Thermodynamic patterns for hydrochemical oxidation of non-ferrous metal sulphide minerals in nitric acid media
The paper represents the results of studying certain physicochemical patterns occurring during hydrochemical oxidation of non-ferrous metal sulphide minerals in nitric acid media. The study was aimed at establishing the thermodynamic probability of the occurrence of particular interactions and determining the most favourable conditions for effecting processes in given modes. Changes in the Gibbs energy and the logarithm of the reaction equilibrium constants at various process temperatures are calculated to assess the possibility of various reactions between nitric acid and the main minerals present in sulphide raw materials of non-ferrous metals. For the purpose of visualising thermodynamically stable compounds when changing the oxidising conditions of the studied heterogeneous systems, Purbe Eh-pH diagrams were constructed. In order to obtain most accurate prediction of obtaining the necessary interaction products of nitric acid and the studied sulphide minerals, the equilibrium component distribution was calculated for liquid and solid phases of the studied systems. All thermodynamic calculations were performed using the HSC Chemistry software (Finland). As a result of calculations for the Gibbs energy change and the logarithms of the interaction equilibrium constants of sulphide minerals with nitric acid, the significant thermodynamic probability of the reaction occurrence with the formation of the desired compounds is established. By constructing the Purbe diagrams, the necessary conditions for the occurrence of certain interactions and stable state of the detected products across a wide range of potentials and pH values of the heterogeneous systems under consideration are established. The calculations of the component equilibrium distribution in the studied systems confirmed the results of the thermodynamic calculations, relating them to the real hydrochemical conditions of nitric acid leaching in terms of acid consumption for obtain the desired products. The performed study allows an assessment of the reaction progress and the formation of certain products during the interaction of the raw material main components with nitric acid carried out from the perspective of thermodynamic patterns.