Research On Extraction Mechanism And Process Of Lithium From Salt Lake Brine

There exists a large amount of lithium resource at Qinghai and Tibet in China, the world's most valuable salt lake areas. It is very difficult to separate lithium from salt lake brine, since lithium ion content is low, and others ions, such as sodium, potassium, calcium, magnesium ions contents are high in brine. In this work, the extraction mechanism and extraction process of lithium from salt lake brine were studied theritically and experimentally, the moluculor modeling method was used to study the interaction between extraction agent molecular and metal ions, in order to provide a theoretical basis for the optimal selection and improvement on extraction agent in the future.To increase the extraction efficency of lithium from salt lake brine, firstly, lithium ion in West taijnar and Quarhan salt lake brine was concentrated from the lower concentration (<30mmol/L) to a higer concentration (>200mmol/L) by natural evaporation under the ambient environmrntal condition. The evaporation condition, the physical and chemical properties of crsystallized salt, and chemical composition in the concentrated brine, were researched, the suitable brine for the lithium extraction experiment was selected.Then, the lithium ion in the concentrated brine was extracted using a organic phase of tributyl phosphate(TBP)-kerosene-FeCl3. The experimental results showed that the extraction system could recover lithium ion from brine with the higer selectivity, and the extraction process was more efficient and stable. The operating conditions were optimized experimentally by studying the single factors of extraction O/A ratio, extractant composition, molar ratio of Fe3+ to Li+and so on. The optimal condition for the extraction process were: extraction O/A=1.5, TBP%=75%, [Fe3+]/[Li+]=2, [H+]=0.02 mol/L, extraction time=20 min; washing O/A=15; back extraction O/A-20, back extraction [H+]=1 mol/L.Furthermore, the complex compound of lithium ion and TBP was investigated by IR and NMR. The results showed that the interaction among litium ion, FeCl3, TBP was by hydrogen bond. The mechanism was further studied by the molecular simulation. The results showed that LiFeCl4 complex compound and TBP were associated through three coordinated water molecules, and the TBP-kerosene-FeCl3 extraction system can extracted lithium ion with higher selectivity.