Regeneration pH controls lithium recovery and titanium dissolution in H2TiO3/PVC composite beads

Titanium-based lithium adsorbents such as protonated titanate (H 2 TiO 3 , HTO) are promising materials for direct lithium extraction, but their long-term use is limited by titanium dissolution during acidic regeneration. In this work, the role of regeneration chemistry in controlling lithium recovery and HTO stability was investigated using porous HTO/PVC composite beads. Li 2 TiO 3 was shaped into spherical beads by solvent–antisolvent granulation with polyvinyl chloride as binder and subsequently converted to HTO by acid-induced proton exchange. Lithium adsorption and desorption were evaluated through batch experiments, kinetic studies, multi-cycle stability tests, and recirculating packed-bed operation using hydrochloric and sulfuric acid solutions with and without ammonium acetate buffering. The HTO/PVC beads achieved lithium uptake capacities of approximately 20–22 mg g −1 without loss of intrinsic HTO adsorption capacity after shaping. Unbuffered acidic regeneration caused significant Ti dissolution and progressive capacity loss, particularly under strongly acidic and sulfate-containing conditions. In contrast, buffering the regenerant to pH ≥ 3 suppressed Ti dissolution while maintaining efficient lithium desorption. The results are consistent with titanium speciation, where buffering prevents pH excursions into the Ti-solubilization domain without limiting proton-driven Li + /H + exchange. Repeated batch cycling and packed-bed experiments confirmed that buffered regeneration preserves sorbent performance and enables lithium enrichment during regenerant reuse. These findings show that regeneration chemistry, rather than sorbent composition alone, governs the durability of HTO-based adsorbents and provides a practical route to improve their process relevance for direct lithium extraction.