Perchlorate adsorption from aqueous solution on inorganic-pillared bentonites

Abstract

In order to remove perchlorate (ClO4-) from water via adsorption, three modified inorganic-bentonites, such as hydroxy-aluminum pillared bentonite (Al-Bent), hydroxy-iron pillared bentonite (Fe-Bent), and mixed hydroxy-iron–aluminum pillared bentonite (Fe–Al-Bent), were synthesized and characterized. Bench-scale batch experiments were performed to study mechanisms behind the adsorption phenomenon and explore the factors affecting the perchlorate adsorption on pillared bentonites. The significant increase of interlayer spacing, BET surface area and total pore volume suggested a larger amount of active adsorption sites of the pillared bentonites surface and a wider perchlorate channel from the surface to the inner adsorption sites of bentonites, respectively. The results during adsorption process represented that the adsorption capacity of perchlorate followed the order: Fe-Bent>Fe–Al-Bent>Al-Bent. The perchlorate uptake on these three modified bentonites from 0.1mmol/L solution rapidly attained equilibrium within 100min. Pseudo-second-order kinetic model could provide satisfactory fitting of the kinetic data (R2>0.99). The Langmuir model fitted the adsorption isotherm very well (R2>0.98). The thermodynamic analysis indicated that the adsorption process was endothermic and spontaneous in nature. The pH changes appeared to have a little impact on the perchlorate adsorption performance using the Fe-Bent. While perchlorate removal by Al-Bent and Fe–Al-Bent decreased significantly with the increase of pH. Co-existing anions tests showed that the order of anion influence of the adsorption amount of ClO4- on pillared bentonite was PO43->SO42->NO3-. The present study confirmed that inorganic-pillared bentonites would be one of candidates for perchlorate adsorbent.