Mined pyrite and chalcopyrite as catalysts for spontaneous acidic pH adjustment in Fenton and LED photo-Fenton like processes

BACKGROUND The Fenton-based processes have been extensively studied for the treatment of pollutants contained in olive mill wastewater (OMW). These processes have some limitations, such as the need of acidic pH control, the generation of a sludge, and the separation of soluble iron species. Mined pyrite (FeS2) and chalcopyrite (CuFeS2) avoid the problem associated to the sludge formation and the acidic pH adjustment. The catalytic activity of pyrite and chalcopyrite was investigated for the Fenton and LED (light emitting diode) photo-Fenton like oxidation of tyrosol and in the treatment of aqueous mixtures containing phenolic compounds. RESULTS The highest mineralization of TY (85.0%) and lowest Fe leaching (0.89 mg L-1) was obtained by using chalcopyrite and the LED photo-Fenton like process (0.50 mM of TY initial concentration and 19.0 mM of H2O2 stoichiometric dosage). Complete degradation of the phenolic pollutants and a mineralization of 98.0% was also achieved. CONCLUSION Mined chalcopyrite can be an appropriate photo-Fenton like catalyst in the degradation of phenolic compounds found in OMW because it can provide a high TOC removal, proper acidic pH conditions, low leaching of iron species and a small spontaneous formation of H2O2. However, the catalyst stability must be improved to minimize the leaching of metals.