Removal of herbicides from aqueous solutions by adsorption on Al-pillared clays, Fe–Al pillared clays and mesoporous alumina aluminum phosphates

Abstract

Fractionated Al-pillared (code name AZA) and Fe–Al-pillared (code name FAZA) clays and mesoporous alumina aluminum phosphates (AAPs) were contacted with aqueous, atrazine, propazine, prometryne, propachlor, propanil and molinate solutions at a concentration range of between 1 and 20 mg/l, in batch equilibrium experiments in order to determine their adsorption properties. The pillared clays showed an improved affinity which allowed the adsorption of the studied herbicides to occur much more efficiently than in the case of AAPs. The removed amounts of the studied herbicides by using the pillared clay materials reached 95.3% for atrazine, 92.2% for propazine, 98.5% for prometryne, 60.9% for propachlor, 86.8% for propanil and 70.2% for molinate. The iron substitution in FAZA pillared clay did not show great differences in adsorption capacity. The adsorption of s-triazines on mesoporous AAPs decreased with the alkyl substitution of the lateral chains, thus atrazine was the most adsorbed compound. The removal of propachlor by AAPs decreased with the increase of P/Al ratio. The material with P/Al=0.4 ratio was more efficient for the removal of molinate and propanil. The amounts of herbicides decomposed during the treatment were higher for AAPs in comparison with those for AZA and FAZA.