71    TREATMENT OF A METAL-CONTAMINATED
ACIDIC MINE DRAINAGE
Scott D. Boling, Process Chemist
B&V Waste Science and Technology Corp.
Kansas City, Missouri 64112
Edmund A. Kobylinski, Process Engineer
Black & Veatch
Kansas City, Missouri 64114
INTRODUCTION
Acidic ground water with high concentrations of iron, zinc, copper, [lead, cadmium, and aluminum
was draining from a mine into a stream. Because these high metal concentrations violated environmental regulations, the U.S. Environmental Protection Agency (EPA) ordered the owner of the
facility to treat the mine drainage and stipulated that the treated effluent would be subject to acute
toxicity requirements. The mining facility tasked B&V Waste Science and Technology Corp.
(BVWST) and Black & Veatch (B&V) to design a water treatment plant (WTP) that would comply
with the EPA order. Because EPA water quality criteria are based on the toxicity caused by a single
metal in solution, there was some concern that simply reducing the concentration of the metals to
below these standards would not be sufficient to pass the acute toxicity tests.
This paper describes the procedures that were followed to formulate WTP effluent goals believed to
satisfy the toxicity requirements and addresses the procedures used to optimize a proposed treatment
process. Although treated effluent goals were not easily obtained, conventional treatment technologies provided adequate metals removal efficiency without the aid of more advanced technologies,
such as reverse osmosis or ion exchange.
APPROACH TO SOLVING THE PROBLEM
Identifying the Problem
Because of the high concentrations of metals in the mine drainage, the pH of this drainage was
sometimes as low as 2.0. The combination of these and other raw water characteristics, as shown in
Table I, produced a very toxic waste stream that had to be treated to pass EPA acute toxicity testing.
The EPA decreed that the toxicity levels would be based on the survival of the test organisms,
Ceriodaphnia dubia (water fleas) and Pimephales promelas (fathead minnows). For the test organisms to survive, it was believed that the concentrations of metals in the effluent had to be at or below
EPA "Gold Book Values"1 for water quality standards.
For these reasons, there was much concern regarding the selection of treatment process. Two key
concerns had to be addressed. Because many metals were in solution at the same time, there was
concern that some metals might enhance the toxicity of other metals. Most toxicological studies have
revealed that concentrations of certain metals cause toxicity when there is only a single metal in
solution. However, little or no information has been documented on whether there can be a synergistic
effect on toxicity when several metals are in solution. In addition to this concern about effluent
toxicity, the number of different metals in solution posed a serious problem in the selection of
treatment techniques. The mining facility directed that the WTP be designed to use conventional
precipitation processes. Upon review of the list of metals, shown in Table I, the designers observed
that the influent water would contain metals that precipitate under different optimum conditions. For
example, aluminum has a minimum solubility at pH 6.3, while metals such as cadmium and magnesium precipitate better at a much higher pH.
Because of these concerns, a workshop was held with key process designers to develop a process
train and to discuss how the process would be tested and optimized before design of the facility. The
workshop goal was to develop a treatment train that would utilize conventional metals precipitation
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.