What Is ISL Uranium Mining?
Author: James Finch
Author: James Finch
In situ leach mining (ISL), also known as in-situ mining or
solution mining, was first used as a means to extract low
grades of uranium from ore in underground mines. First used in
Wyoming in the 1950s, originally as a low production experiment
at the Lucky June mine, it became a high-production, low cost
method of fulfilling Atomic Energy Commission uranium
requirements at Utah Construction Company's Shirley Basin
mining operations in the 1960s. Pioneered through the efforts
of Charles Don Snow, a uranium exploration and mining geologist
employed by Utah, many of his developments are still used today
in ISL mining.
What is ISL mining? According to the Wyoming Mining Association
website, ISL mining is explained in the following manner. (We
choose Wyoming because it is the birthplace of "solution
mining" as it was originally called.)
"In-situ mining is a noninvasive, environmentally friendly
mining process involving minimal surface disturbance which
extracts uranium from porous sandstone aquifers by reversing
the natural processes which deposited the uranium.
To be mined in situ, the uranium deposit must occur in
permeable sandstone aquifers. These sandstone aquifers provide
the "plumbing system" for both the original emplacement and the
recovery of the uranium. The uranium was emplaced by weakly
oxidizing ground water which moved through the plumbing systems
of the geologic formation. To effectively extract uranium
deposited from ground water, a company must first thoroughly
define this plumbing system and then designs well fields that
best fit the natural hydro-geological conditions.
Detailed mapping techniques, using geophysical data from
standard logging tools, have been developed by uranium
companies. These innovative mapping methods define the geologic
controls of the original solutions, so that these same routes
can be retraced for effective in situ leaching of the ore. Once
the geometry of the ore bodies is known, the locations of
injection and recovery wells are planned to effectively contact
the uranium. This technique has been used in several thousand
wells covering hundreds of acres.
Following the installation of the well field, a leaching
solution (or lixiviant), consisting of native ground water
containing dissolved oxygen and carbon dioxide, is delivered to
the uranium-bearing strata through the injection wells. Once in
contact with the mineralization, the lixiviant oxidizes the
uranium minerals, which allows the uranium to dissolve in the
ground water. Production wells, located between the injection
wells, intercept the pregnant lixiviant and pump it to the
surface. A centralized ion-exchange facility extracts the
uranium from the barren lixiviant, stripped of uranium, is
regenerated with oxygen and carbon dioxide and recirculated for
continued leaching. The ion exchange resin, which becomes
"loaded" with uranium, it is stripped or eluted. Once eluted,
the ion exchange resin is returned to the well field facility.
During the mining process, slightly more water is produced from
the ore-bearing formation than is reinjected. This net
withdrawal, or "bleed", produces a cone of depression in the
mining area, controlling fluid flow and confining it to the
mining zone. The mined aquifer is surrounded, both laterally
and above and below, by monitor wells which are frequently
sampled to ensure that all mining fluids are retained within
the mining zone. The "bleed" also provides a chemical bleed on
the aquifer to limit the buildup of species like sulfate and
chloride which are affected by the leaching process. The
"bleed" water is treated for removal of uranium and radium.
This treated water is then disposed of through waste water land
application, or irrigation. A very small volume of radioactive
sludge results; this sludge is disposed of at an NRC licensed
uranium tailings facility.
The ion exchange resin is stripped of its uranium, and the
resulting rich eluate is precipitated to produce a yellow cake
slurry. This slurry is dewatered and dried to a final drummed
uranium concentrate.
At the conclusion of the leaching process in a well field area,
the same injection and production wells and surface facilities
are used for restoration of the affected ground water. Ground
water restoration is accomplished in three ways. First, the
water in the leach zone is removed by "ground water sweep", and
native ground water flows in to replace the removed contaminated
water. The water which is removed is again treated to remove
radionuclides and disposed of in irrigation. Second, the water
which is removed is processed to purify it, typically with
reverse osmosis, and the pure water is injected into the
affected aquifer. This reinjection of very pure water results
in a large increment of water quality improvement in a short
time period. Third, the soluble metal ions which resulted from
the oxidation of the ore zone are chemically immobilized by
injecting a reducing chemical into the ore zone, immobilizing
these constituents in situ. Ground water restoration is
continued until the affected water is suitable for its
pre-mining use.
Throughout the leaching and restoration processes, a company
ensures the isolation of the leach zone by careful well
placement and construction. The well fields are extensively
monitored to prevent the contamination of other aquifers.
Once mining is complete, the aquifer is restored by pumping
fresh water through the aquifer until the ground water meets
the pre-mining use.
In situ mining has several advantages over conventional mining.
First, the environmental impact is minimal, as the affected
water is restored at the conclusion of mining. Second, it is
lower cost, allowing Wyoming's low grade deposits to compete
globally with the very high grade deposits of Canada. Finally
the method is safe and proven, resulting in minimal employee
exposure to health risks."
ISL mining may be the wave of the future of U.S. uranium
mining, or it may become an interim mining measure, in areas
where the geology is appropriate for IS. Until sufficient
quantities of uranium are required by U.S. utilities to fuel
the country's demand for nuclear energy, ISL mining may remain
the leading uranium mining method in the United States. At some
point, an overwhelming need for uranium for the nuclear fuel
cycle may again put ISL mining in the backseat, and uranium
miners may return to conventional mining methods, such as open
pit mining.
About The Author: James Finch contributes to
http://StockInterview.com and other publications. You can email
James Finch at jfinch@stockinterview.com. All of his archived
articles (with photos, maps and charts) can be read at
http://www.stockinterview.combu
solution mining, was first used as a means to extract low
grades of uranium from ore in underground mines. First used in
Wyoming in the 1950s, originally as a low production experiment
at the Lucky June mine, it became a high-production, low cost
method of fulfilling Atomic Energy Commission uranium
requirements at Utah Construction Company's Shirley Basin
mining operations in the 1960s. Pioneered through the efforts
of Charles Don Snow, a uranium exploration and mining geologist
employed by Utah, many of his developments are still used today
in ISL mining.
What is ISL mining? According to the Wyoming Mining Association
website, ISL mining is explained in the following manner. (We
choose Wyoming because it is the birthplace of "solution
mining" as it was originally called.)
"In-situ mining is a noninvasive, environmentally friendly
mining process involving minimal surface disturbance which
extracts uranium from porous sandstone aquifers by reversing
the natural processes which deposited the uranium.
To be mined in situ, the uranium deposit must occur in
permeable sandstone aquifers. These sandstone aquifers provide
the "plumbing system" for both the original emplacement and the
recovery of the uranium. The uranium was emplaced by weakly
oxidizing ground water which moved through the plumbing systems
of the geologic formation. To effectively extract uranium
deposited from ground water, a company must first thoroughly
define this plumbing system and then designs well fields that
best fit the natural hydro-geological conditions.
Detailed mapping techniques, using geophysical data from
standard logging tools, have been developed by uranium
companies. These innovative mapping methods define the geologic
controls of the original solutions, so that these same routes
can be retraced for effective in situ leaching of the ore. Once
the geometry of the ore bodies is known, the locations of
injection and recovery wells are planned to effectively contact
the uranium. This technique has been used in several thousand
wells covering hundreds of acres.
Following the installation of the well field, a leaching
solution (or lixiviant), consisting of native ground water
containing dissolved oxygen and carbon dioxide, is delivered to
the uranium-bearing strata through the injection wells. Once in
contact with the mineralization, the lixiviant oxidizes the
uranium minerals, which allows the uranium to dissolve in the
ground water. Production wells, located between the injection
wells, intercept the pregnant lixiviant and pump it to the
surface. A centralized ion-exchange facility extracts the
uranium from the barren lixiviant, stripped of uranium, is
regenerated with oxygen and carbon dioxide and recirculated for
continued leaching. The ion exchange resin, which becomes
"loaded" with uranium, it is stripped or eluted. Once eluted,
the ion exchange resin is returned to the well field facility.
During the mining process, slightly more water is produced from
the ore-bearing formation than is reinjected. This net
withdrawal, or "bleed", produces a cone of depression in the
mining area, controlling fluid flow and confining it to the
mining zone. The mined aquifer is surrounded, both laterally
and above and below, by monitor wells which are frequently
sampled to ensure that all mining fluids are retained within
the mining zone. The "bleed" also provides a chemical bleed on
the aquifer to limit the buildup of species like sulfate and
chloride which are affected by the leaching process. The
"bleed" water is treated for removal of uranium and radium.
This treated water is then disposed of through waste water land
application, or irrigation. A very small volume of radioactive
sludge results; this sludge is disposed of at an NRC licensed
uranium tailings facility.
The ion exchange resin is stripped of its uranium, and the
resulting rich eluate is precipitated to produce a yellow cake
slurry. This slurry is dewatered and dried to a final drummed
uranium concentrate.
At the conclusion of the leaching process in a well field area,
the same injection and production wells and surface facilities
are used for restoration of the affected ground water. Ground
water restoration is accomplished in three ways. First, the
water in the leach zone is removed by "ground water sweep", and
native ground water flows in to replace the removed contaminated
water. The water which is removed is again treated to remove
radionuclides and disposed of in irrigation. Second, the water
which is removed is processed to purify it, typically with
reverse osmosis, and the pure water is injected into the
affected aquifer. This reinjection of very pure water results
in a large increment of water quality improvement in a short
time period. Third, the soluble metal ions which resulted from
the oxidation of the ore zone are chemically immobilized by
injecting a reducing chemical into the ore zone, immobilizing
these constituents in situ. Ground water restoration is
continued until the affected water is suitable for its
pre-mining use.
Throughout the leaching and restoration processes, a company
ensures the isolation of the leach zone by careful well
placement and construction. The well fields are extensively
monitored to prevent the contamination of other aquifers.
Once mining is complete, the aquifer is restored by pumping
fresh water through the aquifer until the ground water meets
the pre-mining use.
In situ mining has several advantages over conventional mining.
First, the environmental impact is minimal, as the affected
water is restored at the conclusion of mining. Second, it is
lower cost, allowing Wyoming's low grade deposits to compete
globally with the very high grade deposits of Canada. Finally
the method is safe and proven, resulting in minimal employee
exposure to health risks."
ISL mining may be the wave of the future of U.S. uranium
mining, or it may become an interim mining measure, in areas
where the geology is appropriate for IS. Until sufficient
quantities of uranium are required by U.S. utilities to fuel
the country's demand for nuclear energy, ISL mining may remain
the leading uranium mining method in the United States. At some
point, an overwhelming need for uranium for the nuclear fuel
cycle may again put ISL mining in the backseat, and uranium
miners may return to conventional mining methods, such as open
pit mining.
About The Author: James Finch contributes to
http://StockInterview.com and other publications. You can email
James Finch at jfinch@stockinterview.com. All of his archived
articles (with photos, maps and charts) can be read at
http://www.stockinterview.combu
