Perpustakaan Digital ITB

Lithium extraction from geothermal brines is challenging due to the high concentrations of competing cations—particularly sodium, potassium, and calcium—as well as elevated operating temperatures. Ion-exchange resins represent a sustainable alternative; however, the performance of commercial resins for selective lithium recovery from such brines remains insufficiently explored. In this thesis, a weakly acidic cation-exchange resin, Lewatit MDS TP 208 (LIXR), was investigated with a focus on its preferential adsorption of calcium over lithium. Kinetic studies conducted using lithium solutions prepared in distilled water confirmed a chemically controlled ion-exchange mechanism, with the adsorption behavior following a pseudo-second-order kinetic model. Adsorption isotherms were evaluated using four models—Langmuir, Freundlich, Temkin, and Radushkevich—revealing that the Langmuir model provided the best fit, with a maximum adsorption capacity of approximately 8.83 mg-Li/g-resin. Subsequently, fixed-bed adsorption experiments were designed using a Central Composite Design (CCD), considering four operational variables: temperature, flow rate, initial lithium concentration, and bed height. Dynamic lithium adsorption behavior was analyzed using the Adams–Bohart, Yan, Yoon–Nelson, and Thomas models, with the Thomas model exhibiting the best match with experimental data (R² = 0.999). The calculation results showed the adsorption capacity of the LIXR of 40 mg g-1. In parallel, machine-learning models were developed to predict calcium adsorption capacity and lithium retention time prior to desorption. SHapley Additive exPlanations (SHAP) analysis identified the initial lithium concentration as the most influential parameter, in agreement with Response Surface Methodology (RSM) results. Overall, the combined experimental and predictive analyses demonstrate the potential of LIXR to enhance calcium–lithium separation, providing a strong foundation for more efficient and greener lithium extraction from geothermal brines.