Chapter 32 - Overview of the Extraction of Platinum-Group Metals

Abstract

This chapter provides an overview of the extraction of platinum-group metals or PGM. The ores occur either as sulfides or are associated with sulfides of copper and nickel. It is extracted by first floatation of the sulfide component. This floatation concentrate is smelted and converted to produce a sulfur-deficient matte containing 10,000 to 20,000 g/tonne of PGM along with nickel, copper, iron, cobalt and sulfur. From this PGM-containing material, base metals and the associated sulfur is removed by either slow cooling followed by magnetic concentration or whole-matte leaching. Slow cooling is followed only by Anglo American Platinum's operations in Rustenbug, South Africa. Here, the converter matte is allowed to cool over several days forming large crystals of heazlewoodite, chalcocite, and metal alloy. During cooling, the PGMs get concentrated and are separated by magnetic separation and the copper, nickel and iron are removed by leaching. The platinum concentrate is transferred to precious metals refinery for separation of individual precious metals. In the entire matte leaching process, nickel and copper are leached from the converter matte, leaving the PGMs in the insoluble residue. This residue is treated to remove copper, nickel, iron, selenium, and tellurium and transferred to precious metals refinery. Finally, individual metals are separated and refined to high-purity products for sale. The most important step in refining is the separation of platinum and palladium. Older technologies used ammonium chloride salt precipitation. Later on, solvent extraction was used and most recently, refineries use ion exchange or molecular recognition technology.