Study On Preparation Of Attapulgite-Based Heterogeneous Catalyst And Its Application In Wastewater Treatment

Hard-to-degrade organic pollutants, due to its characteristics of high toxicity, slow speed of microbial degradation, and incomplete decomposition, have aroused people’s wide attention. The hard-to-degrade organic pollutants have become major global environmental problems. Heterogeneous Fenton method, a kind of advanced oxidation technology, is widely used for catalytic degradation of organic pollutants. To develop a kind of catalysts with the characteristics of easy separation and recycling, no or small iron loss, reusable catalysts, stable catalytic performance, and wide using range, heterogeneous Fenton catalysts have become an important field of Fenton catalysis researches.In this paper, a kind of heterogeneous Fenton catalyst Fe₂O₃/attapulgite（ATP） was prepared, using the ancient wet method, loading ferric oxide（Fe₂O₃） on the attapulgite（ATP）. Three hard-to-degrade organics were taken as aiming pollutants, they are sodium dodecyl benzene sulfonate（SDBS） and methylene blue（MB） and Congo red（CR）. The degradation characteristics of the three hard-to-degrade organics in solution with high concentration by Fe₂O₃/ATP/H₂O₂ system were investigated. The influences on the degradation of the organics were studied and the reaction mechanisms of the organics degradation were discussed. The main contents are summarized as follows:（1） Two kinds of attapulgite-base heterogeneous Fenton catalysts, Fe₂O₃/ATP-1 and Fe₂O₃/ATP-2, were prepared by ancient wet method and ordinary hybrid method, respectively. Catalysis and degradation performances of sodium dodecyl benzene sulfonate（SDBS） by these two catalysts were studied and compared. The optimum precursor Fe（NO3）3 concentration of preparing Fe₂O₃/ATP-1 by ancient wet method and the optimum Fe₂O₃ mixed proportion of preparing Fe₂O₃/ATP-2 by ordinary hybrid were examined, which will affect the performances of the catalytic degradation of SDBS.（2） Fe₂O₃/ATP-1 and Fe₂O₃/ATP-2 were analyzed in characteristics by BET, SEM, XRD, FT-IR. From the analysis it is known that loading and mixing Fe₂O₃ with ATP make its porosity and specific surface area decreased, but the catalytic activity increased. And from the analysis we know that the α-Fe₂O₃ characteristic peak is obtained, which proved the catalyst containing Fe₂O₃.（3） The influences on the effect of SDBS degradation by changing H₂O₂ concentration, catalyst dosage, pH value and reaction temperature using the Fe₂O₃/ATP-1 as catalyst and in the presence of H₂O₂ were examined. When pH=4, [H₂O₂]0=0.392 mol/L, Mc=0.5 g/L, T=60 ℃, the removal ratio of SDBS can reach more than 99%.（4） The influences on the effect of MB and CR decolorization by changing H₂O₂ concentration, catalyst dosage, pH and temperature using the Fe₂O₃/ATP-1 as catalyst and in the presence of H₂O₂ were examined. Under various experimental conditions, MB and CR show different decolorization characteristics in the process, which may be due to MB is not an azo dye, but CR is.（5） The stability and reusable performance of the Fe₂O₃/ATP catalyst were studied. After ten times catalytic decolorization experiments, in Fe₂O₃/ATP/H₂O₂ catalytic systems, SDBS degradation and MB and CR decolorization ratios remain high efficiency. Compared the heterogeneous Fenton reaction（Fe₂O₃/ATP/H₂O₂） with homogeneous Fenton reaction（Fe2+/H₂O₂） in degrading SDBS, MB and CR, heterogeneous Fenton reactions have almost the same effects with homogeneous Fenton reactions, but Fe₂O₃/ATP/H₂O₂ system has a wide pH range, and no Fe ion leaching, and the catalyst can be reused.（6） The influences of the pH value of Fe₂O₃/ATP/H₂O₂ system on the degradation of methylene blue were studied, and the changes of solution pH value during the process of degradation process were also examined. Due to the nature of attapulgite clay, the characteristics of H₂O₂ and heterogeneous Fenton reaction features, the pH values of the system change a lot in the process of reaction, the effect of pH of Fe₂O₃/ ATP/H₂O₂ system on the degradation of methylene blue is very large.（7） In order to optimize experimental conditions of MB decolorization, Box-Behnken Design（BBD） of Response Surface Methodology（RSM） was used to design a series of experiments, and the experimental results were fitted with a quadratic polynomial. The variance analysis results show that the quadratic polynomial model is meaningful. In addition, the correlation coefficient of model R = 0.9917, shows that experimental value and predicted value of MB decolorization ratio have good consistency. Under the given conditions determined according to the 3D response surface of MB decolorization experiments, the optimum experimental condition is: H₂O₂ concentration of 58.8 mmol/L, catalyst dosage of 10 g/L, pH value of 2.（8） The influence of MB initial concentration on MB decolorization in the system of heterogeneous catalysis was also studied, and the dynamics equations were fitted. According to the fitting results, L-H equation is the best one to describe the decolorization under different initial concentration of MB. The possible reactions in the heterogeneous system（Fe₂O₃/ATP/H₂O₂） were analyzed, and the concentration changes of MB and H₂O₂ in the solution was deduced. And according to the HPLC-MS on the aromatic ring of the intermediate, the degradation of MB path was put forward.