Separation of lithium isotopes by chemical exchange chromatography

1
Separation of lithium isotopes by chemical
exchange chromatography
D. Axente, Ancuta Muresan
2
7Li (92.6)

• ELEX process, electric driven chemical exchange
  (1951)
• Operated 1953-1956

• COLEX process (Column Exchange) Li Li(Hg)
• Alpha 4 operated 1955-1963 dismantled 1980.
• Alpha 5 operated 1955-1959 dismantled
  1965-1966.
• Employed 10.9x106 Kgs mercury.

3
The mercury-nitric acid purification system,
utilized in COLEX process, was the source of the
major mercury-bearing waste stream at Y-12 plant.
This system discharged a diluted, neutralized
acid waste, containing mercuric nitrate.
910,000 Kgs of mercury have still not been
accounted for. 310,000 Kgs of this material
have been lost in waste streams, evaporation and
spills. It was estimated that 23,269 Kgs of
mercury were released in the air by venting of
mercury vapors and smelting of mercury
contaminated scrap. The COLEX process discharged
108,408 Kgs of mercury to East Fork Poplar Creek,
being contaminated Watts Barr Lake, Poplar Creek
and Clinch River.
4
6Li is utilized to manufacture of the secondaries
of so called dry thermonuclear devices, as 6LiD
(lithium deuteride)
6Li Neutron ? 3H 3He Energy (1) D 3H
? 4He n 17.6 MeV (2)
The neutrons, from a fission of primary device,
bombarded 6Li, liberating tritium, which quickly
fuses with the nearly deuterium of 6LiD. In
France COGÉMA enriched 6Li by chemical exchange
in columns, using Li(Hg) and a solution of LiOH.
5
In 1995 the releases contained 12.1 Kg mercury,
representing a major reduction since 1984, when
they rose to 240 Kg/yr.
Lithium-6 will be used to produce tritium in
magnetically confined nuclear fusion reactors
using deuterium and tritium as fuel.
Tritium will be produced by surrounding the
reacting plasma with a blanket containing 6Li,
where neutrons, from the deuterium-tritium
reaction in the plasma, will react with lithium-6
to produce more tritium (1).
ITER will be designed to produce 500 MW of
fusion power, sustained for up to 400 sec., by
burning of about 0.5 g of deuterium/tritium
mixture in its 840 m3 reactor.
Fusion power offers potential of environmentally
benign, widely applicable and essentially
inexhaustible electricity. These properties will
be needed as world energy increase, while
simultaneously greenhouse gas emissions must be
reduced.
ITER European Union India Japan China
Russia South Korea USA.
6
Separation of Lithium Isotopes

• Chemical exchange methods have been considered as
  useful isotope separation techniques.
• Enriching coefficient e a -1 (3)
• Column chromatography with
• 2.2.1-cryptand resin e 0.014 at 40C
• 2B.2.1-cryptand resin e 0.047 at 20C
• cation exchange resin e 0.00089-0.00171
  at 25C
• ion exchange using hydrous manganese (IV)
  oxide, as ion exchanger, and elution
  chromatography
• The adsorption capacity of MnO2 was 0.5 meq/g.

(4)
7
(5)
(6Li/7Li)0 the isotopic ratio of the lithium
feed solution, of natural isotopic
abundance. (6Li/7Li) the isotopic ratio of an
individual fraction, extracted from the
chromatographic column. ?m/m is the proportion of
lithium in the individual fraction
Fig.1. Separation of lithium isotopes by cationic
exchange chromatography
8
Table 1. Separation of lithium isotopes by ion
exchange chromatography
a Separation Method Exchanger
1.0092 Extraction Lithium manganese oxide
1.0070 Elution Titanium phosphate
1.00171 Displacement Asahi LS-6 fiber
1.0260 Elution Crown resin
1.0140 Displacement Cryptand resin
1.0026 Breakthrough Dowex 50x24
1.0016 Breakthrough Cubic antimonium acid
1.0140 Extraction LiMn2O4
1.0210 Elution MnO2
Dong Won Kim, Bull. Korean Chem. Soc., 2001,
Vol.22, No.5, 503-506
9
Criptands are macrobicyclic polydentate ligands
that Lehn has termed, e.g. R CH2O C6H3 N2O5
J.M. Lehn, Nobel Lecture, Angew. Chem. Int. Edn.
Engl., 27, 89 (1988)
A cryptand (crypt) has a rigid molecular cavity
and can form a complex, e.g. NH4 (crypt)Cl, in
which the ligand encapsulates the cation with a
bicapped trigonal prismatic coordination
polyhedron. Polymers with a cryptand, as an
anchoring group, are called cryptand polymers.
Cryptand (2B,2,1) polymer is able to bind to
alkali and alkaline cations and stability
constant of potassium is highest among alkali
cations. Therefore stability constant of amonium
ion is estimated to be high.
10
Ion exchange resin (1,12,15-triaza-3,4
9,10-dibenzo-5,8-dioxacycloheptadecane), named
NDOE bonded Merrifield peptide resin D.W. Kim
et. al., J. Radioanal. Nucl. Chem., Vol. 242, No.
1, (1999), 215-218
The absorption capacity 0.2 meq/g dry resin. The
lighter isotope, 6Li, concentrated in the
solution and the heavier isotope, 7Li, in the
resin phase.
The distribution coefficient of Li, between
resin and solution, was determined
Ci and Cf are the concentrations of initial and
final electrolyte solution. M is the mass (g) of
dry resin. V is the total volume (cm3) of the
solution.
(6)
11
NDOE resin was slurried in ammonium chloride
solution and then was packed in a water jacketed
glass column (32 cm length, 0.1 cm I.D.). 1 ml of
500 ppm solution of Li in H2O was loaded on the
top of the resin. 2.0 M NH4Cl solution was used
as an eluent for lithium isotope separation.
The effluent was collected as fractions and
isotopically analysed. The separation factor a
1.0201 was found. a 1.035 were reported by the
same author, using monobenzo-15-crown-5 and
reduced dibenzo pyridino diamide azacrown, as
anchor groups, respectively. a 1.068 was
obtained on N3O3 azacrown ion exchanger.
Fig.2. Distribution coefficient of Li on NDOE
resin for different concentrations of NH4Cl
12
Yasutoshi Ban et. al., J. Nucl. Sci. Technol.,
vol. 39, No 3, 279-281 (2002) prepared a B15C5
resin in porous silica beds, with uniform size,
60 µm, for lithium isotope separation.
The volume of silica beads is not changed by the
outer solutions the expansion and shrinking of
the packed resin are avoided.
Two runs of column experiment were performed with
21 g of B15C5 resin packed in a glass column (0.8
cm i.d., 100 cm long), at 35C.
Dibenzo-15-crown-5 ether
13
The resin packed in the column was washed with
pure water and charged with mixture solution of
methanol and 12 M HCl (70 vol. ). Then 0.55 M
LiCl, dissolved in the same mixture solution, was
fed into the column by a high pressure pump. The
effluent was collected in small fractions.
14
The total amount of lithium in the B15C5 resin
(7)
Qtot Co(VFB Vd)
Co is the concentration of lithium in the feed
solution VFB is the volume of the breakthrough
point (where the concentration is Co/2) Vd is the
dead volume of the column.
The total Li adsorption capacity of the B15C5
resin was 0.15 mmoles/g. If the column contains
21 g of resin, therefore Qc 3.15 mmoles.
15
Table 2. Determined isotopic ratios of lithium in
the sample fraction
Fraction No 7Li/6Li
12 13.36
13 12.64
14 12.47
15 12.40
16 12.37
17 12.40
18 12.40
19 12.34
Original feed 12.34
16
The heavier isotope is enriched in the solution
phase, in the front of lithium band.
e7/6 Sqi(1 ro)7ri 7ro / 7roQtot(1
7ri)
(8)
In Kims work Chromatography of lithium was done
in an elution manner, where the lithium band
showed a bell shaped concentration profile.
17
Y. Barré et al., Separation des isotopes du
lithium par chromatographie ionique avec des
ligands greffes sur silice, Conférénce
Internationale sur les isotopes stables at les
effects isotopique, 20-25 Juin 1999, Carry le
Rouet, France developed a silica grafted resin,
that presents greater isotope separation factor
and better kinetic than with conventional organic
resins.
Silica allows the use of silane chemistry, which
gives strong, stable bonding of organic ligands
to the support, by the reaction of surface
silanols with methoxy silanes.
18
Fig.6. Flow diagram of the plant for lithium
isotope separation by continuously displacement
chromatography
19
The four columns, each 100 cm length, 1-2 cm
i.d., are serially connected. At the bottom of
each column the pH-meter measures and records
continuously the solution pH. At the both end of
the columns there are selector valves, which
change the solution flow in order to continue the
development of the lithium band as long as is
necessary. The adsorption band of lithium is
moved continuously through the columns, in order
to realize adequate separation of isotopes. 7Li
is enriched in the front of the band, in
solution, and 6Li at the rear of the band, in
adsorbent phase. The degree of enrichment, at
each boundary, increases with the distance
travelled by the band, until a steady state is
reached. After a certain period of operation
enriched 6Li and 7Li are recovered from the
recycling line, through a selector valve, and
equal amounts of feed lithium are fed to the
enrichment column.
20
Conclusions
The methods for lithium separation, based on
lithium isotope exchange 7Li/6Li in the system
Li - Li(Hg) has been abandoned in USA according
to high level of mercury pollution of the
environment and big mercury risk of the workshop
personnel.
In France, Japan, Russia, etc., the research work
for a new lithium isotope separation technology,
efficient and clean toward environment, are in
progress.
Lithium enriched in the lighter isotope, 6Li, is
used in weapons components, in the form of
Lithium deuteride and is necessary for nuclear
fusion reactors in the frame of ITER Program.
Using the ligands, with a good selectivity
towards lithium isotopes, grafted on small silica
particles, is very promising because combines a
high selectivity with a good isotope exchange
kinetic and an important mechanical stability.
These characteristics would be considered in
order to develop a new technology for lithium
isotope separation.