Copper(II) oxide solubility behavior in aqueous sodium phosphate solutions at elevated temperatures

A platinum-lined, flowing autoclave facility is used to investigate the solubility behavior of copper(II) oxide (CuO) in aqueous sodium phosphate solutions at temperatures between 19 and 262°C. Copper solubilities are observed to increase continuously with temperature and phosphate concentration. The measured solubility behavior is examined via a Cu(II) ion hydrolysis/complexing model and thermodynamic functions for the hydrolysis/complexing reactions are obtained from a leastsquares analysis of the data. Altogether, thermochemical properties are established for five anionic complexes: Cu(OH)₃^–, Cu(OH)₄^2–, Cu(OH)₂(HPO₄)^2–, Cu(OH)₃(H₂PO₄)^2–, and Cu(OH)₂(PO₄)^3–. Precise thermochemical parameters are also derived for the Cu(OH)⁺ hydroxocomplex based on CuO solubility behavior previously observed (Ref. 3) for pure water at elevated temperatures. The relative ease of Cu(II) ion hydrolysis is such that Cu(OH)₃^– species become the preferred hydroxocomplex for pH9.4.Prepared for presentation at the Fourth International Symposium on solubility Phenomena, Rensselaer Polytechnic Institute, August 1990.