ИСТИНА

One of the homogeneous catalytic systems proposed for the degradation of organic dyes in wastewater is the Fenton reagent (Fe2+/Fe3+/H2O2). Significant disadvantages of Fenton's reagent are the inability of its regeneration, the narrow intervals of pH at which are oxidative transformations of organic compounds and the necessity of extracting metal ions from the purified water. The use of heterogeneous catalysts, in particular zeolites, separation from water and regeneration which is not particularly difficult, can solve most of these problems. In addition to iron, other transition metals can also catalyze the formation of hydroxyl radicals from H2O2. In turn, the disadvantage of heterogeneous catalysts is their instability in aqueous solutions, as in use there is leaching of active components in solution. The degree of leaching depends on the nature of active components and the carrier, as well as conditions of catalysis. General requirements for the heterogeneous catalyst are resistant to oxidizing environments, accessibility for interaction with hydrogen peroxide present in the solution. Sorption capacity of catalyst relative to the organic substrate also plays a significant role. It is desirable that the contribution of sorption in the totality of all processes was negligible. On the basis of granulated synthetic zeolites NaY and HY without binders by means of ion exchange followed by heat treatment at 350-500 оС samples of Со- and Fe-catalysts were obtained, which showed activity in the oxidation of organic dyes with Н2О2. By XPS it was shown that cobalt and iron are on the surface of the carrier in the form of ions Co2+ and Fe3+. Zeolite FeHY resistant to leaching at pH 6-9. In acidic medium leaching of Fe-ions was high, and it decreased with increasing temperature of calcination of the zeolite. For zeolite CoNaY calcined at 400 and 500оС was observed minimal leaching of cobalt into the solution in a weakly acidic environment. The CoHY zeolite showed high catalytic activity at a pH of 3, but virtually all of the cobalt ions released into the solution. The results showed that FeHY and CoNaY are most effective and stable under the oxidation of the anionic dye in weakly acidic and alkaline media. Heterogeneous Fenton-type process in wastewater treatment technology will be carried out before biological treatment, which is carried out at pH of 6-9. Zeolites CoNaY and FeHY because of their high catalytic activity and stability in weakly acidic and alkaline media may be promising for application in process of oxidative degradation of organic dyes by H2O2 with subsequent biological purification.