title: Enhancement of the reductive transformation of pentachlorophenol by polycarboxylic acids at the iron oxide-water interface.
abstract: The enhancement effect of polycarboxylic acids on reductive dechlorination transformation of pentachlorophenol (PCP) reacting with iron oxides was studied in anoxic suspension. Batch experiments were performed with three species of iron oxides (goethite, lepidocrocite and hematite) and four species of polycarboxylic acids (oxalate, citrate, succinate, and tartrate) through anoxic abiotic reactors. The chemical analyses and morphological observation from scanning and transmission electron microscopy showed that different combinations between polycarboxylic acids and iron oxides produced distinct contents of Fe(II)-polycarboxylic ligand complexes, which significantly enhanced PCP transformation. Generation of the surface-bound Fe(II) depended on concentration of polycarboxylic acids. The optimal concentration for the enhancement was 2.0 mM oxalic acid. The dechlorination mechanism was further demonstrated by generation of chloride ions. The results suggest that surface-bound Fe(II) formed on the iron oxides surface appears to be a key factor in enhancing PCP transformation, and the mole ratio of oxalate to surface-bound Fe(II) (oxalate/Fe(II)) acted as an indicator of the enhancement effect. The enhancement mechanism attributes to strong nucleophilic ability and low reductive potential of the equivalent Fe(II)-polycarboxylate complexes. Therefore, the enhancement effects might be helpful for understanding the natural attenuation of reducible organic pollutants at the interface of contaminated soil in anoxic condition.
authors.affiliation: Guangdong Key Laboratory of Agricultural Environment Pollution Integrated Control, Guangdong Institute of Eco-Environment and Soil Sciences, Guangzhou 510650, PR China. cefbli@soil.gd.cn
authors.forename: Fangbai
authors.initials: F
authors.lastname: Li
authors.forename: Xugang
authors.initials: X
authors.lastname: Wang
authors.forename: Yongtao
authors.initials: Y
authors.lastname: Li
authors.forename: Chengshuai
authors.initials: C
authors.lastname: Liu
authors.forename: Fang
authors.initials: F
authors.lastname: Zeng
authors.forename: Lijia
authors.initials: L
authors.lastname: Zhang
authors.forename: Mingde
authors.initials: M
authors.lastname: Hao
authors.forename: Huada
authors.initials: H
authors.lastname: Ruan
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D004785:Environmental Pollutants / Q000737:chemistry; D005290:Ferric Compounds / Q000737:chemistry*; D058085:Iron Compounds / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D008903:Minerals; D010084:Oxidation-Reduction; D010416:Pentachlorophenol / Q000737:chemistry*; D011739:Pyrimethamine; D014867:Water
chemical_list: D002264:Carboxylic Acids; D004785:Environmental Pollutants; D005290:Ferric Compounds; D058085:Iron Compounds; D008903:Minerals; D014867:Water; C094886:goethite; C000499:ferric oxide; D010416:Pentachlorophenol; D011739:Pyrimethamine