Coking Wastewater Preparation And CWPO Composite Fe-MMT Degradation

In recent years, with the rapid development of both the global economy and the China’s economy, foundamental industries, such as the iron and steel, were promoted enormously. Thus, the demand of coke, which is the basic raw material of iron and steel production, sharply increased. Because China lakcks of oil and fine gas, it requires that we use coal as fuel, which is aboundant in China, during the manufacturing process. Consequently, coking becomes an important factor in industry areas. However, the process of coking produces toxic compounds and refractories organic wastewater, threatening aquatic organisms, plants and human health. Therefore, the treatment methods of coking wastewater have reciecved much concern of environmental research.This paper selected two main pollutants (phenol and quinoline) of coking wastewater as the research object, using simulating coking wastewater (ratio of phenol and quinoline was3:1). We prepared a series of the catalyst (Fe-Cr-MMT、Fe-Cr-Al-MMT) by ion exchange method, applying montmorillonite (MMT) as a carrier and transition metals (Fe ion) as the active component. The catalytic behavior and stability of prepared materials were analysed by COD removal of simulating wastewater and the ion leaching, when applying the catalysts for catalytic wet hydrogen peroxide oxidation (CWPO) degradation of coking wastewater. Further, different preparation conditions on catalytic behavior and optimal reaction conditions were discussed.According to the investigation of Fe/Cr mole ratio of the Fe-Cr-MMT catalyst, we found that when the mole ratio of Fe/Cr was7/3, the COD removal rate reached to86.3%, and the leaching of Fe ion was0.98mg/L, Cr ion was1.50mg/L, respectively. The characterization results of prepared clays by XRD and BET indicated that the montmorillonite layer spacing reached d001=22.06A and the maximum specific surface area was62.6m2.g-1, when the mole ratio of Fe/Cr was7/3. However, Fe-Cr-MMT catalyst presented a drawback that the active component erosion was serious.Thus, this paper intended to propose a solution to overcome this problem. Based on the original research in a laboratory, we prepared the ternary metal catalyst Fe-Cr-Al-MMT (Fe/Al=2/8) by adding Al ion, and discussed the influences of Fe/Cr mole ratio, calcination temperature and the ultrasonic effect on the catalytic activity. All samples were characterized by BET, TG-DTG, ICP, EDX, XRD and FT-IR. The results indicated that: when the mole ratio of Fe/Cr was7/3, ultrasonic power was100W and roasting for5h under350℃, the Fe-Cr-Al-MMT catalyst obtained dooi=19.11A and its specific surface area was enlarged as3.6times as the original montmorillonite. The optimal reaction conditions for CWPO degradation of coking wastewater was that: when the reaction temperature was60℃, the initial pH was5.0, the H2O2additive concentration was2100mg/L and the catalyst additive concentration was1.0g/L, the COD removal rate could reach to85.6%, the leaching quantity after5hours treatment is0.98mg/L for Fe ion and0.92mg/L for Cr ion, respectively.After using the catalyst in four consequetive runs, the COD removal of wastewater remained approximately80%, demonstrating that the Fe-Cr-A1-MMT was a stable catalyst. The analysis of degradation mechanism illustrated the H2O2decomposition reaction number was n=1.75and activation energy was Ea=7.08kJ/mol.Last, we discussed the influences of the addition of Y into the pillared clay on the structure and catalytic activity of the Fe-A1-MMT catalyst. It suggested that Y could improve the crystal formation of FeOOH and distribution of metal ions on the surface of clay. Y acted as a cocatalyst by improving the stability of the catalyst.