On the Fenton degradation mechanism. The role of oxalic acid

Alegría, Yamila; Liendo, Fernando; Núñez, Oswaldo

doi:10.3998/ark.5550190.0004.a49

Cited by 9 publications

(1 citation statement)

References 14 publications

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“…In any case, intermediates were not found, and C was almost completely balanced. Alegrı ´a et al (26) have proposed a scheme for oxalic acid oxidation with Fenton's reagent that includes the formation of Fe(II) and Fe(III) complexes. Acetic acid oxidation was negligible (less than 5%), increasing slightly when temperature and catalyst dose were increased.…”

Section: Evolution Of Organic Acidsmentioning

confidence: 99%

Chemical Pathway and Kinetics of Phenol Oxidation by Fenton's Reagent

Zazo

Casas

Mohedano

et al. 2005

Environ. Sci. Technol.

557

279

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Phenol oxidation by Fenton's reagent (H2O2 + Fe2+) in aqueous solution has been studied in depth for the purpose of learning more about the reactions involved and the extent of the oxidation process, under various operating conditions. An initial phenol concentration of 100 mg/L was used as representative of a phenolic industrial wastewater. Working temperatures of 25 and 50 degrees C were tested, and the initial pH was set at 3. The H2O2 and the Fe2+ doses were varied in the range of 500-5000 and 1-100 mg/L, respectively, corresponding to 1-10 times the stoichiometric ratio. A series of intermediates were identified, corresponding mainly to ring compounds and short-chain organic acids. Most significant among the former were catechol, hydroquinone, and p-benzoquinone; the main organic acids were maleic, acetic, oxalic, and formic, with substantially lower amounts of muconic, fumaric, and malonic acids. Under milder operating conditions (H2O2 and Fe2+ at lower concentrations), a great difference was found between the measured total organic carbon (TOC) and the amount of carbon in all analyzed species in the reaction medium. This difference decreased as the doses of H2O2 and Fe2+ increased, indicating that the unidentified compounds must correspond to oxidation intermediates between phenol and the organic acids. To establish a complete oxidation pathway, experiments were carried out using each of the identified intermediates as starting compounds. Dihydroxybenzenes were identified in the earlier oxidation stages. Muconic acid was detected in catechol but not in the hydroquinone and p-benzoquinone oxidation runs; the last two compounds were oxidized to maleic acid. Oxalic and acetic acid appeared to be fairly refractory to this oxidation treatment. A detailed knowledge of the time evolution of the oxidation intermediates is of environmental interest particularly in the case of hydroquinone and p-benzoquinone because their toxicities are several orders of magnitudes higher than that of phenol itself. The time evolution of the intermediates and TOC was fitted to a simple second-order kinetic equation, and the values of the kinetic constants were determined. This provides a simplified approach useful for design purposes.

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Section: Evolution Of Organic Acidsmentioning

confidence: 99%

Chemical Pathway and Kinetics of Phenol Oxidation by Fenton's Reagent

Zazo

Casas

Mohedano

et al. 2005

Environ. Sci. Technol.

557

279

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The role of iron on the degradation and mineralization of organic compounds using conventional Fenton and photo-Fenton processes

Hermosilla

Cortijo

Huang

2009

Chemical Engineering Journal

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a b s t r a c tThe role of iron on the degradation of different organic compounds, differing in their structure (aliphatic versus aromatic) and iron complex formation capacity, by conventional and photo-Fenton processes was investigated. Results show that these chemical characteristics can affect the degree of treatment in terms of COD and TOC removals. While aromatics exhibited a fast and great reduction in the COD by the conventional Fenton process, aliphatic compounds, apart from acetic acid, required the presence of UV light to enhance treatment results. EDTA and oxalic acid responded very positively to UV irradiation in both COD removal and mineralization, reaching the highest values showed by aromatics; and results depended on the intensity of the UV light applied. Phenol and 4-nitrophenol responded favourably to UV irradiation in terms of mineralization and slightly in COD removal. Reductions in the COD were almost total (95.99%), while only an 80% of reduction in the TOC was achieved, for the best photo-Fenton treatment of oxalic acid, phenol and nitrophenol. 60% COD and 40% TOC removals were achieved correspondingly in the case of EDTA. Acetic acid showed almost no mineralization and low COD removal (≈20%) when treated by a conventional Fenton process; and did not enhanced results when assisting the treatment with UV light. Photo-regeneration of ferrous ion and photo-decarboxylation of iron carboxylates are assessed in the framework of these results.

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