Benezeth, P;
Berninger, U-N;
Bovet, N;
Schott, J;
Oelkers, EH;
(2018)
Experimental determination of the solubility product of dolomite at 50–253 °C.
Geochimica et Cosmochimica Acta
, 224
pp. 262-275.
10.1016/j.gca.2018.01.016.
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Abstract
The ‘dolomite problem’, the scarcity of present-day dolomite formation near the Earth’s surface, has attracted much attention over the past century. Solving this problem requires having reliable data on the stability and kinetics of formation of this mineral. Toward this goal, the solubility of natural dolomite (CaMg(CO3)2) has been measured from 50 to 253 °C in 0.1 mol/kg NaCl solutions using a hydrogen electrode concentration cell (HECC). The obtained apparent solubility products (Kapp-sp-dol), for the reaction: CaMg(CO3)2 = Ca2+ + Mg2+ + 2CO32−, were extrapolated to infinite dilution to generate the solubility product constants for this reaction (Ksp°-dol). The derived equilibrium constants were fit and can be accurately described by log10 Ksp°-dol = a + b/T (K) + cT (K) where a = 17.502, b = −4220.119 and c = −0.0689. This equation and its first and second derivatives with respect to T were used together with corresponding aqueous species properties to calculate the revised standard state thermodynamic properties of dolomite at 25 °C and 1 bar, yielding a Gibbs energy of formation (ΔfG298.15∘) equal to −2160.9 ± 2 kJ/mol, (log10 Ksp°-dol = −17.19 ± 0.3); an enthalpy of formation (ΔfH298.15∘) of −2323.1 ± 2 kJ/mol, an entropy (S298.15∘) of 156.9 ± 2 J/mol/K and heat capacity (Cp298.15∘) of 154.2 ± 2 J/mol/K (uncertainties are 3σ). The dolomite solubility product derived in this study is nearly identical to that computed using SUPCRT92 (Johnson et al., 1992) at 200 °C, but about one order of magnitude higher at 50 and 25 °C, suggesting that dolomite may be somewhat less stable than previously assumed at ambient temperatures.
| Type: | Article |
|---|---|
| Title: | Experimental determination of the solubility product of dolomite at 50–253 °C |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1016/j.gca.2018.01.016 |
| Publisher version: | https://doi.org/10.1016/j.gca.2018.01.016 |
| Language: | English |
| Additional information: | This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | Dolomite solubility product, Thermodynamic properties, Stability |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10046117 |
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