The Study Of Arsenic And Selenium Occurrence In Municipal Solid Waste Incineration Fly Ash

Municipal solid waste(MSW) could be effectively disposed by incineration, but it brings the problem of trace elements pollution at the same time. Some of the trace elements are easily volatilized such as arsenic(As) and selenium(Se), during the incineration, a part of them are enriched in fly ash and the other escape in the gas phase. The speciation transformation of As and Se during MSW incineration not only determines the toxicity of final products, but also their releasing characteristics through flue gas or fly ash. In this study, a method for the determination of As and Se speciation in MSW incineration fly ash was developed by high performance liquid chromatography(HPLC) coupled with hydride generation atomic fluorescence spectroscopy(HG-AFS). With this method, the occurrence of As and Se in MSW incineration fly ash samples collected from different MSW incineration plants were analyzed. Thus the speciation transformation routes of As and Se could be inferred, and furthermore, the transfer ability of As and Se from fly ash to environment was discussed. The main results are as follows:The occurrence of As and Se in fly ash were determined by their speciation transformation routes during incineration. At higher temperatures, a large proportions of As was immobilized in fly ash by reaction with Fe/Al containing mineral compounds and predominately presented in the form of As(V). Only a small fraction(0.34~9.56%) of As in fly ash was in the form of As(III) which was captured through physical adsorption by Ca O or activated carbon injected during flue gas purification process. For selenium, it could also been captured in fly ash through chemical reactions or physical adsorptions, but the speciation of Se in fly ash was totally Se(Ⅳ) according to the difference of chemical properties between As and Se. The generation of silicon aluminate contributed to the immobilization of As and Se in fly ash matrix.The stability of As and Se in environment was affected by their occurrence in fly ash. The results of short-term batch leaching experiments showed that p H value palyed a very important role in the leaching of As and Se from fly ash. For arsenic, the fraction of watersoluble and ion-exchangeable speciation was small, thus the leaching of As was dominated by the balance between dissolution and sediment. For selenium, its leaching was affected not only by the balance between dissolution and sediment, but also the balance between adsorption and desorption due to more water-soluble and ion-exchangeable speciation. According to the longterm column leaching experiments results, the stability of Fe As O4 was stronger than Ca3(As O4)2 in fly ash. During 15 days’ leaching experiments, the leached out ratio of Se(55.88~66.35%) was significantly higher than As(17.12~22.56%), which indicated the transfer capability to environment of Se was stronger than As in fly ash. So the basic data obtained could help the predication of transfer capability to environment of As and Se in fly ash. Thus the stability of As and Se in fly ash could be improved, lowing the control of the release of As and Se during MSW incineration.