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World Coal
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June 2016
Coal News
Coal News
A
new study from researchers at
Duke University has analysed
the critical rare earth element content
and extraction potential for coal ashes
of various US coals with a view to
uncovering a potential new source of
these hard-to-find materials. The research
also offers a potential new pathway for
dealing with the US’s existing coal ash
storage sites – in the headlines following
the coal ash spill into the Dan River,
North Carolina, in 2014.
The results showed that Appalachian
coal contains the most rare earth elements;
however, if extraction technologies were
cheap enough, there are plenty of rare
earth elements to be found in other sources
as well.
“The Department of Energy is investing
US$20 million into research on extraction
technologies for coal wastes, and there is
literally billions of dollars’ worth of rare
earth elements contained in our nation’s
coal ash,” said Heileen Hsu-Kim, the Mary
Milus Yoh and Harold L. Yoh, Jr. Associate
Professor of Civil and Environmental
Engineering at Duke.
“If a programme were to move forward,
they’d clearly want to pick the coal ash
with the highest amount of extractable rare
earth elements, and our work is the first
comprehensive study to begin surveying
the options,” Hsu-Kim said.
As part of their research, the team from
Duke University took coal ash samples
from coal-fired power plants located
mostly in the US Midwest and that burn
coal from all over the country, including
the three largest sources: Appalachia,
southern and western Illinois and the
Powder River Basin (PRB). The content of
rare earth elements was then tested using
hydrofluoric acid, which is much stronger
and more efficient than industrial
methods, but is too hazardous to use on a
large scale.
The results showed that ash collected
fromAppalachian coal has the highest
amount of rare earth elements at
591 mg/kg. Ash from Illinois and the PRB
contains 403 mg/kg and 337 mg/kg,
respectively.
The researchers then used a common
industrial extraction technique featuring
nitric acid to see how much of the rare
earth elements could be recovered. In this
round of tests, ash fromAppalachian coal
proved to be less successful, having the
lowest extraction percentages. Ash from
the PRB saw the highest. According to
Hsu-Kim, this might be because the rare
earth elements in the Appalachian coal ash
are encapsulated within a glassy matrix of
aluminium silicates, which nitric acid does
not dissolve very well.
“One reason to pick coal ash from the
Appalachian Mountains would be for its
high rare earth element content, but you’d
have to use a recovery method other than
nitric acid,” said Hsu-Kim. “For any future
venture to begin an extraction programme,
the recovery method will need to be
tailored to the specific chemistry of the coal
ash being used.”
One alternative extraction method tried
by the Duke researchers involved ’roasting‘
the coal ash with an alkali agent before
dissolving it with nitric acid. Even though
the process hadn’t been optimised for
recovery purposes, the tests showed a
marked improvement in extraction
efficiency.
“The reagents we used are probably too
expensive to use on an industrial scale, but
there are many similar chemicals,” said
Hsu-Kim. “The trick will be exploring our
options and developing technologies to
drive the costs down. That way we can tap
into this vast resource that is currently just
sitting around in disposal ponds.”
A
nglo American has commissioned
longwall operations at its
Grosvenor metallurgical coal mine in
the Bowen Basin of Queensland. The
Grosvenor project, which was approved
for development at the end of 2011 when
metallurgical coal prices were at their
peak, delivered the first coal from its
longwall seven months ahead of schedule
and more than US$100 million below
budget, the company said in a press
statement.
Anglo American expects Grosvenor to
produce 3.2 million saleable t in 2016. At
full capacity, the longwall operation will
be capable of producing 7.5 million tpy of
saleable coal.
“We have delivered the Grosvenor
metallurgical coal project ahead of
schedule and below budget,” said
Seamus French, CEO of Bulk
Commodities at Anglo American. “We
look forward to shipping the mine’s
high-quality product to our steel
customers across Asia as production
begins to ramp up in the months ahead.”
Yet Grosvenor’s future is uncertain.
Anglo American is in the process of
divesting its coal business, including
Grosvenor, as part of a strategic refocusing
on its copper, platinum and diamond
businesses. “While Grosvenor may not fit
Anglo American’s strategic portfolio
choices, its long-term commercial
attractiveness is beyond question,” French
concluded.
USA
Research points to coal ash as a potential source of rare earth elements
AUSTRALIA
Anglo American produces first coal from Grosvenor longwall operation
