The Method Research For Simultaneous Reduction Of Hexavalent Chromium Anddecolorization Of Organic Dyes

In recent years, because hexavalent chromium [Cr(VI)] was used in the electroplating, metal manusfacture, oil purification, synthetic dyes and other industries, a large number of artificial sources of chromium was released into the soil and water bodies. Industrial dye wastewater that was discharged into natural water bodies has been difficult with a variety of industrial operations in industry wastewater treatment, causing serious environmetal pollution problems. Hexavalent chromium and industrial dyes may be present in water bodies at the same time. Although co-treatment of Cr(VI) and dye has been attracted, it is still a great challenges. The purpose of this paper is the simultenious reduction of hexavalent chromium and decolorization of orange II in two systems that is the iron(III)- organic acid and zero-valent iron(Fe0) – organic acid.Firstly, the simultaneous reduction of Cr(VI) and decolorization of Orange II in the homogeneous systems composed of ferric sulfate and citric, tartaric, oxalic acids was examined. Experimental results showed that three systems of Fe3+/Cit、Fe3+/Tar、Fe3+/Oxa are both reductive and oxidative under sunlight, and Cr(VI) and Orange II could be reduced and decolored simultaneously. In the three kinds of acid, oxalic acid system had the best efficiency in simultaneous reduction and decolorization of Cr(VI) and Orange II, while citric acid system had worst effect; although tartaric acid system had a very high efficiency for reduction of Cr(VI), the decolorization efficiency of Orange II was significantly worse than oxalic acid system. The necessary photoirradiation was an extremely important condition to ensure the activity of chemical oxidation of these three system, but the impact of introduction of extra- photoirradiation on the basis of sunlight was not the same for the three systems: extra- photoirradiation was favorable for reduction of Cr(VI) and decolorization of Orange II in Fe3+/Cit system, it was almost no impact for Fe3+/Tar system, but was unfavorable in the Fe3+/Oxa system.Reduction of Cr(VI) and decoloration of Orange II were related to the concentration of citric acid in light-assisted Fe3+/Cit system. Within a certain concentration range, the higher concentration of citric acid, the better reduction of Cr(VI) and decoloration of Orange II. However, enhanced effect was not obvious when the concentration was too high. The appropriate concentration of citric acid was 2.4 mmol / L. Reduction of Cr(VI) and decoloration of Orange II was also related to the solution p H in light-assisted Fe3+/Cit system. The lower the p H value, the more conducive reduction of Cr(VI) and decolorization of orange II and the optimum p H was 3.0. Reduction rate of Cr(VI) and decolorization rate of Orange II were increased with increasing concentration of Fe(Ш). If the concentration was too high, enhanced effect was not obvious. In the concentration range studied, 0.2mmol / L was suitable. It was also found that the system composed of solid phase iron corrosion products(ICPs) and citric acid or oxalic acid under extra- photoirradiation was also effective to reduce Cr(VI) and decolorize Orange II simultaneously, and ICPs / Oxa system had a higher efficiency. This revealed that ICPs had a potential application in environmental remidation.For zero-valent iron(Fe0)- organic system, the necessary photoirradiation is an extremely important condition for simultaneous reduction of Cr(VI) and discolorization of Orange II in Fe0/Oxa system,. Fe0/Oxa system in the sunlight could cause Cr(VI) and Orange II to be reduced and decolorized effectively(under the given experimental conditions, after 60 min, reduction rate of Cr(VI) and decolorization rate of Orange II reached 46% and 85%, respectively.). The impact of introduction of extraphotoirradiation on the basis of sunlight was adverse for Fe0/Oxa system(after 60 min, reduction rate of Cr(VI) and decolorization rate of Orange II were changed to only 2% and 71%, respectively.). For Fe0/Oxa system, fairish lower dosage Fe0 could get higher reduction rate of Cr(VI) and decolorization rate of Orange II.Fe0/Tar system in the sunlight could enable Cr(VI) and Orange II to be reduced and decolorized effectively at the same time. The impact of introduction of extra-photoirradiation on the basis of sunlight was favorable for decolorization of orange II, but unfavorable for the reduction of Cr(VI). Comparing Fe0/Oxa with Fe0/Tar,Fe0/Tar system was more favorable for reduction of Cr(VI), but unfavorable for decolorization of Orange II; Fe0/Oxa system was more favorable for the decolorization of Orange II, but unfavorable for reduction of Cr(VI). In addition, the effect of Fe0 dosage in Fe0/Tar system was unlike to Fe0/Oxa system in terms of reduction of Cr(VI) and decolorization of Orange II. Reduction of Cr(VI) and decolorization of Orange II were related to the concentration of tartaric acid and the solution p H. Within the range studied, the suitable concentration of tartaric acid was 1.2mmol / L and suitable p H was 3.0.The present work also made a preliminary investigation of simultaneous reduction of Cr(VI) and decolorization of methylene blue, another organic dye, in systems of iron(III)- organic acid and zero-valent iron(Fe0)- organic acid. It was found that light-assisted Fe3+/Cit system was also able to simultaneously reduce Cr(VI) and decolorize methylene blue, and the effect of p H on decolorization rate of methylene blue is nearly the same to Orange II. In terms of zero-valent iron- organic acid systems, Fe0/Tar and Fe0/Oxa could also effectively reduce Cr(VI) and decolorize methylene blue. Fe0/Tar system was more favorable for reduction of Cr(VI), while Fe0/Oxa system more favorable for discolorization of methylene blue.