With a spate of huge stories breaking in the past few weeks, you might not have caught the massive environmental crisis in northern Mexico that began earlier in August.
According to the Associated Press, local politicians claim that Grupo Mexico, a private mining company in Sonora with a troubling track record of hazardous waste violations in Mexico and the U.S., was slow to report a disastrous fault in its leaching ponds, which hold industrial acid used in the mining process. The spill released around 10 million gallons of acid into the Bacanuchi and Sonora Rivers.
whaaat the FUUUCK
Ok everyone let’s talk about ACID ROCK/MINE DRAINAGE
Don’t let the freaky orange color throw you off, it’s totally fixable. The biggest problem isn’t how to do it— it’s getting the mining company to pay for it. Now that it’s escalated into dumping ARD into the United States I’d say the odds are… well, relatively good. : P
Acid rock drainage is a 100% natural phenomenon where anytime pyrite (iron sulfide- fool’s gold) is exposed to oxygen, it oxidizes into iron oxides (rust). This can happen on its own just via slow chemical reactions. But it’s usually sped up by extremophile bacteria that get their energy by splitting pyrite into rust. Sort of like how plants get theirs from splitting water (using light as a catalyst), but with pyrite.
Why do these bacteria have to be extremophiles? Because cutting all that sulfur loose makes sulfuric acid. Yum! Then the sulfuric acid starts to eat away at everything else in the mine. Most metals don’t dissolve well in neutral-pH water, but dissolve really well in very acidic water. The most common metal in most rocks is iron. So that freaky orange color is… most just rust.
Ok, so that’s the chemistry. Now let’s talk physics! Acid rock drainage is something that happens naturally in some areas whenever there’s pyrite exposed to the surface and/or groundwater. Because any exposed pyrite tends to get eaten away by ARD and disappear over the geological timeframe, the most common time for there to be exposed pyrite is when people cut into rock to make mines, roadcuts, etc. That’s why ARD is a phenomenon mostly associated with mining. Mines are usually below the water table so you have to constantly pump water out. When a mine is abandoned they stop pumping, so it fills up with water and the ARD bacteria start doing their thing. (That’s one of the reasons it’s so hard to get mining companies to pay for cleanup— it mostly comes out of abandoned mines or sections of mines. Ones they’re not making money on anymore. And that’s assuming the company that made that mine even still exists. Sometimes it’s gone bankrupt in the meantime.)
How do you clean this mess up? There are several approaches. Probably the cheapest is
1) Stop the leak, obviously.
2) Dump a bunch of ground-up limestone on the mess to neutralize the acid. It’ll fizz and make bubbles. Super fun.
3) Build a wetland! The two ingredients of acid rock drainage are ACID and OXYGEN. The lime neutralizes the acid. Now you’ve just got to take the dissolved metals in that water (mostly iron, but also heavy metals like lead, cadmium, etc) and un-dissolve them e.g. make them react chemically with something else so that they become a solid again. (Precipitation.) Raising the pH with the lime helps a lot since that raises the pH to where those metals don’t dissolve well anymore. There’s a lot of other complex chemistry that happens in wetlands to help complete that process including complexation with organic matter etc. Bottom line, wetlands are good at scrubbing junk out of water and giving those locked-up metals somewhere to sit in the corner and think about what they’ve done.
There are significant design challenges to pulling off a constructed wetland, like “finding a place where water already collects (so it will actually stay wet) that’s also owned by somebody who’s ok with turning whatever it used to be into a wetland.” Anyway the moral of the story is the science behind cleaning this shit up is easy. It’s getting different groups of people to get their act together and just DO it that’s hard.
*ARD is not to be confused with other more nefarious things that come out of mining, including but not limited to dissolved or powdered ores containing naturally-occurring radioactive metals, cyanide from leach piles (it’s one of the only things that dissolves gold so some mines just make giant piles of ore and trickle cyanide through it— yeah, sometimes it spills, go figure) etc. What we’re seeing here is actually the cute little brother of foul mine discharges.
Additionally, the “20,000 people go without water” thing hits something that discussions on environmentalism often miss. First-world environmentalism was basically started by a bunch of rich guys who liked to go fly fishing, and it shows. “We need our beautiful wild spaces so we can go visit them and be refreshed in our souls!” they said.
This vision of environmentalism has no room for people who actually LIVE in those “wild spaces.” If you live in an urban area where your water needs are met by a giant first-world water treatment infrastructure, yeah, your environmental concerns are going to boil down to aesthetics (and a desire to escape those ugly urban infrastructures that… ensure your survival). But if you depend on the river for food and drinking water, it’s life or death.
Good article with more info on the spill (x)