Solubility and Stability of Nesquehonite (MgCO₃·3H₂O) in NaCl, KCl, MgCl₂, and NH₄Cl Solutions

This work reports the stability and solubility of nesquehonite in several salts (NaCl, NH 4 Cl, MgCl 2, and KCl) over the temperature range of (15 to 35) °C. The needle-like nesquehonite used in this work was prepared by the reaction of analytical pure MgCl 2 with Na 2 CO 3 . The concentration investigated for all salts was up to 4 mol·dm −3 NaCl, 3.5 mol·dm −3 NH 4 Cl, 4 mol·dm −3 MgCl 2, and 1.0 mol·dm −3 KCl at ambient temperature. The solubility of nesquehonite in pure water was found to decrease with temperature within the temperature range in which nesquehonite is the stable phase. In NaCl solutions, the solubility of nesquehonite initially increases to a maximum value and then decreases gradually with an increase of the common salt concentration. It was further found that the addition of MgCl 2, NH 4 Cl, or KCl causes the solubility of nesquehonite to increase due apparently to complexation. XRD and SEM examination of the equilibrated solids showed that nesquehonite is stable in pure water up to 50 °C, but its stability region becomes smaller in concentrated brines.