| Lithium carbonate is one of the most important products in lithium industry,and its purity,particle size,degree of agglomeration and crystal morphology are the critical properties in the manufacture of lithium-ion battery.Although the existing production process of battery-grade lithium carbonate can meet the quality requirements in purity and particle size,there are still some problems such as complicated process route,severe crystal breakage and irregular morphology in final product.Therefore,the reactive crystallization process of lithium carbonate from lithium sulfate and sodium carbonate was studied in this work,which aims to achieve the mass production of monodisperse battery-grade lithium carbonate crystals.Based on modeling and optimization of traditional reactive crystallization process,the preparation conditions of monodisperse lithium carbonate crystals and agglomeration mechanism in reactive crystallization process were explored in order to develop a novel multi-stage cascade crystallization process.Firstly,the traditional reactive crystallization process of lithium carbonate was modeled and optimized using response surface method to explore the possibility of the battery-grade lithium carbonate crystals production.The effects of temperature,feeding rate,solution concentration,and stirring rate on yield,scale formation,particle size and particle size distribution were investigated.The prediction model of each response was obtained by multiple regression fitting of experimental data,the significance of prediction model and each factor as well as response surface were also analyzed.Taking the highest yield,the least scale formation,the smallest particle size and the narrowest particle size distribution as targets for multi-objective optimization,the results showed that traditional reactive crystallization process is difficult to produce battery-grade lithium carbonate crystals.Then,the preparation conditions of monodisperse lithium carbonate crystals and agglomeration mechanism in reactive crystallization process were explored in order to provide a theoretical support for the development of a novel crystallization process.The conditions for synthesis of monodisperse lithium carbonate crystals(crystallization at high temperature,low supersaturation and short residence time)were investigated by reactive crystallization experiments and the effect of temperature and supersaturation on morphology of lithium carbonate crystals was aslo discovered.During a continuous observation of crystallization in petri dish and crystallizer,it was proposed that the crystal agglomeration mainly results from the special nucleation and growth behavior rather than collisions of well-formed crystals.The crystallization process of lithium carbonate in aqueous system was studied in situ based on the process analysis technique.It was confirmed that the agglomeration rate of lithium carbonate is extremely fast and the serious fouling of crystallizer may originate from the heterogeneous nucleation on the wall.Finally,based on the study of preparation conditions for monodisperse lithium carbonate and agglomeration mechanism,the multi-stage cascade crystallization process was de veloped from an industrial perspective in order to make a better control of temperature,supersaturation and residence time in crystallization process.The obtained products are monodisperse lithium carbonate crystals with regular morphology,which purity and particle size are obviously better than those produced by the traditional reactive crystallization process.Although there is still a gap compared to the commercial battery-grade lithium carbonate products,the lithium carbonate crystals produced by multi-stage cascade crystallization process are still competitive in market because of its shorter production process route.In addition,the purity analysis revealed that the precipitation of impurities incorporate with lithium carbonate crystals in reactive crystallization was dependent on two mechanisms:adsorption into surface and solvent inclusion,and a small amount of washing water could greatly improve the purity of final product.The multi-stage cascade crystallization process was further simulated using Aspen Plus software,the mixing temperature and recycle ratio were determined for process optimization. |
