Solid-Solute Phase Equilibria in Aqueous Solution. XI. Aqueous Solubility and Standard Gibbs Energy of Cadmium Carbonate

Abstract

The solubilities of CdCO₃ (otavite) in aqueous NaClO₄ solutions have been investigated as a function of ionic strength (0.15 ≤ I/mol-kg⁻¹ ≤ 5.35, 25°C) and temperature (25°C ≤ T ≤ 75°C, I = 1.00 mol-kg⁻¹). A new Chemsage optimization routine was employed to simultaneously evaluate solubility data from this work and other sources, as well as standard electrode potentials determined at different ionic strengths. With the Pitzer equations the solubility constants, ${}^*K_{{\text{ps0}}}^{\text{I}}$, were extrapolated to infinite dilution resulting in log ${}^*K_{{\text{ps0}}}^{\text{0}}=6.14 \pm 0.10$ and the ternary ion-interaction parameters ^Sθ_Na,Cd = 0.19 and $\psi _{{\text{Na,Cd,VClO}}_{\text{4}} }=-0.037$ at 25°C. In addition, the following set of thermodynamic quantities can be derived from the present solubility data for otavite: Δ_f G ^Θ = −674.2±0.6 kJ-mol⁻¹; Δ_f H ^Θ = −755.3±3.4 kJ-mol⁻¹; S ^Θ = 93±10 J-mol⁻¹K⁻¹. However, the present solubility data are also consistent with a recent determination of the standard entropy of otavite which leads to a recommended set of thermodynamic quantities [Δ_f G ^Θ(CdCO₃) = −674.2±0.6; Δ_f H ^Θ(CdCO₃) = −752.1±0.6; S ^Θ(CdCO₃) = 103.9±0.2].