Kinetic and thermodynamic study on adsorption of cadmium from aqueous solutions using natural clay

Heavy metal pollution poses a great risk for the environment and the human health. Cadmium is among the most common pollutants found in wastewater, known for its great toxicity even in small doses. This work aims to study the removal of cadmium using natural Moroccan clay (MC). The clay was characterized using X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy, BET, and SEM. The effects of several experimental parameters on the clay adsorption capacity towards cadmium ions, such as MC dose, initial concentration and contact time, initial pH, and temperature were studied. The kinetic models Pseudo-first order, Pseudo-second order, and Elovich are evaluated to identify the adsorption process. The adsorption mechanism was determined by the use of the adsorption isotherms: Langmuir, Freundlich, and Temkin model. The results show that the heavy metal retention obeys the Pseudo-second order (R²≥0.99). The Langmuir isotherm model provided the best fit (R²≥0.99) to the experimental data for the adsorption of Cd(II) by MC as compared to the Freundlich and Temkin model. The maximum monolayer adsorption capacity of Cd(II), using the Langmuir model equation, is equal to 5.25 mg/g. The adsorption is a spontaneous and an endothermic process characterized by a disorder of the medium.