Abstract
In this research, the adsorption efficiency of nitric acid (HNO₃)-modified kaolin (MK) clay for the removal of methylene blue (MB) from aqueous solutions was examined. The influence of key operational parameters, including contact time and the initial concentration of MB, on the adsorption performance was systematically studied. Experimental findings indicated that the optimal conditions for MB elimination were achieved at an initial dye concentration of 350 mg/L and a contact duration of 80 minutes. Structural and compositional alterations on the adsorbent surface before and after adsorption were characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR) analyses. The adsorption data were found to be consistent with the Langmuir isotherm model, suggesting that both chemisorption and irreversible interactions played a role in the process. The maximum adsorption capacities of MB were determined to be 32.26, 34.13, and 35.46 mg/g at 25, 35, and 45 °C, respectively. Kinetic modeling demonstrated that the adsorption process followed the pseudo-second-order (PSO) model. Overall, the study highlights that modified kaolin is a promising, low-cost, and efficient adsorbent for the removal of methylene blue dye from wastewater.