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 (η) 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 [CO₃ ²⁻], 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.