Precious metals from electronic waste in seconds

Date:
October 4, 2021
Source:
Rice University
Summary:
Flash Joule heating recovers valuable and toxic metals from
electronic waste. The process allows for "urban mining" of
resources that could be a win for the environment as well as for
manufacturers.



FULL STORY ==========================================================================
In what should be a win-win-win for the environment, a process developed
at Rice University to extract valuable metals from electronic waste
would also use up to 500 times less energy than current lab methods and
produce a byproduct clean enough for agricultural land.


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The flash Joule heating method introduced last year to produce graphene
from carbon sources like waste food and plastic has been adapted to
recover rhodium, palladium, gold and silver for reuse.

A report in Nature Communications by the Rice lab of chemist James
Tour also shows highly toxic heavy metals including chromium, arsenic,
cadmium, mercury and lead are removed from the flashed materials,
leaving a byproduct with minimal metal content.

Instantly heating the waste to 3,400 Kelvin (5,660 degrees Fahrenheit)
with a jolt of electricity vaporizes the precious metals, and the gases
are vented away for separation, storage or disposal. Tour said that
with more than 40 million tons of e-waste produced globally every year,
there is plenty of potential for "urban mining." "Here, the largest
growing source of waste becomes a treasure," Tour said.

"This will curtail the need to go all over the world to mine from ores
in remote and dangerous places, stripping the Earth's surface and using
gobs of water resources. The treasure is in our dumpsters." He noted
an increasingly rapid turnover of personal devices like cell phones
has driven the worldwide rise of electronic waste, with only about 20%
of landfill waste currently being recycled.



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"We found a way to get the precious metals back and turn e-waste into
a sustainable resource," he said. "The toxic metals can be removed
to spare the environment." The lab found flashing e-waste requires
some preparation. Guided by lead author and Rice postdoctoral research associate Bing Deng, the researchers powdered circuit boards they used
to test the process and added halides, like Teflon or table salt, and
a dash of carbon black to improve the recovery yield.

Once flashed, the process relies on "evaporative separation" of the
metal vapors. The vapors are transported from the flash chamber under
vacuum to another vessel, a cold trap, where they condense into their constituent metals.

"The reclaimed metal mixtures in the trap can be further purified to
individual metals by well-established refining methods," Deng said.

The researchers reported that one flash Joule reaction reduced the concentration of lead in the remaining char to below 0.05 parts per
million, the level deemed safe for agricultural soils. Levels of arsenic, mercury and chromium were all further reduced by increasing the number
of flashes.

"Since each flash takes less than a second, this is easy to do,"
Tour said.

The scalable Rice process consumes about 939 kilowatt-hours per ton
of material processed, 80 times less energy than commercial smelting
furnaces and 500 times less than laboratory tube furnaces, according to
the researchers. It also eliminates the lengthy purification required
by smelting and leaching processes.

Co-authors of the paper are Rice alumnus Duy Xuan Luong, graduate students
Zhe Wang and Emily McHugh and research scientist Carter Kittrell. Tour
is the T.T.

and W.F. Chao Chair in Chemistry as well as a professor of computer
science and of materials science and nanoengineering. The Air Force Office
of Scientific Research (FA9550-19-1-0296) and the Department of Energy (DE-FE0031794) supported the research.

========================================================================== Story Source: Materials provided by Rice_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Bing Deng, Duy Xuan Luong, Zhe Wang, Carter Kittrell, Emily
A. McHugh,
James M. Tour. Urban mining by flash Joule heating. Nature
Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-26038-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211004140300.htm

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