Kell hydrometallurgical process for extraction of platinum group metals and base metals from flotation concentrates
KS Liddell, MD Adams

The Kell Process has been developed for the extraction of platinum group metals (PGMs)and base metals from sulphide flotation concentrates. The process has been successfully tested on several different sulphide flotation concentrates, including those from the UG2 chromitite horizon and the Platreef mafic/ultramafic layer. It has been shown to provide high (>95 per cent) and selective extraction efficiencies for the key valuable metals, i.e. Pt, Pd, Rh, Au, Ni, Co, and Cu.
The Kell Process consists of several commercially proven unit operations. S, Ni, Co, and Cu are first selectively removed by use of a pressure oxidation step during which the dissolution of PGMs is minimized. The residue from pressure oxidation is subjected to a thermal treatment to ensure efficient PGM recovery by subsequent chlorination. All the core steps are very similar to well-proven conventional unit operations in common use, as are the subsequent metal recovery steps to provide marketable end products. Typical metallurgical responses of flotation concentrates from UG2 and Platreef to the Kell Process are provided, and key outcomes of an energy comparison study with smelting are summarized in this paper.
Kell presents a potentially substantial improvement in PGM concentrate processing technology, in terms of economics via muchreduced power costs, ease of processing, and various environmental benefits. It allows for the treatment of high-chromium low-grade ‘dirty’ concentrates, such as secondary concentrates from the platinum industry’s ‘mill-float-mill-float’ (MF2) flotation circuits and concentrates from retreatment of tailings. It allows greater concentrate mass pulls, has higher tolerance to gangue intergrowths in concentrates, and its use can provide substantial increases in overall PGM recovery. Its adoption would be a step change in the platinum industry, and given the commercially proven unit operations embodied in the Kell Process, at much-reduced risk compared with other more experimental technologies. Since the initial process development work, significant improvements and refinements have been introduced as a result of further comprehensive testing and process modelling. Pilot-scale testing and engineering study work is in progress for several selected sites.
Keywords: Kell, platinum, palladium, rhodium, PGM, nickel, copper, UG2, Merensky, Platreef, concentrate, flotation, smelting, matte, hydrometallurgy, leaching, pressure oxidation, roasting, chlorination, refining, metal recovery, energy consumption.