Hydrometallurgy of lithium: Selective separation from geothermal brines using chitosan-lithium ion sieve composite

This study investigates the selective recovery of lithium (Li) from geothermal brines using a chitosan-coated lithium manganese oxide composite (CTS/LMO). Geothermal brines from Germencik and Tuzla in Türkiye, characterized by distinct physicochemical properties, were used to evaluate adsorption performance. The Freundlich isotherm provided the best fit for the adsorption data, indicating heterogeneous and multilayer adsorption, with maximum adsorption capacities of 3.622 mg/g for Germencik and 3.556 mg/g for Tuzla derived from the Langmuir isotherm. Kinetic studies revealed that lithium adsorption followed a pseudo-first-order model for Germencik (R2 = 0.992) and a pseudo-second-order model for Tuzla (R2 = 0.914). The intraparticle diffusion model identified boundary layer diffusion as a significant rate-limiting step, with diffusion rate constants of 0.365 mg/g·h0.5 for Germencik and 0.588 mg/g·h0.5 for Tuzla. Mechanistic studies demonstrated ion exchange as the dominant adsorption mechanism, supported by adsorption energy values of 8.64 kJ/mol for Germencik and 9.13 kJ/mol for Tuzla. Optimal conditions yielded lithium recovery efficiencies of 95% for Germencik and 80% for Tuzla, with the differences attributed to variations in salinity and ionic composition. CTS/LMO effectively retained Li up to 241 BV with 69.03% efficiency, while desorption peaked at 43 mg/L at 9 BV, achieving 76% elution efficiency in column operation with a model solution. These findings demonstrate the potential of CTS/LMO as an efficient and sustainable adsorbent for Li recovery from geothermal brines, contributing to the growing demand for Li in renewable energy applications.