本文转自《MINING》发表的题为“Mining technologies could capture ‘billions of tonnes of CO2 per year,’ says UBC prof”的报道

作者：Carl A. Williams - The Northern Miner

日期：2020.04.28

原文链接：https://www.mining.com/mining-technologies-could-capture-billions-of-tonnes-of-co2-per-year-says-ubc-prof/

The world needs to limit global temperature increases to between 1.5 and 2 degrees Celsius by the end of this century to avoid devastating climate change, according to the Intergovernmental Panel on Climate Change, a United Nations body that provides policymakers with scientific information about climate change.

Atmospheric concentrations of CO2 are now well over 400 parts per million and global emissions are currently around 36 billion tonnes of CO2 per year.

With emissions expected to increase, most experts believe that the 2 degrees Celsius warming target will not be met. To stabilize the global climate, they say, we will need to achieve net negative emissions by pulling more CO2 out of the atmosphere than we emit.

The mining industry could play a significant role in helping to achieve this, according to Greg Dipple, a professor in the Department of Earth, Ocean and Atmospheric Sciences and a member of the Mineral Deposit Research Unit at the University of British Columbia (UBC).

For the last decade, Dipple has been studying how ultramafic rocks, which contain magnesium silicate often found in mine tailings, naturally draw CO2 from the air and trap it by forming new carbonate minerals that are stable and can permanently lock-in carbon.

“We will not achieve our global warming targets by simply reducing our emissions,” said Dipple in a telephone interview with The Northern Miner.

“To limit global warming, we will need to capture CO2 from the air and store it indefinitely. With the right materials, we can use existing mining technologies to do this at the scale of potentially billions of tonnes of CO2 per year.”

He estimates that reducing just 10% of a mine’s tailings could be sufficient to offset the annual carbon emissions produced by a mining operation, and is now working with other researchers and mining companies to develop technologies that can accelerate these natural processes and be scaled-up to capture CO2 emissions from mining operations.

In a process called carbon mineralization, chemical weathering of tailings rich in alkaline earth metal-bearing silicate and hydroxide minerals react with CO2 in the air to form carbonate minerals, like magnesium carbonate.

A stable cement-like mineral, magnesium carbonate can store carbon in a benign state for thousands of years or more, permanently removing CO2 from the atmosphere.

Dipple is spearheading UBC’s Bradshaw Initiative for Minerals and Mining (BRIMM), which is working on a carbon sequestration project to study how the process can be accelerated and then replicated on a scale large enough to sequester CO2 emissions generated from mine site operations.

The project is a collaboration between UBC, the University of Alberta, Trent University in Ontario, the Institut national de la recherche scientifique in Quebec and three mining companies, De Beers Canada, FPX Nickel (TSXV: FPX) and Giga Metals (TSXV: GIGA).

Funding for the work comes from a $2 million grant from the Natural Resources Canada Clean Growth Program and from cash and in-kind payments from the companies, as well as support from Geoscience BC, the British Columbia Geological Survey, the Geological Survey of Canada and the governments of British Columbia, Yukon and Northwest Territories.

“While carrying out some field tests at BHP’s Mount Keith nickel mine in Western Australia, we found that the mine’s tailings pile was passively removing CO2 from the air and capturing around 40,000 tonnes a year,” said Dipple.

“Without even realizing it, the company was offsetting around 11% of the mine’s total greenhouse gas emissions.”

The natural sequestering of carbon usually occurs over timescales of hundreds of thousands to millions of years.

Since mines crush the ore into a fine-sized rock to extract valuable minerals, the reactive surface area dramatically increases, which rapidly speeds-up the reaction.

A natural process that can take millions of years can “now be achieved in a year or so,” according to Dipple.

“Although we have confirmed rapid mineral carbonation within days to weeks in a laboratory setting, the next challenge is to replicate it at much larger volumes in the field,” explained Dipple.

“The funds are supporting field trials of new technologies for accelerating the reaction between CO2 and the magnesium silicate-rich mine tailings from two mining locations in Canada.”

The first field trials took place last summer at De Beers Group’s Gahcho Kué diamond mine, an open-pit operation with three kimberlite pipes, located 280 km northeast of Yellowknife in the Mackenzie district of the Northwest Territories.

“We are looking at the potential of processed kimberlite to sequester CO2 emitted by the mine’s diesel generators,” said Sarah McLean, Environmental and Permitting Manager for De Beers Group, in a telephone interview with The Northern Miner.

Following simulations on flue gas injection through different blends of fine and coarse grain processed kimberlite, which provided valuable information on reaction rates and scaling considerations, two field trials were conducted.

In the first test, CO2 gas was injected at 720 milliliters per minute into 264 kg of mixed coarse and fine processed kimberlite packed into a six-meter pipe.

The pipe was then monitored for CO2 leakage from unreactive material, which, according to Dipple, occurs after around 90 minutes.

However, even after 44 hours of continuous monitoring, no CO2 was observed to have exited the pipe, and the total inorganic carbon content of the blended kimberlite was found to have increased by 0.36 kg of CO2.

For the second test, the team wanted to evaluate CO2 injection in two dimensions as well as the effectiveness of fines in trapping the gas.

So, they injected CO2 at 240 milliliters per minute into five outlet ports in a 180 kg rectangular slab of mixed fine and coarse grain tailings sandwiched between layers of finely processed kimberlite.

Once again, an analysis of the total inorganic carbon content of the carbonate minerals formed during the test confirmed the sequestration of 0.28 kg of CO2.

“The tests demonstrated the effective reactivity of the processed kimberlite and confirmed its ability to sequester carbon under field conditions,” said McLean.

“Learnings from these trials are being used to inform the design of industrial-scale tests scheduled for the summer. Hopefully, they will demonstrate that processed kimberlite can effectively and economically capture carbon and reduce the carbon footprint of our mining operations.”

Although the reactivity of the processed kimberlite can vary substantially within and between mines, McLean believes they may be able to offset “as much as 20% of total emissions from Gahcho Kué based on the results from the field trials.”

The company is also investigating other methods to accelerate the sequestration process, including different ways of distributing the processed kimberlite and the use of chemical additives and biological processes.

In the other field trial, also scheduled for the summer, Dipple and his team are looking to investigate the potential of waste tailings to capture CO2 from the air at PFX Nickel’s Decar Nickel District property, located around 90 km northwest of Fort St. James in central British Columbia.

The Baptiste deposit, one of several mineralized zones at the property, is hosted by an ultramafic complex dominated by serpentine formations and contains highly reactive brucite, the mineral form of magnesium hydroxide, making it an “an excellent candidate for a CO2 capture project,” according to Dipple.

“We are delighted to be involved in the project and are excited to understand more about the carbon sequestration potential of the planned mine at the Baptiste mineralized zone,” said Martin Turenne, FPX Nickel’s president and CEO, in a telephone interview with The Northern Miner.

A recent assessment by Ian Power, an assistant professor at Trent University and one of the collaborators on the BRIMM carbon sequestration project, forecast tailings from the proposed Baptiste mine to be around 40 million tonnes per year. And, if complete carbon mineralization was economically feasible at the mine, he estimated that approximately 18 million tonnes of CO2 per year could be sequestered, approximately a quarter of B.C.’s annual GHG emissions.

By extrapolating results from laboratory tests carried out on exploration samples collected at the property, Power estimates that a tailings facility covering about 5 sq. km could be capable of capturing around 17,000 tonnes of CO2 per year.

And on the assumption that the bedrock contains around 1.5% by weight of brucite, he estimates that around 400,000-500,000 tonnes of CO2 per year emitted by the mine could be entirely offset through carbon mineralization, and around a quarter of B.C.’s annual GHG emissions.

“The project represents a significant step towards the development of more sustainable mining practices by offering the prospect of a carbon-neutral mine as well as other benefits, such as dust management and the stabilization and cementation of tailings piles,” said Turenne.

In addition to field trials, Geoscience BC is also contributing $259,680 to the BRIMM carbon sequestration project to support the development of a ‘carbon sequestration potential index’ for rock formations across British Columbia.

“For the first time in the world, we are attempting to map the carbon storage potential of serpentinite rock across an entire mountain chain,” explained Dipple.

“The map will help to identify future opportunities for carbon capture and storage projects across the province.”

Ultramafic rocks and their associated serpentinite products are abundant in B.C., with highly serpentinized rocks offer the highest potential for sequestering CO2.

Because alterations in the rocks are commonly associated with changes in physical properties, Dipple and his team are looking to quantify these changes by assaying samples collected from several locations across British Columbia, including Atlin, King Mountain, the Decar area and the Turnagain intrusion.

By understanding the relationship between the alteration and physical properties of the formations, the researchers hope to develop a carbon sequestration potential index on both a provincial scale to identify sequestration targets and on the mine-scale level to characterize and classify tailings.

“The project will provide us with a better understanding of natural ways to manage greenhouse gas emissions generated not only by mining companies in British Columbia but also by other industries operating in the province,” said Brady Clift, a geologist and Manager (Minerals) at Geoscience BC.

(Carl A. Williams – This article first appeared in The Northern Miner on March 16)