Platinum group metals refining

Fig. 5.1 Platinum group metal refining unit -closer to a...

Secondary Platinum-Group Metals. For many PGM appHcations, the actual loss during use of the metal is small, and hence the abihty to recover the PGM efficientiy contributes greatiy to the economics of PGM use. Typical sources of PGM for secondary refining iaclude jewelry and electronics scrap, catalysts, and used equipment, eg, from the glass industry. 

Rhodium is recovered from platinum and other ores by refining and purification processes that start by dissolving the other platinum group metals and related impurities with strong acids that do not affect the rhodium itself Any remaining platinum group elements are removed by oxidation and bathing the mixture in chlorine and ammonia. 

The coordination chemistry of sulfoxides with transition metals is a much-studied topic.87 Academic interest has often centred on their ambidentate donor ability, while dimethyl sulfoxide (DMSO) is of intrinsic importance as one of the most effective aprotic solvents known. Higher sulfoxides have found application in the extraction of metals during refining processes and some potential in the separation of platinum group metals has been noted.88... 

Most metals can be electrolytically deposited from water-free melts of the corresponding metal salts. It is well known that aluminum, lithium, sodium, magnesium, and potassium are mass produced by electrolytic deposition from melts. Industrial processes for the melt-electrolytic production of beryllium, rare earth metals, titanium, zirconium, and thorium are also already in use. Pertinent publications [74, 137, 163] describe the electrolytic deposition of chromium, silicon, and titanium from melts. Cyanidic melts are used for the deposition of thick layers of platinum group metals. It is with this technique that, for instance, adhesion of platinum layers on titanium materials is obtained. Reports concerning the deposition of electrolytic aluminum layers [17, 71-73, 94, 96, 102, 164, 179] and aluminum refinement from fused salts [161] have been published. For these processes, fused salt... 

All the platinum group metals are isolated from platinum concentrates which are commonly obtained either from anode slimes in the electrolytic refining of nickel and copper, or as converter matte from the smelting of sulfide ores. The details of the procedure used differ from location to location and depend on the composition of the concentrate. Classical methods of separation, relying on selective precipitation, are still widely employed but solvent extraction and ion exchange techniques are increasingly being introduced to effect the primary separations (p. i 147). 

The platinum-group metals (Ru, Os, Rh, Ir, Pd and Pt) are rare (Figure 23.1) and expensive, and occur together either native or in sulfide ores of Cu and Ni. Three sites of mineral deposits in the former Soviet Union, Canada and South Africa hold the world s reserves. The main source of ruthenium is from wastes from Ni refining, e.g. from pentlandite, (Fe,Ni)S. Osmium and iridium occur in osmiridium, a native alloy with variable composition 15-40% osmium and 80-50% iridium. Rhodium occurs in native platinum and in pyrrhotite ores (Fei S, n = 0-0.2, often with <5% Ni). Native platinum is of variable composition but may contain as much as 86% Pt, other... 

The platinum group metals (Ru, Rh, Pd, Os, Ir, and Pt), Ag, and Au are called precious or noble metals. Nobility and catalytic activity are unique properties of precious metals, that result in a wide range of applications, such as catalysts in various industrial fields, in electronic industries, and in jewelry. The chemical and physical properties of each precious metal are shown in Table 1. The determination of precious metals attracted the interest of analysts and developed rapidly because these metals are valuable and rare, and also very important for many products. Their concentration levels are very low in many natural sources, metallurgical intermediates, and environmental samples. Furthermore, precious metals are collectively handled in the analytical chemistry field, because of the close resemblance of their chemical properties and behavior. Precious metals are the subproducts in copper, zinc, or lead smelting and refining, which is the most important source of precious metals. Whereas many analytical methods for the ultratrace determination of precious metals in environmental or biological samples were recently published with the development of high-sensitivity analytical instruments, the classical fire-assay has been widely applied for the accurate determination of expensive precious metals. 

The first step in the refining of the platinum group metals (PGMs) is the dissolution of the sulfide matte residue from the base metals refinery. This is done by reaction at high temperature with concentrated HCl and CI2 gas under pressure. Under these conditions the PGMs are oxidized and form stable chloro species. Iridium achieves the oxidation state Ir(IV), while rhodium attains only the 3+ state. The chloro species in solution are thus [AuCy, [PdCy, [PtCy -, [RhCy, and [IrCy -. Gold, palladium, and platinum are easily removed. The separation of rhodium from iridium can be achieved by solvent extraction with tributylphosphate from the acidic HCl... 

Du Preez, A. C. and Preston, J. S. 2002. The solvent extraction properties of di-n-hexyl sul-phoxide in relation to the refining of platinum-group metals. In Proceedings international solvent extraction conference, eds. K. C. Sole, P. M. Cole, J. S. Preston, and D. J. Robinson, vol. 2, 896-901. Johannesburg South African Institute of Mining and Metallurgy. 

Rimmer, B. F. 1989. Refining of platinum group metals by solvent extraction. In Precious metals 1989, ed. B. Harris, 217-226. AUentown, PA International Precious Metals Institute. 

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