CHAPTER 2: LITERATURE OVERVIEW
2.7 PRODUCTION
Platinum is obtained from large-scale underground ore mining and recycled metal (Hughes, 1980). The ore is concentrated following flotation and smelting operations, and individual metals are separated and refined by complex chemical treatments that require sophisticated chemical technology. During the refining the concentrate is dissolved in aqua regia (nitro- hydrochloric acid) or concentrated hydrochloric acid through which chlorine gas is bubbled (Cl2/HCl). Hexachloroplatinic(IV) acid or sodium hexachloroplatinate(IV) is formed and in both cases addition of ammonium chloride leads to the formation of ammonium hexachloroplatinate(IV), a yellow salt (Hughes, 1980; IPCS, 1991).
After several purification processes there is a second precipitation of this complex salt, which is then filtered off, dried and calcined at 600-700°C to yield a crude platinum metal sponge, which undergoes further refining. Finally, after heating up to 1000°C a grey metal sponge of platinum
>99.9% pure is produced (Hughes, 1980). There are other methods of purification: e.g.
platinum can be reduced to the metal from aqueous solution of its salts, whereby a black powder of platinum metal (platinum black) is produced (Mastromatteo, 1983; IPCS, 1990;
Beliles, 1994). Hexachloroplatinic(IV) acid, the most important platinum compound (formed when platinum is dissolved in aqua regia), is isolated as the hydrate and is the source of many other platinum compounds (Beliles, 1994).
The world production of platinum group metals (40–50% of which is platinum) has increased steadily over the past two decades, with a total of 127 tonnes in 1971 rising to 270 tonnes (with108–135 tonnes of platinum) in 1987 (Loebenstein, 1988) and 152 tonnes in 1995 (WHO 2000). In 2005, the world supply of platinum amounted to 225 tonnes, an increase of roughly 50% compared with the period 1995-2000. Most of this supply originated from mine production (78%), the remainder from Russian exports (10%) and secondary sources (10%) such as scrap (recovery from auto catalysts). South Africa is by far the major mine producer accounting for 90%, followed by Canada (4%), Zimbabwe (3%), and the USA (2%). Demands are expected to increase further due to the increasing demand for autocatalysts and the anticipated further development of fuel cells. (Health Council of the Netherlands, 2008).
2.8 USE
Platinum has exceptional catalytic properties and is used in the chemical and petroleum industries in hydrogenation, isomerisation, cyclisation, dehydration, dehalogenation and oxidation reactions (Mastromatteo, 1983; Beliles, 1994). Major uses are in ammonia oxidation, in the production of nitric acid and in the catalytic upgrading of the octane rating of gasoline.
Platinum and some inorganic platinum compounds are used in Sweden for naphtha-reforming to upgrade the octane rating of gasoline and during the production of organic base chemicals e.g. for cleaning of gases (Health Council of the Netherlands, 2008). In the past few years platinum and its salts are mainly used in the automotive industry (as catalysts in automobile exhausts). A motor vehicle catalytic converter contains 1-3 g of platinum. Catalytic converters were introduced in 1975 in the United States to meet the stringent emission limits of the Federal Clean Air Act, and became mandatory in the European Community in 1993. Platinum-rhodium or platinum-palladium catalysts are used to control emissions from automobile exhausts and oxidize carbon monoxide and unburnt hydrocarbons and in the case of platinum-rhodium, nitrogen oxides are reduced (Bradford, 1988; IPCS, 1991).
In Finland at least four products containing platinum are used as catalysts or laboratory chemicals. Few data on the chemical composition or the amounts used have been obtained, but it has been stated that 300 kg/year of platinum (tetraammineplatinum hydrogencarbonate) is used by a producer of automobile catalysers (personal communication, V. Riihimäki, Finnish Institute of Occupational Health; cited in Lindell, 1997).
Resistance to many forms of corrosion and strength at high temperatures are other significant properties of platinum and it is often alloyed with other platinum or base metals used in electric contacts for relays, printed circuits (in the electronics industry), laboratory and plant apparatus, electrochemical anodes, spinnerets used for synthetic fibre extrusion, bushings for the production of fibreglass and vessels used for example in glass-making industry. Platinum is also used to produce a silvery lustre on ceramic glazes (Mastromatteo, 1983; Bradford, 1988;
IPCS, 1991; Beliles, 1994). Some alloys containing platinum are used in dentistry and medicine and include dental and neurological prostheses, for recording electrical activity, and for pacemaker electrodes. Potassium tetrachloroplatinate(II) possibly may be used as a dental drug (dentine desensitiser) (Kanematsu et al., 1990). Certain platinum complexes, like cisplatin and its analogues are used as anticancer drugs for the treatment of testicular and metastatic ovarian tumours and in lung and bladder cancer (Lindell, 1997; Health Council of the Netherlands, 2008).
Platinum salts may be used e.g. in the manufacture of platinum catalysts, for electroplating, and for photographic applications. Hexachloroplatinic(IV) acid may be used in platinising alumina or charcoal in catalyst production (IPCS, 1991). A number of salts can be used in the electrode- position of platinum. Industrial items e.g. aviation components, electrodes, turbine blades and wire, as well as jewellery and decorative items may be electroplated with platinum. Potassium tetrachloroplatinate(II) (used as a toner in the developing of photographic paper) and potassium hexachloroplatinate(IV), are soluble platinum salts used in the photographic industry (Mastromatteo, 1983; Woolf and Ebert, 1991). In 2005, 62 tonnes of platinum were used in Europe, of which about 76% was used in the automotive industry (catalysts). Germany, United Kingdom, and France used about 4% in jewellery and 2% in electronics, and Germany used about 2% in dentistry. Worldwide, 51% of the amount produced was used in the automotive industry, 12% in jewellery, 4% in electronics, and 4% in chemical/petroleum refining with smaller amounts (1%) used in dentistry and medicine (as anti-cancer drugs such as cisplatin and carboplatin) (Lindell, 1997; Health Council of the Netherlands, 2008).
Before the introduction of automobile catalytic converters most of the platinum was used as catalysts in the chemical and petroleum industry. Platinum sales are reported in Table 4 for the different United States industries before and after the introduction of automobile catalytic converters.
Table 4. Platinum sales to various types of industry in the United States before and after the introduction of automobile catalytic converters (IPCS, 1991).
Industry kg/year (1973) % of total (1973) kg/year (1987) % of total (1987)
Automobile - - 18817 71.3
Chemical 7434 36.3 1920 7.5
Petroleum 3844 18.8 739 2.8
Dental and medical 868 4.2 479 1.9
Electrical 3642 17.9 1821 7.1
Glass 2255 11.0 285 1.1
Jewellery and decorative 697 3.4 177 0.7
Miscellaneous 1732 8.5 1430 5.6
Total 20472 100 25668 100