Adsorption studies on the removal of coloring agent phenol red from wastewater using waste materials as adsorbents

Bottom ash, a waste of thermal power plants, and deoiled soya, an agricultural waste material, were employed for successful removal and recovery of hazardous phenol red dye from wastewaters. The adsorption characteristics and operational parameters were determined by monitoring different parameters such as effect of pH, effect of concentration of the dye, amount of adsorbents, contact time, and temperature. The equilibrium data were analyzed on the basis of various adsorption isotherm models, namely Langmuir, Freundlich, Tempkin, and Dubinin-Radushkevich. The highest monolayer adsorption capacity has been obtained for the phenol red-bottom ash system (2.6 × 10^-5 mol/g) at 50 °C. Different thermodynamic parameters such as free energy, enthalpy, and entropy have been calculated and it was concluded that with the increase in temperature adsorption increases, indicating the endothermic nature of the process for both adsorbent materials. Kinetic parameters were derived from pseudo-first-order and pseudo-second-order kinetics. Differentiation between particle and film diffusion mechanisms operative in the present study has been carried out. The column regeneration characteristic has been also investigated and recovery percentage greater than 90% was obtained for both adsorbents by utilizing acidic eluent.