title: Process development for elemental recovery from PGM tailings by thermochemical treatment: Preliminary major element extraction studies using ammonium sulphate as extracting agent.
abstract: Mine tailings can represent untapped secondary resources of non-ferrous, ferrous, precious, rare and trace metals. Continuous research is conducted to identify opportunities for the utilisation of these materials. This preliminary study investigated the possibility of extracting major elements from South African tailings associated with the mining of Platinum Group Metals (PGM) at the Two Rivers mine operations. These PGM tailings typically contain four major elements (11% Al2O3; 12% MgO; 22% Fe2O3; 34% Cr2O3), with lesser amounts of SiO2 (18%) and CaO (2%). Extraction was achieved via thermochemical treatment followed by aqueous dissolution, as an alternative to conventional hydrometallurgical processes. The thermochemical treatment step used ammonium sulphate, a widely available, low-cost, recyclable chemical agent. Quantification of the efficiency of the thermochemical process required the development and optimisation of the dissolution technique. Dissolution in water promoted the formation of secondary iron precipitates, which could be prevented by leaching thermochemically-treated tailings in 0.6M HNO3 solution. The best extraction efficiencies were achieved for aluminium (ca. 60%) and calcium (ca. 80%). 35% iron and 32% silicon were also extracted, alongside chromium (27%) and magnesium (25%). Thermochemical treatment using ammonium sulphate may therefore represent a promising technology for extracting valuable elements from PGM tailings, which could be subsequently converted to value-added products. However, it is not element-selective, and major elements were found to compete with the reagent to form water-soluble sulphate-metal species. Further development of this integrated process, which aims at achieving the full potential of utilisation of PGM tailings, is currently underway.
authors.affiliation: Council for Geoscience, Private Bag X112, Pretoria 0001, South Africa; Department of Geology, University of Pretoria, Lynnwood Road, Pretoria 0002, South Africa.
authors.forename: Sameera
authors.initials: S
authors.lastname: Mohamed
authors.affiliation: Department of Chemistry, University of Pretoria, Lynnwood Road, Pretoria 0002, South Africa.
authors.forename: Elizabet M
authors.initials: EM
authors.lastname: van der Merwe
authors.affiliation: Department of Geology, University of Pretoria, Lynnwood Road, Pretoria 0002, South Africa.
authors.forename: Wladyslaw
authors.initials: W
authors.lastname: Altermann
authors.affiliation: Council for Geoscience, Private Bag X112, Pretoria 0001, South Africa; Chemical Resource Beneficiation, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa. Electronic address: fdoucet@geoscience.org.za.
authors.forename: Frédéric J
authors.initials: FJ
authors.lastname: Doucet
mesh_terms: D000645:Ammonium Sulfate / Q000737:chemistry*; D008670:Metals / Q000032:analysis*; D008906:Mining; D059027:Recycling / Q000379:methods*; D013019:South Africa; D018505:Waste Management / Q000379:methods*
chemical_list: D008670:Metals; D000645:Ammonium Sulfate
keywords: Ammonium sulphate; Metal recovery and extraction; PGM tailings; Solid–solid reaction; Thermochemical treatment