Study On Controlled Synthesis Of Spherical Calcium Carbonate

Spherical calcium carbonate has many outstanding advantages,such as large specific surface area,good dispersibility,fluidity and solubility.It has important applications in papermaking,plastics,electronics,ink and ceramics.At present,the common preparation methods of spherical calcium carbonate are carbonization process,microemulsion method,simulated biomineralization method and metathesis method.The carbonization process needs to control a series of factors,such as the proportion of gases and the way of adding gases,which is complex and difficult to control;Microemulsion method requires the preparation of microemulsion,which makes the crystallization reaction of calcium carbonate in microemulsion droplets,and is not suitable for large-scale industrial production.In order to reduce energy consumption,simplify operation and facilitate industrial production,the advantages of biomineralization and metathetic reaction are combined well.In the presence of boric acid,spherical calcium carbonate with stable morphology and uniform particle size was prepared by ion exchange precipitation reaction in liquid phase.Firstly,calcite spherical calcium carbonate crystals were prepared by metathesis(ion exchange)precipitation with boric acid as controlling agent,calcium chloride and sodium carbonate as raw materials.The effects of the concentration of mineralization control agent,reaction temperature,reaction time and the ratio of reactants on the particle size and morphology of calcium carbonate were studied.The results show that when the concentration of boric acid is 0.4 mol/L,the dropping rate of saturated sodium carbonate solution at 20 ? is 4.9 mL/min,the concentration of reactant is 0.1 mol/L,the aging time is 60 min,the reaction temperature is 50 C and the ratio of reactants is 1:1,the spherical calcium carbonate particles obtained are uniform and minimum in size,with an average particle size of 1.57 ?m.Secondly,calcite spherical calcium carbonate crystals were prepared by metathesis(ion exchange)precipitation with boric acid as controlling agent,calcium nitrate and sodium carbonate as raw materials.The effects of reaction factors on the particle size and morphology of calcium carbonate were investigated in the same way.The optimum reaction factors were determined as follows: the concentration of boric acid is 0.4 mol/L,the dropping rate of saturated sodium carbonate solution is 7.8 mL/min at 20 ?,the concentration of reactants is 0.1 mol/L,the reaction time is 90 min,the aging time is 120 min,the reaction temperature is 50 ? and the ratio of reactants is 1:1,the spherical calcium carbonate particles obtained are uniform in size and the minimum average particle size is 1.36 ?m.In the research process,the morphology,crystal structure,phase and particle size of the products were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),infrared spectroscopy(IR)and centrifugal particle size analyzer.The theoretical basis and support were provided for the study.The controlling mechanism of the synthesis reaction was preliminarily explored based on the characterization results.