Selecting an appropriate tailings storage facility is a crucial step towards mitigating your site’s environmental and operational risks. There is no ‘one size fits all’ approach to tailings storage, since the optimal storage method depends on a variety of factors.
The site’s topography and climatic conditions, environmental and other regulatory constraints, local socioeconomic factors, and the physical and chemical nature of the tailings themselves all require consideration.
The method of tailings disposal works hand-in-hand with the style of storage facility used. Depending on the amount of water that is extracted prior to disposal, the tailings may reach their final storage destination in a slurry, thickened, paste, or dry filter cake form. Generally speaking, more water extracted at the disposal stage means higher upfront capital expenditure but lower long-term site rehabilitation costs.
Which type of tailings storage facility is best for your site? Here’s an overview of the options to help you decide.
In-Pit Tailings Storage Facilities
This method might seem an obvious choice for open cut mines, where completed open pits can be repurposed as vessels for tailings storage. The upfront costs of establishing in-pit storage facilities are generally quite low, with limited construction works required. The tailings are typically pumped to their final destination in a slurry or thickened form, although supernatant water recovery is often possible via in-pit pumps.
While in-pit storage is relatively simple to set up and offers many short-term benefits, care should be taken to avoid underestimating its true long-term costs. For instance, there is the risk of sterilising any remaining resources within the pit, which could potentially impact the site’s future earnings. Then, there’s the lengthy land rehabilitation period that may apply following the site’s eventual closure, which should be factored into the whole-of-life cost calculations.
Surface Tailings Storage Facilities
Surface or out-of-pit tailings storage facilities have many variations, the choice of which is largely informed by the specific site’s conditions and topographical layout. Tailings are typically either pumped or gravity-fed from the processing plant to their storage location, which may range in structure from a reservoir-style containment facility to a flat section of ground.
Valley storage facilities take advantage of the site’s natural topography, combined with engineered retaining walls, to contain tailings. A perimeter or ring containment wall is an alternative that works better on relatively flat ground to store tailings in a dam-like structure. In both instances, tailings are discharged as a slurry, and supernatant water is collected via a decant facility.
Another surface storage option involves a series of cells or ‘paddocks’ into which tailings can be deposited, sometimes on a rotational basis. This method facilitates consolidation and drying of the tailings and negates the need to construct an expensive water-retaining containment wall.
Alternatively, thickened slurry can be deposited directly onto relatively flat ground – known as central thickened discharge – with appropriate allowances made for surface water management where required. Disposal of thickened slurry is sometimes combined with mechanically enhanced evaporative drying methods, such as pressure filtration, as seen in the alumina industry.
Underground Tailings Backfill
In some instances, tailings can be formed into a cemented paste and delivered underground to backfill mined out underground stopes. This process is usually reserved for coarser-grained types of tailings, since the dewatering cost is higher for finer-grained tailings, which also achieve a lower final shear strength in the backfill once hardened.
Co-Disposal of Tailings and Waste Rock
The waste rock from a mining site is typically disposed of independently of the tailings, creating two separate waste streams. However, economic and environmental benefits can sometimes be achieved through co-disposing of these different waste products in a single location. Successful co-disposal has been achieved by dumping benign waste rock at one end of a completed open pit, and benign thickened tailings at the other.
Integrated disposal of waste rock and paste tailings is a slightly different option, which involves the two materials being mixed together prior to disposal. The integrated product may take the form of a pumpable slurry or a dense paste, the latter of which can sometimes be used as a sealing material, providing both waste products are geochemically benign.
Filtration and Dry Stacking
Dewatering tailings beyond the paste state creates dry, solid cakes that may be transported via a conveyor or truck to their final storage location. These filtered tailings may then be placed, spread or compacted to create a stable ‘dry stack’. This method of disposal and storage is typically favoured in arid or desert regions, where water conservation is of utmost importance, hence the cost-intensive dewatering process is warranted.
Dry stacking facilitates progressive site rehabilitation, and is also advantageous on sites with difficult or constrained topography that may prevent the construction of a conventional tailings dam. However, the numerous advantages of the dry storage method must be considered in context of its high capital and operating costs.
Selecting the Best Tailings Storage Facility for Your Site
At Hall Water & Tailings, we have a strong track record in delivering successful tailings management solutions to the mining and heavy industrial sectors. We will collaborate with you and your team to construct a new tailings storage facility or address any challenges relating to your existing tailings storage facility.
Simply contact us on +61 (7) 5445 5977 and our experienced team will guide you through the process.