Research Of Preparation Of Precipitated CaCO₃ And Nano-CaCO₃ With Limestone

The demand of precipitated cacium carbonate is increasing continuously, while our native cacium carbonate productions trailed developed country because of lower production value, so it is necssary to develope new preparation technique to promote competitive ability of our native cacium carbonate productions.In this research limestone was chosed as raw materials to prepare calcium oxide with high activity, then precipitated cacium carbonate and Nanometer cacium carbonate were prepared by carbonation method, in which process the effects of reactant's concentration and temperature, insufflate rate of CO₂, stir speed and shape control agents on the shape and particle size of the CaCO₃ were studied.The results of research show limestone with 4～8mm particle size was calcined under 950℃for 4 hours or 1000℃for 2 hours, then calcium oxide with high activity could be got. Using 10%wt Ca(OH)₂ suspension made by calcium oxide and water, with 1000r/min stir speed and 2L/h·g Ca(OH)₂ insufflate rate of CO₂, precipitated calcite CaCO₃ with average grain size less than 2μm and brightness 93.8% was obtained. Tempetature was an important factor in the carbonation process of nanometer cacium carbonate's preparation, and the initial temperature of carbonizing reactant should be controlled below 25℃. Grain size of CaCO₃ was minishing when the insufflate rate of CO₂ from 0.36 increased to 0.8L/h·g Ca(OH)₂, then with the increasing insufflate rate of CO₂, product's grain size is getting steady and Particulate of Cubic CaCO₃ about 40nm was obtained, but the reaction time decreased continually. CaCO₃ with grain size about 100nm was obtained when stir speed was 300rpm, and when the stir speed increased to 600rpm, 40nm CaCO₃ particle was produced, at the same time, the reation time was getting less.In the presence of sodium citrate of 2%wtCa(OH)₂, chain-like calcite nano-CaCO₃ which length-to-diameter ratio was 9 was obtained. In this reaction systerm, continuously adding calcium hydroxide and controlling the speed of insufflate rate of CO₂ simultaneously, snowflake and chain-like shaped particles of CaCO₃ were yielded. As the chelate agent of Ca²⁺, EDTA2Na absorbed to the surface of CaCO₃ crystallite had better tropism ability than sodium citrate. In the presence of EDTA2Na of 2%wtCa(OH)₂, chain-like calcite nano-CaCO₃ of which length-to-diameter ratio was 38 was yielded.