Speciation and thermochemical modeling of the ternary system CuSO4 – H2SO4 – H2O in the temperature range 273.15–373.15 K

Abstract

In this work, models have been developed that allow to estimate the ionic speciation and solution properties, such as: water activities, solubilities, densities, and ionic conductivities in the ternary system CuSO4 – H2SO4 – H2O in the temperature range 273.15 – 373.15 K, which constitutes the basis of hydrometallurgical processes to produce copper cathodes by electrowinning and copper sulfate pentahydrate by crystallization. For this, a parameterization of the required mathematical models was carried out, such as: the Pitzer ionic interaction model, the HKFmoRR equation of state (EOS), and the Appelo model, using the hydrogeochemical code PHREEQC in coupling with the optimization software PEST. These models allowed standard deviations of 0.3 %, 1.2 %, 0.3 % and 9.6 % for water activities, copper sulfate pentahydrate solubilities (CuSO4·5H2O), densities, and ionic conductivities, respectively, in the ternary system studied. The calculated ionic speciation results showed that the main dissolved species were: Cu2+, SO42-, CuSO40, H+, and HSO4-. The concentration of free sulfate ion (SO42-) decreases as the total concentration of sulfuric acid increases, due to the ion association and formation of complexes HSO4-, CuSO40, and H2SO40. This work provides new values of the Pitzer interaction parameters as a function of temperature, mainly those related to the neutral complex CuSO40 and H2SO40 (λni and ζnij).