By Rhiannon Hoyle
SYDNEY -- Global miners searching for new ways to handle mining
waste following deadly spills in Brazil in recent years are
reaching a frustrating conclusion: Many promising options aren't
proven at large scale.
Companies have traditionally held waste -- mixtures of mud, rock
and water, known as tailings -- behind dams near their mines.
However, that practice has come under intense scrutiny following
the January collapse of a dam in Brazil owned by Vale SA, which
killed 270 people, and another deadly spill four years earlier at
an operation jointly owned by BHP Group Ltd. and Vale in the
country.
Techniques investigated by mining companies include waste
stacked in big, dry mounds; new additives to thicken waste and make
it more stable; and experiments with high-powered magnets that can
sort ore without water.
The companies hope to develop a technology that makes storing
waste less dangerous. One goal is to prevent liquefaction, a
process whereby seemingly solid materials suddenly behave like
liquids, which occurred during some of the worst recent accidents,
including the dam spills in Brazil. So far, none of the new
techniques being considered are widely used.
Two years ago, in Chile's northern Atacama Desert, BHP and
partners tested a plant that they hoped would lessen the problem of
waste. The plant used equipment that filtered mine waste from water
so that it could be stored as dry piles. The technique has been
used at small mining operations, such as the La Coipa mine in
Chile, which is owned by Kinross Gold Corp. and currently inactive.
However, BHP wanted to know if it could be used at high-production
mines known as "super pits," such as its Escondida site in
Chile.
The results were disappointing. While technically feasible, the
plant wasn't reliable enough and the volumes of processed waste
missed expectations.
"Upon trial completion, the internal decision was made not to
progress," a BHP spokesman said. Still, the company said it would
use information gleaned during the trial to determine whether
technical hurdles could be overcome in time.
Estimates on how many tailings dams exist globally vary.
According to the Global Tailings Review -- established by groups
including the United Nations Environment Programme -- there are
more than 3,500 active dams. But that figure may underestimate the
number of dams and doesn't include the thousands no longer in use,
other experts say.
Many mining companies have long relied on upstream dams, which
involve piling tailings like a stairway. The design is among the
simplest and least expensive, but it is also seen by experts as the
most prone to failure.
Upstream dam structures are built from the same mining waste
they are designed to restrain. Unlike other dam types, upstream
structures mainly depend on the actual waste, or tailings, for
their stability, rather than contain it behind an engineered
structure.
An independent report that followed the 2014 collapse of
Imperial Metals Corp.'s Mount Polley tailings dam in Canada
recommended that miners adopt technology to remove water from their
waste before storing it. The report said there were no major
technical hurdles in the way of doing so.
In addition to safety, advantages can include conservation of
water and a reduced risk of groundwater contamination.
Rio Tinto recently installed filter-press technology at its
Vaudreuil alumina refinery in Quebec that can dry bauxite waste for
storage. It now takes 17 minutes to dry residue, compared with
three years using traditional methods, the company said.
A year ago, Vale bought New Steel from investment fund Hankoe
FIP for $500 million to secure a technology that can separate
low-grade ore using magnets. The method, which doesn't require
water, isn't ready for a large-scale trial, Vale said.
Not everyone is convinced that dry stacking waste is currently a
workable solution. Lindsay Newland Bowker, an environmental risk
manager in Maine who studies accidents at mining dams, thinks the
technical hurdles are significant because of the low grades of ore
that companies are digging up. Some components of the process don't
work at high altitudes, where many mines sit, and others are only
effective for small volumes.
Meanwhile, she said, dried material could still become saturated
with water, leak, or become eroded over time.
"I call it the dry-stack myth," Ms. Bowker said. "And I am
trying, as a community environmentalist, to get people to stop
demanding it."
Mining companies have promised to publish a new standard for
handling waste by early next year, recognizing investors could lose
faith with an industry seen as slow to change. They also fear
regulators taking longer to approve projects.
California-based X Prize Foundation, the organization founded by
entrepreneur Peter Diamandis, plans to offer a $20 million prize
pool next year to find a technology that can eliminate mine waste.
The initiative is backed by Anglo American PLC and BHP, among
others.
Many companies also have high hopes for precision mining, which
shares similarities with keyhole surgery, as new technologies
promise to unlock narrow veins of metals with little or no
waste.
But adoption could be slow, as global miners and investors have
touted the benefits of super pits in recent years, said Chris
Vernon, a research program leader at CSIRO, Australia's national
science agency. "Everybody understands moving a lot of rock," he
said.
Write to Rhiannon Hoyle at rhiannon.hoyle@wsj.com
(END) Dow Jones Newswires
December 22, 2019 07:14 ET (12:14 GMT)
Copyright (c) 2019 Dow Jones & Company, Inc.
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