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·SiO 2 ; Al 2 O 3 ); 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 Na 2 O; 0.7–9.7 SiO 2 ; 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, Na 2 O, SiO 2 ) 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.