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Evaluation of the Adsorption Capacity of the Coconut Shell and Palm-Kernel Shell Adsorbents Powder for the Sorption of Cadmium (11) Ions from Aqueous Solution

Environmental contamination of toxic metals accumulation in food chain is of global concern. Biosorption type of adsorption process is an economical tool in waste water treatment which is an alternative metal adsorption compares to high cost conventional methods like precipitation and reverse osmosis. The study examined adsorption capacities of two palm shell powder absorbents in the removal of Cd (11) ions from synthetic waste water. Coconut (Cocos nucifera) and palm-kernel (Elaeis guineensis) shell powder adsorbent used for Cd (11) ion sorption were developed from agricultural bye products. The procedure involved comparison of the performance of these adsorbents with each other by metal binding capacities, initial metal ion concentrations, ionic strengths and contact time. The adsorption capacities per unit gram of each of the adsorbents at equilibrium time, optimum pH, 200 r p m speed, 25 o C temperature under 10 to 50 mg kg -1 initial metal concentration was determined. The binding capacities for Cd (11) ion are 5.34 to 37.42 mg kg -1 for coconut shell relative to 0.32 to 4.75 for palm-kernel shell adsorbent at optimum contact time of 5 hrs. The long contact time for the sorbent metal adsorption indicated that the predominant mechanism was physisorptions. The optimum pH value for, Cd (II) ion removals on coconut and palm kernel shells powder are 5.0 and 6.0, respectively. Adsorption kinetics was verified by pseudo-first order (Lagergren) rate and pseudo-second order (Ho-model) rate models. The kinetic of the sorption mechanism indicate that pseudo-first order model provides a more appropriate description of the Cd (11) ion sorption on the adsorbents. Adsorption isotherms patterns of both adsorbents were modeled using Langmuir and Freundlich isotherms. Based on correlation coefficient (R 2 ) values, equilibrium data found fitted well to the Freundlich isotherm. It is concluded that the two palmshells can be use as an effective adsorbents for removal of toxic Cd (11) ion but coconut shell has the greater potential over palm-kernel shell.