Abstract
Aragonite, a polymorph of CaCO 3, is used in the paper industry as filler and pigment. To determine the reaction conditions used during causticization, the solubility of Ca(OH) 2 and CaCO 3 in NaOH solution and the crystallization behavior of aragonite were investigated. The solubility of CaCO 3 in a NaOH solution reached a maximum value with NaOH concentration. Decrease in the solubility after that value was due to the conversion of CaCO 3 to Ca(OH) 2. In 1 mol/l of NaOH solution containing a concentration of Na 2CO 3 greater than 0.02 mol/l, CaCO 3 appeared to be in a stable phase as compared to Ca(OH) 2. In the crystallization experiments, it was determined that reaction temperature strongly influenced the size, shape, and polymorph of CaCO 3. The highest precipitation of aragonite occurred at 50 °C. At 50 °C, the percentage of aragonite in crystallized CaCO 3 increased as the NaOH concentration in the mother liquor was increased. This result indicates that aragonite was predominantly precipitated in the presence of NaOH.
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