Heterogeneous degradation of precipitated hexamine from wastewater by catalytic function of silicotungstic acid in the presence of H2O2 and H2O2/Fe2+

Abstract

The industrial wastewater produced by hexamine plants is considered as a major environmental polluting factor due to resistance to biodegradation. So the treatment of such wastewater is required. In this work, the removal of hexamine from wastewater and its degradation have been studied. Hexamine was precipitated through formation of an insoluble and stable compound with silicotungstic acid. The oxidative heterogeneous degradation of precipitated hexamine was carried out with hydrogen peroxide (H2O2) aqueous solution and H2O2/Fe2+ under the catalysis of silicotungstic acid. The operating conditions including amount of precipitate, hydrogen peroxide and ferrous ion dosage, temperature, time and pH were optimized by evaluating the removal of total organic carbon from system. A total organic carbon conversion higher than 70% was achieved in the presence of H2O2/Fe2+. The experimental results showed that hexamine can be effectively degraded with H2O2 and H2O2/Fe2+ under the catalysis of silicotungstic acid. It was interesting that the solution of dissolved precipitate with H2O2 can re-react with hexamine after the removal of excess hydrogen peroxide. This observation indicates the catalysis role of silicotungstic acid in the degradation of hexamine. A kinetic analysis based on total organic carbon reduction was carried out. The two steps mechanism was proposed for the degradation of hexamine.