Aqueous Cadmium Ions Removal by Adsorption on APTMS Grafted Mesoporous Silica MCM-41 in Batch and Fixed Bed Column Processes

Highly ordered mesoporous MCM-41silica with hexagonal structure was synthesized using extracted amorphous silica from sedge (Carex riparia) ash. Obtained mesoporous materials functionalized by 3-(Aminopropyl) trimethoxysilane (APTMS) and their structures characterized by means of X-ray diffraction (XRD), nitrogen adsorption-desorption, thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. As-synthesized material were applied for adsorption of Cd(II) metal ions from aqueous solution in batch and fixed bed column systems. Batch adsorption process was carried out to evaluate initial ion concentrations, sorbent dose, contact time, pH and temperature. The equilibrium data were analyzed using the Langmuir and Freundlich isotherm by nonlinear regression analysis. The kinetics study reviled that data from the experiments fitted well to the pseudo-second order equation than pseudo-first order. Thermodynamic parameters reviled that the adsorption process strongly depended on temperature and the adsorption capacity increased by increasing the temperature of the system, indicating the endothermic behavior and spontaneous nature of adsorption. For continuous adsorption experiments, NH2-MCM-41 adsorbent was used and breakthrough curves were analyzed at different bed heights, flow rates and initial metal ion concentrations. The Thomas and bed depth service time (BDST) models were used to determine the kinetic constants and to predict the breakthrough curves of each component.