Adsorption of Zn (II) and Cd (II) from Aqueous Solution using Natural Clay: Equilibrium, Kinetic Studies and Effect of Thermal Activation of Adsorbent on Adsorption Capacity

Natural clay containing some metal oxides and dolomite was used as an effective adsorbent to remove heavy metals such as cadmium and zinc. Thermal activation of natural clay was exploited as an efficiency method to improve and increase its effectiveness in removing these metals. The maximum removal efficiency value of natural clay for zinc and cadmium ions were 21.3 (mg.g-1) and 33.33 (mg.g-1) respectively. This clay had a maximum zinc and cadmium removal capacity at pH above 4, contact time 25 min and 5 min for zinc and cadmium respectively, and adsorbent mass 4 (g.l-1). Thermal activation of natural clay at 900 °C increases this capacity to 83.33 (mg/g) and 90.909 (mg/g) for Zinc and Cadmium respectively. The pseudo second order model and the equations of Freundlich and Langmuir are the most adequate to represent the experimental data of kinetics and isotherms of adsorptions of Zn (II) and Cd (II) by natural clay respectively. The Langmuir model maintain the most adequate equation to represent the isotherm of adsorption of zinc and cadmium by thermal activated natural clay.