Research On A Novel Technology For Extracting Lithium From Lepidolite Via Multi-phase Reactor And Fluorine Chemical Method

With the rapid development of new energy materials and electric vehicles,the world's demand for lithium resources has soared.Due to the harsh environment in high altitude areas,the expansion of production capacity of lithium obtained from brine's resources has a lot of limitations.Thus,the development of the technology of lithium extraction from ores is an important way to satisfy the new energy development in the world.There are currently some problems,e.g.high energy consumption,low comprehensive utilization and big difficulties of the development of low-grade lithium ore,existing in the process of lithium extraction from ores.Based on the fluorine chemical method to extract lithium from low-grade lithium ores studied previously by the project group,research on the technology for extracting lithium from lepidolite via fluorine chemical method was proposed for the first time in our paper under the gas-liquid-solid pipeline reactor system.The experimental results show that the crystal lattice of lithium mica is completely destroyed in the reaction system of lepidolite,sulfuric acid and fluosilicic acid under the condition of normal temperature(25 ?).The result is?GT(?)(298K)=-81933.36J/mol(1mol HF)through thermodynamic calculation,which indicates that the reaction can be carried out spontaneously at a low temperature.According to the analysis of pipeline reactor fluid and state of fluorine in the fluid reaction system under above system,fluorine element is the key component to destroy the structure of lithium mica crystal,which is converted in the reaction system with various gas-liquid-solid forms such as hydrogen fluoride,fluoride,silicon tetrafluoride and fluosilicic acid.Hydrogen fluoride and silicon tetrafluoride are easy to volatilize in sulfuric acid system at a certain temperature and dissolve in water.The pipeline reactor makes the volatile gas containing fluorine be absorbed into the reaction solution again continuing to participate in the corrosion of lepidolite during the flowing process,so as to promote the reaction of lithium mica.It is a good solution to solve the problem of reduction of fluorine contents during the reaction caused by the fluorine-containing gas easily volatilizing in conventional stirring reactor.Analysis about the fluidization characteristics of the mineral particles in this reaction system indicates that when the particle size of the powder is 100 mesh,the carrying velocity of mineral particles is 1.68cm/s.And the continuous pipeline reaction devices designed on the basis of above analysis have obtained good experimental results in laboratory.Study on process of pipe reactor shows that a concentration of 15%fluosilicic acid is suitable for the fluorine chemical reaction.And the weight ratios of each ingredient were as follows:fluorosilicic acid to mineral powder ratio 1.6 and sulfuric acid to mineral powder ratio 0.8.Concentration of fluosilicic acid and sulfuric acid used in ingredients was 15%and 80%respectively.Experiments were conducted on conditions of reaction temperature 80 ?,particle size 400 mesh and reaction time 15min.Meanwhile,the extraction rate of lithium was 99.4%,and the extraction rate of other components was 96.4%for K,81.4%for Al,97.6%for Rb and 96.7%for Cs.According to the study on leaching and fluorine cycle in the process,the optimum leaching conditions of residues were as follows:liquid-to-solid of 3,leaching temperature 95 ?,leaching time 30 min and stirring speed 250r/min.The leaching rate of lithium could be up to 99.0%under above optimal conditions.Research on the insoluble residue under the conditions of optimum reaction and leaching illustrates that the recycling rate of fluorine in fluorosilicic acid is 94.6%(using the fluorine content of fluorosilicic acid to calculate)during the reaction when the residue is not calcined.The content of fluorine in insoluble residue before calcining is 4.72%.However,the recycling rate of fluorine can reach 100.8%as the slag is calcined at 400? for 2 h.The result of XRD pattern analysis shows that the fluorine elements in insoluble residue exist mainly in the form of fluorosilicate and fluoroaluminate.The content of fluorine in insoluble residue decreases from 4.72%to 0.94%after calcining at 500? for 2 h,and the volatilization rate of fluorine in the lithium mica ore is 68.7%(using the fluorine content of raw ores to calculate).The results show that the combination of multi-phase pipeline reactor and fluorine chemical method is an efficient and novel technology route with great industrialized application prospect,which can significantly reduce the reaction time and temperature.