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The solubility of BaCO3(cr) (witherite) in CO2-H2O solutions between 0 and 90??C, evaluation of the association constants of BaHCO3+(aq) and BaCO30(aq) between 5 and 80??C, and a preliminary evaluation of the thermodynamic properties of Ba2+(aq)

Geochimica et Cosmochimica Acta

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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 BaCO3(cr) = Ba2+(aq) + CO32-(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 + 0.121098T - 20011.25/T - 236.4948 log T where T is in degrees Kelvin. The log K of BaCO3(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 BaHCO3+(aq) and BaCO30(aq) Three different methods were used to evaluate the association constant of BaHCO3+(aq), and all yielded similar results. The temperature dependence of the association constant for the reaction Ba2+(aq) + HCO3-(aq) = BaHCO3+(aq) is given by log KBaHCO3+ = -3.0938 + 0.013669T. 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 Ba2+(aq) + CO2-3(aq) = BaCO03(aq) is given by log KBaCO30 = 0.113 + 0.008721T. 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 BaCO3-CO2-H2O 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 ??fH?? and ??fG?? of Ba2+(aq) to -532.5 and -555.36 kJ ?? mol-1, respectively, for agreement with solubility data. ?? 1986.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
The solubility of BaCO3(cr) (witherite) in CO2-H2O solutions between 0 and 90??C, evaluation of the association constants of BaHCO3+(aq) and BaCO30(aq) between 5 and 80??C, and a preliminary evaluation of the thermodynamic properties of Ba2+(aq)
Series title:
Geochimica et Cosmochimica Acta
Volume
50
Issue:
10
Year Published:
1986
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
2225
Last page:
2233
Number of Pages:
9