Thermodynamic analysis of pyrometallurgical processing of secondary copper smelter dusts

The object of research is secondary dust formed during melting of metallurgical dusts, slags and clinker, containing copper, zinc, precious metals, etc., on a shaft (S) and thermal (T) furnaces, not having realization and technologies of further processing, of the following composition, % (S/T): 1,5/2,1 Cu; 35,0/14,2 Pb; 19,1/11,8 Zn; 10,7/31,6 As; 1,4/0,9 Sb; 3,7/3,5 S; 4,4/2,0 Fe; 1,8/6,3 CDs; 0,4/1,9 Sn; 0,3/0,6 Te; 0,5/0,4 Bi; 1,0/0,6 [g/t] of Au; 71,8/29,6 [g/t] of Ag. The purpose of the work consists in justification of pyrometallurgical technology of processing secondary dusts, providing extraction of lead and zinc in a collective concentrate (Pb-Zn product), and also transfer of arsenic to separate product suitable for disposal. When performing balance calculations of equilibrium compositions in heterogeneous system “gas - liquid - solid” the Equilibrium Composition function of the Outotec's Chemical Reaction and Equilibrium Software HSC Chemistry program was used. Made an assumption that products of the reduction smelting of secondary dusts are: a gas phase into which pass volatile compounds of sulfur, zinc, arsenic; the slag received with fluxes (CaO•SiO2; Al2O3); a matte-speiss phase - iron-arsenical compounds; a metal phase - a lead alloy. In the roasting mode (600-650 °C) of secondary dust undesirable transition of easily sublimated compounds of arsenic to a gas phase amplifies in process of increase of initial content of the element in raw materials and decrease of lime amount in furnace charge. During melting (1300-1350 °C) of the furnace charge containing secondary dust (~ 32 % of As) and specific amounts of components to the mass of dust, %: 25.0 lime; 80.0 Fe-turnings; 9.0 mineral coal, the matte-speiss phase of composition, %: 26.3-29.6 As; 59.3-61.4 Fe; 0.7-1.7 Pb; 0.1-0.2 Zn has been received, which can be considered as the As-product suitable for disposal. Application of thermodynamic prediction (Equilibrium Composition function) with a variation of specific amounts of the following components of furnace charge to the mass of secondary dust, %: 1.0-14.5 Na2O; 0.7-9.7 SiO2; 1.3-14.8 CaO; 4.1-31.1 FeO; 1-10 C; 20-47 Fe, showed that decreasing the amount of reducers (Fe, FeO, C) and increasing the amount of flux components (CaO, Na2O, SiO2) in the system in the studied intervals, it is possible to increase the content of arsenic in the slag phase from ~ 20 to ~ 65 %. Range of application of results is the prediction of equilibrium compositions of the formed phases at pyrometallurgical processing of the intermediate products and wastage of the enterprises of nonferrous metallurgy.