Adsorption of Di-N-butyl Phthalate onto Nutshell-Based Activated Carbon. Equilibrium, Kinetics and Thermodynamics

The adsorption of di-n-butyl phthalate (DBP) from aqueous solution was studied in a batch adsorption system. Activated carbons from coals, coconut shell and nutshell were evaluated to determine the most effective adsorbent. Kinetic and equilibrium studies were investigated at various initial DBP concentration (3–6 mg/ℓ), adsorbent dosage (40–140 mg/ℓ), suspension pH (3–9) and temperature (25–55 °C). Equilibrium adsorption isotherms were analyzed using the Langmuir, Freundlich and Temkin models. The experimental isotherms were S-type, with the Freundlich isotherm giving a good description of the data obtained at lower DBP concentration. The pseudo-first-order, pseudo-second-order and intra-particle diffusion models were used to fit the kinetic adsorption data. It was found that the adsorption of DBP followed pseudo-first-order kinetics, with the adsorption rate being controlled by both film and pore diffusion. The enthalpy, entropy and Gibbs' free energy constants were calculated. It was found that the adsorption was spontaneous and endothermic, with favourable adsorption capacities being observed at higher temperatures.