Aqueous speciation of sulfuric acid–cupric sulfate solutions

Abstract This work presents the development and use of an ion-association multicomponent equilibrium model and the application of an ion-interaction model developed by Pitzer, to simulate the distribution and concentration of chemical species (speciation) in sulfuric acid–cupric sulfate solutions in the 0– 200 g / l H 2 SO 4 and 0– 50 g / l Cu(II) concentration range and 15–70°C temperature range. The model consists of a set of equations that represent the equilibrium relationships for the ionic reactions and the mass balances for the components present in the system. The effect of ionic strength was taken into account by correcting the equilibrium constants using a relationship proposed by Davies. Several species can be formed at various pH and temperature values, the principal ones being: HSO 4 − , H + , SO 4 2− , Cu 2+ , and CuSO 4 (aq). Simulations show that concentrations are highly dependent on pH. Sulfuric acid speciates mainly as bisulfate ion (HSO 4 − ) and hydrogen ion (H + ) at pH values lower than 1. Calculations including Davies’ relationship show very good agreement with experimental values for the ionic conductivity of the solution. The conductivity of the aqueous CuSO 4 –H 2 SO 4 solution decreases as cupric sulfate is added, due to the resulting decrease in hydrogen ion concentration. The model presented in this work can be applied to predict and to analyze the solution composition in electrolytic copper processes such as leaching, electrowinning and electrorefining, as well as the purification of industrial solutions used in hydrometallurgical processing.