The induced crystallization reaction in a CaCl2-Na2CO3solution system will be initiated under the precondition that the concentrations of Ca2+ and CO2-3 are in the metastable region. A critical value is the boundary point of the metastale region, which was investigated in this study by the electric conductivity method. Various factors that influence the critical value, such as temperature, pH, reaction time and agitating strength, were investigated, and graphs of the metastable region of the CaCl2-Na2CO3 solution system were drawn under various conditions. The results showed that lower temperature, higher pH and proper agitating strength are favorable for decreasing the electric conductivity when the critical value appeared in the solution, or to expand the metastable region. Taking maneuverability and cost into consideration, the optimal reaction conditions for induced crystallization of the CaCl2-Na2CO3 solution system were: temperature 25 ℃, pH 9.0,agitating time 10 min and agitating strength 200 r/min. Under such conditions,the induced crystallization reaction was guaranteed to proceed in the metastable region if the relation between the concentration of Ca2 + and CO2-3 was satisfied according to 3.496 × 10 - 10 [Ca2+]-1.1826 ＜ [CO2-3]＜ 4.96 × 10 -9 [Ca2+]-1%CaCl2:-Na2CO3溶液体系中c(Ca2+)和c(CO32-)处于介稳区中,是该体系诱导结晶反应能够进行的前提条件.临界值点是介稳区的边界点,应用电导率法测定CaCl2-Na2CO3溶液体系的临界值点,对影响临界值的温度,pH,反应时间和搅拌强度等因素进行了研究,绘制了不同条件下CaCl2-Na2CO3溶液体系的介稳区.结果表明,降低温度.增加溶液的pH,搅拌强度适中能够降低出现临界值时的电导率,增加介稳区的面积.考虑到试验的可操作性和成本等因素,确定CaCl2-Na2CO3溶液体系诱导结晶反应的最佳条件:温度为25℃,pH为9.0,反应时间为10 min,搅拌强度为200 r/min.在最佳反应条件下,c(Ca2+)和c(CO32-)满足3.496×10-10[ca2+]-1.182 6<[CO3-2]<4.96×10-9[Ca2+]-1时,诱导结晶反应能够在介稳区中进行.
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