The Effects of Goethite on Formation of Chloro Compounds from the Chlorination of Hydroxybenzoic Acids in Water

Abstract

The amounts and forms of hydroxybenzoic acids adsorbed on goethite (GT) were examined i n aqueous suspensions and the effects of GT on formation of chloro comp ounds, chloroform (CF) and trichloroacetic acid (TCA), in water were discussed quantitatively. The analysis of adsorption behavior and FT-IR spectra of hydroxybenzoic acids in the presence of GT showed that these compounds are chemisorbed on GT. It was elucidated from FT-IR spectroscopy that m-hydroxybenzoic acid (MHBA) and p -hydroxybenzoic acid (PHBA) are adsorbed on GT, forming either monodentate complexes with an Fe atom of GT surfaces or binuclear complexes with two adjacent Fe atoms, while salicylic acid (SA) is strongly chemisorbed to form chelate complexes by coordination of carboxyli c and phenolic li gand to an Fe atom.8 El * I L. t 1992 No.1The effect of the presence of GT on the chlorination processes was found in all cases, that is based on the exchange of surface hydroxyls of GT. The other effect of the presence of GT on the chlorination processes is not remarkable in the cases of MHBA and PHBA, b ut in the cases of SA in pH 4 buffer solution, the yields of CF and TCA decreases steadily as the adsorbed SA increase. It could be concluded from the discussion on the reaction mechanism of the chlorination of hydroxybenzoic acids that this result is attributed to the chemisorption of SA on GT by chelation.