Mechanism And Process Study On Lithium Separation From Alkaline Solution Using HBTA/TOPO Extraction System

Depletion of fossil energy and increased attention to environment protection is making exploration and development of novel energy an international priority.Lithium,a key material in electrical vehicles and controllable nuclear reactors,bears strategic significance in national energy security.In recent years,development and industrialization of lithium resources has progressed rapidly,with lithium carbonate capacity fast increasing.However,the effectiveness of Li recovery is reduced as a result of discharge of a large amount of alkaline lithium-containing tail liquid in the production process.In this study,key elements affecting lithium extraction,extraction kinetics,complex structure,extraction process and other factors for the synergistic system of benzoyltrifluoroacetone（HBTA）and trioctylphosphine oxide（TOPO）were investigated.The main research scope and results are as follows.（1）The results of extraction equilibrium experiments show that the p H of the solution is required to be alkaline when extracting lithium in HBTA/TOPO extraction system.At p H=7～12,the extraction rate of lithium increases with the increase of p H.The synergistic experiment showed that the TOPO synergistic effect was the best.When the molar ratio of TOPO to HBTA in the organic phase was 1:1,the synergistic coefficient reached the highest value of 10.98.The saturation loading lithium experiment of HBTA/TOPO synergy system showed that the extraction process was an equimolar extraction of HBTA and lithium.Temperature experiments show that increasing the temperature favors the extraction of lithium.（2）Under the condition of p H=2～10.6,the extraction effect of Li⁺is stronger than that of Na⁺,K⁺,and the extraction system can effectively extract Li⁺from the aqueous solution containing Li⁺,Na⁺and K⁺;When the equimolar concentration of Li⁺and Ca²⁺and Mg²⁺are simultaneously contained,the extraction of Mg²⁺and Ca²⁺is preferred over Li⁺.The extraction system is not suitable for extracting and separating Li⁺from a solution containing Mg²⁺or Ca²⁺.When the solution contains Li⁺and equimolar concentrations of transition metal ions such as Fe³⁺,Co²⁺,Ni²⁺,the extraction order of the synergistic system is Fe³⁺>Ni²⁺>Co²⁺>Li⁺.（3）The kinetics of lithium extraction by HBTA/TOPO synergistic system was investigated by Lewis cell method.The experimental results show that the extraction process is a chemical reaction control process,and the extraction reaction mainly occurs at the two-phase interface.In the extraction process,the reaction orders corresponding to Li⁺,HBTA and TOPO are all first-order,and the kinetic equation of lithium extraction by HBTA/TOPO is R_Li=4.35[Li⁺]_aq[HBTA]_org[TOPO]_org;the step of forming the final complex of Li⁺with HBTA and TOPO is the rate-determining step;Stripping process of the loaded organic is controlled by chemical reaction and occurrs at the two-phase interface,the reaction orders of Li⁺_org and HCl_aq are both first-order,the kinetic equation of stripping process is R_Li,st=1.22×10^-1[Li⁺]_org[HCl]_aq;It is deduced that the exchange of H⁺in the aqueous phase with lithium in the complex Li·BTA·TOPO is the rate-determining step of the reaction.（4）Infrared spectra of the HBTA/TOPO synergistic system loaded by extracting lithium,sodium,potassium were investigated.The results show that the main functional group of the extraction is the hydroxyl in HBTA,the addition of TOPO contributes to the enolization of the diketone extractant.The single crystal of the complex formed by the extraction of alkali metal ions was obtained for the first time.The structure of the complex formed by HBTA and Li⁺was confirmed by X-ray diffraction,as well as complexes confirmed by diketone,organophosphorus and alkali metal ions,the stoichiometric relationship between the extractant and the extracted ions in the complex is clarified.This achievement reveals the complexation law and structure-activity relationship of the extraction process at the molecular level,which provides a powerful theoretical guidance for the design of the extractant and the optimization of the system.（5）Taking the mother liquor of Li₂CO₃ production in a Qinghai company as feed solution,the extraction process was carried out using HBTA/TOPO synergistic extraction system.A whole process containing three-stage extraction,three-stage scrubbing,three-stage stripping and one-stage regeneration was determined by experiments.Through the process,over 95%of lithium in the feed solution could be recovered,lithium concentration of obtained solution is 20 g/L with less than 1.0 g/L impurities.The whole process extraction experiment proves that the system has good industrial application prospects.Using the extraction process similar to the above,a lithium recovery process was carried out on the nickel-cobalt tail liquid of a waste lithium battery in an enterprise in Ningbo,the total yield of lithium reached 95%.This process realizes lithium recovery from the spent Li Bs tail liqour.The research results lay a certain theoretical foundation and design basis for further process amplification.（6）Using Li₂CO₃ mother liquor from Qinghai Salt Lake Group as the feed solution,a25-day 20-stage process amplification experiment was carried out on the mixer-settler.The whole process data was stable,and the average lithium concentration of the obtained lithium-rich solution reached 28 g/L.The total impurity content is less than0.5 g/L and the total yield of lithium is 95%.Through the full-component analysis of the equilibrium samples,the distribution rule of lithium and other ions(Na⁺,K⁺,Ca²⁺,Mg²⁺,etc.)in the separation,purification and concentration of each extraction process was clarified.This research provides a scientific basis for efficient lithium recovery from Li₂CO₃ mother liquor.