Screening of catalytic activity of natural iron-bearing materials towards the Catalytic Wet Peroxide Oxidation of Orange II

Natural materials were evaluated in the Catalytic Wet Peroxide Oxidation of a commonly used azo-compound, Orange II. Volcanic ash, black sand, pumice and Montanit300 (R) were selected for evaluation. The materials were thoroughly characterized by several techniques (XRD, SEM/EDX, BET surface area and pore size distribution, TPD, Mossbauer spectroscopy, etc.). Peroxidation experiments were performed varying reaction temperatures (50-80 degrees C), catalyst loads and pH value (3-8). Complete decolouration was reached in most experiments; however, mineralization levels, peroxide consumptions and stabilities differed between materials. The activity of Fe leached during the reaction was evaluated and a combination of heterogeneous and homogeneous mechanism cannot be discarded. Thus, the materials may behave as Fe dispensers. Long-term stability experiments were also performed. While Montanit300 (R) showed a decreased performance (20% activity reduction in 16 h) due to a higher leaching (20% Fe loss), ash and pumice performances remained almost steady at pH = 3 (Fe loss: 3% ash and 1.3% pumice). Mineralization levels obtained were outstanding (40-70%) and comparable to performances showed by more sophisticated catalysts. The use of these natural materials will optimize the Fenton process economics, since they are unexpensive, abundant and require only minimal modifications.