The Processes And Mechanisms Of Abiotic Degradation Of Dyes By Zero-valent Iron

Zero-valent iron (ZVI) technologies for contaminated land and groundwater remediation have attracted much attention in recent years. Due to its low cost and benignity to environment, ZVI has been applied to deal with the reducible inorganic and organic contaminants. In this paper, reactive brilliant red X-3B (X3B) was used as a model pollutant of azo dye to examine the reductive capacity of the ZVI/H2O system. Rhodamine B (RhB) was used as a model pollutant of xanthene dyes to examine the oxidative capacity of the ZVI-based Fenton process with low dose of H2O2and the pH value over4.0was concentrated. The degradation kinetics and mechanism of X3B and RhB were discussed.(I) Degradation of X3B by ZVI in aqueous solution was investigated. The effects of ZVI dosage, initial concentration of X3B and initial pH value on the degradation of X3B were examined. The removal of X3B decreased with the increase of pH value and initial concentration of dye, but increased with the increase of ZVI dosage. The degradation of X3B could be described by the pseudo first-order kinetic model, and linear correlation coefficient R2>0.96. The degradation of80mg·L-1X3B achieved best with1.0g·L-1ZVI at pH4.0.The intermediates of X3B were analyzed with UV-Vis spectrophotometry and ion chromatography and the mechanism of reductive degradation of X3B was also discussed. The ion chromatography analysis showed that there were no Cl-and SO42-produced through ZVI/H2O systems, indicating that chloride ion and sulphonic groups could resist cut off from triazene ring and naphthalene ring, respectively.(Ⅱ) Degradation of RhB by ZVI-based Fenton process with H2O2was investigated. The effects of H2O2concentration, ZVI dosage, and initial concentration of RhB and initial pH value on the degradation of RhB were examined. The removal of RhB decreased with the increase of pH value and initial concentration of dye, but increased with the increase of ZVI dosage and H2O2concentration up to top then decreased. The degradation of RhB could be described by the pseudo first-order kinetic model, and linear correlation coefficient R2>0.90. The optimum degradation condition for50mg·L-1of RhB is pH=4.0with ZVI dosage1.0g·L-1and H2O210mmol·L-1.The results showed that the degradation and mineralization of RhB occurred with low dose of H2O2and ZVI. The intermediates of RhB were analyzed with UV-Vis spectrophotometry and ion chromatography and the mechanism of oxidative degradation of RhB was also discussed. The reactive oxygen species (·OH) produced in ZVI-based Fenton process with H2O2is the key to the degradation of RhB by ways of N-de-ethylation, chromophore cleavage, ring-opening and mineralization. It can be seen that about70%of RhB decomposed into CO2and H2O within30min.