Dirty carbon gets cleanup duty
Unique new process converts acidic waste into harmless rock
The distances between points of interest in the Yukon are vast, but those daylong drives gave mining executive Doug Eaton time to think.
He’s thought about a lot of things, including the carbon footprint of fossil fuel-burning electricity generators used to power remote mines.
“We don’t get much sun, and the wind is variable, so there aren’t a lot of viable alternatives,” said Eaton, president and CEO of Strategic Metals. “I wanted to come up with a solution that had the social licence needed to develop a project.”
He was also pondering ways to convert the acidic waste from gold and silver mines into a stable, benign form that could simply be harmlessly shovelled back into the ground.
“The Faro lead/zinc mine was developed back in the ’60s — in the way that mines were run back then — and the company went into bankruptcy,” said Eaton.
Cleaning up the notoriously polluted Yukon mine site could cost the Canadian government as much as $800 million, according to a report by Indian and Northern Affairs Canada.
Because the acid rock drainage is often loaded with iron-based minerals, Eaton thought that captured carbon dioxide emissions could supply the carbon atom required to convert iron sulphides into iron carbonate, a relatively innocuous mineral called siderite.
“The more I thought about it, the more I thought it should work,” he said.
Eaton put UBC Prof. Lee Groat to work to solve the problem.
Helping those carbon atoms make the switch was a bit trickier than expected. That is, until an accidental electrical short circuit provided just the jolt needed to catalyze the reaction in their acidic solution and form siderite.
“We were trying to make the reaction more robust when we noticed that, when a thermocouple we were using to measure the temperature of the water was in the solution, it worked,” said Eaton. “When it wasn’t in the solution, it didn’t work, and it turned out there was a short in the thermocouple.”
Convinced of its potential, Eaton spawned Terra CO2 Technologies to commercialize the resulting technology, which has the potential to vastly reduce the costs associated with acid rock drainage at active and decommissioned mines.
Terra’s process ticks several boxes for the industry, sequestering carbon from captured CO2 emissions, treating acid rock drainage that bedevils many mine sites, and, as a bonus, it produces sulphuric acid suitable for industrial applications. Terra’s innovation is about to graduate from the laboratory bench-top to a warehouse prototype, which will be built early next year to process trucked-in mine waste.
If the technology co-operates, Terra hopes to field test its systems at the Britannia Mine site south of Squamish and at the Faro Mine.
Parent firm Strategic has invested $1 million in Terra, which plans to raise an additional $4 million. The company has also attracted innovation grants from the National Research Council’s Industrial Research Assistance Program, MITACS and BCIC Ignite.
“The mining industry is our primary target, but this technology could be useful to other CO2-emitting industries, such as cement production, certain types of fertilizer production, and coal-fired electric plants,” said Terra CEO Dylan Jones.
The technology has grown up quickly in part because electrolytic processes are so widely used in industry already. “These processes are used every day all over the world, for a million applications, from electroplating to creating unique chemical compounds,” said Jones. “It already exists, just not in the way we’re using it.”
Patents have been granted in the U.S. and Canada, with applications pending in Australia, Europe and Japan.
Of course, it’s one thing to demonstrate a chemical process in the lab and quite another to make it work in the field, said Scott Dunbar, head of the NBK Institute of Mining Engineering at UBC. Local conditions and the complex cocktail of contaminants in the waste material can foil even the most robust reaction.
“The field is just messier than the lab and there are always unexpected complications,” he said.
Dunbar’s colleague, chemical and biological engineer Vikram Yadav, is leading the development of an ambitious mine wastewater treatment process, one that uses organic material to extract dissolved metal from tailings ponds.
By coaxing the organic material to give up electrons in a powered “microbial cell,” dissolved metals can be turned into a solid.
“We’re working with copper right now, because it has some value, but it should work with any metal,” Dunbar said.
By varying the current, they have been able to selectively and sequentially turn other metals in a near-pure form. In the lab, at least.
Yadav will use a recent grant from UBC’s GOE 2 project for radical innovation to build a prototype of the cell to test in the field.
Extracting value while reducing future costs from mining’s greatest liability would be a game-changer.
At a mine site, the high-grade ore goes for processing, while lowgrade ore is stored for years and not processed until the mine is decommissioned, if ever. Storing processed rock and low-grade ore for decades is an expensive and environmentally risky proposition.
Dunbar argues that mining companies could save themselves long-term pain by processing the low-grade ore in parallel with the high-grade, using a technology like the microbial cell.
“If you leave the low-grade material there, it will just oxidize ... and become a source of contamination,” he said.
“Because they cost a few tens of thousands of dollars, rather than millions, it’s a really low barrier to entry for a contractor or a First Nation to get into the metal-extraction game.”
Because the ore is processed on the fly, it would greatly reduce the need for costly remediation at the end of a mine’s life.
“There’s (an opportunity) there for companies that just farm out the remediation of tailings and waste to contractors to actually do something useful with them,” said Dunbar. “Otherwise, they’re just a liability.”
• Dunbar’s research could eliminate the need to dig rock altogether. His idea for “in situ mining” involves injecting a metal-harvesting solution into the earth and then extracting and processing the captured metals without moving a stone.
• Geological engineering professor Greg Dipple is hoping to use mine waste as a way to reliably sequester carbon dioxide captured from industrial emissions. Field tests are expected to start in the next two years.
• UBC engineering professor Sue Baldwin is working with anaerobic bacteria that have the ability to consume or remove heavy metals from mine tailings.
There’s (an opportunity) there for companies that just farm out the remediation of tailings ... to actually do something useful with them.