Research On The Degradation Efficiency And Mechanism Of Mcresol By NH₂OH/Fe²⁺/PMS System

With the acceleration of industrialization in China,the discharge of phenolic wastewater has increased greatly,as a large coal province,Shanxi produces a large amount of coking wastewater every year.Studies have shown that the content of m-cresol in coking wastewater can reach to 90 mg/L,and m-cresol is highly toxic,it has serious toxic effects on humans and the environment even at a low concentrations.For the past few years,Fenton and Fenton-like advanced oxidation techniques have been widely used in the treatment of refractory organic compounds,to treat industrial waste water containing phenols efficiently,a Fenton-like system of HA/Fe²⁺/PMS based on sulfate radical and hydroxyl radical was applied to dispose m-cresol as the targeted contaminant,the degradation efficiency of different Fenton systems was compared,and the effect of reaction conditions on the degradation efficiency of m-cresol in HA/Fe²⁺/PMS system was investigated,at last,the degradation mechanism of m-cresol in HA/Fe²⁺/PMS system was studied.The main research results are as follows:?1?Compared with Na₂S₂O₃,NaHSO₃,NaNO₂,VC and other reducing agents,the addition of HA can maximize the oxidation efficiency of Fe²⁺/PMS system,the removal rate of m-cresol in HA/Fe²⁺/PMS system was better than that in Fe²⁺/PMS system,Co²⁺/PMS system and HA/Fe²⁺/PDS system in 10 min;the addition of EDTA,citric acid,oxalic acid,formic acid and other common organic compounds can reduce the degradation efficiency of m-cresol in the HA/Fe²⁺/PMS system,the reason is that these organic compounds can react with the active free radicals produced in the system,moreover,some organic compounds can produce complexation with Fe²⁺/Fe³⁺in the system,further reducing the degradation efficiency of m-cresol in the system.?2?The effects of reaction temperature,initial pH of the system,Fe²⁺concentration,PMS dosage,HA concentration and initial concentration of m-cresol on the degradation efficiency of m-cresol were investigated.It adopt Box-Behnken response surface method to optimize reaction conditions and fit out that regression model,under the condition of reaction temperature 25?,initial solution pH 4,m-cresol initial concentration of 1mmol/L,the optimal conditions for m-cresol removal were found to be Fe²⁺concentration of 0.5 mmol/L,PMS dosage of 5 mmol/L,HA concentration of 2.5 mmol/L,with a removal rate of m-cresol 92.84%.The change of m-cresol concentration in HA/Fe²⁺/PMS system conforms to the second-order reaction kinetic model,and the activation energy Ea=30.72 kJ/mol.?3?Free radical quenching experiments showed that sulfate radicals and hydroxyl radicals were the main active species in the HA/Fe²⁺/PMS system;once the reaction began,a large number of highly oxidizing active free radicals were generated in the system,and the concentration ratio of Fe³⁺/Fe²⁺in the system was increased,so the ORP value in the system increased rapidly;according to the three-dimensional fluorescence spectrum,the fluorescence region of m-cresol is mainly concentrated in the two regions of peak A:Ex/Em=276/296nm and peak B:Ex/Em=232/296nm,the degradation of m-cresol was accompanied by the continuous weakening or even disappearing of fluorescence intensity in these two regions.