Study On Preparation And Mechanism Of Calcium Carbonate With Special Morphology Using Dolomite As Raw Material

Vaterite and aragonite,as a metastable form of calcium carbonate,have excellent physical and chemical properties.In recent years,vaterite and aragonite have received more and more attention in the field of biology and medicine.There are fewer reports on products prepared without the use of additives.Dolomite has abundant reserves in my country,and the preparation of high value-added chemical products using dolomite as raw material is still a research hotspot.In this work,the controlled synthesis of vaterite and aragonite was realized in the CaCl₂-NH₃-CO₂ reaction system without additives.The effects of reaction temperature,NH₃ was introduced for time,CO₂ flow rate,CO₂ was introduced for time,mixing speed and aging time on the product were discussed.The formation mechanism of vaterite and aragonite is explained.Vaterite was prepared at 20℃～40℃,and the influence of reaction conditions on the product was discussed.The suitable conditions for preparing vaterite were determined to be reaction temperature of 30℃,ammonia was introduced for time of 60min,CO₂ flow rate of 80 ml/min,and speed of 700r/min,CO₂ was introduced for time of 90min to get the optimal product.Analysis and characterization of the product found that the vaterite content was 97.69%,and the purity was high.The product is loose and porous,with a specific surface area of 32.653m²/g and an average pore size of 2.972nm,which provides a good space for its application in biology and medicine.At 80°C～95°C,aragonite calcium carbonate with different morphologies of spindle,irregular cube,strip and hexagonal prism was obtained by changing the reaction temperature and CO₂ was introduced for time.The morphology of the hexagonal prism is characterized and analyzed,and the diameter of the product is 0.5-3μm,the length is 1-30μm,and the molecular formula is CaCO₃·¹/（12）Ca（OH）₂·1/3H₂O.Both vaterite and aragonite are prepared from ACC to vaterite（aragonite）.NH₄⁺-NH₃ buffer system is formed in the solution during the reaction,which not only increases the solubility of CO₃^2-,but also provides a stable solution environment for the growth of vaterite and aragonite.Mg²⁺in dolomite played a favorable role in the growth of vaterite and aragonite.