The removal of cadmium(II) ions from aqueous solution by adsorption on kaolinite (KAO.1) and metakaolinite (MKB) was investigated depending on the initial concentration, adsorbents dosage, initial pH of solution, and contact time. The influences of those factors have been experimentally verified by a batch method at (27±3 °C). These results have showed that the amount of cadmium(II) ions adsorbed increases with increased contact time and that equilibrium adsorption is reached in 10 minutes, the optimum value of pH was 8.0 and the effect of absorbent dose for the uptake of cadmium(II) ions by kaolinite and metakaolinite was found to decrease by increasing the adsorbent dose. The experimental results obtained are described by Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich (D-K-R) isotherm models. The Langmuir and D-K-R adsorption isotherms described the adsorption data very well. The maximum adsorption capacity; Q max , determined from the Langmuir adsorption isotherm studies was found to be 7.407 and 9.174 mg/g for KAO.1 and MKB respectively. Pseudo-first order, pseudo-second order, Elovich and the intraparticular diffusion kinetic models were used to describe the kinetic data obtained. The experimental data fitted well to the pseudo-second order kinetic model, which indicates that 12Jean Serge ESSOMBA et al.chemical adsorption is the rate-limiting step. The results indicate that kaolinite and metakaolinite adsorb cadmium(II) ions efficiently and could be employed as a low-cost alternative in waste water treatment for the elimination of cadmium(II) ions.

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Egusi seed shells (ESS) were used as precursor for the preparation of two activated carbons (ACs) following H 3 PO 4 and ZnCl 2 activation. The effect of factors controlling the preparation of ACs such as chemical activating agent concentration (2-10 M), activation temperature (400˚C-700˚C) and residence time (30-120 min) were optimized using the Box-Behnken Design (BBD). The optimized activated carbons based H 3 PO 4 (ACP) and ZnCl 2 (ACZ) were characterized by N 2 adsorption, elemental analysis, atomic force microscopy (AFM), Boehm titration and Fourier transformed infrared (FTIR) techniques. The specific surface area was found to be 1053.91 and 1009.89 m 2 •g −1 for ACP and ACZ respectively. The adsorbents had similar surface functionalities and were both microporous. The effect of various parameters such as initial pH, concentration, and contact time on the adsorption of nitrate ions on ACP and ACZ in aqueous solution was studied. ACZ demonstrated better adsorption capacity (8.26 mg•g −1) compared to ACP (5.65 mg•g −1) at the same equilibrium time of 20 min. The adsorption process was governed by a "physical interactions" phenomenon for both adsorbents.

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