The solubility of CaMoO4(c) and an aqueous thermodynamic model for Ca2+-MoO 4 2 -ion-interactions

The solubility of powellite [CaMoO₄(c)] was studied in aqueous Na₂MoO₄, CaCl₂ and Ca(NO₃)₂ solutions ranging in concentrations from 1×10^–4M to 1.0M and over equilibration times extending to 36 days. Our experimental data were interpreted using the aqueous ion-interaction model of Pitzer and coworkers. The Ca²⁺–MoO₄^2– ion-interactions were found to be analogous to Ca²⁺–SO₄^2–. The use of Ca²⁺–MoO₄^2– ion-interactions parameters (⁽⁰⁾=0.2, ⁽¹⁾ = 3.1973 and ⁽²⁾) and a logK_sp of –7.93 gave excellent predictions of all of the experimental data. Commonion ternary interaction parameters such as MoO₄^2––Cl^– or MoO₄^2––NO₃^– were not required.