Preparation Of Battery-Grade Lithium Carbonate By LiCl-NH₃·H₂O-CO₂ Gas-Liquid Reactive Crystallization

As one of the most basic and stable lithium compounds,Li₂CO₃ has wide industrial applications in lithium-ion batteries,materials and pharmaceuticals.With the rapid development of the new energy industry,Li₂CO₃ plays a vital role in energy storage and wireless equipment.The primary lithium resources in nature mainly include lithium ore and brines,and the recovery of lithium from secondary resources of lithium-ion batteries has also received increasing attention.In industry,lithium extracting from ore and brines is directly precipitated by Na₂CO₃ to obtain Li₂CO₃ and the preparation process is extensive,thus the purity of Li₂CO₃ is low and the particle size is uncontrollable.In view of the uncontrollable traditional process and the poor quality of product,this study proposes a novel system for preparing Li₂CO₃ by LiCl-NH₃·H2O-CO₂ gas-liquid reaction crystallization.Based on the supersaturation with nucleation and growth control mechanism,the decoupling analysis of the crystallization process was carried out by online and offline means.The study focuses on the characteristics of metastable system and crystallization process,kinetics of nucleation and growth and particle size regulation mechanism.Several main conclusions were drawn from this study:（1）The characteristics of crystallization process were studied.NH₃ H₂O is believed to be able to inhibit the recarbonation of Li₂CO₃ crystals,thus simplifying the carbonation process.Increasing NH₃ H₂O concentration can significantly increase the absorption efficiency of CO₂,enlarge the supersaturation of Li₂CO₃ and improve the[Li+]conversion ratio.The existence of NH₃·H₂O led to more temperature-sensitive absorption of CO₂.Both temperature and supersaturation are important parameters that influence the crystallization rate of Li₂CO₃ significantly.（2）The solubility of Li₂CO₃ in the combination system of NH₃ H₂O and NH₄Cl was measured.When the NH₃ H₂O concentration was constant,the solubility increased with the increase of NH₄Cl concentration.When the concentration of NH₄Cl was low,the solubility of Li₂CO₃ decreased with the increase of temperature,which was consistent with the solubility of Li₂CO₃ in water.However,when the concen tration of NH₄Cl was higher,the solubility of Li₂CO₃ increased with increasing temperature.（3）The crystallization kinetics of Li₂CO₃ was studied.The apparent activation energy was found to be 23.55 kJ/mol,which indicates that the crystallization of Li₂CO₃ was controlled by a combination of surface reaction and diffusion.The activation energy of nucleation was found to be 79.15 kJ/mol,indicating that the primary nucleation rate was greatly affected by temperature.The order of growth rate with respect to supersaturation was determined to be 6.81.The surface energy of Li₂CO₃ obtained by supersaturation was 22.03 mJ/m2,and the surface energy obtained by induction period was 18.80 mJ/m2,the results prove that it is feasible to calculate the nucleation rate through FBRM.The growth activation energy was found to be 26.79 kJ/mol,which is less than nucleation activation energy.（4）The relationship of Li₂CO₃ particle size with secondary nucleation and growth rate was investigated.With the increase of temperature,the supersolubility of Li₂CO₃ decreased,leading to the secondary nucleation rate decreased and the growth rate declined,which caused the temperature positively correlated with Li₂CO₃ particle size.The supersaturation affected the secondary nucleation and growth rate,that is the dominant mechanism for Li₂CO₃ crystallization,thereby obtaining Li₂CO₃ products with different sizes.The greater the supersaturation,the nucleation process was dominant and the growth process was weakened,thus the crystal size was smaller.（5）The particle size and morphology of Li₂CO₃ were regulated by additives and microbubbles.By adding PAA,spherical clustered Li₂CO₃ particles formed by agglomeration of flaky monomers were obtained.The addition of（NaPO₃）6 could obtain relatively dense spherical particles formed by agglomeration of flaky monomers.The addition of Na₄P₂O₇·10H₂O,PEI,SDBS could slow down the declining of pH and delay the nucleation of Li₂CO₃,thus enlarge the MSZW and strengthen the nucleation process,thereby effectively reduce the crystal size.Among which,Na₄P₂O₇·10H₂O had the greatest influence,with the mean size of Li₂CO₃ reduced by about 48%.Microbubbles were generated and the gas-liquid interface was increased thus the mass transfer was enhanced from the nano-scale,with the local supersaturation improved as well;In addition,the presence of microbubbles caused the formation of reaction microdomains near the gas-liquid interface,which facilitated the nucleation and inhibited the agglomeration of Li₂CO₃.As a result,the particle size of Li₂CO₃ decreased,which was reduced by 47%-65%compared to conventional conditions.