Experimental determination of calcite solubility and the stability of aqueous Ca– and Na–carbonate and –bicarbonate complexes at 100–160 °C and 1–50 bar pCO2 using in situ pH measurements

International audienceThe solubility of calcite was measured at 100, 120, 140 and 160°C at 1-50 bar pCO2 in10-3-0.1 mol·kg-1 NaCl solutions using a new experimental setup involving in situ pH measurements with high-temperature solid-contact H-selective glass and two types of reference electrodes: i) Ag/AgCl in 3.5 M KCl, saturated AgCl placed in a Teflon extensible container with liquid junction, and ii) solid-contact high-T Na-selective glass electrode in the cell without liquid junction. The stability constants of NaHCO3° and NaCO3-aqueous complexes formation were determined in NaCl-Na2CO3/NaHCO3 solutions in CO2-free media and under 10 bar pCO2 from 100 to 160 °C. These values allowed calculation of the pH of the calibration solution in the system NaCl-CO2-H2O used in the cell without liquid junction with Na+-selective electrode as a reference. This highly stable, low-cost electrode system can be recommended for routine pH measurements at 4 < pH < 10 in sodium-bearing solutions up to 160°C and the critical point of CO2. The values of the stability constants of CaCO3° and CaHCO3+ aqueous complexes and calcite solubility product were generated at 100, 120, 140 and 160 °C allowing a description of the solubility of calcite in a wide range of pH and pCO2