Study On Synthesis Of Manganese-based Catalysts By Precursor Anions/Cations Optimization And Its Catalytic Ozonation Performance Of Bio-treated Coking Wastewater

Coking production enterprises are one of the main sources of refractory organic wastewater.In order to respond to the national environmental protection standard“13th Five-Year”development plan,it is indispensable for stable and efficient deep treatment of coking wastewater tail water.In the field of advanced treatment of coking wastewater tail water,heterogeneous catalytic ozonation technology has been a research hotspot due to its excellent organic oxidation efficiency.Therefore,a manganese-based catalyst with superior catalytic performance by precursor anions/cations optimization was synthesized,and it was applied to catalytic ozonation of coking wastewater tailwater.An advanced treatment method for coking wastewater tail water was established by optimizing the catalytic ozonation process parameters,and it can make the effluent meet"Coking Chemical Industry Pollutant Emission Standard"?GB16171-2012?.The main conclusions are as follows:?1?The single-factor experiment was carried out to determine the preparation conditions of the redox precipitation method of the manganese-based catalyst:the precipitation pH is 1.5,the initial Mn²⁺and Mn⁷⁺molar ratio is 3:1,the calcination time is 4.5 h,and the highest calcination temperature is 400°C.Based on the preparation method,the effects of four precursor anions(NO₃^-,AC^-,SO₄^2-,Cl^-)on manganese-based catalysts were investigated.Manganese-based catalysts A₁(SO₄^2-),A₂?AC^-?,A₃?Cl^-?,A₄?NO₃^-?prepared by four different precursor anions were used to catalyze ozonation treatment of coking tail water simulated wastewater.The order of catalytic activity of the four catalysts is A₄?NO₃^-?>A₂?AC^-?>A₁(SO₄^2-)>A₃?Cl^-?.According to the characterization results of BET,XRD and XPS of the four catalysts,the crystal structure,specific surface area and surface element valence of the four catalysts are significantly different.Among them,the catalyst A₄?NO₃^-?has large specific surface area,small grain size,many crystal defects,and high relative content of Mn³⁺and adsorbed oxygen.Under the combined action of these structural characteristics,the catalytic activity of catalyst A₄?NO₃^-?is higher.?2?Based on the one-component manganese-based catalyst A₄?NO₃^-?,three kinds of precursor cations Ce³⁺,Fe³⁺and Cu²⁺were introduced to prepare composite catalyst.Three series of composite catalysts Mn-Fe?5%-40%?,Mn-Cu?5%-30%?and Mn-Ce?5%-30%?were prepared by changing the introduction concentration of each metal ion.The catalysts with strong catalytic activity in each series were Mn-Fe?30%?,Mn-Cu?20%?,and Mn-Ce?15%?.Under the conditions of pH of 7,temperature of 15°C and ozone concentration of 2.6 mg/L,the reaction was carried out for 120 min,and the COD removal rates of wastewater using composite catalysts Mn-Fe?30%?,Mn-Cu?20%?and Mn-Ce?15%?were 34.99%,51.42%,27.73%,respectively.According to the characterization results of BET,XRD and XPS of the three composite catalysts,compared with the one-component catalyst A₄?NO₃^-?,the introduction of three metal ions changed the structural characteristics of the catalyst to a certain extent.The introduction of Ce³⁺increases the specific surface area of the catalyst,reduces the average crystal size of the catalyst,and increases the relative content of Mn³⁺and adsorbed oxygen on the catalyst surface,which ultimately leads to enhanced catalytic performance of the catalyst.The introduction of Cu²⁺and Fe³⁺both reduce the effective specific surface area of the catalyst,and the decrease of the active reaction site leads to the weakening of the catalytic activity of the catalyst.?3?The optimized prepared manganese-based catalyst was used to catalyze ozonation to treat the actual coking wastewater tail water.By optimizing the catalytic ozonation process parameters,it was determined that the initial pH of the water was7.2,the gas flow rate was 2 L/min,the ozone concentration was 3.5 mg/L,and the catalyst dosage was 6 g/L,the reaction temperature was 35±1°C.When the reaction reaches 120min,the residual COD concentration of water is 60.3mg/L,the color of water is less than 5 times,and the water quality can reach"Coking Chemical Industry Pollutant Emission Standard"?GB16171-2012?.