Experimental determination of the solubility product of dolomite at 50–253 °C

Abstract

The solubility of natural dolomite was investigated from 50 to 175 °C in 0.1 mol/kg NaCl solutions using a hydrogen electrode concentration cell (HECC). The resulting apparent solubility products (Qsp-dol) for the reaction Dolomite = Ca 2+ + Mg 2-+ 2 CO3 2were extrapolated to infinite dilution to generate the equilibrium constants for this reaction (Ksp°-dol),. Retrieved equilibrium constants are based on a constant standard state isobaric heat capacity (o rp C ) of-789.832 J/mol/K for this dolomite hydrolysis reaction and can be accurately described using log10 Ksp°-mgs = a + b/T (K) + cT (K), where a = 18.1777, b =-4400.8736 K and c(fixed)=-0.06919 K-1. Resulting constants are nearly equal to those determined from SUPCRT92 (Johnson et al., 1992) at 200 C, but as much as 1.8 orders of magnitude more negative at 50 °C, suggesting that dolomite is somewhat more stable than previously assumed. Standard equilibrium constants generated in this study were used together with corresponding properties for the aqueous species to calculate revised standard state thermodynamic properties for dolomite.

Solubility of the hydrated Mg-carbonates nesquehonite and dypingite from 5 to 35 °C: Implications for CO2 storage and the relative stability of Mg-carbonates

“…The standard molar Gibbs free energy of formation of nesquehonite calculated from our data was in very good agreement with that determined by Robie and Hemingway (1973), and Langmuir (1965), and the standard molar enthalpy of formation calculated from our data was in very good agreement with Robie and Hemingway (1973) (Table 3). The nesquehonite solubility product calculated from our data decreases slightly with increasing temperature, consistent with the solubility of other Mg-and Ca-carbonate minerals (Table 2) (e.g., Königsberger et al, 1999;Marion, 2001;Bénézeth et al, 2011Bénézeth et al, , 2018Gautier et al, 2014), and temperature dependence reported for nesquehonite solubility in previous studies (Dong et al, 2008;Wang and Li 2012). However, the temperature dependence is not signficant outside 3σ uncertainty (Table 2; Figure 5).…”

Thermodynamic Modeling of CO2-N2-O2-Brine-Carbonates in Conditions from Surface to High Temperature and Pressure

“…The logarithmic concentrations of Mg 2+ , Ca 2+ and H + in the solution at equilibrium with dolomite are provided in the literature [54]. A comparison between the experimental results from Bénézeth et al [54] and the results calculated using this model is shown in Figure 9. The trends of the measurements varying with temperature are also obtained by this model.…”

“…In NaCl solutions, dolomite solubility increases with NaCl molality in the lower salinity range (0-1.5) but decreases in the higher salinity range (1.5-6). To address the so-called "dolomite problem", Bénézeth et al [54] measured natural dolomite (CaMg(CO 3 ) 2 ) solubility with a temperature range of 50 to 253 ( • C) with 0.1 (molal) NaCl solutions using a hydrogen electrode concentration cell. The logarithmic concentrations of Mg 2+ , Ca 2+ and H + in the solution at equilibrium with dolomite are provided in the literature [54].…”

“…To address the so-called "dolomite problem", Bénézeth et al [54] measured natural dolomite (CaMg(CO 3 ) 2 ) solubility with a temperature range of 50 to 253 ( • C) with 0.1 (molal) NaCl solutions using a hydrogen electrode concentration cell. The logarithmic concentrations of Mg 2+ , Ca 2+ and H + in the solution at equilibrium with dolomite are provided in the literature [54]. A comparison between the experimental results from Bénézeth et al [54] and the results calculated using this model is shown in Figure 9.…”

“…Aqueous species concentration in equilibrium with dolomite obtained from experimental results[54] and the calculated results by this model at various temperatures.…”