Sorption of the ionizable pesticide imazamox by organo-clays and organohydrotalcites

Abstract

The ability of two montmorillonites, SWy-2 and SAz-1, one hydrotalcite, HT [(Mg3Al(OH)8)2· CO3· 4H2O], and some of their organoderivatives (organoclays and organohydrotalcites) to sorb the ionizable pesticide imazamox (2-[4,5-dihydro-4-methyl-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5- (methoxymethyl)-3-pyridinecarboxylic acid) was determined at different pH levels to determine their potential use as sorbent materials for ionizable organic pollutants. At the pH of the sorbents (pH 6-7), the anionic form of imazamox predominated and the calcined product of HT (HT500) was found to be the best sorbent for imazamox anion. Negligible sorption of imazamox anion was measured on the pure clays, on hydrotalcite and organohydrotalcites, whereas sorption on organoclays was moderate and highly irreversible. Decreasing the pH led to a great increase in the sorption capacity of the organoclays, due to formation of molecular imazamox, which had a great affinity for the interlayer organic phase of the organoclays. In contrast, extensive dissolution of the hydroxide structure of the hydrotalcites at low pH limited their use as sorbent material in acidic conditions.