Decomposition of 2-chlorophenol employing goethite as Fenton catalyst II: Reaction kinetics of the heterogeneous Fenton and photo-Fenton mechanisms

Abstract The kinetics of the degradation of 2-chlorophenol (2-CP) employing both the heterogeneous Fenton and photo-Fenton reactions using goethite as the solid catalyst is studied. The photoreactor was irradiated with a 350–400 nm wavelength light. The kinetics is based on 19 steps of a combined heterogeneous–homogeneous mechanism derived for the thermal Fenton reaction [see companion article by the authors: Ortiz de la Plata et al. (2009)] [1] . For the photo-Fenton alternative, two more steps are needed. Some of the specific kinetic constants of the reaction scheme are approximately known. However, for the heterogeneous “thermal” Fenton reaction, three new unknown constants were required and were attained from experimental data obtained in this and the previous work. The parameters were (i) the reaction of the HO radical with 2-CP, (ii) the proton induced iron dissolution and (iii) the reductive induced iron dissolution [1] . In the case of the heterogeneous photo-Fenton reaction steps, the radiation field in the reacting system was described by solving the complete radiative transfer equation inside the reactor. With this purpose, the knowledge of the needed goethite optical properties were previously characterized [2] . Combining the dark and the irradiated experiments 21 kinetically consistent parameters were achieved for the proposal of a feasible mechanism. They are valid for both systems; making the two primary quantum yields of the photoreaction equal to zero, the “dark” Fenton reaction performance is properly described by the remaining 19 specific rate constants. These results are independent of the used experimental apparatus and can be safely used for scaling-up purposes within the range of the explored variables.