n g s ys te m b e u se d o r t h a tc h e m i c a l a t t a c k o n g r i n d i n g m e dia h a st o b e a vo id ed . The a v a i l a b i l i t y an dq u a l i t y o f manpower m ig h t d i c t a t e t h ed e g r e e o f s o p h i s t i c a t i o n i n t h ea p pr o a c h t o c i r c u i t d e s i g n an dc o n t r o l . C o n s i d e ra t io n s t h a t maya p p l y t o a l a r g e o p e r a t i o n may n o th o l d t r u e f o r a small p l a n t , a n d i ne a ch c a s e t h i s becom es a q u e s t i o n o fe c o n o m i c s . A s m a l l p l a n t i s ar e l a t i v e term, i t s t i l l h a s t o b el a r g e e no ug h t o b e e c o n o m ic a ll yf e a s i b l e , a nd t h i s may v a r y w i t h manyf a c t o r s , b u t co mm in utio n c i r c u i td e s i g n c o n s i d e r a t i o n s may a l s o b ea f f e c t e d . F o r l a r g e p l a n t s many o ft h e s e r v i c e f u n c t i o n s s u c h a s r o a d s,r a i l r o a d s , w a r e h ou s i ng , e t c . , a r ep a r t o f t h e b a s i c d e s i g n w i th o u tw h i c h a l a r g e p l a n t c a n n o t bec o n t e m p l a t e d . T h e r e i s s u c h a t h i n ga s e co no m ic s o f s c a l e . F o r s m a l l e rp l a n t s , f a c t o r s s u c h as a c c e s s i b i l i t yo r l o c a t i o n may b e a m uch mo rec r i t i c a l c o s t c o n s i d e r a t i o n . S u p p lyo f c r i t i c a l i t e m s n e c e s s a ry t o d a i l yo p e r a t i o n s , s uc h a s s p e c i f i c r e a g e n t sf o r f l o t a t i o n , a v a i l a b i l i t y o f p r o p e rr o d m e d i a o r 1 0- 12 .7 cm (4-5 i n . )b a l l s f o r s e m i - a u t o g e n o u s mills mayb e d e c i s i v e f a c t o r s i n c i r c u i ts e l e c t i o n , e s p e c i a l l y if t h ee c on o m ic s o f s c a l e ha v e be enr e s e a r c h e d . M ore o f t e n t h a n n o t ,s u p p l y firms w i l l s e t up s p e c i a lo p e r a t i o n s t o s e r v i c e a m a j or m ineo p e r a t i o n , w h i l e s m a l l p l a n t s d o n o th a v e t h a t k i n d o f l e v e ra g e . The s i z e


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SELECTION OF COMMINUT ION CIRCUITS

a nd number o f u n i t o p e r a t i o n sr e q u i r e d f o r a smaller p l a n t , s a y u pt o 4 , 53 6 mtpd ( 5 , 0 0 0 s t p d ) , c a ni n f l u e n c e c a p i t a l c o s t and o p e r a t i n gc o s t s i g n i f i c a n t l y when o n ec o n s i d e r s , a s a n e xa m pl e, t h e s p a c ea nd l a b o u r r e q u ir e m e n ts f o r a f i v es h i f t s p e r week v e r s u s a t e n s h i f t sp e r week c r u s h i n g p l a n t p r o d u c i n g t h esame r o d o r b a l l m i l l f e e d t o n n a g e .W ith l a r g e r p l a n t s , e q ui p m en t i sm a nu fa ct ur ed t o c o p e w i t h l a r g e ri n c r em e n t a l i n c r e a s e s i n t h r o u gh p u ta n d t h e r e i s o f t e n less f l e x i b i l i t yi n t h e number o f c r u s h in g s h i f t so p e r a t e d p e r w eek.

One c o n s i d e r a t i o n , w h ic h i so f t e n o v e r r i d i n g , i s t h e e f f e c t o ff u t u r e p l a n s f o r p l a n t e x p a n s i o n o nt h e s e l e c t i o n o f c r u s h i n g an dg r i n d i n g e qu ip m en t. F o r l a r g e rp l a n t s , p r o ce s s i n g l i n e s a r e u s u a l l ya dd ed w h e re as w i t h v e r y s m a l l p l a n t s ,a n i n c r e a s e i n b a l l c h a rg e an d m i l ls pe ed c a n a c h ie v e s i g n i f i c a n ti n c r e a s e s i n t h r o ug h p u t.

SPECIFIC SITUATIONSUranium

The c om m in utio n p r a c t i c e s i n t h eu r a n i u m m i n i n g i n d u s t r y o f N o r t hA meric a d i f f e r c o n s i d e r a b l y b e tw e enC an ada a n d t h e U n i t ed S t a t e s . T h e s ed i f f e r e n c e s a r e p r i m a r i l y a r e s u l t o fv a r i a t i o n s i n o r e t y p e s f ou n d i n t h et w o c o u n t r i e s .C an ad ia n o r e s a r e c l a s s e d as" ha rd r o c k w a nd o c c u r a s v e i n s as a tB e a v e r l o d g e , A t h a b a sc a B a s i n a n d t h eW o l la s to n F o ld i n S a s k at c h e w an o r a sc o n g l o m e r a t e s as a t E l l i o t L ake an dAgnew L ak e i n O n t a r i o . C a n a d i a nc o n g l o m e r a t e s e x h i b i t p a r t i c u l a r l ys t r o n g a dh e s i o n w hic h r e q u i r e s t h a tt h e q u a r t z p e b b l es c o n t a i n e d t h e r e i nh av e t o be gro un d i n o r d e r t o r e l e a s et h e u r a n i f e ro u s v a l u e s i n t h ec e m e n ti n g medium. L i b e r a t i o n s i z e s

of 50% minus 200 mesh a r e common.U.S. o r e s , on t h e o t h e r h a n d ,

o c cu r a s s a n d s t o ne s s uc h a s i nWyoming, Te xa s, New Me xico an d on t h eC o l o r a d o P l a t e a u . The s a n d s t o n eg r a i n s a r e e s s e n t i a l l y b a r r e n a nd c a nb e r e l e a s e d by m o d er a t e g r i n d i n g f ro mt h e i n t e r g r a n u l a r c em en t wh ic h i su r a n i f e r o u s . T y p i c a l m esh o f g r i n df o r t h e s e o r e s i s 80% mi nus 35 mesh .T he e a r l y p r o d u c e r s i n C an ad ap r o c e s s e d o r e s fro m t h e B e a v e r lo d g ea r e a o f S a s k at ch e w an a nd f ro m t h eB a n c r o ft a nd E l l i o t L ak e a r e a s o fO n ta r i o . T h e i r m i l l i n g c i r c u i t s werec o n v e n t i o n a l c r u s h i n g a nd g r i n d i n g i n

t h e u s u a l m u l t i - s t ag e f a s h i o n .A 1 hough t h e E l l i o t L akec o n g l o m e r a t e s w e r e c a p a b l e o fg e n e r a t i n g p eb b l e s , p e b b l e m i l l i n gwas n o t i n c o r p o r a t e d u n t i l much l a t e rd u r i n g p l a n t e x p a n s io n s e .g . t h eQ u i r k e m i l l . C o n se q ue n tl y , a l lm a t e r i a l was c r u s h e d a nd g ro u n d t ot h e l i b e r a t i o n s i z e o f t h e u ra ni u mm i n e r a l i n t h e m a t r i x . T he M ada wask am i l l a t B a n c ro f t i n c o r po r a t e d p e b b lem i l l i n g as p a r t o f i t s r e a c t i v a t i o ni n 1978 t o p r o c e s s a p e g m a t i t e o r e .

T h e re h a s b ee n a r e c e n t t r e n dt ow a rd t h e u s e o f s e m i - a u to g e n o u sg r i n d i n g a s a move t o e l i m i n a t ep o t e n t i a l h a z a r d s o f r ad o n g a s w h ichi s r e l e a s e d i n t o t h e a tm o sp h er ed u r i n g t h e c r u s h i n g p r o c e ss . Byg r i n d i n g i n a w e t e nv i ro n m en t w i t h a sc o a r s e a f e ed a s p o s s i b l e , r ad o n i sd i s s o lv e d i n w a te r . The o p e r a t i o n a tB e av e rl od g e p i o n e e r e d t h i sd e ve l op m e nt i n 1 96 4 w i t h t h ei n s t a l l a t i o n o f a d ou bl e- co m pa rt me ntm i l l , 5.8 m d i a . x 5 .2 m ( 1 9 f t . d i a .x 1 7 f t . ) f i t t e d w i t h a c e n t r a lp e r i p h e r a l g r a t e d i s c ha r g e . The m i l li s powered by a 2 ,0 00 HP m oto r ,a c c e p t s a ja w c r u s h e r p r o d u c t ( s e t a t152 mm O.S.S. 1, u s e s 0 .7 5 k g / t( 1. 5 l b . / t o n ) o f 1 52 mm ( 6 i n c h )b a l l s a n d is i n c l o s e d - c i r c u i t w i t h as t a t i c s c r e e n . O th e r o p e r a t i o n sw h ic h h a ve t a k e n a d v a n ta g e o f t h i sc o n c e p t a r e R ab b i t Lak e ( f o r m e r l yG u l f M i n e r a l s o f C a na d a) , w h ic h h a s aSAG m i l l - b a l l m i l l c i r c u i t , B l u e w a t e r( A n a co n d a M i n e r a l s Co .) , P a n n a M a r i a( C h e v r o n R e s o u r c e s I n c . ) , C h u r ch Rock


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DESIGN, INSTALLATION OF COMMINUTION CIRCUITS(K err McGee Nuclear Cor po ra tio n) ,Bear Creek (Rocky Mountain EnergyCo.) and L-Bar (S oh io ), a l l of whichemploy single-stage semi-autogenousgrinding i n c lose d-ci rc ui t withscreens or cyclones.

Primary crushing followed byimpact crushing and single-stage rodmill ing t o produce a coarse grind i spract ise d by other opera t ions i nWyoming and New Mexico. Cluf f Lake(AMOK , SMDC), Saskatchewan, i s usingconventional crushing and single-st ag e rod mi llin g. The rod m i l l i sreplaced by two-stage b a l l mi llin g bysome op er at or s i n t he G ran ts, NewMexico ar ea and the fin en es s of grin di s dependent upon whether a sandstoneor a limestone type ore i s beingprocessed. The Key Lake p ro je c t i nnorthern Saskatchewan w i l l employ agyratory crusher, hammermill ands ing le -s t age ba l l m i l l c i r c u i t .

The requirements of governmentaland in du st ri al heal th monitoringagencies and labour do and w i l lcont inue to be fac tor s inf luencingthe design of comminution circuitsfor uranium ores.Iron

The comminution practices i n their on ore indu stry a re some of themore var ied . Iro n or es can range i ncharacter from blocky magnetites,l i k e the Minnesota taco nite s, tospecular hemat i t es , s imi l a r t o theLabrador and Quebec o re s and t oweathered ores of goethi te orl imonit e which a re l a t e r i t i c i n the i rphysical behaviour s im i lar t o oresfrom Venezuela o r Western A us tr al ia .Each part icular ore type is processedusing certain established methods ofcomminution. But even he re th eprac t i ces can vary s ig n i f i ca n t ly a scan be i l l us t r a t ed by the pla nts i nMinnesota tr e a ti n g magneticta co ni te s. These averag e 25-35% Feand about 60-70s of the total i smagnetic or e. The or e i s very hardand abrasive and must be ground to80-955 minus 44 microns for

l ibe rat ion . There are e ightpe l le t iz in g operations. These are a tButler Taconite, National Steel,Hibbing Taconite, Minntac, Eveleth,Minorca, Er ie and Reserve.

Reserve and Erie are the olderplants and employ rod and ball m i l lc i r c u i t s . However, of the moremodern plan ts th at were b u il t orexpanded when autogenous grinding waswell accepted, thre e ut il i z e someform of autogenous grinding and threeuse the conventional rod mill-ballm i l l approach.

The two newest plants, Hibtac(started 1976) and Minorca ( 19771,use grinding methods that arecompletely different and yet they arei n c los e proximity t o each other.The Hibtac flowsheet has single-stageautogenous milling while Minorca hasa rod mill-ball mill c i r c u i t .Hibtac's evaluat ion ( 7) of thevariou s flowsheets s ta rte d byobt aini ng a 1,360 m t ( 1,500 ton)

re pr es en ta tiv e bulk sample. The goa lwas the lowest possible ca pi ta l co stwith th e provision th at addit ion alc a p it a l could be expended i foper at ing cost savings returned theaddi t io nal c api ta l within threeyears . Pr io r to p i l o t t es t ing ,labo rato ry bench sc al e stu di es wereconducted to indicate that the orel ib er at ed a t 80% minus 44 microns.A 1 ern a ti v e flowsheets wereinvest igated in the fol lowing order:- Rod mil l- ball m i l l combination.This conventional taconitef lowsheet was se lec ted a s thebase for economic comparisons.- Autogenous-ball m i l l c i r cu i t .

I t showed a 16% lower c a p i t a lc o s t and a 15% lower op era tingc o st compared t o th e base case .- Autogenous-pebble m i l l c i r c u i t .Pebbles were extracted from the

autogenous m i l l . This f lowsheetgave lower operating costs, butthe c ap i ta l costs were


15/26


a p p r ox i m a te l y t h e s am e a s t h er o d m i l l - b a l l m i l l f l o w s h e e t .However, when compared t o th ea u t o g e n o u s - b a l l m i l l f l o w s h e e tt h e o p e r a t i n g c o s t s a v in g sp a y b a c k w a s m o r e t h a n t h r e ey e a r s . D u ri ng t h e o p e r a t i o n o ft h e a u t o g e n o u s - p e b b l e m i l lf lo ws he et , a n i n t e r e s t i n g e f f e c twas no ted . Removal o f 5% o f t h ec r u d e o r e f e e d a s 25-75m mp e b b l e s r e s u l t e d i n a 15-202i n c r e a s e i n t h e p r im a rya u t o g e n o u s m i l l t h r o u g h p u t .T hi s i n d i c a t ed t h a t a c r i t i c a ls i z e was p r e s e n t i n t h e m i l l .- A u t o g e n o u s - b a l l m i l l - c r u s h e r(ABC) c i rcu i t . I t was foundt h a t by c r u s h i n g a p p r o x i m a t e l y5% -10% o f t h e c r i t i c a l m a t e r i a l ,b a se d on c r u d e f e e d r a t e , a 20%i n c r e a s e i n t h r o ug h p u t c o u l d b ea t t a i n e d . I t w as a l s o f ou ndt h a t t h e f i n e n e s s o f g r i n d c ou ldb e c o n t r o l l e d b y v a r y i n g t h eam ount and t h e s i z e o f m a t e r i a lc r u sh e d . T h i s f l o w s h e e t h ad t h elo we st c a p i t a l c o s t o f a l lt e s t e d . H ow ev er, t h e s i n g l e -s t a g e g r i n d in g c i r c u i t had amuch l o w e r o p e r a t i n g c o s t an d s ot h e ABC f l o w s h e e t w a se l i m i n a t e d .S i n g l e - s ta g e a u t og e n o u s c i r -c u i t s . L i b e r a t i o n c h a r a c t e r i s -t i c s o f t h i s o r e i n d ic a t e d t h ep o s s i b i l i t y t h a t a s i n g l e -s t ag eg r i n d in g c i r c u i t c o ul d p ro du cet h e r e q u i r e d c o n c e n t r a t e g r a d e .A s i n g l e - s t a g e a u t o g e n o u s m i l lg r i n d in g i n c l o s e d - c i r c u i t w i thwe t drum magn e t s and cyc lo ne sr e q u i r e d c o n s i d e r a b l y m o r e p o w e rt ha n an y o f t h e o t h e r f l o w s h e e t st e s te d . T h is a l t e r n a t i v eg e n e ra t ed a 1 4% l o w er c a p i t a lc o s t a n d a 2 7% l o w e r o p e r a t i n gc o s t c om pared t o t h e b a s e c a s e ,i n s p i t e o f t h e h i g h e r u n i tpower consumpt ion . T h i s lowero p e r a t i n g c o s t r e t u rn e d t h ei n cr e as e d c a p i t a l i n 2 .7 y e a r s .Compared t o th e ABC f lo w sh ee t ,t h e c a p i t a l c o s t was h i g h e r

b u t t h e o p e r a t i n g c o s t w as 1 1%l o w e r . A g ai n, o n e s h o u l d n o t et h a t s e l e c t i o n o f t h e s i n g l e -s t a g e f l o w s h e e t w as n o t b a s e d o npow er e f f i c i e n c y b u t o n o v e r a l le co no m ic c o n s i d e r a t i o n s .I n t h e c a s e o f M i n o r c a vs 2 .6m i l l i o n l t p y p l a n t , f o u r g r i n d in gf l o w s h e e t s w e r e c om p a re d : i ) Rodm i l l - b a l l m i l l , i i ) B a l l m i l l - b a l l

m i l l , i i i ) A utog en ou s m i l l - b a l l m i l l ,a n d i v ) A u t o g e n o u s m i l l - p e b b l e m i l l .T he e c o n o m i c a l c o m p a r i s o n w as d o n e i ng r e a t d e t a i l . I t show ed t h a t t h e r o dm i l l - b a l l m i l l c i r c u i t had t h e l o w es tc a p i t a l c o s t . The a u t og e n o u s- p e bb l em i l l f l o w s h e e t was lo w e r i n o p e r a t i n gc o s t , b u t n o t s i g n i f i c a n t l y l ow er t oj u s t i f y t h e h ig h er c a p i t a l c o s t s .Copper and Molybdenum

C r us h in g a nd g r i n d i n g p r a c t i c e su se d i n t h e p r o c es s in g o f N or thAmerican copper and molybdenum oresh a ve be en i n f l u e n c e d o v e r t h e y e a r sby t h e f o l l o w i n g f a c t o r s :- O re t y p e : w h e th e r t h e o r e i s al ow - g ra d e p o r p h y r y o r h i g h e r -g r a d e m a s s i v e s u l p h i d e .- R eg io n: w h e t h e r p l a n t d e s i g na l lo w s f o r t h e p r o c e s s in g o fw et , s t i c k y o r e s o r i g i n a t i n gfrom open p i t s i n a r e a s o f h i ghr a i n f a l l , f ro z e n o r e d u r i n gp r ol on g ed w i n t e r s o r , i n a m oree q u i t a b l e c l i m a t e , m u l t i -s t ag e

c r u s h i n g a nd s c r e e n i n g b y t a k i n ga dv an ta ge o f t h e o p e r a t i n g c o s tm axim t h a t i t i s " c h e ap e r t oc r u s h t h a n t o g r in d t1 .- Throughpu t : w h e t h e r ap a r t i c u l a r c o n ce p t f o r e qu ip m en ts e l e c t i o n and p l a n t d e s i g n a td i f f e r e n t l e v e l s o f t h ro u gh pu tc a n d e m o n st r a te s a v i n g s i nc a p i t a l a nd o p e r a t i n g c o s t s ,m i ni m iz e p r o d u c t i o n l o s s e s an dp r ob le m s a t s t a r t - u p a nd show am ore a t t r a c t i v e r a t e o f r e t u r no n in v e s tm e n t c om pared t o a l t e r -n a t i v e s .


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DESIGN, INSTALLATION OF COMMINUTION CIRCUITS

- Ore ch a r ac t e r i s t i c s : w he th ert h e o r e i s hard and abras ive ors o f t and poss ib l y c layey.- Technolo~y: whether th er e a rel i mit at io ns placed on equipments i z i ng and th e number of u ni tsemployed by th e cu r re n t s t a t e oftec hnol ogic al development, e.g.m i l l sh e l l , head and ge ar des igno r competent rod length .

- Power co st : whether u n i t powerconsumption f o r one conce pt i smore o r l e s s i n compar ison t oa l t e r n a ti v e s and i n t h e l a s tan a ly s i s co n t r i b u t e s t oward ah i gh e r o v e r a l l o p e r at i n g c o s t .

- Sampling: whether th e c os t sincurred fo r development ,co l l e c t i o n and t e s t i n g of b ulks am p le s o f s i g n i f i c an t o r e t y p eswithin an orebody cand em on st ra te a s a t i s f a c t o r y r a t eof re tu rn on invest ment comparedt o a l t e rn a t i v e s a f t e rc o n s id e r a ti o n of o t h e r c a p i t a lco s t s .Unt i l 1967, convent ional

crushing and gr in di ng had been th enormal cand ida te f o r p rocess ing bo thmassive sul phi de and porphyry-typecopper or es , with t h e number ofs t ag es being dependent upon ope rat orp re fe rence and co s t ana lys i s .Commissioning of autogenous and semi-autogenous ci r c u i t s i n North Americabegan i n New Mexico i n 1967 and s i n c ethen other p lants have come on s t reami n Br i t is h Columbia, Arizona andColorado. For th e purposes of t h i spaper, discussion of molybdenum oresw i l l be included under porphyry-typeore s , even though they a r e usua l lya s s o c i a t e d w i th g r a n i t i c s t o c k s.

Conven tiona l p ra c t ic e has var ieddepending upon op er at or pre fere nceand t o some ex t en t d i f fe ren ces can beass igned reg iona l boundar ies . In th eporphyry copper province ofsouthwestern United S ta te s and

nort hern Mexico, fo r inst anc e,s ing le - s tage ba l l m i l l ing has foundgr ea te r accep tance than rod mi l l -ba l lm i l l combinations over a span of Some40 ye ar s. Even though mult i-sta gecrushing and screening i s r eq u ir ed t op r e p a r e b a l l m i l l feed, i t i s claimedth a t s av in g s i n o p e ra t i n g co s t andin c r ea s ed av a i l ab i l i t y ( u p t o 9 8% )c a n o f f s e t h i gh e r c a p i t a l c o s t sa s s o c i a t ed w i th t h e ex t r a s c r een ingand mate r i a l s handl ing capaci tyr eq u i r ed f o r p r epa r a t io n of a f i n e rfeed. Typical p l an ts range i nthr oug hpu t from ASARCO Si l v e r B e l l a t11,800 mtpd ( 13,000 spt d) through t oh v a l S i e r r i t a a t 83,400 mtpd ( 92 ,0 00s tp d ) . C i t i e s S e r v i ce ' s P in to V al leyp l a n t u t i l i z e s 5.5 m di a. x 6.4 m(18 f t . d ia . x 21 f t . ) b a l l m i l l s i nt h e f i r s t i n s ta l l a t i o n of t h i s m i l ls i z e i n North America f or such anapplication. Throughput i s 43,000mtpd (47,5 00 st pd ) .

Rod mill-ball m i l l combinationsa r e t he normal choice f or massivesulp hid e ores and, u n t i l 1971, werea l s o s e l ec t ed f o r l a r g e t on nageporphyry copper and molybdenum oresi n Canada. S i gn i fi c an t ~ l a n t s r e a s.foll ows: Gi br al ta r 37,200 mtpd( 41,000 s tpd) , Endako 25,400 mtpd(28,0 00 st p d ) , Brenda 27,200 mtpd(30 ,000 s tpd ) , w i th excep t ions t os i n g le - s t ag e b a l l m i l l i n g p r a c t i c e i nAri zo na being ASARCO Miss io n20,40 0 mtpd (22,5 00 st pd ) , ANAMAXTwin Bu tt es 36,300 mtpd (40,000 st pd )and Magma Copper Company I s San Manuelpl an t 58,000 mtpd (64,000 st pd) . Theprime ob jec t ive i n des ign ing p la n tst o t r e a t t h e low-grade o r e s ofBri t ish Columbia dur ing the 1960 'swas, and s t i l l i s , t o minimizeca p i t a l and o p e r a t i n g co s t s andmaximize throughput by i ns ta l l i n g th el a r g e s t p r a c t i c a l p i ece o f equipmentt h en i n e x is t en c e, e.g. 4.1 m d ia .(13-1/2 f t . ) rod mills and i n t h e1 9 7 0 f s , 5 . 0 m dia . (16-1 /2 f t . ) b a l lm i l l s . An added b e ne f it wasprov is ion o f a compac t p lan t s izewhich i s important when consideringenergy and hea t ing co s t s i n a co ldc l im a te .


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A s ore g rades con t inued t odec l ine and un i t opera t ing co s t s t oe sc a l a t e , a t t e n t i o n was t u rn ed t o t h eadvantages of e l imin at ing secondary-t e r t i a ry c rush ing and sc reen ingpla nts through t he u se of autogenouso r semi-autogenous gri nd in g.

Cap i t a l and opera t ing c os tsavings were s i gn i f ic an t enough t oencourage some opera tor s t o ta ke t heplunge. Their ded ica t io n has ensuredt ha t semi-autogenous gr in di ngc i r cu i t s , a t l e a s t i n B r i t i s hColumbia, can achieve a va i la b i l i t i e sof 92% and i n one c as e (Lornex) 94%.In order of commissioning datecommencing i n 1967, t h e fol lo win gpl an ts have been brought on stream:UV I n d u s t r i e s , New Mexico 2,700 mtpd(3,000 s tp d ), Utah Mines Ltd. Is la ndCopper 29,900 mtpd (33, 000 s t p d ) ,Newmont Mines Ltd . Similkameen13,600 mtpd (15,000 s t p d ) , LornexMininu Corp. Ltd. 43,500 mtpd(48,000 stpd) , Cyprus Pima expansion12,700 mtpd (14,000 s t p d ) , ClimaxHenderson 27,200 mtpd ( 30,000 stpd) ,Afton Mines 6,350 mtpd (7,0 00 s t p d ) ,CYP~U S Bagdad 36, 300 mtpd(40, 000 s t p d ) , Highmont Mining Corp.22,700 mtpd (25,000 s tp d) andQuintana Minerals Corp. Hil lsb oro,N.M. 13,600 mtpd (15, 000 s tp d) . Thel a s t op e

factors which influence selection of comminution circuits

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