An exploration of ideas that could help make the reuse of waste and tailings more economically viable
Over the past 15 years, the mining industry has begun to incorporate the concepts of sustainable development and sustainable mining practice across the life cycle of mineral operations. This requires addressing economic issues and community impacts and concerns, as well as environmental protection, and is captured in part by the phrase ‘design for sustainability’ (McClellan et al, 2009). Over the same period, the industry has seen a gradual decrease in ore grades for many mineral commodities. As a result, large volumes of tailings and mine waste rock are being produced around the world, and it is expected that the annual production volumes of these materials will increase, even if there is not a significant change in the demand for materials.
Another related thread of change has been the realisation that societies need to move away from linear economies (raw materials, production, consumption and disposal) toward more circular ones. This will help societies become more resource efficient, which is defined by the United Nations Environment Program (2011) as reducing the total environmental impact of the production and consumption of goods and services, from raw material extraction to final use and disposal. The goal is to create ‘more with less’ and deliver greater value with less input. Circular economies require thinking in terms of the waste hierarchy (reduce, reuse, repurpose, recycle, recover, landfill). The challenge is that the waste hierarchy was originally designed to address embodied mineral content in products, rather than mine waste and tailings generation. It will need to be reconsidered in a mine life cycle context, focusing on a value-based conception of waste (Van Ewijk and Stegemann, 2016).
In parallel with these changes, it has remained an imperative in the mining industry to dispose of waste materials as economically as possible while protecting the environment. Single handling of these materials has been the main target, which reduces the life cycle costs of their management but may make reuse of waste and tailings technically more difficult or economically infeasible.
This article explores a rethinking of the large-volume earthen material waste issue at mines. The underlying theme is that some or all of these materials can be resources for the future that potentially have value and so can positively contribute to sustainable development. These resources can:
- offer economic gains to firms, communities and societies
- contribute to environmental wellbeing
- enhance social interactions with the previously mined landscape
- reduce governance commitments if proper policies are put in place.
Each of these topics will be briefly explored. This will be followed by a discussion of approaches to manage design and operations to allow for future resource recovery.
Magnus Ericsson from the Luleå University of Technology has reported that there are currently approximately 75 major tailings re-mining projects globally. Minerals such as gold, diamonds and copper are being reclaimed. One of the most successful economic projects in using tailings as a resource is the Ergo Project, which involves large-scale tailings hydraulicking and reprocessing of gold tailings in the Johannesburg area of South Africa. The project was established in the 1980s and has gone through multiple renewals. After removing the tailings and recovering gold and uranium, the land is made available for housing developments. The remaining tailings are deposited in a consolidated tailings facility south of the city.
Another recent example of land reuse is Peabody Coal’s Ereen coal mine reclamation in Mongolia, in which a large portion of the reclaimed land was turned into hay paddocks that the local herding community can harvest for their own herds or sell for income. Local herders also serve as environmental monitors, providing them with an additional income stream (The Asia Foundation, 2009).
In another major project being undertaken in Kimberley, South Africa, De Beers is processing tailings from its now-closed local diamond operations. Its tailings plant is producing 800 000 carats of diamonds a year. However, this project is not without challenges as illegal mining is common. The company reports illegal miners caught on their land to the police, but that has not stopped the problem because many local people believe that De Beers is done with mining and the land where the tailings are stored belongs to the town, not the company.
Where longer-term care and maintenance is required, upskilling of local residents to carry out environmental monitoring and maintenance work is an obvious source of ongoing income, particularly for mines located in remote rural areas of developing countries where such income may make a significant contribution to families and communities. In a clear example of ‘shared value creation’, this type of arrangement is more cost-effective than the complicated travel and logistical arrangements required to send outsiders to the site for monitoring, while contributing income and increased capacity to the local community. In this context, shared value means aligning the business interests of extractives companies with community needs and priorities.
It takes time and energy to set up the governance mechanisms so that these arrangements are consistent with local community norms and capacities, and to ensure that the new resources continue to be shared collectively.
The design and construction of tailings containment structures is usually part of every major mining project. It is much more effective to concentrate or clean the mined product close to the mining facility than transport it elsewhere.
In cases where mining does not require backfilling of stopes, storing tailings back in underground mine voids is a rather expensive exercise and is commonly avoided. However, following a number of tailings dam failures, mine planners have started considering the idea of underground permanent storage. Alternatively, contemporary mining facility designs provide post-mining land uses of tailings impoundments as these are mandated by environmental legislation and permitting procedures in many parts of the world. For example, a number of tailings impoundments in North America are being turned into solar farms. In addition, tailings ponds may be designed ex ante to have better environmental properties (Edraki et al, 2014), which can be accomplished by better management of the water, reagents and minerals remaining in the tailings. For example, sulfide flotation has been implemented for tailings to produce non-reacting products that will not produce acid or sulfates. This approach is also being investigated for a number of development projects.
However, very few designs view tailings impoundments as a potential resource. Recent research (Harrison, Power and Dipple, 2012) shows that some tailings (ultramafic) can be used effectively in the sequestration of carbon by converting CO2 to carbonate minerals.
Another technology that is being investigated on a worldwide scale is geopolymerisation. Under this process, a ‘paste’ can be created through a relatively simple chemical reaction. Depending on the components present, the paste can be designed to ‘bond’ with different waste streams, such as mine tailings. This process can transform tailings into a new supply of raw materials for infrastructure construction, including roads and highways (Ahmari, Chen and Zhang, 2012) and even commercial buildings (Ahmari and Zhang, 2012).
Natural Resources Canada has a green mining initiative that ‘targets the development of innovative energy-efficient technologies required for mining to leave behind only clean water, rehabilitated landscapes and healthy ecosystems’ (Natural Resources Canada, 2016). Recent publications (Tisch et al, 2012, 2015) present the results of studies on biomass production on closed tailings facilities for green energy production.
Environmental accidents are usually the result of the alignment of several adverse scenarios. Statistically speaking, there is always a probability that an accident will occur. The failure of the Fundão tailings dam at the Samarco mine in Brazil is a recent example of how the cumulative effects of multiple small design and construction flaws, combined with operating decisions, can lead to an environmental and social disaster (Morgenstern et al, 2016). As such, an environmentally friendly tailings facility could be designed as a group of smaller facilities with multiple end uses that can diversify potential impacts, reducing the risk profile both for the operation and for other stakeholders, including local communities.
The concept of redesigning for smaller, multiple facilities also opens potential new opportunities for post-mining management or economic opportunities as ‘debundling’ from large, technologically complex and high-capex designs provides more opportunities for national or local businesses to play a role.
Social interactions with the landscape
It is common to construct mine waste facilities as geometric forms that do not necessarily approximate features in the natural environment. Landform engineering is an important aspect of the mine closure and reclamation process. Landscape architectural planning during the early stages of mine planning can also be implemented. Large flat areas on the top of mine waste facilities may be used as future agricultural lands, an activity currently being developed in China. Conversely, where potential future land use is not a pressing need, community members may prefer a landscape that has a more natural form. To the degree that (non-liquid) waste and tailings piles are given shapes that are inconsistent with natural land forms (ie too many angles and flat tops and not enough curvature and randomness), they may be considered unattractive.
In either case, an important aspect of achieving a design that contributes to social well-being is the early engagement of communities to understand their expectations of the mine landscape during and following operations. This implies an early engagement process, but relationships to the landscape are not necessarily unchanging, nor are social needs or values. Engagement should be ongoing and agreements revisited on a periodic basis as new opportunities may develop or the local peoples’ needs or expectations of post-mine land use may change over time. This has been seen in community agreements that were supposed to serve for the full mine-life of a more than 20-year operation, yet as employment, educational levels and generational changes advance, new agreements are needed to reflect the changing needs and aspirations of the parties. Early impact and benefit agreements in Canada did not include consideration of the need to update agreements, but second-generation agreements today tend to be negotiated as ‘living documents’.
Mine waste facilities can be long-term regulatory and corporate liabilities if they produce contaminated effluents. Acid rock drainage and metal leaching is a major problem at many mine sites and may be difficult, or even impossible, to control once started. However, these facilities may still be a resource for the recovery of metals. Further technology development may allow for the future recovery of low-concentration metals from the effluent.
Mine waste governance
Ongoing monitoring of mine waste facilities during the post-closure period may provide employment to local communities. Ideally, these sites should be relinquished from operator to original landowner or new institution after satisfactory completion of closure activities, thereby reducing governance commitments. However, sufficient regulatory oversight should be exercised to identify potential future site disturbances for the recovery of metals or other perceived resources.
There are several governance implications from the community and civil society side. First, in many developing countries, there is little or no regulatory requirement or oversight of the closure process for operations and even less so for exploration. As a result, assuming a meaningful/credible regulatory role may not be appropriate at this stage. However, progress is being made in many jurisdictions in this regard, and it is expected that pressure from communities, as well as from financial institutions in accordance with the Equator Principles, will influence more uniform international approaches.
Problems may still be posed when there are ongoing environmental liabilities associated with a project. In this case, longer-term bonding may be needed as a long-term or perpetual care site cannot be considered closed or the liability relinquished. The governance commitments from mining companies must also be robust for sites that require ongoing monitoring, maintenance and operations (such as water treatment plants).
A local institution to receive funding, manage the oversight role and pay local monitors can be an intermediary strategy for transferring economic opportunities to the local area when there is poor government oversight and a lack of capacity in the local community. This could be an existing institution, or a foundation could be set up with ongoing funding that pays for environmental management of a site while providing ongoing seed money for social development programs. These programs could improve local social stability and reduce the risks to the remediated areas that can stem from poverty and pressure on resources.
A range of options is available to manage project design, operations and closure to increase the opportunities for resource recovery. These options include:
- Ongoing community engagement, especially with respect to envisioning the future of the area.
- Careful consideration of a wide range of alternatives for all aspects of project development, including mining method, processing options, mine waste materials management options and site selection for mine waste facilities.
- Complete characterisation of all materials to identify the presence of specialty metals (eg rhenium in copper ore bodies), combined with a value-based conception of waste that estimates the resource value of the materials. This should be supplemented with a rethinking of the waste hierarchy in the context of mining and mineral processing so that there is not an automatic presumption of disposal.
- The EU is working to devise a new mineral policy, the goal of which will be to incorporate both primary and secondary minerals in mineral supply/production policy. The challenge is that policy, law and regulation of mining in virtually all cases resides in separate legislation and ministries to waste management. If mine waste and tailings are to be redefined as sources of secondary materials, there will need to be coordination across government agencies to ensure that the rules within one domain do not conflict with rules in another.
- Life cycle planning for the project on an ongoing basis, combined with design for sustainability. For waste and tailings, this implies storage in a manner that will make reprocessing of waste and tailings more feasible, rather than less. This may potentially conflict with the goal of minimising the surface footprint of waste.
- To identify best-fit, post-closure uses and align design, management and closure activities, work should be done early in the project cycle to identify economically useful and desired scenarios after closure, with input from stakeholders.
- Increasingly, dialogue and early-stage agreements are being used to address the concerns of local populations and to set up agreements to protect key social and environmental values. For effective planning, the economic use after closure should become part of the prior agreements with communities that can contribute to overall project acceptability.
- The challenge of developing participatory mechanisms to ensure that the input of local populations is representative and includes the people who are most concerned with and effected by the impact.
- Post-mining land use is an important aspect of mine planning. It is possible that specific plans for future site uses are developed with community support and that the project is sold to another company. While the future site use plans can be transferred, the new owner may consider ongoing resource recovery from the mine waste or new orebodies as the preferred site option. This will put the new owner’s expectations in direct conflict with the carefully assembled future land use plans, and the new owner will have to work closely with the community to maintain its support as the plans develop.
- Careful record keeping of material movement to waste rock and tailings facilities is essential to allow future identification of material locations. Without having good records of
material locations, selective re-mining may not be possible.
- Complete, as-built plans should be prepared during operations and closure
to confirm the locations of all potential waste materials that must not be disturbed and the thickness of engineered covers etc. This information is essential for ongoing environmental protection if re-mining is done.
Operational and societal challenges remain, and more will be identified as the efforts of embracing the potential of mine waste as a resource intensifies. The first challenge is to agree on the stakeholders and their approach to identifying the data collection needs for a specific project, as well as identifying the entity that will be responsible for maintaining the site records. Corporate control of this may not be the optimal approach, but governments may not be in a position to be the custodians of it either.
Ahmari S, Chen R and Zhang L, 2012. Utilization of mine tailings as road base material, in Proceedings GeoCongress 2012, pp 3654-3661.
Ahmari S and Zhang L, 2012. Production of eco-friendly bricks from copper mine tailings through geopolymerization, Construction and Building Materials, 29:323-331.
Asia Foundation, The, 2009. Land reclamation: a Mongolian citizen’s guide [online]. Available from: http://sgpmongolia.org/upload/Land%20reclamation.pdf
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Harrison A L, Power I M and Dipple G M, 2012. Accelerated carbonation of brucite in mine tailings for carbon sequestration, Environmental Science & Technology, 47(1): 126-134.
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Natural Resources Canda, 2016. Green mining initiative [online]. Available from: www.nrcan.gc.ca/mining-materials/green-mining/8178
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Tisch B, Hargreaves J, Beckett P, Lock A and Spiers G, 2012. Post-mining agriculture for biofuels on tailings: an overview of results from the Green Mines Green Energy (GMGE) initiative, in Proceedings ICARD Conference, Ottawa.
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