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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.
