Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/1999
Publication Date: N/A
Interpretive Summary: The most widely used method to cleanup contaminated sites is the removal of the organic pollutants by binding them to charcoal. Because of the character of their surfaces, clays are very good at binding certain types of organic molecules, but poor for other types of compounds. The binding capacity of the clays however, can be significantly enhanced by replacement tof metals on the clay surface with certain types of organic molecules (organoclays). In present paper, we used the herbicide imazamox as a test compound to comparatively evaluate the ability of two clays and their organoderivatives (organoclays) as potential sorbents for cleanup of negatively charged organic molecules, which are a concern because they are weakly retained by most soil and sediment components. The results of this work showed that negatively-charged imazamox was moderately bound to clays within the organic chemicals on the surface whereas very little was bound to pure clays. It was shown that once the imazamox was bound, it did readily come off the organoclay. While the results appear promising, additional research is still needed to determine if these types of organoclays would be economically viable for cleanup of contaminated soil and water.
Technical 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 (organo-clays 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.