Research Of The Oxidation Degradation Of The Dyes By The Sulfate Free Radicals Generated By Sodium Persulfate

Persulfate is one of the strongest oxidants in the aqueous solution. Its many advantagesmake it have broad prospects in the degradation and mineralization of the pollutants.PS isvery stable at room temperature which is required to be activited by light,heat or transitionmetals(Fe²⁺and others),etc, to generate SO₄^-· oxidative degrading pollutants. As the mostwidespread metal ion in nature, Fe²⁺is wide used in the activation of S2O82-. But thepersulfate advanced oxidation processes participated by ferrous have manydisadvantages,such as high requirements of the pH value of the liquid, low rates ofmineralization of pollutants, competing the SO₄^-·with the pollutants and rapid conversion toFe3+.All these disadvantages limit the oxidative capacity of the persulfate oxidation method.To solve this issue the heat/ZVI system and small molecule acid complexed ferrous were usedin this study instead of ferrous ions to activate PS.Fistly, effects of temperatures, PS concentrations and ZVI dosages on AO7decomposition were investigated in sole heat and ZVI activating systems. The degradationresults of two systems were compared for choosing a better activating way for AO7degradation and finally the two activating ways were combined for getting the best AO7degradation efficiency. The degradation of AO7by Heat/PS systems followed pseudo first-order kinetics and the reaction rates increased with the reaction temperatures elevating inroom temperature to90℃range, and also increased when initial PS concentrations variedfrom1to12mM. For ZVI activating systems （ZVI/PS systems）, the degradation rate ofAO7was highest when ZVI dosage was0.2g, and it reached to95.6%within90min.Comparing ZVI/PS systems with Heat/PS systems, the results showed that the ZVI activationwas a more effective way to activate PS than the heat activation for AO7degradation. AO7degradation processes by ZVI/Heat/PS systems were two-stage pseudo first-order kineticprocesses, and the combining of two activating ways greatly increased the reaction rates. Bythe addition of ZVI to the Heat/PS system, the apparent activation energy E_aof AO7degradation reduced from the original130.26kJ·mol^-1to27.70kJ·mol^-1.And then the influences of pH and complexing agents on degradation of reactive brilliantblue KN-R by ferrous activated persulfate were investigated, and the complexed and the uncomplexed system were compared. Because the lower the pH the more quickly will be thedissociation of S2O82-to the SO₄^-and the ORP of the dominant radical SO₄^-in the acidiccondition is higher than the dominant radical OH in the alkaline condition, KN-R degradationrates in acidic condition are far outweigh in the neutral and alkaline conditions. When pHvalue was3, the residual rate of KN-R was17.0%within3hours by EDTA system with thelowest PS consumption rate32.3%, so EDTA was the best complexing agent choice in acidiccondition. When pH value was7, the residual rates of KN-R were11.3%，12.4%within3days by EDTA, citric acid system with the PS residual rates28.9%，28.0%respectively, soEDTA, citric acid were the better choices in the neutral condition. When pH value was10,glucose acid, citric acid, EDTA and tartaric acid systems all had the similar KN-Rdegradation rates and PS residual rates, so all could acted as the complexing agents.when thesystem contained trace amounts of ferrous, the addition of complexing agent would greatlyimprove the degradation rate of pollutant, from original52.5%to79.3%of3d, so PS issuitable for in situ chemical oxidation （ISCO）.Finally pathways of heat-activated oxidative degradation of AO7in PS aqueous solutionwere studied. AO7has two structures in aqueous solution,the hydrazone form and the azoform.The absorption spectrum of AO7in water is characterized by two bands in theultraviolet region and by two bands in the visible regionwhich are due to the benzene ring,naphthalene ring and the chromophore-containing azo linkage of AO7, respectively.In the heatactivated PS oxidation system at70℃, the rank of the degradation efficiency of each groupsof AO7was the chromophore> naphthalene ring> benzene ring.And their degradationprocesses in3h、2h、2h were pseudo first-order kinetic processes,with the dynamic rateconstants were0.026min^-1,0.009min^-1,0.003min^-1respectively.The pH of the solutiondecreased rapidly during the experiment, dropping from6.2at t=0to3.0at t=8h, whichindicated the formation of acid products.Naphthalene,2-naphthol, phthalic acid may beconsidered as primary degradation products of the dye originating from oxidative cleavage ofthe molecule in the vicinity of the azo bond. Smaller aromatic intermediates containingdimethyl benzene, ethylbenzene, benzoic acid, phenol and other intermediate products werealso detected. But small molecule acids didn’t appear.