Lithium Selective Extraction From Carbonate-type Salt Lake Brine

With the rapid development of new energy vehicles,lithium salts,as the main raw material for new energy vehicle power batteries,are in short supply.About 80%of the lithium in China is deposited in the salt lake brine,and the carbonate salt lake,which is one of the important components of the salt lake lithium resources,is difficult to be exploited efficiently and economically due to its high alkalinity and high carbonate content.In this paper,a new technological route of preparing Li₂CO₃ by"electrochemical deintercalation/intercalation-phosphate precipitation conversion"was proposed for the efficient lithium extraction from carbonate-type brine.On this basis,according to the low concentration of Ca²⁺and Mg²⁺in carbonate-type brine,the direct lithium extraction by seed-induced precipitation with phosphate was explored.The main research contents and conclusions are as follows:（1）Lithium selective extraction from carbonate-type salt lake original brines by electrochemical de-integration/integration method.The cyclic voltammetry curves of Li Fe PO₄ electrode in carbonate-type brines with high sodium and low lithium were studied.The results show that the Li Fe PO₄ electrode has a higher lithium embedding potential than the sodium embedding potential in the brine,and the selective extraction of lithium can be achieved by regulating the electrode potential.The Li Fe PO₄/Fe PO₄ electrochemical system was used to extract lithium from carbonate-type brine,revealing that the optimization of Li Fe PO₄physicochemical index,electrode macroscopic morphology and electrolytic cell can improve the lithium extraction performance of the system.In particular,the average current efficiency reaches 87.71%when the sealed membrane stack electrolyzer was used for lithium extraction.Finally,from the perspective of practical application,the cycling performance of Li Fe PO₄ electrode in carbonate-type brine was studied,and the results showed that the adsorption capacity of the electrode decayed during the cycling process,but still had good selectivity.（2）Phosphate precipitation for selective removal of impurities and efficient precipitation of lithium from lithium-rich solutions.Based on the differences in the solubility of Ca²⁺,Mg²⁺,and Li⁺phosphates,a phosphate stepwise precipitation method was used for selective removal of impurities and efficient precipitation of lithium from the lithium-rich solution.The optimal window for the removal of impurities by phosphate was determined by thermodynamic calculations.The removal rates of Ca²⁺and Mg²⁺reached 99.14%and 97.52%,respectively,within the optimal window.To address the problem of poor lithium phosphate precipitation at low temperature and low lithium concentration,the seed-induced precipitation method was proposed to enhance the lithium precipitation process.The results showed that the lithium precipitation rate reached82.50%with the addition of lithium phosphate seeds at 1.5～2 times of the theoretical precipitation amount.（3）High-efficiency conversion of Li₃PO₄.The separation of Li⁺and PO₄^3-from Li₃PO₄ was achieved by the precipitation conversion method,and a high concentration lithium-rich solution was obtained in one step,which effectively reduced the energy consumption of lithium extraction.The optimal windows for the conversion of Li₃PO₄ by Ca²⁺and Fe³⁺were determined to be p H>4.25 and 3.0<p H<3.25,respectively.Based on the thermodynamic calculations,Ca Cl₂ and Fe Cl₃ solutions were used to convert Li₃PO₄,respectively.The results showed that the conversion of Li₃PO₄ using Fe Cl₃ solution was better than Ca Cl₂ solution,and the conversion rate of Li₃PO₄ by Fe Cl₃ solution could reach more than 83%under the optimal conditions.（4）Preparation of battery-grade Li₂CO₃.In order to increase the Li₂CO₃ yield during the preparation process,the effect of reaction parameters on the Li₂CO₃ preparation process was investigated in detail,and the optimal reaction conditions were determined.For the problem of high sodium content in Li₂CO₃,it was confirmed that the sodium content of Li₂CO₃ could be reduced by regulating the experimental parameters.The results showed that the sodium content of Li₂CO₃ which was prepared at the reaction temperature of 95℃and stirring rate of 900 rpm could reach the standard of battery-grade Li₂CO₃ after three times of washing.（5）Direct lithium extraction from carbonate-type salt lake concentrated brines by seed-induced precipitation.In response to the problem of long induction period of the process for direct lithium extraction from brine by phosphate,a seed-induced precipitation method was proposed to enhance the lithium precipitation process,which effectively increased the lithium precipitation rate.Firstly,the influence of experimental conditions on the activity of the seeds was studied,and the optimal conditions for the preparation of active seeds were determined.Then,the surface energy of Li₃PO₄ crystal（110）facet was determined to be 0.067 J/m² higher than that of（101）facet by first principles calculation,which revealed the intrinsic reason for the higher activity of Li₃PO₄ seeds with fully exposed（110）facet.Based on the preparation of active seeds,the lithium precipitation effect of the seed-induced precipitation was further investigated,and the results showed that the lithium precipitation rate could reach 60.06%when the addition of seeds reached 60 g/L.This paper contains 56 figures,25 tables,and 143 references.