MODELING SELENITE SORPTION IN RECLAIMED COAL-MINE SOIL MATERIALS

Selenite (SeO32-) sorption in soils has been correlated with pH, soil mineralogy, and soil solution composition, factors that are often high ly variable with respect to mine soil materials. Selenite equilibrium and adsorption batch studies were conducted with four mine soil materi als to determine adsorption parameters that could be used to develop a model to predict Se retention. Initial mass, Freundlich, Langmuir, an d other relationships were explored to describe adsorption and retenti on 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 t ube. Time-dependent analysis consisted of duplicate treatments of two SeO32- levels and reaction times of 2, 6, 24, 48, 168, 336, and 504 h. Adsorption studies were arranged in a 3 x 10 x 4 factorial design (th ree replications, 10 SeO32- concentrations, four soils) and equilibrat ed for 14 d. Selenite sorption as a function of pH in each material wa s also examined. Selenite sorption of 10 mu g Se/g soil was not greatl y affected by pH between pH 4 and 8, except in one sample where sorpti on 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. Th e Freundlich and Langmuir isotherms did not effectively predict Se sor ption.