Mining to clean up our… mining?
The ultimate juxtaposition
Re-mining old mine waste. That’s a welcoming idea, isn’t it? In fact, it makes the words sustainable and mining actually work together.
Tungsten, tin, indium, silicon – some of the key elements making up these words you are reading right now (literally). Taken from the ground, now in your hands, unfortunately they’ll likely end up on the ground again soon, returned to the earth from whence forth they came. Just with a little extra emission on the side.
The LCD screen. A friend to many, a foe to many.
The tin? It probably came from a large body of granite rock containing ‘economically viable’ amounts of the mineral cassiterite – formula: SnO4. It’s also one of the few metals which have been traded by humans for more than 5,000 years.
So that means for 5,000 years we’ve been digging up the ground, taking a little bit of cha-ching tin ore from each load, and putting the rest of the destitute into nice little ‘waste’ rock piles elsewhere. That’s the general gist of mining, and it always has been. Let’s not worry about that waste pile though. After all, it’s just natural rock. Sure, it has some elevated levels of commodities, but my century-old refining method just isn’t good enough to extract tin from rock at a grade of <0.35% tin-to-rock.
And what about the environmental concerns from these mine “tailings”? Well when uneconomical rock with elevated levels of particular elements is concentrated in one place and exposed to atmospheric reactions, things can go a bit awry for the natural environment.
When tailings attack
Ore sulphides oxidise and produce sulfuric acid, heavy metals are mobilised, thick algae blooms. It becomes inhospitable for most life, and the ecology suffers all the way downstream.
It may look pretty, but you don’t want to drink that.
The residents at Royal George in Tasmania were told not to, on the premise that the old Brookstead Tin mine tailings (pictured) in their backyards was (and still is) making the water, well, blue.
And green. And red. 36,000 m3 of waste rock dumped between the 1880s and 1928, when the tin mine was operational, now excretes 60 times the maximum safe level of arsenic in its drainage waters.
But don’t forget – humans are smart. We work towards solutions for problems. We can treat mines and their tailings to neutralise acidic runoff, or immobilise heavy metals – whatever the problem may be. There are plenty of examples of successful site rehabilitations around the world, and Australia is in fact one of the world’s leaders when it comes to acid mine drainage (AMD) prevention (spending ~$530 million per year). But it isn’t cheap; at $100,000 per hectare, treatment is almost tantalising as a process to rely on.
Is the best defense a good offense?
Bringing me back to the ultimate juxtaposition: can sustainable mining – the remining of old tailings – be seen as an opportunity for cost-effective mine tailing rehabilitation? Our recovery rates – dictated by the latest in milling, processing and refining technologies – are constantly increasing; we are able to extract commodities from ore grades which would have been seen as economically unviable a century ago.
What this means is many of those old waste piles are being targeted for recoverable commodities, especially strategic metals of the modern age found in your LCD screen, like indium. Brookstead tin mine dumped the last of its tailings nearly 90 years ago. If not more tin, could it be that its blue-stained boulders are rich in high-demand strategic metals today?
If Royal George tailings doesn’t hold potential, perhaps some of the 50,000 other abandoned mine sites in Australia will.
And the upsides of remining waste? Old tailings piles’ sizes and concentrations are reduced; there is less need to set up new and expensive mining operations; environmental degradation can be mediated in a more cost-effective way.
Of course, current technicalities need to be overcome. But the future is promising; older tailings hold increasing opportunity as technology improves. Coal, tin, cobalt, lithium – the list goes on. When the environmental and social impacts become too costly, and as resources become more and more depleted, the appeal in the concept of sustainable mining ever grows.