Study On Treatment Of Metal Complex Dyes By Heterogeneous UV-Fenton Process

In this paper, degradation and mineralization of three traditional metal complex dyes (Neutral Bordeaux GRL, Neutral Blue BNL and Neutral Pink BL) by heterogeneous UV-Fenton process with Fe-pillared bentonite as catalyst were studied. The effects of temperature, UV wavelength, hydrogen peroxide concentration and initial pH values on dyes degradation by heterogeneous UV-Fenton process were evaluated. At the same time, the degradation kinetic of metal complex dyes under different conditions was analyzed. The stability and reuse exploitability of Fe-pillared bentonite were probed; the adsorption capability of heavy metal ions which existed in three dyes on the catalyst was investigated also. Whether the heterogeneous UV-Fenton process could treat the metal complex dyes with high efficiency in both treating organic structure and removing heavy metal ions were studied primarily. The main research results are as follows:(1) The heterogeneous UV-Fenton process has highly effective ability of degradation and mineralization on the three traditional metal complex dyes referred above. The degradation rates of 98.8%,95.1% and 73.2% at 30min and the mineralization rates of 88.4%,82.2% and 68.8% at 120min could be obtained when the metal complex dyes were Neutral Bordeaux GRL, Neutral Blue BNL and Neutral Pink BL respectively, and the degradation process accords with first order reaction equation.(2) Fe-pillared bentonite could effectively remove the free heavy metal ions which were produced during the dye degradation process. After treatment, the concentration of Co,Cr and Cu was 0.943mg/L,0.384 mg/L and 0.628mg/L respectively, which was lower than the emission standards. The experiment of adsorption showed that the absorbability of Fe-pillared bentonite on the heavy metal ions was sequenced as follows:Cr(â…¢)>Cu(â…¡)> Co(â…¡)>Cr(â…¥); the absorption accorded with Freundlich adsorption isotherms on Cr(â…¢) and Cu(â…¡), Langmuir adsorption isotherms on Cr(â…¥), Freundlich and Langmuir adsorption isotherms on Co(â…¡). It should be pointed out that most of the complex ions in the metal complex dyes are Cr and Fe-pillared bentonitet showed novel ability on removing Cr(â…¢) when it reused directly, the concentration of was 0.384mg/L,0.324mg/L and 0.270mg/L respectively at the end of reaction(3) Temperature did not highly affect the degradation of metal complex dyes referred above by Heterogeneous UV- Fenton process, reaction activation energy on degradation of these dyes was 12.7 KJ/mol,16.3 KJ/mol and 37.7 KJ/mol respectively. The quantum yield for the photolysis of Fe(â…¢) significantly decreases as the light wavelength increases, which lead to decrease of metal complex dyes degradation in heterogeneous UV-Fenton system. As H2O2 is both the generation source and the trapping agent of hydroxyl radicals in the process, a higher concentration's effectiveness is limited in improving the degradation rate. The effect of initial pH values on degradation rate was different because of the different structures of dye.(4) Iron leaching could be detected during the degradation of metal complex dyes by heterogeneous UV- Fenton process. However, these iron ions leached from catalyst could be adsorbed onto the catalyst again after the organic pollutants were mineralized completely, which shows good stability of the catalyst. The catalyst also could keep high catalystic efficiency on dye degradation and mineralization when it reused directly. For example, The degradation rate of Neutral Bordeaux GRL was 99.65%,99.67% and 99.74%(at 40min) and mineralization rate of Neutral Pink BL was 82.2%,92.8% and 93.9%(at 120min) respectively.