Equilibrium cuprous concentrations in copper sulfate–sulfuric acid solutions containing 50–110 g/L Cu+ 2 and 10–200 g/L H2SO4 at 50–95 °C

Copper sulfate (66–323 g/kg H2O; ~ 25–110 g/L Cu+ 2) and sulfuric acid (10–233 g/kg H2O, ~ 10–200 g/L) solutions were reacted with copper metal at temperatures between 50 and 95 °C to form Cu+ until equilibrium was attained. Samples were collected into an NH4Fe(SO4)2·12H2O solution to convert cuprous to ferrous, which were then titrated with standard Ce(IV) using very dilute ferroin as the indicator. In order to estimate solution compositions in volumetric units (e.g. g/L) the densities of the parent CuSO4–H2SO4 solutions at the reaction temperatures were used. Some additional density data, beyond that available in the literature was needed. Density as a function of temperature and masses of CuSO4 and H2SO4 per kg of water was fitted to an empirical equation. Density was also estimated based on known concentrations of Cu+ 2 and H2SO4 in g/L and temperature using an alternative correlation. Cuprous concentrations were determined as mol/kg of sample. Cuprous concentrations in g/L were fitted to an expression of the form: = V e − W / T Cu + 2 X Y H 2 SO 4 2 + Z H 2 SO 4 + 1 [Cu+], [Cu+ 2] and [H2SO4] are in g/L at specified temperature T (K) and V–Z are empirical constants. The empirical expression simulated the measured [Cu+] to within ± 3.6%. The cuprous concentrations were also fitted to the same type of equation using concentrations on the molal scale. These matched the experimental values to within ± 3.5%. Varying sulfuric acid concentrations were found to have only a modest influence on the equilibrium cuprous concentrations. With 10–200 g/L H2SO4 and a given [Cu+ 2] the difference between the highest and lowest [Cu+] was 7% at most. At 95 °C with a solution containing 107–109 g/L Cu+ 2 and 10–200 g/L H2SO4, the [Cu+] was 1.70–1.75 g/L.