Battery Electrode-Based Lithium Recovery from Geothermal Brines

Abstract

Driven by the electrification of transport sector the demand of lithium for battery application is increasing exponentially. The major sources for lithium are continental brines and hard minerals where the production comes along with consumptive water requirements and energy intensive processing and extraction. Therefore, it is of tremendous importance to consider alternative, non-conventional, sources and to develop more efficient and environmentally benign Li extraction methods. Geothermal brines can have significant Li concentrations (150–240 mgLi+ L−1)[1] and could represent an attractive sustainable lithium source. Implementing electrochemical methods for lithium extraction offers further advantages of high Li-selectivity, minimal waste production and low water consumption.[2] Here, we present a dual-ion battery type setup for the selective electrochemical Li-adsorption and desorption from geothermal brines. The chloride concentration in brines is a thousand times higher than that of Li+, hence, both species can be captured at opposite electrode sides. In the dual-ion setup presented in this work, Li+ are stored in a Li-selective LiFePO4(LFP) battery electrode and Cl− are stored using bismuth oxychloride (BiOCl) as counter electrode that has shown excellent Cl− storage capabilities and chemical stability in chloride-ion batteries and desalination batteries.[3] In the second step, both ions are released in a recovery solution to yield a Li-rich solution that could be further processed into battery-grade lithium hydroxide or carbonate. The stability of LFP in aqueous solutions and high Li -selectivity makes it a favored candidate for the electrochemical recovery of Li from natural solutions, where a diverse mixture of cations and anion is present.[4] Therefore, we examined the stability of the electrodes in brine solutions by XRD, indicating good reversibility and no intercalation of competitor ions. In addition, the Li-selectivity in extraction/recovery experiments was analyzed by ICP-OES and influences of different process parameters (e.g. current density, pH, temperature) were investigated. The results demonstrate that the LFP/BiOCl dual-ion battery setup is a feasible and promising low cost method for environmentally friendly Li extraction from geothermal brines.