Prccipitation phenomena of calcite and research for apparatus and operational conditions

研究了氯化钙溶液与碳酸钠溶液反应沉淀碳酸钙的过程。在该反应中，碳酸钙中间体在反应初期生成，然后在反应液中转化为方解石和球文石的混合物，中间体的转化是本研究的重点。在中间体共存的反应料浆中加入氯化钠晶体，以方解石沉淀为主。加入氯化钠晶体的晶粒尺寸影响方解石的晶粒尺寸和析出数量，在中间体共存的反应浆液中，方解石的晶体生长速度较快。另一方面，方解石主要通过氯化钙溶液和碳酸氢钠溶液之间的反应而沉淀。在该反应中，方解石的析出数与碳酸氢钠的量有关，认为碳酸氢根离子的分解促进了中间体向方解石的转化，并以双射流反应结晶法沉淀银工业为例，沉淀碳酸钙为方解石和球文石的混合物，未发现方解石占优势沉淀的操作条件。研究了方解石在固定液中的结晶现象。结果表明，方解石和球霰石的混合物沉淀的平均过饱和度范围内，这是计算值的pH值从100至250。而方解石的析出则在平均过饱和度小于50或大于280的范围内。

Calcium carbonate precipitated by the reaction between calcium chloride solution and sodium carbonate solution was studied. In this reaction calcium carbonate intermediate was came out in the initial reaction step, and then transformed to mixture of calcite and vaterite in the reacting solution, and transformation of intermediate was focused in this study. Sodium chloride crystal was added to reacting slurry in which intermediate was coexisted, calcite was precipitated dominantly. Crystal size and precipitated number of calcite was affected by the crystal size of added sodium chloride crystal and crystal growth rate of calcite was obtained in the reacting slurry which intermediate was coexisted. On the other hand, calcite precipitated dominantly by reaction between calcium chloride solution and sodium bicarbonate solution. In this reaction, precipitated number of calcite was correlated with the amount of sodium bicarbonate and it was considered that transformation of intermediate to calcite was promoted by decomposition of bicarbonate ions.In the case of double jet reactive crystallization method wihch is applied for precipitation of silver halide industry, precipitated calcium carbonate was mixture of calcite and vaterite and it was not found the operational conditions which calcite precipitated dominantly. Therefore nucleating agent were considered to be necessary in this system.Crystallization phenomena of calcite in the stationary solution was studied. It was found that mixture of calcite and vaterite was precipitated within the range of average supersaturation which was calculate by the values of pH from 100 to 250. But the calcite was precipitated in the range of average supersaturation under 50 or over 280.