Thermodynamic Modeling of the Fe(II)–Fe(III)–Cu(II)–H₂SO₄–H₂O Solution and Its Application to Determination of Redox Potential during Copper Electrorefining up to 70 °C

Abstract

A thermodynamic model of the Fe­(II)–Fe­(III)–Cu­(II)–H2SO4–H2O system is developed and shown to reliably simulate the species distribution in the industrial copper electrorefining electrolyte from 25 to 70 °C. The previously developed model of the Fe­(II)–Fe­(III)–H2SO4–H2O system under leaching conditions was first evaluated, and it proved that its applicability can be extended to a much higher acid concentration (185 g/L). Cu­(II) species were then identified, and their thermodynamic data were collected and assessed for modeling calculations. Results reveal that after addition of a high amount of copper (40–50 g/L), Fe­(II) is still distributed as free Fe2+, FeHSO4 +, and FeSO4°; Fe­(III) is distributed as free Fe3+, FeSO4 +, FeHSO4 2+, and Fe­(SO4)2 –. Cu­(II) is dissolved as Cu2+, CuSO4°, and CuHSO4 +. The proposed model was validated by reliable and accurate prediction of the measured redox potential throughout all solution conditions. An expression developed previously to predict the redox potential can still be applied in this work. Analysis of speciation results strongly supports that the redox potential of acidic iron sulfate solutions with such a high acid and copper concentration can still be solely determined by the Fe3+/Fe2+ couple. The pH and effective ionic strength were also obtained and discussed. These findings contribute to further investigation on speciation of other solutions during copper production.