Selenium removal from contaminated

Biological activity can be used in two ways for the bioremediation of metal-contaminated soils to immobilize the contaminants in situ or to remove them permanently from the soil matrix, depending on the properties of the reduced elements. Chromium and uranium are typical candidates for in situ immobilization processes. The bioreduction of Cr(VI) and Ur(VI) transforms highly soluble ions such as CrO and UO + to insoluble solid compounds, such as Cr(OH)3 and U02. The selenate anions SeO are also reduced to insoluble elemental selenium Se°. Bioprecipitation of heavy metals, such as Pb, Cd, and Zn, in the form of sulfides, is another in situ immobilization option that exploits the metabolic activity of sulfate-reducing bacteria without altering the valence state of metals. The removal of contaminants from the soil matrix is the most appropriate remediation strategy when bioreduction results in species that are more soluble compared to the initial oxidized element. This is the case for As(V) and Pu(IV), which are transformed to the more soluble As(III) and Pu(III) forms. This treatment option presupposes an installation for the efficient recovery and treatment of the aqueous phase containing the solubilized contaminants. 

Kharaka Y. K., Ambates G., and Presser T. S. (1996) Removal of selenium from contaminated agricultural drainage water by nanofiltration membranes. Appl. Geochem. 11, 797-802. 

Gleason KJ, Yu J, Bunge AL, and Wright JD. Removal of selenium from contaminated waters using emulsion liquid membranes. In Bartsch RA, Way JD, eds. Chemical Separations with Liquid Membranes, Washington, DC American Chemical Society, ACS symposium series 642, 1996 342-360. 

A small fraction of selenium may exist in the gaseous state in the atmosphere (Table 7.2). However, the majority of atmospheric selenium is expected to be present in particulate form (NAS 1976). Removal of atmospheric selenium occurs primarily through wet and dry deposition and its association with sub-micrometer aerosols (Mosher and Duce 1983, NAS 1976, Jickells etal. 1984). Selenium is emitted naturally into the atmosphere mainly in the form as dimethylselenide (Jiang et al. 1983). Major producers of dimethylselenide are plants and soil bacteria (Terry et al. 2000). Through bacterial and phytovolatilization substantial amounts of selenium may be removed from selenium-contaminated soil. Inor-... 

Activated alumina s role in a water filter is similar to that of carbon. When water comes into contact with it, it attracts and removes certain contaminants, notably arsenic, fluoride, selenium, and LEAD. When activated carbon and alumina are used together, the filter can be highly effective in removing lead, as well as a number of other contaminants. Success of lead removal varies from brand to brand. 

Removal of Selenium from Contaminated Waters Using Emulsion Liquid Membranes... 

In this study, aiming to apply the system for removal of selenium from contaminated waste water, immobilization of selenium into the hydrate of calcium alumino-zincate has been studied. To further enhance the immobilization efficiency, adding calcium hydroxide to the present system, its effect on sorption of selenium by hydration of calcium alumino-zincate has been studied and stoichiometrically discussed. 

Phytoremediation is also being developed for dealing with soils contaminated with high levels of selenium in California again B.juncea seems to be particularly effective in accumulating the contaminant from soil, and all plants tested were more effective at removing selenate than selenite (92). This is an interesting contrast to bacterial systems, where selenite reduction is more commonly found than selenate reduction. 

Sodium selenite has also been incorporated into styrene—butadiene mbber and used in a pellet form which results in the slow release of selenium into water. These pellets have been placed in lakes in Sweden which have fish contaminated with mercury owing to high levels of that element in the water. The selenium released by the pellets reacts with mercury to form insoluble, heavy mercury selenide which setties to the lake bottom and removes mercury from the ecosystem (126). 

Sulfide ores usually contain small amounts of mercury, arsenic, selenium, and tellurium, and these impurities volatilize during the ore treatment. All the volatilized impurities, with the exception of mercury, are collected in the dust recovery systems. On account of its being present in low concentrations, mercury is not removed by such a system and passes out with the exit gases. The problem of mercury contamination is particularly pertinent to zinc plants since the sulfidic ores of zinc contain traces of mercury (20-300 ppm). The mercury traces in zinc sulfide concentrates volatilize during roasting and contaminate the sulfuric acid that is made from the sulfur dioxide produced. If the acid is then used to produce phosphatic fertilizers, this may lead to mercury entering the food chain as a contaminant. Several processes have been developed for the removal of mercury, but these are not yet widely adopted. 

A New Bedford Harbor Sawyer Street site in Massachusetts has been designated as a superfund site due to PCB contamination of river sediments. Commodore was one of three companies chosen to conduct demonstration studies on-site under contract to Foster Wheeler Environmental Company. The river sediment was first washed with diisopropylamine by the Ionics RCC B.E.S.T process [35], producing an oil concentrate. The PCB level in the B.E.S.T concentrate was approximately 32,800 ppm. Dioxins/furans (TEFs) were also present at 47 ppm. This concentrate was reacted with SET in the SoLV process to destroy the PCBs and dioxins (Table 4). After treatment, the PCB level was 1.3 ppm, well below regulatory requirements for disposal in nonhazardous waste landfills. Dioxins were also readily remediated. This study also illustrates that the SoLV process can remove metals from substrates. The concentrate received was found to have lead, arsenic, and selenium in high parts-per-billion levels. After treatment with the SoLV process, the levels were below detection limits. The metals were... 

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