Metal-based adsorbents for lithium recovery from aqueous resources

Highlights

• Comprehensive review on synthesis methods, extraction mechanisms, and adsorption performances of metal-based Li adsorbents

• Comparison of advantages and challenges of different metal-based Li adsorbents

• Application case study on Al-based adsorbent in Li recovery from the Qarhan Salt Lake

• Techno-economic analysis and future perspectives towards the development of metal-based Li adsorbents

Abstract

The continuous increase of demand for lithium (Li) chemicals in industrial applications calls for exploring affordable Li production and sustainable options beyond land mining. Thus, aqueous resources, such as geothermal brine, salt lake brine, and seawater, play an essential role in continuous Li supply due to abundant storage and low cost. Adsorption technology is promising in Li recovery with the advantages of attaining high selectivity for Li over other major ions present in aqueous resources at low cost and low energy demand with facile synthesis processes that enable practical large-scale production. Metal-based adsorbents are conspicuous among various adsorbents for presenting the visible prospect closest to industrial applications. This review presents a comprehensive summary and critical analysis of the synthesis methods for metal-based adsorbents, the mechanisms for Li selective recovery, and the performance of Li adsorption. The advantages and challenges are discussed for different adsorbents and preparation methods. A specific focused case study on an industrial application of Al-based adsorbent production and Li recovery processes and operations on an engineering and economic scale is discussed in detail to provide a comprehensive overview of the practical industrial application of metal-based adsorbent.

Introduction

Lithium (Li) has become one of the most crucial elements in this century in various industries because of its electrochemically active property and high specific heat capacity [1], [2]. Fig. 1 shows diverse applications and distribution of identified Li resources on land. Fig. 2 presents annual Li consumption from 2010 to 2020 and the distribution of extractable Li reserves with existing technologies [3], [4], [5], [6], [7], [8], [9]. The applications cover batteries, ceramics, lubricating greases, air treatment, catalysis, etc. Notably, in recent five years, the expansion of batteries for electric vehicles and other electric devices has been accelerated rapidly by the concept and policies of replacing traditional fuel energy to clean renewable energy in many countries [9], [10], [11]. The boom of global Li consumption, from 24.5 kt in 2010 to 93.0 kt in 2021 [4], challenges the supply of Li from conventional ore resources. On that note, recovering Li from aqueous sources exhibits significant advantages as an alternative Li resources, as about 75 % of Li on land is stored in geothermal brines, oilfield brines, and the salt lakes in South America, China, and Australia [12], and the reserve in the ocean is even over 16 thousand times than that on land [9].

The main approaches to extracting Li from brines include conventional evaporation precipitation [13], solvent extraction [14], [15], [16], and adsorption [17], and emerging technologies such as electrochemical methods [18], [19], [20], [21], [22], membrane-based technologies [14], [23], [24], [25], [26], [27], and reaction-coupled separation [28]. The predominant factors that influence selecting a method for Li extraction are the practical applicability of the method, the co-existing contaminant multivalent coions (namely the Mg/Li mass ratio), and the effects of other competing co-existing ions, such as Na⁺, K⁺ [29], [30], [31], [32]. The widely used evaporation precipitation method is limited to applying in the high Mg/Li ratio brines due to the complex and time-consuming pre-processes of removing co-existing ions [12], [33], [34]. The solvent extraction method for extracting Li from multi-ion-existing brines shows undesirable sustainability since the organic solvents can corrode the process equipment and the solvent leakage pollutes the environment [35], [36]. Electrochemical Li capture systems [37], including capacitive deionization (CDI) [38], [39], [40] and electrodialysis (ED) [41], [42], [43], [44] based on electrochemically switchable ion exchange (ESIX) rely on the external electric field, thus being limited by problems of high cost and energy consumption. Membrane-based technologies for Li recovery contain membrane capacitive deionization (MCDI) [45], [46], [47], selective electrodialysis (SED) [21], [26], [32], [44], nanofiltration (NF) [24], [48], ion-imprinted membrane (IIM) [49], [50], and membrane distillation crystallization (MDC) [51], [52], driven by external stimuli such as thermal gradient, pressure, and electric field [53], [54], [55], [56], [57]. These technologies have vast potential to develop in the next generation roadmap, yet the difficulties of energy consumption, separation efficiency, and membrane durability limit their industrialization. Reaction-coupled separation technology for the separation of Mg/Li by co-precipitating Mg-ions and foreign Al-ions with an alkali solution is still at the start-up stage [28], [29].

Compared to the above technologies, the adsorption method shows an excellent balance of high Li selectivity, simple and efficient operation process, good applicability to most brine resources, high economical advantage, and less environmental impact [58], [59]. It utilizes Li-selective adsorbents to uptake Li from a multi-ion aqueous environment and then desorbs them with some solvents, thus extracting Li. The principle requirements for proper adsorption materials cover high Li selectivity, adequate adsorption capacity, and suitable operation stability [60]. As shown in Fig. 3, the mainly studied Li adsorbents involve inorganic, organic, and composite adsorbents. Organic adsorbents, such as crown ether and polymer ion-exchange resin, are limited for applications due to the hazardous organic raw materials and the complex synthesis processes. Inorganic adsorbents include metal-based adsorbents and natural mineral-based adsorbents. The selection of the latter ones strongly depends on cost and resource quantity, impeding promoted applications in different brine source areas. Nowadays, metal-based adsorbents have become the hotspot and keystone of the research on Li adsorbents. The merits of metal-based Li adsorbents, including high Li capture capacity, low regeneration loss of raw materials, excellent Li selectivity, robust cycle performance, and relatively less energy consumption, qualify them as promising environmentally-friendly candidates for Li extraction from aqueous solutions containing different ions [61]. The pilot- and commercial-scale applications have been developed in Li recovery cases from the Qarhan Salt Lake by Qinghai Lakelithium Co., LTD. The related case study is developed in Section 3.

Previous review papers on Li recovery focused on 1) membrane-based [14], manganese-based [62], and MOF-based [8] Li extraction materials, 2) electrochemical methods [18], [41], [63], and other industry production methods [64], [65] from one specific brine source [13], [66] or region [67], 3) brine and mineral management perspectives [68], [69]; however, thus far, almost no comprehensive reviews concerning the developments of all metal-based adsorbents for Li recovery from sorts of brines. This review emphasizes the synthesis methods and Li adsorption performances of the current and the emerging metal-based Li adsorbents. Simultaneously, the techno-economic analysis is studied based on the application case of aluminum-based adsorbent in Li recovery from the Qarhan Salt Lake. The challenges and potential opportunities to implement on the future engineering scale are also discussed.