Thermodynamic Model for BiPO4(cr) and Bi(OH)3(am) Solubility in the Aqueous Na+–H+– $\mathrm{H}_{2}\mathrm{PO}_{4}^{-}$ – $\mathrm{HPO}_{4}^{2-}$ – $\mathrm{PO}_{4}^{3-}$ –OH−–Cl−–H2O System

Abstract

Prior to this study no data for the solubility product of BiPO4(cr) or the complexation constants of Bi with phosphate were available. The solubility of BiPO4(cr) was studied at 23±2 °C from both the over- and under-saturation directions as functions of a wide range in time (6–309 days), pH values (0–15), and phosphate concentrations (reaching as high as 1.0 mol⋅kg−1). HCl or NaOH were used to obtain a range in pH values. Steady state concentrations and equilibrium were reached in 9.0, Bi(OH)3(am) is the solubility controlling phase. Reliable values for the Bi(OH)3(am) solubility reactions involving Bi(OH)3(aq) and \(\mathrm{Bi}(\mathrm{OH})_{4}^{-}\) and the formation constants of these aqueous species are also reported.