New gold rush flattens Johannesburg's famous mining dumps (2014 Article)
New gold rush flattens Johannesburg's famous mining dumps (2014 Article)
A new gold rush is hitting Johannesburg, literally flattening the South African city whose Zulu name “Egoli” means City of Gold.
Good article that shows how mine dumps can be reclaimed to support human use (drive in) and how re-mining of wastes can be feasible in some cases
I don't know much about gold mining specifically, but I know the way some ores are separated is by crushing rock and essentially sifting off the metal, leaving behind coarse sand that still contains some metal. Processing beyond that is harder, so mining companies do the math on the price of the metal to determine if it's worth it. Often the technology or price changes later on, so previous tailings become economically recoverable.
The most common way I know they recover gold is with cyanide. I'm pretty sure it can be done safely, but plenty of places have banned it for the danger. I'm not sure if I'd trust these companies to do this further recovery with better environmental and human health considerations.
Historically, the crushing, sifting, and sluicing was the way to go. They still use cyanide to extract gold, but it's done in a much more enclosed manner. For instance, they'll put a bunch of crushed rock in huge vats, leach it with cyanide, recover the product, and then either recycle the cyanide or send it through water treatment. Tailings are then stored in a tailings storage facility. For some low-grade ores they'll use an acid heap leach, where they take ore, and pour sulphuric acid over it. I'm not a mine process engineer, but I do know a bit having worked in the industry indirectly.
Env. and human health concerns are always important. Mostly what I wanted to show with this article was that there's sometimes a chance for remining and that can be a good thing in some cases - in this case, they got rid of a waste pile and likely put it further away from people.
Yeah, I suppose if anything, that material isn't going to be dropped right back where they pulled it, so that's going to be a big benefit.
I'm not up on all the chemistry involved, but would either the cyanide process or acid leeching also pull out the other heavy metals that they are concerned about? If so, that should make the tailings at least more inert, right?