Calcite solubility in Na–Ca–Mg–Cl brines

This study investigated calcite solubility approached from undersaturation in geologically relevant Na–Ca–Mg–Cl synthetic brines (35 to 200 g l− 1 TDS) at CO2 partial pressures of ∼ 0.1, 0.5 and 1.0 bar at 25 °C. Total carbon dioxide content, total alkalinity and total calcium content were measured and the carbonic acid species distribution and ion activities calculated using the Pitzer equation-based program EQPITZER. Stoichiometric (pKsp⁎) equilibrium constants ranged from 6.4 to 4.8, decreasing with increasing brine TDS. In general, good agreement was found between measured and predicted solubility data. Evaluation of the Ca2+ and CO32− activity coefficients with EQPITZER in brines