Adsorption potential of macroporous Amberlyst-15 for Cd(II) removal from aqueous solutions

The macroporous ion exchange resins are unique and most suitable for the adsorption of heavy metal ions due to their porous three-dimensional structures and large specific surface areas. In the current investigation, a macroporous sulphonic acid cation exchange resin Amberlyst-15 was implemented for the adsorption of Cd (II) using batch adsorption technique to evaluate its removal efficiency. The characterization of resin surface was performed by several techniques: Scanning Electron Microscopy/Energy dispersive X-ray Spectroscopy (SEM/EDS), Thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) surface area and Point of zero charge (PZC). The effects of various experimental parameters such as time, temperature, concentration, pH and dosage amount were examined in detail. The optimum pH for maximum uptake of Cd(II) onto the Amberlyst.15 was observed at pH 3 showing the efficient working of resin under highly acidic conditions. The results also proved that Amberlyst-15 showed tremendous adsorption potential toward Cd(II) removal; 99.95% removal within 30 min reaction time and 2.01 mmol g-1 maximum adsorption capacity at 323 K. The adsorption data was well described by Langmuir adsorption isotherm and pseudo second order models. The thermodynamic parameters revealed that the adsorption was endothermic, spontaneous and feasible process with increased randomness at resin surface. The free energy of adsorption (E) (13-15 kJ mol-1) determined from Dubinin-Radushkevitch (D-R) model proved the ion exchange reaction mechanism for Cd(II) adsorption. The experimental results reported herein validate that Amberlyst.15 resin is a promising adsorbent for the enhanced removal of Cd(II) and other toxic metals from contaminated water and waste effluents.