Hello everyone!
In my last post, I mentioned about 4 different Acid Mine Drainage (AMD) prevention strategies and how, unfortunately, most of them often fail. Therefore, in this post, I will explore the remediation methods of AMD.
AMD remediation technologies can be divided into two categories: active treatment and passive treatment.
#1 Active Treatment
Active treatment is also known as chemical treatment which involves the addition of chemicals in order to raise pH and precipitate metals (Daniel, 2014). A variety of chemicals can be used. The most commonly used ones are: limestone, hydrated lime, caustic soda, soda ash, calcium oxide, anhydrous ammonia, magnesium oxide, and magnesium hydroxide (Roychowdhury et al., 2015). Each one of these chemicals has different properties, costs, and some differences in how they can be delivered. Hence, the selection of chemical(s) would depend on site-specificity, technical and economic factors. If you are interested, I would suggest you read the paper by Daniel, 2014 for a more informative method of how each chemical is used.
One of the major advantages of active treatment is that it does not require additional land or construction. Active treatment is usually fast and effective in removing both acid and metals. However, the major disadvantage is that it requires a continuous supply of chemicals and energy to perform efficiently. Chemicals and manpower cost to maintain the system increases significantly. The efficiency of the system is dependent on regular maintenance and chemical supply which makes it difficult to control for remote areas (Roychowdhury et al., 2015).
#2 Passive Treatment
Passive treatment makes use of natural processes, unlike adding chemicals, to treat AMD. It often involves the diversion of water into ponds or wetlands to go through natural or biological treatments that can achieve similar results as chemical treatments (Daniel, 2014). One of the most used passive systems is constructed wetland. There are different types of constructed wetlands namely aerobic (<30cm in depth) and anaerobic (Roychowdhury et al., 2015).
Various wetland plants like Typha sp., Juncus sp., and Scirpus sp. can regulate water flow, stabilize and accumulate metal precipitates, and maintain microbial population (Johnson & Hallberg, 2005). With constructed wetland, it is important to allow plants to establish before AMD is applied as plants can suffer “transplantation shock”. This would make them more susceptible to environmental changes, slow growth and development, and in the worse case, kill the entire wetland (Skousen et al., 2015). Besides wetlands, there are other treatment methods like the Anoxic Limestone Drains (ALD) that utilize the natural qualities of limestone to add alkalinity to the water as it dissolves.
The construction of the passive treatment system depends on several factors and most of the time, a mix of systems is necessary to reach standards required. The initial installation cost of these systems are very expensive and require periodic monitoring and maintenance. In addition, high cost is also incurred from the removal and disposal of the considerably large amount of sludge formed (Roychowdhury et al., 2015).
AMD is highly variable according to site conditions which makes remediation an even more challenging task. Long-term and consistent monitoring is required as AMD can exist for a very long time. I have previously mentioned in my post on AMD that most hard rock mines end up failing to meet requirements after various measures in place. It is therefore of great importance that continued research is done for a more effective, viable, and sustainable remediation system.
That brings me to the end of this post.
See you guys soon!
References
Daniel, K. (2014) “Effective Treatment Options for Acid Mine Drainage in the Coal Region of West Virginia”. Theses, Dissertations and Capstones. Paper 857.
Johnson, D. B., & Hallberg, K. B. (2005). Acid mine drainage remediation options: A review. Science of The Total Environment, 338(1-2), 3-14. doi:10.1016/j.scitotenv.2004.09.002
Roychowdhury, A., Sarkar, D., & Datta, R. (2015). Remediation of Acid Mine Drainage-Impacted Water. Current Pollution Reports, 1(3), 131-141. doi:10.1007/s40726-015-0011-3
Skousen, J. G., Sexstone, A., & Ziemkiewicz, P. F. (2015). Acid Mine Drainage Control and Treatment. Agronomy Monographs Reclamation of Drastically Disturbed Lands, 131-168. doi:10.2134/agronmonogr41.c6
