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AMD Treatment

Treatment of AMD
In 1968, Pennsylvania instituted strict effluent discharge limitations on mine operations. Many mining companies used chemical treatment methods to meet these new effluent limits. In these chemical treatment systems, the acidity is buffered by the addition of alkaline chemicals such as calcium carbonate, sodium hydroxide, sodium bicarbonate or anhydrous ammonia. These chemicals raise the pH to acceptable levels and decrease the solubility of dissolved metals. Precipitates form and settle out of solution. But these chemicals are expensive and the treatment system requires additional costs associated with operation and maintenance as well as the disposal of metal-laden sludges.

Passive Treatment of AMD

As early as 1978, many variations of AMD passive treatment systems were studied by numerous organizations in laboratories. During the last 15 years, passive treatment systems have been implemented on full-scale sites throughout the United States with promising results. The concept behind passive treatment is to allow the naturally occurring chemical and biological reactions that aid in AMD treatment to occur in the controlled environment of the treatment system, and not in the receiving water body.

Passive treatment conceptually offers many advantages over conventional active treatment systems. The use of chemical addition and energy consuming treatment processes are virtually eliminated with passive treatment systems. Also, the operation and maintenance requirements of passive systems are considerably less than active treatment systems.

The first passive technology involved the use of natural Sphagnum wetlands to improve the water quality of AMD without causing other detrimental impacts on the ecosystem. Although this concept had its limitations, it spawned research and development into other passive treatment technologies that did not follow the natural wetland paradigm.

Designing a passive treatment system for AMD requires the understanding of mine water chemistry, and available treatment techniques. Sampling the AMD affected water and analyzing its chemistry is extremely important in the selection of appropriate treatment technologies.


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