Study On High Performance Liquid Phase Oxidation Of Organic Wastewaters Catalyzed By Iron-containing Hydrotalcites

As a refractory industrial wastewater,textile and dyeing wastewater has attracted the attention of environmental protection departments.Textile effulents were of intense color,high concentration,high COD and poor biodegradability,which will endanger human beings and organisms.The processing requirements of textile and dyeing wastewater treatment is hard to be satisfied using conventional wastewater treatments.Advanced oxidation processes?AOPs?have been considered as an efficient method.Fe²⁺can decompose H₂O₂ to hydroxyl radicals??OH?in traditional Fenton reaction,?OH can nonselectively degrade organic compounds,but iron sludge is generated during the reaction process,and it is difficult to be recycled.To overcome these drawbacks,solid catalysts with high catalytic activity,stability,recyclable utilization were employed in heterogeneous Fenton process,such as supported iron-based materials,iron minerals,and iron?hydr?oxides.Among them,the improvement of hydrotalcites and metal acid salts are more obvious.Therefore,in this study,MgFe-layered doubled hydroxide?MgFe-LDH?and MgCoFe-LDH were occupied as catalysts to establish heterogeneous Fenton systems.High crystal purity,stable layered structure and high catalytic activity prepared by simple methods.The main research achievements are listed as follows:?1?MgFe-LDHs were prepared by co-precipitation method.MgFe-LDH was high-crystallized with the ratio of[Mg²⁺]/[Fe³⁺]at 3:1,was occupied to establish MgFe-LDH/Fenton system,and excellent catalytic activity were proved.?OH on the catalyst surface played the predominant role,which is responsible for the degradation of MB.The optimal experimental conditions were found to be 0.5 mmol/L H₂O₂,0.50 g/L MgFe-LDH,at initial pH 2.00,97.26%degradation efficiency of MB?10 mg/L?was achieved at 20±2?in 1 h,with 58.09%COD removed,and utilization efficiency of H₂O₂ reached 205.55%.?2?Kinetics of MgFe-LDH/Fenton reaction was described.MB degradation in MgFe-LDH/Fenton system can be described well by pseudo-first-order kinetic model,the reaction rate constant is 0.226 min^-1 under the optimal condition,and the reaction active energy was 31.248 kJ?mol^-1.?3?Mechanism of MgFe-LDH/Fenton reaction was proposed.H₂O₂ is adsorbed on the surface of MgFe-LDH,and is catalytically decomposed to?OH and?O₂,those are able to oxidize MB.?4?MgCoFe-LDHs were prepared by co-precipitation method.MgCoFe-LDH with the ratio of[Mg²⁺]/[Co²⁺]/[Fe³⁺]at 2.0:1.0:1.0 was high-crystallized and much superior catalytic activity.MgCoFe-LDH was occupied to establish MgCoFe-LDH/Fenton system,that has shown good performance in a wider range of pH values compared to MgFe-LDH/Fenton system,and the doped of cobalt accelerates the reaction.The optimal experimental conditions were determined to be 0.50 mmol/L H₂O₂,0.50 g/L MgCoFe-LDH and initial pH 2.50,97.13%degradation efficiency of MB?10 mg/L?was achieved at 20±2?in 1 h,with 71.52%COD removed,and the reaction active energy was 25.634 kJ·mol^-1.?5?Mechanism of MgCoFe-LDH/Fenton reaction was proposed.The generation of Fe²⁺rely on the reduction of Fe³⁺by Co²⁺on the surface of MgCoFe-LDH,which promotes the decomposition of H₂O₂ to produce?OH,that is able to oxide MB.?6?The effects of inorganics including NaCl,Na₂SO₄,Na₂CO₃,Na₂S₂O₃,CuSO₄,Na₂S on the degradation of methylene blue in MgCoFe-LDH/Fenton was investigated.The degradation of MB in MgCoFe-LDH/Fenton was resisted with the addition of NaCl,Na₂SO₄,Na₂CO₃,Na₂S₂O₃,CuSO₄,Na₂S,but promoted as increasing the concentration Na₂S.