Research On The Degradation Of Reactive Brilliant Red X-3B By Hydroxylamine Enhanced Fe²⁺/persulfate System

Dyeing wastewater has characteristics of high chromaticity,high toxicity and refractory.It would threaten to the ecological security and human health serious if discharged into the environment directly.As a result,it is urgent to develop and improve wastewater treatment technology to alleviate the severe situation of water pollution.In the advanced oxidation method,the technology of using Fe²⁺to activate persulfate（PS）has the advantages of simple operation,low cost,high efficiency,so it has a good application prospect.However,the application of this technology was greatly restricted due to some shortcomings in the traditional Fe²⁺/PS system,such as the slow transformation from Fe³⁺to Fe²⁺,the low PS utilization rate,and the accumulation of iron sludge precipitation.In this study,from the perspective of promoting Fe³⁺/Fe²⁺circulation in the system,the traditional Fe²⁺/PS system was strengthened by using cheap and easily available reducing agents in water treatment.The main details of study were as follows:This study first investigated the effects of sodium thiosulfate（Na₂S₂O₃）,sodium bisulfite（Na HSO₃）,sodium nitrite（Na NO₂）,and hydroxylamine hydrochloride（HA）on the degradation of reactive brilliant red X-3B in the Fe²⁺/PS system.Research had identified that the addition of HA promoted the degradation of X-3B to the greatest extent,and the removal efficiency of X-3B could achieve 89.5%after 10 minutes of reaction.Then,this research carried out a series of single factor experiments for HA to strengthen Fe²⁺/PS system,and investigated the effects of Fe²⁺concentration,HA concentration,PS dosage and initial p H on the degradation of X-3B.The kinetic fitting results showed that the variation of X-3B concentration with time in the HA/Fe²⁺/PS system was more in line with the second-order reaction kinetic model.Based on the results of single factor experiments,the response surface method（RSM）was used to analyze the interaction between the factors and optimize the experimental conditions.Under the optimal conditions of p H=3.0,Fe²⁺=0.09 mmol/L,HA=0.13mmol/L and PS=1.0 mmol/L,the removal efficiency of X-3B achieved 89.98%,which was consistent with the predicted value of the model（91.13%）.Under the above-mentioned optimal experimental conditions,the influence of coexisting substances on the degradation of X-3B in the HA/Fe²⁺/PS system was further explored.The results showed that SO₄^2-,K⁺,Na⁺,Mg²⁺and Ca²⁺has no obvious inhibitory effect on the degradation of X-3B.The inhibitory effect of Cl^-and NO₃^-on the degradation of X-3B was increased with increasing the concentration.The inhibitory effect of oxalic acid,EDTA,formic acid and acetic acid on the degradation of X-3B in the HA/Fe²⁺/PS system was as follows:EDTA≈oxalic acid>formic acid>acetic acid.Finally,this study explored the mechanism of HA strengthening Fe²⁺/PS and the degradation pathway of X-3B.Comparing the changes of total iron（TFe）and Fe²⁺concentrations in the Fe²⁺/PS and HA/Fe²⁺/PS systems,at p H=3.0,after 10 minutes of reaction,the Fe²⁺concentration in the traditional Fe²⁺/PS system decreased to 0.0065mmol/L and the concentration of TFe was 0.0302 mmol/L.In the HA/Fe²⁺/PS system,the concentration of Fe²⁺was 0.0495 mmol/L and the concentration of TFe was0.0642 mmol/L.HA could effectively promote the reduction and conversion of Fe³⁺to Fe²⁺.Free radical quenching experiments showed that the contribution rate of sulfate radical（SO₄.^-）and hydroxyl radical（·OH）to the degradation of X-3B in the HA/Fe²⁺/PS system accounted for 56.72%and 37.33%,respectively,they were the main active free radicals in the system.The results of electron paramagnetic resonance（EPR）spectroscopy showed that the addition of HA increased the production of SO₄.^-and·OH.After 120 minutes of reaction,the total organic carbon removal efficiency in the traditional Fe²⁺/PS system was 9.71%,but it was increased to 31.69%in the HA strengthening system.UV-Vis spectroscopy and GC-MS detection results showed that as the reaction processed,the conjugated structure,naphthalene ring and triazinyl group in X-3B molecule were destroyed by oxidation.X-3B undergoes a hydroxylation and oxidative ring-opening reaction to generate long-chain hydrocarbons.Eventually,it was further mineralized into CO₂and H₂O.