Chemical synthesis of CaCO3 minerals at low temperatures and implication for mechanism of polymorphic transition
Gen-Tao Zhou, ; Yong-Fei Zheng,
published: Sep 26, 2001
ArtNo. ESP154017603004, Price: 29.00 €
Polymorphs of calcium carbonate were synthesized in a temperature range of 0 to 90 °C by the slow decomposition of Ca2+-Mg2+-HCO3-Cl--H2O or Ca2+-Mg2+-Na+-HCO3- -Cl--H2 solution and the overgrowth with SrCO3, BaCO3 or PbCO3 as seed crystals. The results show that an increase in temperature favours the formations of metastable aragonite and unstable vaterite, and that an increase in Mg2+ concentration or a decrease in Ca(HCO3)2 solution concentration promotes the formation of aragonite. The processes and mineralogical mechanisms of polymorphic transition from aragonite to calcite and from vaterite to calcite were investigated by means of XRD and SEM techniques. The results indicate that the rates of polymorphic transition from aragonite to calcite and from vaterite to calcite in aqueous solution are very fast, only within the time order of a day or far shorter, and that their mechanism of polymorphic transition is related to dissolution-reprecipitation process.