Solubility of CuO(s) in highly alkaline solutions

The solubility of tenorite, CuO(s), has been measured at 25 °C and 60 °C as a function of total hydroxide concentration, [OH−]T, at constant ionic strength (I = 5 or 6 mol kg− 1) in Li(OH,ClO4)(aq) and Na(OH,ClO4)(aq) media. Additional measurements were also made in highly concentrated (≥ 6 mol kg− 1) NaOH(aq) and KOH(aq). The solubility (S) of CuO(s), measured as the total concentration of dissolved Cu(II) by atomic absorption spectroscopy, decreased at approximately constant [OH−]T in the order LiOH ≫ NaOH > KOH and increased with temperature and [OH−]T in all media. Plots of log S against log [OH−]T were linear with a slope of ~ 2.0, indicating, consistent with UV–Vis spectra, that the only significant Cu(II) species in solution was Cu(OH)42 −(aq) under all conditions studied. Detailed analysis indicates that previous studies overestimated S because of the presence of fine particles of CuO(s). Using equilibrium constants and SIT parameter values derived from the present experimental data, the solubility of CuO(s) could be described with good precision up to the highest hydroxide concentrations investigated in all media.