CO_(2)微气泡强化纳米碳酸钙的制备及传递-反应分析

Preparation of nano-calcium carbonate intensified by CO_(2)micro bubble and transfer-reaction analysis

控制碳酸钙的粒径大小和粒径分布是碳化法制备高质量纳米碳酸钙的关键。采用间歇鼓泡碳化法制备纳米碳酸钙,考察了操作参数(气体流量、初始浆料浓度)、气泡类型(普通气泡、微气泡)对碳酸化反应速率和沉淀碳酸钙的粒径大小及分布的影响规律,同时深入分析了反应过程中稳定区和突变区随气泡类型的变化规律。结果表明,在使用普通气泡时,增加二氧化碳气体流量有利于二氧化碳的吸收和碳酸钙粒径的减小;在小塔中使用普通气泡,随着初始浆料浓度增加,在低浓度下,减小碳酸钙粒径,当浓度升高到一定程度后,对反应时长和物质混合的影响会促进晶体增长,使碳酸钙粒径增加。采用微气泡后会显著减小沉淀碳酸钙的粒径,同时,二氧化碳气体流量不再影响碳酸钙的粒径分布,表明气液传质过程不再是控制步骤。

Carbonization is one of the common methods to prepare nano calcium carbonate.Controlling the particle size and particle size distribution of calcium carbonate is the key to the preparation of highquality nano-calcium carbonate by carbonization.Different operating conditions have different effects on the reaction products.The particle size and size distribution of calcium carbonate can be effectively controlled by controlling different reaction conditions to improve the mass transfer and reaction conditions in the slurry.In batch-operated bubble column reactor,gas flow rate and bubble size are factors affecting mass transfer.This study investigates the influences of operation condition(gas flow rate,initial slurry condition),bubble type(ordinary bubble,micro bubble)on carbonation reaction rate and particle size distribution of calcium carbonate.Furthermore,the effects of bubble type on the stable region and abrupt change region in carbonation reaction process are analyzed.The experimental results show that when using ordinary bubble,the increase of CO_(2)flow rate accelerates the reaction process and reduces the particle size of calcium carbonate,but it does not affect the time of abrupt change region.With increasing the slurry concentration,the particle size first decreases and then increases in small-diameter column with ordinary bubble.However,when using micro bubble,the particle size of calcium carbonate is significantly reduced,and the time of abrupt change region decreases with the increase of gas flow rate.Moreover,the CO_(2)flow rate is no longer an influential factor on calcium carbonate particle size,which means that the gas-liquid mass transfer process is not the rate controlling step of carbonation reaction.This study provides some references for studying the application of micro bubbles in calcium carbonate crystallization.