Minewaste rehabilitation and Circular Economy
It is somewhat ironic that as mining searches for and digs up valuable new resources, it is often simultaneously spewing out potential resources at the waste end of the operation. This opens up the possibility of applying circular economy principles post-mining to better develop resource efficiency and improve the environment simultaneously.
Introduction
Mining despite being an essential component for any economy is often a wasteful and polluting industry. With increasing awareness about the immediate need to focus on the integration of sustainable development investors and the community in general increasingly pressure the industry to address these issues, some companies are rising to the challenge. It’s somewhat ironic that as mining searches for and digs up valuable new resources, it is often simultaneously spewing out potential resources at the waste end of the operation. Tons of some rare earth minerals, for example, are locked up in waste dumps because it simply isn’t (or wasn’t) economical to go back and extract them. Either that or they’re too toxic to risk handling without expensive, and advanced, technology.
Incidentally, speaking of household waste[1] (and for comparative purposes), globally we produce around 1.8 billion tonnes (2 billion tons) of it a year or about 54.4 tonnes (60 tons) per second. The global construction industry is predicted to double their waste to 2 billion tonnes [2] (2.2 billion tons) per annum by 2025. Agriculture produces around 1 billion tonnes (1.1 billion tons) of waste globally each year. Both are considered highly wasteful industries yet their figures don’t even begin to compare to mining’s 100 billion tonnes [3].
It is becoming increasingly apparent that current methods of collecting and storing mining waste are not an ideal long-term solution. Rather, they’re an economically unfeasible, environmental time bomb waiting to go off. The January 2019 disaster in Brazil at one of Vale’s operations has highlighted this yet again. Unfortunately, waste management issues are only going to increase as the need for commodities like rare earth escalates and most in the industry agree something more needs to be done sooner rather later. Reprocessing tailings dams on operational projects are already common practice in the industry but usually only if there is enough money to be made from doing so. A good example of this is going back to treat polymetallic tailings produced by gold extraction when there are economic quantities of copper, lead, zinc, cobalt and nickel.
When it comes to historic waste, the situation, unfortunately, isn’t as clear-cut. Quite often, these old waste dumps are an unknown quantity and as such, present some problems. Before any attempt can be made to reprocess one, a resource calculation needs to be done. That costs money. Then the findings have to be presented as a business case to potential investors. That too costs money.
Experts believe that a dynamic interaction across these five areas will drive the mindset change for re-thinking mining wastes. It includes social dimensions, geoenvironmental aspects, geometallurgy specifications, economic drivers, and legal implications. At its core is the overarching question: “How can the mining industry create new economic value, minimise its social and environmental impacts and diminish liability from mining waste?”
We produce around 1.8 billion tonnes (2 billion tons) of it a year globally or about 54.4 tonnes (60 tons) per second. The global construction industry is predicted to double their waste to 2 billion tonnes (2.2 billion tons) per annum by 2025. Agriculture produces around 1 billion tonnes (1.1 billion tons) of waste globally each year.
Understanding Mining Waste
Mine waste facilities mainly consist of waste rocks dumps and tailings dams, requiring appropriate management both in the short- and long-term[4].
Waste Rocks Dumps: Mining operations produce large quantities of waste rocks, which often has little or no valuable minerals. Waste rocks contain coarse, crushed, or blocky material covering a range of sizes, from very large rocks to fine particles. The current practices of dumping waste rocks by trucks, or draglines in the case of coal mines, create very large layered structures with preferential flow paths, which are conducive for the generation of acid and metalliferous drainage (AMD)—a significant challenge to mine owners, regulators, and other stakeholders. AMD, generated through the oxidation of sulphide minerals (mainly pyrite) in waste rocks, comprises poor-quality leachate typically characterised by acidic pH and high concentrations of sulphate, iron, and heavy metals.
Remediation of acid-producing mine waste and treatment of mine water can be costly. Management costs for AMD have been estimated globally at approximately US$ 1.5 billion per year [5], while the overall environmental liabilities are estimated to be more than US$ 100 billion [6]. Integration of an AMD management plan, from the early phases of exploration until final closure, can help to decrease the environmental impacts. Various low-cost waste products have been used to manage AMD[7]. Fly ash has been used to help neutralise AMD, improve the quality of degraded soils, and as a part of a cover system designed to isolate potentially hazardous mining waste. Waste rocks can also be a resource of minerals and metals, or have other applications at the mine site or elsewhere, such as backfill for open voids and underground mines, landscaping, capping for waste facilities, soil components and soil additives (e.g., for neutralizing infertile alkaline agricultural soils), aggregate and construction materials, and alternative raw materials for cement and concrete.
Tailings Dams
Volumetrically, mine tailings impoundments are among the largest man-made structures in the world[8]. Furthermore, tailings dam failures account for the major mining-related environmental disasters [9]. A major recent failure happened in January 2019 when Vale’s iron ore tailings dam in Brumadinho, Brazil collapsed and killed at least 206 people.
Another catastrophic event happened in November 2015 when a tailings dam at the Samarco Mine, Brazil, collapsed, releasing more than 43.7 million cubic meters of water and mine waste
In September 2008, 277 people died in an accident caused by iron ore tailings release from a dam break in Shanxi Province, China[10].
Similar to waste rocks dumps, tailings may generate AMD and, apart from the catastrophic failure of dam walls, may pose chronic environmental and human health issues due to the dispersion of contaminants by dust and seepage. Tailings may also contain mineral processing reagents, including salts and cyanide. There is also an increasing interest in new technologies to recycle and utilize mine tailings more effectively. For example, the alkali-activation of some mine tailings allows binders with sufficient compressive strength to be used as mine backfill or raw material in the construction industry. However, such materials can be used with cementitious binders, such as Portland cement, slag, lime, and gypsum[11].
Disposal of mining waste and tailings[12]
Disposal of coarse mining waste consists in conversing large areas with dumps or in filling abandoned open-pits By order of importance, the disposal of tailings is generally by:
a. Terrestrial impoundment: Terrestrial deposition is the predominant method for tailings disposal. It concerns fine waste and slurries such as mill tailings. The principle of tailings dams (or ponds) is to dispose of the tailings in an accessible condition that provides for their future reprocessing (once improved technology or a significant increase price makes it profitable).
b. Underground backfilling: This method is possible only for ore deposit without communication with an aquifer. Such an operation is usually costly and will be carried out for stability and safety reasons.
c. Deepwater disposal: The disposal of tailings and solid waste directly into bodies of water although sometimes used in past operations, is rapidly becoming non-authorised as a standard practice due to the significant pollution effects it can have on the receiving waters and the possible subsequent impacts on the livelihoods of the local communities.
d. Recycling: Recycling is not classified as disposal. Waste rock may have no market at the moment occurs. If a market will emerge later, the rock stored temporarily can be sold as aggregate when environmental specifications are met. With new techniques, the tailings can be reprocessed.
What is the mining industry doing about the waste challenge?
Sanitising waste dumps that contain millions of tonnes of material is an expensive exercise though so it invariably doesn’t get done until or unless the situation becomes critical. Companies focus instead on interim measures like containment and the capture of whatever leaches out, which brings us back to where we started. Namely, that these are not sustainable and that cleaning the stuff up so it can be put back into the ground as clean fill or safely reused for other things is by far the best solution all round.
This is exactly what happened at the Kilembe copper mine in Uganda where the tailings are typically around 80% pyrite and cause acid mine drainage. To avoid ongoing problems, the company ran the tailings through a tank bioleaching process to convert the sulphides. During the process, they were able to recover some of the cobalt that was in the tailings. The project was upscaled to convert all 900,000 tonnes of stored tailings with enough cobalt being extracted to pay for the process. Unfortunately, though, this will usually only be done when companies can expect the same results as Kilembe and that’s not always going to be the case.
Vale’s recent experiences could well prompt more companies to consider it in this light! The Brazilian miner is staring at lawsuits, class actions and a huge $4.9 billion US in costs and lost revenue in the wake of its Brumadinho tailings dam failure. Some of its employees are also facing criminal charges.
If companies like Comstock and its partners Oro Industries and Mercury Cleanup are any indication then some in the industry are moving in the direction of circular economics. The Nevada-based company is looking at ways of recovering mercury from tailings dumps. Mercury is one of the banes of mining, including artisanal gold mining. In the past, reports have found this sector of the industry alone uses some 1000 tonnes (1.1 tons) of it. Therefore, any safe and effective way to remove and recycle mercury from waste should get the industry’s attention in a big way. Comstock is planning to use their Comstock Lode gold and silver deposit as a crash test dummy using technology developed by Oro and Mercury Cleanup.
B9 Plasma, Inc., has successfully applied its patented Scavitron technologies[13] to mining influenced waters. Scavitron is the first treatment system designed to convert dissolved solids to stable precipitates, allowing for recovery of valuable minerals during processing. This breakthrough technology transforms the laborious and cost-intensive chore of mine water clean-up into a novel industry as well as a profitable endeavour. Scavitron applied on-site, replace conventional methods of ultrafiltration and alleviates the need for chemical additives. The B9 Plasma team is currently conferring with the mining industry and the military to find the most expedient means to market. Scavitron has no direct competition as yet; industry rumour has it that Brazilian & Canadian mining principals are furrowing towards that end as they, too, seek a way to ease the impact of their 200 years of accumulated mining waste.
Circular Economy Aspirations for Mine Rehabilitation and Waste Management
The mining sector is represented mainly by linear activities, being the major supplier of resources to modern society, nevertheless, the concept of a circular economy can help to improve the sector’s sustainability performance[14]. The aim would be to optimise the total material cycle from mining to manufacturing and to extend the product use phase, including the reuse and recycling of any waste streams arising in industrial and consumer activities to ensure overall resource efficiency and resilience[15]. Eco-efficiency and resilience have been identified as key characteristics of a sustainable mining operation, where optimising extraction and minimising the amount of valuable material in the waste would help to address problems, such as a declining ore grade, decreasing economic viability, and increasing mining legacies[16].
Under the conventional linear economy model, the current trends in mining, such as decreasing ore grades and higher tonnage rates, would continue escalating the problem with mining waste, and its associated inherent risks. Where feasible, replacing open-cut mining with underground mining will make a significant reduction in waste generation. Alternative approaches, whether they relate to better waste disposal techniques, such as paste and thickened tailings, better-mined land rehabilitation practices, or waste rocks and tailings reuse, recycling, and reprocessing, are urgently needed. The industry will need to move progressively to “closing the loop” strategies, which will dramatically reduce the quantities of wastes[17]
Another important and inherent part of the circular economy approach is the introduction of disruptive innovations[18]. In mining, these can include, for example, the integration of tailings reprocessing with mined land rehabilitation, and using the post-mine landscape for new economic activities and development. Two recent examples of such innovative thinking originate from North Queensland in Australia. Kidston Renewable (solar and hydro) Energy Hub has been developed on the historic gold mine site, with the reuse of two open pits at different elevation levels as part of energy generation and storage[19]
The New Century mine project involves reviving zinc concentrate production after mine closure, based on the reprocessing of historic tailings and taking responsibility for the final rehabilitation of the mine site.
The circular economy articulates the importance of closed-loop systems which reduce the need for the extraction and processing of new resources. This can be extended further to the overall impact of mining activities, with a particular focus on “getting more from less”. As such, within the mining and metals sector, following the 3R waste-reducing principle (reduce, reuse, recycle) can make a significant contribution. This includes examples across two categories:
(a) Circular economy sensu stricto:
Improving water and material reuse through cyclic systems and innovative technologies;
Maximizing reuse of waste and by-products;
Collaborating with the manufacturing sector to design adaptable and easy-to-repair products;
Better marking of materials and alloys to aid identification at end-of-life and allow subsequent reuse and recycling.
(b) Efficiency measures as part of the circular economy in a wider sense:
limiting the use of raw materials and balancing supply and demand;
Improving recovery rates in mining and mineral processing;
Minimizing waste generation such as tailings, gas emissions, and wastewater;
Developing feasible options for lower grade ores;
Extending the life of a resource, material, product, or service through better planning for future applications and reuse
Several different strategies for limiting mining waste and/or the associated environmental impacts have been classified by their ability to generate additional economic value and potentially decrease the environmental legacy of mining operations[20]. However, the best outcomes can be achieved with proactive waste management, which would combine ore body characterisation, mine planning, ore processing, waste disposal, re-processing, recycling and reuse, and finally land rehabilitation in one integrative approach[21]. This would be a crucial contribution that the mining industry can make towards the circular economy.
About the Author
Utkarsh Akhouri (LinkedIn) is an alumnus of Indian Institute of Technology, Kharagpur and has over 5 years of experience in the field of Mineral Economics, Governance, Raw Material Security and Circular Economy. He is currently leading a European Mineral Policy Think Tank as its COO and has participated in several inter-governmental projects promoting sustainability in the mining sector.
References
[1] https://www.theworldcounts.com/challenges/planet-earth/waste/waste-from-households
[2] https://www.transparencymarketresearch.com/construction-waste-market.html
[3] https://www.mining.com/circular-economics-reprocessing-waste-and-mining/
[4] https://www.mdpi.com/2075-163X/9/5/286/htm#B25-minerals-09-00286
[5] Lottermoser, B.G. Mine Wastes: Characterization, Treatment and Environmental Impacts, 3rd ed.; Springer: Berlin, Germany, 2010
[6] MEND. Mine Environment Neutral Drainage Manual; Volume 3: Prediction. Mend 5.4.2c; Mine Environment Neutral Drainage (MEND) Program: Vancouver, Canada, 2000.
[7] Jones, S.N.; Cetin, B. Evaluation of waste materials for acid mine drainage remediation. Fuel 2017, 188, 294–309
[8] Davies, M.P. Tailings impoundment failures are geotechnical engineers listening? Geotech. News Vanc.2002, 20, 31–36
[9] MMSD. Report of the Workshop on Finance, Mining and Sustainability: Exploring Sound Investment Decision Processes; Mining, Minerals and Sustainable Development Project (MMSD); International Institute for Environment and Development (IIED): Paris, France, 14–15 January 2002
[10] Ke, X.; Zhou, X.; Wang, X.; Wang, T.; Hou, H.; Zhou, M. Effect of tailings fineness on the pore structure development of cemented paste backfill. Constr. Build. Mater. 2016, 126, 345–350.
[11] Fang, Y.; Gu, Y.; Kang, Q.; Wen, Q.; Dai, P. Utilization of copper tailing for autoclaved sand-lime brick. Constr. Build. Mater. 2011, 25, 867–872.
[12]https://ec.europa.eu/environment/waste/studies/mining/0204finalreportbrgm.pdf
[13] https://www.mining.com/web/b9-plasma-inc-turns-mining-waste-into-wealth/
[14] Lèbre, É.; Corder, G.; Golev, A. The role of the mining industry in a circular economy: A framework for resource management at the mine site level. J. Ind. Ecol. 2017, 21, 662–672.
[15] Corder, G.D.; Golev, A.; Fyfe, J.; King, S. The status of industrial ecology in Australia: Barriers and enablers. Resources2014, 3, 340–361.
[16] Lebre, É.; Corder, G. Integrating industrial ecology thinking into the management of mining waste. Resources 2015, 4, 765–786.
[17] Rankin, W.J. Towards zero waste. AusIMM Bull. 2015, 2015, 32–37.
[18] Forum for the Future. Circular Economy Business Model Toolkit; Forum for the Future, Unilever; 2016; Available online: https://www.forumforthefuture.org/project/circular-economy-business-model-toolkit/overview
[19] Genex Power. Kidston Renewable Energy Hub. Available online: https://www.abc.net.au/news/2018-06-20/kidston-renewable-energy-hub/9890600
[20] Golev, A.; Lebre, E.; Corder, G. The contribution of mining to the emerging circular economy. AusIMM Bull. 2016, 2016, 30–32
[21] Edraki, M.; Baumgartl, T.; Manlapig, E.; Bradshaw, D.; Franks, D.M.; Moran, C.J. Designing mine tailings for better environmental, social and economic outcomes: A review of alternative approaches. J. Clean Prod.2014, 84, 411–420.