Selenite (SeO2-3) sorption in soils has been correlated with pH, soil mineralogy, and soil solution composition, factors that are often highly variable with respect to mine soil materials. Selenite equilibrium and adsorption batch studies were conducted with four mine soil materials to determine adsorption parameters that could be used to develop a model to predict Se retention. Initial mass, Freundlich, Langmuir, and other relationships were explored to describe adsorption and retention of Se in these soils. For equilibrium and adsorption studies, 25 ml of solution was added to 2.5 g of soil in a polyethylene centrifuge tube. Time-dependent analysis consisted of duplicate treatments of two SeO2-3 levels and reaction times, of 2, 6, 24, 48, 168, 336, and 504h. Adsorption studies were arranged in a 3 X 10 X 4 factorial design (three replications, 10 SeO2-3 concentrations, four soils) and equilibrated for 14 d. Selenite sorption as a function of pH in each material was also examined. Selenite sorption of 10 μg Se/g soil was not greatly affected by pH between pH 4 and 8, except in one sample where sorption decreased at pH 6. Initial mass isotherms were very similar for Se additions up to 20 mg/kg for all soils and predicted Se sorption very similar to the experimental data for these and 12 additional soils. The Freundlich and Langmuir isotherms did not effectively predict Se sorption.
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