Crystallization of CaCO3 in Aqueous Solutions with Extremely High Concentrations of NaCl

The effect of NaCl at extremely high concentrations from 3.5 to 14 wt. % on the crystallization of CaCO3 was investigated in depth. The static test experiment verified that the Ca2+ retention efficiency (eta) of NaCl on CaCO3 scale increased from 31.06% (3.5 wt. %) to 41.56% (14 wt. %). Based on the calculation of supersaturation rations, the high concentration of NaCl could reduce the activity coefficients of [Ca2+] and [CO32-], thus reducing the actual concentration of CaCO3. The CaCO3 deposition rate constants (k) showed that NaCl slowed down the rate of CaCO3 crystallization. The X-ray diffraction (XRD) testing disclosed that the growth of (1 0 4) and (1 1 0) faces from calcite was impeded, while the formation of (1 1 1) face from aragonite was induced by the increasing concentration of NaCl. The inductively coupled plasma optical emission spectrometry (ICP-OES) results indicated that Na+ could be doped into CaCO3, leading to the one-dimensional crystal growth. It was further proved that NaCl heightens the efficiency of the typical phosphate inhibitors (2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) and 1-hydroxyethane-1,1-diphosphonic acid (HEDP)) on prohibiting the scale of CaCO3.