Analysis of the solubility equilibria of yttrium carbonate in aqueous perchlorate media using the Pitzer and Brønsted–Guggenheim–Scatchard ion-interaction models

Abstract

The solubility of yttrium carbonate has been studied at 25.0 °C by measuring the H⁺ concentration of yttrium perchlorate solutions in contact with the solid phase and saturated with CO₂–N₂ gas mixtures. Measurements were made in mixed Y(CIO₄)₃–NaClO₄ media, where the yttrium concentration varied from trace levels up to 1.00 mol dm^–3, and the total perchlorate concentration from 0.3 to 3.00 mol dm^–3. Some measurements were also made in 0.01 mol dm^–3 NaCl using trace concentrations of Y^III. The Pitzer model gave an excellent description of the solubility data for the equilibrium Y₂(CO₃)₃(s)+ 6H⁺⇌ 2Y³⁺+ 3CO₂(g)+ 6H₂O, in the entire concentration range when using tabulated Pitzer parameters for rare-earth perchlorates as a model for Y(ClO₄)₃, and experimentally determined values for the additional parameters necessary to describe the mixed electrolyte effects. The equilibrium constants at trace concentrations of yttrium at each perchlorate concentration level investigated were, within the uncertainty of the experiment, the same when using both the Pitzer and Brønsted–Guggenheim–Scatchard method. The same was also the case for the extrapolated equilibrium constants at zero ionic strength, whee log *K_s0 is equal to 21.37 ± 0.26 and 21.68 ± 0.18, respectively.