Experimental Study On The Removal Of Phenol From Water By Heterogeneous Catalytic Persulfate

Phenolic pollutants are widely exist in industrial wastewater such as printing and dyeing,petroleum processing,and pharmaceuticals.They are widely distributed,difficult to degrade,and highly toxic,not only pose a potential threat to human health,but also pose a major challenge in water ecological protection Therefore,it has become a hot research direction to explore a phenolic wastewater treatment technology with low cost and wide application range.The advanced oxidation technology using persulfate（PS）as oxidant has the characteristics of strong oxidation,high p H adaptability,easy transportation and storage,and can effectively degrade complex organic pollutants.Bimetallic heterogeneous catalysts are widely used because of their relatively low cost and easy recovery compared with the external energy and homogeneous catalytic systems.In this experiment,magnetic Mn Fe₂O₄was obtained by coprecipitation method as a catalyst for PS.The Mn Fe₂O₄was characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,and transmission electron microscopy（TEM）.The microscopic structure,aspect,and composition of the catalyst were analyzed.Considering that peroxydisulfate（PDS）and peroxymonosulfate（PMS）are two commonly used agents for PS,in this experiment,Mn Fe₂O₄/PDS and Mn Fe₂O₄/PMS coupling systems were used to degrade phenol containing wastewater,respectively.The results showed that in Mn Fe₂O₄/PDS system,when the initial p H=7,PDS was 2.4 mmol/L,Mn Fe₂O₄was 1.2 g/L and the initial concentration of phenol was 30 mg/L,88.75%of phenol could be degraded in 240 min.In the Mn Fe₂O₄/PMS system,when the initial p H=4.5,the PMS was 0.8 mmol/L,the Mn Fe₂O₄was 1.2 g/L,and the initial concentration of phenol was 30 mg/L,98.40%phenol could be degraded in 40 min,and when the initial p H=11,phenol could be completely degraded in 20 min.The stability test of the catalyst showed that the catalysts in Mn Fe₂O₄/PDS and Mn Fe₂O₄/PMS systems had certain reusability,but the catalytic effect could significantly decline as the number of cycles of Mn Fe₂O₄was accumulated.In this study,the types of active substances involved in the degradation of phenol were investigated.Methanol,tert-butyl alcohol,ethylenediaminetetraacetic acid disodium,and sodium azide were used as quenching agents of sulfate radical(SO₄^·-),hydroxyl radical（·OH）,hole（h⁺）and singlet oxygen（¹O₂）,respectively,for quenching experiments.The results showed that the main active substances involved in phenol degradation in Mn Fe₂O₄/PDS and Mn Fe₂O₄/PMS systems were hole and singlet oxygen.The reaction mechanism of phenol degradation by Mn Fe₂O₄/PDS was inferred from the type of active substances.The intermediate products and degradation path of phenol degradation were speculated,and the removal effects of TOC in Mn Fe₂O₄/PDS and Mn Fe₂O₄/PMS systems were investigated.The results showed that both systems had a certain mineralization effect on phenol.