Investigation on the Lithium Extraction Process with the TBP–FeCl₃ Solvent System Using Experimental and DFT Methods

Abstract

Lithium has been a high-demand element with the rapid development of lithium-ion batteries. The recovery of lithium from salt lake brine via solvent extraction is considered a promising technique. In this study, the solvent extraction process in the tributyl phosphate (TBP)−FeCl 3 /brine system was investigated. The order of metal ions competitively combining with TBP−FeCl 3 was Li + > Na + > K + > Mg 2+ , and the compositions of main cationic extraction complexes were Li(TBP+ , and Mg(TBP) 2 (H 2 O) 4 2+ , respectively. The energy decomposition analysis showed that the electrostatics was the major interaction between the metal ions and the solvent (TBP and water). Compared with water, TBP bound more competitively with the metal ions. The calculated species distribution results showed that the ferric ion reacted with the chloride ion to form FeCl 2 + , FeCl 3 , and FeCl 4 − in high Cl − concentration brine. Co-extractant FeCl 3 was found to exist in the organic phase in the form of FeCl 4 − upon comparing the experimental and simulated spectra. Furthermore, the length of the Fe−Cl bond increased and the charge on the iron element was distracted when the FeCl n 3−n complexes coordinated with the water molecules. This indicated that FeCl 4− was more stable in the TBP solvent environment and it can be extracted from the aqueous phase. The results help us understand the extraction mechanism in essence and develop a high-efficiency extraction solvent for industrial lithium recovery.

A review of lithium extraction from natural resources

“…The solvent extraction method has been widely used in metallurgical and chemical industries, and research on this method to extract lithium from brines has also developed rapidly. The most commonly used system is tributyl phosphate (TBP) combined with FeCl 3 [130][131]. TBP has high selectivity to Li + under the synergistic effect of Fe 3+ .…”

A density functional theory insight into the extraction mechanism of lithium recovery from alkaline brine by β‐diketones

“…For the TBP‐FeCl 3 based extraction recovery of lithium from salt lake brine, Zhou et al once determined the ion association extraction mechanism by experimental methods 24 . Subsequently, Sun et al conducted a theoretical calculation on the ion association process by the DFT method 10 . However, to the β‐diketones, the existing investigations are mainly focused on the extraction process development and there is a huge lack in the theoretical study.…”

“…However, this solvent system requires the aqueous chloride concentration >6 mol/L so that it is only suitable for the high Mg/Li ratio salt lake brine. 10 On the other hand, the representative β-diketones extractants mainly include 4,4,4-trifluoro-1-(thiophen-2-yl)butane-1,3-dione (TTA) [11][12][13] and 1-phenyl-3-heptyl-1,3-propanedione (PHPD). 14 They are usually used together with organic phosphine to compose a synergist extraction solvent system.…”

“…Especially, the mixed solvent of TBP/FeCl 3 /P507 was proposed further to avoid the use of high concentration HCl in the stripping process, which has been applied in Qinghai, China. However, this solvent system requires the aqueous chloride concentration >6 mol/L so that it is only suitable for the high Mg/Li ratio salt lake brine 10 . On the other hand, the representative β‐diketones extractants mainly include 4,4,4‐trifluoro‐1‐(thiophen‐2‐yl)butane‐1,3‐dione (TTA) 11–13 and 1‐phenyl‐3‐heptyl‐1,3‐propanedione (PHPD) 14 .…”

Recovery of lithium from salt‐lake brine by liquid–liquid extraction using TBP‐FeCl3 based mixture solvent

“…Meanwhile, the high chloride ion concentration solution environment was necessary for the generation of stereo-symmetric FeCl 4 À so that it can be combined with the cationic extraction complex by an ionic association effect. [42][43][44] Hence, the brine was usually required to have a chloride ion concentration greater than 6 mol/L when the solvent extraction technology was applied. [45,46] Hence, the salt-lake brines were usually concentrated in advance before the extraction process.…”