Studies On The Preparation Of High Purity Lithium Carbonate By The Method Of Hydrogenation And Decomposition

With the continuous development of the area of new materials and new energy sources,the application of lithium compounds in the field of high technology has been expanding.High-purity lithium carbonate is not only widely used of cathode materials in lithium ion battery and electrolyte raw materials,but also a kind of vital raw material for the preparation of surface acoustic wave element single crystal materials,All of these come about a new growing consumption for high-purity Li2CO3 inevitably,and its prospects of development and application are broad.This paper focuses on the preparation of high-purity lithium carbonate by the method of hydrogenation and decomposition.The hydrogenation reaction of industrial grade lithium carbonate,the adsorption and separation of impurity ions in the hydrogenation solution by ion exchange resin,and the decomposing and crystallization of lithium bicarbonate are involved.Atomic Absorption Spectroscopy(AAS),Inductively Coupled Plasma Spectroscopy(ICP-OES),X-Ray Diffraction(XRD),Scanning Electron Microscopy(SEM),and Laser Particle Size Analyzers were used to determine the impurity ion content and the crystal structure of the intermediate and product of lithium carbonate.Additionally,morphology and particle size distribution were analyzed and tested.The hydrogenation reaction process of lithium carbonate was studied.According to the characteristics of the non-catalytic gas-liquid-solid three-phase complex reaction system,the effects of CO2 gas flow rate,stirring speed,solid-liquid ratio,temperature,and reaction time on the hydrogenation reaction were investigated.The content of lithium ions in the solution was determined by AAS,and the process conditions were optimized.The kinetics of hydrogenation of lithium carbonate was described by the condensation model.The results show that the hydrogenation of lithium carbonate is mainly controlled by membrane diffusion within the experimental range.The macroscopical kinetic equation can be expressed as x = k(t + tc),and the apparent activation energy of the reaction process is-5.30 kJ/mol.To study the effect of ion exchange resin type and process conditions on the removal efficiency of impurity ions Ca2+,Mg2+,Na+,K+ in the solution.The adsorption exchange capacity of the ion exchange resin is calculated to optimize the process parameters.The isothermal adsorption mechanism was explored by the equilibrium isothermal adsorption model.The results showed that 732 resin has good adsorption effect on calcium,magnesium,sodium and potassium ions,and the removal rate increases with the increase of the amount of resin and adsorption time,and the D401 chelating resin has high selectivity for Ca2+ and Mg2+.Under the optimum conditions,the saturated adsorption capacity of 732 resin for magnesium,calcium,sodium and potassium ions can reach 34.66 mg/g,52.82 mg/g,33.58 mg/g and 35.88 mg/g,respectively.As for D401 chelate resin,the saturated adsorption capacity for magnesium and calcium can reach 27.26 mg/g and 43.21 mg/g.Under the 15 BV/h flow rate of hydrogenation liquid,293 K of the temperature and the 8.0 of the solution pH,the removal of Ca2+,Mg2+,Na+,K+ ions in the hydrogenation solution is obvious.The removal rates reached 58.65%,49.52%,40.51%and 35.10%,respectively.Langmuir isotherm equation and Freundlich isotherm equation are used to fit the experimental data.The results show that the adsorption of Mg2+by 732 resin and D401 chelate resin is more in line with the Langmuir isotherm equation and it belongs to monolayer adsorption.In order to determine the decomposing crystallization parameters of lithium bicarbonate,the effects of decomposition temperature,stirring speed,concentration of lithium bicarbonate solution,seed addition amount,and number of mother liquor cycles on the purity,yield and morphology of lithium carbonate products were studied.The results showed that the lithium bicarbonate solution(solid-liquid ratio 1:30,after decontamination by ion exchange resin)was subjected to the of 363 K of decomposition temperature,500 rpm of the stirring speed,90 min of the decomposition crystallization,and no-addition seed crystals.Under the process conditions,the yield of lithium carbonate is 60.12%,and the purity of the product is more than 99.9%.The mother liquor is recycled through 3 cycles,the yield of lithium carbonate reaches 93.73%.Three times repeated experiments were carried out under the optimal process conditions.The purity of lithium carbonate was more than 99.9%,which reached the standard of high purity lithium carbonate(≥99.9%)in non-ferrous metals industry,and the lithium carbonate crystal grain size is distributed from 18 μm to 130 μm.It is a kind of normal distribution of the particle size.