thumbnail

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

By:
and
DOI: 10.1016/0016-7037(86)90077-3

Links

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 logK = 607.642 + 0.121098T − 20011.25/T − 236.4948 logT where T is in degrees Kelvin. The logK 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−1and −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 logKBaHCO3+ = −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 bylogKBaCO30 = 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 ΔfH° and ΔfG° of Ba2+(aq) to −532.5 and −555.36 kJ · mol−1, respectively, for agreement with solubility data.

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
DOI:
10.1016/0016-7037(86)90077-3
Volume
50
Issue:
10
Year Published:
1986
Language:
English
Publisher:
Elsevier
Description:
9 p.
First page:
2225
Last page:
2233
Online Only (Y/N):
N
Additional Online Files(Y/N):
N