Selective extraction of lithium from alkaline brine using HBTA-TOPO synergistic extraction system
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 research has emphasized recovery of lithium from brine, geothermal water and seawater. Lithium production from brine water has now become more important due to its vast availability, process simplicity and cost effectiveness compared to its production from other resources [6]. Solvent extraction is economical, efficient, and environmentally friendly method for the separation of dilute solutions comparing with other method such as adsorption, precipitation and membrane method [7], [8], [9], [10], [11], [12].
Typically lithium recovery process from brine water involves solar evaporation of raw brine followed by removal of magnesium, calcium, boron and sulphate by a number of precipitation and membrane filtration process [13], [14]. The purified solution is then further concentrated via evaporation using extra energy to more than 20 g/L Li. Lithium carbonate product is finally obtained by precipitation with sodium carbonate. Commonly, mother liquor with 1.5–2.0 g/L lithium and 45–53 g/L sodium in it was discharged due to massive energy consumption to concentrate it. Seeking a proper extraction system for recovery of lithium from this part of brine is significant, while successfully applied TBP systems on lithium extraction from brine solution such as TBP-FeCl3-kerosene or TBP-ILs-kerosene was not suitable here due to requirement of brine acidity [15], [16], [17], [18].
β-diketone and neutral donor system is applied in extraction field widely, such as extraction of lanthanide and actinide and recovery of transition metals. Fuli et al. [19] extracted zinc from ammoniacal/ammonium sulphate solutions using a mixture of β-diketone and great synergistic effect was speculated. Yuko et al. [20] 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. [21] separation 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 in lithium separation was studied early. Healy [22]investigated different electron donor in synergistic extraction with HTTA, it was claimed that sequence of efficiency of the donors is TOPO>TBP>DBA>TPPO>EHA>NM. Seely et al. [23] 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. [24] extracted lithium using HTTA 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.
β-diketone extraction system has great potential in lithium separation from alkaline metal ions, and lithium separation from sulphate and chloride solution was reported before [25], [26].
In the present work, the synergistic extraction system containing HBTA and TOPO was first used to investigate the extraction behavior of lithium in aqueous carbonate media, and first applied to recovery lithium from authentic alkaline brine. Regeneration of HBTA-TOPO system was first proposed in present work which enabled the organic phase to circulate smoothly.
Using HBTA-TOPO as organic phase and alkaline brine as aqueous phase, a five-stage extraction process including extraction, scrubbing, stripping and regeneration was proposed according to the results. In general, this extraction system demonstrated great industrial potential due to its high capacity and stability as well as simplified extraction process which could be applied to authentic carbonate type brine.
Section snippets
Reagents and apparatus
Lithium chloride monohydrate (>97% purity; Sinopharm Chemical Reagent Co., Shanghai, China).
4,4,4-trifluoro-1-phenyl-1,3-butanedione(HBTA)(>98%; purity; Aladdin industrial Co., Shanghai, China).
Trioctylphosphine oxide(TOPO)(>98% purity; Aladdin industrial Co., Shanghai China).
Ion concentration of brine in study is as follow: (see Table 1).
Instruments used are as following: strong shaker (SR-2DW; TAITEC), centrifuge (TDL-40B-W, Shanghai Anting Scientific Factory), ICP-AES(ICAP6500 DUO; America
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 8.93 to 13.13 for the HPTA-TOPO system, the results revealed the plot of initial pH versus extraction ratio and equilibrium pH. As shown in Fig. 1, lithium extraction efficiency continuously increased as pH value of aqueous phase increased. And the data showed that lithium extraction efficiency reached 80% at equilibrium pH 8.0. Former study
Conclusions
The extraction of lithium from alkaline solution was investigated with synergistic extraction system containing HBTA and TOPO. Lithium extraction by 0.05 M HBTA and 0.1 M TOPO could reach to 97% at equilibrium pH 11.2 from simulated brine which contains lithium 0.138 g/L. the ΔH value for this system was found to be negative, indicating the exothermic nature of the extraction process. Extractant HBTA and TOPO showed obvious synergistic effect and extraction stoichiometry indicted coordinate number
Acknowledgements
This work was supported by National Nature Science Foundation of China - Qaidam Salt Lake Chemical Joint Scientific Research Funds (No. U1407203 and No. U1607104).
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