Applied Catalysis B: Environmental 144 (2014) 252–260 Contents lists available at ScienceDirect Applied Catalysis B: Environmental jo ur nal home p ag e: www.elsevier.com/locate/apcatb Remediation of soil polluted with herbicides by Fenton-like reaction: Kinetic model of diuron degradation Juana M a Rosas ∗ , Fernando Vicente, Elena G. Saguillo, Aurora Santos, Arturo Romero Dpto Ingenieria Quimica, Facultad de Ciencias Químicas, Universidad Complutense Madrid, Ciudad Universitaria S/N, 28040 Madrid, Spain a r t i c l e i n f o Article history: Received 11 April 2013 Received in revised form 18 June 2013 Accepted 1 July 2013 Available online 12 July 2013 Keywords: Diuron Trisodium citrate Kinetic model Modified-fenton Soil remediation a b s t r a c t 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 0.167 mmol kg -1 . Diuron oxidation experiments were performed in a batch reactor in both aqueous phase and slurry system at different concentrations of H 2 O 2 , 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 H 2 O 2 decomposition in the aqueous phase has been found negligible. On the contrary, a significant unproductive decomposition of H 2 O 2 by the soil was observed. Diuron oxidation rate was strongly dependent on the iron concentration and, in lower extent, on the H 2 O 2 concentration, in both aqueous phase and slurry system. A kinetic model, including diuron desorption, CT adsorption, H 2 O 2 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 aque- ous phases, and the H 2 O 2 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. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Herbicides are the most extensively type of pesticides used in agriculture. Among them, haloaromatic herbicides are considered a persistent class of chemicals [1]. Diuron (N ′ -[3,4-dichlorophenyl]- N,N-dimethylurea) is an herbicide, belonging to the phenylamide family and the subclass of phenylurea, used to control a wide variety of annual and perennial broadleaf and grassy weeds. This com- pound is also used on many agricultural crops such as fruit, cotton, sugar cane, alfalfa and wheat, but is more widely applied for long- term pre-emergence weed control in non-crop areas [2,3]. It is relatively persistent in soil, with half-lives from 1 month to 1 year [4]. Its persistence in soil is due to a combination of three proper- ties: chemical stability, low water solubility and strong adsorption to soil particles [5]. Agricultural use of herbicides results in rela- tively low soil contamination (diffuse contamination). However, in places where production or storage activities are carried out, a high concentration of these herbicides can be found in the soil caused by spillage, loading and rinsing operations or direct dumplign into ∗ Corresponding author. Tel.: +34 91 394 41 71; fax: +34 91 394 41 71. E-mail addresses: jmrosas@quim.ucm.es, nanirosas@yahoo.es (J.M. Rosas). soil disposal sites. These practices may be responsible for approxi- mately 45% of cases of ground water contamination [6,7]. In situ chemical oxidation (ISCO) by Fenton’s reagent seems to be a viable technology for the remediation of contaminated soils by pesticides [7–9]. In this technique, a strong chemical oxidant is injected into the contaminated surface to destroy the targeted contaminants [10]. Among the oxidants employed in ISCO, the Fen- ton’s reaction is widely used for the remediation of contaminated soil and groundwater, with a large number of in situ applications [11–13]. In order to solve the acid pH requierement of the classical Fenton process, chelating agents can be used in a modified Fenton or Fenton-like reaction [14,15]. In spite of the big potential of Fenton’s reagent for soil remedia- tion, few works have focused in the assessment of a kinetic model for contaminants abatement in the aqueous-soil system. And they do not consider separately in the kinetic the solid and aqueous contaminant concentration [16,17]. On the contrary, a large num- ber of kinetic studies have been carried out on Fenton reactions in aqueous solution [18,19]. Besides of the assumed mechanism in aqueous solution, the particular features of the soil presence (desorption, surface reac- tions, diffusion, etc.) should be taken into account [20]. It has been usually considered that the mechanism of Fenton-like reactions 0926-3373/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcatb.2013.07.011