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Turning mine sites into carbon vaults

Dr Alison Shaw explains how a carbon sequestration project developed and initiated by De Beers at its mines sites, could eventually help to mitigate climate change on a much larger scale

One of the best parts of my job is meeting like-minded people and getting to share in their passion for their work.

In June, my research for a magazine feature on diamond mining led me to David Petrie who handles communications for the De Beers Group. We marvelled over the company’s work in carbon sequestration – formerly known as Project Minera, now renamed Project CarbonVault – and agreed that we would both like to learn more about it.

Fast forward six months and we got the opportunity to make that happen…

Dr Alison Shaw leads De Beers' CarbonVault project
Dr Alison Shaw leads De Beers’ CarbonVault project

Dr Alison Shaw is a senior geochemist at Lorax Environmental Services. A geologist by training, Shaw moved into environmental consulting eight years ago.

Today, she is using her background in research and knowledge of how carbon and water move through volcanogenic systems to help mining companies with their environmental monitoring and waste management programmes.

Shaw’s technical expertise and experience of working both in and alongside various mining companies made her the perfect person to lead CarbonVault.

Which is how we came to be talking to one another on opposite sides of the Atlantic on a very gloomy evening in late November…

“I fully support fundamental research, but I also feel like if we want to change the path we’re on and find solutions, then we need to be a little more proactive,” Shaw told me. “So, this project is very near and dear to me in terms of what it’s trying to achieve.”

Creating carbon-neutral mines

As part of its overall drive towards sustainability, De Beers is working to create carbon-neutral mining operations, and the roadmap for that includes various strategic thrusts.

Some are designed to reduce the carbon intensity of operations through more efficient processes, some to replace fossil fuels with renewable or sustainable energy sources, and some to recover carbon emissions.

Which is where CarbonVault comes in…

The project – which is essentially an R&D initiative – was initiated in 2017. It’s based on the principle of sequestering carbon dioxide (CO2) and locking it away within processed kimberlite (the type of rock in which diamonds are found) as a solid, stable mineral phase.

It’s a naturally occurring process, albeit a slow one, and De Beers is looking for ways to harness the natural properties of its kimberlite mine waste and accelerate the process to negate the effects of mining and help combat climate change.

Shaw explained: “The primary objective is to offset mining emissions. Mining is a pretty energy intensive process so it’s important to manage and mitigate emissions as much as possible.

“Kimberlite is somewhat unique in that it has a high magnesium and calcium content and that means it has a higher ability than most rocks to react with CO2. Kimberlites come from very deep in the earth, so they’re a little bit out of equilibrium with surface conditions and that also means they react readily with CO2.

Natural carbonate veining in a kimberlite rock from Venetia mine. Image: Alison Shaw/De Beers
Natural carbonate veining in a kimberlite rock from Venetia mine. Image: Alison Shaw/De Beers

“As rock is broken or crushed up during mining processes and fresh surfaces are exposed, they react with CO2 in the atmosphere.”

Kimberlites belong to a group of rocks known as ultramafics, which generally contain high levels of magnesium and calcium. This makes them naturally more amenable to a weathering process or chemical reaction known as carbonation.

Shaw explained: “It’s not a property that is unique to kimberlites, but it is unique to the ultramafic rock group as a whole… There are various different commodities that are mined from ultramafic rocks including many platinum group elements, chromite and nickel…

“The higher the magnesium content of the rock, the greater the opportunity for mineral carbonation. The mineralogy of the rock really controls the ability to effectively promote carbonate reactions.”

De Beers is majority owned by Anglo American, the world’s largest producer of platinum, so the technologies developed as part of Carbon Vault could potentially have much wider applications than originally planned.

“This project definitely has high reaching implications,” Shaw told me. “If we can find technologies that are able to promote these reactions more effectively, then De Beers will be sure to share that with the community, because it’s all for the greater good.”

Carbonation, four ways

There are various ways to accelerate mineral carbonation, but Carbon Vault is focusing on four…

“The first thing you need is a source of cations (positively charged ions), in this case magnesium or calcium, which are available to react with carbon dioxide. And the second is CO2, either from exposure to atmospheric CO2, or you might have another source of CO2 that’s at a higher concentration,” said Shaw.

“In the first case, we can apply physical methods to enhance the reaction; there are ways to manage waste that ensure the crushed rock receives higher exposure to CO2.

The research team from UBC setting up the Gahcho Kué field trial experiments. Image: Alison Shaw/De Beers
The research team from UBC setting up the Gahcho Kué field trial experiments. Image: Alison Shaw/De Beers

“For example, you can till the surface of the kimberlite waste, you can spread it out over large areas, or you can modify the amount of water that’s available to promote the reactions.

“We’re also looking at chemical methods to increase the rate at which the magnesium and calcium are released from the rock, in order to promote mineral carbonation. Carbonation is really a weathering reaction, it breaks down the minerals within the rock so certainly, there are chemicals that can be used to try to accelerate that processes.

“Then there are biological methods that use microbes to accelerate those reactions. Microbes can not only increase the rate at which magnesium and calcium are released from the rock but can also draw CO2 out of the atmosphere and into the biomass, thereby providing a source of carbon.

“The final method we’re looking at is using flue gas injection; at some of the mining operations, particularly those in northern Canada, there’s a significant source of flue gas. We’re investigating ways to inject that gas into a pad of processed kimberlite to promote mineral carbonation.

“Flue gas has a very high concentration of CO2 – around 10% – whereas in the atmosphere it’s only present in low concentrations, about 400ppm.

“Those are the four different technologies that were looking at, and it’s very exciting because we’re just starting to get some results back from field trials.”

The technologies are being trialled at different mine sites – Venetia in South Africa and Gahcho Kué in Canada – depending upon the processes used and climatic conditions present.

Each technology stream is being led by a different research group; a team of researchers at Canada’s Trent University are working alongside De Beers on physical enhancement, the University of Alberta on chemical enhancement, the University of Queensland on biological enhancement and the University of British Columbia on flue gas injection.

This truly is a global effort.

The field trial experiments using processed kimberlite from Venetia mine – including De Beers staff and research teams from University of Alberta and Trent University
The field trial experiments using processed kimberlite from Venetia mine – including De Beers staff and research teams from University of Alberta and Trent University. Image: Alison Shaw/De Beers

Harnessing geomicrobiology

Given my recent foray into synthetic biology, I wanted to find out more about the biotechnology thread which is being led by Dr Gordon Southam at the University of Queensland.

“Dr Southam works in a field known as geomicrobiology,” Shaw told me. “For this particular project, his team is working to identify which microbes are responsible for the weathering reactions using DNA analysis. They’re then targeting specific organisms to grow up in a bioreactor so they can be used to promote those reactions effectively.

“The team did some preliminary work, sort of a proof-of-concept, that showed we can effectively increase the rate at which carbonation occurs. That was scaled up for the field trials which were initiated in February 2020 on material from the Venetia mine in South Africa.”

The team added biomass that was collected as films from the mine site and then grown up over several weeks to months, to the processed kimberlite and is monitoring how the rate of carbonation compares to a control sample with no biomass added.

With biological processes, it’s important to target organisms that thrive naturally in the mine environment, because most have certain conditions that they like and don’t like. If the microbes aren’t compatible with conditions at the site where the technology will be implemented, then the carbonation won’t be effective.

“The trials were initiated just before Covid-19 hit,” Shaw explained. “Obviously, the researchers haven’t been able to go back to do the care and maintenance that they might like to. We’ve relied heavily on the De Beers staff to collect the appropriate samples and keep those experiments running.

“Over the next year, we’ll be collecting the results and, hopefully, those will allow us to develop mine site pilots on an even larger scale.

“My understanding is that, just in terms of general weathering reactions, it’s possible to increase the natural rates by a factor of 10 or even 100. So, there is a lot of potential.”

Work in bioengineering for carbon sequestration purposes could uncover promising applications for microbes in tailings management too.

“Dr Southam’s team is working on multiple projects, including some in the field of bio-cements; these can be used to help stabilise slopes, particularly at tailings impoundments,” said Shaw. “It’s an important area of research, given the tailings dam failures we’ve seen in recent years and the potential environmental and social impacts associated with those.

“The other area is bioleaching and bio-recovery, particularly for rare earth elements which are critical for the renewable energy sector.”

Possibilities outside of mining

I vowed to check in with Shaw next year to find out how work on CarbonVault is progressing. Once a project captures my imagination, I can rarely let it go.

Dr Shaw examines the Fine Residue Deposit (FRD) facility at Venetia mine. Image: Alison Shaw/De Beers
Dr Shaw examines the Fine Residue Deposit (FRD) facility at Venetia mine. Image: Alison Shaw/De Beers

“It’s definitely different from what most mining companies are doing to reduce their carbon footprint,” she said. “I think De Beers really values the fact that the kimberlite rocks are unique, and it gives them this amazing ability to take advantage of that and do things in a different way to everybody else.”  

In terms of other carbon sequestration projects that are ongoing, CarbonVault offers a slightly different solution because of the ability to capture carbon in a solid mineral phase.

Most carbon capture projects take CO2 in a fluid phase and inject it into deep sedimentary rock layers, but there is a question around how long that fluid will remain stable at different locations.

“In the case of CarbonVault, this is a solution that has the potential to really make a difference and to effectively trap the carbon for a long period of time,” said Shaw. “We know that carbonates are stable; look at the cliffs of Dover in the UK.”

It has a lot of potential, which is why I was so keen to cover this project on The Intelligent Miner. Research into carbon sequestration is one more way in which the mining industry can help society to fight back against climate change and feed into creating a better world.

“It’s going to take innovations from various different spaces in order to come up with solutions that will help bring atmospheric CO2 levels down,” Shaw agreed. “This work could be a part of that.

“If a solution developed and implemented at mine sites initially could be applied more globally, then that would be an amazing story wouldn’t it?

It sure would, I agreed wholeheartedly.

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