Controllable Preparation And Morphology Control Of Insoluble Carbonate Microspheres

Difficult soluble carbonate with special morphology and particle size distribution（PSD）,such as calcium carbonate（CaCO₃）,strontium carbonate（SrCO₃）,barium carbonate（Ba CO₃）,have important applications in ink,electronics,military and other fields.The coprecipitation and carbonation method are important processes in the production.However,the traditional coprecipitation and carbonization methods are often limited by the mixing effect of reaction materials,resulting in large particle size,wide PSD.Moreover,it is difficult to control the morphology of particles.How to effectively solve the problems,find suitable additive to adjust the particle morphology and select efficient mixing mode to strengthen the coprecipitation reaction,has been an attractive research topic.The miniature Y-jet mixer is used to enhance the mixing efficiency to prepare strontium carbonate（SrCO₃）microspheres by using co-precipitation method.Ethylenediamine tetraacetic acid disodium（EDTA-2Na）is used as additive to control particle morphology.The effects of EDTA-2Na concentration,reactant concentration and flow rate on the morphology and PSD of SrCO₃particles are studied.The experimental results show that the orbicular spherical SrCO₃particles can be obtained with EDTA-2Na as additive,and the molar concentration ratio of EDTA-2Na to SrCl₂,R_E,is the key factor affecting the morphology and size of SrCO₃particles.With the increase of R_E,the shape of SrCO₃particles changes from bundle to flower and then to ball.When R_E=0.2 and the concentration of reactant is 0.1 mol/L,the volume-weighted average particle size(d₄₃)obtained is 2.77μm,and the particle size distribution（PSD）is very narrow.The mechanism of EDTA-2Na regulating SrCO₃morphology is also discussed.When boric acid（H₃BO₅）is used as additive,the spherical SrCO₃particles could still be obtained.With the molar concentration ratio of H₃BO₅to reactant R_Hincreasing gradually,the d₄₃experienced a process of first becoming smaller and then becoming larger.The fast co-precipitation is further extended.EDTA-2Na is used to prepare calcium carbonate（CaCO₃）and barium carbonate（Ba CO₃）with special morphology.Calcite type CaCO₃particles are prepared.The results show that CaCO₃particles are massive particles without EDTA-2Na.When the molar concentration ratio of EDTA-2Na to CaCl₂,R_aincreases,the morphology of the particles changes from massive to rod and then to dumbbell.When R_a=0.2 and the reactant concentration is 0.1 mol/L,the CaCO₃particles are very uniform rod structure,with a smallest d₄₃of 4.05μm.Using barium chloride（Ba Cl₂）and sodium carbonate（Na₂CO₃）as raw materials to prepare barium carbonate（Ba CO₃）particles,when the concentration ratio of EDTA-2Na to Ba Cl₂,R_Bincreases,the particles gradually change from rod to dumbbell-shaped particles,and finally to spherical particles.The eutectic carbonates of Sr and Ca are prepared using EDTA-2Na as additive.The influence of the concentration ratio of Sr and Ca on the morphology and size of eutectic particles is investigated.Finally,carbonization reaction is enhanced by a novel long-short blades（LSB）impeller to prepare spherical CaCO₃particles.The effects of EDTA-2Na addition and Ca（OH）₂concentration on the morphology and PSD of CaCO₃particles are studied.The results show that when the molar concentration ratio R_Aof EDTA-2Na to Ca（OH）₂is 0.125,calcite CaCO₃particles with narrow PSD and spherical morphology can be prepared,and the particle size is about 1μm-3μm.Monitoring the reaction time shows that with the increase of R_A,the reaction time becomes longer and the carbonization process slows down.By fixing R_Aand increasing reactant concentration,it can be found that the morphology of CaCO₃is deteriorated,which is consistent with the phenomenon of coprecipitation method for CaCO₃preparation.