Adsorption, Kinetic and Thermodynamic Study for Removal of Nickel Ions by Activated Carbon from Palm Kernel

Palm kernel (PK) was activated by chemical activation (HNO3 at 230oC) to remove Ni(II) ions from aqueous solutions. Physicochemical properties of PK were reported. FT-IR analysis revealed changes in wave numbers and absorbance indicating Ni(II) adsorption onto activated carbon-PK surface. Energy dispersive X-ray fluorescence technique was used to determine the content of metals in activated carbon-PK and showed the metals found in activated carbon-PK were in recommended human usages. The maximum removal of Ni(II) ions was to be 49.7% at pH 4.6 and the equilibrium reached at 80 min. The removal efficiency of Ni(II) ions increased as the dosage of activated-PK increases and the optimum amount of activated carbon-PK dose was found to be 70 mg. The optimum pH was 4.6. The isotherm, kinetics and thermodynamics were studied. The Ni(II)- activated carbon-PK adsorption was found to follow the Freundlich isotherm based on correlation coefficient (R2) values and to be physical adsorption from the mean free energy found by Dubinin-Radushkevich, which confirmed by isothermal microcalorimetry data and the heat of sorption process using Temkin Isotherm model to be 1.58 kJ/mol. The adsorption kinetic data were described well by a second order, with the kinetic constant rates in the range of 1.82-83.5 g/g.min and was not controlled by intra-particle diffusion model. The thermodynamic studies showed that the Ni(II)-ACPK adsorption process is exothermic due to the negative values of ∆H (-30.9 J/mol) and is physical nature process due to the negative values of ∆S (-14.9 J/mol). The magnitude of Ea is 15.04 kJ/mol, which is proven the physical adsorption in nature.