Removal of Hexavalent Chromium from Electroplating Wastewater Using Chitosan-Modified Montmorillonite Composites

Hexavalent chromium discharged in electroplating industry wastewater is a potent carcinogen and genotoxin regulated at very low maximum contaminant levels, demanding highly efficient removal technologies that are both effective and economically accessible for small and medium Nigerian industrial operators. This study prepares and characterises chitosan-modified montmorillonite nanocomposites using montmorillonite clay sourced from Ogun State, South West Nigeria, and evaluates their performance in removing hexavalent chromium from synthetic and real electroplating wastewater. Composite preparation involves acid activation of montmorillonite, intercalation with chitosan solution under controlled pH, and cross-linking with glutaraldehyde. The composites are characterised by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, Brunauer-Emmett-Teller surface area analysis, and zeta potential measurement. Batch adsorption experiments systematically investigate pH, contact time, initial hexavalent chromium concentration, adsorbent dosage, ionic strength, and temperature effects on removal efficiency. Adsorption kinetics, equilibrium isotherms, and thermodynamic parameters are determined and the removal mechanism is evaluated using extended X-ray absorption fine structure spectroscopy to distinguish between adsorption and reduction pathways. Fixed-bed column experiments are conducted and the Thomas, Adams-Bohart, and Yoon-Nelson breakthrough models are applied. Real electroplating wastewater from an Ibadan facility is tested to validate performance under complex matrix conditions. Cost analysis compares the composite against commercial activated carbon. Findings contribute new knowledge on clay-polymer composite adsorbent performance for industrial chromium remediation in Nigeria. Keywords: hexavalent chromium, chitosan-montmorillonite, adsorption, electroplating wastewater, composite adsorbent