Brazil disaster throws spotlight on tailings management

Pollution to a reservoir caused by the Samarco tailings breach in 2016. Image: Flickr - Felipe Werneck/Ibama

The mining industry suffered a shock when the Brumadinho tailings disaster occurred in Brazil in January. Safe to Work examines the response so far.

Brazil experienced its worst ever environmental disaster with the collapse of Dam 1 at Vale’s Córrego de Feijão iron ore mine in Brumadinho, Minas Gerais in January.

The collapse of the upstream-style dam led to the deaths of an estimated 300 people, causing widespread condemnation.

It was also the Brazilian iron ore major’s second tailings failure in just over three years, following the Bento Rodrigues dam breach that killed 19 people in the same region in November 2015.

The Brumadinho incident has caused a ripple effect across the global mining industry, prompting responses from various Tier 1 mining companies, particularly to reinforce the safety of their upstream dams.

Tailings dams are generally constructed in one of three ways: upstream, downstream and centreline.

Upstream tailings dams, which are generally cheaper to build than their counterparts, begin construction with a dyke that continually expands upwards with the construction of raising lifts built in a trapezoidal pattern to accommodate waste as the tailings level rises.

These lifts are constructed on a bed of spigots (or a tailings beach) at the pond’s perimeter, a construction technique that introduces liquefaction to the sand or soil used to construct the lifts.

This contrasts with downstream dams, which build on the dam wall successively away (downstream) from the tailings pond, and centreline dams, where dykes are built vertically on top of each other.

In light of January’s Feijão incident, the Brazilian Government has decided to ban upstream tailings dams altogether by 2021.

The International Council of Mining and Metals (ICMM) has, meanwhile, elected to use an independent panel to develop new international tailings standards for its 27 members, a laundry list of the world’s leading mining companies that includes Vale, Glencore and Anglo American.

BHP chief executive officer Andrew Mackenzie praised the ICMM, saying the mining industry needs to act with greater urgency to make sure such incidents don’t happen again.

“While we don’t yet know the cause of the dam failure, we will review all lessons as they emerge and apply them to further upgrade the construction and operation of our dams,” he comments at a mining conference.

BHP was involved in the 2015 Bento Rodrigues tailings disaster through its Samarco joint venture with Vale, though the company settled a class action in August last year for $US50 million ($70 million) with no admission of liability.

The Doce River in the aftermath of the November 2015 Samarco tailings breach in Brazil.

 

BHP spin-off South32 was among the first mining companies to highlight its dam management standards in response to the incident with comments it placed near the start of its 2019 first half report. The company is also active in Brazil through a share in the Brazil Alumina bauxite operation.

The company highlighted its operational tailings dam inventory, which included 18 active dams and 15 inactive dams, capital expenditure on tailings dams over the past two years, and other tailings-related history dating back to May 2015.

This was in stark contrast with the company’s half-year reports for 2017 and 2018, which did not mention tailings management or tailings dams at all.

Rio Tinto followed by posting what was perhaps the most dramatic response to the disaster, announcing that it would review the tailings and water storage facility management standards it launched in August 2015 and last updated in 2017.

The company has 51 tailings facilities in Australia, nine of which are built using the upstream method.

“Rio Tinto is committed to play its part in any industry response, including an independent expert review,” Rio Tinto chief executive Jean-Sébastien Jacques says.

Anglo American, meanwhile, made a point of noting in its 2018 full year report that the dam at its Minas-Rio mine in Brazil is not constructed using the upstream methods favoured by Vale due to risks associated with the country’s high rainfall.

University of Queensland professor David Williams, director of the Geotechnical Engineering Centre at UQ’s School of Civil Engineering, tells Safe to Work that this is not necessarily the case, however.

“Water must be kept well away from the embankment, which may still be possible in a wet climate, provided that water is well-managed,” he explains. “There are upstream tailings dams in Canada, which is considered a wet climate.

“Tailings deposition towards a water-retaining embankment, resulting in a decant pond (water) against the embankment, relies on a well-designed, constructed and operated downstream embankment with appropriate measures to maintain a low phreatic surface (water table) within the embankment, well inside the downstream face.”

Williams says there are several factors that contribute to safe upstream tailings dam construction, including desiccation of the tailings beach to provide a foundation of sufficient strength for raising, low seismicity, a limited rate of rise in tailings, and good tailings deposition management with drying periods between lifts.

Technology is a key factor improving tailings safety monitoring and management. New South Wales-based tech company Otus Intelligence Group has developed a system it says can provide a ‘first line of defence’ by using satellite imaging to identify potential issues arising at tailings dams (as well as other infrastructure projects such as road and rail networks) that couldn’t be seen otherwise.

The dry bed of the historic Brukunga pyrite mine tailings dam in South Australia, which has been undergoing remediation since 1980.

This includes miniscule surface movements that can’t be picked up by other means, including drones and ground workers. While the satellite technology itself is not brand new, Otus hopes that its technology helps mining companies delineate the information in a way that can be more easily digested by the top brass.

“Our approach is to deliver something for less technical users that have to make the decisions at corporate level,” Otus managing director Marc Beaudry explains.

“When managing tailings, for example, decision typically comes from a corporate level, because it involves a huge financial risk for the companies. The novelty of our approach is how we deliver the data to be used by a less technical audience.”

The system scans large areas for signs of activity and if something is found that warrants further analysis, recommendations are implemented to improve surface-level monitoring.

This also has other safety benefits as it removes the necessity of having workers enter often remote and dangerous tailings areas, allowing for more efficient deployment on the ground.

“We turn the lens of multiple satellites on to one site to try to find the answer to why it is moving. In most cases, it was an excess of water in the tailings that was putting excess weight on the dam itself,” Beaudry explains.

The Brumadinho disaster is a wake-up call that has forced the industry to tighten its management of tailings dams.

While the full ramifications of the incident won’t be felt for some time, recent trends such as real-time monitoring of embankment pore pressures and deformations, satellite imaging, co-disposal of dewatered tailings and waste rock, and overall structural improvements will help to mitigate future risks.

As Williams says, “Any major tailings dam failure impacts the entire mining industry, not just the particular company involved, and stakeholders expect an increased focus from major mining companies on tailings dams in response.”

This article also appears in the April-June 2019 edition of Safe to Work.