CREDITS: (GRAPHIC K. FRANKLIN/
SCIENCE
; (DATA DANIEL CORDIER/U.S. GEOLOGICAL SURVEY MINERAL COMMODITY SUMMARIES (2022
SCIENCE science.org 11 FEBRUARY 2022 • VOL 375 ISSUE 6581 601A
s chemists scramble to find ways to re-
claim valuable metals from industrial
waste and discarded electronics, one
team has found a solution that sounds
a little like magic: Zap the trash with
flashes of electric heat.
Rare earth elements (REEs) present an
environmental paradox. On one hand, these
dozen or so metals, such as yttrium and neo-
dymium, are vital components of wind tur-
bines and solar panels, and cheap sources
of REEs could give those green technologies
a huge boost. On the other, mining REEs
causes billions of dollars of environmental
damage each year. Because the elements oc-
cur in low concentrations, mining companies
have to chew through tons upon tons of ore,
stripping and gutting landscapes. Moreover,
REEs are often mixed with radioactive ele-
ments, and extracting them creates low-level
nuclear waste.
Old electronics and other industrial waste,
in contrast, are rich in REEs. But existing
recycling methods are inefficient and expen-
sive, and require corrosive chemicals such as
concentrated hydrochloric acid. For every en-
vironmental problem that REEs could solve,
they seemingly introduce two more.
The new process could help break that log-
jam. This week in Science Advances, a team
led by organic chemist James Tour of Rice
University reports using pulses of electrical
heat to make it easier to extract REEs from
industrial waste. The technique is roughly
twice as efficient as current methods and
uses far more benign chemicals.
“It’s a very interesting approach,” says
Amir Sheikhi, a chemical engineer at Penn-
sylvania State University, University Park,
who studies REE extraction. “With a pretty
short, high-temperature treatment ... these
rare earth elements are set free.”
Tour’s team tested its process on fly ash,
a powdery gray byproduct of burning coal
that contains concentrated levels of the
REEs originally present in the coal. The re-
searchers mixed the ash with carbon black
to improve electrical conductivity, and then
placed the mixture in clear quartz tubes 1 to
2 centimeters wide and 5 to 8 centimeters
long. Capacitors on the ends of the tubes
sent a pulse of current through, causing the
tube to flash yellow-white and produce a
tiny puff of smoke. The temperature of themixed powders spiked to 3000°C within
1 second, then rapidly cooled.
That spike of heat does two things. When
coal is burned as fuel, microscopic bits of
glass form inside and trap REEs, making
them hard to extract. But the bursts of elec-
tric heat shock and shatter the glass, freeing
the rare earths. Flash heating also induces
chemical changes: Phosphates of REEs trans-
form into REE oxides, which are more solu-
ble and easily extractable.
As a result of these changes, Tour’s group
can use less corrosive solutions to extract the
REEs. Tour’s team gets by with concentra-
tions of hydrochloric acid 120 times lowerthan current extraction methods, and still
manages to extract twice as much. “It’s so di-
lute,” Tour says, “that—well, I wouldn’t do it,
but I think you could drink [it].”
In addition to fly ash, Tour’s team has
extracted REEs from so-called red mud—a
byproduct of making aluminum—and from
electronics. In the latter case, the team gut-
ted an old laptop and ground its circuit board
into powder to experiment with.
Many government officials are keen on
grabbing REEs from waste, rather than min-
ing them, for economic as well as environ-
mental reasons. China has long dominatedthe international REE market (see graphic,
left), and Japan, the European Union, and the
United States have complained to the World
Trade Organization that China uses its near-
monopoly to curtail exports and drive up
prices. (Japan has since explored measures
such as dredging up REE-rich mud from
the deep ocean floor, which isn’t exactly eco-
friendly.) Relying on a foreign supplier for
REEs puts countries “at an economic disad-
vantage if not a natural security disadvantage,”
says Steven Winston, an independent chemi-
cal engineer and former vice president of
Idaho National Laboratory who has studied
mining waste. Flash heating of waste might
open an alternate supply.
But hurdles remain. After the REEs are
extracted, they need to be separated into in-
dividual elements for different applications.
That “is still a big challenge,” says Heileen
Hsu-Kim, an environmental engineer at
Duke University who studies REE extrac-
tion. Companies usually use organic sol-
vents such as kerosene, which themselves
cause environmental problems or are dif-
ficult to recycle. To address such concerns,
Sheikhi’s team fashioned biodegradable cel-
lulose into filaments sporting “hairs” with
functional groups that selectively bond to
and capture neodymium, a vital component
in the magnets in wind turbines.
Moreover, Tour’s process would need to
be massively scaled up to make a differ-
ence. Sheikhi points out that “typically,
high-temperature processes are expensive.”
But Tour’s team argues that because flash
heating is speedy, costs are low, just $12 per
ton of fly ash. As for scaling up, the team
previously developed a flash heating pro-
cess to transform old tires and plastics into
graphene (Science, 31 January 2020, p. 496),
and a spinoff company has already scaled
that process up using larger flash heaters.
If Tour’s method does work out, there’s
plenty of industrial waste to have at. Every
year, humankind produces 40 million tons
of electronic waste, 150 million tons of red
mud, and 750 million tons of coal fly ash,
much of it piled in giant mounds. Consider-
ing that burning coal helped create our cur-
rent environmental mess, it would be fitting
if the spark for green technologies could be
extracted from its waste. “We don’t need any
more coal to be burned for this [recycling]
process to work,” Tour says. “We have suffi-
cient mountains of this forever.” jBy Sam KeanMATERIALS SCIENCEAn electric jolt strips valuable metals from waste
New method can pull rare earth elements from electronic waste and coal ash
2020 production of rare earth oxides
(tons)0 50,000 100,000 150,OtherRussiaMadagascarIndiaThailandAustraliaMyanmarUnited
StatesChina1%1%1%1%1%9%13%16%57%NEWS | IN DEPTHChina’s rare earth dominance
Rare earth elements are vital components of green
technologies. Other countries have complained that
China uses its market dominance to drive up prices
by limiting exports.