| Nitrogen heterocyclic compounds（NHCs）have the characteristics of wide coverage,high biological toxicity,and low biodegradability.Because of the high chemical stability,the NHCs were hard to be degraded in wastewater,causing serious harm to water and humans.At present,the degradation technologies for NHCs have problems such as harsh reaction conditions,incomplete oxidative degradation and high cost,etc.The chemical oxidation method has advantages in degrading toxic and refractory organics due to its wide processing range,fast degradation speed.In this paper,indole,quinoline and pyridine were selected as typical representatives of NHCs.High-performance liquid chromatography detection,Fe（Ⅱ）and Fe（Ⅲ）concentration detection,capture of hydroxyl radicals and gas chromatography measurement methods were used.The optimal reaction conditions for Fe（Ⅵ）oxidative degradation of indole,quinoline and pyridine were determined,a dynamic model was established,the oxidation products were identified,and the reaction pathways were speculated to find out the reaction mechanism of Fe（Ⅵ）and the combined process to oxidize indole,quinoline and pyridine.The effect of Fe（Ⅵ）on the oxidation of indole,quinoline and pyridine in simulated coking wastewater was investigated,to provide a theoretical basis for the oxidative removal of NHCs in actual wastewater.The main research conclusions were as follows:（1）The optimal condition for oxidation of indole by the pH was 7,the temperature was 25℃,Fe（Ⅵ）was that the mass ratio of Fe（Ⅵ）to indole was 15,and in this condition,the removal rate of indole reached 77.91%within 15minutes.The first 7s of Fe（Ⅵ）degradation of indole was the rapid response stage,and the degradation rate of indole conformed to the quasi-first order reaction kinetic model.The rate constants of the reaction were 0.13468 s-1under neutral conditions.The degradation pathways of indole by Fe（Ⅵ）included the transfer of oxygen atoms,dehydroxylation,addition and oxidation of hydroxyl groups.（2）Sequential batch addition of Fe（Ⅵ）and Fe（Ⅵ）/H2O2could effectively improve the removal rate of indole.When the number of dosing was 5 times,the removal rate of indole increased from 77.91%to 92.9,while the removal rate indole was 87.3%when the ratio of Fe（Ⅵ）to H2O2was 1:5 dosing.（3）The degradation of quinoline by Fe（Ⅵ）mainly occurred in the first 1s.The reaction was basically completed within 10 minutes.At a temperature of25℃,a pH of 5,and a ratio of quinoline to Fe（Ⅵ）of 1:5,the removal rate of quinoline reached 81.16%.Sequential batch addition of Fe（Ⅵ）could effectively improve the removal rate of quinoline.When the number of dosing was 4 times,the removal rate of indole increased from 81.16%to 96.12%.The degradation pathways of quinoline by Fe（Ⅵ）included the transfer of oxygen atoms,dehydroxylation,addition of benzene rings,addition and oxidation of hydroxyl groups.The final products wereα-hexylcinnamaldehyde,perillaldehyde and dihydrocarvol.（4）The Fe（Ⅵ）oxidative degradation of pyridine was basically completed within 5 minutes.Under the conditions of a temperature of 25℃,a pH of 7,and a ratio of pyridine to Fe（Ⅵ）of 1:3,the removal rate of pyridine reached 36.89%.Sequential batch dosing of Fe（Ⅵ）for 4 times,the removal rate of pyridine increased to 43.0%.However,the Fe（Ⅵ）/H2O2,Fe（Ⅵ）/persulfate combined process did not help to increase the removal rate of pyridine.The degradation pathways of pyridine by Fe（Ⅵ）included pyridine hydroxylation,cleavage of NC bonds,and further oxidation of hydroxyl groups.Finally,2,3-dimethylpentanal and 2-methylpentanone were formed.（5）Soluble organic matter in coking wastewater may affect the oxidative degradation of indole,quinoline and pyridine by Fe（Ⅵ）,but Fe（Ⅵ）still has a high selectivity for the removal of NHCs. |
