Brazil dam collapse highlights failings in mining industry
ACCORDING to experts, cost is holding the mining industry back from achieving safer tailings management, as it is unwilling to spend on more safely storing its waste. Meanwhile, tailings storage facilities (TSFs) continue to collapse, and the rate of failure is increasing.
Tailings are the waste product of ore processing. Rock is crushed and put through a chemical process to recover the valuable component, leaving behind a slurry of fine uneconomic rock and chemical effluent that is stored in tailings dams.
On 25 January Dam 1 of the Córrego do Feijão iron ore mine collapsed in Brumadinho, Minas Gerais, Brazil. The collapse released a torrent of muddy slurry which buried the surrounding area, including the site’s administrative building and canteen, reaching as far as the nearby community. Hundreds of people were affected. As we go to press, 169 are confirmed dead, all of them identified. 141 people are missing.
Reuters reports (https://reut.rs/2E7C6xS) that according to an internal Vale document, the company knew that Dam 1 was at risk of collapse. According to the news agency, the report, dated 3 October 2018, states that the chance of collapse for the dam was 1 in 5,000. This is twice the “maximum level of risk” tolerated by internal guidelines. The dam was reportedly placed within an “attention zone”, and it was stated that “all prevention and mitigation controls” should be applied.
According to Reuters, in an emailed statement Vale said: “There is no known report, audit or study with any mention of an imminent risk of collapse at Dam 1 in the Córrego do Feijão mine in Brumadinho.”
“To the contrary, the dam had all its certificates of safety and stability attested to by local and foreign specialists.”
This incident is the latest in a series of serious TSF failures. According to World Mine Tailings Failures (WMTF) there was a significant increase in the failure rate between 1998–2007, and 2008-2012. WMTF predicts that the upward trend will continue. The WMTF database is a record of all the failures and significant adverse events associated with the deposition and storage of mineral tailings. It contains information for events from 1915 onwards.
Two other recent, notable failures are the 2015 collapse of the Fundão tailings dam also in Minas Gerais, Brazil, and the 2014 Mount Polley tailings dam in British Columbia, Canada.
The Fundão tailings dam collapse resulted in the deaths of 19 people, the destruction of a nearby town, and the contamination of several kilometres of downstream river. The dam was owned by Samarco, a joint venture of BHP Billiton and Vale. An ensuing investigation discovered that the dam failed because of design laws. Flaws in the design of the dam allowed the tailings to become saturated and begin to liquefy. During liquefaction materials such as sand lose their strength and stiffness and behave more like a liquid. In Fundão the process was accelerated by small earthquakes which initiated a mudslide.
The Mount Polley dam collapse did not result in fatalities, but nevertheless attracted a lot of attention because it happened in British Columbia. The mining regulations, as well as the design and operational practices of the province had been considered exemplary.
Following Mount Polley, British Columbia commissioned a report from an expert review panel to investigate. The panel found that the dam collapsed because it was built on a weak foundation, though the collapse might have been prevented had the dam not been built steeper than originally designed.
The collapse of Dam 1 is not yet understood but investigations are underway. However, it is evident that the disasters of Fundão and Mount Polley could have been avoided at key points throughout the tailings management process.
The Chemical Engineer spoke to four experts – David Chambers, Dirk Van Zyl, Steven Vick, and Michelle Ash – who shared their thoughts on how safety could be improved.
“There are improvements in practices – best practices – that can be implemented for existing tailings dams,” said Vick. “In my opinion…these things can and should make incremental improvements in the safety of these structures.”
Vick is geotechnical engineer who has been specialising in the area for around 50 years, and he was on the panel that investigated the collapse of Mount Polley.
To elaborate on the notion of best applicable practices (BAP) Vick refered to the Mount Polley report, which discusses several practices that could be adopted.
These include improved corporate governance, which Dirk Van Zyl advocates as a way to improve tailings dam safety. Van Zyl is a Professor of Mine Waste Management at the University of British Columbia, and he was also on the Mount Polley expert panel. “To me it really comes down to a governance commitment,” he said. “It’s a commitment that companies must have to move towards zero failures.”
Industry continues to show that its decisions are more dependent upon cost, than safety
The report uses the example of the Towards Sustainable Mining (TSM) initiative, which was launched by the Mining Association of Canada (MAC) in 2004. TSM embraces several guides on the management of tailings facilities. The report recommends mining operations proposing TSF in British Columbia should be required to be members of MAC - to ensure adherence to the TSM – or an equivalent programme. Embracing such initiatives would ensure awareness of responsibilities at the highest corporate levels, the report says.
Another BAP recommended in the Mount Polley report is the establishment of independent tailings review boards (ITRBs). These boards can provide third-party advice on the design, construction, operation and closure of TSFs.
However, “there was an independent tailings review board at Fundão, but [the incident] still happened,” said David Chambers, a geophysicist and President of the Center for Science in Public Participation (CSPP). CSPP is a non-profit corporation that provides technical assistance on mining and water quality to public interest groups and tribal governments.
“They think that these little steps that they’re taking like implementing ITRBs…that’s going to solve all the problems. Well it won’t,” said Chambers.
These boards can only have an effect if they have the power to really say what they think and companies take the recommendation regardless of cost, said Chambers. The Mount Polley report states that ITRBs only work if they have “unqualified support and commitment at the highest corporate levels”.
Other BAP recommendations include enhanced regulatory capacity and improvements in professional practice, and if implemented correctly these could enhance the safety of tailings dams.
Though Vick advocates for the implementation of best practices he recognises that alone these will not be enough to improve the safety of tailings dams. “We’re still dealing with a technology here that’s 100 years old, and these improvements and practices can only take you so far,” he said, adding “we really need to look at changing the technology”.
Whilst BAPs focus on the performance of the tailings dam, best available technology (BAT) concerns the tailings deposit itself. The goal of BAT is to assure the physical stability of the deposit.
“The overarching goal of BAT is to reduce the number of tailings dams subject to failure,” says the Mount Polley report. One way of achieving this, is using alternative means of tailings storage. “Putting it underground, if you have sufficient space, is a good solution,” Van Zyl said. Mined-out pits are an option for surface operations and backfilling for underground mines.
But Van Zyl also explained that these methods are not necessarily applicable at all sites and should be considered on a site-specific basis, as there are potential environmental impacts such as groundwater effects. In addition, operations may not allow for it, such as the blockcaving used for large copper mines which does not allow for backfilling.
Another, safer storage option is filtered tailings. Filtered tailings, also known as “dry stack” tailings are tailings that are dewatered to a high degree to produce a solid material which can be transported by conveyor or truck. At the TSF they are spread and compacted to form an unsaturated tailings deposit. The result is an immobile material that isn’t susceptible to high mobility flow slides, like those witnessed in British Columbia and Brazil.
Though filtered tailings are currently employed by industry to allow backfilling or enable water recovery, “we very seldom see dry tailings employed as a safety consideration,” explained Chambers. But widespread use is held back by cost, he added. The technology is expensive, and there are also issues of scale so though it may be viable for small operations mining 2000 t/d, for example, it would be more difficult to employ in large operations mining 80,000 t/d, for example.
Chambers mentioned the alternative of dry closure by less expensive means, such as by draining tailings. This could still make a “significant difference,” he said.
In addition to the above there are also novel technologies out there which could help to reduce risk.
For example, EcoTails technology, which was developed by gold production company Goldcorp and FLSmidth, a global mining and cement company.
The EcoTails process combines filtered tailings with waste rock to create a geotechnically stable and stackable product called Geowaste. The method eliminates the need to keep conventional slurry tailings contained and submerged in water. EcoTails reduces the overall risk posed by tailings by eliminating the use of wet tailings dams.
Though “typically it’s metallurgical engineers that are involved in mine processing,” said Chambers, chemical and process engineers can contribute to efforts to improve tailings technologies. For example, Chambers suggested that chemical and process engineers could contribute by improving dewatering processes. As with other measures and technologies that could improve safety, dewatering technologies are hindered by cost. Faster, more scalable techniques with reduced costs could make dry tailings less prohibitive. Chemical and process engineers “can help us design the properties of the tailings,” Vick said.
Industry continues to show that its decisions are more dependent upon cost than safety. For example, it continues to employ the upstream method for building tailings dams. “The only reason you build an upstream tailings dam is because it’s cheaper than building a downstream tailings dam,” said Chambers.
In the upstream method the face of the dam is not built in a single phase as with a hydroelectric dam, instead the face is built up in stages as the tailings are added and their depth increases. The face of the dam is built from the coarser portion of the tailings themselves and is built over the finer slurries it is designed to hold back. Centreline and downstream dams also use tailings material but are considered safer. Downstream dams are considered the safest.
The Vale dam which recently breached was an upstream dam, as was the Samarco dam which collapsed in 2015. In Chile, upstream dams
are banned because of the country’s high seismicity.
On 18 February Brazil announced that it is banning upstream dams, Bloomberg reported (https://bloom.bg/2twOkKv). The decision was published in Brazil’s Diário Oficial da União, the official journal of the federal government. The resolution of the country’s National Mining Agency (ANM) states that dam owners are to decommission or remove upstream dams by August 2021. By 15 August of this year owners should have completed a technical plan for the dams, which should at minimum include plans for reinforcing existing structures or building new retention structures, Bloomberg says.
Vale itself has already begun decommissioning its ten inactive upstream dams. The company decided to decommission its 19 upstream dams in 2016, following the collapse of Fundão. Since then only nine had been decommissioned. The remaining dams are now part of an accelerated decommissioning project.
However, upstream facilities shouldn’t necessarily be completely discounted. In dryer climates where tailings are likely to be dried out, upstream dams are less problematic. Countries such as Australia and South Africa tend to use this method widely. In addition, they can be engineered safely. It is simply that they are “unforgiving” said Vick, adding “everything has to be done right, and it has to be done in the right conditions.”
Chambers advocates for the industry moving towards a mindset that considers safety first. “Safety needs to be the primary consideration in the design, construction, and operation of these dams. Right now, cost is the main driver,” he said. “I’m not saying that cost shouldn’t be considered, I’m saying that cost needs to be subordinate to safety.”
However, Michelle Ash disagrees that cost is the main factor holding industry back. Ash is the Chair of Global Mining Guidelines Group (GMGgroup), a network of companies aiming to drive change in the mining industry. “I think that is a very simple answer to quite a complex problem,” she said. “One could boil it all down to that, but I don’t think that’s fair.”
“There are limitations on some of the alternatives,” as well as new technologies and the ability to advance them. She added that industry is already taking some steps in order to achieve safer tailings dams, but further innovation and change will require a lot of “time and focus”.
Vick discussed the need for industry to change the way it thinks about tailings and mining operations as a whole. It should integrate the way it views the three “subsystems” of mining. The first subsystem is the mine itself, where the ore is extracted. The second subsystem is the mill, where ore is separated from the rock. The last subsystem, the tailings, are simply considered the waste.
“The practice has been to optimise those subsystems, each one working on its own, and independently.” But “that doesn’t necessarily give you the optimal system overall, and that is the problem that needs to be attacked.”
“I really think that the way that companies have managed their tailings really harps back to the historic view,” said Van Zyl. The view is that “it’s waste and therefore we need to spend as little money as we can on that.”
By considering the system as a whole, it might be easier to make better decisions with regards to the entire operation. For example, a change in thinking in this direction could enable easier planning for disposal of tailings in mined-out pits.
Matters of tailings dams safety are not one-size-fits-all. Similar to the example of the use of underground storage methods, aspects of management must be considered on a site-specific basis in order to make the right decisions. And to do this, “we need to make safety paramount,” said Chambers.
After the collapse of the Fundão tailings dam in Mariana, Vale implemented various changes with the aim of avoiding a similar incident, including: detailed emergency action plans; external audits; implementation of modern warning systems, with sirens for emergencies; and population registrations. Furthermore, when Vale CEO Fabio Schvartsman took over in 2017 he suggested Vale change its motto to “Mariana, never again”. Regardless, none of the actions taken prevented the collapse of Dam 1, which was built in 1976 by Ferteco Mineração and acquired by Vale in 2001.
Considering the lack of movement made towards safety by the industry itself, David Chambers stressed the role of government. “I think we need changes in the laws and the regulation,” he said. “I think in order to implement safety first, that has to come from government.”
But governments cannot bear the burden of ensuring the safety of tailings dams alone, though they can certainly play a role and encourage the industry to move towards safety, agreed all of the experts.
“There are moves in that direction,” said Vick. The Mount Polley report recommended that independent review boards be created, and British Columbia has implemented that. He explained that the province also now has a structure in which individual consulting boards at individual mines report to an “uber” board, which reports to the government. “The idea there is to have people who are highly qualified technically, who provide a conduit of recommendations and so forth that the government can implement.” British Columbia also instituted other recommendations given by the review panel. Currently, the province is a global leader in mine tailings storage regulation.
In addition to government, Chambers suggested that there may be a role for non-governmental organisations, such as the UN Environmental Programme (UNEP), which could create a database of tailings dams and failures. An organisation could make a “legitimate appeal” to countries and encourage them to release data that would promote transparency about TSFs. Even communities might have a role to play, suggested Van Zyl.
Industry needs to act, but there are roles for others outside the industry which could encourage this action. “I think it’s a combination of everything,” he added.
It is evident that there are actions that the mining industry can take to improve safety, but it either isn’t taking them, or isn’t implementing them correctly. This needs to change, and the industry has to move towards a zero-failure rate, the Mount Polley report says.
Industry has to acknowledge what must be done and move away from the idea of tolerable risk and failure. As the report says: “First Nations will not accept this, the public will not permit it, government will not allow it, and the mining industry will not survive it.”
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