Laterite-modified chitosan - An advanced geo-enhanced solution for hexavalent chromium remediation

Chitosan was chemically modified with silica enriched laterite (SEL) to synthesize a novel composite material, chitosan-silica enriched laterite (CSEL), designed for enhanced adsorption of Cr(VI) ions. Native chitosan, while environmentally friendly and biodegradable, exhibits a relatively low adsorption capacity for Cr(VI). SEL, a mining byproduct found beneath bauxite and often dismissed as waste due to its low alumina content, enhances both the adsorption capability and the thermal stability of the composite. The CSEL material was synthesized and extensively characterized through Fourier Transform-Infra Red (FT-IR) to identify functional groups, Thermogravimetry-Differential Thermal Analysis (TGA-DTA) for thermal behaviour analysis, Scanning Electron Microscopy (SEM) for surface morphology examination, Energy Dispersive X-ray Fluorescence (EDX) for elemental composition, and X-ray diffraction (XRD) to determine the crystalline structure. The efficacy was evaluated by batch adsorption experiments, which were enhanced via Response Surface Methodology (RSM). The adsorption process adhered to the Langmuir isotherm model, suggesting monolayer adsorption on a uniform surface. Under optimal conditions of pH 3.0, a contact time of 60 min, an adsorbent dose of 100 mg, and a temperature of 303 K, the maximum adsorption capacity (qm) was determined to be 21.05 mg g- 1 . The process followed a pseudo-second-order reaction mechanism, indicating that chemisorption was the predominant interaction. The thermodynamic analysis showed that the process is exothermic, driven by enthalpy changes, and becomes less effective at elevated temperatures. The adsorbent demonstrates remarkable regeneration ability and retains its efficacy even amidst the complexity of diverse ions present in aquatic environments. These conclusions underscore the promise of CSEL as a highly efficient and stable material for removing Cr(VI) in wastewater treatment processes.