Incorporation of inorganic matrices through different routes to enhance the adsorptive properties of xanthan via adsorption and membrane separation for selective REEs recovery

The development of new strategies for the recovery of rare earth elements (REEs) is associated with their wide range applications, leading to ever-increasing global demand. Herein, two inorganic matrices (layered double hydroxide (LDH) and silica (SiO₂)) were employed to enhance the adsorption capacity of biopolymer (xanthan gum). The fabrication of nanocomposites was done by in-situ and ex-situ approaches. The fabricated xanthan nanocomposites were characterized to analyze their morphology, surface area, thermogravimetry, charge, and structural properties. The in-situ synthesized (InXL and InXS) nanocomposites exhibit stability and high removal efficiencies toward REEs in the single-component system. The adsorption of La, Y, Nd and Dy on InXL and InXS was endothermic in nature and followed by Langmuir isotherm displaying the homogenous adsorption with maximum adsorption capacities of 191.02, 214.89, 231.58 and 245.42 mg/g, and 192.82, 186.16, 183.93, and 171.86 mg/g, respectively. In a multi-component system, InXS displayed preferential adsorption for La, which could be selectively recovered by the simultaneous application of both materials. The post-adsorption results of REEs adsorption on InXS inferred that the possible mechanism involved was only electrostatic interaction between hydroxyl and carboxyl groups, meanwhile, ion exchange and surface complexation also occurred in case of InXL. The incorporation of InXL in mixed matrix polymeric membrane showed potential for removal of La, Y, Nd and Dy, implying that fabricated nanocomposite could be utilized efficiently in other modules for recovery of REEs. The high adsorption capacities for nanocomposites prepared via simple route yielding good reusability has the potential to be used for the recovery of REEs from the waste stream.