Solubility of ZnO and hydrolysis of ZnCl2 in KCl melts

Abstract

An oxide-ion specific electrode has been used to measure the solubility of ZnO in KCl by potentiometric titration of ZnCl₂ in KCl with oxide. The solubility product of ZnO was found to be 2.3 × 10^–8 mol² kg^–2 at 1073 K. On the addition of ZnCl₂ to oxide ion solutions a zincate species was formed, ZnO^2–₂, with a formation constant of 3 × 10^–12 mol³ kg^–3. Attempts to isolate K₂ZnO₂ have been unsuccessful.

The effect of HCl on dissolved oxide ion in ZnCl₂(33.3 mol.%)–KCl has been studied over the temperature range 733–873 K. Treatment of this salt with HCl yields an oxide concentration of ca. 10^–10 mol. kg^–1, but this rapidly increases to ca. 10^–3 mol kg^–1 when the salt is held under argon, through reaction with trace amounts of water in the gas.

The equilibrium reaction: H₂O(g)+ 2Cl^–⇌ 2HCl(g)+ O^2– has been studied and the equilibrium constant is given by: log K= 2.514 – 8163/T