Failure is not an option - reconsidering tailings dams
Tailings dams were once almost an afterthought in the design and management of mines. But a series of high-profile tailings dam failures and the resultant scrutiny from media, investors and insurers has led to significant changes in how the dams are designed, operated, monitored and managed over their entire lifecycle.
Friction sat down with world-leading tailings dam expert, Professor David Williams from The University of Queensland to find out how things are changing for the better.
Across more than 40 years of researching, teaching and consulting on mine waste management and mine closures, Professor David Williams has seen tailings dams evolve from a minor consideration to a crucial area of mine design, risk mitigation and management.
The Director of the Geotechnical Engineering Centre at The University of Queensland’s School of Civil Engineering said high profile tailings dam failures had led to a loss of confidence and trust in the critical infrastructure, and the companies responsible for their establishment and maintenance.
“Historically, tailings dams were seen as a cost or an add-on by mining businesses,” Professor Williams said.
“It was a case of ‘find me a suitable valley and I’ll build a tailings dam to store the tailings’”.
The aftermath of the Brumadinho dam collapse in 2019. (Image by Ibama, Wikimedia Commons)
But after tailings dam failures, such as the deadly Brumadinho failure in Brazil in 2019, and the decimation of El Cobre in Chile following a 7.4 Richter magnitude earthquake in 1965, the industry and stakeholders knew things had to improve.
“We had to change our approach. There were too many marginally stable or at-risk dams, and too many failures. It was an unacceptable performance,” Prof. Williams said.
Insurers and investors also needed trust and certainty to support the industry into the future. In response to the Brumadinho failure, the International Council on Mining and Metals (ICMM), the United Nations Environment Programme (UNEP), and Principles for Responsible Investment (PRI) co-convened and launched the Global Industry Standard on Tailings Management.
Formed with the ultimate goal of zero harm to people and the environment, the Standard aims to prevent catastrophic failure and enhance the safety of mine tailings facilities across the globe.
Comprising of six topic areas, 15 principles and 77 auditable requirements, the Standard requires operators to consider the impact of the tailings facilities on communities in the area, as well as improving design, construction, operation, maintenance, monitoring and closure practices.
At the time, ICMM’s then CEO Tom Butler said the Standard set the bar for all mining companies to work together to make all tailings facilities safer.
“Members have committed that all facilities with ‘Extreme’ or ‘Very high’ potential consequences will be in conformance with the Standard within three years of today, and all other facilities within five years,” Mr Butler said in 2020.
Since the launch of the Standard, ICMM members have explored approaches and technologies to minimise and ultimately eliminate tailings waste from the mine life cycle.
Current ICMM CEO Rohitesh Dhawan said ICMM’s recently released Tailings Reduction Roadmap and wider Tailings Innovation Initiative would serve as a catalyst for advancing more partnerships between industry and technology innovators to find solutions to reduce tailings waste.
“Catastrophic tailings failures in recent years, including at South Africa’s Jagersfontein mine, have brought into sharp focus the need for urgent action to produce less tailings as we supply the metals and minerals that are critical for the energy transition and sustainable development,” Mr Dhawan said.
“If we continue to use traditional production processes, we run the risk of multiplying tailings waste many times over.
“There is no easy solution, and we will continue to need tailings storage facilities into the future. However, this initiative signals our clear intent to act with urgency and purpose to find ways of minimising or potentially eliminating waste at every stage of the mining cycle.”
Five aspects of metal and mineral recovery have been identified by ICMM as having the potential to eliminate or dramatically reduce the generation of tailings:
Precision geology: Geological techniques, processes or models that have the ability to better characterise the ore body for downstream processing, maximising ore and minimising waste rock being mined which will have an impact on tailings generated.
Precision mining: Mining approaches or technologies that minimise or eliminate waste rock being mined which will have an impact on tailings generated.
Precision segregation: Segregation and liberation technologies that are able to optimise metal and mineral recovery or produce more benign tailings.
In situ and ex situ recovery: Leaching techniques that can optimise metal and mineral recovery and minimise and/or eliminate the volume of waste rock produced which will have an impact on tailings generated.
Tailings enhancement and valorisation: Different ways to create value from tailings, or ways to minimise the requirement for tailings storage.
While the search for solutions is underway, operators had already increased consultation with experts to ensure best practices are built into tailings dam design and construction. Prof. Williams said this reflected a shift in mindset, switching tailings dams from an afterthought to an important functional part of the mine.
He said while topography, water, seismic activity and post closure use are key considerations for the design of a tailings facility – economics is often a major factor in decisions.
“One of the biggest impediments for the mining industry is to grapple with net present value accounting with a high discount factor. If you delay expenditure, discounting back to today’s dollars, it appears to be cheaper. However, this can lock in unintended detrimental consequences.
“What we need is a whole life cycle of the mine accounting mindset. That way, you could close the mine at any time with the tailings facility fully integrated into the mine’s rehabilitation plan.”
While things are changing, Prof Williams warned there was no “silver bullet” for stopping tailings dam failures.
“The key to ensuring a functional tailings dam is to build a stable landform behind which the tailings can safely be stored, and to then ask to what degree do you de-water the tailings to be stored behind it?” he said.
“We also need better recognition of the importance of the settings of the site. Obviously, if it’s a highly seismic site, like in Chile or Peru on the Pacific’s Ring of Fire, design needs to accommodate that.
“If the tailings facility is in Brazil or the wet tropics, rainfall is a driver that needs to be factored into the design, site selection and monitoring.”
Prof. Williams also strongly advocated for closure design for extreme consequence, as has been required by ANCOLD And CDA for many years, and is advocated by the Standard.
“In these cases, it’s important to design for in-perpetuity flooding and seismic events, taken as a one in 10,000-year event. But many tailings facilities are designed for the operational life of one in 100 or one in 1000-year events. We need to design with closure in mind.”
