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Within the scop e of this study the leaching process of Cu, Zn, Co, Mo from the complex polymetallic sulfide concentrate with high Fe, As, which was produced in Central Kazakhstan using two methods is examined. The metal concentrations in the concentrate were 0.27% Cu, 0.026% Zn, 0.464% Co, 0.057% Mo, 15.51% Fe, 7.38% As. Nitrogen oxides formed in the processes of leaching were absorbed with water, the return of absorption product to the operation of leaching allowed reducing the consumption of nitric acid. The single-stage nitric acid leaching experiment was carried out at the leach concentrate productivity of 170±20 g/h, 80±2 °С, liquid/solid mass ratio (L/S) 6/1, leach time of 10.7 h, and nitric acid (57%) consumption of 0.12±0.01 l/h. The degree of capture of nitrous gases reached 97.8%. In these conditions Cu, Zn, Co, Mo, Fe, As were obtained with dissolution efficiencies of 96.98, 64.92, 99.99, 95.39, 80.13 and 99.80% respectively. Concentrations of NO3–, H+ and redox potential in the leachate were 88.7 g/l, 1.82 mol./l and 741 mV, respectively. The two-stage counter-current nitric acid leaching experiment was carried out at the leach concentrate productivity of 170±20 g/h, 80±2 °С, L/S 6/1, leach time of 26.8 h, and nitric acid (57%) consumption of 0.06±0.006 l/h. The degree of capture of nitrous gases reached 97.8%. In these conditions Cu, Zn, Co, Mo, Fe, As were obtained with dissolution efficiencies of 99.11, 85.23, 100.00, 88.60, 77.24 and 85.56%, respectively. Concentrations of NO3–, H+ and redox potential in the leachate were 46.7 g/l, 0.35 mol/l and 658 mV, respectively. Compared to single-stage leaching, two-stage counter-current nitric acid leaching allo ws the significant economy of nitric acid (256 g of 100% HNO3 per kilogram of concentrate), which is reduction of 48%. Moreover, counter-current leaching enables reduction in concentrations of NO3–, H+ and redox potential in the leachate. The further studies should focus on possible reduction in nitric acid consumption by lowering concentration of NO3– in leachate. The authors appreciate participation of I. A. Parygin, VNIPIpromtekhnologii in this study.

Gas-air mixtures that form in nitric acid leaching of sulfide raw materials possess the following peculiarities making a negative impact on trapping of nitrogen oxides: elevated temperature, different oxidation level of nitrogen oxides, slow oxidation of NO in region of low concentrations, and instability of the resulting gas-air mixture flow. Therefore, well-known methods of trapping nitrous gases shall be adapted to specific sulfide raw material. We propose a process flow diagram for trapping nitrous gases formed during nitric acid leaching of sulfide concentrates at atmospheric pressure on the example of Zhezkazgan concentrate. The paper addresses theoretical aspects of the use of water-ore pulp, concentrated sulfuric acid, process water and alkaline agents for trapping nitrous gases, and typical reactions of interaction of the proposed absorbents with nitrogen oxides. The choice of water-ore pulp as an absorber was made because of similarity between the mechanism of absorption of nitrogen oxides for neutral and alkali ore suspensions and the one for alkali solutions: nitrogen dioxide and nitrous anhydride are absorbed with formation of a solution of nitrates and nitrites. Due to availability in a liquid phase of ferrous iron along with NO2 and N2O3, acidic suspensions are also capable to absorb nitric oxide, to some extent, with formation of Fe(NO)SО4 complex. Process water absorbs only nitrogen dioxide, with formation of nitric and nitrous acids. Nitrous acid is an unstable compound in acidic environments and decomposes with formation of water and nitrogen oxide. At the stages of trapping nitrogen oxides with water-ore pulp and process water (circulating solution), it is recommended conditioning of gas-air mixtures by choosing the volume of additionally introduced air, in an amount to provide the highest rate of nitrogen oxide oxidation. At the stages of sulfuric acid and alkaline trapping of nitrogen oxides, it is recommended conditioning of gas-air mixtures by selecting the volume of additionally introduced air and the oxidation time of nitrogen oxide that provide an equimolecular mixture of NO and NO2. A distinctive feature of the use of water-ore pulp, concentrated sulfuric acid, process water and alkaline agents for trapping nitrous gases is possibility to use the products of absorption at the stage of sulfide concentrate leaching. The extended tests of trapping nitrous gases have been conducted. The plant capacity by the gas-air mixture ranged 17–21 m3/h, and by leached concentrate — 12–15 kg/h. In this case, the degree of capturing nitrous gases reached 96.8%. Return of the products of absorption of nitrous gases in the form of condensate, water-ore pulp, nitrosyl sulfuric acid, nitric acid solution, nitritenitrate lye allows to reduce the nitric acid consumption by 7–10 times relative the values obtained without using the trapping system. In this case, the degree of copper extraction into the leaching solution was 97.7%. The extraction degree of silver, rhenium, zinc was respectively 98.0%, 99.0%; 98.5%.