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Chemistry of nickel and copper production from sulphide ores
Nickel is one of Zimbabwe's principle metallurgical exports. It is processed to a very high level of purity and hence has a high value. The economics of nickel production can be difficult, as the selling value of nickel varies tremendously with time, from a low of US$ 3 900 per ton in late 1998 to US$ 10 100 per ton in May 2000, and to US$ 8 500 less than a year later. By contrast, copper is essentially a minor product in Zimbabwe, although still of significant value. It is now produced mainly from ores which are mined and processed in order to obtain more valuable products: nickel and gold. Sulphide copper ore was mined until recently near Chinhoyi, and processed at the nearby Alaska Refinery, producing crude (blister) copper which was then electrolytically refined. These mines have since closed, but the smelter and refinery now aim to process concentrates and matte from elsewhere. As will become clear, this process, although simpler, has many similarities to that for the combined nickel copper process. Copper is also produced at the relatively new Sanyati Mine, where the process involves acidic heap leaching of oxide ore, solvent extraction to concentrate the copper solution, and subsequent electro winning of the copper.
The Zimbabwe Science News Volume 34 Number 3&4, December 2000, pp. 61-65