Modelling of Remazol Black-B Adsorption on Chemically Modified Waste Orange Peel: pH Shifting Effect of Acidic Treatment

Abstract

The adsorption of Remazol Black-B (RBB) onto two different types of agricultural waste derived-adsorbents; dried-orange peel (DOP) and chemically modified orange peel (CMOP), was performed. The adsorption rate, capacity, and the dye removal efficiency were investigated in terms of initial pH ranged between 2.0 to 10.0 of the dispersion and the operating temperature of 25 °C, 35 °C, 45 °C. The Langmuir and Freundlich adsorption models were applied to the experimental data to model the adsorption equilibrium, and evaluated by regression analysis. The results indicated that the Langmuir model was more suitable to describe the adsorption equilibrium of RBB over CMOP. According to Langmuir model, while the highest RBB uptake capacity of DOP was determined as 62.4 mg.g-1 at pH 2.0 and 25°C, this value was figured out for CMOP as 84.4 mg.g-1 at pH 8.0 and 45°C. Furthermore, the adsorption kinetics followed both the pseudo-second order and the saturation type kinetic models for each adsorbent-dye system. The thermodynamic parameters of adsorption including the Gibbs free energy change (ΔGo), the enthalpy change (ΔHo), and the entropy change (ΔSo) were obtained by using thermodynamic equations. These parameters were calculated as-4.24 kJ.mol-1, 43.77 kJ.mol-1, 0.16 kJ mol-1.K-1 for CMOP respectively whereas for DOP-3.58 kJ.mol-1,-19.79 kJ.mol-1,-0.05 kJ mol-1.K-1.