Removal of roxarsone from aqueous solution by Fe/La-modified montmorillonite

Roxarsone is an organoarsenical compound widely used as a feed additive in animal husbandry and might result in the contamination of inorganic arsenic in aquatic environment. Montmorillonite is an economical adsorbent with many advantages. In this study, Fe/La-modified montmorillonite (Fe/La-Mt) was prepared, characterized, and investigated for the removal of roxarsone from aqueous solutions. Brunauer-Emmett-Teller (BET) analysis confirmed the increase in specific surface area and pore volume of montmorillonite after modification. FESEM analysis showed that Fe/La-Mt formed flake structure and the structure was collapsed after being calcined (C-Fe/La-Mt). The adsorption results indicated that the adsorption capacity of Fe/La-Mt onto roxarsone is higher than that of C-Fe/La-Mt. The adsorption process of roxarsone onto Fe/La-Mt and C-Fe/La-Mt can be well described using pseudo-second-order model and interpreted using the Langmuir isotherm. Thermodynamic analysis indicated that the adsorption was a spontaneous and endothermic process. The adsorption capacity reduced slightly when solution pH increased from 2.5 to 8.0. The ion of greatly decreased the adsorption of roxarsone onto Fe/La-Mt. X-ray photoelectron spectroscopy analysis confirmed the loading of arsenic (V) onto the surface of Fe/La-Mt. The high adsorption capacity in a wide pH range demonstrated that Fe/La-Mt can be used potentially for the removal of roxarsone from aqueous solution.