Decolorization And Degradation Of Direct Acid Red 4BS By A New System Of Fe(Ⅱ)/Fe(0) Activation Of Ferric Iron

Azo dyes has played an important role in the textile industry,it is widely used in ink,paint,rubber,printing paint paste.Its output accounted for about 70%of the total dye.Advanced oxidation technology which based on sulfate radical（SO₄^-·）has been developed rapidly in recent years and is widely used in water treatment.SO₄^-·is a free radical with a higher oxidation-reduction potential（SO₄^-·2.5³.1V,OH·=1.9².7V）.SO₄^-·has more selective when oxidizing the target compared with OH·.In solution,SO₄^-·has a survival period of 3×10^-5 to4×10^-5 s,which three orders of magnitude higher than OH·(2×10^-8 s),so SO₄^-·have more time to react with organic matter.Therefore,it has a far-reaching and significant efficient to make use of SO₄^-·for the oxidative removal of azo dyes.First,carried out homogeneous reaction about Fe（Ⅱ）,UV/Fe（Ⅱ）-EDTA/PDS is advanced innovatively.Different combinations of activation processes were investigated,（1）:PDS/UV;（2）:PDS/Fe（Ⅱ）;（3）:Fe（Ⅱ）-EDTA/PDS;（4）:Fe（Ⅱ）-UV/PDS;（5）:UV/Fe（Ⅱ）-EDTA/PDS.It obtains the best effect which EDTA chelated Fe（Ⅱ）to activate PDS under UV,decolorization rate is 80.0%within 10 minute.The experiments were optimized by changing the initial concentration of PDS,Fe（Ⅱ）/EDTA,inorganic anions and other factors.The results show that the most appropriate concentration of PDS is 15mmol/L.At the most optimal Fe（Ⅱ）/EDTA ratio of 5:1,the 4BS can decolorize 93.6%within 5 min when the initial concentration was 0.0380mmol/L.It follows second-order kinetics model.The inorganic anions such as HCO₃^-,Cl^-,NO₃^-,SO₄^2-show obviously negative effects for the degradation of 4BS when the inorganic anions were 100mmol/L,decolorization ratio reduced 66.9%,13.2%,12.1%,9.43%,respectively.The relationship between structure and characteristic absorption was analyzed by UV-Vis spectroscopy,and speculated that the 4BS degradation pathway is as follows:Benzene is broken first,then azo bond cleaves and naphthalene ring cracks.In the presence of PDS-Fe（Ⅱ）-EDTA,the UV radiation can effectively enhance the activation of the persulfate to form SO₄^-·free radical,which can decolorize Azo dyes.The decolorization ratio of 4BS was up to 98.1%within 10 min under the optimum reaction conditions[PDS:Fe（Ⅱ）:EDTA=15:5:1]in UV-PDS-Fe（Ⅱ）-EDTA system.Secondly,the heterogeneous reaction of ZVI was carried out,and the 4BS was degraded by ZVI activated PDS.The conditions of PDS concentration,ZVI concentration,pH and temperature were changed.The results show that the decolorization effect of red 4BS gradually increased with the increase of PDS concentration and ZVI concentration,30mg/L red 4BS decolorization rate increased by 86.05%and 31.43%at 20min,both obtain the first-order reaction kinetics equation.PH has a great influence on the experiment,the decolorization rate are 9.41%and 95.57%at90minute under PH are 10.42 and 3.03,respectively.Although the temperature can accelerate the red 4BS decolorization,PDS utilization reduced by 12%when temperature increased from 20 ^oC to60 ^oC.The influence of temperature on the degradation rate of red 4BS was in accordance with the Arrhenius model（R²=0.988）,and activation energy is 14.44KJ/mol.Free radical scavenging by tert-butanol and isopropanol as molecular probes show:degradation of red 4BS by ZVI activated persulfate is a free radical dominant reaction process by SO₄^-·.Finally,the study combine SO₄^-·AOPs（Advanced Oxidation Technology）and iron carbon micro electrolysis technology,proposes a new activation system Fe-AC/PDS,to degradate effectively red 4BS.The results show that the decolorization rate of red 4BS increased continuously in the first 20 minutes of the reaction,but then tends to be slow when Fe:AC>3:1,the decolorization rate of red 4BS reached the maximum of 94.7%when Fe:AC=3:1.the 4BS decolorization rate increased with the increasing of PDS concentration,but there was no significant change when PDS more than 5mmol/L.The initia l pH have significant effect for red 4BS degradation in Fe-AC/PDS system,the decolorization rate of red 4BS reached 98.8%、96.2%、94.7%in acidic and neutral solutions when pH=3.02、4.67、7.32,respectively,the decolorization rate was only 24.5%、18.7%in alkaline solution when pH=9.38、10.78,respectively.Inorganic salt anions have an inhibitory effect for the decolorization of red 4BS in Fe-AC/PDS system with cation has the opposite effect.To discuss the mechanism of red 4BS degradation in Fe-AC/PDS system.