Study On Selectively Leaching Lithium From Lepidolite By Recirculating Fluoridize And Acidolysis Method

The traditional lithium extracting method from lepidolite have a lot of disadvantages,such as high energy consumption,high equipment requirements,more pollution to environment,low lithium extraction ratio and tediously flow.To overcome these drawbacks,a new hydrometallurgical method of selectivity leaching lithium from lepidolite is proposed in this thesis.The kinetic and leaching behavior of lithium from lepidolite with hydrochloric acid leaching based on the shrinking core model?SCM?were studied at 333³63K.The results show that the diffusion step is the rate-controlling step and the value of activation energy is 42.79k J/mol.To assist the leaching process of lithium NaF is introduced into the system.when the molar ratio of NaF to total aluminum in lepidolite is 0.5,the apparent activation energy is reduced to 28.10kJ/mol.Effect of leaching process parameters on leaching ratio of lithium were studied.Dosage of NaF,temperature and acid concentration play a significant role on lithium extraction while the effects of reaction time and liquid to solid ratio are not serious.When the concentration of hydrochloric acid was 24wt.%and the liquid to solid ratio was 3.0:1,the leaching ratio of lithium was 99.56%,but the concentration of fluorine and aluminium in leaching solution is at a high level.The structure of lepidolite was thoroughly hydrolyzed,and the phase of leaching residue were Si O₂ and NaAlSi₃O₈.In order to ensure high leaching ratio of lithium and reduce the concentration of fluorine and aluminum in the leaching solution,the dosage of NaF was adjusted to chang the molar ratio of fluorine to aluminum in the system,sodium fluoro-aluminate was precipitated in the leaching process.Experimental results show that when the concentration of hydrochloric acid was 24wt.%,the liquid to solid ratio was 3.0:1,and the dosage of NaF is 4.0 times of total aluminum in the minerals,the leaching ratio of lithium was 96.20%,the content of aluminum and fluorine in leaching solution was reduced to1.6g/L and 3.1g/L respectively,the residual acid was 23.13g/L?calculated by HCl?.High fluorine leaching residue phase were SiO₂,NaAl Si₃O₈ and additional Na₅Al₃F₁₄.NaF was recovered from the high fluoride leaching residue by alkali leaching,and the separation of fluoride and aluminum was realized.The effect of reaction conditions on the regeneration of NaF was studied by conditional experiments.The dosage of NaOH,liquid to solid mass ratio,reaction temperature and reaction time play a significant role on NaF regeneration.The experimental results show that under the most economical and efficient reaction conditions and controll the final pH value of the system within 10.0¹0.5,the regeneration ratio of NaF was 92.27%,aluminum was not detected in the leaching solution.The final leaching residual phases are SiO₂,NaAlSi₃O₈ and Al?OH?₃,which can be used in the production of ceramics.