Some Observations on the Chloride Based Treatment of Nickel-Copper-Cobalt Mattes

摘要

Smelting of nickel sulphide concentrates produces a liquid Fe/Ni/Cu/Co/PGM sulphide, also called furnace matte, from which nearly all of the iron and most of the sulphur are removed by air oxidation at approximately 1200℃, in a process called converting. The sulphur is emitted from the converter as SO_2. The final product is called finished or converter matte, or simply "matte", and is cooled slowly, or fast by water granulation, depending on subsequent processing. The smelting route is still the most elegant and economical method to remove the iron and gangue impurities as a disposable slag from such concentrates on a large scale. It is practised in smelters worldwide. Producing saleable nickel, cobalt, copper and PGM's (Platinum Group Metals) from these mattes has been achieved by a variety of methods, mainly hydrometallurgical. Refining processes based on sulphate chemistry were the logical first choice, followed by carbonyl, ammoniacal and chloride based processes. This paper specifically compares sulphate and chloride systems. Chloride based refining was pioneered successfully by Falconbridge at its Nikkelverk, Kristiansand-S, Norway refinery and has been adopted at refineries in France and Japan. The advantages of treating matte by the chloride route for past and future producers are discussed in the paper, with particular emphasis on the low cost of cobalt recovery, if solvent extraction can be applied. The latter depends on creating a nickel chloride leach liquor with a high chloride normality, which dictates the lixiviant to be either super-azeotropic HC1 or chlorine gas. Process recovery of the lixiviant from the solubilised nickel chloride is imperative for environmental and cost reasons. Problems and opportunities with applicable recovery systems for HCl and Cl_2 will also be addressed in detail. Finally, some speculation is presented as to how recent chloride technology developments could be used to advantage in chloride based processing of mattes.