Solvent extraction of lithium from ammoniacal solution using thenoyltrifluoroacetone and neutral ligands
Introduction
Lithium resources are crucial raw materials for various industry-related products, such as cathode materials for rechargeable batteries, light aircraft alloys, catalyst, and controlled nuclear fusion fuel [[1], [2], [3], [4], [5]], which play a vital role in energy market and economy under the energy shortage condition. With the explosive development of lithium battery, the demand of lithium has been accelerated.
Due to the depletion of lithium ores, recent researches have emphasized recovery of lithium from aqueous resources such as brine, geothermal water and spent lithium ion batteries.
Solvent extraction is verified an economical, efficient, and environmentally friendly method for metal recovery from dilute solutions comparing with other method such as adsorption, precipitation and membrane methods [[6], [7], [8], [9], [10], [11], [12]]. Various extraction system have been employed for recovery of different metal ions. Among the systems, β-diketone and neutral donor system is applied in extraction field widely, such as extraction of lanthanide and actinide, as well as recovery of transition metals. Fuli et al. [13] extracted zinc from ammoniacal/ammonium sulfate solutions using a mixture of β-diketone and great synergistic effect was speculated. Yuko et al. [14] separated Lns(III) with pivaloyltrifluoroacetone and MePhPTA, separation factor were 2.0 and 1.4 for Sm/Nd and Sm/Eu respectively. Weng Fu et al. [15] separated copper from synthetic ammoniacal chloride using three sterically hindered β-diketone: 1-phenyl-3-heptyl-1,3-propanedione(I), 1-phenyl-4-ethyl-1,3-octanedione(II) and 1-(4′-dodecyl)phenyl-3-tert-butyl-1,3-propanedione(III), the results indicated that copper selectivity of β-diketone increased as steric hinderance increased.
β-diketone for lithium separation has been intensively studied early. Seely et al. [16] studied fluorinated β-diketone HFDMOD in lithium separation from alkaline metal ions and alkaline earth metal ions. It was found that β-diketone showed strong selectivity for lithium over alkaline ions while poor selectivity over alkaline earth metal ions. A three stages extraction and two stage scrubbing process was proposed by this study. Ishimori et al. [17] extracted lithium using HTTA (2-thenoyltrifluoroacetone) and 1,10-phenanthroline (phen) in various organic solvent, the lithium adduct obtained in this study was Li(tta)(phen). The separation factor of this system is higher than HTTA-TOPO-benzene system. However, difficulties in synthesis, high toxicity to environment, high solubility in water constrain popularization and application of these extractants above.
In general, synergistic extraction system consisting of β-diketone and neutral ligand has great potential in lithium recovery from alkaline solutions, and lithium separation from sulphate and chloride solution was reported before, while lithium recovery from ammoniacal solution was seldom reported [18,19]. In order to develop applicable extraction systems to recover lithium from ammoniacal solution, lithium extraction by HTTA and different co-extractants and diluents was investigated. By comparing lithium extraction effect, HTTA-TOPO-kerosene system was selected as the preferable extraction system to recover lithium from ammoniacal solution. To further elucidate the extraction behavior of the system, extraction mechanism, thermodynamic parameters, stripping and regeneration conditions were also studied.
Section snippets
Reagents and apparatus
The structures of organic reagents used in the experiment were listed in Table S1 in Supplementary materials. Other inorganic reagents such as MgCl2, NH3H2O and HCl used in experiments are all analytical reagents.
Instruments used are as following: strong shaker (SR-2DW; TAITEC), centrifuge (TDL-40B-W, Shanghai Anting Scientific Factory), precious pH meter (S220; Mettler Toledo, Swiss), ICP-AES(ICAP6500 DUO; America Thermo Scientific, USA), thermostat water bath vibrator(THZ-82A; LangYue
Effects of aqueous pH
In the extraction process, pH value of aqueous phase played an important role. In the present study, initial pH of aqueous phase varied over a range from 10.63 to 13.09 for the HTTA-TOPO system, the results revealed the plot of equilibrium pH versus extraction ratio and logD. As shown in Fig. 1, lithium extraction efficiency continuously increased as pH value of aqueous phase increased and reached maximum at equilibrium pH = 8.08. Former study [20] indicated that the enolic hydrogen atom of the
Conclusion
In present work, lithium recovery from ammoniacal solution by HTTA and neutral ligands was studied. The experiments results showed that HTTA-TOPO-kerosene extraction system was feasible and effective for separation of lithium over alkali metal ions. Synergistic effects of neutral donors were investigated and TOPO showed strongest synergistic effect compared with other reagents. To further investigate the nature of this extraction process, extraction mechanism and thermodynamic parameters was
Acknowledgement
We gratefully acknowledge the financial supporting for this work from National Natural Science Foundation of China (No. U1407203, No. U1707601).
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