Solid-solute phase equilibria in aqueous solution. XI. Aqueous solubility and standard Gibbs energy of cadmium carbonate

The solubilities of CdCO3 (otavite) in aqueous NaClO4 solutions have been i nvestigated as a function of ionic strength (0.15 less than or equal to I/m ol-kg(-1) less than or equal to 5.35, 25 degrees C) and temperature (25 deg rees C less than or equal to T less than or equal to 75 degrees C, I = 1.00 mol-kg(-1)). A new Chemsage optimization routine was employed to simultane ously evaluate solubility data from this work and other sources, as well as standard electrode potentials determined at different ionic strengths. Wit h the Pitzer equations the solubility constants, *K-ps0(I) were extrapolate d to infinite dilution resulting in log *K-ps0(0) = 6.14+/-0.10 and the ter nary ion-interaction parameters (S)theta(Na,Cd) = 0.19 and psi(Na,Cd,ClO4) = -0.037 at 25 degrees C. In addition, the following set of thermodynamic q uantities can be derived from the present solubility data for otavite: Delt a(f)G(-) = -674.2+/-0.6 kJ-mol(-1); Delta(f)H(-) = -755.3 +/- 3.4 kJ-mol(-1 ); S- = 93 +/- 10 J-mol(-1) K-1. However, the present solubility data are a lso consistent with a recent determination of the standard entropy of otavi te which leads to a recommended set of thermodynamic quantities[Delta(f)G(- )(CdCO3) = -674.2+/-0.6;Delta(f)H(-)(CdCO3) = -752.1+/-0.6; S-(CdCO3) = 103 .9+/-0.2].