Although mining practices often vary greatly according to the material produced and the value of the deposit, one common denominator is that mining of materials containing sulfide minerals creates acid mine drainage (AMD). AMD is one of the mining industry’s major environmental challenges.
A number of drivers influence the process selection for treating mine drainage waters. These include environmental regulations and the public’s growing demand for increased environmental stewardship. There are also a growing number of local and regional initiatives demanding that bioaccumulative chemicals of concern, both inorganic and organic, be treated to ever-lower levels in discharge water.
Consideration of AMD discharge is a major factor that influences treatment option decisions, including the purpose for which the water is to be treated and the method selected for disposal of the concentrated waste. In some cases, new water treatment technologies can efficiently allow for the marketing of mine pools as valuable resources.
New or expanded steam electric power plants frequently need to turn to nontraditional alternate sources of water for cooling. For example, six power plants in northeastern Pennsylvania currently use mine pool water as cooling tower makeup water. In addition to using AMD for cooling tower makeup water, there is a growing interest in providing the additional treatment required to use AMD water as boiler feed at steam electric power plants.
Mine Drainage Water Requires Additional Treatment
Although the use of mine drainage water as makeup water for power plants with closed-cycle cooling technology can often provide a number of advantages, including lower costs and a water source of sufficient volume, capacity, and sustainability, this water requires additional treatment before use in a power plant, for several reasons:
- The water salinity is high, frequently in the range of 2 g/l to 10 g/l.
- Dissolved and precipitated metals are present, including iron, manganese, aluminum, copper, zinc, cadmium, nickel, selenium, and boron.
- High levels of sulfate concentration, due to the oxidation of sulfide minerals contained in the ore, are present.
- The water is usually 100% saturated in calcium sulfate or in some cases much higher.
To arrive at the optimized process for the particular circumstances requires analytical data on the source water with both bench-scale testing and pilot testing to ensure that the processes selected are reliable and easy to operate.
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