WWRC 95-03
Modeling Selenite Sorption in Reclaimed Coal Mine Soil Materials
Abstract
Selenite (Se032-) 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 got soil in a polyethylene
centrifuge tube. Time-dependent analysis
consisted of duplicate treatments of two
Se032- levels and reaction times of 2, 6, 24,
48, 168, 336, and 504 h. Adsorption studies
were arranged in a 3x 10 x 4 factorial
design (three replications, 10 Se032- 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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