Platinum Group Metals (PGMs) include six rare metals known for their exceptional physical and chemical properties, such as resistance to corrosion and oxidation, electrical conductivity, and catalytic activity. The most economically significant PGMs are platinum, palladium, and rhodium, while ruthenium, iridium, and osmium are less prevalent and less in demand . PGMs are in high demand across various sectors, including automotive, jewelry, industrial applications (such as the chemical, petroleum, dental, medical, and glass industries), and investment. The introduction of catalytic converters has notably increased PGM demand, especially for platinum and ruthenium .
PGMs are typically associated with nickel-copper sulphides found in magmatic rocks. They are produced either as primary products or as by-products of nickel and copper mining, depending on the ore's metal concentrations. The primary PGM deposits are rare and geographically concentrated. South Africa leads global production, contributing 58%, followed by Russia at 26%, and smaller contributions from Zimbabwe, Canada, and the United States. Notable deposits include the Bushveld Complex in South Africa, the Great Dyke in Zimbabwe, and the Sudbury deposit in Canada.
PGM ores often contain base metals such as nickel, copper, and cobalt, along with gold and other trace elements. Primary minerals associated with PGMs include pyrrhotite, chalcopyrite, and pentlandite, with varying recovery challenges. Advances in processing technology are necessary to efficiently recover PGMs from these complex mineral matrices.
Base metal refining for PGMs typically utilizes the Sherritt-Gordon sulphuric acid pressure leach process, widely adopted in Western refineries. This process involves leaching finely ground matte under increasingly oxidizing conditions to separate PGMs from base metals. Various refining techniques include:
PGM refining involves classical and advanced methods. Classical refining processes are based on PGM chloride chemistry, including precipitation, redissolution, and thermal reduction. However, these methods often result in poor initial yields and lengthy refining times.
Crundwell et al. classify PGM refining techniques based on their method of separating platinum and palladium. Major South African companies use different methods: Lonmin Platinum employs precipitation, Anglo Platinum uses solvent extraction, and Impala Platinum relies on ion-exchange . Other notable processes include:
Several non-smelter-based processes are developed for PGM extraction:
The processing of PGMs involves complex and varied methods tailored to the specific mineralogical and chemical characteristics of the ores. Advances in refining technologies, including solvent extraction, molecular recognition, and non-smelter-based processes, continue to enhance the efficiency and yield of PGM recovery. The choice of process is influenced by the ore composition, the desired purity of the final product, and economic considerations. As global demand for PGMs remains strong, ongoing research and development are crucial for improving processing techniques and addressing the challenges of PGM extraction and refining.