Hello everyone!
In my previous post, I talked about the importance of predicting Acid Mine Drainage (AMD). However, with current technology predicting the potential for AMD formation is costly and of questionable reliability. Therefore, the prevention and mitigation of AMD become increasingly more important. I will be talking about some prevention and mitigation strategies for AMD here.
To stop the formation of sulfuric acid, sulfur-containing ores have to be prevented from coming into contact with oxygen and oxidizing. The control and prevention methods include: controlling water migration, separation and blending waste with alkaline materials, and dry and wet covers. Based on site conditions and nature of the waste, suitable methods are then implemented. Much of my discussion below will be based on the paper by Kuyucak, 2012.
#1 Control Water Mitigation
This method restricts the amount of water flowing through these potentially acid-forming waste. Clean water flows can be intercepted and diverted away with the help of properly designed ditches. Groundwater mitigation could also be controlled using underground structures like grout curtains and slurry walls. Rain falling on the waste dump surface can be collected using diversion ditches to waste storage sites and be treated. Such diversion ditched may include liners or armors to minimize potential infiltration into the ground.
#2 Separation and Blending
During the mine operation, waste rock with high sulfur percentage can be separated and be disposed of in specifically designed storage areas. In addition, the waste can either be encapsulated with alkaline material/benign waste/non-acid producing material or blended to form a mixture as shown in the picture below (Kuyucak, 2012).
#3 Dry Cover
Covers, caps, and seal can be used to isolate or encapsulate the waste to prevent contact with air or water or both. A low permeability soil cover containing a layer of compacted can be used to cover the waste rock. The top layer can also be vegetated to reduce water infiltration and erosion. Geomembranes such as polyvinyl chloride (PVC) or high density polyethylene (HDPE) can also be used. Despite their effectiveness, soil covers have been found to be very costly to implement in various areas.
#4 Water Cover
Water covers have been shown to be a more economical option to dry cover and oxygen has a low solubility and diffusion rate through water. Therefore, oxidation of the waste materials can be reduced and is considered to be effective for long term control method. However, the implementation is limited to site conditions with respect to hydrology, topography and availability of water nearby. However, in many cases, the water flowing out from waste ponds still needs to be treated to neutralize acidity and removal of metals before it is released into the environment (Coil et al., 2014).
Unfortunately, acid prevention strategies often fail. Isolating large quantities of acid-generating waste and rock proves to be very challenging, either above or underground, and in many cases is almost effectively impossible. Once the acid has been generated and toxic metals dissolved into it, the water is also expensive to treat.
That brings me to the end of this post!
See you guys soon!
References
Coil, D., McKittrick, E., Mattox, A., Hoagland, N., Higman, B., & Zamzow, K. (2014, October 29). Acid Mine Drainage. Retrieved September 25, 2020, from http://www.groundtruthtrekking.org/Issues/MetalsMining/AcidMineDrainage.html
Kuyucak, N. (2012). Acid Mine Drainage Prevention and Control Options. Retrieved October 01, 2020, from http://www.imwa.info/docs/imwa_1999/IMWA1999_Kuyucak_599.pdf
