High Removal of Cadmium (II) from the Aqueous Phase Using Douala Kaolinitic clay as a low cost Adsorbent: Correlation between Specific Surface area, CEC and Chemical Function

This study evaluated the Cd²⁺ encapsulation capacity in the aqueous phase of three natural kaolinitic clays, Arg-G, Arg-V and Arg-Y, from three localities in the Douala sub-basin. The clay materials were characterized by standard methods (XRF, XRD, FTIR, CEC and BET). Cd²⁺ adsorption tests were performed in batch mode and the influence of parameters such as contact time, pH and initial Cd²⁺ concentration was examined. Physicochemical characterization showed that the Arg-G clay had more active sites (Si/Al < 1) than Arg-V and Arg-Y for a specific surface area and cation exchange capacity of 41.48 m²/g and 26.00 meq/g respectively. The kinetic data showed that physisorption is the kinetically decisive step via the pseudo-first-order (PFO) model. The half adsorption time t_1/2 ˂ 5 min parameter indicated a high retention affinity of Cd²⁺ for clay adsorbents. Equilibrium data were best predicted by isotherms in the order D-K-R > Sips > Freundlich for Arg-G. Physisorption governs the cadmium ion fixation process. Based on the Sips isotherm, Arg-G exhibited a higher maximum adsorption density of 186.58 mg/g than Arg-V and Arg-Y (22.86 mg/g and 39.88 mg/g respectively). This work highlights the high adsorption performance of Arg-G clay from the Ndogpassi locality as a durable, low-cost adsorbent for trapping metal ions in water.