Led by Brendan Duprey, director of the SKRI, the team has found using a mix of grasses, shrubs and trees strategically placed around tailing facilities can reduce the occurrence of windblown air pollutants by as much as 40%. 

Mitigating the amount of airborne dust around mine sites is especially important to nearby residents and local waterways as dust collected from tailings has been found to contain "significant amounts of arsenic and lead," a 2020 report in the Journal of Toxicology and Applied Pharmacology read. 

The article entitled "Early Life Inhalation Exposure to Mine Tailings Dust Affects Lung Development" examined the effects of mine tailings dust exposure on populations living in arid regions. 

The researchers in that study linked dust inhalation with respiratory health outcomes. Citing a 2016 study on a community in northern Chile, the paper suggested: "a considerable increase in the risk for respiratory diseases closer to the two mines, and only beyond a minimum distance of more than 1800 meters, the health impact of the mine dusts was considered to be negligible."

ICMM has also voiced its concern over the particulates blown from tailing facilities. The international oversight organisation seeks to ensure mining companies reduce and mitigate those contaminants through the Global Industry Standard on Tailings Management unveiled in 2020. 

"If not managed properly, tailings can have chronic adverse impacts on the environment and human health and safety, with pollution from effluent and dust emissions being potentially toxic to humans, animals or plants," the ICMM website notes. "To conform with the Standard, operators must use specified measures to prevent the catastrophic failure of tailings facilities and to implement best practices in planning, design, construction, operation, maintenance, monitoring, closure and post-closure activities." 

Wanting to offer a natural mitigation tool, Duprey was inspired by a village near the Aksu gold mine in Kazakhstan. 

"There are about 3,833 people who live there, and they live right next to the tailing facilities. So this dust is blowing around; it poses a serious risk due to the negative impacts of dust," said Duprey. "And they were looking for something to mitigate those impacts. And also, not to be outrageously expensive." 

What is phytocapture? 

Combining data from environmental impact assessments with supercomputer functionality, Duprey and the researchers deployed vegetative barriers around tailings facilities by utilising a process they developed called phytocapture. 

Duprey was inspired by a village near the Aksu gold mine in Kazakhstan

Keeping simplicity at its core, Duprey told Mining Magazine's deputy editor, Georgia Williams, about the process and its benefits. 

"You don't need to overly engineer everything," Duprey said of the process that relies on native trees and vegetation. "Go back to the basics of how we used to do stuff." 

Phytocapture relies on vegetation at varying heights to capture and absorb dust, preventing it from blowing beyond the barrier. Duprey described the waxy leaves of some deciduous trees catching dust and eventually absorbing it. 

Coniferous trees are less absorbent. However, with tight pine needle patterns from the ground to the top, conifers can trap dust, as do the shrubs and the grasses. 

For Duprey, the process comes down to creating canopies of various heights to capture tailings dust at all levels. 

"When you think about how dust is blowing around from a tailing, you have the horizontal blowing of the dust, which means it blows directly off the top and just goes straight across the top.  Then you have dust that rolls down the bottom of [the facility]. And then you have other dust that kind of swirls around in the air, three ways the dust is blowing," he said. "So, you need taller vegetation to capture this higher dust. But you also need low-lying grass to capture the low-lying dust and then something in the middle to capture whatever is blowing in the middle." 

Region-specific 

One tree that Duprey and his team have found to be ideal for phytocapture is the poplar, which is pollution-resistant and grows quickly. However, selecting suitable trees for each vegetative barrier is highly dependent on the locale and what plants and trees are native to an area.

The process comes down to creating canopies of various heights to capture tailings dust at all levels 

 Moreover, the toxicity of the soil where the tailings are located is also a crucial component of foliage selection.

While poplars may be ideal in Kazakhstan and Canada, they are not suitable for extremely arid regions of South America; that's where the site assessment and modelling come in. 

"It's a practical application, the idea of taking science and applying it practically to solve real-world problems," Duprey. 

Over the last four years, Duprey and his team have applied phytocapture vegetative barriers at two mining projects in Kazakhstan and an additional urban site. They are also in talks to deploy phytocapture barriers at mines in Australia and South Africa. 

"We have specific software that we use. We didn't create the software, but we created the technique and the methodology to do everything from the site assessment, collecting the data, running it on the computer in different designs, and then working with the companies to ensure that they plant the vegetation correctly," said Duprey. 

Part of that modelling includes assessing what contaminants are in the soil and tailings, how much a company wants to spend on the barrier and how many trees and shrubs they would like to use. 

"The design depends on the location and the problem," he said. "It is a scientific process that uses raw data from the environmental impact assessment reports to quantitatively suggest different scenarios." 

By using a mix of vegetation, the process can begin capturing the contaminated dust immediately, and those rates steadily improve as the trees and larger canopy grow and mature. 

Over the last four years, Duprey and his team have applied phytocapture vegetative barriers at two mining projects in Kazakhstan

On average, a mining company can expect to reduce airborne dust by 30%-40%, said Duprey. 

"The most I've seen is 38%; that was the most for dust [suppression]," he said. "But for other types of pollution, like ozone, it can be 70% a significant reduction. But still, 40% of the total is a lot." 

Dual benefit 

In addition to reducing the amount of airborne contaminants and toxic dust, the phytocapture vegetative barriers align with ESG goals and can be included in a research or sanitary protection zone budget. 

"In Kazakhstan -and I've done some investigation, and it is the case in some other countries- you're required by law to have a certain amount of the territorial area covered by vegetation, sanitary zone requirement laws," said Duprey. "[So] they have to do it anyway, they'll have like 30% of the territory needs to be covered with vegetation, so there's already a budget for that." 

He also referred to research budgets, which are mandated by some countries. These budgets require mining companies to earmark a certain percentage of their budget to research. 

"And the research budget can cover the sanitary zone protection requirement costs," said Duprey. "So, it saves the company money because they can use the research budget to plant trees because it's part of a research design." 

The phytocapture process can also reduce haul road dust and improve air quality in city settings.

Despite being a promising dust reduction process, Duprey is quick to note that phytocapture is not a permanent, one-size-fits-all solution. 

"It's a mitigating technique, it doesn't solve the problem, it just makes it less harmful," he said.