platinuminsouthafrica (metalreviewseries no.3) · company, potgietersrust platinum...

J. S. A fr. Inst. Min. Metal/., vol. 85, no. 6,Jun. 1985. pp. 165-185

Platinum in South Africa(Metal Review Series no. 3)

by R.C. HOCHREITER*. D.C. KENNEDYt. W. MUIR:I:. and A.I. WOOD§

SYNOPSIS , , .The paper gives a technical re'fiew of the history, occurre!1ce, mining, met~lIurgy, and end-uses of the platlOum-

group metals in South Africa, with most emphasIs on platinum and pal~adlum. , .The platinum industry has grown, from the first discovery of the metal 10S~uth A.fnca (10the central !ransvaal)

in 1923, to the present time, when the country is the largest producer of platinum 10the world, supplYing almost70 per cent of the platinum on the world market.

SAMEVATTING .,11 '

.d b 'kDie referaat gee 'n tegniese oorsig oor die geskiedenis, voorkoms,. ontglnnlng, m~ta urgle en eln ge rU! e van

die platinumgroepmetale in Suid-Afrika, met die k!em veral. op platln,um e.n pal!adl~m. .Die platinumbedryf het sedert die eerste ontdekklOg van die met~allO ~uld.-Afnka (IO.Sentral-Transvaal) 101923

gegroei tot waar die land vandag die ~rootste produsent van platinum 10die wAreld IS en byna 70 persent vandie platinum op die wAreldmark voorslen.

HISTORY AND GEOLOGYI-5

Discovery of Platinum in South AfricaIn 1923 Mr Adolf Erasmus discovered an unusual

platinum deposit near Naboomspruit, in centralTransvaal. Quartz veins infilling brecciated fault zoneswithin the felsites of the upper phase of the BushveldComplex yielded significant platinum values, and thesewere exploited on a limited scale from 1924 to 1926.

While in themselves short-lived as commercial enter-prises, these discoveries aroused fresh interest in platinumprospecting in the Transvaal, and in 1924 Mr AndriesLombaard obtained platinum grains in a panned concen-trate from a stream bed on the farm Maandagshoek inthe Lydenburg district. Mr Lombaard brought thisdiscovery to the attention of Dr Hans Merensky, whodevised a prospecting programme to establish the sourceof the platinum grains. Unfortunately, this proved to bea pair of small pipe-like bodies of limited areal extent,which were relatively rich but insignificant in terms ofore reserves.

Undeterred, Merensky continued the search, and in thelatter part of 1924 he discovered a layered gently dippingplatiniferous pyroxenite on the farm Maandagshoek. Farfrom being a small pipe-like body of negligible extent,this appeared to be a continuous horizon, traceable forkilometre after kilometre on strike. Although he did notrealize it at the time, Dr Merensky had found the world'slargest known repository of the platinum-group elements(PGE).

History of PlatinumIt is unlikely that platinum or the PGM were recognized

as separate elements by the early civilizations, although. Mining Engineer, P.O. Box I, Bleskop, 0292 Transvaal.

t Chief Geologist, Rustenburg Platinum Mines (Rustenburg Section),P.O. Box I, Bleskop, 0292 Transvaal.

t Manager Metallurgical, Rustenburg Platinum Mines (AmandelbultSection), P.O. Box 2, Chromite, 0362 Transvaal.

§ Senior Manager Marketing, Johannesburg Consolidated InvestmentCompany Ltd, P.O. Box 590, Johannesburg 2000.

@ The South African Institute of Mining and MetalIurgy, 1985.SA ISSN oo38-223X/$3.oo + 0.00. Paper received September 1984.

platinum has occasionally been found in artifacts fromancient Egypt. The best known example is a strip of nativeplatinum set in a box that is ornamented with gold onone side and silver on the other. One of the metallic in-lays on the side ornamented with silver was establishedby French scientists in 1900 to be platinum. There wasno evidence that the Egyptian craftsmen had treated thispiece any differently from the rest, and its occurrence wasprobably quite fortuitous.

The earliest probable reference to the PGE in Euro-pean literature was made in 1557 by a gentleman of theunlikely name of J ulius Caesar Scaliger. At the time hewas engaged in vigorous scientific disagreement with afellow Italian, who, among other things to which Scaligertook exception, had defined metal as 'a substance thatcan be melted and which hardens on cooling'. Havingset his opponent reeling with mercury, Scaliger deliveredthe coup de grace as follows: 'Metal you say is somethingthat can be melted but when it cools remains hard. . .Moreover, I know that in Honduras, a district betweenMexico and Darien, there are mines containing asubstance which it has not hitherto been possible to meltby fire or by any of the Spanish arts. Thus we see thatthe word melt cannot be applied to all metals'. Thisspirited exchange was followed by a whole series ofreferences from South America over many years to awhite or grey metal that was difficult to melt. It was refer-red to variously as papas de plata, smiris Hispanica, orplatina.

Finally, in 1879 a German geologist, Theodor Wolf,published a paper describing his findings in the districtof Esmeraldas in north-western Ecuador. He had un-earthed from local burial mounds a tiny ingot ofplatinum, which he analysed. It contained 84,95 per centplatinum, 4,6 per cent palladium, rhodium, and iridium,6,94 per cent iron, and around 3,5 per cent copper. Laterwork suggested that the inhabitants of the Esmeraldasdistrict had mastered the techniques of working withplatinum long before the Spanish invasion.

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY JUNE 1985 165

It is ironic that one of the first recorded uses ofplatinum was thoroughly fraudulent. Unscrupulous in-dividuals used to alloy it with gold as witness the follow-ing report by Mr William Brownrigg in 1750: 'I am toldthat one Mr. Ord, formerly a Factor to the South SeaCompany, took in payment from some Spaniards Goldto the value of five hundred pounds sterling which beingmixed with Platina was so brittle that he could not disposeof it, neither could he get it refined in London, so thatit was quite useless to him'.Rustenburg. Various small companies were formed to ex-ploit the deposit, including Premier Rustenburg PlatinumLtd, Eerstegeluk Platinum Mines Ltd, and the Rusten-burg Platinum Company. These were taken over by theJohannesburg Consolidated Investment Co. Ltd (J.C.L)in 1926, and just three years later a J .C.L-administeredcompany, Potgietersrust Platinum Ltd, started produc-tion from the Merensky Reef.

Production has continued ever since, and today threelarge-scale mining concerns are engaged in winningplatinum from the Bushveld Complex. These are J.C.L'sRustenburg Platinum Mines Ltd, Gencor's ImpalaPlatinum Ltd, and Lonrho's Western Platinum Ltd.

Hy 19:1':l,the Merensky Reef had been traced on theeastern limb of the Bushveld Complex for a distance of150 km, and in the western limb for about 200 km (Fig.1), thus making it by far the largest platinum deposit inthe world. But yet another surprise was in store.

~~ i8~~:I,~"~ 1i~r.':."",IQ] ~~~::'LD

~.

."Of,,"R6

Fig. 1-Oeology and mines of the Bushyeld Complex

As far back as 1908, Messrs A.L Hall and W.A. Hum-phrey had published a report in which they noted thatcertain chromitite layers within the Bushveld in the

Rustenburg area and in Sekhukhuneland assayed up to2,6 g of platinum per ton. Chromitite layers continuedto yield sporadic platinum values for many years, andit was only upon systematic prospecting within the lowerportion of the Bushveld sequence following the discoveryof the Merensky Reef that there was located in theRustenburg and Lydenburg districts a particularchromitite layer that carried persistent PGE values of be-tween 3,5 and 29 g/t. This chromitite layer lay anywherebetween 20 and 370 m below the Merensky Reef, and itsdon, obscured tfie ~iriIepoferltiaJ"ot tne-'afea rdf"fnahyyears. It is now clear that substantial platinum deposits,which are unusually enriched in copper and nickel, areto be found here.

Geological Setting of the Merensky and U.G.2 ReefsBoth the Merensky Reef and the U .G.2 chromitite layer

occur as distinct, persistent layers within the giganticlayered intrusive known as the Bushveld Complex, whichunderlies an area of about 40 000 km2 in the centralTransvaal.

Some two thousand million years ago, a majormagmatic event occurred, which resulted in vast volumesof molten rock from within the Earth's mantle being in-jected into the higher-level crustal rocks of the TransvaalSupergroup. This injection probably took the form of aseries of pulses that introduced successive units ofmagma, each of which differed subtly from thatpreceding it. Some differentiation of individual layersmay also have taken place as different minerals crystal-lized out at different temperatures, and the net result ofthese processes was that the Bushveld Complex becameclearly stratified into distinct compositional units (Fig. 2).

In general, there is a transition from high-temperaturerock types that are rich in magnesium in the lower por-tion of the Bushveld Complex, to low-temperature silica-and iron-rich rocks at the top.

In terms of the PGE, the most important unit is theCritical Zone (Fig. 3), which consists in its lower part ofa series of chromitite layers within pyroxenite, and in itsupper part of a series of cyclically repetitive triplets ofchromitite, pyroxenite, and norite. The Critical Zone isdivided rather unimaginatively according to thechromitite layers into the Lower Group, Middle Group,and Upper Group. The basal chromitite of each unit isidentified by being numbered according to its group fromthe bottom upwards, e.g. LG.l, LG.2 etc., for LowerGroup chromitites, M.G.l, M.G.2 for Middle Group,

166 JUNE 1985 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

-

UPPERZONE

GRANITES, ETC

- - - MAIN MAGNETITE

MAINZONE

MOSTLY GABBRO

f- - - MERENSKY

CRITICALZONE

NORITE, PYROXENITECHROMITITE

BASALZONE

UNDIFFERENTIATEDNORms, ETC

MARGINALZONE

Fig. 2-Generallzed stratigraphy of the Bushveld Complex (afterWillemse and Von Gruenewalt, 1969)

and so on (Fig. 3). As can be seen in Fig. 3, there areno fewer than thirteen of these chromitite units in theCritical Zone in the Rustenburg area. Of all thesechromitites, only the U.G.2 carries significant platinumvalues throughout the Bushveld Complex.

Near the top of the Critical Zone is an assemblage thatcould be described as the penultimate happening of theCritical Zone event. It looks like an abortive attempt toform yet anot?er chromitite-pyroxenite-norite triplet, forall the essential components are there. The chromitite,however, is extremely poorly developed. The pyroxenitevaries in width from around 60 cm to a maximum ofabout 3 m. This relatively insignificant assemblage is theMerensky Reef.

A few metres above the Merensky Reef occurs the finalchromitite-pyroxenite. This is the Bastard Reef, and its

MERENSKY

UPPERGROUP

U.G.2

U.G.1

M.G.4

MIDDLEGROUP

M.G.1

L.G.7

LOWERGROUP

L.G.1

Fig. 3-Stratlgraphy of the Critical Zone

chromitite is so poorly developed as to be absent in manyplaces. It is not significantly platiniferous. Above theBastard Reef, the norites of the Critical Zone give wayto the thick, monotonous gabbros of the Main Zone,which appear to represent a new and compositionally dif-ferent infusion of magma into the Bushveld Complex.

The rocks of the Critical Zone crop out around themargins of the Bushveld Complex (Fig. 1) and diprelatively gently towards its centre. This meant thatmining operations could be initiated at small cost fromsurface, and it is only now after half a century of pro-duction that some mines are approaching reasonabledepth. This generally shallow dip is important, becausethe thermal gradient within the Bushveld rocks, whichmay well be linked to the Earth's mantle through feederchannels, is almost three times as steep as that in the Wit-watersrand gold mines.

Merensky ReefSubstantial mining operations on the Merensky Reef

began in the Rustenburg area, and for this reason theRustenburg area has always been considered to be the'type locality' of the orebody.

The Merensky Reef at Rustenburg normally consistsof a coarse-grained 'pegmatoidal' feldspathic pyroxenitecontaining appreciable phlogopitic mica. It is really verynarrow, varying in width from 15 to 40 cm. The top andbottom contacts of the coarse-grained material are usuallymarked by thin chromitite layers a few millimetres thick.Immediately above the top chromitite layer is a brownishpyroxenite that is around 60 cm thick. This is known asthe 'Merensky pyroxenite'. Directly below the bottomchromitite is a light-coloured norite. PGM occur withinthis assemblage in two different forms.

A relatively small proportion of the PGM forms alloyswith iron. These ferroplatinum alloys are very dense, andthis is used to advantage in their recovery.

By far the greater part of the PGE associate as com-plex sulphides within base-metal sulphides. Three prin-cipal base-metal sulphides occur in the Merensky Reef.These are, in order of decreasing abundance, pyrrhotite(FeS), pentlandite (Fe,Ni,)S, and chalcopyrite (CuFeS ).As the platinum minerals occur within and associat~dwith these sulphides, the Merensky Reef yields substan-tial copper and nickel as byproducts, together with minoramounts of cobalt and selenium. The lack of thesebyproducts makes the U. G.2 a somewhat less attractiveproposition, the unit value of its ore being usually lessthan that of the Merensky Reef.

All six of the PGE and gold are found within theMerensky horizon. Their proportional percentages are ap-proximately as follows:

PtPdAuIr

57!lJo25!lJo

4!lJo1!lJo

RuOsRh

8!lJo1!lJo4!lJo.

The high ratio of platinum to palladium substantially in-creases the unit value of Merensky ore.

The base-metal sulphides and their associated PGE arenot restricted to the Merensky Reef itself but aredi~seminated for some way into the hangingwall pyrox-emte and the footwall norite, thus facilitating sto-


ping widths of 70 to 90 cm. This is of considerablemetallurgical significance in that a concentrator may haveto process a mixture of three different rock types, eachwith its own grindability and recovery characteristics.

It should be remembered, however, that the Merenskyhorizon varies considerably throughout the BushveldComplex and, for that matter, within the Rustenburg areaitself. In the eastern and southern Bushveld, the Meren-sky pyroxenite is strongly developed, and much of themineralization is located within it. The pegmatoidal phasemay be absent, or if it is present it may be virtually bar-ren. In the western and south-western Bushveld, thepegmatoidal phase is strongly developed, as are thechromitite contact layers.

The nature of the Merensky Reef has a direct bearingupon the distribution of sulphides, and hence FOE,within the one horizon. Three forms of the MerenskyReef within the Rustenburg area and their POE distribu-tions are illustrated in Fig. 4. It is clear from the diagramsthat the highest POE values occur near or associated withthe chromitite seams, and that the distribution of the POEdetermines the composition of the ore that is sent formilling.

Structure of the Merensky ReefThroughout the Bushveld Complex, the Merensky Reef

is affected to a varying degree by the phenomenon known

NORMAL REEF. ., .. . . . . . .

er-----------------

0 0 0 . . . .Cr-----------------

CONTACT REEF

. 0 0 . . . .Cr -----------------

WIOE REE F

Cr-----------------

REFERENCE

rz;:--l--- CHROMITlTE

E=.:J SEAM

D. .--- MERENSKY

. 0 PYROXENITE

D.0

--- MERENSKY.. REEF

~ --- FOOT WALL

~ NORITE

Fig. 4-Dlstrlbutlon of PGE In various types of Merensky Reef

as 'potholing'. Potholing seems to be a characteristic oflarge layered complexes, and within the Bushveld Com-plex the Merensky appears to be a particularly vulnerablehorizon when compared with other economic layers suchas the 0.0.2 and the LO.6.

In brief, potholing occurs when the Merensky Reef (orother horizon) suddenly slumps, cross-cutting its ownfootwall (Fig. 5). The hangingwall rocks descend concor-dantly with the potholing stratum. The size and amplitudeof these structures vary from a few metres across and ametre or so deep, to severe disturbances that may be300 m across and up to 90 m deep. They tend to be ap-proximately circular in plan. Their cause is not clear, butthey seem to have a strong association with late-stagevolatile activity.

""

",,""

"

,/'ASTARDREEF

~~!~~Fig. 5-Sectlon through a typical pothole

In many cases, pothole reef is unmineable since it isoften highly disturbed, and sometimes even absent savefor a thin, virtually barren pyroxenite. The frequency andseverity of these disturbances may govern the choice ofmining method in any given area.

Faulting occurs on the reef horizon, but this is generallyon a relatively small scale. These faults rarely throw morethan a few metres, and their principal effect on miningoperations is to weaken the hangingwall substantially.Most are relatively low-angle reverse faults, which maybe considerably serpentinized. Particular care must beexercised in support design under these fault planes.

Major dykes are an important structural factor in thewestern Bushveld. While most of the dykes are doleritic,they are accompanied in the Rustenburg area by largesyenite dykes associated with the Pilanesberg intrusiveevent. The dykes tend to cluster into groups of four orfive within a relatively confined zone, and may followpre-existing lines of weakness. Two major trends are ap-parent in the Rustenburg area, namely northwest-southeast and east-west.

These dykes have a significant effect on mining in thatthey induce a horizontal stress component that is not nor-mally present beyond that induced by shallow miningoperations. Severe shearing is commonly present on thedyke margins, and water is occasionally intersected in thevicinity of the dykes.

MINING METHODS

In addition to the publications referred to directly inthis section, there are several others of interest. These aregiven as numbers 6 to 10 in the list of references.

Mining methods at present are restricted tounderground operations, although the Potgietersrus limb,Platreef, could lend itself to future open-pit mining. Anyexploitation system must be aimed essentially at theremoval of a narrow sheet of platinum-rich rock contain-


ed within the mass of the Bushveld Complex.Where the Merensky Reef outcrops on surface, such

as at the Amandelbult Section, an inclined-shaft systemis ideally suited to the exploitation of the tabular, gentlydipping (at approximately 10 degrees) orebody. At inter-vals of about 1 km along the reef outcrop, inclined shaftsare sunk on or below the reef in order to gain access tothe first 1200 m of ore. Since inclined shafts becomeuneconomic to operate beyond a certain depth, verticalshafts are sunk at specific locations to take over fromthese inclined shafts when the ore so exposed has beenmined out (Fig. 6).

SOUTH NORTHSO",'"~

, 1000m

MAIN CROSSCUTSTO REEF

FURTHER INCLINED SHAFTSIN FOOTWALL OF OREBODYGIVING ACCESS TO DEEPERLEVE LS

Fig. 6-Schematlc section through a typical shaft at RustenburgPlatinum Mines, showing the major development

Access to the reef plane from these vertical shafts isby means of a series of horizontal tunnels or 'maincrosscuts', which are the main access for men, materials,services, ventilating air, and the transport of broken rock.

The main crosscuts are driven to a point below the reefplane where the competency of the rock is favourablysuited for the siting of footwall haulages, approximately25 m below the reef horizon, which require long lifespans;for example, in the Rustenburg area the Boulder Bedhorizon is the most suitable. Footwall haulages arehorizontal tunnels that are parallel to the strike of thereef. Should distances from the shaft to the reef becomeexcessive, only every second or third level has a maincrosscut, and a system of interlevels closer to the planeof the reef is used with access to these interlevels via shortmaterial inclines.

At intervals of approximately 150 m along the foot-wall haulages, crosscuts are driven to intersect the reef.From this point, inclined tunnels on the reef plane, knownas raises and winzes, are driven on dip. Boxholes, or ore-passes, are mined at an inclination of 60 degrees upwardsfrom the crosscuts to intersect the raise above at inter-vals determined by the stope layout, viz panel length.From these raises and winzes, the orebody is mined byan operation known as stoping.

Four distinct underground mining methods are in useon South African platinum mines1,11,12.The methods aretermed the scattered mining method (mechanized andBilby methods), and longwall mining method, and theup-dip mining method.

Scattered Mining MethodsMechanized Method

The scattered mining method (Fig. 7) is used wheregeological disturbances (e.g. potholes) prohibit the min-ing of extensive areas. From the original raise, which

becomes the centre gully of the stope, a series of panelsis advanced in the direction of strike. Advance strikegullies or A.S.G.s form the top and bottom limit of eachpanel. A.S.G.s are always kept slightly ahead of the ad-vancing panels to establish a free face for blasting andfor purposes of exploration, and to facilitate the removalof ore.

~D

D

CD TEMP SUPPORT

CDROLLING SCATTER PILE

D CD PCRM. STICK SUPPORT

D "\:1<", @ 2dm PILLARS. DIP

,'" GJ 0,601,2mTIMBERPACKSV

0 ~~,', ",', @AS.GWINCH

1,O~J,I,,', ' , ,,-""~ G) FACE WINCH POSITION, ,

" \"",D 0 ~.9 D'

,

".y,"'"" , @ CENTRE GULLEY WINCH

'1', ,

" '"

:' -fo~"o "\\";~~'"

", /~"'",~,

:1::: ',,\/,0,'"D ',' '\;'" "d-

':"q,~v< .G",

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0,

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,

D 'Do

D '9 '

D '0', ,

,"ji:~m

0

:

~~, ", " " ", ", '

: ' 1 8';,,

" '0,

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'", ,,

'

O"".~~

", <"",."

'",0

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0 0

Fig. 7- The scattered mining method

The broken ore is removed from the panel by meansof a system of scrapers (hence the term mechanized)13.A face scraper is rigged by means of a series of snatch-blocks and steel ropes to run along the face of each panel(Fig. 8). A 22 kW double-drum electric winch sited within30 m of the panel is used to pull the scraper. The ore isscraped down-dip into the A.S.G. (The night-shift per-sonnel remove ore from the whole length of the face ofthe panel for 2 m perpendicular to the face, to the startof the scatterpile (Fig. 7). The day-shift personnel thenremove ore from behind the scatterpile to the standardthickness required (hence the term rolling scatterpile). Thepurpose of the scatterpile is to eliminate widespread scat-tering of the ore from the blast and to confine the brokenore within reasonable distance of the face (since the scat-terpile extends from footwall to hangingwall). Blastingbarricades may similarly be used to confine the scatter-ing of the ore.

The ore pulled into the AS.G.s is scraped into the cen-tre gully by use of a second (37 kW) winch (Fig. 8). Final-ly, the 55 kW centre-gully winch scrapes the ore into 'box-


A \ G

e~:.Ji ~ ~..:;:;::]1 THE FACE CLEANING SIGNALLING DEVICE

AND FACE WINCH

2 THE FACE CLEANING WINCH BELlWIRE

SUSPENDED ALONG THE DOWNDIP SIDE

OFTHEA.SGUPTOTHEFACE

3. AT THIS POINT THE SIGNAL OPERATORSIT, AND SIGNALS THE FACE AND AS G

WINCH DRIVE",

THE A S G CLEANING SIGNALLING

DEVICE AND WINCH POSITION

S THE BELL WIRE FOR A S G CLEANINGBROKEN ORE

SCRAPED

DOWNDIP ON

NIGHTSHIFT

0DIP

ORE

SCRAPED

~

0

ON0

D;YSH~T

~n~f

TANDEM ASG

SCRAPERSCOOPS

A.S G

Fig. 8- The arrangement for panel scraping

holes' or ore-passes fitted with a screen or grizzly (thesize of which is determined by the size of the desiredcrusher feed), leading down to the crosscuts below (Fig.9). The ore is then loaded into hoppers and pulled bysmall electric or diesel locomotives to conveyor transferpoints or to the main shaft itself, where it is hoisted tosurface. On surface it is tipped into surge bins, fromwhere it is transported to the mill (the route of the orefrom stope to mill being the same for all four methods).

Venlllatian\ boxhole Baxholes

5 N

Faolwallhaulage Cra~e".'iut ta Travell ing way

raise la reef

(nat to scale)

Fig. 9-Section showing the layout of boxholes or ore-passesalong a cross-cut

The support system generally used for scattered min-ing is the stick-and-pillar methodl4. A series of smallpillars is left in situ on the plane of the reef as the panelis blasted (Fig. 8). These pillars are sited at the top ofeach panel. Support of the worked-out area is by meansof wooden timber props 150 mm in diameter. A row ofprops is installed along dip as the panel is advanced onstrike and kept within a maximum standard distance fromthe panel face, e.g. 8 m (Fig. 10). Face props are install-ed as temporary support along the face of the panel forthe protection of the workers responsible for drilling andblasting. Mat packs are installed along both sides of the

A.S.G.s and centre gully, which are important accessroutes.

Bilby Mining MethodThe Bilby method is similar to the mechanized

scattered-mining method but differs mainly in the methodof removal of the broken ore. Hand lashing is employed,with two lashing persons per cutting (Fig. 11). The oreis lashed into Bilby cars operating on monorail striketracks along which the Bilby cars (Fig. 12) are pushedtowards the centre gully. At this discharge point, stopblocks allow easy tipping of the car into the centre gully,where a scraper is used to pull the ore into the boxhole.The Bilby method has the inherent flexibility that theA.S.G.s need not be straight, as is necessary for scrapergullies. Hence, in geologically disturbed areas, panels canbe maintained on reef (although the panel length changes)by simple swinging of the AS.G. along a local strike.

Support may take on various patterns, and a popularsystem is shown in Fig. 11.

A notable feature of the Bilby method is that it is verylabour-intensive, utilizing approximately twice thenumber of persons as in mechanized stoping methods.

LongwaU Mining MethodThe longwall mining method is well suited to the ex-

ploitation of large, geologically undisturbed areas of reef.It requires numerous panels on dip (Fig. 13) advancingin unison along the direction of strike.

Again, the ore is removed by means of face and A.S.G.scrapers. A notable feature is that each A.S.G. has a box-hole, which is developed ahead of the stope along withthe other footwall development. De-stressing of the lat-ter development by initial overstoping is not necessaryat present mining depths (1000 m, 30 MPa). Normal foot-wall norites have uniaxial compressive strengths of about190 MPa. Boxholes are planned 100 m apart in theA.S.G.s, and the winches are moved forward shortly afterholings have been effected and grizzlies installed. Facewinches are always closer to the panel than A.S.G.winches.

The support system used differs from the scatteredmining system in that cement-grout packs are used aboveand below the A.S.G.s and as dip ribs (Fig. 14). Thesepacks consist of circular steel rings connected withpolypropylene netting on the inside, in which is placeda polypropylene knitted bag. This is wedged against thehangingwall by means of four sticks and is then filled withgrout that is pumped underground from a cementationplant on surface. Scatter piles may be used to contain theblast and avoid contamination of the worked-out backareas. Recently, however, blasting barricades have beenintroduced, especially in areas where the hangingwall con-ditions are bad (Fig. 15).

Up-dip Mining MethodThe up-dip mining method is so called because the

panels are advanced in an up-dip direction (Fig. 16). Verylittle cleaning of the blasted areas is needed. The blastof the more advanced panel is directed at the solid sideof the dip gully (Fig. 16), and the blast of the laggingpanels is directed at the scatterpile, which is left in place,resulting in most of the blasted rock being concentrated


SECTlOX

I--I

3,0", -I.. 3,0",II

le- 1,5", ~ 1,5", --1

~ 0,9 -ef- 0,9 --I

--fI

I-- 2,0", ~ :10-1,2",'" '--- 2,5m --+- 2,Om 2,0111:~

I I I'. ',','

,'d

:" :"','-".', '... , .

'""",'

REEF IS FOOTWA 1.1-

Fall .!: 2"1,,,

Fig. 10-Strike section showing the positions of the scatterpile and support

0 1S0mm diameter sticks

-mat packs

~

Fig. 11-Layout of a Bllby stope (person A lashes into gully aand person B into gully b)

in the dip gully. A dip-gully scraper then scrapes the oredown to boxholes.

The support system used may vary, with dip rib pillarsbeing left at standard intervals along strike. Stick sup-port is used in the worked-out area. When the panels haveadvanced to the level above, strike pillars are left forregional support.

Off-reef development is minimal, requiring only foot-wall drives or haulages, a boxhole for each dip gully, andan access raise. However, extensive on-reef developmentof reef drives and up-dip raises necessitates carefulplanning.

DrillingDrilling is generally conducted with hand-held

pneumatic jackhammers, with a crew of two personsperdrill in the stopes, and one person per drill in develop-ment aided by an airleg.

Drilling patterns in the stopes and development endsare shown in Figs. 17 and 18 respectively. Hole directorsare utilized to ensure parallel drilling of holes: the minermarks off the direction of the top and bottom holes(about 70 degreesto the dip) every3 m; the machineassis-tant then places the hole director into the previous hole,and the subsequent hole will be drilled parallel to and atthe correct burden and spacing to the previous hole.A.S.G.s are drilled to a simple burn-cut pattern. Thelength of drill steel used is 1,2 m. Stoping widths vary

Fig. 12-Mounted underneath the Bilby car at the centre of gravity is a guide wheel, which runs on the monorail In the A.S.G.s

JUNE 1985JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY 171

0

00

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Fig. 13-Diagrammatlc plan showing the longwall method ofstoplng

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Fig. 14-L.ongwall support pattern for normal ground conditions

from 70 to 150 cm. Mechanization of drilling operationshas been attemptedl5 but is not used at present.

Development ends (haulages and cross cuts) are ex-cavated by the use of drag rounds or burn cuts. Advancesof 2 to 3 m are gained per blast, depending on the lengthof drill steel used. Burn cut rounds are drilled for raises,winzes, and ore-passes.

Raise boring is used mainly on shaft sinking andboxholingl6.

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Fig. 15-Hydraullc props and blast barricade for friable ground

, ,

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.,

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Su ppor! may take thp farm CIf rogulardip pillars. mafpacks. sticks or cClmbina-lions thprpof

Fig. 16-Layout for up-dlp stoplng

BlastingThe explosive predominantly used is ammonium nitrate

fuel explosive (Anfex). This is loaded into the blastholesby means of loaders operated by compressed air, givinga constant charge per stope blasthole of 0,7 kg and 1,5 kgper 2 m of development blasthole.

When water-resistant explosive is required; Dynagel60,a stick explosive, is favoured in diameters of 22 mm and25 mm. The latter is used for lifter and water-filled holesin development ends.


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SidlOg - -=:""~(d~;:~ E

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.

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~-~.:~Fig. 17-Examples of the drilling patterns used in stoplng

Capped fuses, 0,9 m in length with the MKl connec-tor 8D, are used to detonate Anfex without the use ofprimer charges, and MKl 6D fuses 1,8 m long are usedfor nitroglycerine-based explosives.

Slow (30 to 45 s/m) igniter cord is used for develop-ment owing to its high resistance to moisture, and IC 57(13 to 26 s/m) or S.c.9 (8 to 16 s/m) is used for the se-quential firing of stope blastholes.

Other explosives are used, but for more esotericapplications Western Platinum Ltd has manufactured itsown Anfo mixture explosives!?

CleaningStope cleaning has already been described in some

detail, viz the use of scrapers. The subsequent cleaningis done by hand lashing, and the worked-out areas arethen swept with hand brooms and sweeping tools, or arewashed down as required.

Development cleaning -is accomplished by means ofpneumatic shovel loaders, which lash the broken rockdirectly into 6 t hoppers (i.e. 8 hoppers per 2 m blast).Tidying up is done by hand lashing.

Raises and winzes are cleaned simply by rigging of ascraper to the blasted end and scraping of the broken rockto a convenient boxhole.

Grade ControlThe value distribution within the Merensky Reef is a

positively skewed log-normal distribution with semi-variogram ranges of the order of 20 m in all directions.The low sample variances, compared with those for goldand base metals, and almost pure nugget-effect natureof the semi-variograms render kriging proceduresinefficient.

Grade can be controlled most effectively by the keep-ing of ore dilution to a minimum. After the reef has beenphotographedl8, and the top and bottom chromiteseams, the stoping width, and the reef position have beenidentified along regular points in each panel, the resultsare averaged by a computer using digitizers. Printoutsgiving the best cut and stoping width for optimum graderecovery are then supplied to the stopers.

Sampling is carried out periodically, but is more a con-firmation method than a grade-control method.

VentilationThe high geothermal gradient of the Bushveld Com-

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Fig. 18-Examples of the drilling patterns used In development

plex (21,2 °C/km) gives rise to a comparatively hightemperature in the working environment. At depths of1000 m, virgin-rock temperatures of 43°C can be ex-pected, compared with 27°C and 31°C in the gold minesof the Witwatersrand and Orange Free State respective-ly. However, wet-bulb temperatures are lower owing tolimited autocompression, and a wet-bulb temperature of27,5°C is generally maintained. (The future planned min-ing depths of 1200 m will call for a consideration ofrefrigeration plants to reduce the temperatures of theworking place from 45 to 26°C.)

A limited number of workers are put through heat-tolerance tests (HTT) at wet-bulb temperatures. of 31,3°Cfor working in areas of higher temperature.

Ventilation requirements are based on a requirementof 3.6 m3I s per kiloton of ore broken per month.

Development ends are ventilated by the use of auxiliaryfans, and dust suppression is accomplished with delayed-operation water blastsl9.

LabourTens of thousands of men are employed throughout

the platinum mines. The administration of this labour isextensive and costly, and involves continuous recruitmenttogether with training, accommodation, catering, recrea-tion, medical services, and an on-going labour-relationsprogramme20. '

The South African platinum industry recruits its ownlabour force through a network of offices and employ-ment representatives throughout South Africa and the in-dependent States, in addition to Lesotho, Mozambique,and Botswana; whereas the gold mines use the recruitingorganization of the Chamber of Mines of South Africa.The Black personnel represent over a dozen differenttribes and speak a dozen different languages and dialects.

Preferential employment opportunities are afforded tothose employees who have had previous service on theplatinum mines. Most of the new recruits are unskilledand unsophisticated, with little or no education. Thus,the first education encountered by many is in the in-dustry's employment. The lingua franca of the entireSouth African mining industry, Fanakalo, is included inthe training programme, as well as first aid, loss control,safety, and simulated-job instruction.

Computerized labour control is in widespread use onSouth African platinum mines, because of the largenumber of personnel employed2l,22.

JUNE 1985 173JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

Long- Scat-wall tered Bilby Up-dip

35 35 15 35

7,5 7,0 8,0 8,0

90 90 50 9075 for normal reef

15 15 15 152000 2700 2000 3100

Short periods of employment with regular leave are en-couraged with a view to stabilization of the labour force.All employees are covered by insurance in the event ofinjury or death, with free hospitalization, and compen-sation for loss of earnings and any permanent disability.Educational assistance for degree, diploma, and cer-tificate purposes is available to all employees, who alsoare provided with single or married accommodation. Acommunications network based on tribal customs andtraditions is maintained to ensure healthy and progressivelabour relations.

EfficienciesThe efficiencies achieved by the platinum mines in

South Africa compare very favourably with those on thegold mines and, although many reasons can be put for-ward, the platinum mines continue to return higher effi-ciencies in tabular reef mining. Table I gives an overallindication of the efficiencies attained in recent years.

TABLE1EFFICIENCIES ON SOUTH AFRICAN PLATINUM MINES

Stoping

Area mined per undergroundworker, ca

Area mined per caseof explosive, ca

Output per undergroundworker, t

Average stoping width, cmMonthly advance, mArea mined per contractor, ca

Development

Per underground worker, m

Per contractor, mPer case of explosive, m

5,53001,0

ca = centare = 1m2

Rock MechanicsWell-defined structural weaknesses divide the hang-

ingwall into large fragmented blocks. Broken rock canhave good structural properties, but these are lost whentensile stresses are present, which leads to bed separation.Thus, a necessary design criterion is that the full thicknessof rock up to a plane of weakness within the tensile zoneshould be supported. As most platinum mines are shallowto moderately deep,the tensile zone extends far into thehangingwall, and this dictates the types of support to beused.

Traditionally, as in all the mines in South Africa.timber support was used in conjunction with waste stow-ing. This support system proved to be very labour-intensive, and when waste stowing was abandoned, onlytimber matpacks were used. However, owing to the in-crease in depth and span of the workings, timber packswere inadequate to cope with the support demands. Scat-tered mining also contributed to the elimination of mat-packs as support, and timber sticks were introduced intothe stoping environment. These support units were foundto be adequate for face support, but were unable to fulfilthe requirements of regional suppore3. Small reef pillarswere introduced in some mines, while other mines in-troduced barrier pillars to achieve the designed support.

With the small reef pillars24, inelastic as well as elasticclosure is allowed to take place, but detachment isprevented in the hangingwall, which in turn reduces theactual tensile zone. Barrier pillars, on the other hand,limit the span and thus prevent any form of inelasticclosure, but often result in large quantities of strainenergy being stored in them, which could lead to violentfailures of these pillars. In most mines in the BushveldComplex, the convergence in the mined-out area isgenerally very limited. Timber matpacks require substan-tial deformation before any support is generated, and toovercome this grout packs were introduced as internalsupport and are now used in longwall stopes. Today muchwork is being done with support systems utilizing rapid-yield hydraulic props, blast barricades, and profiledtimber props to enhance productivity without sacrificingsafe underground support.

METALLURGY OF PGM

As already mentioned, the occurrence of PGM in theores of the Transvaal is most complex. Apart from themultitude of platinum-group minerals present, theirassociation is also diverse. The three main base-metalminerals present are chalcopyrite, pentlandite, andpyrrhotite. The platinum-group minerals can occur asassociations with any of these minerals, or as discrete par-ticles within the gangue minerals. It has also beenestablished that PGM can occur in :;olid solution withinthe lattice of base-metal minerals, e.g. palladium inpentlandite. Recent research work has also indicated thatPGM metals can occur within the lattice of the gangueminerals, which, with present known extraction tech-niques, renders them non-recoverable. In addition to theabove, in areas of the orebodies the base-metal mineralshave been altered and so made more refractory.

The range of minerals present, their relative densities,shape, discrete particle size, and association, all thereforepresent a challenge to the metallurgist in optimizing theprimary extraction process. This challenge is heightenedby the fact that the deposits currently being exploited arenot constant in mineralization, either along strike or downdip. Similar problems are encountered in the final separa-tion and refining processes, where, owing to the similarchemical properties of the various PGM, sophisticatedtechniques have had to be developed to give the desiredseparation and levels of purity.

Currently, the extraction process can be divided intoseveral different stages:(1) comminution of the ore and concentration by

physical techniques such as gravity concentration andflotation,

(2) pyrometallurgical concentration producing copper-nickel sulphide mattes,

(3) hydrometallurgical separation of the base metals andconcentration of the PGM product, and

(4) final refining to produce the individual PGM.

There are potential processes that claim to eliminatethe necessity for one or other of the earlier stages2S.26.

Primary ConcentrationComminution

Initially, mining was limited to the upper regions of


the orebody, Le. the oxidized zone, and, after crushingand milling, the extraction process was limited to gravity-separation methods5.27. It was only as mining progress-ed deeper into the sulphide zones and a viable treatmentroute for flotation concentrate was developed that flota-tion became an economic proposition.

The comminution processes used at present followestablished practice. Crushing is normally carried out intwo or three stages in either open or closed circuit. Thesmall stoping width in the majority of the mines resultsin the run-of-mine ore having a much smaller sizedistribution than that in conventional base-metal mining.It is practice, in Rustenburg Platinum Mines, to removeboth the primary floatable-size fines and those generatedduring the crushing process by wet screening ahead ofthe second crushing stage. This material is normallytreated on an independent flotation circuit.

The grinding circuits vary in configuration. Earlierplant design favoured two-stage grinding, consisting ofball mills in open circuit followed by closed-circuit ballmills. Newer plants tend to be based on single-stageclosed-circuit ball mills.

Impala Platinum Limited, owned by Gencor, whichstarted operations in 1968, is the only known platinumventure to eliminate conventional crushing and utilizeautogenous milling of run-of-mine ore. However, it isunderstood that, when market demands require higherthroughput rates, the mills will be converted to a semi-autogenous mode by the addition of steel balls.

From the milling point of view, the ore from theMerensky Reef is extremely hard. Bond indices of more

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than 20 kW, hit have been monitored, which can be com-pared with indices in the region of 16 kW' hit of normalgold ores.

The extreme range of mineral densities within the ore,from 2,7 for talc to between 16,0 and 17,0 for ferro-platinum, causes problems in the grinding and classifica-tion circuits. Good recovery requires that the ore shouldbe ground to a size range adequate to ensure the libera-tion of the valuable minerals. However, the classificationprocess, now mainly based on cyclones, does not differen-tiate between small particles of high-density minerals andlarger particles of lower-density minerals. It is thereforeessential for the metallurgist to control the circuit to en-sure adequate liberation for the subsequent flotation stagewhile avoiding overgrinding of the denser minerals.

To obviate this problem, corduroy tables were initial-ly used to remove the denser floatable-size particles fromthe mill discharge prior to the classification stage. In someplatinum mines, the corduroy tables have been replacedby Davcra cells, which are utilized as unit cells within thegrinding circuit. Although their presence has increasedthe problem of grinding-circuit control, their contribu-tion in preventing overgrinding and improving recoveryhas been proved conclusively. A typical comminution cir-cuit is illustrated in Fig. 19.

Gravity and Flotation ConcentrateAs mining progressed in depth, the proportion of oxide

ore decreased and that of sulphide ore increased. The in-crease in sulphide ore reduced the proportion of PGMthat could be recovered by gravity processes and increased

R

IJJ'A'

Fn.'.~ESILOS

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Fig. 19-A typical comminution circuit


that proportion recoverable by flotation. There has beencontinual controversy as to whether the removal of'metallics', by gravity concentration is advantageous orwhether flotation alone will give the desired recovery.

The term metallies is misleading in that the materialreferred to contains little metallic material. It consists offerroplatinum, braggite (Pt,Pd,Ni)S, cooperite (Pt,Pd)S,sperrylite (PtAs2), laurite (RuS2), and other denserminerals, base-metal sulphides, and chromite.

In practice most producers now rely on flotation alonefor the primary recovery of the liberated minerals,although gravity separation is still utilized to separate the'metallics' from the flotation concentrate produced. Cor-duroy material still remains the best material availablefor the collection of the fine minerals containing thePGM. Although there has been much experimentationon the development of substitutes that would reduce thelabour-intensiveness of the process, none has so far giventhe collection efficiency or ratio of concentration that canbe obtained from well-operated corduroy tables. The'cords' concentrate is redressed on a series of James tablesto produce a high-grade concentrate.

The advantages of the gravity-concentration processare as follows.(a) A high-grade concentrate is produced, reducing the

cost of subsequent treatment.(b) The smelting stage is bypassed, eliminating the losses

associated with that process.(c) Because the smelting stage is eliminated, the sales

value of the metals is realized much earlier and theprocessing inventory is reduced.

The flotation circuits employed are designed essentiallyfor the flotation of base-metal sulphides; PGM arerecovered as a consequence. However, it should be notedthat the base-metal head content of the ore is well belowthe tailings value of many conventional base-metal flota-tion circuits. It is only the presence of the PGM thatmakes the process economical.

The normal flotation circuits involve roughing,scavenging, and multistage cleaning to produce a concen-trate of the desired grade. The required residence timedepends on the mineralization of the ore. The base-metalminerals are essentially chalcopyrite, pentlandite, pyr-rhotite, or alteration products of these. Pyrrhotite isnotoriously slow-floating, and the residence times in therougher and scavenger circuits therefore tend to be ex-tended. Studies28 have shown that the floatability ofpyrrhotite greatly increases under acidic conditions, andthis was substantiated both by tests carried out on oresfrom the Stillwater Complex29 and by research work atJohnson Matthey on ores from the Merensky Reef. Thisprocedure is not yet practised on an industrial scale, andflotation normally occurs at natural pH.

The flotation reagents normally consist of coppersulphate as an activator, xanthate or a xanthate-dithiophosphate mix as a promoter, a frother, and agangue depressant. Until recently cresylic acid was themost common froth er in use, either alone or with mixesof alcohol-base frothers. The current tendency is awayfrom the use of cresylic acid to frothers that are easierto handle and of more consistent composition. Owing tothe talcose nature of the ore, use is made of a ganguedepressant, which is normally an organic colloid. Dex-

trin, natural and modified guars, and starch have all beenused.

The concentrates produced, after the removal of agravity concentrate if practised, are subjected to thicken-ing and filtering prior to smelting. At Western PlatinumLimited (Lonrho) and Impala Platinum, filtration is omit-ted because the concentrate is subjected to spray dryingprior to smelting.

The flotation tailings are thickened before being im-pounded within tailings dams. It is common practice, cer-tainly within the Rustenburg group, to cyclone the tail-ings prior to thickening, the cyclone under flow and thethickener under flow being recombined for disposal. Thispractice reduces the loading on the thickeners and im-proves the ease of operation. A typical flotation circuitis shown in Fig. 20.

As noted earlier, fines removed from the crushing cir-cuit by wet screening and classification, where practis-ed, are floated separately. This is done because theirviscosity requires an entirely different flotation densityfor optimum recovery. Similarly, owing to the finenessof the material, the unit surface area and surfacecharacteristics are different from those of normal flota-tion feed, and different rates of reagent addition arerequired.

SmeltingThe decrease in ores amenable to gravity-concentration

methods and the increased reliance on flotation for therecovery of sulphide materials in the early 1930s posedan additional problem to the metallurgist of how to enrichthe flotation concentrate to render it suitable for refining.

The first process, the chlorination process, wasdeveloped by K.L. Graham and his associates in the RandMines Laboratories. It started with roasting of thesulphide concentrate to a dull-red heat to eliminatesulphur and oxidize the base metals. The roasted concen-trate was then mixed with salt and placed in a chlorina-tion furnace maintained at a temperature of between 500and 600°C while chlorine was passed over the surface ofthe material. The PGM and base-metal sulphides werethus converted to water-soluble chlorides. The materialwas treated with acidified water and the enriched solu-tion separated from the residue by filtration. The insol-uble residue was cyanided for the recovery of gold. Cop-per was precipitated from the solution as a carbonate.After the removal of the precipitated copper, the PGMwere precipitated as a black powder by agitation with zincdust. The dried precipitate after roasting had a PGM con-tent of 70 per cent, and was suitable for refining. A smallplant using this process was constructed, but it proveddangerous to health and was shut down.

A paper' published in 1961 states 'other methods oftreating the concentrate were under intensive investiga-tion, but one of the most successful and which is nowadopted was to smelt to copper nickel matte. Preliminarywork was carried out on this method, notably by H.R.Adam at the Government Areas Laboratory, but it wasMessrs. Johnson Matthey who first successfully used thismethod on a large scale'. However, Wagner5 in 1929outlined processes developed by Krupp and Chemical andMetallurgical Corporation Limited, which appear to bevery similar to the Johnson Matthey process.


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Fig. 20- Typical flotation and filtration circuits

Initially, the concentrates produced by RustenburgPlatinum Mines were smelted by Johnson Matthey atBrimsdown, U.K. In 1937, the first blast furnace and asmall (2,4 m in diameter) Great Falls type of converterwere commissioned at Klipfontein (Rustenburg). Thesmelter was expanded to four blast furnaces, 3,0 by0,36 m at the tuyere line. The furnaces were water-jacketed and run with tapped spouts into a forehearth.Various methods of feed preparation were tried, includingsintering on a small Dwight Lloyd machine. The methodeventually adopted was to dry the concentrate in a Butt-ner Turbo dryer, and pelletize the resulting powder inLurgi pelletizing discs. The green pellets were fed togetherwith coke, limestone, and iron ore into the furnaces. Thematte was tapped periodically and blown in one of threeupright converters. The white metal was cast, crushed,and bagged for dispatch to the refineries. The converterslag was also cast and returned to the furnace. The blast-furnace slag was continuously tapped and granulatedprior to disposal.

An increased market demand for platinum, coupledwith lack of expansion room at their existing smelter,resulted in the decision by Rustenburg Platinum Minesin 1967 to construct a new smelter at their Waterval site.The then recently introduced anti-pollution laws, com-bined with the increasing cost of blast-furnace operationsand the low cost of electric power, favoured an electricfurnace. The furnace chosen was an Elkem 19,5 MVArectangular submerged-arc furnace. It is of interest tonote that, while Rustenburg Platinum was the first com-

pany in South Africa to decide to use such furnaces, Im-pala Platinum commissioned their smaller furnace in1968, when that mine started operations.

The Rustenburg process has been described by Mostertand Roberts3O. The furnace has a rating of 19,5 MVA,with energy input by means of three pairs of electrodesrated at 6,5 MVA per pair. The electrodes are of theSoderberg type and are 1,25 m in diameter, each with acurrent density of 2,65 AI cm2. The electrode distancecentre to centre is 3,4 m between phase pairs and phases.The secondary voltage of the transformer can be variedbetween 170 and 350 V, with a maximum electrode cur-rent of 32 400 A.

The concentrate is dried in Buttner dryers. The driedconcentrate (7 per cent H2O) is fed to pelletizing pans,which are 3 m in diameter and produce pellets 15 mm indiameter with a moisture content of 10 per cent and abreaking strength of 5 to 6 kg. No binding agent is used.The pellets are dried to 2 per cent moisture in roto-Iouvredryers, and the crushing strength increases to between 9and 13 kg. The pellets and fluxes, mostly limestone andoccasionally iron ore, are fed through a proportionalweighing system. Molten converter slag is returned to thefurnace through a launder at the matte-tapping end wall.Furnace slag is tapped continuously and granulated priorto treatment in a slag-grinding and flotation circuit. Matteis tapped at regular intervals and converted in Peirce-Smith type converters. The converter matte is cast intomoulds, crushed to minus 25 mm, and bagged fordispatch to the refiners.


Electric-furnace submerged-arc smelting is also prac-tised by Impala Platinum Limited and by WesternPlatinum. It is understood that the converter matte fromall three smelters is of similar composition, assaying 1500to 2000 g/t PGM, approximately 50 per cent nickel, 28per cent copper, 1 to 2 per cent iron, and approximately21 per cent sulphur. A typical smelter flowsheet is givenin Fig. 21.

U.G.2 ReefThe U.G.2 Chromite seam has not been exploited to

any great extent, mainly owing to economics and the dif-ficulties in effecting a clean separation between thechromite, the base-metal sulphides, and the platinum-group minerals. Difficulties are also experienced duringthe smelting stage owing to the tendency of the chromiteto 'freeze' in the slag and build up in the furnace.

Most platinum-producing companies have beenresearching the primary recovery and smelting processesto develop viable processes for the exploitation of thisdeposit. Understandably, the companies are reticentabout publishing their results.

The National Institute for Metallurgy, now the Coun-cil for Mineral Technology (Mintek), has also carried outconsiderable research on these ores. They have shown thatgood recovery and separation of the PGM and chromitecan be obtained by the use of a combination of gravity-separation and flotation methods, and good recovery ofthe PGM alone by flotation31.32.

J .C.I. has patented a process for the smelting of a con-centrate with a high content of chromium33. This in-volves the smelting of the concentrate in the presence ofa carbonaceous reductant to produce a slag phase, a mattephase, and a ferronickel alloy containing PGM.

Texas Gulf was well advanced on the treatment ofU.G.2 concentrates by the use ofthe expanded precessiveplasma process. Again, the current state-of-the-art hasnot been published.

It is known that Western Platinum are successfullyexploiting the U.G.2, utilizing conventional flotationtechniques for the recovery of the PGM. The chromite-rich tailings are impounded in separate tailings dams forfuture treatment, and the flotation concentrate is smeltedin a circular submerged-arc electric furnace either aloneor with Merensky concentrate.

As a result of the stringent anti-pollution regulations,all current smelting operations have associated sulphuricacid plants for the treatment of converter off-gases. Theseprocesses are not described here, and the reader is refer-red to a paper by Plasket and Ireland that describes themanufacture of sulphuric acid at Impala PlatinumLimited34.

Separation of Base MetalsOriginally, all the converter matte (white metal) pro-

duced by Rustenburg Platinum Mines (the sole producerin South Africa until 1966) was treated by Johnson Mat-they at their Brimsdown Works, in the U.K. The processused was the Or ford process (or 'tops and bottoms' pro-cess), in which the matte is smelted with salt cake andthe copper is passed to the 'tops' and the nickel to the'bottoms'. The two elements were separated physicallyand recovered by roasting and dissolution as sulphates.


However, a new process was soon introduced in whichthe copper sulphide 'tops' are blown to blister copper andcast into anodes for electrolytic refining. The nickelsulphide 'bottoms' are ground and roasted to oxide form.The nickel oxides are reduced to metallic nickel with coalin a reverberatory furnace, and are cast into anodes forelectrolytic refining. The anode slimes from both electro-lytic sections contain the platinum metals and are thentreated in a platinum refinery.

In 1954 Matte Smelters (Pty), a company jointly own-ed by Rustenburg Platinum Mines and Johnson Matthey,started operations in Rustenburg, using the Brimsdownprocess to treat part of the smelter matte. In the mid 196Osfollowing commercial transactions, Rustenburg Platinumas part of the deal agreed to supply Engelhard Mineralswith a quantity of gravity concentrate and matte arisingfrom tributed mining areas. This material was treated intwo plants in Newark, New Jersey.

The separation process utilized by Engelhard involvedmelting of the matte and casting it into anodes. Theanodes were subject to electrolysis, the contained cop-per being deposited at the cathode. The nickel remainedin solution in the sulphuric acid electrolyte, while theplatinum metals reported to the anode slimes. The cop-per cathode was refined, and the nickel sulphate solutionwas purified and crystallized. The anode slimes weretreated chemically to remove sulphur and concentrate thePGM, which were then extracted and purified35.

Johnson Matthey also developed a direct electrolysisprocess for converter matte similar to the Engelhard pro-cess, which was used at Brimsdown. J .c.1. ResearchLaboratories developed a pressure-leaching process inwhich the nickel and copper were dissolved in successivestages and recovered by electrowinning. The PGM re-mained in the residues, which were upgraded prior torefining. This process was introduced to Matte Smeltersin 1966.

With the start of opertions at Impala Platinum Minein 1968, Union Corporation established a refinery at EastGeduld, near Springs. The converter matte is treated bythe Sherritt Gordon pressure-leaching process, which in-volves successive stages of acid-oxidation leaching. Nickelis removed in the first stage, and, after being modifiedwith ammonium sulphate, the solution is reduced withhydrogen under pressure to produce a nickel powder.Copper is removed in the second stage and recovered byelectrowinning. The residue from the second stage isleached further under acid conditions, and the finalresidue, rich in PGM, constitutes the feed to the metalsrefinery of Impala Platinum, which is situated on thesame site. It is understood that the process36 has sincebeen modified, but exactly how is unknown.

In 1974, Rustenburg Platinum Mines and MattheyRustenburg Refiners commissioned a new plant for thetreatment of converter matte by a process that had beendeveloped by Johnson Matthey and piloted at Rusten-burg. In the process, the cooling rate of the convertermatte is controlled from the commencement of solidifica-tion to at least the completion of crystallization, produc-ing at least two phases within the matte: a PGM-freenickel-copper matte, which is non-magnetic, and a PGM-rich phase, which is magnetic. The phases are separatedby grinding of the matte and magnetic separation, each

DISINTEGRATOR PELLErr"NGOISC

FLUXSTORAGE

WEIGHER

CONE CRUSHER

Fig. 21-A typical smelter flowsheet

phase then being treated separately. The nickel-coppermatte is subjected to two-stage acid leaching under anoverpressure of air. The primary leach is an oxidizingpressure leach with sulphuric acid, the leaching solutionbeing a mixture of tankhouse spent electrolytes. Condi-tions are controlled to maximize the dissolution of nickelwhile retarding the dissolution of copper. The resultantsolution is then purified for the removal of the copper,iron, lead, and cobalt prior to recovery of the nickel byelectrowinning. The cobalt removed from the solution ispurified and produced as crystals of cobalt sulphate. Theresidue from the primary leach passes to the second leach.Spent electrolyte from the copper tank house is utilizedas the leaching solution. The resultant leach liquor,following purification (specifically the removal ofselenium) is subjected to electrowinning for the recoveryof copper..

The cleaned magnetic concentrate is also subjected tothree stages of leaching, nickel and copper being dissolvedin sulphuric acid and the leaching conditions beingcarefully controlled to minimize the dissolution of PGM.After filtration, the leach residue is suitable for dispatchto the PGM refinery. The solution rich in base metalsjoins the solutions from the leach of the non-magneticfraction for the recovery of the base metals.

The flowsheet for the recovery of the base metals isillustrated in Fig. 22. All the converter matte fromRustenburg Platinum Mines is now treated by thisprocess37.

Refining of PGMIn the early stages of the industry, virtually all the refin-

ing of the PGM from South African ores was carried outby J ohnson Matthey at their Ratton Garden Refinery,and latterly at their Royston Plant. Engelhard were alsoinvolved in refining a very small proportion of the PGM.

nSTACK

PRECIPITATOR~ PRECIPITATOR

r~FLUE DUST TO MILL VIA II ,~ THICKENERS

Im" FLUE

GAS

CONVERTER

SLAGReTURN

WEIGHING

ANDDISPATCH

~11 MATTE

L [1)11 I I11 1111I\' njA'"

MOULDSUU CRUSHER

~

As the demand for platinum increased, it becamenecessary to increase the refining capacity, and in 1969a plant, also totally owned by Johnson Matthey, waserected at Wadeville, near Germiston. In 1968, after thestart of Impala's operations, their refinery at Springs wascommissioned. In 1971, Western Platinum started opera-tions, the converter matte produced being treated atFalconbridge Refinery, in Norway. The PGM-containingresidues were refined by Engelhard Industries until 1974,when Lonrho opened their own refinery at Brakpan.

I-A;..mi=-~~ ;-~~~~DUEI ~ "Y-,:--'-- Yi,: LL :-d i L-tl

\ iOC~tt~!flt-

ff

-r~~~ - ~~~~DUE

I I ~ I 'REM~V~ I R~MOVAl: I ! I I

I L _I I t SEl'NIUM.

~ ~ I RESIDUE: I

~hJ;~~~ - -r-~f~~~~~~~i~l I I \ L, c~~:~;

I : i:::

~I I , - t I ! COBALTI I I

--t--I ---SULPHATE\ : : I I CRVSTAlS

: L+ , i :

f

:N, ElEC TRowlNNING : : 1 !I ~ I ~ ElECTRDWINNING

',,::,~OI ~--L~~~~--~::::::I ,

'

{

,-A ~ D"SOlVE~ ~

Y ---

I

NiIOH),

SODIUM I

:RU~,,":C~~~ -CAU5TIc -CAU5TIc

L1}-----SODA I

~.I SOOIUM

PRECIPITATION 1 --r ~~~-:~AA,Ti1 1

LEACHING{

PURIFICATION

Fig. 22-Flowsheet for the base-metal refinery

JUNE 1985 179JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

The refining of PGM is a complex operation, involv-ing the separation and purification of the six PGM metals(platinum, palladium, osmium, ruthenium, iridium, andrhodium), gold, and silver. The conventional or classicalprocess depends on selective precipitation of the metalsfrom solution, the chemistry of the process being basedessentially on the techniques originally used to isolate theelements. The complexity leads to many different variantsof processes relying on the same chemistry. The opera-tions of Matthey Rustenburg Refiners at Royston can beregarded as typical modern practice.

The gravity concentrate is roasted for the removal ofsulphur, and leached for the removal of soluble basemetals. The residue is then dissolved and reducedchemically to precipitate a crude gold. Hydrolysis atabout pH I precipitates deleterious base metals, whichare filtered off. The solution is then oxidized, andruthenium and osmium tetroxides are distilled off. Fur-ther hydrolysis precipitates rhodium and iridium, togetherwith copper. Semi-refined platinum is then precipitatedby the addition of ammonium chloride, followed by theprecipitation of palladium as a complex amine. A parallelstream is employed for the treatment of the product fromthe leaching process used on the copper-nickel matte.

The semi-pure platinum and palladium complex pro-ducts are calcined and red issolved before being subjectedto a similar process route that leads to the output of pureproducts. The other PGM are refined individuallythrough a number of stages utilizing the characteristicsof their ammonium complexes for the extraction of theindividual metals.

A description of the Engelhard process has beenpublished35, and an outline of a further variation to theconventional process is given by Edwards38. The majorobjection to these techniques is that the separation isnever ideal, necessitating multistage purification and com-plex recycles.

Considerable research work has been carried out onthe development of less complex and more efficient pro-cesses. Both Johnson Matthey and Mintek evolved pro-cesses utilizing solvent-extraction and ion-exchangetechniques, although the two processes differ in manyrespects. The solvent extraction of gold is well known andhas been used commercially for some years. The gold isextracted as AuCl4 with reagents such as methyl isobutylketone and dibutyl carbitol. The gold is recovered asmetal by direct reduction from the organic phase.Platinum can be removed in the absence of palladium,and gold by ion exchange, if iridium is in the Ir(III) oxida-tion state, using tri-n-octyl amines. The extraction ofpalladium based on hydroxy-oximes is in use, which,when coupled with accelerating additives, overcomes theslow kinetic reactions.

The extraction of ruthenium from the chloro-speciesis difficult. However, the removal of these as tetroxidesby the distillation of carbon tetrachloride extractant isknown. Iridium can be oxidized to the Ir(IV) state andextracted by the use of amine solvents, and rhodium canbe recovered by either ion exchange or conventionalprecipitation methods. The chemistry and kinetics involv-ed in both the Johnson Matthey and Mintek processesare described in various papers39-42.

The Mintek process employs a novel pre-Ieaching treat-

ment in which the concentrates are alloyed withaluminium, which, it is claimed, greatly enhances leachingin hydrochloric acid in the presence of chlorine. The alloy-ing procedure is covered by patent43. The J ohnson Mat-they process is in use commercially at Royston. It isunderstood that the Mintek process is either partly ortotally used by Impala at Springs and by Lonrho atBrakpan44-46.The flowsheets of both processes are givenin Fig. 23, which shows the difference in approach.

The advantages claimed for the solvent-extraction pro-cesses are as follows:(a) increased operational safety by the elimination of the

allergenic problems created by some platinumcompounds,

(b) reduced overall processing time,(c) improved primary yields of each element,(d) total recovery of all the elements, and(e) reduced recycling, and thus reduced process

inventory.

With such advantages it is likely that the solvent-extraction process will be used in any future installation.

END USES OF PGM

In terms of the South African industry, platinum is ofprime concern, with palladium and rhodium attractingmore attention than ruthenium, iridium, and osmium.The uses of platinum, and to a certain extent its associatedmetals, are split into two main disciplines: one dependingon their unique physical and catalytic properties, and theother on the more esoteric precious nature of the PGM,i.e. their store of value. The industrial and scientific usesdepend on their physical properties, and the use ofplatinum in jewellery and as an investment medium reliesmainly on its rarity.

JewelleryPlatinum in jewellery has roots in history, being a

popular metal before the Second World War, when owingto its strategic value in industry it was withdrawn fromthe jewellery market. Its return has been slow, hinderedby a lack of knowledge about the metal in consumermarkets. Apart from its rarity, platinum has greaterstrength than silver and gold, which gives it superiorstone-setting qualities and the potential to be used indelicate and unique designs. It is usually alloyed withother PGM and some base metals to improve the metal-working characteristics. Palladium, rhodium, and iridiumare among the other PGM used. In Europe and NorthAmerica, the hallmarking standards specify at least 95per cent platinum, but in Japan, where the main alloy-ing metal is palladium, specifications range from 80 percent platinum upwards. The Japanese platinum-jewelleryindustry is the largest in the world and at its peak con-sumed almost one-third of the world production. In addi-tion, the Japanese jewellery industry is a significant con-sumer of palladium. The demand for platinum injewellery in the U.S.A. is relatively small, but in EuropeWest Germany is leading a fledgling industry that hasdoubled its demand for platinum in the past two years.

InvestmentThe use of platinum in the production of coins and bars


Johnson Matthey's Solvex Process

Concentrate

IDissolve

IFilter- Residue- Treat - Ag

IDiscard

Solvent - Au + Base metals - Solvent - Auextraction extraction 2

IBase metals

Solvent - Pdextraction 3

IDistillation - Redistillation - Os

JuSolvent - Pt

extraction 4

ISolvent - Ir

extraction

IIon exchange - Rh

IBase metals

Fig. 23-Comparlson of the Johnson Matthey and Mlntek processesfor the refining of the PGM

(palladium bars are also produced) specifically for the in-vestment market is a recent development. Interest inplatinum, and to a lesser extent palladium, has grownwith the popularity of gold as an inflation hedge, andwithin the past three years platinum bars in sizes rangingfrom 10 tr. oz down to 1 g have been marketed inAmerica, Europe, and Japan. These are designed forhoarders rather than for speculators. The year 1983 sawthe launch by the Isle of Man of a 1 oz platinum coinas an investment vehicle. Simultaneously, platinum in-gots of various sizes were launched in America, Europe, .

and Japan.

Industrial UsesTheir physical properties have resulted in a wide variety

of industrial uses for the PGM. Among these are highmelting points, an ability to resist attack by most mineralacids and chemicals other than halogen elements, and aselectivity in catalytic uses. Th~ major uses are found inthe chemical, electrical and electronic, glass, andautomotive industries.

Automotive IndustryThe use of platinum in the automotive industry is fairly

recent, resulting from emission-control legislation in theU. S.A., and rivals jewellery as the largest single use inthe world. The exhaust gases are passed over a catalystthat contains platinum, palladium, and rhodium in theratio 67:26:7, which converts the hydrocarbons, carbon

Mintek Process

Concentrate

IFormation of

aluminiumalloy

ILeaching of- Base-metalbase metals effluent

ICI/HCIleaching

IAu-Ag

precipitation

IFilter - Au-Ag

I

cake

Solvent - Pd + Pt - Solvent - Pdextraction extraction 2

II

DistillationPt

-Os

ISolvent - Ru

extraction 3

IIon - lr

exchange

IRh

purification

IBase metals

-Rh

monoxide, and nitrous oxide to harmless emissions. Theratios of PGM in catalysts vary considerably, dependingon the size of the engine and the automobile manufac-turer. The approximate quantity of PGM per automobileis 2,4 g.

At present, legislation in the U.S.A. is confined in themain to gasoline-powered automobiles. Standards havebeen proposed for the control of particulates from diesel-powered engines, which is likely to result in an increasedusage of platinum. Japanese automobile emissions aresimilarly controlled, significant amounts of platinumbeing required by Japanese manufacturers for vehicularexhaust catalysts.

A major new market for the use of PGM in automobileemission control is expected to arise in Western Europe.U nleaded gasoline is expected to be phased in over thenext decade, which will allow the use of PGM catalysts,but some countries are not prepared to wait beyond 1986,which is likely to precipitate the introduction of catalysts.The expected demand arising from Western Europe couldeventually match that from the U .S.A.

Also in the automobile application, research anddevelopment continue into the use of PGM in a catalyticengine. The main purpose of the use of catalysts is toreduce compression ratios and thereby enhance fueleconomy and reduce toxic emissions.

Glass IndustryThe glass industry utilizes the high melting points of


the PGM and their resistance to the abrasive nature ofmolten glass. In the manufacture of high-quality and op-tical glass, unalloyed platinum, platinum alloyed withrhodium, or platinum cladding of molybdenum andrefractories is used in the construction of the equipment.Platinum does not contaminate molten glass. In themanufacture of glass fibre, platinum. often alloyed withrhodium or in a grain-stabilized form, is used in themanufacture of bushings and spinnerets.

Chemical IndustryIn the chemical industry, PGM are used extensively as

catalysts, as well as in chemical analysis and in laboratoryequipment such as crucibles, forceps, combustion vessels,and filters. Protective devices made from platinum-rhodium alloys are used in the manufacture of burstingdiscs. PGM are also used in anodes in the manufactureof hydrogen peroxide.

The major catalytic use is in the production of nitricacid. Platinum alloyed with rhodium is drawn into finewire and woven into a gauze. Several of these gauzes areinstalled together in reactors where the catalytic oxida-tion of ammonia occurs. Gauzes of platinum alloys, whenin use, give up part of their mass to the gas stream thatis flowing across them. To reduce this loss, catchmentgauzes of palladium alloy are fitted downstream, andthese recover 70 per cent of the platinum lost. The mainuses of nitric acid are in the manufacture of fertilizersand explosives, the latter being widely used in the min-ing and demolition industries.

Other main catalytic uses are the reforming ofpetroleum to higher-octane fuels, the production ofaromatic chemicals, and the production of hydrocyanicand sulphuric acids. Palladium and rhodium are used inthe catalysis of fat and polymer hydrogenation reactions,rhodium being prominent in hydroformylation reactions.Ruthenium and its complexes are extremely versatileoxidation catalysts. They catalyse the oxidation of vir-tually any oxidizable organic functional group, and, bychoice of the appropriate conditions, the oxidation reac-tions can be made to proceed in high yield and selectivi-ty. They are used in the reforming of natural gas, the pro-duction of diesel fuel, and the synthesis of ammonia.

Electronics IndustryThe electrical and electronics industry is one of the

growth areas for PGM. Palladium is predominant in theelectro-mechanical industry, relying on its resistance tocorrosion for its application in connectors, sensors, andrelays. Mechanical switching devices in telephone ex-changes were a major application, but this is being replac-ed by electronic switching.

By far the major use of palladium in th~ electronicsfield is in 'thick film' hybrid integrated circuits (ICs). A'thick film' is a metal-glass suspension deposited ontoa substrate by silk-screen printing and bonded to thesubstrate by firing at very high temperatures. Rutheniumis also used in considerable quantities in the 'thick film'application. The palladium in ICs forms conductors a~dcapacitors, and the ruthenium forms resistors. Together,these are the basis for virtually all modern telecom-munication systems and digital displays. Platinum is usedon similar applications where reliability is more critical.It is technically the best metal for 'thick film' circuits,

its higher melting point allowing for higher firingtemperatures, and therefore stronger bonds to thesubstrate or dielectric.

Other Industrial UsesOther industrial uses of PGM occur in the manufac-

ture of thermocouples, which are used mainly in the steelindustry, in the cathodic protection of steel structures incorrosive environments, and in the manufacture of fumedetectors. There is a demand for PGM brazing alloys,and platinum-cobalt alloys are used in the making ofpowerful magnets.

PGM, palladium in particular, have the ability to ab-sorb up to 800 times their own volume of hydrogen atroom temperature. This property is utilized in steady-statediffusion technology to purify hydrogen. Palladium-silver alloys are used in portable hydrogen plants and toclean up waste gases, recovering hydrogen as a usefulsource of fuel.

MedicineOn the medical side, platinum has found application

in the prophylactic and therapeutic aspects of both humanand veterinary science. One particular compound, CISplatinum 11, is now an established drug for the treatmentof genito-urinary types of cancer, and second-generationcompounds, having a reduced toxicity, are at an advancedstage of development. Osmium is used in the manufac-ture of drugs for the treatment of arthritis. One othermedical application in which platinum is used is in themanufacture of heart-assist pacemakers. The noblecharacter of the metal makes it ideal for minimizingadverse reaction by the body.

In dentristry, PGM confer hardness, strength, and cor-rosion resistance on dental alloys. Palladium, as a resultof its relatively low price compared with that of gold orplatinum, is now the most favoured metal, but its use inalloys is limited to 25 per cent, above which the alloybecomes too hard. Base-metal alloys are cheapersubstitutes.

PowerThe final area, which is more a use for the future, is

in the area of power generation. There are several aspects,but the main one appears to be a catalytic use inphosphoric acid fuel cells. The fuel cell is the basicbuilding block of a power plant that generates electricityby catalytically combining hydrogen and oxygen to formwater. Extensive research and development are being con-ducted in Japan and the U.S.A., where the technologyhas been demonstrated, but its reliability so far has beenuncertain. It is unlikely that considerable commercializa-tion will occur before 1990.

Among other uses, platinum is employed in electrodesfor the generation of magnetic hydrodynamic power, andfor the impregnation of steel used in the manufacture ofgas turbine blades, and could be used in the future in thephoto-dissociation of "water to produce hydrogen as a fuelusing sunlight as a source of energy.

Current Market SituationThe main platinum producers of the world are concen-

trated in the U .S.S.R. and South Africa, and on a verylimited scale in Canada. South African producers haveat times been responsible for up to 94 per cent of Western


World production. Accurate information about theSoviet production is difficult to obtain, but it is believedthat the U .S.S.R. produces approximately 30 per cent ofthe world's supply, leaving almost 70 per cent to be at-tributed to South African companies.

Producers have various options in distributing thePGM in the marketplace. Major individual users, whonormally require a stable, predictable, and reliable supplyover long terms, have tended to contract direct with pro-ducers. The latter used to maintain a stable price indepen-dent of the free market, but in recent years they have settheir daily prices in line with the free market save forspecial long-term contracts, which still carry stable prices.As users invariably need the PGM in fabricated form,it is usual for the metals to be delivered to fabricatorsat some stage for the manufacture of actual product. Analternative, which is generally the preferred case, is thepurchase of the product from fabricators who havesecured the PGM supply themselves. Most fabricatorshave long-term contracts with producers for a basic sup-ply, and rely on free-market sources for the additionalrequirements. The free market has developed con-siderably in the past decade, and has become an impor-tant intermediary between producers, fabricators, andend-users. The main participants in the market are theprecious-metal dealers and traders. They operate in-dependently or in conjunction with fabricators and pro-ducers, securing deals between themselves and betweenend-users and fabricators.

Official markets also exist that provide a centralized,organized facility for market participants to trade andlayoff price risk. The first market to develop futurestrading in platinum was the New York Mercantile Ex-change (NYMEX). Trading started in a platinum futurescontract in 1956, followed by a palladium futures con-tract in 1968, but it is only in the past five years thatsignificant trading volumes have been recorded. However,much of the increased volume has been attributed tospeculator interest, which has become a large influenc-ing factor on the price. The price established in opentrading on NYMEX has become an important referenceprice around the world. Other references on the worldprice for platinum are the price fixes established in Lon-don twice a day at 10.15 a.m. and 4.15 p.m. by two ma-jor dealers, Ayrton Metals and Samuel Montagu. Asecond futures market for platinum was opened in Tokyoin 1984, which provides another forum for hedging. Thelatest development is the possible establishment of aplatinum options market on NYMEX.

Platinum Statistical PositionThe supply and demand in the Western World is shown

in Table 11, and the demand by application is shown inTable III for Japan and Table IV for North America.In regard to these tables, the following should be noted.

(1) Differences occur between the totals for each yearin Tables III and IV and those in Table 11as a resultof rounding off of values.

(2) The supply figures are estimates of sales by the minesof primary p-latinum. The demand estimates shownin this paper are net figures, the demand in each sec-tor being the total purchases by consumers less anysales back to the market. Thus, the annual totals

represent the amount of newly mined metal that isacquired by consumers in any particular year.

(3) Movements in stocks in a particular year reflectchanges in stocks held by other than primary refinersand final consumers, such as metal in the hands offabricators, dealers, banks, and individuals. Apositive figure indicates an increase in stocks, in-cluding some platinum bought for investment; anegative figure indicates a rundown in stocks.

(4) Hoarding is the long-term holding of metal for in-vestment. In this paper, hoarded metal is defined asinvestment bars and coins weighing 10 oz or less. The'other applications' sector in Table 11includes somelarger bars or ingots acquired for investment pur-poses, especially in Japan.

Table V gives some indication of the breakdown ofplatinum and palladium demand into end-uses. Forpalladium, the electrical and electronics usages are givenseparately for more detail, but the chemical uses arereported collectively. The use in each category can becalculated in troy ounces from the total palladium con-sumption, which is approximately 3 million ounces.

ACKNOWLEDGEMENTS

The authors thank Rustenburg Platinum Mines, Ltd(Rustenburg Section, Amandelbult Section) and J ohan-nesburg Consolidated Company Ltd for their assistancein the draughting and typing of this paper. Messrs J. vanRooyen and G. Holder are thanked for their assistancein the sections dealing with ventilation and rockmechanics. The critical comments of Mr R.B. Sutherlandand Mr R.R. Will were greatly appreciated.

REFERENCES

1. BEATH.CB., COUSINS. CA., and WESTWOOD.R.J. (1%1). The ex-ploitation of the platiniferous ores of the Bushveld Igneous Com-plex with particular reference to the Rustenburg Platinum Mines.Proceedings Seventh C. M. M.!. Congress, vol. I, p. 217.

2. BARTHOLOMEW. R. History of platinum exploitation in SouthAfrica. Johannesburg, Johannesburg Consolidated Investment Co.,Internal report, 1982.

3. McDoNALD. D., and HUNT. LB. A history of platinum and itsallied metals. London, Europa .Publications, 1982.

4. W AGNER. P.A. Preliminary report on the platinum deposits in thesouth eastern part of the Rustenburg District. Washington, V.S.Geological Survey, Mem. no. 24. 1926.

5. WAGNER. P.A. The platinum deposits and mines of South Africa.Cape Town, Struik, 1929.

6. MILES. D.J. The recovery operations at No. 4 shaft, BafokengSouth Mine, following the breach of the No. 1 tailings dam. Papersand Discussions, Assoc. Mine Managers S. Afr., 1974-1975. p. 501.

7. BOVELL. R.C. Bafokeng Mine-a general description of the firstthree years of operation. Ibid., 1970-1971. p. 213.

8. KORF. CoW. Notes on the sliping of the raise-bored ore-pass atSpud Shaft. Ibid., 1976-1977. p. 271.

9. HINDLE. E. V. Some devices in use at Rustenburg Platinum MinesLtd (Rustenburg Section). Ibid., 1962-1963. p. 1107.

10. BEATH. CB. The application and maintenance of standard min-ing practices on Rustenburg Platinum Mines. Ibid., 1956-1957. p.365.

11. CHADWICK. J .R. Impala Platinum preparing to pass 1 000000ounces yearly. Wld Min., vol. 33, no. 12. 1980. p. 42.

12. NEwMAN. S.C. Platinum. Trans. Instn Min. Metal/., Sec. A (Min-ing Industry), vol. 82. 1973. pp. 52-68.

13. MILES. D.J. Some methods of improving the utilisation and pro-ductivity of Black labour on the mines of Impala Platinum Ltd.Papers and Discussions, Assoc. Mine Managers S. Afr., 1974-1975.p.479.


1977 1978""uu.,u,,,

Sales in Cbblaand Eastern Europe 2 4

Movementin stocks (decrease) (6) (5)

Total demand 78 82

TABLE IIIJAPANESE PLATINUM DEMAND (TONS)

Usage 1977 1978 1979 1980 1981 1982 1983 1984

Jewellery 26,1 26,0 18,4 13,7 19,4 19,3 17,4 19,4Autocataiyst 2,5 5,6 6,2 6,5 5,9 5,3 5,3 5,3Chemical 0,3 0,3 0,3 0,3 0,3 0,3 0,3 0,5Electrical 0,5 0,5 0,4 0,4 0,5 0,6 0,6 0,9Petroleum 0,6 0,5 0,3 0,5 0,5 0,5 0,5 0,6Glass 0,9 1,2 1,2 1,2 1,6 1,4 1,9 2,3Hoarding 0,2 0,5Others 3,3 2,3 1,7 6,5 7,6 5,3 3,4 5,9

-34,2 36,4 28,5 29,1 35,8 32,7 29,6 35,4

TABLE IVNORTH AMERICAN PLATINUM DEMAND (TONS)

Usage 1977 1978 1979 1980 1981 1982 1983 1984

Jewellery 0,5 0,6 0,5 0,5 0,5 0,5 0,5 0,5Autocatalyst 11,0 13,4 20,8 13,7 13,4 14,2 13,1 16,2Chemical 2,8 4,4 4,0 3,6 1,6 2,5 3,1 4,0Electrical 3,0 3,1 4,0 4,5 2,2 2,2 2,8 3,0Petroleum 2,5 3,3 6,1 4,4 1,7 0,6 0,5 0,5Glass 2,0 3,1 3,1 1,6 0,6 0,3 0,5 0,9Hoarding 1,2 1,2 0,9Others 2,8 2,3 3,0 2,3 1,9 0,6 0,8 1,1

24,6 30,2 41,5 30,6 21,9 22,1 22,5 27,1


TABLE 11PLATINUM STATISTICAL POSITION (TONS)

1979 1980 1981 1982 1983 1984

(3)

871588

(4)

735

787

763

84

Source: Rustenburg Platinum Mines, Johnson Matthey

--"

TABLE VEND-USES OF PLATINUM AND PALLADIUM

Commodity End-use %

Platinum Autocatalyst 28Jewellery 30Electrical/ electronics 7Petroleum refining 1Glass 5Hoarding 7Other 11Chemicals 11

Palladium Autocatalyst 7Jewellery 9Electrical/electronics 7/25Dental/medical 23Petroleum refining 7GlassHoardingOther 3Chemicals 19

14. KORF.e.W. Stick and pillar support on Union Section, Rusten-burg Platinum Mines. Ibid., 1977-1979. p. 71.

15. VANDERMEULEN.W.J., and HARRISON.e.R. The Demag stopedrill rig. Ibid., 1976-1977. p. 219.

16. FORSDICK.W.G. Notes on the sliping of a 1,82 m raiseborer holeinto a 6,096 m ventilation shaft at Rustenburg Platinum Mines Ltd(Rustenburg Section). Ibid., 1974-1975. p. 69.

17. SAFFEY.A.A., and MEIKLEJOHN.T.e. The manufacture of am-monium nitrate fuel oil mixture explosives on Western PlatinumLtd. Ibid., 1974-1975. p. 277.

18. SAFFEY.A.A. Underground stope face photography as an aid tograde control at Western Platinum Ltd. Ibid., 1974-1975. p. 523.

19. BEATH.C.B. Delay blasting in development ends with delayedoperation of water-blast. Ibid., 1958-1959. p. 241.

20. SUTHERLAND.R.B. Platinum mining in South Africa. Presentation,Pilanesberg Room, Sun City, Bophuthatswana, 1984.

21. HARRISON.C.R. A badge reader labour control system at Rusten-burg Platinum Mines, Ltd. Papers and Discussions, Assoc. MineManagers S. Air., 1978-1979. p. 375.

22. HARRISON,e.R. Self service lamp room at Rustenburg PlatinumMines, Limited, Rustenburg Section. Ibid., 1978-1979. p. 361.

23. BUDAVARI,S. Rock mechanics in mining practice. AustralasianInst. Min. Metal/., Series 5, 1982.

24. WIGGILL.R.B. Effect of different support patterns on stratabehaviour. J. S. Air. Inst. Min. Metal/., 1963.

25. BARR. W.M. Recovery of precious metals values from ores. V.S.Patent 3,988,415. 1976.

26. ELECTROHEATPRoPRIETaRY LTD. Improvements in the recovery ofvalues from ores containing precious metals and gold. S. Air. PatentApp. 73/5634, 74/6550.

27. PRENTICE, T.K., and MURDOCH. R. Recovery of platinum from thedunite rocks at Onverwacht, Transvaal. J. Chem. Metal/. Min. Soc.S. Air., 1929.

28. HANG e.S., COOKE. S.R.B.C., and IwAsAKI, I. Flotationcharacteristics of pyrrhotite with xanthates. Trans AIME MinBranch, 1954.

29. BENNETS. J., MORRICE, E., and WONG. M.M. Preparation ofplatinum-palladium, flotation concentrate from Stillwater Com-plexOre. U.S.B.M. Report on Investigation 8500.

30. MOSTERT. J.e., and ROBERTS.P.N. Electric smelting at RustenburgPlatinum Mines Ltd of nickel-copper concentrate. J. S. Air. Inst.Min. Metal/., 1973.

31. OVERBEEK, P.W" et al. The recovery of chromite and platinumfrom the UG 2 Upper Chromitite Layer of the Bushveld IgneousComplex at the Pandora Mine. Johannesburg, National Institutefor Metallurgy, Report 1941.

32. OVERBEEK.P. W. Pilot-plant tests for the recovery of chromite andnoble metals from the UG 2 Reef at Maandagshoek. Ibid. 211.

33. JOHANNESBURG CONSOLIDATED INVESTMENT CO. LTD. Smelting pro-

cess. S. Air. Patent App. 77/4202. 1977.34. PLASKET. R.P., and IRELAND. D.A. Ancillary smelting operations

and sulphuric acid production at Impala Platinum Ltd. J. S. Air.Inst. Min. Metal/., 1976.

35. PAPADEMETRIOU. T., and GRASSO. J .R. Recovery of preciousmetals from South African mattes. Metall. Soc. AIME, Paper selec-tion 70-59, 1970.

36. PLASKET.R.P., and ROMANCHUK.S. Recovery of nickel and copperfrom high grade matte at Impala Platinum by the Sherritt Process.Hydrometal/., no. 3, 1978.

37. MATTHEY RUSTENBURG REFINERS. J. S. Air. Inst. Min. Metal/.,1981.

38. EDWARDS. R.I. The refining of the platinum-group metals. Johan-nesburg, National Institute for Metallurgy, Report 1744, 1975.

39. REOVILL, L.R.P., and CHARLESWORTH. P. The application ofsolvent extraction to platinum group metals. International SolventExtraction Conference, Liege, 1980.

40. CLEARE. M.J., CHARLESWORTH, P., and BRYSON. D.L Solventextraction in platinum group metal processing. J. Chem. Tech.Biotech. 29. 1979.

41. CLEARE, M.J., GRANT. R.A., and CHARLESWORTH. P. Separationof platinum group metals by the use of selective solvent extractiontechniques. Proceedings Extraction Metallurgy 81. London, Institu-tion of Mining and Metallurgy, 1981.

42. EDWARDS R.I. Selective solvent extractants for the refining ofplatinum-group metals. International Solvent Extraction Con-ference, Toronto, 1977.

43. NATIONAL INSTITUTEFORMETALLURGY.A process for the treatmentof mixtures of platinum group metals and gold. S. Air. Pat. App.750593. 1975.

44. MATTHEY RUSTENBURGREFINERS. Improvements in and relating tothe refining of metals. S. Air. Pat. App. 747921. 12th Dec., 1974.

45. MATTHEY RUSTENBURGREFINERS. Improvements in and relating tothe separation of metals. S. Air. Pat. App. 747922. 12th Dec., 1974.

46. NATIONAL INSTITUTE FOR METALLURGY. The separation andpurification of platinum and palladium. S. Air. Pat. App. 763679.1976.

Platinum-group metalsA seminar on platinum-group metals is being planned

by the International Precious Metals Institute (IPMI).The Seminar will be held from 6th to 9th October, 1985,in Washington, D.C.

The programme is being organized by J. Michael Shar-ratt (Manville International Corporation), David C. Fen-ton (Johnson Matthey, Inc.), Juergen F. Schroeter(Engelhard Corporation), and Donald A. Corrigan(Handy & Harman).

Sessions are being scheduled to provide almost equalemphasis to each of the six platinum-group metals.

Papers will be presented on mining, supply, and demana,as well as on important or unique applications for theindividual metals including aspects of the broadeningusage in automobile catalytic converters.

The programme will appeal to industrial users,materials and procurement specialists, research scientists,members of the financial and investment community, andkey personnel in the government sector.

Additional information can be obtained from theIPMI, ABE Airport, Government Bldg, Allentown, PA18103, U.S.A. Telephone: 215/266-1570.


Characterization of rock mass

The South African National Group of the InternationalSociety for Rock Mechanics is to hold a Symposium onRock Mechanics Characterization at Mintek, Randburg,on 8th November, 1985.

In rock engineering it is not generally practical to carryout sufficient numbers of large-scale tests and measure-ments to define with certainty the overall behaviour ofa rock mass. Rock masses are therefore characterized bymeans of parameters such as geological factors and prop-erties, which can be obtained from simple, inexpensivemeasurements and index tests. The Symposium is aimedat creating a greater awareness of the benefits of rock-mass characterization for design in rock engineering. Em-phasis will be placed on practical aspects.

Provision has been made for standard papers, whichwill be presented at the Symposium, and for shorttechnical notes, which will not be presented but onlypublished in the proceedings.

The topics are as follows:

. Geological factors (weathering, jointing, etc.). Rock-mass classification

. Laboratory and in situ testing for characterization

. Computer data analysis.

All enquiries relating to the Symposium should beaddressed to:

The Organizing CommitteeRock Mass CharacterizationNational Mechanical Engineering Research InstituteCS I RP .0. Box 395Pretoria 0001Telephone: (012) 86-9211 ext. 2128 Mr W.L. van Heerden

(011) 726-3020 Miss S.A. ThorpeTelex: 3-21312 SATelegrams: NA VORSMEG.

Flotation reagentsFor a number of years, the Council for Mineral

Technology (Mintek) has expended a considerableamount of research into the nature of the interactions in-volved in the selective recovery of minerals by flotation.The combination of reagents used in practice, such as thetype of collector, frother, and depressant, the necessityfor an activating agent, and the use of a combination ofdifferent reagents as the collector, can vary significantlyfrom mine to mine although the same valuable mineral(e.g. pyrite, coal) is recovered at each mine. It is felt thata symposium on this subject will highlight the problemsas well as the solutions developed by the various minesand manufacturers of reagents. In addition, the possibletheoretical interactions and association of the variousreagents will be considered.

Mintek is to hold a Symposium on the Current andFuture Usage of Flotation Reagents in the South AfricanMineral Industry on 25th October, 1985, in Randburg.

Papers on the following topics will be presented:

. Reagent assessment on a laboratory scale. Collector development

. Adsorption mechanism of depressants

. Improved copper recovery with the correct reagent. Amine collectors in pyrite flotation

. Advances in reagents for coal flotation

. Modification of depressants

. Use of mixed collectors. Hard water in the flotation of apatite

. Development of frothers. Application of polyglycol ethers

. Newcollectorsin the flotation of sulphideores.Enquiries should be addressed to The Conference

Secretary (C. 30), Mintek, Private Bag X3015, Randburg,2125 South Africa.

Asian miningAsian Mining '88, the third conference"in the series

devoted to topics that cover the minerals industry-geology, mining, mineral processing, and metallurgy-will be organized by The Institution of Mining andMetallurgy, in association with other international bodies,and held at the Putra World Trade Centre, Kuala Lum-pur, Malaysia, from 8th to 11th March, 1988.

As in the earlier conferences (held in Singapore in 1981and Manila, Philippines, in February 1985), specific at-tention will be paid to topics that are of particularrelevance to the Asian region, and technical tours and

an associated international exhibition of equipment, pro-ducts, services, etc., for the minerals industry will bearranged.

.

Requests for further information and copies of Con-ference circulars should be made to

The Conference OfficeThe Institution of Mining and Metallurgy44 Portland PlaceLondon WIN 4NREngland.


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