Solubility of Litharge (α-PbO) in Alkaline Media at Elevated Temperatures.

An inert, flowing autoclave facility was used to investigate the solubility behavior of α-PbO (litharge, tetragonal) in aqueous solutions of morpholine, ammonia and sodium hydroxide between 38 and 260 ∘C. Lead solubilities increased from about 0.4 mmol-kg−1 at 38 ∘C to about 4.5 mmol-kg−1 at 260 ∘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. [ABSTRACT FROM AUTHOR]