Solubility of litharge (α-PbO) in alkaline media at elevated temperatures

An inert, flowing autoclave facility was used to investigate the solubility behavior of alpha-PbO ( litharge, tetragonal) in aqueous solutions of morpholine, ammonia and sodium hydroxide between 38 and 260 degrees C. Lead solubilities increased from about 0.4 mmol-kg(-1) at 38 degrees C to about 4.5 mmol-kg(-1) at 260 degrees C and were relatively insensitive to the concentration and identity of the reagent used to control the pH. The measured lead solubilities were interpreted using a Pb(II) ion hydroxocomplexing model and thermodynamic functions for these equilibria were obtained from a least-squares analysis of the data. A consistent set of thermodynamic properties for the species Pb( OH)(+), Pb(OH)(2)(aq) and Pb(OH)(3)(-) was obtained that will permit accurate lead oxide solubility calculations to be made over broad ranges of temperature and alkalinity.