Elsevier

Journal of Membrane Science

Volume 530, 15 May 2017, Pages 185-191
Journal of Membrane Science

Further investigation into lithium recovery from salt lake brines with different feed characteristics by electrodialysis

https://doi.org/10.1016/j.memsci.2017.02.020Get rights and content

Highlights

  • Brines with different feed characteristics were treated by electrodialysis (ED).

  • The selective affinity of a Selemion CSO membrane was evaluated.

  • The mass transfer of this process was discussed via a thermodynamic analysis.

  • A specific transfer phenomenon in a brine system was found and explained.

  • ED was verified to have wide adaptability for lithium recovery from various brines.

Abstract

Although lithium resources are abundant in the salt lakes located in West China, the majority of these resources have a high Mg/Li ratio, which is problematic because traditional precipitation methods are unsuitable for lithium recovery from this type of brine. In our previous work, constant-current electrodialysis (ED) was applied to comprehensively investigate the effects of operating conditions on the Li+/Mg2+ separation, however, the experimental study considering the feed characteristic diversity and the theoretical analysis of the ionic transfer process considering the feed composition complexity were remained to be perfected. This work focused on resolving the remained questions therein. Initially, we determined the ion-exchange isotherm of the CSO membrane. The selective affinity towards divalent cation was validated, which laid the foundation for the development of the electric double layer (EDL). Then, we investigated the effects of applied voltage on the separation performance and optimized the power mode. The constant-voltage was verified to be a superior power mode compared to the constant-current applied in our previous work. Thereafter, the feed solutions characterized by different Mg/Li ratios, Na/Li ratios, and sulfate concentrations were treated by constant-voltage ED, wherein the partitioning principle was further explained via a thermodynamic analysis of the aqueous species distribution of ions. The results showed that in a high-salinity aqueous system, mass transfer was significantly affected by the complexity of the ions’ existing forms, which notably determined the steric hindrance and charge effect. As a specific transfer phenomenon, we found that sulfate ions provided large benefit to lithium recovery in the salt lake brine system. A natural brine experiment also showed that lithium recovery can be effectively achieved by ED. These observations indicated that ED has a wide adaptability for lithium recovery from brines with different feed characteristics.

Introduction

Recognized as a “critical material” [1], lithium's primary applications have been lithium-ion batteries (35%), ceramics and glass (32%), lubricating greases (9%), air treatments (5%), continuous casting mold flux powders (5%), and polymer production (4%) [2]. Among these, the extensive use of lithium-ion batteries, which represent the largest potential growth area for lithium compounds in global end-use markets, has significantly increased the consumption of lithium resources in recent years [2]. Minerals and brines are currently the major types of primary lithium resources [3]; among them, the average brine deposit is significantly larger than the average pegmatite deposit [4] (brines and minerals, respectively, account for 62% and 38% of the lithium-rich resources [5]). As currently the most abundant sources of lithium [6], brine deposits have drawn increasing interest for purposes of lithium extraction. In an aqueous system, it is difficult to separate lithium from magnesium due to their similar ionic properties. Thus, lithium extraction from a brine with a low Mg/Li ratio is easier and more economical [7]. Several methods, such as adsorption [8], [9], extraction [10], [11], [12], nanofiltration (NF) [13], [14], [15], [16], [17], and electrodialysis (ED) [18], have been developed to recover lithium from brines with high Mg/Li ratios.

As a highly selective separation process [19], ED based on ion-exchange membranes is indispensable for separation of ionic species [20]. Ion separation between monovalent and multivalent ions can be achieved by ED with ion-selective exchange membranes [21], [22], [23], [24], [25], [26]. Van der Bruggen et al. [22] indicated that a membrane's selectivity may also be influenced by the applied voltage, but variation in permselectivity versus applied voltage was not considered in their work. The concentration ratio between divalent and monovalent cations was considered to determine separation performance in Kabay's study [25]; however, the range of concentration ratio studied was narrow. Lambert [27] noticed that the transfer behavior of sulfate and chloride was unusual due to the existence of cation–sulfate complexes, but the effect of anion species on cation transfer behavior was not considered. In these current studies, separations were achieved with relatively simple electrolyte-solution systems, which have low ionic strengths and in which each ionic species has similar ionic activity. Thus, the general separation principle suggested in these studies may not be suitable for a salt lake brine system, as the existing forms of ion species in these aqueous systems with a high concentration of electrolytes are complex. Additionally, the brine system has an extremely strong total ionic strength, and thus, the ionic interactions and charge effects are strong. The concentration of co-existing ions, such as sodium, potassium, and sulfate, differ considerably in different types of brine, which may influence the applicability of ED for lithium recovery. In our previous study [18], it was shown that the ion-fractionation of Li+/Mg2+ can be effectively achieved by ED from a binary feed solution with a high Mg/Li ratio. Nevertheless, the experimental study considering the feed characteristic diversity of brines was remained to be further perfected. In particular, the effect of the anion species on separation performance has not yet been discussed. And the mass transfer considering the composition complexity of brine system should be further explained.

In this study, constant-voltage ED using a batch mode of operation was performed to recover lithium from brines with different feed characteristics. As derived from our previous study, the power mode was optimized. In addition, the feed solutions characterized by different Mg/Li ratios, Na/Li ratios, and sulfate concentrations were treated by constant-voltage ED, wherein the partitioning principle was further explained via a thermodynamic analysis of the aqueous species distribution of ions and the ion-exchange membrane's properties. Then, a typical natural brine with a high Mg/Li ratio was treated to validate the applicability of lithium recovery via ED.

Section snippets

Experimental setup

An Asahi Glass Co. DW-1 ED stack was used in a batch recycling setup comprising 40 repeating cells, each consisting of a cation exchange membrane (Asahi Glass Selemion CSO) and an anion exchange membrane (Asahi Glass Selemion ASA). Each membrane had dimensions of 18×55 cm2 with an effective area of 0.0507 m2 and electrical resistance of 2.0–2.3 Ω-cm2. As shown in Fig. 1, the same setup as our previous study [18] was used, which consisted of four separated circuits for the dilute, concentrate,

Ion-exchange isotherm

The ion-exchange isotherm of a CSO membrane at 25 °C is shown in Fig. 2. As shown, divalent counter-ions were preferentially adsorbed by the CSO cation-exchange membrane. It was only when the fraction of monovalent counter-ions in the binary electrolyte solution system became undeniably dominant (close to 1.0) that the adsorption ratio for monovalent ions increased significantly. It has been reported that the ions that are better retained in the ion-exchange membrane are transported more slowly

Conclusions

This study aimed to verify the adaptability of ED with monovalent selective ion-exchange membranes for recovering lithium from salt lake brines with different feed characteristics. The ion-exchange isotherm of a Selemion CSO membrane was initially determined, which verified that divalent counter-ions were preferentially adsorbed by the CSO cation-exchange membrane without the influence of an electric field. Then, constant voltage ED was performed to treat lithium-containing solutions with

Notes

The authors declare no competing financial interests.

Acknowledgment

The research was supported by Natural Science Foundation of China (U1407120) and the National 863 Program (2012AA061601).

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