Have you ever wondered what they are?

Mining and mineral extraction have an important role in our world, providing materials we rely on and use in our day-to-day lives. During these activities, waste materials such as waste rock and tailings are produced, some of which can be problematic and require management to prevent impact on the environment and human health (Martin, Davies, Rice, Higgs, & Lighthall, 2002). This Insight explores management considerations associated with designing, building and operating a tailings storage facility (TSF).

What are Tailings?

Tailings are the fine materials left over from the processing of ore; typically, they are comprised of clay, waste minerals and water. Tailings may also contain other substances, such as heavy metals and residual chemicals used during processing activities. These substances can, if not managed correctly, impact groundwater and surface water and be harmful to plants and animals. To reduce these impacts, tailings waste is typically placed in purpose-built facilities, known as Tailings storage facilities (TSF). Well-designed and built TSFs provide safe and secure management options for the tailings while also allowing for the recovery of water.

Schematic of a Tailings Storage Facility (WEA, 2024)
Figure 1 Schematic of a Tailings Storage Facility (WEA, 2024)

Environmental Protection

In Australia, tailings management has been identified as a key risk and is, as a result, a priority for the Government and the community. To ensure the risks associated with TSFs are managed correctly, each state and territory has established a hierarchy which typically comprises of International Standards, legislation, industry guidance, guidelines, and codes of practice (Figure 2).

Internationally recognised standards, such as the Global Industry Standard on Tailings Management and the Good Practice Guide on Tailings Management, inform best management practices across the globe.  These standards aim is to prevent significant environmental or physical harm and to integrate social, environmental, and technical considerations (ICMM, UNEP, PRI, 2020; ANCOLD, 2024).

In Western Australia, TSFs are managed through approvals processes established under the WA Environmental Protection Act 1986 and the Mining Act 1978. It is also expected that a TSF is designed, built, operated, and closed in accordance with recognised international and national standards set out by ICMM and ANCOLD, respectively. State departments, such as the Department of Energy, Mines, Industry Regulation and Safety (DEMIRS) and the Department of Water and Environmental Regulation (DWER), provide material used by mining operators to guide compliance with best management practices (Figure 2). By adhering to regulations and using the provided guidelines, miners can minimise environmental risks and contribute to sustainable tailings management.

Figure 2 Framework adopted in WA to minimise impact from Tailings Storage Facilities
Figure 2 Framework adopted in WA to minimise impact from Tailings Storage Facilities

Disposal Methods and Facilities Types

There are numerous ways to dispose of tailings, each with its own advantages and disadvantages. Tailings disposal will either occur sub-aerially, where tailings are pumped above the water, or sub-aqueously, where tailings are deposited below the water. The latter method is often used to dispose of material with high sulphide content to avoid the production of acidic tailings by minimising oxygen exposure (Dixon-Hardy & Engels, 2007). Prior to disposal into a facility, tailings may be thickened, filtered, or dried through water removal and screening processes. The facility chosen to dispose of the tailings will vary according to water availability, energy supply, climate type, ore production rates, economics of the mine, and topography (Watson, Corser, Pardo, Christian, & Vandekeybus, 2010).

A range of TSFs are used to dispose of tailings, from disuse pits to large, engineered facilities.  Below are a number of more common facility types.

Paddock Storage Facilities

This style of facility is the most traditional and widely used, with approximately 96% of all tailings waste facilities in Australia being of this type (DCCEEW; Blue Environment, 2022). These facilities typically receive tailings that are 25-45% solid area comprised of engineered walls and basin which are impervious to water and are typically built above ground (Figure 3 (BHP, 2021)). This method is usually the most cost-effective, but it requires a high standard of engineering design to manage the associated risks effectively.

Figure 3 BHP conventional TSF
Figure 3 Typical example of a conventional large-scale tailing facility (BHP, 2021)
In-Pit Disposal

In-pit tailings disposal involves placing wet tailings in an old open pit mine, or dry tailings in either underground or open-pit mine voids (Figure 4). This method can reduce the costs associated with constructing purpose-built TSFs and is convenient for the operator. Despite seeming like a simple solution to tailings storage, it is only appropriate where groundwater is not relied upon as a water resource because there is a high risk of groundwater contamination (Engels J. , 2024). Despite this, the method is useful for storing tailings that have the potential to generate sulfides. Some considerations for this method are that it requires significant groundwater monitoring, may compromise the stability of surrounding mines, and requires extensive design planning to maintain the hydrological and physical stability of the facility (Cacciuttolo & Atencio, 2023).

Figure 4 In-Pit Tailings
Figure 4 In-pit tailings disposal of an old open-pit mine (Cacciuttolo & Atencio, 2023).
Valley Fill Facilities

This disposal method places tailings in the area created by joining the sides of a valley together with an engineered embankment, much like a dam wall (Dixon-Hardy & Engels, 2007). This method can accommodate large amounts of material, is often utilised in high topographies, and can be incrementally built upwards to increase storage volume (Figure 5). In contrast, the disadvantage is that it is vulnerable to rain events and external sources of water which may cause the wall to fail due to the high load pressure exerted on it.

Figure 5 Valley Fill example
Figure 5 Valley impoundment storage facility
(Teck, 2024)
Co-Disposal

This method involves producing an integrated mixture of fine and coarse tailings material after the water is extracted from the tailings (Martin, Davies, Rice, Higgs, & Lighthall, 2002). If thoroughly mixed and processed to be chemically benign, this material is more structurally stable than other methods because it has less interaction with oxygen, is less permeable to water, and has less potential to develop sulfide-derived acid (Engels, 2006). It can be a valuable by-product and has a range of applications, such as replacing natural clays as sealants or civil infrastructure. However, fully integrating the fine and coarse materials can be expensive.

Dry Stack Disposal

This method is where tailings material is removed from water and filtered of existing chemicals to form a fine dirt-like material, which can be compressed into pellets (Figure 6). This allows easy transportation to a storage facility, usually a remediation or fill site. The chemical concentration and material type of the dry tailings will determine what type of storage facility will be needed and, hence, what level of isolation is required to minimise water interaction and dust generation. If not managed correctly, there may be a risk to people, groundwater contamination or oxidation of sulphides (Dixon-Hardy & Engels, 2007). Removing the interaction with water and air to reduce the risk of contamination and dust generation is often a challenge.

Figure 6 Dry stacking tailings
Central Thickened Discharge Facility

This method utilises paste tailings, which are thickened and then deposited in the centre of a cone-shaped Impoundment (Figure 7). Often, the paste is placed on a slope to allow greater water recovery and reduce space requirements (ICOLD; UNEP, 2001). Higher water recovery rates and less water mobilisation supports the increasing use of this method, yet it requires a greater management effort, can higher operating costs, and is vulnerable to groundwater interaction (Engels, 2024).

Figure 7 Jon Engels example
Figure 7 Example of a facility using Central Thickened Discharge Disposal by Jon Engels (Engels, 2024)
Subsea Deposition

This method involves pumping tailings material into river systems or the ocean (Figure 8 (DOSI, 2019)). It may be used in areas where building a storage facility is not viable due to seismic instability, high rainfall, or health and safety considerations. Although this method is highly convenient, the environmental risks to aquatic systems should be carefully considered and ultimately minimised.

Figure 8 Deep Sea Tailings
Figure 7 Deep Sea tailings disposal (DOSI, 2019)

Choosing the Right Disposal Methods: Key Factors

Selecting the most suitable disposal method involves careful consideration of the tailing’s characteristic, and site-specific variables that determine a method’s suitability (Patterson, Piggot, & Casey, 2020). Assessing these thoroughly is essential to ensure the chosen method aligns with public health, heritage, ecological, and landowner values. The following details some key environmental and site factors that need consideration.

Site Conditions

Site selection is essential to minimise risks of facility failure and seepage. It is important to consider the local conditions such as surface water, topography, ground density, climate, geology, geomorphology, and groundwater (DMP, 2013). When designing a facility, it is critical to understand the local conditions such as foundation permeability, earthquakes and construction material characteristics to ensure the stability of these variables. Other factors considered include heritage significance, existing land use, surrounding areas, and other practical considerations for processing and optimising efficiency.

The Environment

Groundwater, surface water and air pollution can occur as a result of poor tailings management and facilities designs (Souza, Marin, & Hackspacher, 2017). Events such as unseasonal rain, river overflows, soil instability, earthquakes, and any other weather or climatic event may cause overtopping or erosion, thus posing an environmental risk. These events should be minimised as much as possible by placing the TSF in a location that reduces the interaction of any impacts such as weather, climate or natural environmental events. Such management actions could include changing the topographic location and proximity to surrounding surface water flow, or designing the facility to handle the predicted maximum rain events, and incorporating the use of liners and underdrainage systems to assist in environmental protection (Solgi, 2017).

Tailing Thickness

Tailings must have the right properties to allow them to be transported/pumped to and from the facility for further processing or drying out. Flocculants, dispersants, and filters may be used to adjust viscosity, elasticity, and solid concentration to minimise water in the material (Plog, 2015). This is an essential consideration when pumping wastes such as pastes or slurries using spigot deposition.

Chemical and Biological Reactivity

The treatment process and facility design depend on the chemicals used, the reactivity and/or stability of the minerals, and the environment’s sensitivity to them. Tailings often have a high chemical diversity, which can lead to various chemical and mineralogical reactions such as hydrolysis, oxidation, and leaching (Cacciuttolo, Cano, & Custodio, 2023). These reactions may lead to potential environmental impacts such as soil and groundwater contamination.

Water Use

Water management is one of the most important design aspects in TSFs to minimise environmental hazards and uphold stakeholder values. TSF design facilitates continuous water recycling, reduces the reliance on natural water systems and reduces contamination risk. Although water is used to facilitate the movement of soluble chemicals in ore processing, externally sourced water can cause the TSF to overflow, which may cause environmental and social damage (Cacciuttolo, Cano, & Custodio, 2023; Souza, Marin, & Hackspacher, 2017).

Tailings Management

Tailings disposal is an important consideration for the mining industry and community. When selecting a disposal method, it is important to consider local conditions, select a method that presents the least risk to the environment and the people that use the land around the facility, that adheres to regulatory requirements and adopts best practices.

If you or your organisation would like advice and support on tailings management and disposal, Integrated Sustainability should be able to assist. Please email us at enquiries@integratesustainability.com.au or call us at 08 9468 0338.


References

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