Overcoming Mineral Scaling Challenges in Lithium Extraction from Geothermal Brines: The Roles of Silica, Fe(II), and Mn(II) in Electrochemical Intercalation.

Electrochemical lithium intercalation has emerged as a promising direct lithium extraction (DLE) technology owing to its high lithium selectivity and avoidance of chemical usage. While geothermal brines are a rich source of lithium ions (Li+), they also have high concentrations of coexisting constituents, including Fe(II), Mn(II), and silica, which can form scaling layers on the electrode surface, thus presenting substantial challenges for Li+ extraction. This study systematically investigates the effects of Fe(II), Mn(II), and silica on Li+ extraction by lithium iron phosphate (LiFePO4, LFP) electrodes and the mechanisms underlying performance degradation. Through cycling experiments in impurity-laden solutions, we demonstrate that Fe(II) severely compromises LFP electrode performance, reducing capacity, Faradaic efficiency, and Li+/Na+ selectivity. This performance degradation is attributed to the formation of an iron (hydr)oxide scaling layer and the bonding of Fe2+ ions with oxygen atoms in the LFP lattice, leading to accelerated reconstruction of the crystal structure. In contrast, Mn(II) and silica cause minimal performance loss despite contributing to scaling. Finally, we propose a cost-effective pretreatment method to remove Fe(II) from geothermal brines, extending the LFP electrode lifespan while maintaining high Li+/Na+ selectivity. These findings provide critical insights for scaling mitigation in electrochemical lithium extraction from complex brine sources.