Iron selenium adsorption

Heavy metals such as copper, zinc, lead, nickel, silver, arsenic, selenium, cadmium and chromium may originate from many sources within a rehnery and may, in specihc cases, require end-of-pipe treatment. Some agencies have set discharge limits that are beyond the capability of common metals removal processes such as lime precipitahon and clarihcation to achieve. Other treatment processes such as iron coprecipitation and adsorption, ion exchange, and reverse osmosis may be required to achieve these low effluent concentrations [52]. 

Izumi, F. (1993) Rietveld analysis program RIE-TAN and PREMOS and special applications. In Young, R.A. (ed.) The Rietveld Method, Oxford, Oxford University Press, 236-253 Jackson, B.P. Miller, W.P. (2000) Effectiveness of phosphate and hydroxide for desorption of arsenic and selenium species from iron oxides. Soil Sci. Soc. Am. J. 64 1616-1622 Jain, A. Raven, K.P. Loeppert, R.EI. (1999) Ar-senite and arsenate adsorption on ferrihy-drite Surface charge reductions and net OEI-release stoichiometry. Environ. Sci. Techn. 

Laboratory methods. Huorimetry has been used widely for selenium analysis in environmental samples but is being superseded by more sensitive instrumental methods. Some of the instmmental methods used for arsenic speciation and analysis can also be used for selenium. In particular, HPLC and HG can separate selenium into forms suitable for detection by A AS, AFS (Ipolyi and Fodor, 2000), or ICP-AES (Adkins et al, 1995). Only Se(IV) forms the hydride, and so Se(VI) must be prereduced to Se(IV) if total selenium is to be determined. This is normally achieved using warm HCl/KBr followed by co-precipitation with La(OH)3 if necessary (Adkins et al., 1995). KI is not used, since it tends to produce some Se(0), which is not reduced by HG. La(OH)3 collects only Se(IV), so the prereduction step to include the contribution from Se(VI) is required before co-precipitation. Other methods of preconcentration include co-precipitation of Se(IV) with hydrous iron oxide or adsorption onto Amberlite IRA-743 resin (Bueno and Potin-Gautier, 2002). 

The iron oxide and clay content of soils and sediments can affect the bioavailability of selenium markedly. The strong pH dependence of adsorption is an important control. Maximum adsorption occurs between pH 3 and pH 5 and decreases as the pH rises. Organic matter also removes selenium from soil solution, possibly as a result of the formation of organometallic complexes. Addition of PO4 to soils increases selenium uptake by plants, because the PO ion displaces selenite from soil particles making it more bioavailable. Conversely, increasing the concentrations of PO4 in soils can... 

Balistrieri, L.S. and Chao, T.T., Adsorption of selenium by amorphous iron oxyhydroxide and manganese dioxide, Geochim. Cosmochim. Acta, 54, 739, 1990. 

Aly and Huang discussed the removal of several cations such as barium, iron, vanadium, and selenium, and several chlorine, fluorine, and cyanide compounds. More recently, activated carbons have also been used for the adsorptive removal of sulfides, nitrates, chlorides, chlorites, and chlorates, cyanides, " boric acid, borax, and borates, as well as certain metals such as lithium, cerium, iron, strontium, and dysposium from the aqueous phase. 

Kostial et al. [37] demonstrated that 5-7 day old rats absorb at least 55% of single oral doses of Pb-203 while Forbes and Reina [20] reported that absorption was high prior to weaning but decreased rapidly thereafter. Garber and Wei [22] found that fasting enhanced lead absorption in mice. Low dietary levels of calcium, iron, zinc, copper, selenium, and vitamin D have been reported to enhance lead adsorption [64]. 

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