Ligand immobilized novel hybrid adsorbents for rare earth elements (REE) removal from waste water: Assessing the feasibility of using APTES functionalized silica in the hybridization process with chitosan

This experimental study was aimed at checking the potential of employing commercially available amino functionalized silica gels in synthesizing the ligand immobilized hybrid materials rather than the conventional method of utilizing Tetraethyl orthosilicate (TEOS) precursors for the removal of REE from the waste water. The parameters used for the optimization of the synthesis process included the influence of silanes (3-Aminopropyl triethoxysilane APTES/methyltrimethoxy silane MTM), types of ligands (1 – (2-Pyridylazo) 2-naphthol (PAN) and acetylacetone (Acac)), molecular weight and degree of deacetylation of chitosan. Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer Emmett and Teller (BET) and Zeta potential (ZP) analysis were employed to understand the surface characterization of the hybridized adsorbents. The adsorption of La³⁺, Sc³⁺ and Y³⁺ was investigated further in detail using the hybridized PAN adsorbent to understand the effect of initial solution pH, contact time, temperature and initial adsorbate concentration. Single/multi-component system was studied through batch adsorption tests to assess the affinity towards target REEs and the intra series adsorption behavior of light/heavy REEs was also inspected.