POWER October 2016 - 34

COAL
2. Beneficial usage is spreading. Synthetic gypsum, a by-product of the flue gas desulfurization
process, is an easily applied soil amendment that supports sustainable agriculture.
Courtesy: We Energies
gregate for concrete, asphalt, and masonry;
and as an abrasive to improve traction during
snowy or icy conditions.
Rare Earth Elements
Finding new methods to gain value from
CCPs is an ongoing process. Adams said
people have been trying to develop commercially
viable ways to extract various metals
from ash for a long time.
" Every once in a while, we'll get a call from
somebody who'll say, 'You know, I can extract
gold from ash,' " said Adams, noting that gold
extraction has been achieved in the laboratory,
but not on a commercial scale. " Obviously,
when it comes to extracting metals like that,
you'd have to process a tremendous amount
of ash to get the kind of quantities that would
make commercial sense. "
Extracting rare earth elements (REEs)
from coal ash could be a different story, however.
The REEs comprise 17 elements from
the periodic table (Figure 3). Although REEs
are rarely found in their elemental form, they
can be extracted from coal-and coal ash.
REEs are considered important to
the
bottom boilers, such as slag-tap and cyclone
boilers-is in high demand for use as blasting
grit and roofing granules. Bottom ash, a
course- to fine-grain sand-like material collected
from dry bottom pulverized coal boilers,
compacts a lot like sand. Therefore, it
can be used for structural fill; backfill; road
bases and sub-bases; drainage media; agU.S.'s
national security, energy independence,
environmental future, and economic
growth. Myriad products used today rely on
REEs, including satellite communications,
guidance systems, capacitors, sensors, lasers,
fiber optics, medical imaging, ultravioletresistant
glass, photo-optical glass, batteries,
fuel cells, super alloys, catalysts, magnetics,
computer components, and microwave power
tubes, to name just a few.
Due to their importance, it shouldn't be
surprising that the U.S. Department of Energy's
National Energy Technology Laboratory
(NETL) has implemented a program focused
on developing technologies for the recovery
of REEs from coal and coal by-products. A
couple of examples of the work being done
include a Duke University project to develop
and demonstrate bench-scale hydrometallurgical-based
technology to separate and concentrate
REEs from coal fly ash and other coal
combustion residuals, and Battelle Memorial
Institute's project to validate the economic viability
of a closed-loop acid digestion process
for recovering REEs from coal ash. At least
eight other projects are in progress with the
goal of developing viable REE recovery techniques,
including at universities in North Dakota,
Kentucky, West Virginia, Wyoming, and
at NETL's own research center.
" There's concern at the federal level that
the rare earths that we are using in the U.S.
are predominantly coming from China, " said
Adams. " We don't want to be held hostage
by that supply, so NETL is working on that
now, vigorously, to try to determine if it's
feasible in the end-if there's any commerCIRCLE
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