Organo-montmorillonites as adsorbent materials for thiophanate-methyl removal: adsorption-desorption studies and technological applications

Abstract

Thiophanate-methyl (TM) is a fungicide widely used in post-harvest treatment of pears and apples. The wastewater of this treatment usually is discharged to the natural rivers without treatment, with the consequent concern about the contamination of these waters. The fungicide adsorption on montmorillonites (Mt) and organo-montmorillonites (organo-Mt) can be a good alternative for wastewater treatment containing fungicides, used as filtering materials or flocculants. The TM adsorption on Mt and organo-Mt samples was studied in batch and column systems. Different organo-Mt samples were obtained, by cationic exchange reaction with octadecyltrimethylammonium (ODTMA) and didodecyldimethylammonium (DDAB) bromide at different surfactant loading. The anionic nature of the TM generated a very low adsorption in raw Mt, while the organo-Mt samples showed an increase of TM adsorption with the content of the surfactant. These results suggest two different types of interactions between organo-Mt samples and TM. At low surfactant contents, the adsorption occurs predominantly through hydrophobic interactions between the TM and the surfactant. While when the surfactant content is above the CEC value, additionally stronger interactions appear across water bridges between the TM molecules and the surfactant ammonium group. The similar TM adsorption percentages attained by organo-Mt with DDAB than those with activated carbon, points out the first material as a promising adsorbent that could be used to remove TM from wastewater in batch and also as filters or flocculants.