Prccipitation phenomena of calcite and research for apparatus and operational conditions

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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.