Enhancement effects of chelating agents on the degradation of tetrachloroethene in Fe(III) catalyzed percarbonate system

Abstract

The performance of Fe(III)-based catalyzed sodium percarbonate (SPC) for stimulating the oxidation of tetrachloroethene (PCE) for groundwater remediation applications was investigated. The chelating agents citric acid monohydrate (CIT), oxalic acid (OA), and Glutamic acid (Glu) significantly enhanced the degradation of PCE. Conversely, ethylenediaminetetraacetic acid (EDTA) had a negative impact on PCE degradation, which may due to its strong Fe chelation and HO• scavenging abilities. However, excessive SPC or chelating agent will retard PCE degradation. In addition, investigations using free radical probe compounds and radical scavengers revealed that PCE was primarily degraded by HO• radical oxidation in both the chelated and non-chelated systems, while O2•− also participated in the non-chelated system and the OA and Glu modified systems. According to the electron paramagnetic resonance (EPR) studies, the presence of HO• in the Fe(III)/SPC system was maintained much longer than that in the Fe(II)/SPC system. The results indicated that the addition of CIT, OA or Glu indeed enhanced the generation of HO• in the first 10 min and promoted degradation efficiency by increasing the amount of Fe(III) and maintaining the concentration of HO• radicals in solution. In conclusion, chelated Fe(III)-based catalyzed SPC oxidation is a promising method for the remediation of PCE-contaminated groundwater.

Enhancement effects of reducing agents on the degradation of tetrachloroethene in the Fe(II)/Fe(III) catalyzed percarbonate system

“…For example, the magnitude of PCE degradation in 5 min increased from approximately 4% to 98%, 53%, 59% and 10% for the HAH, SS, ASC and SA reagents, respectively. The much slower rate of degradation observed for the control is consistent with the results of previous research [29], which demonstrated that more than 30 min was required for the complete degradation of PCE in the Fe(III)/SPC system in the absence of reducing agents, even when high concentrations (10 mM) of Fe(III) and SPC were used.…”

“…S1 in Appendix A. Supplementary data) [29] and Fe(II) catalyzed SPC systems [19] can degrade PCE effectively. However, the degradation rate is significantly different because of different PCE degradation pathways as well as the different concentrations of Fe(II) present.…”

Generation of hydroxyl radicals by Fe-polyphenol-activated CaO2 as a potential treatment for soil-borne diseases

“…The Fe(III)-activated CaO 2 exhibited several limitations, such as precipitation of the iron as ferric hydroxide (Fe(OH) 3 ), which does not readily redissolve and inhibits the oxidation process 41 . The addition of chelating agents such as citric acid, tartaric acid, oxalic acid, and glutamic acid has been proposed as a way to overcome these drawbacks 41 , 42 . We believe that the caffeic acid and chlorogenic acid present in coffee grounds probably contributed to the Fenton process by reducing Fe 3+ to Fe 2+ and/or served as electron donors binding Fe 2+ to maintain the activity of Fe in the reduced state in the Fenton cycle.…”

Fundamentos e aplicação do percarbonato de sódio para remediação de solos e águas subterrâneas por oxidação química

“…O principal composto usado para a ativação do PCS é o ferro, na forma bi ou trivalente. O ferro (II) é o mais comum em testes de degradação de contaminantes orgânicos, porém, o uso do ferro (III) vem ganhando um destaque em alguns estudos (MIAO et al 2015c;FU et al 2016aFU et al , b, 2017aCUI et al 2017).…”

“…Desta forma, a eficiência do sistema oxidativo poderá ser mantida (MIAO et al 2015b. No entanto, altas concentrações de peróxido de hidrogênio (> 20 mmol L -1 ) podem promover um auto-consumo do radical hidroxila (Equação 24) (SILVA et al 2011) e consumo do radical hidroxila por reação com o peróxido de hidrogênio, produzindo o radical hidroperoxila (Equação 25) (MIAO et al 2015c). A tabela 3 sumariza algumas das vantagens e desvantagens do uso dos sistemas catalisados por Fe(II) e Fe(III).…”