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.