Research On Application Foundation And Development Of New Extraction System For Extraction Of Lithium Ions From Salt Lake Brines With High Magneisium-Lithium Ratio

Lithium is widely used in various fields of industrial production due to its excellent physical and chemical properties,especially the application in new energy vehicles,which gradually increases the demand for lithium products.Since the lithium resource in salt lake brines occupies most of China's lithium resource reserves,the extraction of lithium ions from salt lake brines has gradually become the main route for obtaining lithium resouces.Among many estraction processes for lithium ions from salt lakes brines,solvent extraction method is an ideal choice for separating lithium ions from salt lake brines with high magnesium-to-lithium ratio due to its low cost,automatic control and easy to industrially amplify.There are two main problems in the extraction process of the traditional extraction system(TBP-FeCl3-kerosene).One is that the structure of FeCl4-is unstable and easy to lose,resulting in a decrease of extraction efficiency of lithium ions.The other one is that TBP is easy to be degraded during long-term contacting with high concentrations of acid and alkali.In response to these problems,the combination of P204 and Fe3+was introduced to reconstruct the new TBP-FeCl3-P204-kerosene extraction system.After optimizing the extraction conditions,the optimal operating conditions for extraction consist of 10%P204+40%TBP+kerosene,Fe3+/Li+molar ratio as 1.6,and phase ratio as 1.The final single-stage extraction efficiency of Li+was 52.71%.Water and mixture of 1.5 mol/L MgCl2+0.15 mol/L LiCl were separatetly used for washing.90.64%of Mg2+was washed away with the phase ratio as 70 by using the former as washing agent.The washing efficiency for Mg2+could reach up to 95.37%when the phase ratio was 20 by using the latter as washing agent.The washing loss of Fe3+was 0%for both washing processes.The stripping efficiency of Li+decreased with the increase of the phase ratio with water as the stripping agent.Finally,the result of UV and Raman characterizations proved that TBP combined with Li+and FeCl4-,while P204 only combined with Fe3+.When the Cl-concentration is low,Fe3+remains in the organic phase by combining with P204.However,when the Clconcentration is high,FeCl4-is formed again for re-extraction of Li+by TBP.Both the above processes can solve the problem of Fe3+loss.Although the introduce of P204 could effectively solve the problem of Fe3+loss,the addition of P204 has an inhibitory effect on Li+extraction.In order to increase the lithium extraction efficiency and the separation factor of lithium to magnesium,and to solve the problem of FeCl3,a new extraction system with TOP as extractant,NaBPh4 as co-extractant and 2-octanone as diluent was screened and constructed.The single-stage extraction efficiency of Li+reached 83.60%by optimizing the volume fraction of TOP,the addition amount of NaBPh4 and the phase ratio.After washing the extracted organic phase with a mixed solution of LiCl+NaCl,both the concentrations of impurities Mg2+and K+were less than 1 mg/L.After stripping the washed organic phase three times by using Na2CO3 or NaHCO3 solution,the stripping efficiency of Li+reached up to 99%.The ?Li+/Mg2+maintained at the range of 6000 to 7000 during ten cycles of extraction process,demonstrating that the new extraction system has good cycle stability.Finally,by using FT-IR characterization,it was found that P=O of TOP was the main functional group for metal ions,and C=O of 2-octanone showed a co-extraction effect.The NMR spectrum results verified that the binding ability of TOP to metal cations followed the sequence Li+>Na+>Mg2+,indicating that the extraction system preferentially and selectively extracts Li+.The advantage of the two new extraction systems both can avoide the use of acid and alkali,save the regeneration steps,reduce the equipment costs,and improve the long-term stability of the organic phase.