Platinum group metals solvent extraction

The application of these methods is described in some detail for recovery of base metals and platinum group metals in Sections 9.17.5-9.17.6 focusing mainly on solution-based hydrometal-lurgical operations, largely those involving solvent extraction, because the nature of the metal complexes formed is usually best understood in such systems. NB. Extraction of lanthanides and actinides is not included as this subject is treated separately in Chapters 3.2 and 3.3. 

Vest, P. Schuster, M. Konig, K. H. Influence of tin(II) chloride on the solvent-extraction of platinum group metals with N,N-di-normal-hexyl-N -benzoylthiourea. Fresenius J. Anal. Chem. 1991, 339, 142-144. 

Preston, J. S. du Preez, A. C. Solvent extraction of platinum-group metals from hydrochloric acid solutions by dialkyl sulphoxides. Solvent Extr. Ion Exch. 2002, 20, 359-374. 

Cleare, M. J. Grant, R. A. Charlesworth, P. Separation of the platinum-group metals by use of selective solvent extraction techniques. Extr. Metall. 81, Pap. Symp. 1981, 34-41. 

Merdivan, M. Aygun, R. S. Kulcu, N. Solvent extraction of platinum group metals with N,N-diethyl-N -ben-zoylthiourea. Ann. Chim. 2000, 90, 407 112. 

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... 

Solvent extraction of platinum-group metals and gold 806... 

The use of amine salts in the commercial solvent extraction of the platinum-group metals from chloride solutions is described in Section 63.3.2.5. 

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 occur jointly as alloys and as mineral compounds in placer deposits of varying compositions. Ru and Os are separated from the PGM mix by distillation of their volatile oxides, whereas platinum, iridium, palladium, and rhodium are separated by repeated solution and precipitation as complex PGM chlorides, or by solvent extraction and thermal decomposition to sponge or powder. PGM scrap is recycled by melting with collector metals (lead, iron, or copper) followed by element-specific extraction. 

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... 

Cleare, M. J., Charlesworth, R, and Bryson, D. J. 1979. Solvent extraction in platinum group metal processing. /. Chem. Tech. Biotech. 29 210-224. 

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. 

Solvent extraction is proposed as a suitable method for PGMs (platinum group metals) recovery from low concentrated sources. Several extractants have been studied and proposed, e.g., hydroxyoximes, alkyl derivatives of 8-hydroxyquinoline, dialkyl sulphides, hydrophobic amines and quaternary ammonium salts, derivatives of pyridine and pyridinecarboxamides. However, the problems of a slow extraction rate or low metal separation remain to be solved. Looking for extractants permitting possibly fastest extraction of Pd, two phosphonium ionic liquids, i.e., [QP][C1] and [QP][Bis], have been used (Cieszynska et al., 2007 Cieszynska, 2010 Cieszynska Wisniewski, 2010, 2011). To overcome problems caused by the high viscosity of ILs, the mixtures with toluene have been used for extraction, similarly as for extraction of Zrf+. 

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