Economics of Coal Mine Drainage Treatment
H.G. BHATT, Assistant Chief Sanitary Engineer
Michael Baker, Jr., Inc.,
Beaver, Pennsylvania 15009
INTRODUCTION
The damaging environmental effects of mine drainage pollution has been a topic of
discussion for over 60 years. The restoration of the streams affected by mine drainage would
involve expenditure of large sums of money. The environmental protection agency estimated the cost for "at source" abatement of mine drainage and water treatment range from
$218 million to $656 million for a 20-year period. Garvey believes the high figure is too low
and should be in the neighborhood of two billion dollars. The object of this paper is to
evaluate the capital and operating cost of the various methods of mine drainage treatment.
Although there is no "typical" mine drainage, waters discharging from mines can be
divided into four general classes as shown in Table I.
TABLE I
CLASSIFICATION OF MINE DRAINAGE
Class II
Class III
Partially Oxidized
Oxidized and
Class IV
Class I
and/or
Neutralized and/or
Neutralized and
Acid Discharges
Neutralized
Alkaline
Not Oxidized
pH
2-4.5
3.5-6.6
6.5-10.5
6.5-8.5
Acidity, mg/1
CaCO,
1,000-15,000
0-1,000
0
0
Ferrous Iron, mg/1
500-10,000
0-500
0
50-1,000
Ferric Iron, mg/1
0
0-1,000
0
0
Aluminum, mg/1
0-2,000
0-20
0
0
Sulfate, mg/1
1.000-20,000
500-10,000
500-10,000
500-10,000
Source: ln-house Studies, Environmental Protection Agency
After Hill (I), 1968.
The wide variations in mine drainage characteristics indicate that a number of
treatment methods may be applicable. The capital and operating costs of the following mine
drainage treatment methods are discussed: 1) Neutralization (acid mine water with high
ferrous iron content and Acid mine water with high ferric iron content); 2) Flash
Distillation; 3) Ion Exchange; 4) Reverse Osmosis; 5) Submerged Coal Refuse Combustion
Process; 6) Freezing; 7) Electrodialysis; 8) Foam Separation; and 9) Neutradesulfating
Process.
NEUTRALIZATION
Neutralization is the most widely used method of treating coal mine drainage.
Neutralization historically has been applied to Class I and II mine drainage (Table I).
Being cheap, calcium alkalies are widely used for neutralization, however, after
treatment with calcium alkalies, the effluent has a higher hardness, may have a sulfate
concentration up to 2,000 mg/1. Disposal of sludge generated is also a big problem and
affects the economics of neutralization by calcium alkalies in as much as the cost of sludge
disposal will also need to be incorporated in the total cost of treatment.
When using limestone as a neutralizing agent, ferrous iron must be oxidized to ferric
iron with the formation of free acid before calcium carbonate can react to neutralize the
mine water and precipitate all iron.
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