Recovery of critical elements enriched from red mud and bauxite by sorption process

In this study, batch adsorption studies were carried out to recover the rare earth elements (REE) La, Ce and Nd from aqueous solutions enriched by acid leaching and roasting and water leaching processes from red mud and bauxite. In addition to commercial resins, microcapsules were prepared from natural materials and used as adsorbents, and comparison was performed between resins and microcapsules as well as red mud and bauxite samples. The effects of adsorbent amount, concentration, temperature, pH and contact time parameters on the adsorption process were examined. Using the results of concentration experimental studies conducted for REE recovery, isotherm parameters were calculated by drawing Langmuir, Freundlich, D-R and Scatchard adsorption isotherm curves. Moreover, with contact time data, kinetic study of the process was carried out by applying pseudo-first-order and pseudo-second-order kinetic models. Furthermore, reaction thermodynamics were studied with temperature data and ΔSo standard entropy (kJ/mol.°K), ΔHo standard enthalpy (kJ/mol) and ΔGo Gibbs Free Energy values were calculated. In addition to these studies, characterization studies of adsorbents were carried out with BET, FTIR and SEM+EDX analyses. As a result of the experimental studies, optimum conditions were determined and the maximum adsorption efficiencies obtained under these optimum conditions were determined to be over 99.75% in resins and 97.25% in natural materials, which shows that these adsorbents are efficient adsorbents for REE recovery. The data obtained as a result of kinetic studies indicates that the results are mainly correspond to the pseudo-second order kinetic model. Additionally, according to the results of isotherm studies; compliance with Langmuir and Scatchard isotherm models was observed. In addition, the results obtained as a result of thermodynamic studies show that in most of the samples the process is exothermic, there is tendency of the adsorbents towards ions, and in all samples spontaneous nature of the adsorption process is achieved.