Development And Research On New Technologies For Selective Extraction Of Lithium From Salt Lake Brines And Lithium Precipitation Mother Liquor

Lithium is a key element in the strategic development of the country’s new energy and nuclear industries,and the demand is currently increasing sharply.As a country with large lithium resources,nearly 80%of the lithium resources in China are stored in salt lake brines.With the gradual depletion of ore lithium resources,obtaining lithium resources from brines has replaced itas thecurrent main way.The solvent extraction method has become one of the core methods for extracting lithium from salt lakes due to its advantages of high selectivity and easy scale-up.In order to speed up the diversified and refined development of the lithium industry,increase the comprehensive utilization efficiency of salt lake resources,and realize the cyclic utilization of lithium resources of the precipitation lithium mother solution,it is urgent to develop and study the new extraction technologies of lithium from salt lake brines with high Mg/Li and lithium precipitation mother liquor.The traditional extraction system for salt lake brines with high magnesium-lithium ratio is TBP-Fe Cl₃-kerosene system,the main problems of which consist of easy loss of co-extraction agent,and the great infullence of the stability of the organic phase by using acid and alkali.In order to solve the above problems,in this paper,an efficient extraction system of TBP,Na BPh₄and phenethyl isobutyrate was constructed for extraction experiments.By optimizing extraction conditions,the single-stage extraction effciency of Li⁺reached up to 85.70%,and the separation factor of Li⁺and Mg²⁺was 1175.The organic phase was washed with a mixed solution of Li Cl and Na Cl,and the impurity ions were washed below 3 ppm.Then the organic phase was stripped with sodium bicarbonate as stripping agent for five times,and the stripping efficiency of Li⁺closed to 100%.After the ten cycles of stability inspection,the extraction efficiency of Li⁺remained stable at about 84%,indicating that the new extraction system had good cycle stability.Finally,the NMR characterization results verified this extraction mechanism,explained why the extraction system had a good effect on the separation of lithium and magnesium.Moreover,the whole process avoided the use of strong acid and alkali and the Na HCO₃one-step method was adopted to shorten the extraction process,which reduced the corrosion of equipment and met development requirements of green and environmental friendly.It is ugent to recover the 17%lithium resources remaining in the lithium precipitation mother liquor formed during the production reaction of Li₂CO₃by adding Na₂CO₃in the lithium extraction process of salt lake.Since the lithium precipitation mother liquor has the characterizations of high concentration of Na and alkalinity,while theβ-diketone extraction agent which is often used to separate brine with high sodium-to-lithium ratio can’t be widely used due to its high toxicity and water solubility,in this paper,a new green and efficient ionic liquid extraction system was screened and constructed.That is,FILs[Hmim][BTA]was synthesized by using4,4,4-Trifluoro-1-phenyl-1,3-butanedione（HBTA）and1-Hexyl-3-methylimidazolium chloride,and the successful synthesis was verified by FT-IR and ¹H NMR characterizations.The organic phase system was formed with this ionic liquid as extractant and 2-octanone as diluent,and the experimental conditions of each section were optimized.After optimization,the single-stage extraction efficiency of Li⁺reached up to 94%.By using Li Cl solution as the washing solution,the washing efficiency of Na⁺was above 98%.When HCl was used as stripping reagent,the stripping efficiency of Li⁺reached up to 99%.The raffinate was used as the regenerant of the organic phase.During the ten cycles of extraction process,the extraction efficiency of Li⁺maintained at about 86%.Finally,ionic association extraction was verified as the extraction mechanism by slope analysis method,ultraviolet and infrared characterizations.