Executive Summary
Facilities built to store mine tailings pose both physical and geochemical risks that must be managed throughout the life of the facility, from design and construction, through to the closure of the mine and beyond. In Canada, most mines manage their tailings as a slurry deposited behind containment dams (designated in this report as “conventional tailings facilities”). In the wake of small and large-scale tailings facility failures, the risks posed by conventional tailings facilities are coming under increased scrutiny. Although one root cause has not been identified for all tailings dam failures, a common contributing factor to the higher consequence of failure includes the storage and behaviour of water within the facilities. This has led the industry to reconsider alternatives to conventional tailings facilities, including dewatering tailings prior to deposition (e.g. thickened, paste and filtered) as well as different facility types (e.g. downslope, cone, and “dry” stack/pile).
The objective of tailings management is to safely store tailings and reduce the risks, particularly over the long-term. To this end, “dry” closure significantly reduces physical risk and needs to be balanced against potential geochemical risks. Tailings planning and operation should be focused to long-term post closure considerations and as such should be a primary consideration when assessing potential technologies and facility types.
Driving the interest in dewatered tailings is a desire to reduce the physical risk posed by conventional tailings facilities. Although the technology exists to build safe dams, the industry has not been able to achieve zero failures. Currently, creating paste and filtered tailings for disposal is more costly than conventional tailings, unless other factors are important cost drivers: dam cost, water cost, a lack of community acceptance, or the fact tailings would be better stored underground.
Turning slurry tailings into paste has been an industry and research focus for more than a decade, but it has not achieved broad acceptance in the industry. More recently, interest has moved towards filtered tailings; costs are decreasing and larger throughput plants are being proposed. These innovations may make filtered tailings an increasingly attractive, lower-physical-risk option compared to conventional or paste tailings. However, other factors need to be considered when selecting a tailings management strategy (e.g. site conditions, geochemical risks, long-term closure risks, environmental impacts and social impacts).
This report presents a snapshot of the current state-of-practice in the Canadian mining industry. It looks at the technologies used to dewater tailings, how tailings are placed and managed, and evaluates their relative efficacy in addressing physical and geochemical risks. It also identifies opportunities for further research and development. The reader will gain an understanding of the strengths and limitations of tailings dewatering technologies, deposition practices, and how these choices apply to specific sites and mining projects compared to conventional practices. The report should help guide which technologies and strategies should be considered for a project, taking into account site conditions, project constraints (e.g. production schedule), tailings’ physical properties (e.g. grain-size, and plasticity), and geochemical properties (e.g. the potential for tailings to generate metal leaching (ML) and/or acid rock drainage (ARD)).
A tailings management strategy considers many aspects of disposal, including; facility types (e.g. conventional, thickened/paste, filtered), tailings technologies (e.g. segregation, co-disposal, in-pit or underground backfill, dewatering – thickening and filtering, etc.), and operational, environmental, socio-economic, and closure considerations. This study focuses on tailings facility types and dewatering technologies and presents an assessment of alternative tailings technologies and facility types in comparison to conventional slurry facilities.
More specifically, this study aims to (1) present the use of dewatering tailings technologies and associated facility types alternative to conventional in Canada (or in other locations with similar climates), (2) evaluate the applicability and efficacy of the alternatives at reducing physical and geochemical risk compared to conventional tailings facilities, and (3) identify opportunities for further research and development. This study is not exhaustive and does not assess all alternate tailings management strategies or considerations (e.g. social considerations), nor the various types of dams, dikes and retention structures, which are also a key component to tailings management technologies and approaches.
The following approach was applied for this study: ♦Step 1 – Identify the current state-of-practice and projects using alternative technologies in Canada through literature review, database research, and a questionnaire sent to all Canadian mine sites. ♦Step 2 – Evaluation of the alternatives, comparing tailings management technologies and costs using the information compiled as part of the identification of the current state-of-practice and the case study information provided by select mine sites. ♦Step 3 – Assess applicability to Canadian mines and identify knowledge gaps. Lessons learned from the case histories in the context of mining in Canada were summarized and knowledge gaps identified for further research.
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