Remediation of soil polluted with herbicides by Fenton-like reaction: Kinetic model of diuron degradation

Abstract

Catalytic diuron degradation in soil by modified Fenton or Fenton-like reaction has been studied and a kinetic model including the rates of all physical and chemical processes involved in both aqueous and soil phases has been developed and validated.The soil selected, a sandy clay loam one, was artificially spiked with a solution of diuron dissolved in methanol, obtaining a final diuron concentration of 0.167mmolkg−1. Diuron oxidation experiments were performed in a batch reactor in both aqueous phase and slurry system at different concentrations of H2O2, trisodium citrate (CT) as chelant, and Fe(III) as catalyst.Because of the neutral pH achieved by adding CT, the oxidation rate of CT and H2O2 decomposition in the aqueous phase has been found negligible. On the contrary, a significant unproductive decomposition of H2O2 by the soil was observed. Diuron oxidation rate was strongly dependent on the iron concentration and, in lower extent, on the H2O2 concentration, in both aqueous phase and slurry system.A kinetic model, including diuron desorption, CT adsorption, H2O2 decomposition by soil, and diuron oxidation in both soil and aqueous phase was proposed. The kinetic parameters were obtained by fitting the experimental data to this model. The predicted values of diuron abatement, in both soil and aqueous phases, and the H2O2 simulated conversion values were in good agreement with the experimental ones. Moreover, the obtained results suggest that kinetic of diuron desorption to the aqueous phase was enhanced due to the chemical reaction.