Planning a safe and environmentally conscious closure of a mine generally starts well before anything has been extracted from the ground.
Veolia’s Industrial Business Development Manager, Mike Russell said this wasn’t always the case.
“Historically, some mining companies viewed closure as ‘lock the gate and walk away’,” Mike said.
“But that’s just not acceptable any more.”
Most mining companies now have comprehensive environmental management strategies as part of their closure plans, and some states in Australia have bond programs that require miners to put down money upfront to cover the cost of cleaning up their sites.
“Mine closure is as much about safely closing the mine as it is about what you do with the land going forward,” Mike said.
This includes returning the land back to a more natural state, rather than leaving a legacy of holes in the ground and piles of waste rock.
In some cases, mining companies can even create a supplementary business out of the regenerated land.
“There are examples in New South Wales’ [NSW] Hunter Valley where the land has been repurposed and specifically planted with crops to allow livestock grazing,” Mike said.
“And in Western Australia, one of the big iron ore companies runs quite large hay plantations, which is used as feedstock for cattle elsewhere in the state.”
Into the void
Water treatment is a vital part of ensuring there are no ongoing negative environmental impacts once a mine is closed, particularly in the case of classic open-cut operations.
If these mines aren’t sealed properly, the voids can fill with rainwater. This water reacts with the residual materials in the mine and becomes contaminated.
Left untreated, this water could contaminate groundwater sources or leach into the environment surrounding the mine.
“Every time it rains you end up with more water you need to deal with,” Mike said.
“You can end up with large volumes of water retained in mining pits that is highly acidic and contaminated with a number of heavy metals and other materials.”
This means the water must be treated on-site or transported to a treatment facility - which is not an easy process when you consider the scale and location of such remote operations.
Once it has been treated to the correct standard, the water is often discharged into the environment or used in agriculture.
Better than the cure
Of course, it’s better to prevent the problem rather than have to solve it. This is the approach of Energy Resources of Australia (ERA), which mines uranium near Kakadu National Park in the Northern Territory.
ERA is planning to stop operations at its Ranger mine in 2021 before closing by January 2026, and Mike said the company had spent years preparing for this.
“It’s about making sure whatever is left is isolated from the wet, tropical environment, so you’re not generating more wastewater every time it rains” Mike said
“It’s a very methodical process to make sure that the contaminants are locked away, and that you minimise the generation of any future contaminated water effluent.”
Contain, control, manage
The work doesn’t always end once a mine has been shut down. Instead, Mike said Veolia works on a number of sites where there is an ongoing environmental issue that has to be managed.
For example, at a coal mine in England, a small amount of groundwater still finds its way into the old mine, despite it being properly closed.
“The water builds up and becomes contaminated, so it has it be dealt with,” Russell said.
“It’s not a huge volume but it does occur year after year. We have a long-term contract to run an on-site water treatment plant that deals with the accumulated contaminated water and treats it to an agreed level so it can be discharged to the environment.
“This could go on for five, 10 or 20 years after the closure of the mine because that environmental risk remains. It requires ongoing management to safeguard the environment.”
Alternative uses
As well as helping to protect the environment, Veolia is also looking at ways to repurpose old mines. For example, its Woodlawn Bioreactor, near Goulburn in NSW, is a waste facility built on a former copper and zinc mine site.
“As a waste management company, we were looking for the ideal opportunity to create a new landfill for Sydney in the early 2000’s,” Mike said.
“We identified a mine that had recently closed, and we saw it as an opportunity to do something beneficial for the local community by repurposing the mine as a waste landfill.”
Since 2004, the site has been capturing methane gas emitted by the waste it processes at its bioreactor and using it to generate energy for about 30,000 homes.
“We’re trying to maximise the beneficial reuse of resources, whether it’s water or waste or energy. It’s that circular economy mindset; we want to repurpose waste materials or even assets like a closed mine.”
- Mike Russell, Industrial Business Development Manager