Time to talk about tailings dams

Molly Lempriere 27 March 2019 (Last Updated March 27th, 2019 09:53)

A horrendous accident in Brazil this January claimed the lives of hundreds after a tailings dam operated by Vale collapsed, releasing a deadly wave of iron tailings and mud. Tailings dams are notoriously dangerous and have claimed lives before, so are there other alternatives and what can be done to make them safer?

Time to talk about tailings dams
The collapse saw 12 million cubic metres of mud and sludge spilled into the local environment. Credit: TV NBR, via Wikimedia

On 25 January, a tailings dam at the Córrego do Feijão mine in Brumadinho, in the Minas Gerais region of Brazil collapsed, spilling 12 million cubic metres of mud and sludge. At the time of writing, 215 people were confirmed dead, with a further 91 are missing.

“The Brumadinho dam failure in Brazil is a human and environmental tragedy and our thoughts are with those who have lost loved ones, or have family members, friends or colleagues who are still missing,” says International Council for Mining and Metals (ICMM) CEO Tom Butler.

Vale CEO Fabio Schvartsman said: “Most of those affected were Vale employees. I’m completely torn apart by what happened.”

This tragedy is far from the first time a tailings dam such as this has collapsed; in 2015 another Vale affiliated dam in Samarco also collapsed, killing 19 people and releasing 50 million tons of iron mining waste into the Doce River. Until the Brumadinho collapse, Samarco was considered Brazil’s worst ever single environmental disaster.

Notoriously dangerous

Tailings dams have a long history of ruptures and collapses. In this century alone, there have now been 11 serious dam failures. This number also appears to be on the rise, according to figures produced by researchers at World Mine Tailings Failures (WMTF).

“Without major changes to law, regulation, and to industry practices, as well as without new technology that substantially reduces risk and increases loss control, our current prediction is for 19 very serious failures between 2018 and 2027,” states the WMTF.

Tailings dams have been used for over a hundred years and are the most common disposal system for mining waste, having really taken off in the second half of the 20th century as technology improved. “They enable large scale and long-term storage of waste from the mineral extraction process,” explains Butler.

They are colossal structures, generally considered to be some of the largest man-made structures on Earth, and are huge feats of civil engineering. Brazil’s largest tailings dam, the Maravilhas II dam, for example, stands 90m high and has been built up over 20 years. But they are much more likely to collapse than water dams, largely due to their industrial function.

“Embankment dams are prestigious structures used to profitably store water, whereas tailings dams are required for the storage of unwanted waste, desirably at minimum cost,” states the report ‘Tailings Dams: Risk of Dangerous Occurrences’, published in Geoenvironmental Engineering.

Furthermore, the dams tend to be altered throughout their lifespan, generally increasing in size as the mine life is extended. This gradual building process increases the chance that conditions could change, or supervision could fail.

There are multiple reasons why a tailings dam may collapse. These include “excessive amounts of heavy rain or poor foundations,” explains GlobalData mining analyst Alok Shukla. “Or tailings liquefaction, which can also lead to leakages into surface and groundwater and are a threat to wildlife.”

Brazil seems to be worst affected by tailings dams collapses, with the Samarco disaster, among others, still very present in the country’s consciousness.

“Since the year 2000, there have been around 50 tailings dam failure related cases around the world; of these Brazil accounted for 14% cases,” says Shukla. “Brazil has over 80 upstream tailings dams; these are the cheapest to build and are generally less stable than other types of tailings dam.”

Do they need to improve or be removed?

Tailings dams are the most common means of waste disposal in the mining industry because of their ability to hold huge amounts of material, as well as their cost effectiveness. However, there are alternatives that will undoubtedly receive renewed interest from mining companies following the recent disaster.

“Riverine tailings disposal is used at a small number of operations,” says Butler. “In some situations, tailings have been disposed of in inland lakes. Deep sea tailings disposal may be an option depending upon the location of a mine. Tailings can also be stored underground in mined out voids by a process commonly referred to as backfill.”

However, all of these options have downsides, and most are inappropriate for mine operations of the scale of those such as at Brumadinho. The mine produced iron ore, and while it was one of Vale’s smaller mines, it still produced 7.8 million tons of iron ore in 2017 and had been running for years. The dam was set to be decommissioned, as it was no longer in operation having reached capacity.

While tailings dams are inherently risky, there are things that can be done to try and ensure their safety.

“Certain points can be taken into consideration in order to make tailings management much safer,” says Shukla. “These are minimising water held in the tailings storage facility; thickening or filtering of tailings; widening the dam crest to prevent the dam’s erosion; placing the sand to infill natural voids and cracks; [and using a] monitoring system equipped with latest technologies even to detect the slightest movement in soil.

“After a mine’s closure, reclaim the site with vegetation and erosion resistant surfaces, as well as rely on qualified and experienced professionals to take care of tailings dam’s operations.”

The Brumadinho tailings dam was considered safe by an independent auditor, German firm TÜV SÜD, as recently as September 2018, which has raised questions as to whether even following best practice is enough to ensure safety.

The beginning of the end for tailings dams disasters?

The exact cause of the Brumadinho dam disaster is as yet uncertain, although static liquefaction is generally considered the most likely source. However, it is currently hard to learn lessons from it, which will undoubtedly come as more details about the collapse become clear.

“Clearly the industry has a challenge in this area,” says Butler. “Despite the two major failures in recent years that resulted in loss of life, tailings dam failures are low probability events, albeit with devastating consequences. We need to find out what has happened in this incident and respond accordingly.

This is a sentiment Shukla agrees with; he predicts that the disaster could lead to the adoption of alternative waste disposal systems.

“Certainly this tragedy will push miners to be extra careful when coming to manage the tailings dam operations. Tailings dam failures cause huge loss of life, as well as being some of the worst environmental disasters miners face and cause huge economic losses. Miners will certainly be looking at adopting more stable dam types, as well as dam monitoring systems equipped with the latest and most sensitive devices that can detect even minute soil movements. Furthermore, they will be hiring qualified and experienced professionals to look after tailings dam operations,” he says.

Already, Brazil is looking to ban upstream dams in an effort to improve safety; of the country’s 740 tailings dams, there are 88 upstream ones currently in operation. Vale itself has taken action since the disaster to speed up the decommissioning of its 10 upstream dams.

“Upstream dams are waterlogged and therefore susceptible to cracks that can cause bursts,” says Shukla. “Recently Brazil’s mining agency announced its plan to ban upstream tailings dams used for storing mining waste.”

Other mining companies have shared plans to rethink their use of tailings dams following the Brumadinho disaster, and experts have reaffirmed that if waste management practices don’t change, this will not be the last tailings dam disaster.

“We conduct regular monitoring audits and our dams are subject to independent third-party reviews,” said Simone Niven, Rio Tinto’s head of corporate relations. “Even so, our technical teams are working very hard, right now, to consider what more we can and should do. We will take part in any industry-wide response.”

For now, Vale has established two teams to investigate the cause of the collapse: the Extraordinary Independent Consulting Committee for Support and Recovery and the Extraordinary Independent Consulting Committee for Investigation. Meanwhile, work is still underway to recover the bodies of those still lost in the mud, before the clean-up of the area, as large as 300 football pitches, begins.