Ion Exchange
Treatment of Acid Mine Drainage
J. J. STERNER, Engineer
Homer Research Laboratories
Bethlehem Steel Corporation
and
H. A. CONAHAN, Consulting Engineer
Engineering Department
Bethlehem Steel Corporation
Bethlehem, Pennsylvania
INTRODUCTION
Mine water pumped from active mines and flowing from abandoned mines
frequently contains relatively high concentrations of dissolved iron (both ferrous
and ferric) and acidity as well as other dissolved ions such as aluminum, calcium,
and magnesium. Recent legislation by the Commonwealth of Pennsylvania requires the treatment of acid mine drainage (AMD) from active mines to meet the
effluent standards established by the Pennsylvania Sanitary Water Board. The key
items in this set of standards are: no greater than seven mg/1 iron, alkalinity
greater than acidity, and pH between 6. 0 and 9. 0.
Lime neutralization of AMD is one treatment that is known to be effective
and is currently being used (1). However, the resulting precipitate settles to a
final thixotropic sludge which contains hydrated ferric and aluminum hydroxides
and may be more than 99 per cent water, i.e., less than one per cent solids. The
volume of the sludge produced may amount to more than 10 per cent of the original AMD discharge, depending on the original concentrations of iron and aluminum. The disposal or storage of this sludge, which dries and compacts poorly,
represents the most difficult aspect of AMD treatment via lime neutralization.
The large storage lagoons, which will be needed to contain this production of
sludge, will take the land out of productive service and will be hazardous for many
years after being filled.
As part of a broad research program directed toward developing more effective
and economical methods for handling the AMD problem, we undertook experimental and pilot plant studies of ion exchange as a means for producing a concentrated waste stream which would contain the iron, aluminum, and other cations in AMD and could be handled more conveniently and economically than the
sludge from lime neutralization. The estimated regenerant cost for a minimum-
volume, concentrated waste stream as well as the solids concentration of sludges
obtained by treatment of this waste stream are stated for the particular AMD
treated.
PILOT PLANT TEST PROGRAM
Preliminary experimental work with small fixed beds of ion exchange resins in
one-half and one in. diameter glass columns showed that it was technically
feasible to remove iron from AMD by ion exchange. On the other hand, the low
efficiency of regenerating the resin in the small fixed-bed apparatus made it impractical to determine minimum regenerant requirements or to obtain a highly
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