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A SURVEY OF PRODUCTIVE RESOURCES IN RELATION TO INDUSTRIAL USES

By L. B. Hunt, M.SC., Ph.D., and F. M. Lever, A.R.c.s.: Ph.D. Johnson Matthey & Co Limited

future supply position, and to put into Increasing industrial uses of platinum perspective some of the trends in the ap- and its associated metals - , plications of the platinum metals in their , , and major areas of growth. - have occasionally given rise Before we turn to this discussion, however, to doubts as to the future availability there are a few essential factors that must be of adequate supplies. This has some- made clear: times discouraged research workers from (I) Unlike , platinum is not used for considering the advantages of these monetary or speculative purposes, and metals in their search for new routes or only to a limited extent for decorative for new products in the chemical and uses. We are dealing with an industrial allied industries. This paper, pre- , vital to a number of chemical or sented at the Symposium on the metallurgical processes which, taken Platinum Metals organised by together, account for between 80 and the American Chemical Society during 90 per cent of the total demand. its meeting in New York in September, (2) Platinum and its allied metals are used outlines the very substantial productive in industry only where their inherent resources now associated with these properties are essential to a successful metals and relates them to the trends operation or process. Many established in their applications in industry. uses of fifty or a hundred years ago have disappeared with the advent of new and cheaper materials, while many Every chemist is familiar with the six newer applications have become es- metals of the platinum group, and most will tablished. be well aware of the chemistry of their (3) By comparison with the base metals, a complex salts upon which their separation very high proportion of the platinum and refining-as well as their methods of metals used in industry is refined and re- analysis-are based. Not so much is known used repeatedly, often without change about the extraction of these metals from their of ownership. Figures for production or about the scale upon which these therefore relate only to newly-mined operations are conducted to provide the metals to meet increasing demands chemical and other industries with their from technologically advanced indus- needs, and in consequence misconceptions tries. A considered estimate of the have sometimes arisen as to their availability total amount of platinum in circulation for new products or processes. in the world to-day would be between It is the intention in this paper to outline 25 and 30 million troy ounces. the chemistry of the extractive methods (4) There has been a great deal of dis- employed, to submit data on the present and cussion about a shortage of platinum

Platinum Metals Rev., 1969, 13, (4), 126-138 126 The shallower portions of the Rustenburg platinum mines are worked from inrlined haulages such US this, sited ubout 2,500 feet apart, while the deeper areas have been opened up by means of jke verliraE shafts runging in depth from 500 to 2,500 feet. A further shaft is now being sunk to exploit the body to a depth of 3,000 feet. All together some eighteen miles of out- crop are being mined. Rustenburg is the lurgest underground opera- tion in . em- ploying over20,000 workers, and is the largebt producer of platinum metals in the world. Total reserves in this part of South Afrira have been estimnted to be in ex- cess of 200,000,000 ounres of plutinum

for industrial uses during the last be made available, the only condition few years. In fact there has been no being that responsible forecasts of absolute shortage, and although demand usage are provided upon which to base has increased very substantially, almost further programmes of expansion in all industrial needs have been met mining and smelting facilities. At any by the main primary sources, South conceivable rate of production the ore Africa, and . The reserves available will ensure continuity impression of shortage has stemmed of operations at the South African from the wide disparity in the selling mines well into the next century. prices for South African and Canadian platinum, on the one hand, and that for Sources of the Platinum Metals the metal coming from Russia and Prior to World War I the greater part of certain other minor producers. The the then modest needs for the platinum metals shortage is thus one of relatively low- was met from alluvial or placer deposits in cost platinum only. The widely held Russia and the Republic of Colombia, but belief that Russia has withdrawn as a this type of primary material now represents major supplier to the West is untrue. only a very minor part of world production, In fact the amounts exported year by the two remaining sources today being year have remained fairly constant, Goodnews Bay in Alaska and the Compania although constituting a diminishing Minera Choco Pacific0 in Colombia. proportion of a larger usage. The discovery of extensive deposits of (5) Increased supplies of new metal can platinum-bearing - ores in

Platinum Metals Rev., 1969, 13, (4) 127 The ore isjrst crushed in a series of jaw crushers and is then fed to the primary and secondary ball mills

Canada and South Africa some forty or mines to respond more quickly and effectively fifty years ago has given rise to a major to increasing demand, and output from this industry which now provides by far the source has been increased more than fourfold greater part of the Western world’s needs, over the past five years, with further ex- while broadly similar deposits in the Urals pansion already in hand. Rustenburg is in and elsewhere in Russia have been worked fact the world’s largest source of platinum, more recently. In all these three major and the only major mine whose main activity producing countries the platinum content of is the production of the platinum metals. the runs only to a fraction of an For this reason, although methods of ounce per ton, and many millions of tons of extraction in other countries are broadly ore have therefore to be mined, milled and similar, it is the techniques adopted by smelted each year. The processes of ex- Rustenburg and by their refiners Johnson traction involve basically the smelting and then Matthey that will be mainly described here. the electro-refining of copper and nickel, followed by the recovery, separation and Extraction and Refining refining of the platinum metals themselves. The deposit worked by Rustenburg Plat- South Africa differs, however, from Canada inum Mines forms part of the Mercnsky and the USSR in one important respect. Reef of the . The Rustenburg mines in South Africa are This reef, named after the geologist Hans worked primarily for the platinum metals, Merensky who was responsible for the pros- yielding copper and nickel as by-products, pecting programme that led to its discovery whereas the International Nickel and Fal- in the 1920s, has been traced on outcrop a conbridge mines in Canada, and also the distance of some 75 to 80 miles along both Russian deposits, are essentially sources of the eastern and western limbs of the Complex. copper and nickel with the platinum metals The eighteen miles of outcrop which are as by-products. This difference is of major mined at the two operations, the Rustenburg importance in enabling the South African section a few miles to the East of the town,

Platinum Metals Rev., 1969, 13, (4) 128 and the Union section about sixty miles to ground whenever a greater demand for the North, are considered to contain the platinum has arisen-one reason why highest grades of the entire Complex. Rustenburg has been able to follow world Platinum values at these two sections show demand so closely. In the shallower portions a very even tenor, the platinum being partly of the deposit inclined haulages are sited in the form of , invariably about 2,500 feet apart, while the deeper alloyed with as ferro-platinum, and areas have been opened up by means of five partly as the sulphide, and sulph- vertical shafts ranging in depth from 500 to , these always occurring in intimate 2,500 feet. A further shaft is currently being association with the sulphides of iron, copper sunk to exploit the ore body to a depth of and nickel. Associated with platinum, the 3,000 feet. predominant metal, are smaller proportions The ore is first crushed in a series of jaw of palladium, ruthenium, rhodium, iridium crushers and fed to the ball mills which are and osmium, in this descending order of in closed circuit with hydrocyclone classifiers. concentration. This stage is followed by gravity concen- The platinum-bearing reef averages only tration on corduroy tables to separate the some twenty inches in thickness, but its coarse particles of platinum-bearing regularity makes for relatively straight- and the free metallic particles. The corduroy forward mining. It persists to depths beyond concentrate is dressed on an elaborate system the limits of practical mining, and the reserves of shaking tables up to a final high grade down to a depth of 3,000 feet are immense. concentrate which is sent directly to the The length of strike and the comparative Johnson Matthey refineries in England. shallowness of the deposit have made possible The tailings from the tables are returned the rapid development of large areas of to the mill circuit, the final pulp from here

Flotation concentrates are smelted to a copper-nickel-iron matte. This is cast into moulds, broken up and sent to the rrjineries for extruction of copper, nickel and the sixplatinum metals

Platinum Metals Rev., 1969, 13, (4) 129 In the electrolytic nickel re$neries pure nickel cathodes are produced while the platinum metals riccumulate in the anode residues and are removed for separation and refining being treated in a series of thickeners before metals and sulphur. The content of platinum going to the flotation plant, which recovers group metals is about 50 ounces troy per most of the remaining platinum-bearing ton (0.15 per cent). The treatment of this minerals. The flotation concentrates, con- material may be divided into two steps, first sisting mainly of nickel, copper and iron the removal of nickel and copper to produce sulphides with the balance of the platinum a rich platinum group metal concentrate, metals, are thickened, filtered, dried and followed by chemical treatment of this pelletised, ready for the smelter. concentrate to separate and purify the The initial stage in the recovery of the individual metals. platinum metals is to smelt to a copper- Two processes are in operation to achieve nickel-iron matte in a series of blast furnaces. the first aim. The older process, the Orford This matte is then tapped periodically into or top-and-bottom process, involves the ladles, transferred to a group of convertcrs, smelting of the copper-nickel matte with and blown to a high-grade matte which is sodium sulphide. This results in the for- cast into moulds and then brokcn up in a mation at high temperature of two immiscible jaw crusher. Part of this converter matte liquids, a heavier nickel sulphide phase is shipped to the Johnson Matthey smelter containing the platinum group metals and a in England, the balance being treated by lighter sodium copper sulphide phase con- Matte Smelters, a joint subsidiary of Johnson taining gold, and only minor amounts Matthey and Rustenburg, in a plant adjacent of platinum group metals. These two liquid to the mine. phases are separated and allowed to solidify. Rustenburg converter matte contains about The sodium coppcr sulphide is blown with 46 per cent of nickel, 28 per cent of copper, air in a Bessemer converter to produce together with small amounts of other base blister copper which is further refined and

Platinum Metals Rev., 1969, 13, (4) 130 then cast into anodes. These are electro- to pure metal. The filtrate from the crude lytically refined to produce marketable copper, ammonium chloroplatinate is oxidised to leaving an adherent anodic residue containing precipitate ammonium chloropalladate. This the noble metals present in the copper “tops”. is dissolved and decomposed by boiling with The nickel sulphide “bottoms” are ground, water to produce a solution of ammonium roasted, and the resultant nickel oxide chloropalladite. Ammonia is added to convert reduced to metal which is cast into anodes. the palladium to tetramminepalladous These are also refined electrolytically to chloride. On acidifying the solution with produce pure nickel and an anodic residue hydrochloric acid there is precipitated diam- containing the platinum metals. The minedichloropalladium which is calcined to residues from the copper circuit and the yield pure palladium sponge. nickel circuit are together roasted and The original insoluble residue is fused with leached with sulphuric acid to produce a oxidising alkaline fluxes and the cooled melt concentrate, containing about 65 per cent of leached with water. Osmium and ruthenium platinum group metals. are removed and separated by distillation of The second process being operated to their volatile tetroxides, being subsequently produce a platinum group metal concentrate converted to metal by thermal decomposition from the matte involves the leaching with of a suitable compound. The iridium and sulphuric acid under pressure of the finely rhodium remaining in the solution after ground matte. This results in the removal of distillation are recovered as sodium chloro- copper and nickel as sulphates followed by complexes which are converted to ammonium their recovery by normal electro-refining compounds for calcination to metal. techniques. The residue, containing the All these calcinations are carried out under platinum metals, is treated to remove iron carefully controlled conditions in electrically oxide and to produce a concentrate suitable heated muffle furnaces, to produce the metals for chemical refining. as sponges or powders suitable for melting. Final concentration and separation of the platinum metals is carried out in the Johnson World Production Matthey refinery in England, but an ad- DeaIing first with South Africa, Rustenburg, ditional refinery is now under construction in whose output has been increased from some South Africa to supplement supplies by 200,000 ounces of platinum in 1963 to 850,000 treating some part of the output of Matte ounces a year at present, has a further ex- Smelters. pansion programme in hand to yield I,OOO,OOO It is only possible to outline briefly the ounces a year by 1971, and has just announced chemical treatment of these concentrates, plans to increase production to 1,200,000 and this account gives only a simplified ounces by 1973. picture. The concentrate is first attacked Corresponding increases have, of course, with to dissolve gold, platinum taken place in the output of the other members and palladium, the residue comprising the of the platinum group of metals - palladium, more insoluble metals iridium, rhodium, rhodium, ruthenium, iridium and osmium. osmium and ruthenium. The solution is This has been achieved by very substantial treated with ferrous chloride to remove gold capital expenditures on the sinking of new and to the filtered solution is then added shafts, the installation of additional grinding, ammonium chloride to precipitate crude milling and flotation equipment, and the ammonium chloroplatinate. This is calcined building of an additional modern smelting and the impure sponge re-dissolved. Am- plant, together, of course, with a consequent monium chloride is added to precipitate the expansion in all the facilities and services. pure platinum compound, which is calcined The expenditure involved in the expansion

Platinum Metals Rev., 1969, 13, (4) 131 The initial stage in the Johnson Matthey met process re$nery involves digestion of the enriched concentrates with aqua regia to dissolve the platinum and palladium, leaving the iridium, rhodium, ruthenium and osmium as insoluble residues to be treated separately programme over the seven years 1967 to Thus a total annual output from the 1973 will probably exceed $130 million. Western world of over 1,500,000 ounces will Today Rustenburg constitutes the largest be available in the early seventies, and it is underground mining operation in the Re- reasonable to assume that this will be sup- public of South Africa, its two mines to- plemented by whatever the USSR may gether extending more than cighteen miles contribute to Western supplies. from one end to the other, and providing Palladium naturally follows the same trend about 60 per cent of the Western world’s in expanding output as platinum itself, but needs of platinum. here the relationship between individual By the end of the present year there will producers is somewhat different. The be a new South African producer, Impala Canadian ores contain more palladium than Platinum, from which can be expected an platinum, while in South Africa the reverse output of about 50,000 ounces in 1970,rising is the case. Western World production from perhaps to 150,000 ounces in two years’ time, these two sources together with the minor The output from Canada is likely to be producers is now running at around 550,ooo upwards of 200,000 ounces a year, and no ounces a year, with the USSR over- significant change is expected from the topping this figure considerably. Looking existing smaller producers. ahead some five years or so, Rustenburg, There is unfortunately no real basis for within the framework of its present expansion estimating production from the USSR, but plans, could produce around 500,ooo ounces this is undoubtedly geared to her growing a year. To that could be added rather less outputs of nickel and copper. All that can be than IOO,OOO ounces from Impala, depending said is that after taking care of her internal upon this producer’s aspirations in platinum. and expanding needs of platinum, some- Canadian output should continue to provide thing like 300,000 ounces of metal a year have between 250,000 and 300,000 ounces a year, been exported. and other sources will make a modest contri-

Platinum Metals Rev., 1969, 13, (4) 132 This section of the Johnson Matthey re$nery - the largest of its kind in the world -handles the precipitation, re-dissolving and re-precipitation of platinum and palladium bution. Thus a total Western output of this, arising mainly from the ebb and flow something like 850,000 ounces a year can be of competitive technological developments. expected, while it is likely that the substantial During the last five years the consumption of deliveries of palladium made by Russia in newly-mined platinum has been approxi- recent years will continue. mately 30 per cent in the chemical industry, The remaining four platinum metals are about 25 per cent in petroleum reforming, similarly closely governed in terms of output 20 per cent in electrical and allied uses, and by platinum production. Currently ruthen- 10 per cent in the glass industry, with some ium output is running at 90,000 to IOO,OOO 15 per cent covering dental, medical, ounces a year, rhodium at around 80,000J and miscellaneous applications. iridium at 25,000 ounces and osmium at Thus the use of platinum is not associated 13,000 ounces. Some scaling up of all these with one or two industries, and many of its production figures will of course follow from applications are in areas of industrial growth. the expansion of platinum production. What trends are discernible in these various fields of interest ? Trends in Demand Present indications are that over the next two Nitric Acid Production years production and demand for platinum One of the largest demands for platinum will be fairly well in balance. In the succeed- comes from the nitric acid industry, where it ing few years the prospect is naturally not so is used-mainly alloyed with 10 per cent of clear, but a simple projection of present rhodium-in the form of gauzes for the technologL suggests that Western World oxidation of ammonia. The Western World’s demand for new metal will lie between about output of nitric acid now exceeds 20 million 1,200,000 and 1,700,000ounces a year. tons per annum, and it is estimated that this There are of course a number of imponder- output represents a platinum gauze inventory ables in trying to arrive at such estimates as of around 200,000 ounces, excluding the

Platinum Metals Rev., 1969, 13, (4) 133 The new generation of platinum cat- alysts containing an addition of rhen- ium have given improved performance in petroleum rejorming, but the continual increase in severity of operation is expected to require an increasing level of platinum supply to the petroleum industry

they will find acceptance in the industry for the time being. In the very long term, it is possible that the nitric acid route to nitrogen fixation may be re- placed by direct fixation processes using homogeneous catalysts. The platinum metals, particu- larly ruthenium, have been inten- sively studied to provide suitable weight of gauzes that most plants carry as catalysts for such a process, but at the present spares. Nitric acid manufacture represents time no viable route is in sight. the largest direct platinum metal consuming process, in that a small but significant pro- Atmospheric Pollution portion of the gauzes installed is irrecover- The excellent catalytic properties of ably lost in the high temperature oxidising platinum-particularly as an oxidation conditions encountered in the plant. This catalyst-make it likely that it will be used in metal loss represents only 3 to 4 per cent of a number of systems designed to oxidise the total costs of manufacturing nitric acid, undesirable or harmful organic odours or and the recently developed platinum recovery other atmospheric pollutants. The pollution process using gold-palladium gauze immedi- control industry is a comparatively new one, ately below the platinum gauzes should serve and is growing very rapidly as increasing to reduce appreciably even this small pro- public attention is focused on the problem in portion of the costs contributed by the use of almost every country, while legislative pres- platinum. sures mount to force offenders to adopt The major outlet for nitric acid is in the suitable control systems. Already platinum manufacture of nitrate fertilisers for which catalysts are used to oxidise a number of the demand is growing steadily throughout unpleasant pollutants in several industries, the world-particularly in the under- for example in wire enamelling, in abattoirs developed countries. The ammonia oxidation and in meat or fish processing. Platinum route to nitric acid is now very well estab- catalysts are also increasingly adopted by the lished and is unlikely to be superseded by nitric acid industry to reduce the harmful and alternative processes in the foreseeable near corrosive nitrogen oxides that are emitted future. Alternative cataIysts, using transition with the tail gases from most plants. metal oxides such as oxide, have been The problems resulting from the emission studied for a number of years as possible of unburnt hydrocarbons, alternatives to platinum, but their relatively and nitrogen oxides in the exhaust gases from short operating lives makes it unlikely that internal combustion engines have received a

Platinum Metals Rev., 1969, 13, (4) 134 World production of chlorine by the electrolysis of brine is about 25 million tons a year. Some large estimates of platinum consumption as platinised-titanium anodes in this industry are now unlikely to be realised since the development of a ruthenium oxide coating on titanium great deal of attention. Several platinum- catalyst manufacturers have been able to containing catalyst systems have already been make use of this to give improved perform- developed and await commercial exploitation. ance while maintaining the same platinum Legislation under consideration in several percentages in their products. In other cases countries-notably in the USA-could a lowering of platinum levels has been made dramatically affect the future of platinum possible, at least for the time being. It is still consumption in this field in one of two ways : clear that the more platinum contained in a either the conventional petrol engines will reforming catalyst, the better is its perform- have to be universally fitted with catalytic or ance. The continual increase in operating other exhaust gas purification systems, or the severities coupled with the rising demand for use of lead additives may be increasingly high octanes and for aromatics will almost controlled, resulting in a corresponding certainly require an increasing level of supply increase in the need for platinum in petroleum of platinum to the petroleum industry, but reforming operations. Either way, it seems this increase will probably be spread over a likely that public pressures for the need to number of years. control atmospheric pollution in the urban Fuel Cells centres of the world’s industrial countries Fuel cells have for a long time been under will result in a demand for platinum using intensive development for a number of appli- systems, although, of course, modifications cations. Among the favourite potential to engine design may also help to overcome applications has been the electrically powered part of the problem. motor-cary using the fuel cell as an alternative Petroleum Reforming to the internal combustion engine. Early The recent introduction of rhenium into work in the deveIopment of fuel cell systems reforming catalysts has a synergistic effect on indicated that the platinum metals were the performance of the platinum, and some supreme in their combination of catalytic and

Platinum Metals Rev., 1969, 13, (4) 135 corrosion resistant properties. More recent anodes will be used for chlorate production, work, however, based on the erroneous ruthenium oxide on titanium will be pre- assumption that insufficient platinum would ferred in the very much larger chlorine manu- be available for their future needs, has led facturing industry. researchers to develop some potential alter- Organic Electrosynthesis natives to platinum in certain applications. The field of organic electrosynthesis is Although it now seems unlikely that platinum receiving very considerable attention from electrocatalysts will find applications in fuel research workers in the universities and in cells for major mass market applications, it is industry. Here also selective electrocatalysts very probable that specialised fuel cells for are required, and it is possible that some selected applications will use them. Consider- systems may be developed using platinum able effort is being devoted towards providing metals on suitable supports. platinum electrocatalysts that make much more effective use of the platinum component Heterogeneous than has been possible hitherto, and indi- Other than in petroleum reforming opera- cations are that this work will be successful. tions, platinum is not at present widely used Chlorine Production in industrial heterogeneous catalytic systems. The use of platinised-titanium anodes in Palladium is much more widely employed, the production of chlorine and chlorates by particularly in liquid phase hydrogenation the electrolysis of brine has received consider- reactions. Hydrogenation of a wide range of able attention in recent years, and some very compounds has grown very markedly in large estimates of platinum and iridium- recent years in the general chemical, dye- platinum consumption have been made. At stuffs and pharmaceutical industries, and the present, however, it appears likely that while future application of platinum group metal iridium-platinum deposited on titanium catalysts, particularly palladium, supported

The steadily increasing production of aiscose rayon calls for large quantities of platinum in the form of spinnerets in platinum-gold or rhodium-platinum alloys for the continuous extrusion of many thousands of threads

Platinum Metals Rev., 1969, 13, (4) 136 The manufacture of glass jibre involves the rapid flow of glass at around 1,400"C through a series of orijices which must retain their size and alignment. The electrically heated bushings are universally made in rhodium-platinum alloys on a range of suitable carriers is likely to Electrical Uses increase significantly. For the electrical industry no major change Homogeneous Catalysis in the usage of platinum (or rhodium with Organo-metallic chemistry is the most which it is so often alloyed) is foreseen. rapidly expanding of all branches of chemistry Light duty contacts, electric furnace wind- and although the use of compounds and ings, thermocouples, cobalt-platinum alloy organic complexes of the platinum metals as permanent magnets, resistance thermometers homogeneous catalysts is only in its industrial and precision potentiometers represent the infancy at present, this is a field of application major applications in this field, while metal- likely to grow dramatically in the next lising preparations based upon platinum, decade. Rhodium in particular has been palladium and ruthenium are growing in found, in its numerous complexed forms, to demand for capacitors, resistors and other be a most effective homogeneous catalyst in thick film electronic components. hydrogenation, hydroformylation, carbonyla- Some 60 per cent of the total usage of tion and other reactions, while ruthenium palladium is in the electrical industry mainly complexes are also showing indications of for telephone contacts in the cross-bar great potential usefulness. switching system adopted in the USA and Viscose Rayon Japan. This system will eventually be super- Substantial amounts of platinum are in use seded by the electronic exchange, but it is not in the viscose rayon industry in the form of expected that the demand for palladium will spinnerets made from platinum-gold or fall for a further year or two. rhodium-platinum alloys, but recovery and In light duty contact applications, particu- re-use are virtually complete and this larly for sliding surfaces such as slip-rings, industry does not therefore create a significant electrodeposited rhodium has for many years demand for new metal. been established and is growing in usefulness.

Platinum Metals Rev., 1969, 13, (4) 137 Improved methods of electrodepositing both ing demand. Its most recent announcement palladium and ruthenium have more recently of yet another programme of increasing pro- shown the advantages of these two metals, the ductive capacity to yield 1,200,000 ounces of former in replacing gold in electronic applica- platinum a year by 1973--with, of course, tions and the latter as a less expensive alterna- corresponding increases in the output of the tive to rhodium. other platinum group metals-gives any re- assurance that might still be needed on their Glass Manufacture long-term policy. Simply and briefly ex- The protection of refractories from attack pressed, this is to take all steps that might be by molten glass-and thus the avoidance of necessary, jointly with Johnson Matthey as contamination-is a major problem in the smelters and refiners, to ensure to industry glass manufacturing industry, and a large and throughout the world adequate and con- growing demand for platinum arises here. tinuing supplies of the platinum metals. Stirrers, tank blocks and other equipment In making this latest decision to expand controlling the flow of molten glass are thus still further, the possibility has been faced clad with platinum sheet of about 0.25 mm that it could conceivably give rise to some in thickness, and it has been well established excess of capacity and a situation of over- that this practice has always resulted in the should it be production of a particular type of glass at a supply. On the other hand, more economic price either by the production found that the projected output is not likely of a purer glass or of one with greater freedom to be adequate for the indicated demand, from defects. there will be no hesitation on the part of The manufacture of glass fibre-an indus- Rustenburg in increasing still further the try that has grown rapidly and that is now mines’ productive capacity, or on Johnson expanding considerably in less well-developed Matthey’s part in extending once again their countries-involves the rapid flow of glass at smelting and refining facilities. around 140o0C through a series of orifices The question then arises of how long pro- which must retain their size and alignment. duction at this or any higher rate can be continued. It is difficult to assess with any Platinum, or more generally 10 per cent rhodium-platinum, is universally employed high degree of accuracy the amount of for the construction of the trough-shaped platinum contained in the South African bushings used in this process. The cost of the deposits and so to give an indication of the platinum employed, including the interest on potential reserves of metal, but prospecting the investment and the refining and re- operations which have been carried out by manufacturing of the bushings, represents Rustenburg for many years on the Merensky only about 3 per cent of the selling price of Reef have enabled it to build up a compre- the glass fibre. hensive knowledge of the potentialities of both the very substantial areas over which it has The Future mining rights and of the remaining areas. To To sum up these trends in the demand for arrive at a realistic estimate of the total platinurn and its allied metals is not a simple reserves, account must be taken of the grade matter, but irrespective of the several uncer- of ore available and the feasibility of mining tainties in the situation or of short-term operations at increasing depths. Within this fluctuations in consumption, the overall pic- framework, and assuming reasonable price ture remains one of growth based upon levels for an arbitrarily selected of the increasing industrialisation and upon the next 30 years, it is estimated that the overall normal growth of the established applications. reserves of platinum that could be economi- Rustenburg has demonstrated clearly over cally exploited during this period amount to the years its determination to meet this grow- not less than 200 million ounces.

Platinum Metals Rev., 1969, 13, (4) 138