Study Of Refractory Organics' Oxidation From Coking Wastewater Using Jarosite As Catalyst

Coking wastewater is produced during the heat treatment of coal carbonization,gas purification and by-product recovery,it has complex composition,strong toxicity and high organic load.The traditional biological processes have poor treatment effect on refractory organic matter like phenolic compounds,nitrogen-containing heterocyclic compounds and polycyclic aromatic hydrocarbons?PAHs?,which need further treatment.At present,advanced oxidation processes?AOPs?such as ozone oxidation,electrocatalytic oxidation,photocatalytic reaction and Fenton reaction,are considered to be effective means for the degradation of refractory organic compounds.Fenton oxidation has the advantages of high efficiency,rapidity and simplicity.It has been proved to be effective in treating a variety of refractory organics.In Fenton-like oxidation,the heterogeneous catalysts have gradually replaced the homogeneous catalysts due to their low iron ion dissolution and low precipitation.As a heterogeneous catalyst,jarosite has the advantages of high production,low cost and high efficiency.However,the application of jarosite in the treatment of refractory organics from coking wastewater by Fenton-like method is rarely reported.In the study,the feasibility of the treatment for phenol and quinoline by jarosite as Fenton-like catalyst was investigated,and the single factor experiments and degradation mechanism were studied.The X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?characterizations were used to analyze the structure and composition of the catalyst before and after reaction.The effects of initial p H,H₂O₂ concentration and jarosite dosage on the treatment of phenol?quinoline?by Fenton-like method were investigated by single factor experiment.The main oxidizing free radicals were confirmed by methanol quenching experiment.Combined with the TOC removal,H₂O₂ concentration change,iron ion dissolution and UV scanning,the intermediate products and degradation pathway of organics were inferred.The stability and reusability of jarosite catalyst were also investigated.XRD and XPS characterization results showed that the catalyst was a kind of poorly crystallized mineral and contained Fe?K?O?S,etc,which were consistent with the structure and composition of jarosite.The structure and composition of jarosite did not change obviously after five cycles of reaction.On the basis of single factor experiment,the removal efficiency of phenol can reach100%in 80 min when initial p H was 3.0,H₂O₂ concentration was 500 mg/L and jarosite dosage was 1.0 g/L;the removal efficiency of quinoline can reach 100%in 90 min when initial p H was 3.0,H₂O₂ concentration was 500 mg/L and jarosite dosage was 3.0 g/L.The methanol quenching experiment showed that·OH radicals played a major role in the degradation of phenol and quinoline.During the reaction,the concentrations of dissolved Fe²⁺and Fe³⁺were very low?0.13⁵.11 mg/L?and the catalytic effect of dissolved ions on organic compounds is not obvious,indicating that the reaction was dominated by heterogeneous catalysis.Combined with the change of TOC content,H₂O₂concentration and p H value and the UV scanning results,the mechanism of phenol?quinoline?degradation catalyzed by jarosite was analyzed as follows:Fe???on the surface of jarosite catalyzes the decomposition of H₂O₂ to produce·OH,which can decompose organic compounds into a series of intermediate products.Most of the intermediate products are further oxidized by·OH to CO₂ and H₂O.The unmineralized products include oxalic acid,acetic acid,fumaric acid,etc.Finally,the stability and reusability of jarosite have been tested:in the presence of 0.05⁰.5 mol/L Cl^-?SO₄^2-or NO₃^-,respectively,the catalytic oxidation of phenol by jarosite can still achieve more than 93%of removal efficiency;after five cycles of recycling,jarosite can still catalyze more than 90%of phenol.These showed that jarosite is a stable and efficient heterogeneous Fenton-like catalyst.