Kinetic and Thermodynamic Investigation of the Removal of Brilliant Green Dye by Natural Clay from Borno State

Industrial synthetic dyes released into water bodies from textile operations present ecological and human health risks that demand effective treatment solutions. Natural clay minerals offer a low-cost, readily available adsorbent option, and the unexploited natural clay deposits in Borno State provide an opportunity for local environmental remediation material development. This study conducted a kinetic and thermodynamic investigation of brilliant green dye removal from aqueous solution using natural clay from Borno State. The clay was characterised by X-ray diffraction, X-ray fluorescence, scanning electron microscopy, BET surface area analysis, Fourier-transform infrared spectroscopy, and point of zero charge determination. Batch adsorption experiments evaluated the effects of initial dye concentration, contact time, clay dose, pH, ionic strength, and temperature. Equilibrium data were analysed using the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models. Kinetics was investigated using pseudo-first-order, pseudo-second-order, Elovich, and Weber-Morris intraparticle diffusion models. Thermodynamic parameters were calculated at three temperatures. X-ray diffraction identified kaolinite and illite as the dominant clay minerals, with minor montmorillonite. Maximum adsorption capacity of 86.4 mg/g from the Langmuir model was achieved at pH 7, which corresponded to maximum dye adsorption. The pseudo-second-order model best described the kinetic data, suggesting chemisorption. Negative Gibbs free energy changes confirmed spontaneous adsorption. Positive enthalpy values confirmed the endothermic process. The calculated mean free energy from the Dubinin-Radushkevich model confirmed ion exchange as a contributing mechanism. These results establish Borno State natural clay as a promising indigenous adsorbent for dye removal from textile wastewater.

Keywords: natural clay, brilliant green dye, adsorption kinetics, thermodynamics, Borno State