Sorption of AsV on aluminosilicates treated with FeII nanoparticles

Adsorption of arsenic on clay surfaces is important for the natural and simulated removal of arsenic species from aqueous environments. In this investigation, three samples of clay minerals (natural metakaoline, natural clinoptilolite-rich tuff, and synthetic zeolite) in both untreated and Fe-treated forms were used for the sorption of arsenate from model aqueous solution. The treatment of minerals consisted of exposing them to concentrated solution of FeII. Within this process the mineral surface has been laden with FeIII oxi(hydroxides) whose high affinity for the AsV adsorption is well known. In all investigated systems the sorption capacity of FeII-treated sorbents increased significantly in comparison to the untreated material (from about 0.5 to >20.0 mg/g, which represented more than 95% of the total As removal). The changes of Fe-bearing particles in the course of treating process and subsequent As sorption were investigated by the diffuse reflectance spectroscopy and the voltammetry of microparticles. IR spectra of treated and AsV-saturated solids showed characteristic bands caused by FeIIISO4, FeIIIO, and AsO vibrations. In untreated AsV-saturated solids no significant AsO vibrations were observed due to the negligible content of sorbed arsenate.

Clays and aluminosilicates are not selective sorbents for anions thanks to a low pHZPC. A simple Fe-treatment of their surfaces improved the sorption properties significantly. Arsenic oxyanions have been bound to treated sorbent surfaces forming very stable inner-sphere complexes (see the mechanism of As sorption to Fe-hydrated oxides in the figure). The sorption efficiency of Fe-treated aluminosilicates exceeded 95% regardless of the sorbent used.Figure optionsDownload as PowerPoint slide