Materials handling Left to be discovered
What Jensen and her colleagues are trying to determine is how hazardous tailings can be repurposed in a safe, useful and sustainable way. Two definite requirements are that these tailings come in big volumes and that they are fine grained. “We can’t use something that comes from a rare industry in a single place,” she explains, “and we need something that preferably has some kind of reactivity to enhance the performance of the concrete.” Though that is not yet a main priority, she hastens to add.
In order for cement use to be reduced, and a sustainable alternative to fly ash be found, the construction industry needs something that is uniform in quality and comes in large volumes around the world. “That’s one thing we’re investigating,” she notes, but “waste is very different from one mine to another.” However, considering the vast mines peppered around the world in Chile, Australia and Canada, to name a few, “we do have some very big mines that could potentially supply the rest of the world with what is needed”. The positive news, then, is that mine tailings are produced on an immense scale and only a few with “good performance levels” will be required to help plug the gap in SCM availability. As with any research taking on an industry-wide problem, the path to clear and transferable results never did run smooth. While we know that value can be extracted from tailings, and that finding a safe way of doing so is imperative to meet growing demand, much of the waste is toxic, and the remaining percentage usually requires testing and treatment before it can be used. “Tailings often contain residual valuables or heavy metals, which are toxic,” Jensen notes. “This can pose as a threat in terms of how we use it in concrete.” The proposal, then, will be to extract all valuable before the tailings are deposited, and to extract as much value from tailings as possible to save time, money and a cost to the environment.
Supply and demand
The demand – and price – of raw materials has increased steadily for decades, as have the requirements of new and environmental technologies, such as renewable energy. Of particular concern, reports Minerals UK, are ‘raw materials’, which include several substances that the UK is reliant on, such as graphite and cobalt. However, while this has generated more waste, and therefore more potential to find useful tailings, the residual value of these tailings has reduced over the years – a paradigm that is likely to shift in future. Mining produces a substantial amount of waste, which is usually deposited in dams, lakes or valleys. “If it’s done in the wrong way, it can harm the
World Mining Frontiers /
www.nsenergybusiness.com
environment,” Jensen acknowledges. In July 2020, for example, heavy downpours in the woods around a tailing dam in Myanmar resulted in the deaths of approximately 200 miners. The tailing dams, often unstable in structure and built in remote corners of less developed countries, put those who might be scouring the waste for jade or other valuables in grave danger. With an urgent supply chain crisis, the threat of climate change and the reality that vast amounts of toxic waste are being produced and deposited on a global scale, it’s clear why the likes of Jensen are committed to finding a solution that reduces this waste. Simply using these potentially toxic materials in future building projects, or depositing them into areas of natural beauty, does not sound overly appealing. This is what Jensen and her team are set to investigate. “One thing we can say is that [the concentration of tailings in concrete] would be very diluted.”
5–8%
Of total man-made CO2
emissions
are produced by the manufacturing industry.
DTU
“At the moment, we do not see any difference in terms of the leaching of heavy metals from mortar containing mine tailings compared with mortar with no mine tailings.”
The research conducted so far reveals that improper waste disposal practises have resulted in severe environmental hazards including acidic mine drainage (AMD), dust mobilisation, collapse of waste storage facilities, and long-term effects from metal accumulation in biota and soil contamination. These are consequences that leave a lot to be desired, and don’t make the case for using waste as a simple substitution any easier. “We’d mix a small percentage of mine tailings with other materials, so it would never be a high concentration,” Jensen is quick to reassure. The words ‘toxic’ and ‘hazard’ are best avoided in the thrusts of a global health crisis. “We still have to ensure that they don’t leach into the environment during and after the building’s lifetime.” As for Jensen’s research, there is a way to go before they have any conclusive answers, but the team remain positive. “At the moment, we do not see any difference in terms of the leaching of heavy metals from mortar containing mine tailings compared with mortar with no mine tailings.” It seems ‘waste not, want not’ is a phrase both the mining and construction industries would do well to adopt. The research conducted by the DTU is set to assist the sector on a global scale, and ease pressures on increasingly finite resources and possibly outdated methods of extraction. While the granular details are yet to be ironed out, there is hope, and potentially even value, in what was once thought to be valueless. ●
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