Degradation Of P-chloroaniline In Aqueous Solution With Advanced Oxidation Technology Based On Heat-assisted Persulfate

Advanced oxidation technologie based on the generation of sulfate radicals (SO₄^·-) isone of the most effective ways to remove the nonbiodegradable organic pollutants. With itshigh oxidation ability, SO₄^·-has got more and more attention among the study of wastewatertreatment. Persulfate activation is a promised technique to produce SO₄^·-due to thesimpleness of method and mildness of reaction conditions. This study chose heat-assistedpersulfate to generate SO₄^·-to degrade trace p-chloroaniline （PCA） in the wastewater andattempted to provid the basis for a new way to deep treat the chloroaniline wastewater bySO₄^·-.In this thesis, the oxidation of PCA by heat-assisted persulfate in aqueous solutions wasstudied. The degradation kinetics of PCA and the key factors to affect this process wereinvestigated. The reaction kinetics rates and the main free radical under different initial pHconditions were examined. Intermediate products of the oxidation process were characterizedusing LC-MS and GC-MS techniques and the pathways were also analyzed.During the process of heat-assisted persulfate, the PCA degradation was found to followa pseudo-first-order decay model when the persulfate was excessive, and thepseudo-first-order rate constant was related with temperature, initial oxidant concentration,inorganic anions in the solution and the other factors. Under10-50℃, the reaction of PCA andpersulfate has an activation energy of49.97kJ/mol. Raising temperature and increasinginitial persulfate concentration can significantly accelerate the PCA degradation rate. HCO₃^-and H₂PO₄^-in the solution can greatly promote the PCA decomposition, but the influence ofCl-and NO₃^-was very weak.The influence of initial pH of the system on persulfate oxidation of PCA was researched.The results indicated that in the pH range of3to11, a lower degradation rate was obtained atstrong acid system （pH3）, while maximum p-chloroaniline degradation occurred at pH7.SO₄^·-and hydroxyl radical （·OH） produced in the system were determined by molecularprobes methods. Both SO₄^·-and·OH presented during the whole process and SO₄^·-was thepredominant radical at pH <7,·OH gradually increased with the increase of pH of the system.The completely mineralized of PCA during the oxidation by heat-assisted persulfate may need longer reaction time than that during its fully degradation.4-chloronitrobenzene,p-benzoquinone,1-（4-chlorophenyl）-3-phenylurea and5-chloro-2-（（4-chlorophenyl） diazenyl）phenol were identified as the major intermediates of PCA degradation. Tentative pathway forthe degradation of PCA was proposed.