Degradation of photographic developers by Fenton's reagent: Condition optimization and kinetics for metol oxidation

The potential of the Fenton's reagent for oxidation of p-aminophenols, whic h 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 c ompound by Fenton's reagent was examined under dark conditions as a functio n of reagent concentrations and pH used in batch treatments. Under optimal conditions, 0.2 M H2O2, 9.0 x 10(-4) M Fe2 +, pH 3-5 and room temperature, the initial COD of a 5 x 10(-3) M metol solution was reduced by about 50% w ithin 2 h. After this time, additional COD reduction was very slow (about 2 0% in five days). No aromatic compounds were detected about 4 h of reaction indicating that residual organic matter was mainly made up of ring cleavag e products. Metol conversion behaved as a first-order reaction with respect to metol and Fe2 +. Complete destruction of residual organic matter could be achieved at high temperatures (about 60 degrees 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. (C) 2000 Elsevi er Science Ltd. All rights reserved.