WWRC 88-26
Chemistry of Aluminum and Iron Minerals in
Oil Shales Containing Pyrite
Abstract
The ability to properly manage acid mine drainage is
dependent upon understanding the chemistry of Al and Fe associated
with the oxidation of pyritic materials. The objective of
this study was to examine the solubility relationships of Al and
Fe minerals in oil shales containing pyrite under oxidizing
equilibrium conditions. Two eastern oil shales, A New Albany
shale (unweathered, 4.6% pyrite) and a Chattanooga shale (wea-
thered, 1.5% pyrite), were used in this study. Oil shale samples
were equilibrated with distilled-deionized water from 1 to 180
d(l:l solid:solution ratio). The equilibrium solutions were
filtered and the clear solutions were analyzed for total cations
and anions. Ion activities were calculated from total concentrations.
Below pH 6.0, depending upon SO4 activity, Al3+ solubility
was controlled by Al(SO4(OH).5H24O for both shales.
Initially, Al3+ solubility for the New Albany shale showed
equilibrium with amorphous Al(OH)3(s). The pH decreased with
time, and Al3+ solubility approached equilibrium with Al(SO4)-(OH).5H2O.
Below pH 6.0, Fe3+ solubility appeared to be regulated
by a basic iron sulfate solid phase with the stoichlometric
composition of FeOHSO4(s). The results from this study further
indicate that the acidity, in oil shale waters may be produced
from the hydrolysis of Al3+ and Fe3+ in solution.
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