4.14 Geology to the rescue!
It’s not all doom and gloom though. As we understand what the cause of the problem is, we can apply our geological knowledge to solve the problem, and there are a number of options for fixing (‘remediating’) the problems of acid mine drainage.
The simplest options (at least theoretically) involve neutralising the acid waters by addition of an alkali like limestone (CaCO3) or quicklime (CaO). By neutralising the water with other rocky material, the water loses its ability to transport the toxic material off site. The problems lie with collecting the water in the first place, and what to do with the toxic sludge that results. Neutralising the acidic water means that whatever toxic metals are in the water when it’s intercepted quickly precipitate out into a toxic sludge. How you deal with that sludge is a new problem, but at least it is contained, and can be safely taken away for further treatment or storage, rather than being released into the environment.
Another problem for neutralisation is what to use to do the neutralising – the types of mine sites which are formed from sulphide deposits where AMD is a real problem rarely have handy deposits of limestone close by.
By-products of other industries, like calcium silicates from reprocessed steel slag, have been used with some success – and using the by-product of one industrial process to solve the problems created by another industrial process kills two birds with one stone (or hopefully, no birds at all).