Elsevier

Chemical Physics Letters

Volume 754, September 2020, 137740
Chemical Physics Letters

Research paper
The key factors and mechanism study on lithium extraction by TBP-FeCl3 extraction system

https://doi.org/10.1016/j.cplett.2020.137740Get rights and content

Highlights

  • The structure of FeCl3 and FeCl4 were optimized and the theoretical Raman spectra of FeCl3 and FeCl4 were calculated for the first time.

  • The increase of MgCl2 concentration was conducive to the extraction of lithium by investigating the influence of MgCl2. The influence of Cl was greater than that of Mg2+.

  • Fe3+ and Cl were the optimal central ions and ligands for the formation of monovalent anions with high selectivity for lithium by investigating the influence of FeCl3 on lithium extraction.

Abstract

The key factors and mechanism of lithium extraction using tributyl phosphate(TBP) as extractant, kerosene as diluent, and FeCl3 as co-extractant were investigated. The theoretical Raman spectra of FeCl3 and FeCl4 were calculated by DFT. The key factors MgCl2, FeCl3 and TBP were studied. The results suggested the increase of MgCl2 concentration was conducive to extraction lithium and the influence of Cl was greater than Mg2+. Fe3+ and Cl were the optimal central ions and ligands for the formation of monovalent anions. The concentration of TBP should not too much for improving the separation effect of Li+ and Mg2+.

Graphical abstract

The optimized structures of FeCl3 and FeCl4, The theoretical Raman spectra of FeCl3 and FeCl4

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Introduction

The recovery of lithium from aqueous solution containing lithium has renewed the research interest as the rapid development of lithium electric vehicle [1], [2], [3]. The natural aqueous solutions containing lithium include geothermal brines, seawater, oilfield brine and continental brines [4], [5]. The continental brine is the biggest resource for lithium occurrence among these. The salt lake brines take up 71% in the lithium resources in China. The distribution of lithium in salt lake brine is mainly in Qinghai and Tibet. From scientific and environmental perspective the following points are important to consider the extraction lithium from salt lake brine: (1) the higher extraction efficiency [6]; (2) the effectively separation of Li+ and other metal ions [7]; (3) high efficient utilization of resource [8].

In literature various technologies such as precipitation [9], ion-change [10], solvent extraction [11], [12], [13], membrane [14], [15], absorption [16] and electrodialysis [17], [18], [19] had been proposed to extract lithium from salt lake brine. Among these solvent extraction had marked advantages over other methods in the high extraction efficiency of Li+ and high efficient utilization of resource [20], [21], [22]. Therefore, much attention had been paid on solvent extraction.

The extraction system using tributyl phosphate(TBP) as extractant, kerosene as diluent, and FeCl3 as co-extractant was the most typical in extracting lithium from salt lake brine [12], [23], [24]. In the earlier reports, the study of TBP-FeCl3 extraction system mainly focused on the component of extraction system and optimization of extraction conditions. The three diluent kerosene, octanol and methyl isobutyl ketone had been studied to extract lithium from brine by TBP [25], [26]. The feasibility of extraction lithium from brine, using ZnCl2, CrCl3 and FeCl3 as co-extractant, was investigated [25]. Furthermore, NaClO4 had also been used as co-extractant to extract lithium [27]. The salting-out agent played the important role in extracting lithium. The current findings suggested MgCl2, a nature component of brine, was the better salting-out agent [28].

The mixed extraction system based on TBP single extraction system had been extensively studied in recent years. The extraction mechanism, extraction kinetics and extraction thermodynamics were investigated by TBP-BA for recovering of lithium from salt lake brine [29], [30]. MIBK had significantly synergist in extraction lithium when using TBP-MIBK mixed extraction system [21], [31], [32]. A new amide extractant N523 had proved the good ability in extracting lithium [20], [33], [34]. However, there existed much difficult in separating phase when only using N523 as extractant. Therefore, N523 was considered to add to TBP extraction system for extracting lithium [13], [24]. Ionic liquid had been also added to TBP extraction system in recent years and had good results in recovery of lithium and separation of Li+ and Mg2+ [35], [36], [37], [38]. Although those mixed extraction systems displayed well in extracting lithium, the extraction lithium mainly depended on TBP in mixed extraction system [20], [39], [40]. Consequently, it was needed to investigate lithium extraction by TBP deeply and systematic.

In this paper, the key factors and mechanism of lithium extraction using tributyl phosphate(TBP) as extractant, kerosene as diluent, and FeCl3 as co-extractant were investigated. The theoretical calculation was conducted by DFT in order to confirm the interrelation of reaction reagents. The key factors, MgCl2, FeCl3 in aqueous solution and TBP in organic phase, were studied to clarify the roles they played in the process of extraction lithium.

Section snippets

Reagents and instruments

The reagents used in experimental were: LiCl·H2O(purity > 97%; China Pharmaceutical Group Chemical Reagent Co.), MgCl2·6H2O(purity > 98%; China Pharmaceutical Group Chemical Reagent Co.), FeCl3·6H2O(purity > 99%;China Pharmaceutical Group Chemical Reagent Co.), CuCl2·2H2O(purity > 99%;Tianjin damao Chemical Reagent Co.), CoCl2·6H2O(purity > 99%;China Pharmaceutical Group Chemical Reagent Co.), MnCl2·4H2O(purity > 99%;Tianjin Baishi Chemical Reagent Co.), ZnCl2 (purity > 98%;Chengdu Kelong

The theoretical calculation by DFT

To confirm the form of FeCl4 in the extraction process, the quantum chemical calculation was conducted. As Fe3+ was affected by ligand field of Fe3 + and Cl, they were inclined to form weak field and high spin complex. Fig. 1 showed when the complex transformed from FeCl3 to FeCl4, the structure turned from plane triangle into tetrahedron, the Fesingle bondCl bond was stretched and the bond angle diminished. Based on the optimization structure, the theoretical Raman spectrum could be obtained. Compared

Conclusions

In the current work, the key factors and mechanism of lithium extraction using tributyl phosphate(TBP) as extractant, kerosene as diluent, and FeCl3 as co-extractant were investigated. The theoretical calculation was conducted by DFT in order to confirm the interrelation of reaction reagents. The key factors, MgCl2, FeCl3 in aqueous solution and TBP in organic phase, were studied to clarify the roles they played in the process of extraction lithium. The main results were as follows:

  • (1)

    The

CRediT authorship contribution statement

Hui-fang Li: Conceptualization, Data curation, Writing - original draft. Li-juan Li: Methodology, Writing - review & editing. Wu Li: Methodology, Writing - review & editing. Yong-quan Zhou: Visualization, Investigation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was supported by National Key Research & Development Program of China (No. 2018YFC0604800); National Natural Science Foundation of China (No. U1707601); Major Science & Technology Project of Qinghai Province (No. 2019-GX-A5); Key Research & Development Project of Qinghai Province (No. 2019-GX-166); National Natural Science Foundation of China (NO. 21868030) and West Light Talent Program of Chines Academy of Sciences (Doctor Project, 2016).

References (40)

Cited by (10)

  • Mechanism and process for the extraction of lithium from the high magnesium brine with N,N-bis(2-ethylhexyl)-2-methoxyacetamide in kerosene and FeCl<inf>3</inf>

    2022, Journal of Industrial and Engineering Chemistry
    Citation Excerpt :

    Among the various techniques of recovering Li, solvent extraction has drawn much attention worldwide because of its high selectivity in lithium recovery from high Mg/Li mass ratio salt lake brines. The neutral organophosphorus synergistic extraction systems, especially the tributyl phosphate (TBP)/FeCl3-kerosene synergistic system, has already become one of the accomplished systems for lithium extraction from salt lake brines [31,33,35–38]. To explore better extraction effects, synergistic extractants, including dioctyl phthalate (DOP) [28], N,N-bis(2-ethylhexyl)-3-oxobutanamide (NB2EHOTA) [27], N,N-bis(2-ethylhexyl) acetamide (N523) [30], Octanol, ethyl acetate (EA), butyl acetate (BA), methyl isobutyl ketone (MIBK), diisobutyl ketone (DIBK) and 8-hydroxylquiolate [39], were subsequently added to the system to form a variety of new synergistic extraction systems.

  • Modelling of lithium extraction with TBP/P507–FeCl<inf>3</inf> system from salt-lake brine

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    However, these salt-lake brines have high magnesium (Mg) contents and very high Mg/Li ratios (>50) [9], resulting in a large challenge for Li recovery since Li and Mg have very similar physicochemical properties. In recent years, progress has been made in several separation techniques for the recovery of Li from Mg-rich brines, including solvent extraction [10-15], membrane separation [16-18], adsorption [19-21], and electrochemical methods [22,23]. Among them, the solvent extraction method based on a TBP/FeCl3 system is particularly suitable for Li recovery from brine with high Mg/Li ratios because of the high Li/Mg selectivity and low capital and operational costs [13,24-27].

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