In January 2001, Chambishi Metals commissioned a 40MW DC arc furnace using selective carbothermic reduction for processing reverberatory furnace slag stockpile of 20 million tons containing 0.34 to 4.5 % cobalt, and an average of 1.1 % copper. Cobalt occurs as fayalite whereas copper occurs as oxide and sulphide. An atomizer unit to atomize furnace product, molten Co/Cu/Fe alloy, and a pressure oxidation leach process to leach cobalt and copper and separate iron as goethite was also commissioned. Cobalt and copper containing solution is processed in the refinery for production of metals.
The commissioning and ramp up period was much longer than projected due to premature failure of the hearth and other operational problems associated with the feed system, cooling system and power control. Furnace availability was low and affected the throughput and metal production. This had put tremendous pressure on the company due to poor cash flow and non repayment of the capital resulting in sale of 100 % of its share in July 2003. A systematical analysis initiated then, to de-bottleneck the furnace operation, was successful, resulting in attainment of design throughputs. The Plant Historian Database (PHD) was used for the analysis.
Commercial application of the DC arc furnace on smelting of copper smelter slag was unique and therefore required extensive literature search to broaden the knowledge of the theory and the practice.
The thesis shows improvements and modifications carried out on feed system to create charge bank, selection of flux to modify the slag chemistry, modification of alloy chemistry, re-configuration of the power control system and increased atomization capacity. Following the implementation of these, the furnace performance attained design levels.