Vale’s cheap but deadly tailing dams
● The collapse of a Vale tailings dam in Brazil is serving as a wake-up call for an industry that regularly cuts costs by storing mining waste in the cheapest possible way.
The slurry of ground rock and effluents left over after companies extract minerals from the ground has been stored for decades in massive ponds held back by embankments or dams. Their safety, though, depends very much on the design of the ponds.
The Vale dam that collapsed in Brazil last week, and a previous dam that failed there three years earlier, were both built on the go using the “upstream” method, typically the cheapest by far. Under that technique, the wall containing the pond is primarily constructed of tailings, and it’s designed to grow as more effluents are pumped in. A costlier method pre-builds the walls and insulates them.
“There are a lot of calculations people can use for the cost of a failure,” said Dirk van Zyl, a professor of mining engineering at the University of British Columbia. “You not only have the real cash cost to the company, but you also open the whole discussion of what a human life is worth.”
This week, the mining sector is coming face-to-face with the math.
On top of the more than 100 dead and the 276 missing, Vale, the world’s largest iron ore producer, could face damages as high as $7bn (R92bn) for the current disaster, according to Bloomberg Intelligence. That’s more than twice the $3.3bn liability at the Samarco joint venture after the failure of another upstream dam in Brazil in 2015.
Though it’s not yet clear what caused last week’s dam failure, Vale said on Tuesday it will decommission 10 “upstream” dams in the next three years. In the case of Samarco, Brazil’s worst environmental disaster, the miner allegedly ignored warnings of potential risk and altered the dam’s structure as it sought to keep production levels high.
Some countries have already moved to abandon the upstream pond method. In earthquake-prone Chile, where mining is a pillar of the economy, no large tailings dams have ever collapsed. In 1970, upstream ponds were banned there.
Companies in Chile are required to submit their designs for new tailings ponds to authorities for approval. Once built, the installations are closely monitored with companies mandated to submit data regularly to government agencies.
Antofagasta monitors its largest tailings deposits using 76 instruments installed on the wall that constantly send information on stability and safety metrics, the company said in an e-mailed response to questions.
Meanwhile, Brazil’s system of monitoring how mining waste is safely stored involves the miners themselves paying independent consultants to inspect their dams. The companies then present these reports to local officials.
The fluidity of the waste is also key, experts have said. One way to ensure the waste is safely stored is by drying the tailings and stacking them, instead of directly storing the slurry. Dry-stack tailings are more stable and allow miners to recycle some of the water, which can be used in mining processes.
At the same time, that method can be as much as 10 times more expensive, according to Van Zyl.
Governance is key: 2016 recommendations by the International Council on Mining and Metals call for independent monitoring of tailings.
You open the whole discussion of what a human life is worth Dirk van Zyl
Professor of mining engineering at the University of British Columbia