Publication

Abstract : The adsorption of Ni(II) ion from an aqueous solution was successfully carried out using activated carbon prepared from Theobroma cacao (cocoa) shell, an agricultural solid waste biomass. The activated carbon prepared at ambient temperature (TCAC1) and the one prepared at 350 °C (TCAC2) were characterised by the FT-IR, BET, SEM, EDAX and Particle size analysis methods. The effects of the pH, dosage, initial metal ion concentration and agitation time were studied. The maximum adsorption was observed at pH 6 and the adsorption equilibrium was attained within 60 min. Adsorption isotherm data have been analysed, and the data fitted well in the order Langmuir > Redlich–Peterson > Temkin > Freundlich isotherm models. The maximum adsorption capacities of TCAC1 and TCAC2 for Ni(II) ions were calculated from the Langmuir isotherm as 97.59 and 158.8 mg/g, respectively. The kinetics of Ni(II) ion adsorption has been described, using five kinetic models viz, the pseudo-first order, pseudo-second order, Elovich, Intra-particle diffusion and Boyd kinetic models. The pseudo-second order kinetic model fits well with good correlation values. Thermodynamic parameters such as gibbs free energy (ΔG°), the enthalpy (ΔH°) and the entropy change of adsorption (ΔS°) have been calculated and it has been suggested that the adsorption process was feasible, spontaneous and exothermic in nature. The results obtained indicate that the activated cocoa shell prepared at 350 °C, has higher adsorption capacity when compared to the one prepared at room temperature. High surface area and low particle size are the prime factors for the increased efficiency.