Good Tailings Management No Longer OptionalBy Paloma Duran | Thu, 05/20/2021 - 17:44
Multiple tailings storage facility (TSF) failures have increased awareness of the importance of mine waste management. As a result, many mining companies are improving their game by considering key areas for managing tailings throughout the life cycle of a mine and its subsequent closure. However, there is still work to be done and a great deal of room for improvement.
Tailings in Mining
Tailings are high-risk assets that are a by-product of the mineral recovery process, which are generally created when ore is crushed and ground in the milling processes, generating a liquid slurry that contains metal or mineral particles and water. The tailings are pumped to storage facilities that are typically built with earth dams. As the residue gradually dries and compacts, vegetation can be planted to recover the environment. To discharge tailings water to the drainage system or reuse it, it must first be treated to eliminate contamination and potential risks to the environment and local communities.
The management of tailings is a long-term responsibility and must be carried out in accordance with regulatory regimes to make it safe and effective throughout the life of an operation and after its closure, according to the International Council on Mining and Metals (ICMM). Aftercare varies greatly depending on the nature of the tailings. As a result, mining companies must study their residues and implement the best short-term and long-term measures to ensure their physical and chemical stability, as well as proper future land use. Without proper management, tailings can have extreme impacts, as pollution and dust emissions can be toxic. There have been cases where tailings storage facilities fail, causing materials to flood, affecting the environment and sometimes resulting in death.
There are several factors that increase the risk of failure of tailings dams compared to other structures, including a high-water level on the tailings dam slope, lack of monitoring and understanding of its behavior and an inadequate investigation of the dam’s location.
Accidents and Risk Facilities Around the World
On March 28, the Yichun Luming’s TSF in Heilongjiang released 2.53 million m3 of mining waste into a local river system. The waste reached as far as 110km from the mine site, where the chemical oxygen demand reading that measures water quality was 5.7 times higher than normal levels. There were no casualties but the government promised to carry out investigations to identify hidden risks. Currently, the mine and other small supply extensions have resumed operations albeit at a limited scale due to environmental concerns.
The collapse of Minas Gerais in Brumadinho in January is considered the worst industrial accident in Brazil. The tailings dam released a mudflow that killed 270 people and affected the mine's offices, cafeteria and nearby houses, farms, inns and roads. The Brazilian mining company Vale and German auditor TÜV SÜD face charges including murder and environmental crimes. According to investigations, TÜV SÜD inspected the dam before the accident and its analysis did not meet official requirements. Brazilian judges have ordered Vale to repair the damage, involving socio-economic and socio-environmental compensation.
On June 4, a tailings spill at the La Cieneguita mine in Chihuahua operated by Rio Tinto and Pan American Goldfields caused the death and disappearance of seven workers. The failure of the La Cieneguita dam released 249,000m3 of tailings and 190,000m3 of construction material. The Chihuahua Attorney General's Office reported that an investigation was initiated to find out the causes of the accident. PROFEPA reported that the mineral recovery processes at the site did not involve cyanide, so only heavy metals reached the river. However, both the company and the government tried to contain the spill through a 12m rock wall.
Responsible Mining Foundation (RMF) reported that there are 223 billion tons of tailings stored in more than 30,000 tailings storage facilities around the world that are active, inactive and abandoned. RMF highlighted the great risks that exist, especially at abandoned sites because there is no oversight. Approximately a third of the global TSF portfolio requires urgent intervention. The costs to eliminate those risks are high are estimated at US$670 billion.
Promoting Good Tailings Management
The International Council on Mining and Metals (ICMM), the United Nations Environment Program (UNEP) and the Principles for Responsible Investment (PRI) developed the Global Industry Standard on Tailings Management published in 2020. This is the world's first tailings management standard that can be applied to existing and future tailings facilities. The standard has strengthened mining practices by integrating local social, environmental, economic and technical criteria covering the entire tailings facility life cycle, from site selection to post-closure. It also has established higher levels of accountability and expectations about transparency and disclosure of information.
According to hydraulic engineering information center IZW, the keys to avoiding disasters and reducing risks are good data collection, proper design and an efficient monitoring system. However, equipment must be reliable in the long term and the equipment must be inspected and controlled regularly.
Tailings Management in Mexico
The Mexico: Mining Laws and Regulations 2021, NOM-141-SEMARNAT-2003 establishes the specifications and criteria for tailings, including on-site preparation, construction, operation and post-operation of tailings dams. In addition, mining companies must obtain permits, submit a risk assessment, register a Hazardous Waste Management Plan, have environmental insurance and notify the authorities in the event of an accident.
The need to implement global standards and technology to improve tailings management has long been a goal for many mining companies, together with the implementation of best practices and technologies to achieve it. Couer Mining is one example. During Mexico Mining Forum 2021, Mitchell Krebs, CEO of Coeur Mining, said the company pursues high standards and that Coeur's operational risk reduction plan on tailings dams follows authorized international guidelines, effective filtration and hydraulic control systems. Furthermore, Krebs mentioned that the tailings of Palmarejo, Coeur’s operation in Mexico, are classified as non-potentially acid-generating and that any water discharged to the environment passes through a secondary inverse osmosis treatment to comply with environmental regulations.
Bradley Langille, CEO of GoGold Resources, said that his company has generated innovation around tailings. He explained that as a junior company, it is difficult to have great technologies like other mining companies because of limited resources. However, Langille said that GoGold is working to promote ESG practices. At GoGold's Mexico asset, the Parrot project in Chihuahua, the company has been transporting tailings to a heap leach facility located 14km from the city of Parral.
Another company in Mexico that is committed to responsible tailings management is Newmont Corporation. In an interview with MBN, Kimberly Morrison, Senior Director of Global Tailings Management, explained that the company's standards and guidance explicitly cover tailings management, including requirements to ensure safety and stability. Newmont’s TSF in Peñasquito has a perimeter of 11km and a production of 120,000 tons per day. Morrison noted that maintaining long beaches adjacent to the centerline elevations is one of the key success criteria for facility operations.
New Technology to Improve Tailings Management
As tailings and their proper management have spread among operators, companies have developed solutions that are helping mining mitigate the risks and impact of tailings. These solutions are expected to grow and be further promoted as green trends permeate mining and other sectors.
CETCO offers geosynthetic clay liners (GCLs), including liners for tailings dams and heap leach pads. GCLs are a sustainable option as they reduce a project's carbon footprint by reducing fuel consumption. They also minimize the risk of leakage and, according to Michael Donovan, Director of Global Research and Development at CETCO, one of the reasons why tailings dams fail is instability caused by seepage. Another product is CETCO's RESISTEX GCL, which is a hydraulic barrier that provides the highest level of chemical compatibility for industrial waste storage.
Reynolds Soil Technologies (RST) offers services to rehabilitate and treat dams. It has crusting agents to control dust when moisture in tailings dams is recycled. In addition, RST's hydroseeding and hydraulic crushing technologies are also being used for tailings dam rehabilitation to improve land revegetation after the end of the mine's life cycle.
FLSmidht, meanwhile, offers EcoTailsTM and AFP-IV® Colossal filtration solution™ as a smart and sustainable solution for tailings management to eliminate the need for a wet tailings dam and allow almost all of the process water to be reused. These solutions minimize environmental risks, decrease complexity and help mining companies with their social license. In addition, the company has a wide range of solutions that adapt to the needs of miners, including solutions for sand dam tailings, thickened tailings, paste tailing, paste backfill for underground mines, filtered tailings and co-mingled tailings.