The 20 Mt reverberatory furnace slag dump at Nkana in Zambia contains a substantial quantity of cobalt. A 40MW DC arc furnace has been built at Chambishi for the purpose of recovering cobalt from the slag. The technology was jointly developed by Mintek and Anglovaal Mining Ltd (Avmin), and the furnace was designed by Bateman Titaco.Testwork at the 150-250 kW scale was conducted at AVRL, and larger scale piloting was conducted at Mintek (in partnership with Avmin) in a 3 MW DC arc furnace. Approximately 840 tons of Nkana dump slag (ranging from 0.66 percent Co) was processed at power levels around 1-2MW. Good overall cobalt extraction was achieved, and approximately 100 tons of cobalt-bearing alloy was produced (containing 5 to 14 percent Co). This testwork demonstrated that the Nkana dump slag could be processed in a DC arc furnace of suitable design, to produce a cobalt-hearing alloy suitable for further hydrometallurgical processing.Bateman Titaco were contracted to design and build the furnace, and the design team contained representatives from Avmin and Mintek. The project was conceived as a fast-track exercise, and many activities had to be run in parallel. Notable features of the furnace include an ABB power supply, a Concast conductive hearth, the refractory design, and copper cooling in the sidewalls.Power to the furnace was switched on during January 2001.
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