Design Of Tributyl Phosphate-Ionic Liquid Extraction System And Study On Selective Extraction Of Lithium From Brine

Solvent extraction is one of the most promising methods for lithium extraction.However,the traditional extraction system has many shortcomings,such as serious corrosion of equipment and volatile hazards of organic solvents.Therefore,it is necessary to establish new extraction systems for extracting lithium from brine.Ionic liquids(ILs)and deep eutectic solvents(DESs)are considered to be"green"solvents that can replace volatile organic solvents because of their low volatility,low toxicity,and high thermal stability.In this paper,a variety of ILs and DESs were synthesized as co-extractants,and TBP was used as the extractant to establish green extraction systems of TBP-IL or TBP-DES for the extraction of lithium from brine.The optimal extraction process conditions were determined by investigating the influence of factors such as aqueous p H,the volume ratio of aqueous phase(A)and organic phase(O),and the amount of IL or DES on the lithium extraction efficiency and separation coefficient.The extraction mechanism was explored by slope analysis method,combined with FT-IR spectra and UV-vis spectra.These provide a theoretical basis for the improvement of the subsequent extraction system and a new idea for extracting lithium from brine.The main contents are as follows:1.The temperature-controlled IL([BPy]Fe Cl₄)is synthesized as the co-extractant,and the TBP-[BPy]Fe Cl₄ extraction system is established to extract Li⁺from simulated Qinghai salt lake brine with high magnesium-lithium ratio.When volume ratio(A/O)=0.5,initial aqueous p H=7.2,volume fraction of IL in the organic phase is 40%,and temperature is 298 K,the extraction efficiency of lithium reaches 84.2%.Through the study of extraction mechanism,it is found that the ion exchange between Li⁺and[BPy]⁺promotes the reaction,and Li⁺,Fe Cl₄^-and TBP complex to form the extraction compound Li Fe Cl₄·2TBP and then into the organic phase.Through thermodynamic analysis,the extraction of lithium is a spontaneous exothermic reaction.2.Compared with[BPy]Fe Cl₄,the synthesized imidazole-based ILs([Emim]Fe Cl₄,[Bmim]Fe Cl₄,[Hmim]Fe Cl₄)have lower solubility,and the positive charge on the imidazole cation is dispersed to a large extent,which weakens the interaction between anion and cation and makes the exchange process easier.The optimal extraction process conditions of the TBP-[Bmim]Fe Cl₄ system are obtained:volume ratio(A/O)=0.5,initial aqueous p H=7.2,volume fraction of IL in the organic phase is 10%,and temperature is 298 K.Through the study of extraction mechanism,it is found that the ion exchange between Li⁺and[Bmim]⁺promotes the reaction,and Li⁺,Fe Cl₄^-and TBP combine to form the extraction compound Li Fe Cl₄·3TBP and then into the organic phase.Thermodynamic analysis shows that extraction of lithium is a spontaneous exothermic reaction.3.Compared with ILs,the raw materials of hydrophobic deep eutectic solvents(HDESs)are cheap and simple to synthesize.Three HDESs are prepared with different molar ratios of oleic acid(OA)and tetrabutylammonium chloride(TBAC)as co-extractants(respectively denoted as TBAC/OA,TBAC/2OA,TBAC/3OA),and a new green extraction system is established to extract lithium from the lithium deposition mother liquor.When C_NH3·H2O=1.5,volume ratio(O/A)=1,and volume fraction of HDES in the organic phase is 30%,the extraction efficiency of the TBP-TBAC/3OA system for pure lithium solution reaches 76.8%.Through the study of the extraction mechanism,it is found that the ion exchange between Li⁺and[TBA]⁺promotes the reaction,and Li⁺,oleate ions(OA^-)and TBP are complexed to form the extraction compound Li OA·3TBP and then enters the organic phase.The extraction efficiency of the TBP-TBAC/3OA system in the ammonia-containing lithium deposition mother liquor is 56.2%,and the lithium-sodium separation coefficient reaches 20.5.It has the ability to selectively extract Li⁺from the high sodium-lithium ratio of lithium deposition mother liquor.