Selective lithium recovery from XRF melting waste via H₂TiO₃ Ion Sieve

The growing demand for lithium driven by energy storage technologies requires sustainable recovery strategies from secondary resources. In this study, lithium recovery from lithium-rich XRF melting wastes was investigated using a titanium-based lithium-ion sieve via the ion-exchange method. Li₂TiO₃ (LTO) was synthesized by a solid-state method and converted into protonated H₂TiO₃ (HTO) through acid treatment to obtain a lithium-selective adsorbent. Structural and surface characterization confirmed the formation of a stable ion-sieve framework with increased surface area after proton exchange. XRF melting waste, mainly composed of lithium tetraborate and metaborate flux residues collected from cement plants, was subjected to acid digestion to selectively transfer lithium into the aqueous phase while minimizing co-dissolution of competing metals. Adsorption experiments revealed strong pH-dependent lithium uptake with a maximum capacity of ~36 mg.g⁻¹ under alkaline conditions. Isotherm and kinetic analyses indicated that the adsorption process follows the Langmuir model and pseudo-second-order kinetics, suggesting monolayer chemisorption governed by ion-exchange mechanisms. Thermodynamic evaluation showed that lithium adsorption is spontaneous and endothermic. The adsorbent exhibited high selectivity toward Li⁺ in real waste-derived solutions and maintained stable performance over repeated adsorption–desorption cycles with minimal titanium loss. This study demonstrates the feasibility of recovering lithium from XRF melting waste and highlights a new pathway for valorizing lithium and boron-rich residues within a circular economy framework.