Adsorption of atrazine, hydroxyatrazine, deethylatrazine, and deisopropylatrazine onto Fe(III) polyhydroxy cations intercalated vermiculite and montmorillonite.

Abstract

This paper describes the modification of the clay minerals vermiculite (VT) and montmorillonite (MT) by intercalating Fe(III) polymers of different [OH(-)]:[Fe(III)] ratios with the aim of removing atrazine (AT) and its metabolites deethylatrazine (DEA), deisopropylatrazine (DIA), and hydroxyatrazine (ATOH) from aqueous solution. An enhancement of adsorption capacity was observed for both intercalated clay minerals in comparison to the potassium-saturated materials (KVT or KMT). The results showed that different [OH(-)]:[Fe(III)] molar ratios had a small influence on the adsorption capacity, as well as in the basal spacing, BET surface area, and porosity. For the lowest initial concentrations of AT, DIA, and ATOH (0.050 mg L(-)(1)) studied, the modified VT adsorbed almost 80% of AT and DIA, while ATOH was removed at concentration levels below the detection limit of the technique, implying in at least 99.5% of sorption. Weak interaction between intercalated VT and DEA was observed, although a significant adsorption enhancement occurred in comparison to KVT. Within a 24 h interval, desorption of AT and DIA in aqueous medium reached levels close to 20% of the amount initially adsorbed, while for ATOH only 3% of the adsorbed compound was desorbed. The adsorption capacity of the Fe(III)-intercalated VT decreased after the first adsorption/desorption cycle, implying that the material is not suitable for reutilization. The intercalated MT was a powerful sorbent for AT, DEA, DIA, and ATOH, removing all of these chemicals from solution almost quantitatively (sorption greater than 99.5%), even at initial concentrations as high as 1.0 mg L(-)(1). Additionally, desorption of AT, ATOH, and DIA in water was not measurable up to the tube corresponding to the initial concentration of 1.0 mg L(-)(1), suggesting strong irreversible binding of these compounds to the intercalated MT materials. Desorption of DEA from the intercalated MT was between 5 and 30%. Unlike what was observed for VT, the intercalated MT materials were recyclable, keeping an excellent performance when reutilized.