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.