Direct Lithium Extraction (DLE) with Manganese-Based Adsorbents: Selectivity Challenges and Global Perspectives with a Focus on Japan

Direct lithium extraction (DLE) from aqueous resources, including geothermal brines, seawater, and complex saline waters, has emerged as a promising complement to conventional lithium supply routes, such as hard-rock conversion and solar evaporation.Among various approaches, manganese-based lithium-selective adsorbents derived from λ-MnO 2 structures have attracted considerable attention due to their high lithium selectivity and favorable adsorption-desorption reversibility.This review evaluates the four principal DLE pathways-adsorption, ion exchange, solvent extraction, and electrochemical intercalation-and focuses on their reaction mechanisms, technological readiness levels, and operational constraints.Particular emphasis was placed on Mn-based adsorption systems developed in Japan and their applicability in geothermal brine environments.Key process challenges, including multivalent-ion interference, silica fouling, and pH drift, are discussed together with mitigation strategies, such as buffering control, surface stabilization, and hybrid flowsheet integration.