Cape Breton contains 3,200 kilometres of underground mines that are either flooded or in the process of flooding. That’s roughly the distance between Halifax and Calgary. These flooded mine workings contain about 250 billion litres of anoxic water, contaminated with sulphuric acid, high levels of dissolved iron and other heavy metals. As they flood, the mines discharge this water, potentially contaminating groundwater, drinking water, surface water, or the ocean.
Dr. Martin Mkandawire began his role as Industrial Research Chair in Mine Water Management in October 2012. He and his team are working toward a goal to gather and develop best practices on all aspects of mine water management, including mine water discharge remediation, reduction of maintenance requirements, and the potential commercial use of mine water as a geothermal renewable energy source.
Background: Coal mining activities in Cape Breton’s Sydney Coal fields ceased in the late ‘90s after more than two and a half centuries of coal mining; the legacy of which is an extensive network of abandoned underground mine collieries (approximately 3,200 km) and disturbed hydraulic behaviour of aquifers in the Cape Breton area. When mining activities ceased, so did the pumps, with groundwater gradually ?lling the excavated spaces of the former underground mines, forming what are known as “mine pools”. Currently, mine pools in the Sydney Coal Field are estimated to contain roughly 190 million m³ of water. The continuous infusion of groundwater – surface-recharge to these abandoned works has produced conditions under which at least 26 mine water outfalls are or could potentially be discharging water to surface receiving environments within the former Sydney coal field, if not actively intercepted and treated. Of concern is the quality of this water being discharged, and the burden of contamination carried through interactions over time with mineral deposits exposed in the mine works.
Most ore and coal deposits contain pyrite, an iron-disulphide mineral. When interacting with mine water in flooded shafts, the pyrite decomposes in aqueous solution, forming sulphuric acid, increasing the proton acidity of the water. The resulting acidic mine water initiates a chain reaction which further dissolves other minerals in the host rock, enriching these waters with iron, sulphide, and other metals and metalloids. Consequently, the mine pools of Cape Breton’s Sydney Coal Field could pose a high contamination risk to the environment. A progressive realization of the risks and hazards associated with acidic mine water has lead to several investigations and monitoring programs since the 1980’s, as well as development of several mine water treatment plants.
Despite these preliminary studies, not much is known about the hydrogeochemical as well as biogeochemical development and the hydrodynamic behaviour of the mine pools. Consequently, knowledge of the temporal and spatial development of acidic mine water, as well its fate and effects within receiving environments, is crucial to develop management strategies, which include planning appropriate and cost-effective remediation actions and technology. Therefore, the research plan for both the Chair in Mine Water Management and the Chair in Environmental Remediation proposes research activities that will further understanding of the characteristics and environmental impact of mine water while developing cost-effective mine water management processes suitable for use in Cape Breton and beyond.
The Verschuren Centre is one of only a handful of expert mine water centres in the world. The Enterprise Cape Breton Corporation (ECBC) partnership with the Verschuren Centre has created an Industrial Research Chair to gather and develop best practices on all aspects of mine water management.
Dr. Mkandawire and his staff are examining options around the natural, passive discharge of flooded mine water – offering the potential to greatly reduce future management costs in Cape Breton and other mining sites around the world. This area has the additional commercial potential to use the mine water as a geothermal renewable energy source.
- Develop cost-effective and commercially viable technologies for monitoring, abatement and control of acid mine water releases to the environment.
- Acquire a clear understanding of the geochemical, biological and physio-chemical processes governing the fate and effects of pollutants within the mine pools of the Sydney coal fields and those affecting the performance of associated passive treatment plants.
- Employ recent advances in biotechnology and nanotechnology, using this scientific knowledge to develop technologies with the potential to be commercially viable mine water treatment technologies, with partial cost offsetsthrough recovered compounds and minerals (extraction of minerals and precious metals from mine water).
- Harvest geothermal energy from mine water, making mine water management economically appealing.
- Develop novel and efficient approaches to treating mine water through researching the characteristics and behaviour of nanoparticles.