Ural Federal University named after the first President of Russian Federation B. N. Eltsin, Ekaterinburg, Russia:

L. G. Elfimova, Senior Lecturer, e-mail: elg-mtf@yandex.ru
N. G. Ageev, Assistant Professor
S. S. Naboychenko, Professor of the Department “Non-Ferrous Metals Metallurgy”

In this article, HSC Chemistry 6 software (Equilibrium Composition module) was used to create thermodynamic prediction of pressure oxidation leaching of copper-nickel converter matte in sulfuric acid media. A synthetic sample of the material was prepared by admixture of copper-nickel mattes and nickel plants semi-products. According to rational composition of the material and stoichiometric amounts of reagent substances for chemical reactions of the leaching were selected the following variable parameters: sulfuric acid consumption of 0.001–1.0 kmol and oxygen consumption of 0.09, 0.62, 1.2, 1.8 kmol. Possible chemical reactions and equilibrium state diagrams of solid and liquid phases are given. At oxygen consumption of 0.09 kmol – metallic nickel, iron and copper and cobalt sulfide were dissolved. The main nickel phase of the model sample – heazlewoodite (Ni₃S₂), were shown to decompose into NiS and NiSO4. A probability of the refractory compound Ni₃S₄ formation as an intermediate phase were observed. The main copper phase of the model sample – chalcocite (Cu₂S) was shown to dissolve at higher values of sulfuric acid consumption with CuS and CuSO₄(a) formation, however, aqueous copper sulfate wasn’t observed as a product of process due to its exchange interaction with nickel and cobalt sulfides. The possibility of elemental sulfur formation was confirmed. An increase in oxygen consumption up to 1.2 kmol led to decrease in nickel sulfides amount as the leaching products. Significant part of nickel was presented in solution (93%). At oxygen consumption of 1.8 kmol and low sulfuric acid consumption — copper sulfides were partly oxidized with aqueous copper sulfate formation and copper hydroxide and basic sulfate were observed as the main solid phases. An increase in sulfuric acid consumption higher than 0.4 kmol allowed to extract most of the copper into solution with aqueous sulfate formation. A comparison of the thermodynamic prediction data with experimental results (t = 85 ^оC, L/S = 6, P_O2 = 0.23 MPa, [H₂SO₄]/Ni = 0.52, acid consumption 0.54 g/g) was shown significant similarities. Results indicate the possibility of nickel/copper selective separation at the stage of oxidative leaching.

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