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Environment

Mine tailings: reprocess, recover & recycle

Why we'll be hearing an awful lot more about the reprocessing of tailings from mining over the coming years

There has been much talk of tailings this year.

While the technology has been available for some time to allow tailings to be stored in different ways – dry stacking, thickened tailings, paste backfill –  there has, up until now, been little variation from the norm (deposition as slurry in a dam).

Many of the mining companies I’ve spoken to have said that the dewatering technology and logistics required to properly implement dry stacking are prohibitively expensive. However, it is reasonable to assume that, going forward, cost will no longer be an acceptable excuse.

Stakeholders, including investors, are now putting significant pressure on miners to be more socially and environmentally responsible. The ICMM will also publish a global standard for tailings management later this year.

These factors, combined with enhanced interest from the public, mean that every mining company, regardless of size or status, will need to allocate more budget towards tailings management if they wish to retain their social license to operate.

So, how do we make that investment wisely, and how we can recover, or maybe even generate a little revenue from it (silver linings, right?)

Sizing up the opportunity

The ICMM estimates that there are around 3,500 active tailings storage facilities (TSFs) across the globe. The number of inactive facilities is currently unknown due to poor record keeping, although it is safe to assume that there are many.

According to research by mineral processing firm Metso, the quantity of tailings generated each year by the copper industry alone amounts to 2.9 billion tonnes, and iron-ore production adds a further 1.6 billion tonnes.

These are just two metals from the plethora mined globally but, using these numbers, we can start to gauge the scale of the problem.

If global copper production were to remain at the same level for the next 20 years (it won’t, tonnages will increase sharply as grades decline), then 58 billion tonnes of tailings would be produced by that sector alone between now and 2039.

I shudder to think what the actual number will be.

If one cared to look up historic copper production figures and average ore grades, then it would also be possible to estimate the quantity of tailings that reside in legacy facilities.

I’ll be honest, I have better things to do with my time. However, we know that copper has been mined commercially for well over 100 years. We can therefore assume that hundreds of billions of tonnes of copper tailings are currently sitting in TSFs across the globe.

And that’s before we even start to look at tailings generated through other mining activities.

Acceptable metal recoveries from mineral processing vary depending on ore grades and characteristics. However, today, at some mines, it is now possible to recover 95% or more of the contained metal. Thirty or 40 years ago though, processing technologies were generally much less efficient and average recoveries were lower. Metal prices were also much lower.

Metals that weren’t recovered were sent to storage along with tailings. This means that the grade of metals residing in legacy tailings is, in some cases, very high… High enough to make their potential recovery economically attractive when metal prices are right.

Reprocess tailings. Really?

Yes, really.

If the technology exists today to remove up to 90% of water from mine tailings and, if a mining company is going to make that investment anyway to secure its future operations, then frankly, it is irresponsible not to consider reprocessing the tailings that currently sit in its TSFs.

Obviously, the economic viability of reprocessing will vary on a case-by-case basis, but the potential benefits are huge.

The biggest of all is safety. By removing tailings from a TSF, pumping them back to the concentrator and reprocessing them, this not only gives the possibility to recover residual metals, but also water.

Water remains one of the greatest risks to mining operations globally. It is essential to the extraction of metals, and can be very expensive to source, treat and recycle or replace. Water is also difficult to keep in a closed loop, and the loss of water and, potentially, minerals contained within it as solids (tailings) or in solution (acid mine drainage) can be very dangerous indeed.

By reprocessing tailings, dewatering them and then storing them in a dry stack, mines can remove some of the economic, environmental and societal risks associated with tailings stored in slurry.

The water recovered can then be reused, helping to drive down abstraction and logistics costs. As 70% of the mines operated today by the majors are in water scarce regions, that is a business opportunity in itself.

Some of the biggest miners pay hundreds of millions of dollars a year to replace water lost to evaporation. Imagine how much money they could save?

And now we’re back to metals recovery.

I’m going to use a theoretical example here. Say a copper mine produced 1Mt of metal in 1999 at 90% recovery. The remaining 10% of copper, around 111kt, went to tailings. If the average copper price in 1999 was US$1,500/tonne then that 10% represented US$166.5 million of metal.

Fast forward 20 years and at today’s price, US$5,842/tonne, if that material could be reprocessed and an extra 2.5% of copper recovered (or more), then that’s an additional US$162 million+ of revenue. And that’s before we look at the value of the water that could also be recovered.

Yes, that number would need to be offset against the capital cost of new equipment if required, higher processing costs etc. but, given that average ore grades are declining and operating costs are rising, there are now some cases where the reprocessing of tailings works out cheaper than processing virgin material.

Food for thought, no?

Business as usual is not an option

If mining companies want their businesses to be sustainable, then they will seriously have to look at ways to clean up their TSFs, both active and inactive; the sooner the better.

The reprocessing of tailings offers a potentially profitable way to do that, and something tells me we’ll be hearing a lot more about it over the next five years.

 

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