Mining is an all too often wasteful industry. It's also a polluting industry. However, as investors and the community in general increasingly pressure the industry to fix these issues, some companies are rising to the challenge.
It's somewhat ironic that as mining searches for and digs up valuable new resources, it is often simultaneously spewing out potential resources at the waste end of the operation. Tons of some rare earth minerals for example are locked up in waste dumps because it simply isn't (or wasn't) economical to go back and extract them. Either that or they're too toxic to risk handling without expensive, and advanced, technology.
The Centre for Mined Land Rehabilitation, Sustainable Minerals Institute at The University of Queensland in Australia produced a report in 2019 as part of a project on the 'circular economy' in relation to mining. Their estimates around mining waste are interesting, and worrying. Namely, globally large-scale mining projects – some 3,500 of them – churn out one hundred billion (100,000,000,000) tonnes of solid waste between them every year. Translated to imperial tons, that's over 110 billion tons.
Now, if we were talking about everyday, ordinary household waste it would still be a concern but we're not. We are talking about billions and billions of tonnes of often highly toxic waste. Many of the chemicals used to process ore are dangerous and aren't recovered from the waste before it's dumped.
Incidentally, speaking of household waste (and for comparative purposes), globally we produce around 1.8 billion tonnes (2 billion tons) of it a year or about 54.4 tonnes (60 tons) per second. global construction industry is predicted to double their waste to 2 billion tonnes (2.2 billion tons) per annum by 2025. Agriculture produces around 1 billion tonnes (1.1 billion tons) of waste globally each year. Both are considered highly wasteful industries yet their figures don't even begin to compare to mining's 100 billion tonnes.
Furthermore, it's becoming increasingly apparent that current methods of collecting and storing mining waste are not an ideal long-term solution. Rather they're an economically unfeasible, environmental time bomb waiting to happen. The January 2019 disaster in Brazil at one of Vale's operations has highlighted this yet again. Unfortunately, waste management issues are only going to increase as the need for commodities like rare earths escalates and most in the industry agree something more needs to be done sooner rather later.
What The Industry Is Already Doing
Reprocessing tailings dams on operational projects is already common practice in the industry but usually only IF there is enough money to be made from doing so. A good example of this is going back to treat polymetallic tailings produced by gold extraction when there are economic quantities of copper, lead, zinc, cobalt and nickel.
When it comes to historic waste the situation unfortunately isn't as clear-cut. Quite often, these old waste dumps are an unknown quantity and as such, present some problems. Before any attempt can be made to reprocess one, a resource calculation needs to be done. That costs money. Then the findings have to be presented as a business case to potential investors.That too costs money. Add in the processing costs and ultimately, if at the end of the day there isn't a profit to be made, the waste will continue to sit there. Also significantly – an EIT KIC Raw Materials Re-activate project closing workshop held in December 2019 estimated that only around 5% of waste dumps in Europe currently contain enough economically viable minerals to warrant reprocessing them.
So what does one do with the remaining 95%?
Whilst they may not be economically viable in terms of mineral extraction, many do need to be cleaned up (sanitised) because they contain significant amounts of residual sulphides. When these sulphides oxidise it produces acid mine drainage, a serious environmental problem.
Sanitising waste dumps that contain millions of tonnes of material is an expensive exercise though so it invariably doesn't get done until or unless the situation becomes critical. Companies focus instead on interim measures like containment and the capture of whatever leaches out, which brings us back to where we started. Namely, that these are not sustainable and that cleaning the stuff up so it can be put back into the ground as clean fill or safely reused for other things is by far the best solution all round.
Even if extracting minerals from a waste dump isn't profitable in itself, there are still opportunities for the right mind set. It's a case of looking at it as a multiple win win situation. If a waste dump needs to be cleaned up (most do) and it contains enough of a commodity that, if recovered, would cover costs and perhaps even turn a small profit, then it becomes a combined sanitation and value recovery exercise.
This is exactly what happened at the Kilembe copper mine in Uganda where the tailings are typically around 80% pyrite and cause acid mine drainage. To avoid ongoing problems, the company ran the tailings through a tank bioleaching process to convert the sulphides. During the process, they were able to recover some of the cobalt that was in the tailings. The project was upscaled to convert all 900,000 tonnes of stored tailings with enough cobalt being extracted to pay for the process. Unfortunately though this will usually only be done when companies can expect the same results as Kilembe and that's not always going to be the case.
The third approach to dealing with waste reprocessing is to consider it an exercise in sanitation rather than a profit-making venture. The object is to find economical ways to clean the waste so it's not a potential environmental hazard. If re-processing to remove viable minerals and get rid of sulphides does this (as was the case at Kilembe), and works out to be cheaper than traditional sanitisation methods, more companies may consider doing it even when there's no profit in it.
Why would they do it if they can't make money or at least cover their costs?
One only needs to consider the expense of dealing with the consequences of acid mine drainage, tailings dam failures, and so on, to see why cleaning waste to stop it becoming a hazardous bone of contention is a very good idea. It's doing damage control before the damage is actually done. Vale's recent experiences could well prompt more companies to consider it in this light! The Brazilian miner is staring at lawsuits, class actions and a cool $4,954 billion US in costs and lost revenue in the wake of its Brumadinho tailings dam failure. Some of its employees are also facing criminal charges. If only they'd treated the tailings instead of storing them….!
That's the doom and gloom side of the story but as the saying goes – every cloud has a silver lining. Spurred on by consumer, investor and public concerns, companies both within and outside the industry are turning their attention to 'recycling'. It's all part of the 'circular economy' we're going to hear a lot more about over the next few decades. Wikipedia explains it well – "A circular economy …is an economic system aimed at eliminating waste and the continual use of resources."
Is Recycling Alone Enough For A Circular Economy?
In an ideal circular economy, companies will be extracting useful minerals previously considered economically nonviable from their waste. This will help reduce the amount of new ore that needs to be dug up and processed, with flow on reductions in new waste.
At the same time, they will also be removing the dangerous chemicals, potentially for reuse whenever possible, getting rid of sulphides, and leaving only clean 'dirt' behind. This clean and dirt should then be able to used as part of the mine's rehabilitation post mining or for a number of other purposes. Sounds ideal in fact!
If companies like Comstock and its partners Oro Industries and Mercury Cleanup are any indication then some in the industry are moving in the direction of circular economics. The Nevada-based company is looking at ways of recovering mercury from tailings dumps. Mercury is one of the banes of mining, including artisanal gold mining.In the past, reports have found this sector of the industry alone uses some 1000 tonnes (1.1 tons) of it. Therefore, any safe and effective way to remove and recycle mercury from waste should get the industry's attention in a big way. Comstock is planning to use their Comstock Lode gold and silver deposit as a crash test dummy using technology developed by Oro and Mercury Cleanup.
The Comstock Lode is famously the US's first major silver ore deposit, and also the richest. It was discovered in 1859 and subsequently found to contain significant amounts of gold as well. Over its lifetime, the mine has used some 15 million pounds of mercury and the company plans to treat this in a new pilot plant being constructed with its 2 partners. Should the process pan out, it could play a significant role in how the industry deals with an ongoing and toxic waste issue.
Also on the topic of re-purposing mining waste….
We briefly looked at some of the rare earth minerals and where there are currently easily accessible stockpiles of them in this article. We also posed the question Are we mining the wrong things? in another article. Our article on stone paper explored one way in which some of that construction waste mentioned above is being put to good use. Some companies are working in conjunction with local communities to recycle mine water as we discussed in this series of articles:
Innovative Solutions For Solving Water Supply Problems
Mine Water Management In Africa, Japan, And The US