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Many aromatic compounds are oxidized but not completely mineralized by Fenton’s reagent. Little attention has so far been given to the identification of residual organic matter and the evaluation of its toxicity. In this work, the oxidation of metol [ N -methyl- p -aminophenol] by Fe 2+ /H 2 O 2 in the dark as a model for aromatic amines and alcohols was examined. Analysis of oxidized solutions was performed by both LC-electron impact (EI)-MS and LC-electrospray ionization (ESI)-MS. It was checked that the degradation of metol takes place via direct oxidation by Fe 3+ and OH attack. Intermediates amenable to oxidation by OH are basically partially oxygenated aromatic species, dimerization products and polymers. End products not amenable to oxidation by this radical are ferrycarboxylate complexes, which are non-toxic to UC581 bacterial cells. These complexes can be completely destroyed by irradiation with light. The photo-Fenton reaction is therefore an effective choice for the in situ treatment of industrial effluents containing aromatic amines and hydroxylated species.

The potential of the Fenton’s reagent for oxidation of p -aminophenols, which are the main developers used in white and black processes, was assessed. Metol [ N -methyl- p -aminophenol] was chosen as a model. Degradation of this compound by Fenton’s reagent was examined under dark conditions as a function of reagent concentrations and pH used in batch treatments. Under optimal conditions, 0.2 M H 2 O 2 , 9.0×10 −4 M Fe 2+ , pH 3–5 and room temperature, the initial COD of a 5×10 −3 M metol solution was reduced by about 50% within 2 h. After this time, additional COD reduction was very slow (about 20% in five days). No aromatic compounds were detected about 4 h of reaction indicating that residual organic matter was mainly made up of ring cleavage products. Metol conversion behaved as a first-order reaction with respect to metol and Fe 2+ . Complete destruction of residual organic matter could be achieved at high temperatures (about 60°C) or by using the photo-Fenton reaction, which thus opens up prospects for an effective treatment of p -aminophenols in effluents from photographic processes.

The potential of the oxidation of various carcinogenic aromatic amines by Fenton's reagent [Fe(II) + H2O2] for liquid waste treatments was assessed. The insoluble products yielded were amenable to oxidation to ring-cleavage products and ultimately to carbon dioxide. Mineralization was confirmed by mass spectrometry. The kinetics of precipitation was determined from scattering measurements, at 500 nm, of the insoluble substance produced as a function of time. The influence of experimental variables on the removal of aromatic amines from aqueous solutions by formation of insoluble products and ring-cleavage products was established. Complete removal took about 1 and 3 h of treatment overall for the formation of insoluble products and ring-cleavage products, respectively. Residual hydrogen peroxide, iron(II) concentration, chemical oxygen demand and chromatographic techniques were used to determine when the reaction was finished. The iron(II) concentration was found to be crucial to the nature of the end products obtained (insoluble products, ring-cleavage products, CO2).