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Tomra's machine separates valuable material from low-grade rock

Can mining ever go green?

Image credit: Tomra

A quarter of carbon emissions come from mining, but that isn’t the industry’s only environmental challenge.

Two hundred metres below the surface of the Colombian Andes, a row of pews face a gigantic illuminated cross carved into the rock. The Zipaquirá Salt Cathedral is one of the country’s most striking tourist destinations. Constructed in the 1950s in the site of a former salt mine, it draws tens of thousands of pilgrims every year. As the faithful visit the former mine for the forgiveness of their sins, is there a lesson to be learned for miners elsewhere?

The extraction industry does not have the best reputation, especially in terms of environmental and social sustainability. In January this year, at least 248 people died in the Brumadinho disaster in Brazil’s Minas Gerais region after a dam containing tailings (waste) collapsed, and the industry is linked to numerous environmental and social problems around the world. What’s more, a recent United Nations’ (UN) report found that 26 per cent of the world’s carbon emissions stem from extraction and early processing of metals and other minerals.

However, in the last few years the industry does seem to have started taking environmental sustainability seriously. A number of initiatives have been launched by national and international bodies, and new technologies have been introduced that could make mining cleaner and greener.

“In Cornwall, you have kids BMX-ing on the old tin mine tailings,” says Professor Karen Hudson-Edwards of the University of Exeter. “While they do make for good bike ramps, there’s a risk those piles could contain arsenic and other toxic materials.” Hudson-Edwards studies mine waste from current and former operations around the world. In Cornwall, for instance, she has studied the piles of waste left over from the county’s defunct tin mines to assess the quantity of hazardous materials they contain.

Through lab analysis, she and her colleagues assess the toxicity being released from mines and provide guidance on remediation. If, for instance, they discover a high level of acidity in nearby rivers and lakes that have emanated from a mine, they can recommend putting systems in place to raise the pH of the water.

Finding ways to clear up this kind of mine waste is just one of the many problems facing the industry. There is a huge amount of complexity in making current and closed mines ‘sustainable’, with no silver-bullet solution to solving all these problems.

Hudson-Edwards believes that the question needs to be tackled right across the mining value chain. This starts with exploration, mine planning and construction, then mineral extraction and processing, before drawing up sustainable plans for closure and post-closure.

Let’s consider what sustainability might look like at different stages of the mining value chain.

Prospecting for minerals is an activity fraught with financial and environmental risks. Traditional prospecting can require the exploration company to strip back surface area in forests, mountain ranges and deserts to explore whether minerals may be found below. Very often, they come back empty-handed, having caused environmental damage for no purpose. However, new forms of high-tech prospecting reduce that risk.

Lucy Crane is a senior geologist at Cornish Lithium, a firm set up in 2016 to explore the English county’s lithium reserves. Lithium is a metal that is essential for electric vehicle batteries and is relatively abundant in geothermal waters in the region. Crane stresses that the company has been keen to follow environmental and social best practices when exploring for deposits and minimise unnecessary drilling.

It has achieved this by using a sophisticated combination of satellite imagery, drones and 3D mapping of areas below the surface. Given its extensive mining history, Cornwall has over 200 years of maps of former mines. Using modern mapping technology, the company has used these historical data sources (written on paper or even hand-painted on animal-skin vellum) to assess where there are likely to be large deposits of lithium dissolved in geothermal waters. This mapping has saved enormous amounts of trial-and-error exploration. The firm has also focused on collaboration with local communities, the government, and academia to ensure that local people are involved.

Britain's existing tunnels

New life for old mines?

If you could look below the surface of Britain you would find an extensive network of shafts and tunnels from former coal mines. Since the UK abandoned coal mining, most of these have sat idle and many have flooded with groundwater, explains Professor Jon Gluyas of Durham University. At present, the Coal Authority must keep this water circulating to prevent collapses. But what if that water could be used instead?

Every kilometre you dig below the surface of the Earth, the temperature increases by around 25°C, and Gluyas believes that heat could be very useful. Even the UK’s deepest mines aren’t much deeper than one kilometre, and mine water is typically at around 12-16°C, but by using a system of heat pumps and heat exchangers, that water could provide a useful and energy-efficient means of heating homes.

If water from Britain’s mines could be pumped to the surface and passed through this kind of system, energy could feasibly be extracted from it to provide heating and hot water for entire towns and villages – before the cooler mine water is returned underground to naturally warm up again.

The advantage is that countless towns and villages are sitting above former pits – so their residents could get all their heating from those former coal mines.

And, it’s been done before. Gluyas points to towns in Canada and The Netherlands which have already set this method up successfully, and a similar scheme is being developed in the Welsh village of Caerau, near Bridgend.

Once likely sites are selected, the firm will “drill water boreholes into permeable geological structures to intercept the fluids at about 1km deep. We’ll pump this water up to a processing plant at the surface which will have the footprint of a medium-sized supermarket. There, we will extract the lithium from water, and the rest gets injected back underground.” This way, she says, their operations will have far less impact than lithium mines elsewhere, which depend on evaporation in large open-air basins.

Picture an open-cast mine, with huge trucks crawling across the landscape like giant beetles pumping out diesel fumes. That image may soon be a thing of the past if mining conglomerate Rio Tinto’s plans are anything to go by. A spokesman for the business says it has reduced its emissions footprint by almost 30 per cent since 2008 through a range of innovations.

“For example, at our iron ore operation in Pilbara, Western Australia, we have embraced autonomous technology to improve efficiency and reduce our impact on the environment. We now run the world’s largest robots: 2.4km-long trains, which operate between our mines and ports, without a driver, in fully autonomous mode.” He says the firm hopes to reduce emissions from its haul fleet even further by using electric vehicles.

There is also the question of powering mines. Many operations continue to depend on polluting fossil fuels to generate electricity to run drills, provide light, and so on. In many ways, renewable energy sources are ideal for running mines, as they don’t require frequent deliveries of fuel to remote locations. Christopher Sheldon, practice manager with the Energy and Extractives Global Practice of the World Bank, points to the example of Chile, where “18 per cent of all mines are using renewable energy and the target is 70 per cent by 2050”.

‘18 per cent of all mines are using renewable energy and the target is 70 per cent by 2050’

Christopher Sheldon, practice manager, World Bank

When rocks and rubble are removed from a mine, they typically go through four stages of initial processing. First, they are crushed, then they pass through a hopper that gradually feeds the broken-down rubble through a screening and washing machine. Next, they are fed into a mineral-processing mill that grinds out no- or low-value rock and separates it from useful material. This is then sent on to be further processed and manufactured.

According to 2018 research, upwards of 50 per cent of energy used in a mining operation goes on the ‘grinding’ stage of this process. This is time-consuming and inefficient, since very often rocks contain nothing useful.

Fortunately, there are new technologies that aim to make this process more efficient and less wasteful. One is a separation system offered by Norwegian firm TOMRA. The company has developed a machine to be used at mining sites that incorporates a variety of sensors to assess the mineral value of a piece of rock. A spokesperson for the firm explains how it works.

“Input material is evenly fed via a feeder over a transition chute onto a conveyor belt. Then, an electric X-ray tube creates broadband radiation” to penetrate the material. “If the sensor detects material to be sorted out... the detected materials are separated from the material flow by precision-directed jets of compressed air.” Rejected rocks are pushed out of the grinding process and can be sent to waste. And it’s not just X-ray scanning that is available – the firm also has sensors to pick up on colour, transmission and electromagnetic properties as well as size, shape and structure to assess if the material is worth grinding or not.

By minimising the amount of material to be ground down, mining firms can significantly reduce the amount of energy used to get to the pure material and cut their carbon emissions too.

The final part of sustainable mining is to think about closure and post-closure management. Once again, many mines traditionally took little or no responsibility for the environmental and social management of the area once they’d tied up operations. But this is changing too.

Take the Buccleuch site in Scotland. It was set up as an open-cast coal mine, yet the firm behind the mine collapsed during operations and abandoned the site. Once upon a time, this might have simply left a vast scar on the land, yet the owners collaborated with local government to restore the site. Holes have been filled, and trees planted across the area. More significant, though, is the building of a pumped storage hydro site, which makes use of the layout of the pit – the former coal mine will, once the project is complete, be used to generate renewable energy.

Meanwhile, in France, Rio Tinto reports that it is “trialling a passive biological process for water treatment” at one of its closed sites “through the design, creation and maintenance of a sustainable wetland environment instead of a chemical water filtration plant. Not only will this dramatically improve biodiversity, but it also removes the need for continued operation and maintenance activities.”

Hudson-Edwards of Exeter University argues that the mining industry needs to face up to what has happened in the past and acknowledge mistakes that have been made when it comes to environmental management. Nonetheless, she is optimistic about the sector: “Knowledge of good practice is out there – we just need to ensure that it is really followed.”

On a global scale

Climate-smart mining from the World Bank

Whether it’s electric car batteries, solar panels or wind turbines, our growing taste for green technologies introduces a parallel demand for the materials to make them. Lithium is needed in lithium-ion batteries, and various ‘rare earth’ metals are needed in the magnets used in wind turbines.

It would be ironic if the extraction technologies used to source these materials depended on diesel and caused further environmental damage. And this is why the World Bank launched its new Climate Smart Mining initiative. A handful of governments and mining firms have pledged their support to the initiative, which encourages entirely sustainable mining practices.

Christopher Sheldon of the World Bank lists some of the practices the initiative encourages:

• Supporting the integration of renewable energy into mining operations

• Supporting the strategic use of geological data for a better understanding of “strategic mineral” endowments

• Forest-smart mining: preventing deforestation and supporting sustainable land-use practices; repurposing mine sites

• Recycling of minerals: supporting developing countries to take a circular economy approach and reuse minerals in a way that respects the environment.

 

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