Geosynthetics October/November 2019 - 10

UPDATE

FIGURE 2 AMD clarifier slurry at 2% solids versus 65% dry solids from inside geotextile tube

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Geosynthetics | October November 2019

65% solids within 30 days (Figure 2).
Currently, the Omega site has been in
operation for three years, and the geotextile tubes are on level 3. The current
dewatering cell site has a capacity to
receive and dewater the current rate of
AMD flow for 20 years of 24/7 operation.
If the story ended here, by any method of
measurements, the Omega AMD project
would be a success. In fact, the DEP is
adding three of these automated geotextile tube AMD management sites. One
of the new sites has flow rates up to ten
times the Omega project.
In 2017, the U.S. Department of
Defense (DOD) and U.S. Department
of Energy (DOE) initiated a program to
develop domestic sources of rare earth
elements (REE). The REE is a family of
17 elements that are critical and strategic elements for the manufacturer of
communication, energy, defense, and
aerospace products and systems. Since
the early 1990s, more than 90% of all REE
have been mined and refined in China,
and the global demand is growing. Since
2013, domestic REE U.S. sources have
been a congressional concern, according

to the Congressional Research Service.
DOE Secretary Rick Perry stated in
2018 at the National Energy Technology
Laboratory (NETL) Conference that
without a domestic source of REE, the
U.S. economy would be at risk.
In 2017, the University of West
Virginia Water Research Institute began
a study to identify and quantify potential
sources of REE in existing Appalachian
AMD point sources. Some 152 sources
of raw AMD water were sampled in the
Appalachian Basin.
The average concentration of REE
in the AMD point sources samples was
410.6 grams per ton (g/t) of dry solids
(Table 1). According to Ziemkiewicz,
Xingbo and Noble's (2018a) study at
the University of West Virginia, the
dewatered solids in the geotextile tubes
at the Omega mine located in the Central
Appalachian (CAPP) region totaled 397
g/t. Therefore, the geotextile tube technology was retaining 96.7% of available
REE from the AMD flow. In the same
study, it was calculated that each geotextile tube in the Omega dewatering cell
contains 146 dry metric tons of AMD
or 128 pounds (58 kg) of recoverable
REE ore. The NETL April 2018 Summary
Report set the REE Basket Price of
Appalachian Basin recoverable REE ore
at $225 per kilogram. Therefore, each
geotextile tube contains approximately
$13,050 of recoverable REE ore.

Conclusion
When geotextile tube technology was
analyzed as a method for recovering rare
earth elements from acid mine drainage,
it was proven to be extremely efficient
and cost-effective in capturing more than
90% of available REE. Also, the recovery
of REE from the AMD will have a tremendous economic and environmental
benefit to the Appalachian region.

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Geosynthetics October/November 2019

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