Electrochemical Lithium Recovery From Brines in a Circular Economy Approach

FLEXER, V.

EVENTO VIRTUAL

Conferencia; 73rd Annual Meeting of the International Society of Electrochemistry; 2022

International Society of Electrochemistry

Research to develop direct lithium extraction technologies from aqueous sources is fundamental due to the environmental and techno-economic shortcomings of the evaporitic technology currently in use. Electromembrane processes are considered an attractive alternative since they could be much faster than open air evaporation, be more readily adaptable to brines of different compositions, sustainable since they use electrons as reactants, avoiding waste production, the use of chemicals, and decreasing the water footprint. Our group has recently developed an overall membrane electrolysis strategy, schematized in Fig.1, to allow for the selective crystallization of Li2CO3 and other compounds, starting from a natural brine. First, we produce the full abatement of divalent species as the natural brine is electrochemically made alkaline. Next, since no membrane has yet been proved to separate monovalent cations, we aimed for the abatement of Na+ concentration, knowing that Na+ is the only of the three monovalent cations that is able to form a solid with HCO_3^-. In the last stage, we crystallize Li2CO3. Both HCO_3^- and CO_3^(2-)are produced via absorption of CO2 in an electrochemically alkalinized media. A careful equilibrium between current density and the flow of CO2 determines the pH and the predominant species, HCO_3^- or CO_3^(2-) .While the energy efficiency might seem low, the proposed methodology produces several by-products following circular economy principles: Mg(OH)2, Ca(OH)2, Na2CO3, HCl, and H2. In addition, because the sequential process removes a large share of the ions, a large proportion of the volume of the original brine is converted to low salinity water. Experiments have shown that the total dissolved solids in the brine could be reduced to about 50 mg L-1. Instead of producing Li2CO3 via evaporation with a strong water footprint, fresh water could be produced as a by-product of a mining operation, i.e. at the antipodes of current practice.In this talk we will first present data demonstrating the proof-of-concept of the proposed methodology, showing the time-dependent abatement of the different chemical species, and the purity of the different crystalized products. Next, some of our data leading to potential technology implementation will be presenting. Stage 1a (see figure 1) has been studied in depth using experimental design as a function of forced mass transport rate, temperature, and current density. Strategies leading to the avoidance of solid formation within the electrochemical reactors will be discussed. Finally, variations in the applied current density lead not only to operational cost changes, but to different lithium recovery ratios, and products’ purity, a phenomenon that is still under study. A large selection of direct lithium extraction technologies has been proposed in recent years, including both electrochemical, and non-electrochemical approaches. Key to scaling-up any technology is to test proposed methodologies at meaningful concentrations, representative of real brines. Our challenge here is to adapt well-known electrochemical principles to a new chemical system. Valuable Li+ ions are only a very minor component in a complex matrix of very high ionic strength with co-existing cations, most importantly Mg2+ and Na+, displaying chemical properties very similar to Li+. We will show some results on artificial solutions with concentrations different from those of native brines which usually produce unrealistically optimistic results.