The Canadian mining industry is held to some of the highest environmental regulations and social standards in the world. Water protection and management is central to the federal, provincial, and territorial laws that regulate new mines and major expansions, and critically important to all of the peoples who call Canada home.
Responsible and sustainable mine design requires minimizing the footprint during operation and preventing any pollution to surrounding waterways after closure and site rehabilitation. Preparing mine-affected waters to be released from a site, in accordance with local regulations and to ensure an ongoing social licence to operate, is a top priority but traditional water treatment plants can be expensive to construct and maintain over time.
“When you look at operating an active water treatment plant, you are consuming electricity, heating large spaces, and need staff on site all the time to operate the facility. You quickly end up with a large carbon footprint, ongoing light, and noise pollution, and the risks associated with transporting chemicals and reagents great distances to treat the water,” explains Dr Monique Haakensen, president and principal scientist at Contango Strategies, who custom-design passive water treatment systems for mining and energy facilities across Canada.
Passive water treatment systems require no electricity or chemicals, and human operators are replaced by natural bacteria, aside from periodic upkeep and maintenance. Examples include certain wetlands, in-pit and underground in-situ treatments, some types of bioreactors, and certain permeable reactive barriers.
“Passive treatment itself is not new,” explains Haakensen. “People have been using treatment wetlands in mining for over 60 years, but the technology being used now is totally different.”
A combination of increased computer power and a deeper understanding of microbiology has propelled water treatment technologies forward. Understanding how bacteria and microorganisms live and work leads to the design of more efficient water treatment facilities.
“If you’re relying on a microbe to do the work for you, it makes sense to know what microbe you’re working with,” says Haakensen, “Genomics is currently the only method that can tell us what those microbes are.”
Genomics combines biology, genetics, and computer science to see how organisms interact with their environment. Since the human genome was sequenced in the year 2000, and the price of sequencing genes has decreased, genomics has found applications in all sectors, from human health and agriculture to mining and energy.
“It’s a problem-solving tool,” explains Dr. Anikó Takács-Cox, manager for Mining, Energy and Environment Sector at Genome BC, one of six geographic sub-sections of Genome Canada devoted to funding genomics research and expanding its applications. “Using genomics we can link pollution in water directly to it’s source by looking at the microorganisms in the water. By looking at an organism’s genes, the proteins expressed by genes, or the metabolites released by proteins, scientists have worked out how to treat run-off coming from a mine, oil sands operation, or forestry plantation. It’s a genetic fingerprint.”
Bacteria plays the central role in passive water treatment systems at mine sites. A number of bacteria species are able to convert the sulphates that are produced during mineral extraction and processing, back into the original sulphide form and precipitate metals out of the water. These bacteria carry out this process in natural wetlands and can be encouraged to do the same in constructed wetlands under the right conditions.
“Bacteria are everywhere; we don’t need to add them in. We design something like a wetland that will give the right kinds of bacteria the right environment to do the activity we want,” says Haakensen, explaining the four-step process Contango use to custom-design passive water treatment systems for the industry.
The initial step involves looking at the natural plants available and assessing them as habitat for microbes, characterizing the chemistry of the water on and off the mine site, and identifying any carbon sources, such as woodchips, straw, or hay, required to start the biological processes.
Next, they replicate those conditions at an off-site pilot-scale testing facility and control as many variables as possible. In the case of the constructed wetland treatment system (CWTS) planned for the NICO gold-cobalt-bismuth-copper mine in the Northwest Territories, it was even necessary to create synthetic water during these tests to predict the water chemistry at the site. Fortune Minerals Limited has permitted the project but not yet constructed the NICO Mine. The development of a credible water treatment system after closure was a required element of the permitting process to ensure protection of the environment in the long term.
Naturally elevated arsenic is found in the water around the NICO site. For thousands of years, water running off the outcropping mineralized rocks on the hills at the NICO site has picked up arsenic and then flowed through natural wetlands, so the team were able to study how the natural environment was treating the water in the area, and attempt to replicate it.
“The CWTS was chosen because it represents a long-term water quality treatment system that requires little or no maintenance. This was an essential factor for choosing a system that would work under closure and post-closure conditions” says Dr. Rick Schryer, director of Regulatory and Environmental Affairs, Fortune Minerals.
The third stage involves building a demonstration-scale treatment plant on site. At Capstone Mining’s Minto Mine in the Yukon, a demonstration-scale CWTS was built at the end of 2014. Minto Mine is operating at full production from both open pit and underground deposits as of summer 2016, and the CWTS is in its second year of testing. The results to date have been favourable, with signs of treatment for both copper and selenium observed during testing.
“So far, Minto Mine has undergone pilot and demonstration scale testing using actual site water and wetland plants,” explains Ryan Herbert, environment manager at Capstone’s Minto Mine. “This technology was selected as potential solution for water treatment post-closure due to its ability to treat water with limited operational and maintenance requirements. It’s the most passive treatment option available for closure, with the potential to perform over a long period with limited maintenance and operational oversight.”
Passive water treatment systems work under a range of weather conditions, including freezing winter temperatures. At the Minto Mine, the same treatment efficiency was observed at cold temperatures as during the warmer months.
The final stage involves building a full-scale water treatment plant on site. This should simply be a construction project, says Haakensen, as the experimentation and optimization have been worked out during the pilot-scale and demonstration-scale tests.
Passive water treatment technologies are being trialled at a number of sites across Canada and are increasingly being recognized as a sustainable choice for treating water during operations and long after closure. The ideal water treatment plant, says Haakensen, would be different for every single mine, and include 10 to 20 species of microbes carefully selected to suit the specific mineralogy of rocks, soil, and water at the site. Provided with the right conditions, these tiny bugs will help responsible mining companies release clean, mine-affected waters off-site for many years, meeting their regulatory requirements, and addressing the environmental concerns of neighbouring communities.