Patent GB-1366545-A (GB)
Title: Copper refining process
IPC: C22B7/04
Filed: 1971-10-14
Abstract: 1366545 Refining copper; recovering tin and lead LA MTALLO-CHIMIQUE S A 14 Oct  1971 [14 Oct 1970] 47876/71 Heading C7D [Also in Division F4] A process for refining copper and recovering tin and lead from copper-bearing materials and scrap is characterized by subjection of the reaction masses to high degrees of agitation which promotes high mass transfer rates between gas, metal and slag phases, allowing rapid selective reactions to take place at relatively low temperatures and thus minimizing vapourization of lead and tin in the form of their oxides. The operations temperature is generally just above the temperature at which the slag becomes fluid. Process Stages, Fig. 1 (a) A melting furnace is charged with copperbearing materials, solid material containing metallic iron, normally copper-iron scrap, alkaline or neutral flux, e.g. lime, and silica. The charge is melted under a neutral flame. (b) As the temperature of the charge increases, chemically combined copper, lead, tin or nickel is reduced by the metallic iron to form a metal phase and a silicate slag phase. The reduction should be carried out with a neutral or slightly reducing flame, sufficient metallic iron being added that the slag contains effectively no copper, lead or tin, the lead, tin and nickel being concentrated in the black copper phase. Zinc is volatilized, oxidized in the exhaust system and recovered as zinc oxide in a dust collection system. Sufficient silica must be supplied that the iron is predominantly present as a silicate in the slag. (c) The slag is separated from the black copper. (d) Optionally, the black copper is pre-refined by adding silica and subjecting the bath to an oxidizing flame. Zinc and iron contained in the black copper are oxidized and removed in a slag which is recycled to the melting furnace. Conveniently, yellow brass is added at this stage which absorbs the heat of reaction. (e) The black copper is refined by blowing with oxygen which selectively oxidizes metallic impurities. Silica is again added to absorb the oxides and anode-grade copper containing the major proportion of nickel in the original charge, is tapped. The nickel may be recovered from spent electrolyte at a later stage. The oxygenblowing is preferably accomplished in successive operations, refining slags being withdrawn and copper-rich material, e.g. red brass, and silica being added after each operation. The refining slag contains some copper and a higher concentration of lead and tin in the form of oxides. (f) In a preferred embodiment the refining slag is treated with metallic iron and burnt lime under a neutral or slightly reducing flame which selectively reduces the combined copper: this black copper is recycled to the refining bath. Further reduction with metallic iron provides a metal rich in lead and tin, and a spent slag. The metal may be processed to remove any remaining copper or nickel for recycling. In this preferred embodiment, only a stoichiometric amount of iron sufficient to reduce the combined copper is provided prior to recycling of the resulting black copper. In all of the above stages, a high degree of agitation is employed which enables the temperature to be maintained at levels only a little higher than those at which the slags are fluid, e. g. below 1300C preferably around 1180C; thus the lead and tin is gradually concentrated through the stages. Apparatus Three furnaces may be utilized, a melting furnace, a refining furnace and a slag recovery furnace. Each furnace is effectively identical, and is arranged so that it may be rotated at various speeds while at the same time its inclination may be altered, Figs. 3-6 (not shown). The rotational speed of the furnace is gradually increased until the molten bath contained therein is carried up the wall of the furnace and then cascades down again.