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Selenium(IV) and (VI) Sorption by Soils Surrounding Fly Ash Management Facilities

^a Dep. of Agronomy, Purdue University, West Lafayette, IN 47907-2054
^b Div. of Environmental Science and Ecological Engineering, Korea University, Seoul 136-701, Korea
^c Ish, Inc., 804 Salem Woods Dr., Suite 201B, Raleigh, NC 27615-3313

View larger version (19K): [in a new window]   Fig. 1. Selenium sorption as a function of pH expressed as the percentage of Se sorbed relative to Se applied. Applied concentrations were 6.64 µmol L–1 for Se(IV) and 5.22 µmol L–1 for Se(VI), which is mid-range of the concentrations used to construct the multiconcentration isotherms. The ratio of soil mass to solution volume were 1:50 and 1:20 for Se(IV) and Se(VI), respectively.

View larger version (14K): [in a new window]   Fig. 2. The Kd value for (upper) Se(IV) and (lower) Se(VI) for NE1 25–30 soil measured from a single Se concentration in the presence of increasing concentrations of sulfate (SO42–) or calcium (Ca2+) relative to the Kd value measured from the same Se concentration in the absence of Ca2+ or SO42– (KCl solution at I = 0.03). Initial concentrations were 17.55 µmol L–1 and 6.74 µmol L–1 for Se(IV) and Se(VI) with a soil mass/solution volume of 1:50 and 1:20, respectively. Constant ionic strength of 30 mM was achieved by adding appropriate amounts of KCl.

View larger version (25K): [in a new window]   Fig. 3. (A, B) Measured (symbols) Se(IV) sorption isotherms from 1 mM KCl, 1 mM CaCl2, 1 mM K2SO4, and 1 mM CaSO4 and (C, D) Se(VI) sorption isotherms from 1 mM KCl, 1 mM CaCl2, 1 mM K2SO4, and 1 mM CaSO4 and corresponding Freundlich sorption model fits (solid lines).

View larger version (18K): [in a new window]   Fig. 4. Attenuation of Se(IV) and Se(VI) in ash leachate by site soils. Also shown for comparison are dotted lines generated from the Freundlich model fits of the multiconcentration Se isotherms in 1 mM CaSO4. For SE1 48.5 + SE1 60 soils, Freundlich sorption fit were generated by combining the data sets from the two soils.