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The solubility of BaCO 3 (cr) (witherite) in CO 2 -H 2 O solutions between 0 and 90°C, evaluation of the association constants of BaHCO 3 + (aq) and BaCO 3 0 (aq) between 5 and 80°C, and a preliminary evaluation of the thermodynamic properties of Ba 2+ (aq)

Eurybiades Busenberg·Niel Plummer
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Abstract

One hundred and fifty new measurements of the solubility of witherite were used to evaluate the equilibrium constant of the reaction BaCO 3 ( cr ) = Ba 2+ ( aq ) + CO 3 2− ( aq ) between 0 and 90°C and 1 atm total pressure. The temperature dependence of the equilibrium constant is given by log K = 607.642 + 0.121098 T − 20011.25/ T − 236.4948 log T where T is in degrees Kelvin. The log K of BaCO 3 (cr), the Gibbs energy, the enthalpy and entropy of the reaction at 298.15 K are −8.562, 48.87 kJ · mol −1 , 2.94 kJ · mol −1 and −154.0 J · mol −1 · K −1 , respectively. The equilibrium constants are consistent with an aqueous model that includes the ion pairs BaHCO 3 + (aq) and BaCO 3 0 (aq) Three different methods were used to evaluate the association constant of BaHCO 3 + (aq), and all yielded similar results. The temperature dependence of the association constant for the reaction Ba 2+ ( aq ) + HCO 3 − ( aq ) = BaHCO 3 + ( aq ) is given by log K BaHCO 3 + = −3.0938 + 0.013669 T . The log of the association constant, the Gibbs energy, the enthalpy and entropy of the reaction at 298.15°K are 0.982, −5.606 kJ · mol −1 , 23.26 kJ · mol −1 and 96.8 J · mol −1 · K −1 , respectively. The temperature dependence of the equilibrium constant for the reaction Ba 2+ ( aq ) + CO 2− 3 ( aq ) = BaCO 0 3 ( aq ) is given by log K BaCO 3 0 = 0.113 + 0.008721 T . The log of the association constant, the Gibbs energy, the enthalpy and entropy of the reaction at 298.15° K are 2.71, −15.49 kJ · mol −1 , 14.84 kJ · mol −1 and 101.7 J· mol −1 · K −1 . The above model leads to reliable calculations of the aqueous speciation and solubility of witherite in the system BaCO 3 -CO 2 -H 2 O from 0 to more than 90°C. Literature data on witherite solubility were re-evaluated and compared with the results of this study. Problems in the thennodynamic selections of Ba compounds are considered. Newer data require the revision of Δ f H° and Δ f G° of Ba 2+ (aq) to −532.5 and −555.36 kJ · mol −1 , respectively, for agreement with solubility data.

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Eurybiades Busenberg, Niel Plummer. 1986. The solubility of BaCO 3 (cr) (witherite) in CO 2 -H 2 O solutions between 0 and 90°C, evaluation of the association constants of BaHCO 3 + (aq) and BaCO 3 0 (aq) between 5 and 80°C, and a preliminary evaluation of the thermodynamic properties of Ba 2+ (aq). https://doi.org/10.1016/0016-7037(86)90077-3

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