Polymorph transformation and formation mechanism of calcium carbonate during reactive extraction-crystallization process

Distiller waste produced in ammonia-soda process restricts the development of soda industry. In this study, the polymorph transformation and crystallization mechanism of calcium carbonate in the reactive extraction-crystallization coupled process were investigated. The results show that carbon dioxide (CO2) is first absorbed by the organic phase and then transferred to the aqueous phase. Calcium bicarbonate is generated and then decomposed into amorphous calcium carbonate rapidly. Temperature has a significant effect on the polymorph of calcium carbonate. Needle-like aragonite forms preferentially at higher temperatures and spherical and flower-like vaterite forms preferentially at lower temperatures. Both of them will finally transform into rhombic calcite by dissolution and recrystallization. At 20℃, the formation of new vaterite and its transformation to calcite occur simultaneously in the coupled process. The content of vaterite in the particles increases with the increase of CO2 concentration. © All right reserved.