The Heterogeneous Photo Fenton Reaction using Goethite as Catalyst.

GUADALUPE B. ORTIZ DE LA PLATA; ORLANDO M. ALFANO; ALBERTO E. CASSANO

Berlín, Alemania

Congreso; AOP5, 5th Internacional Conference Oxidation Technologies for Water and Wastewater Treatment.; 2009

The Fenton reaction has been known for many years and provides a useful tool for pollutant degradation. A subsequent step was the inclusion of UVA radiation to improve yields and facilitate the process economics with the possibility of using solar radiation. However, the question of the post treatment operations was always raised, concerning the separation of dissolved iron compounds existing in the homogeneous operation of the treated aqueous solution. In the last years it has been suggested to use immobilized iron containing compounds in many different forms to overcome this problem. This technology, known as Heterogeneous Fenton, uses hydrogen peroxide and a solid iron carrier and also offers the possibility of using solar radiation as a primary source of energy for a Photo Fenton alternative (Ortiz de la Plata et al. 2008a).In the present work the influence of radiation was studied for the degradation of the model compound 2-Chlorophenol (2-CP). The Iron oxyhydroxide Goethite was used as a source of iron. The influence of catalyst loading, intensity of irradiation and molar ratio between hydrogen peroxide and contaminant was also examined. The work was performed in a cylindrical, perfectly stirred, batch reactor irradiated from a transparent to radiation bottom that was illuminated with a tubular lamp placed at the focal axis of a parabolic reflector (Fig. 1 and Table 1). The reactor was also equipped with internal glass heat exchangers connected to a thermostatic bath for controlling temperature and an external insulation made of K-Wool. Goethite (Aldrich, particulate, catalytic grade, LOT05002DC), 2-CP (Aldrich, > 99%) and perchloric acid (ByA, ACS, 70% P) to adjust the pH of the suspensions, were employed. The hydrogen peroxide was provided by Cicarelli (ACS, 30% P). 2-CP concentration was monitored through high-performance liquid chromatography (HPLC). A liquid chromatograph equipped with a Waters column LC-18 Supelcosil (Supelco) was used. Total organic carbon (TOC) was measured with a Shimadzu TOC-5000 analyzer and hydrogen peroxide was measured using a modified iodometric technique.Load of catalyst and molar ratio have been studied in a wide range of conditions. Figure 2 represents the dimensionless concentration of 2-CP as a function of time for irradiated and non irradiated conditions. The ratio of hydrogen peroxide to pollutant concentrations (R) was 50 and the load of catalyst is varied between 0.5 and 2 g/L. Experimentally it is clearly observed the appearance of an intermediary, Cl-benzoquinone (ClBQ), which has been identified together with Cl-hydroquinone (ClHQ) by GCMS from reaction samples. During the progress of the degradation of 2-CP, the reaction shows an unusual acceleration. This autocatalytic behaviour, with stronger tendencies at higher temperatures, implies a completely different behaviour than the one typically expected.As can be seen, light improvement is significant. The autocatalytic performance is successfully explained by the joint action of two factors. The evolution of the available iron in the homogeneous phase during the course of the reaction (Lin and Lu, 2007), and the autocatalytic contribution of some of the reaction intermediates in the iron cycle (Chen and Pignatello, 1997). A reaction mechanism has been proposed and parameters has been obtained for the dark reaction (Ortiz de la Plata et al. 2008b). Currently this mechanism is been expanded for irradiated conditions.R. Chen, J.J. Pignatello, Environ. Sci. Technol, 31 (1997) 2309. Y.-T. Lin  M.-C. Lu, Water Sci. Technol. 55 (2007) 101.  G.B. Ortiz de la Plata, O.M. Alfano, A.E. Cassano, Chem. Eng. J., 137  (2008) 396.G.B. Ortiz de la Plata, O.M. Alfano, A.E. Cassano, Proc. of  SPEA5, Sicilia, Italy, 2008. Accepted.