Reversing Mother Nature, Part Two
Author: James Finch

We talked to North America's leading In Situ Leach (ISL)
uranium mining engineers, and had them explain exactly how ISL
worked. Most of the significant ISL operations in the United
States were designed and/or constructed by these engineers.
They explained how ISL mining is really just reversing the
process of Mother Nature.

ISL EXTRACTION AND PROCESSING

During ISL mining, water is pumped to the surface from
production wells that contain uranium in very low
concentrations, on the order of parts per million
concentrations. The next step in the ISL process is to extract
the uranium dicarbonate. Extraction is done by chemically
exchanging ions inside a processing facility. "The ion exchange
process is very analogous to a home Culligan® water softener,"
Anthony revealed. "It removes hardness or calcium from the
water by replacing it with sodium, using ion exchange resins.
If you go to Lowe's or Home Depot, and buy a water softener,
you basically have a home version of a uranium extraction
plant." The main difference is your water softener will have a
cation exchanger. "For a uranium plant to function properly,
you need to use an anion exchange resin, which is specifically
designed to load uranium," Anthony clarified.

And what is this magical "ion exchange resin"? The resin is
comprised of little polymer beads, which are charged particles
having an affinity for uranium anions. "There are literally
millions of these small resin beads in a vessel, which can
adsorb low concentration of uranium in solution," said Anthony.
Adsorption is when something is attracted to something else or
clings to it, like static electricity.

Why do you have to process uranium like this? "In essence, the
ion exchange process is a beneficiation (reduction) process
that concentrates large volumes of low concentrate uranium
solution into a much smaller volume containing a much higher
concentration of uranium," said Anthony. In other words, the
beneficiation is just concentrating the uranium from the large
volume of water in which it is mined into a more compact form.
The preferred means is through an ion exchange.

Anthony gave a real-life example of the beneficiation process,
"Three million gallons of wellfield solution containing dilute
concentrations of uranium, of 100 parts per million minus 0.10
grams/liter, is passed through a bed of ion exchange resin.
This might take 24 hours to achieve if the solution is flowing
at 2,500 gallons per minute. After this length of time, the
resin becomes loaded with approximately 2,500 pounds of
uranium."

STRIPPING THE URANIUM

Stripping the uranium is called the elution process. This is
done through a chemical exchange of positively and negatively
charged ions. Resins are classified by the charge on the active
sites. "The active sites on the resin are positively charged for
anion resins and negatively charged for cation resins," Norris
enlightened us. "The resin's ability to extract chemical ions
from a solution is derived from what's called an active site,"
he continued. "In our case, chloride ions obtained from
ordinary tale salt are used to stabilize or temporarily
neutralize this positively charged active site." The negatively
charged chloride ion sticks to the positively charged site, held
in place by what Norris called "electrostatic forces." When the
negatively charged ions, such as uranyl dicarbonate, are placed
in contact with the solution, it will kick off the chloride and
replace that with the uranyl dicarbonate.

That was the chemistry lesson. Anthony summed it up in a
nutshell, "They just displace it. There's a greater affinity
for the chloride ion to the resin than there is for the
uranium. So, the uranium is stripped from the resin bed." The
processing facility chemically strips the loaded uranium from
the resin by soaking the entire package of uranium-laden resin
in a salt bath solution. "The volume of salt solution is on the
order of 10,000 gallons resulting in a solution concentration of
30 grams/liter uranium," Anthony said, describing the process of
how the uranium becomes concentrated. "The stripped uranium
solution concentration is magnified 300 times more than the
wellfield solution," he informed us. "The concentration level
can now be economically processed for recovery: precipitation,
dewatering, drying and drumming for a nuclear facility."

GETTING URANIUM INTO THE DRUM

After the uranium has been removed from the solution, it is
precipitated. At this point in the processing stage, you have
yellowcake slurry. Up close, it looks like a sort of yellowish
and wet, runny cement mixture. The dewatering process does just
that, it removes the water from the yellowcake mixture.

"I use a filter press, a device that is designed to separate
solids from solutions," explained Anthony. Filter presses are
extensively used in various types of food, chemical and drug
processing across the world. "The uranium solids, now looking
more like yellowcake, are retained in the filter press, where
they can be washed and later air dried, before drying them to a
powder with a low temperature vacuum dryer," said Anthony taking
us step by step through this process.

So what is the filter press and how do you end up with the
finished yellowcake when you're done? "It's a series of plates
and hollow frames, or it could be a series of recessed
chambers," Anthony answered. "Filter cloth is draped over the
plates or chalked in the recessed chambers. The yellowcake
slurry is pumped through the filter allowing the liquid phase
to pass through the filter cloth, trapping the uranium oxide
inside the device." Anthony likes to pack the filter press up
with as much yellowcake as it can hold. "It is then washed with
clean water to displace the chloride ions to a low level,"
Anthony explained. If you don't remove the chloride
concentrations to the acceptable level required by an uranium
enrichment facility, a fine is assessed against that shipment.

The final steps include conveying the yellowcake to the vacuum
dryer. The uranium oxide's color depends on how high or low a
temperature is used to dry the "yellowcake." Patrick Drummond,
the Smith-Highland Ranch plant superintendent, showed us pure
uranium oxide dried at high temperatures. It was nearly black.
After the drying process is complete, the uranium is packaged
up in DOE-approved 55 gallon drums and transported to an
enrichment facility. It is then when the enriched uranium can
finally be used to power a nuclear reactor and provide an
inexpensive source of electricity.


About The Author: James Finch contributes to
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visiting http://www.stockinterview.com. Write to James Finch at
jfinch@stockinterview.com. More information about Harry Anthony
is available at http://www.hanthony.com