Portlandite solubilities in supercritical Ar-H2O mixtures: implications for quantifying solvent effects

Abstract

Experimental studies indicate that changes in the activity of H2O at fixed pressure and temperature exert a strong influence on mineral solubilities in mixtures of H2O with non-polar solvents. These effects must be understood in order to predict mineral solubilities in mixed solvents such as CO2-H2O or CO2-CH4-H2O. In order to isolate these solvent effects, we have experimentally determined the solubility of portlandite in supercritical Ar-H2O mixtures using an extraction-quench hydrothermal apparatus. Solubilities were measured at 2 kb from 400° to 600°C and from a mole fraction of H2O, XH2O, of 0.97 to XH2O = 0.67. The solubility of portlandite decreases as the concentration of argon in the system increases. These changes in the solubility of portlandite at constant pressure and temperature are attributed primarily to changes in the dielectric constant of the bulk solvent. -from Authors