Thematic Articles

If we want to ensure a sustainable future for the human race, we must learn to prevent, minimize, reuse and recycle waste. Reuse of mine wastes allows their beneficial application, whereas recycling extracts resource ingredients or converts wastes into valuable products. Yet, today, many of the proposed reuse and recycling concepts for mine wastes are not economic. Consequently, the great majority of mine wastes are still being placed into waste storage facilities. Significant research efforts are required to develop cost-effective reuse and recycling options and to prevent the migration of contaminants from rehabilitated waste repositories in the long term.

Historical mining and mineral processing have been linked definitively to health problems resulting from occupational and environmental exposures to mine wastes. Modern mining and processing methods, when properly designed and implemented, prevent or greatly reduce potential environmental health impacts. However, particularly in developing countries, there are examples of health problems linked to recent mining. In other cases, recent mining has been blamed for health problems but no clear links have been found. The types and abundances of potential toxicants in mine wastes are predictably influenced by the geologic characteristics of the deposit being mined. Hence, Earth scientists can help understand, anticipate, and mitigate potential health issues associated with mining and mineral processing.

Acid mine waters, often containing toxic concentrations of Fe, Al, Cu, Zn, Cd, Pb, Ni, Co, and Cr, can be produced from the mining of coal and metallic deposits. Values of pH for acid mine waters can range from –3.5 to 5, but even circumneutral (pH ≈ 7) mine waters can have high concentrations of As, Sb, Mo, U, and F. When mine waters are discharged into streams, lakes, and the oceans, serious degradation of water quality and injury to aquatic life can ensue, especially when tailings impoundments break suddenly. The main acid-producing process is the exposure of pyrite to air and water, which promotes oxidative dissolution, a reaction catalyzed by microbes. Current and future mining should plan for the prevention and remediation of these contaminant discharges by the application of hydrogeochemical principles and available technologies, which might include remining and recycling of waste materials.

The bitumen found in the oil sands of northern Alberta, Canada, represents a significant oil resource. This bitumen is extracted either from mined ore or by using in situ methods. The water-based extraction of mined ore creates large volumes of mineral suspensions that are stored in tailings ponds. Remediation of fine tailings has presented challenges. Several new treatment technologies promise to accelerate the remediation process and at the same time recover more water for use in the extraction process. As a world-class oil reserve, and the only commercially developed oil sand deposit, the Alberta oil sands represent an important future oil source, the magnitude of which will depend to some extent on our ability to limit environmental impacts.

Large volumes of waste rock and mine tailings are stored at mine sites. Predicting the environmental impact of these wastes requires an understanding of mineral–water interaction and the characterization of the solid materials at the microscopic scale. The tendency of mine wastes to produce acid or neutral drainage containing potentially toxic metals generally reflects the ratio of primary sulfide to carbonate minerals and the trace element concentrations inherited from the ore deposit, as well as any ore processing that may have created new compounds. Whether potentially toxic elements are released to surface water, groundwater, or bodily fluids (in the case of ingestion or inhalation) depends on the host mineral and the possibility of sequestration by secondary minerals.

Mine wastes are unwanted, currently uneconomic, solid and liquid materials found at or near mine sites. Volumetrically they are one of the world’s largest waste streams, and they often contain high concentrations of elements and compounds that can have severe effects on ecosystems and humans. Multidisciplinary research on mine wastes focuses on understanding their character, stability, impact, remediation and reuse. This research must continue if we are to understand and sustainably manage the immense quantities of historic, contemporary and future mine wastes, given the trend to exploit larger deposits of lower-grade ores.