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How to clean up a mine: From toxic waste to feeding communities
In 1982, the company managing the Santo Niño copper mine in the Philippines packed up and left. There was little consideration for the potentially harmful legacy of the site they abandoned.
But by working with the local communities, researchers from the Natural History Museum and their Filipino and international partners are well on the way to transforming this former mine into farmland.
Follow the winding roads through the tropical mountains of the northern Filipino island Luzon and you’ll find a community dealing with a toxic legacy.
Just outside the city of Baguio is a former copper mine. At its height of production, it was processing almost 8,000 tonnes of ore per day, but since 1982 it’s been abandoned. This left the local people with a whole litany of problems to cope with.
“There are some issues, for example, like the acid mine drainage,” explains Dr Michael Angelo Promentilla, who is the Head of Waste and Resource Management unit of the Center for Engineering and Sustainable Development Research at De La Salle University, Manila. “The water becomes more acidic as the leftover ore is exposed to water and air.”
“There are some indications of soil contamination by heavy metals. These are the things that have an impact on the livelihood of the local community. In this case, if you have this contaminated soil, this can affect the crops and this could influence the risk of ingesting these contaminants.”
But these aren’t the only issues with former mines. Large patches of land have often been deforested and the soil degraded. There’s also the risk of old mines collapsing, contamination left in the form of heavy metals and pollutants and long-term damage to the local environment.
The community lives on the island of Luzon in the northern part of the Philippines. Image courtesy of Dr Anne Jungblut/Bio+Mine.
This is the legacy of mining that the local communities are left to deal with when they may have experienced only a few – if any – of the mine’s benefits.
This is the situation at the Santo Niño copper mine in the Philippines, which has been the focus of a project called Bio+Mine. This is a multidisciplinary project involving researchers from the UK, the Philippines and Australia, including Michael and researchers from the Natural History Museum.
The team worked with the community to understand what they wanted to achieve with the old copper mine. They then analysed the geology, biology and hydrology of the site, before developing targeted interventions to help the community hit their goal of transforming the area to allow them to grow food that’s safe to eat.
The resulting process could potentially be applied to at least a dozen other legacy mines in the Philippines that still need to be cleaned up.
Starting with the rocks
Mining is an essential industry to provide metals for green technology. But when you think of mines, you may picture huge, gaping pits, massive polluting machinery or toxic pools of wastewater left behind when the mine has been exhausted.
Historically, there was often little thought as to the lasting impacts mining leaves on the environment. As a result there are countless disused mines across the world that were closed before the 1970s and have simply been abandoned.
The team took a multidisciplinary approach, assessing the legacy of the mine from the rocks to the plants. Image courtesy of Dr Anne Jungblut/Bio+Mine.
Going into an old mine, the first thing to assess is the geology. Whilst mines are typically good at recording what mineral was being extracted, historically there have been poorer records when it comes to the waste left behind. Some waste might be fairly benign, other materials include harmful substances such as asbestos.
“It can be a range of different materials,” explains Professor Richard Herrington, one of our geologists who has been working on the Bio+Mine project. “There’s the rock that has been taken off the top and put to one side. There’s crushed rock that maybe didn’t have enough metal in it to be that interesting, so went to a dump.”
“And then there’s rock that’s been processed and ground up really finely to have the metals recovered.”
These highly processed materials are known as ‘tailings’. This material can either be wet or dry and is typically stored in large ponds. Tailings are created by grinding the rock into fine particles in water and then adding certain reagents before bubbling air through the solution to encourage the metal-bearing minerals to float to the surface where they can be siphoned off.
This means that the resulting tailings are frequently contaminated not only with the metal that has been targeted, but also the reagents and other minerals present within the rocks.
Risky reactive metals
The very act of bringing minerals that are stable underground to the surface is one of the main causes of contamination at old mines.
“A lot of the metal mines would be looking for minerals that are, for example, quite reactive when they get into the environment,” says Richard.
“A lot of these minerals form at higher temperatures and pressures deep in the Earth. But when they’re uncovered and brought to the surface, some of those are not in equilibrium with the natural environment and they re-equilibrate by reacting with air and water.”
Chalcophyrite is often found in association with other minerals which can cause issues when discarded. ©Shutterstock/Georgy Dzyura
Generally speaking, the biggest risk comes from those minerals which contain sulphides. For example, whilst extracting copper the Santo Niño mine collected a lot of chalcopyrite. This mineral is a sulphide that's rich in copper, but it occurs with another sulphide called pyrite, which only contains iron and sulphur and isn't wanted. Once the copper-rich minerals were removed the mine was left with a lot of discarded pyrite. Its iron and sulphur then react with oxygen to form sulphuric acid.
But this process can also be exacerbated by nature. There are species of bacteria which effectively eat the sulphides and so speed up the creation of acid.
The acid is a problem as it lowers the pH of the water and can cause health issues if consumed. But it can also kick off a chain reaction. Acidic conditions cause other potentially harmful metals and elements to leach from the rocks and get into the water and environment. These are then drawn up by plants and animals, contaminating them as well.
Low-cost solutions for cleaning water
The Bio+Mine project has been working on ways to mitigate these issues.
First, the team visited the site in the Philippines to run tests on the water and material left behind. They sampled water both above and below the mine and in the waste dumps to see how the chemistry changes across the site.
By building up a chemical fingerprint of what this water looked like, they then recreated the contaminated liquid back in the labs in London. This allowed the researchers to figure out how to, for example, increase the pH and remove excessive amounts of copper still present.
Anne (right of picture) has been looking at the microbiology of the water and soil to figure out how these species have been impacted by the mining. Image courtesy of Dr Anne Jungblut/Bio+Mine.
The researchers first tested a novel way to remove the metals using bacteria. Whilst this method was successful, unfortunately it was likely to be too expensive. Instead, the researchers in the Philippines tested an alternative low-cost technology that uses a simple filtration system using locally collected limestone.
“When the limestone touches the acid mine drainage, there’s a reaction,” explains Dr Arnel Beltran, a chemical engineer at De La Salle University, Manila.
“It increases the pH of the water, and when this happens some of the pollutants or heavy metals that are dissolved in the water are precipitated or absorbed by the limestone itself. Basically it reduces the pollutants present and increases the pH.”
This is an achievable remedy for the communities that are living with the legacy of the mine. It helps not only those who rely on this water for drinking and agriculture, but the reduction in acidity of the water can also limit the amount of other harmful elements leaching into the surrounding landscape.
Biological impacts
Another aspect of the material left behind is the rock and soil that has been scraped from the surface and moved to a different location. In the past, little consideration has been given to how this material is managed, but a growing library of research is showing how soil is a living, thriving ecosystem in its own right.
“Soil is a living environment,” explains Dr Anne Jungblut, a microbiologist at the Natural History Museum who has been working on the project. “So if it’s moved somewhere else and it’s in different conditions, then it changes.”
“For example, it might get blown away or it might dry out. This means that there is the question of how to manipulate it so that it supports the growth of vegetation again. Then there’s a question of what the community wants to plant.”
Some samples of the microbiology were analysed in the Natural History Museum, London. Image courtesy of Dr Anne Jungblut/Bio+Mine.
To figure out the health of the soils at the site the team did several biological surveys, including looking at the species of plants and earthworms present. But the key surveys carried out focused on the microbiology of the soils and water.
They found that whilst the species of microorganisms were pretty much the same regardless of where the samples were taken, the communities were different. Those sites that were most contaminated had a higher proportion of microorganisms which were able to, for example, cope with elevated copper and acidic conditions.
Tracking the differences in these microbial communities over time could allow for microorganisms to be used as a bioindicator for how much rehabilitation a decommissioned mine needs.
Could plants help clean contaminated soil?
Microorganisms might play another key role in helping old mines recover. The team have been conducting experiments looking into how plants can take up potentially harmful contaminants and how this could be facilitated by bacteria.
Known as phytoremediation, some plants can clean up soil and water polluted by hazardous contaminants as they draw it up into their tissues. For example, sunflowers are known to extract arsenic from the soil in which they’re growing.
Filippino collaborators are now trying to figure out if they can facilitate this process at the copper contaminated mine. The plan is to inoculate the roots of plants with microorganisms sampled from the site that have an advanced ability to remove the metal from the soil.
“The hypothesis is that inoculating plants with a bacterium that can somehow survive copper might make the plants grow better,” explains Anne. “Or it could help the plants to take up more of the copper.”
“Basically, we’re looking at beneficial microbes as a way to enhance the uptake of metals or the growth of plants. And we’re still working on the results of that.”
After analysing the soil for contamination, experiments are underway to explore which plants grow best and if they can be used to remove the toxic elements. © David Guilingen/Bio+Mine
Because of the potential for plants to draw up hazardous contaminants, local communities have to be careful about what they’re growing in these soils. This is another instance in which the Bio+Mine team are helping.
Depending on what the local communities want to use the land for, the researchers have been able to advise which plants are the safest to grow. For example, if the land is too contaminated to grow food crops, then they can advise on other economically useful plants such as chrysanthemums, which are grown for the Manila cut flower markets and are particularly good at phytoremediation.
This means that the community can still make money from the land whilst as the same time helping it recover, so that in the future they’ll eventually be able to grow food.
Community first
The final, and most important aspect when it comes to cleaning up a mine, are the people living with its legacy. All activities and interventions must be informed and led by the local communities.
When working at the old copper mine in the Philippines, the team collaborated closely with the local village not only to allow them to work on the site, but critically to inform the science that was being carried out.
“When we first visited the community they are very sceptical and hesitant towards us because they have already experienced other people going to their community to do research,” says Michael. “Some were visiting to check if they can reopen the mine, others collecting data and then not returning.”
“That was the main challenge. But we were able to contact the local government and communicate with the barangay captain – the head of the community – and we were able to explain to them what our aim was and what are the things that we wanted to do.”
Before starting any work, the team worked closely with the local community to figure out exactly what it was that they wanted to achieve. Image courtesy of Dr Anne Jungblut/Bio+Mine.
Over the course of the project, the researchers talked to about a third of the 1,500 people who live next to the mine to find out exactly what they want to do with it. Many wanted to be able to create a farm on the site. This then informed the team in part as to what they needed to research and monitor.
“They’re using waste from their animals and they’re mixing it with other vegetation to create a much more sustainable, circular system,” explains Richard.
“So, that was built into parts of the experiments we were doing.”
Future impact
But that’s not the end. The impact of the mine will continue to be felt for years – perhaps even decades – to come. There will need to be more monitoring to assess the outcomes of the interventions on a long-term basis.
As part of this, Richard and Anne have applied for more funding to take the project that one step further.
“We want to empower the people to monitor these implementations going forward,” says Richard. “We’ve given them some advice, but we need to give them the tools then to be able to monitor it themselves.”
They also want to see if the interventions developed for this site can be applied to other mines in the Philippines. Eventually, the goal would be to develop a toolbox of interventions that mining companies can put in place to make sure that local communities aren’t left to deal with environmental fallout of old mines.
“I think we fleshed out what it is we need to know about a site that will enable us then to plan how to better devise a future approved, people and nature positive mine,” says Richard.
“A solution for a site that’s going to be used by a set of different actors, from the mining company to the local people that results in a regenerated site, ready for a sustainable future.”
