Cleaning acid mine drainageIn the other posts after the spill of acid mine waste in Colorado, I&rsqu

Cleaning acid mine drainageIn the other posts after the spill of acid mine waste in Colorado, I’ve covered what acid mine drainage is, why there are so many mines in Colorado, and what exactly happened during the spill (see the links at the bottom). This photo is a great example of what can be done about it – this mine has been remediated and only clean water is flowing down stream.Unfortunately, solving mine waste issues is not easy. The first problem is…every situation is different. Every single mine has different water flow rates, different geology, different contaminants, different climate. What works at one mine won’t necessarily work at another. Some mines even produce alkaline waste – not acidic waste, so treatments that neutralize acid won’t even work there!The first treatment option is preventing acid mine drainage from forming in the first place. The 3 ingredients for dissolved mine waste pollution are: water, oxygen, and exposed, reactive mine waste. Eliminate that combination and you eliminate the waste. This can be done by restoring waste to the holes that were originally dug and capping the system to prevent water or oxygen flow, adding ingredients that use up oxygen before it gets to the mine waste, or even flushing wastes with substances that will coat reactive grains.Unfortunately, the Earth’s surface environment is pernicious. Water gets everywhere and it likes to carry oxygen with it. If you try to bury a mine, water might seep in from the mine itself. If you cover material, a small puncture or erosion of whatever you put on top could open it and even set up the potential of a sudden release. On top of that, moving lots of material is expensive. It’s actually required to refill many mines these days, putting tailings back under ground where they’re no longer exposed, but dealing with tens of thousands of older mines remains a problem.The other responses to acid mine drainage are chemical. Once the dissolved mine waste is generated, chemistry can help deal with it. Chemical based techniques generally can be broken down into two classes – active and passive.Active treatment systems involve actively adding an ingredient that neutralizes the pollution. If you add a base to an acidic stream, you will neutralize the acid, stop the chemical reaction, and force many dissolved toxins and metals to precipitate and form solids. However, this process can be extremely expensive.It requires a constant supply of caustic, alkaline materials – imagine shipping railroad cars full of sodium hydroxide to a site non-stop for centuries. That’s a lot of money and a hazard if the train shipping the material spills. On top of that, the reaction generates waste – dissolved iron will sink out and that has to be removed so that it doesn’t clog the facility. Despite these issues, active systems are used in many places where other methods have not been employed or not found practical.Finally, passive remediation methods take advantage of some natural process that removes acid and pollutants from waters. They’re really neat examples of what you can do if you know some chemistry.The simplest passive method is just dumping a bunch of limestone rocks into the stream; limestone reacts with acidic waters and neutralizes the acid. This can be nice and cheap, but unfortunately it doesn’t work well; neutralizing the acid causes iron to precipitate and that iron tends to cover the limestone, shielding it from future reaction.Modern passive remediation systems therefore are designed to fix this problem through a variety of ways. Sometimes the limestone can be buried, keeping oxygen out of the system so that the iron doesn’t precipitate on the limestone; it does so elsewhere in the setup. The facility you’re looking at here is a design like that – it uses a limestone supply to neutralize the acid and then the water moves into settling ponds where the iron reacts and settles to the bottom before clean water flows downstream.These setups can still need maintenance – this iron was actually pulled from the bottom of one of these ponds to keep it from filling up and it will even be sold to industry as a purified iron source later – but that maintenance needs to happen only every few years or even once a decade or so.In this setup, the construction cost can be high but the maintenance costs are low and spread out over decades. There are sometimes limits to water volume that can be processed or otherwise due to the local geology, but these systems can be quite effective.Finally, there are methods taking advantage of biology. Many of the chemical reactions in these systems give off energy and microbes and plants will take advantage of those reactions. In particular, there are a variety of chemical pathways using the sulfur produced by pyrite chemical reactions that can give off alkalinity or neutralize other dissolved metals. These systems often involve construction of bioreactors or wetlands; places stocked with specific organisms that the water moves through slow enough for chemistry to happen.There are many ways to deal with acid mine drainage; this photo was supplied to us by a consulting company that has built a variety of passive remediation systems throughout streams in the eastern U.S. The main issue of course is…money. Even setting up a cheap but functional system will likely be a multi-million dollar project and even passive systems need plans for long-term monitoring and upkeep. With tens of thousands of mines leaking fluids like these, there just isn’t enough money to keep acid mine waste out of water systems right now.The US Environmental Protection Agency is one of the main organizations that will provide funds to clean up mines that have long-since closed. The EPA is, of course, the organization that ruptured the dam at the Gold King Mine and caused the recent Colorado spill too. That’s the unfortunate reality of this situation; the EPA caused problems, they absolutely deserve criticism for that act, but unless people are paying attention to the mines as they leak and demanding solutions, the EPA can do only so much to fix these mine drainages.-JBBImage credit: Hedin Environmental (with permission)http://www.hedinenv.com/Read more:http://bit.ly/1KnPxqHPrevious posts:http://tmblr.co/Zyv2Js1sav33Zhttp://tmblr.co/Zyv2Js1sgNWkJhttp://tmblr.co/Zyv2Js1skfLuB -- source link

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