Helping to solve mining’s costliest environmental challenge

Acid mine drainage (AMD) is widely acknowledged as the biggest and costliest environmental challenge facing the mining industry. Fortunately, a succession of university-industry research partnerships, funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) over the past two decades, has yielded new approaches to alleviating AMD that are less costly and operationally intensive than conventional methods.

Mining and milling sulphide ore deposits generates large quantities of sulphide-bearing waste rock and finely crushed mill tailings. When exposed to oxygen and water, these waste products generate acid effluents, which can leach heavy metals that contaminate soil and water supplies.

Canada’s mining industry spends more than $100 million annually to control AMD. These costs cover a wide range of activities: the collection and treatment of acid drainage, the construction of engineered structures (impoundments) to contain mining waste products, the relocation of these products to contaminant areas, and the rehabilitation of mine, mill and contaminant areas after operations cease.But the downside of these conventional methods is that they are expensive and require a long-term commitment.

Now the industry has at least one compelling alternative, courtesy of NSERC-funded collaborative research involving Canada’s leading mining companies and Dr.David Blowes, a professor of Earth Sciences at the University of Waterloo with researchers in his Groundwater Geochemistry & Remediation group. Working with companies such as Falconbridge Ltd.(now Xstrata Plc), Inco Ltd. (now Vale Inco) and Placer Dome Inc. (now Barrick Gold), the GGR group has successfully designed and demonstrated a more passive approach to AMD remediation — a biological process that once installed will continue to operate on its own.

The solution is based on permeable reactive barriers (PRBs), which act like purifying filters for water tainted by acidic drainage.The materials in the PRBs, typically organic carbons and iron filings, promote conditions favourable to the growth and function of bacteria that colonize the barrier and remove dissolved metals from the water.

“By adopting an in-situ, passive approach to AMD remediation,”explains Blowes,”we are able to design PRB systems that will stand alone for long periods of time, avoiding the onerous day-to-day management demanded by traditional methods. These systems are particularly well-suited to a lot of remote sites where the mine has closed and the company has no on-site presence.”

Although abandoned mines represent an obvious market for PRB systems, the systems are equally valuable for active mines or those under development, according to Denis Kemp, former director of environmental development at Falconbridge.

“In the past, companies were more inclined to put off dealing with AMD, but that is the more expensive route to go,” observes Kemp, who chairs the industry-led International Network for Acid Prevention. “David’s team has demonstrated that if you fully characterize the problem and apply these reactive barriers from the outset, the industry can realize huge savings over the long term.”

He adds that environmental regulations place demands on mining companies to provide demonstrable proof of how they intend to manage AMD. In many instances, mining companies are required to post substantial bonds as financial guarantees against potential environmental harm from their operations.

“David’s team plays an important role in building confidence with regulators,” he says. “Compared to company officials or private consultants, the university researchers have greater credibility with regulators because they are at arm’s length from the industry.”

The recently released Science and Technology Strategy focuses on environmental sciences and technologies as one of four key priority areas in which Canada will build global research and commercialization leadership. Science and technology is crucial to finding solutions to the complex environmental challenges we are facing. Environmental technology will provide us with the knowledge and tools we need to help protect our environment, and to ensure that future generations have clean air, water, land and energy. The strategy also contains several important policy commitments to strengthen public-private research and commercialization partnerships.

The GGR researchers are also exploring how to mitigate the impact of AMD using wastes from other industries. For example, pulp and paper wastes have been used to successfully create chemically reactive, moistureretaining covers for mine tailings. The covers consume oxygen and stabilize dissolved metals within the tailings impoundment.

In another case, one of Blowes’ students, supported by an NSERC Industrial Postgraduate Scholarship, is examining the use of brewery wastes to combat AMD. The early results are encouraging.