Lithium recovery using electrochemical technologies: Advances and challenges.

Driven by the electric-vehicle revolution, a sharp increase in lithium (Li) demand as a result of the need to produce Li-ion batteries is expected in coming years. To enable a sustainable Li supply, there is an urgent need to develop cost-effective and environmentally friendly methods to extract Li from a variety of sources including Li-rich salt-lake brines, seawater, and wastewaters. While the prevalent lime soda evaporation method is suitable for the mass extraction of Li from brine sources with low Mg/Li ratios, it is time-consuming (>1 year) and typically exhibits low Li recovery. Electrochemically-based methods have emerged as promising processes to recover Li given their ease of management, limited requirement for additional chemicals, minimal waste production, and high selectivity towards Li. This state-of-the-art review provides a comprehensive overview of current advances in two key electrochemical Li recovery technologies (electrosorption and electrodialysis) with particular attention given to advances in understanding of mechanism, materials, operational modes, and system configurations. We highlight the most pressing challenges these technologies encounter including (i) limited electrode capacity, poor electrode stability and co-insertion of impurity cations in the electrosorption process, and (ii) limited Li selectivity of available ion exchange membranes, ion leakage and membrane scaling in the electrodialysis process. We then systematically describe potentially effective strategies to overcome these challenges and, further, provide future perspectives, particularly with respect to the translation of innovation at bench-scale to industrial application.

Scale-up and Modelling of Flow-electrode CDI Using Tubular Electrodes.

A novel design for a flow-electrode capacitive deionization (FCDI) system consisting of tubular electrodes in a shell and tube heat exchanger configuration is proposed. Each electrode consists of a metallic mesh current collector along the inner circumference of a tubular ion-exchange membrane. This tubular FCDI design is suitable for scale-up as it consists of easily manufactured components which can be assembled in an array. An apparatus with 4 tubular electrodes with a large effective area (202.3 cm2) was constructed and shown to provide a high net salt (NaCl) removal rate (0.15 mg s-1 at 1.2 V applied voltage and ∼2000 mg L-1 influent total dissolved solids concentration). A computational fluid dynamics (CFD) model incorporating ion migration and transport mechanisms was developed to simulate the ion concentration and electrical potential profiles in the water channel. The results of CFD modelling highlighted the need to maximize regions of both high potential gradient and high hydraulic flow in order to achieve optimal salt removal. In brief, this study presents a new design approach for FCDI scale-up and provides a computational tool for optimization of this design and future innovative FCDI designs.

Phosphate selective recovery by magnetic iron oxide impregnated carbon flow-electrode capacitive deionization (FCDI).

The recovery of phosphorus (P) from wastewaters is a worthy goal considering the potential environmental and economic benefits. Flow-electrode capacitive deionization (FCDI), which employs flowable carbon electrodes instead of the static electrodes used in conventional CDI, has been demonstrated to be a promising P recovery technology. FCDI outperforms CDI and other competitive technologies in a number of aspects including (i) large salt adsorption capacity and (ii) extremely high water recovery rate. In this study, magnetic (Fe3O4 impregnated) activated carbon particles were prepared and applied as FCDI electrodes. The magnetic carbon electrodes were found to have a strong affinity towards P, facilitating the selective adsorption of P to the magnetic particles through a ligand exhange mechanism. Continuous operation of the FCDI system could be achieved with only three minutes required to separate the electrode particles from the brine stream on application of an external magnetic field. A P-rich stream was produced on regeneration of the exhausted magnetic electrodes using alkali solution. We envision that the use of magnetic carbon enhanced flow-electrodes will pave the way for efficient operation of FCDI as well as the preferential recovery of P.