Limestone #

from the EPA’s Mid-Atlantic Integrated Assessment:

Limestone “is the least expensive [active treatment method] and safest to use for AMD treatment. Essentially, either chunks or ground limestone are added directly to AMD water

Hydrated lime #

from the EPA’s Mid-Atlantic Integrated Assessment:

“This chemical is commonly used because it is cost effective in situations of very high acidity and large water flow. Extensive mechanical mixing is required because hydrated lime does not dissolve in water. It can be bought in bulk as a powder and must be dispensed via a mixer/aerator that mixes it with the AMD water. It is important to not use too much hydrated lime, because any excess should not enter the next stage, a pond within which the metals will settle. Safety goggles must be used when handling this chemical because it can cause blindness.”

Quick lime #

from the EPA’s Mid-Atlantic Integrated Assessment:

“This chemical is highly reactive, relatively inexpensive, and apparently easy to handle in 50lb bags (it can also be bought in bulk). In order to apply pebble quicklime, a water wheel called the Aquafix machine is typically used and placed above a channel of water. Here, quicklime is dispensed into the AMD water where it dissolves over time. Depending on the level of acidity and volume of water flow, appropriately sized feeder bins or silos are place above the machine. These bins hold the quicklime and feed it into the machine, powered by the flow of water.”

Soda ash #

from the EPA’s Mid-Atlantic Integrated Assessment:

Soda ash “comes as solid briquettes and is gravity fed into the AMD water from a hopper mounted over a basket. Soda ash is typically used to treat AMD in remote areas with low volume flows and low amounts of acidity and metals.”

Caustic soda #

from the EPA’s Mid-Atlantic Integrated Assessment:

Caustic soda is used “in remote locations where electricity is not available and flows are low. Caustic soda is gravity fed as a liquid into AMD. It dissolves, disperses, and raises pH very quickly. Because it is denser than water, it should be applied to the surface of a pond where it will then sink. Caustic soda is contained in tanks that can hold up to 8,000 gallons. A line is run from the bottom of the tank and carries the caustic soda to a ditch or pond. Valves control the rate of flow. In the winter, caustic soda can freeze, so the tank may require a heater (which will need to be replaced often because of the corrosive nature of caustic soda) or be buried underground. If it is buried it must comply with strict EPA regulations. Another option is adding potassium hydroxide to the soda, making it solid but also freeze-proof. As a solid, the soda is dispensed as flakes or beads via large drums.”

Anhydrous ammonia #

from the EPA’s Mid-Atlantic Integrated Assessment:

Ammonia “is stored as a liquid, but when it hits the water it turns into a gas and dissolves. It reacts very quickly, rapidly raising pH. Special training and experience is needed to handle the hazardous ammonia, and additional analyses must be performed downstream in order to monitor the biological effects it has on the ecosystem. There are dangerous consequences associated with excessive ammonia application.”