Kinetics for the Removal of Paraquat Dichloride from Aqueous Solution by Activated Date (Phoenix dactylifera) Stone Carbon

For the adsorption of Paraquat dichloride (1,1'-dimethyl-4,4'-bipyridyl dichloride) from synthetic aqueous solutions, batch experiments were carried out to study the kinetics of Paraquat dichloride onto calcium oxide activated date (Phoenix dactylifera) stone carbon powder (particle size dia. about 0.85 mm). Studies were conducted at various initial concentrations of 75 mg/L, 100 mg/L, and 125 mg/L of Paraquat dichloride with 8.0 g/L of adsorbent dose. The equilibrium time was found to be 140 minutes. Maximum removal was observed at pH 9.0. The regression analysis for the experimental data showed that the removal kinetic profiles followed a pseudo-second order kinetic models for all initial concentrations, pH, temperature, and salinity of sorbate. The experimental data were analyzed using Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models. Thermodynamic parameters, such as standard change in Gibbs free energy, standard change in enthalpy, and standard change in entropy, were evaluated, indicating that the overall adsorption process was exothermic and spontaneous in nature.