Application Of A Continuous Technique To Secondary Copper Smelting

CIM Bulletin, Vol. 70, No. 788, 1977

D. H. Pulling and F. A. Garner, Wolfson Secondary Metals Research Group, Department of Minerals Engineering, University of Birmingham, Birmingham, U.K., Dr. Pulling is now with Tolltreck Limited, Droitwich, Worcestershire, U.K.

Statistics for copper consumption from various sources show that the importance of production from secondary sources is increasing. This is of particular significance in countries such as the U.K., which are totally dependent on secondary material for the supply of home-produced copper. A brief survey of the U.K. industry has shown that, in the past, relatively high profit margins have not encouraged high capital investment and development of more sophisticated operating techniques, but set against a background of rapidly escalating operating and energy costs, together with an ever-increasing demand for copper, it is anticipated that the industry will see great changes in the near future. With this in mind, an experimental furnace for continuous smelting of copper-bearing scrap has been developed at the University of Birmingham. This furnace has been designed to combine the conventional operations of blastfurnace or reverberatory smelting, usually followed by converting, in one unit, and incorporates many of the features of the WORCRA and Noranda processes for continuous primary smelting. It consists of a long, sloping channel, constructed of chrome-magnesite refractory, which is charged near the top. Smelting is effected lower down the channel, where_ iron, etc., in the scrap is oxidized and slagged off with silica flux. Provision is made for air injection to increase oxidation rates. Metal can flow from the bottom of the channel, and slag from the top, so that a counter-current flow is achieved. The approximate molten capacity is 25 kg. Various scrap charges, both synthetically made and as supplied from various industrial smelters, have been successfully smelted. Metal of 83-95% Cu has been produced, depending on the original charge composition and the degree of air injection, although air injection was also found to considerably increase the copper loss to slag. Recoveries of other valuable non-ferrous metals in the charge were good. One of the great advantages of this process is the far more efficient heat utilization that can be achieved as compared with the conventional process. Calculations from the heats of oxidation of the various elements removed to the slag show that, for a wide range of scrap of the type normally smelted, the process should be completely autogenous. Although this was never achieved during actual operation of this furnace, due to the large heat losses that cannot be eliminated in such a small furnace, reductions in power input of over 50% have been produced and it is confidently predicted that even greater savings will be possible when the furnace is enlarged.
Keywords: Mineral processing, Smelting, Copper smelting, Continuous smelting, Scrap, Secondary copper, Heat losses, Blast furnaces, Worcra Process, Noranda Process, Electrolysis.