Study On The Crystallization Of Lithium Carbonate

Lithium is an important strategic resource, and the crystallization of Li2CO3 is the key process in the lithium industry. The objective of this research is to provide theoretical guidance and technological support for the production as well as to enrich the basic theory and studying method for the industrial crystallization.According to the development demand of the lithium industry, this research systematically investigated the crystallization processes of Li2CO3 in the preparation of primary product (LiCl+Na2CO3), high-purity product (decomposition of LiHCO3, recrystallization of Li2CO3, LiOH+CO2) and ultrafine powders (anti-solvent reactive crystallization, spray pyrolysis).The unseeded metastable zone of Li2CO3 in aqueous solution was studied by laser method, and the results show the temperature and the feeding rate of Na2CO3 are the two critical factors influencing the supersolubility. The seeded supersolubility of Li2CO3 was measured by FBRM, which shows a larger surface area is beneficial to enhace the supersolubility level.The unseeded induction period and primary nucleation of Li2CO3 was examined by the laser method, and a series of nucleation parameters were obtained such as interfacial energy, contact angle, nucleation order etc. The seeded induction period and secondary nucleation of Li2CO3 was investigated by FBRM and PVM. The adsorption model can explain the effect of seed size and seed loading on the secondary nucleation. A method through comparison between pure breakage/attrition and nucleation process was put forward to distinguish the attrition-induced and surface-induced nucleation quantitatively, which can reveal the contributions of different nucleation mechanisms.The effects of operational conditions on the crystallization in the preparation of primary Li2CO3 product were explored. A variable-temperature reactive crystallization was put forward, which features a high yield, a large and homogeneous crystal size as well as good fluidity. Because the traditional method of kinetic research, which based on the PBE, is not fit to this system, so a novel neural-net work simulation method was presented. The neural net work simulation can be divided into Lagrangian method and Euler method, both of them obtained good results in this crystallization. The novel neural-net work simulation is referential for other complex crystallization processes.Results show a smaller crystal size, a higher temperature and the presence of ultrasound advances the dissolution rate, while the stirring speed has nearly no effect. The evolution of chord length distribution and crystal shape of Li2CO3 particles were monitored by FBRM and PVM respectively. Two method, Avrami model and moment transformation, were adopted to describe the dissolution kinetic processes. The introduction of proper seed, a high initial concentration and a moderate stirring speed is preferred in the recrystallization. This research put forward a recrystallization craft of Li2CO3, and by which good rod crystals were prepared.As for the coupled process of decomposition and reactive crystallization of LiHCO3, the theoretical decomposition temperature was evaluated as 4.25℃.A thermal analysis technique was put forward to characterize the reaction thermal effect by using Labmax reactor, which implied that the reaction became more drastic when the temperature was beyond 90℃. The effects of operating parameters on the apparent reaction rate were investigated, through which a novel empirical correlation was presented to describe the apparent reaction rate as a function of temperature, reactant concentration and stirring speed. The ultrasound-assisted and microwave assisted crystallization kinetics in the decomposition of LiHCO3 were investigated respectively, and the kinetic parameters were achieved. A new craft by using the combination of ultrasound and microwave during the decomposition of LiHCO3was carried out and obtained good results.A falling film tower and a spinning disk reactor were used in the gas-liquid reactive crystallization. Results show the carbonation end point of pH should be controlled within 9.5-10. The effects of operating conditions on the carbonation of LiOH were studied systematically. A neural-net work was set up to describe the complex carbonation of LiOH involving both reactive adsorption and reactive crystallization. The neural-net work simulation can simultaneously give the adsorption rate, crystallization rate and crystal size distribution accurately. An orthogonal experiment was conducted to explore the impacts of operational variables on the carbonation of LiOH in a spinning disk reactor. Results show the introduction of ultrasound, a lower temperature and a lower flow rate of CO2 facilitates the formation of small particles.Several technologies were explored to prepare ultrafine powders of Li2CO3. It was found that the ultrasound-assisted reactive crystallization is a simple and effective method. Two novel reactive crystallization processes, anti-solvent reactive crystallization and anti-solvent-decomposition reactive crystallization were studied, both of them can obtain about submicron crystals. Hollow spheres were prepared by spray pyrolysis of LiHCO3, which are composed of about 200 nm primary particles. The BET surface area of the hollow spheres reaches 7.24 m2/g.