Study On Preparation Of Modified Coal Fly Ash Catalyst For Advanced Treatment Of Coking Wastewater Under Assistance Of Microwave

Fenton is a representative technique of advanced oxidation process,however,the narrow pH range and excess sludge volume limit its industrial application.The development of efficient non-homogeneous catalysts is an effective way to promote the industrial application of Fenton.Fly ash,as a solid waste generated from thermal power plants,contains a variety of transition metal oxides and has the potential to become a Fenton-like catalyst.Coking wastewater is a typical hard-to-degrade industrial organic wastewater,containing polycyclic aromatic hydrocarbons,halogenated hydrocarbons,heterocyclic compounds,cyanide and other toxic substances,and bring challenges to conventional secondary biochemical water treatment systems.In this study,fly ash-like Fenton catalysts were prepared and characterized,and the adsorption performance,catalytic performance,and reusable performance of the catalysts were investigated.The treatment efficiency of the actual coking wastewater was examined in combination with microwave,and the dynamic treatment process of modified fly ash catalytic Fenton-like catalyst,and the mechanism of fly ash catalysts was explored.By comparing the modification effects of four methods namely acid modification,alkali modification,ultrasonic modification and thermal modification on fly ash,sulfuric acid modification was determined as the best modification method for this study.Using orthogonal experiments,the conditions for the preparation of modified fly ash Fenton catalysts by sulfuric acid modification method were optimized.When the sulfuric acid concentration 0.5 mol/L,modification time 60 min,modification temperature 20℃,and solid-liquid ratio 1:5(g/mL),the specific surface area of fly ash catalyst was 1.9 m2/g,which increased about 2 times compared with 0.88 m2/g of the original fly ash.The original ash was smooth spherical microbeads,and the fly ash catalyst had a rough and porous honeycomb structure.The active components(SiO2,Fe2O3)of the catalyst increased and the content of alkaline substances(CaO,K2O)decreased.The maximum adsorption capacity of the modified fly ash was 0.3538 mg/g.For the PNP simulated wastewater,the PNP removal rate reached 92.2%at microwave radiation time 5 min,H2O2 concentration 350 mg/L,pH 3,fly ash dosage 10 g/L,reaction time 35 min,and microwave heating temperature 323 K.The catalyst has excellent reusability and the PNP removal rate was 86.4%after five consecutive cycles of testing.The apparent activation energy of the microwave-assisted Fenton class system for the degradation of PNP is 46.8 kJ/mol.The microwave heating temperature,pH,initial temperature 333 K),the PNP removal rate was stabilized between 87.6%and 91.6%.The temperature concentration of PNP,catalyst dosage,and H2O2 concentration of the system will affect the effect of the treatment system,and the relationship between the apparent rate constant of pollutant degradation and the above-mentioned influencing factors is shown in the following equation:kobs=46509 exp(-5624.5/T)[H2O2]0 0.682[Cata]2.2452[PNP]0-0.739[H+]0.274(R2=0.919)OH is the reactive radical that plays a maj or role in the microwave-assisted Fenton class system and is initiated by lattice iron on the surface of fly ash,which then diffuses into the solution to degrade organic pollutants.A dynamic Fenton-like process of water treatment assisted with microwave was establish,and the PNP simulated wastewater was treated in full-cycle mode for 40 min and then changed to continuous flow to investigate the removal efficiency of pollutants.Under the optimal process conditions(pH 3,H2O2 350 mg/L,catalyst 10 g/L,number of catalyst placement layers 3,microwave heating of the effluent was 333 K,which could not be discharged directly.To reduce the heat loss,a heat exchanger matched with the microwave device was designed to recover the waste heat,saving 37.5%of energy.A microwave-assisted Fenton-like system was established and applied to the treatment of coking wastewater.When the fly ash dosage 20 g/L and microwave radiation time 35 min,H2O2 concentration 350 mg/L,pH 3,the COD removal rate was 57.2%,and the effluent meets the direct discharge standard(COD<80 mg/L)in GB16171-2012《Emission Standard for Pollutants in Coking Chemical Industry》.The COD degradation process are in accordance with pseudo-first-order degradation model.