Mine Closure

2025/2026 Focus: Geotechnical engineering, reclamation, and tailings-derived materials for closure. 

Background

Oil sands operations in Alberta produce large volumes of tailings which are a mixture of water, sand, clay, and residual bitumen. The composition of these tailings varies depending on the process stream. These tailings are stored in external tailing dams or in-pit mined areas that must be eventually reclaimed and decommissioned in the long term. 

Effective mine closure strategies are essential for ensuring the long-term stability of tailings structures and the reclamation of surrounding environments. For terrestrial closure approaches, success largely depends on maximizing water removal from tailings and minimizing the volume requiring long-term management—both of which accelerate reclamation timelines. However, oil sands tailings, particularly fine-dominated deposits (where over 50% weight [wt%] of particles are smaller than 44 μm), pose significant challenges due to their slow consolidation rates. These conditions can delay the initiation of closure and capping activities, resulting in prolonged monitoring and regulatory commitments for operators. 

Current treatment technologies, such as thickeners and enhanced in-line flocculation (eILF), are widely used to improve dewatering efficiency. Thickeners promote dewatering by allowing solids to settle under gravity, while eILF enhances particle aggregation using chemical flocculants, improving fines capture and reducing water content. Despite these advancements, the industry still faces challenges in finding an economical methodology to achieve dewatered tailings with high solids content (greater than 60 wt%) which is essential for meeting reclamation, capping and closure objectives. Moreover, the long-term consolidation behaviour and geotechnical stability of treated tailings deposits are still not fully understood. Addressing these knowledge gaps is vital for developing sustainable and effective mine closure strategies. 

At the same time, oil sands tailings offer an opportunity as feedstocks for value-added processing that generate useful materials for applications at mining sites. To be viable, these processes must clearly demonstrate both economic and environmental benefits. 

Technology and Knowledge Gaps

• Develop operationally practical solutions for capping of soft tailings deposits (such as residual pond-bottom fluid fine tailings (FFT), thickened tailings (TT), froth treatment tailings (FTT, tailing solvent recovery unit [TSRU]) which are being affected by lack of reliable predictions of settlement and understanding of the strengths (related to capping).
• Explore feasibility of outlet design to convey water from the tailings’ facilities post closure (how to manage surface water out of tailings structure at closure and post closure).
• Explore low GHG emissions, low energy intensity, low-waste technologies with minimal processing or simple additives to transform tailings into materials that can be used on mining sites, such as substrates to improve water and land reclamation, capping and mine closure, etc.
• Explore the use of novel materials, including those derived from tailings, to enhance the closure process (geochemical and geotechnical stability).
• Design and implement reclamation strategies that promote development of target ecosystems and landforms to productive states (i.e., possible target land uses, such as forestry, traditional land use, etc.). This work also includes improving technical confidence in achieving a given target ecosystem, considering the variability in surface settlement and water tables, as well as methods for accommodating settlement overtime.
• Develop novel tools including remote sensing for determining progressive reclamation trajectory for large scale areas.
• Sulphide mineral oxidation mitigations for Coarse Sand Tailings in pre or post depositions.
• Explore the mitigations methods to enhance geochemical stability of Froth Treatment Tailings (FTT/ TSRU). 

Preferred Processes and Methods

• Solutions should support long-term environmental sustainability and reduce adverse impacts on surrounding ecosystems during and after mine closure. Approaches should be economically viable, avoiding excessive treatment and resource use and materials should be available in the region (cost-effective). 
• Encourage the development of novel materials and methods that can be applied to future mine closure projects (novel and innovation methods). 
• When TSRU tailings is the feedstock, the preferable form is wet TSRU tailings, before or after separation by gravity (solids in TSRU tailings settle by gravity and form a dense 60 wt.% sediment).
• Excluded from the Call are: active water treatment; methods to separate water from TSRU tailings; methods to convert bitumen/asphaltenes/maltenes into value-added products; methods which use solvents or high temperatures.