2. Chromatographic
• It is possible to realize the
liquid-liquid extraction of Extraction
metallic ions by another
technique: Ion exchange resin.
• An ion exchange resin is an
insoluble matrix (or support
structure) normally in the form
of small (1-2 mm diameter)
beads, usually white or
yellowish, fabricated from an • The trapping of ions takes
organic polymer substrate. The place only with
simultaneous releasing of
material has highly developed other ions; thus the
structure of pores on the process is called
surface of which are sites with ion exchange. There are
easily trapped and released multiple different types of
ions. ion exchange resin which
are fabricated to
selectively prefer one or
several different types of
2
ions.
3. • Advantages of chromatographic extraction
vs. liquid –liquid extraction are:
– Simplicity of use
– Realization of an important number of
successive equilibria in the chromatographic
column
3
4. • There are four main types differing in their
functional groups:
• strongly acidic (sulfonic acid groups, eg.
sodium polystyrene sulfonate or
polyAMPS)
• strongly basic, (trimethylammonium
groups, eg. polyAPTAC)
• weakly acidic (carboxylic acid groups)
• weakly basic (amino groups, eg.
polyethylene amine)
4
5. • TBP absorbed on porous silica that is
hydrophobic by adding methyl groups onto its
surface is used to extract U(VI) and Pu(IV) from
nitric acid solutions.
• Very sensitive separation such as Es 3+ and Fm3+
can be possible, by chromatographic extraction
on column where the stationary phase is
composed of HDEHP/Celite.
• Even though the separation factor KdFm3+/Kd Es3+ =
2.2, an excellent separation is achieved.
5
6. Es(III)/Fm(III) separation by
chromatographic extraction
• Column = HDEHP
8.8% mass/celite,
• S = 0.062 cm2,
• H = 10cm
• Eluent = 0.41M
HNO3
• Flow =
1.1mL/cm2/mm
• T = 60°C
6
7. Ion Exchange resins
• Generalities
• Ion exchange resins are organic polymer
containing polystyrene chains linked
between themselves by divinyl benzene
bridges (DVB).
• On the polymer chains, sulfonic groups
SO3H or quaternary ammonium groups
R4N+ can be added.
7
8. • In the case of sulfonic resins, the proton
can be replaced by metallic actions; the
resin is cationic exchanger.
• In the case of quaternary ammonium
resins, the positive charge must be
neutralized by an anion X- (R4N+, X-), this
anion can be constituted of an anionic
metallic complex MXn(n-m)- with
– n: number of ligands linked to the metal
– m: metallic ion charge,
these resins are anionic exchangers
8
9. Other important parameters
• Exchange capacity
– Expressed in eq/g (dry resin) of monovalent ions H+ (cationic
resin) or anions X- (anionic resin) which enables the
determination of the limiting quantity of metallic ion absorbed by
gram of resin.
– If q0 is the maximum exchange capacity for a monovalent ion, for
a divalent ion, the saturation will be obtained for q0/2. etc…
• Bridging Rate
– Percentage of DVB in the resin which influences the ion
exchange kinetics between phases. The Kinetics to obtain
equilibrium is more rapid when X is low.
• Particle size analysis
– Expressed in mesh (inversely proportional to the diameter of the
spherical grains of the resin ). Partition equilibrium are reached
faster for resins with low particle size (high value of mesh).
9
10. KD
• The partition of a metallic ions M between an
aqueous phase and the ion exchange resin is
characterized by the partition coefficient KD
• KD = CMR * CMa-1
• With CMR = concentration of M in the resin (Mole
for a gram of resin)
• CMa-1 = concentration of M in the aqueous phase
in mole/L
• The dimension of KD is L/g
10
11. Capacity
• Capacity is defined as the number of counter-ion equivalents in a specified amount
of material. Capacity and related data are primarily used for two reasons:- for
characterizing ion-exchange materials, and for use in the numerical calculation of
ion-exchange operations. Capacity can be defined in numerous ways:
• 1. Capacity (Maximum capacity, ion-exchange capacity) Definition : Number of
inorganic groups per
• specified amount of ion-exchanger
• 2. Scientific Weight Capacity Units : meq/g dry H+ or Cl− form
• 3. Technical Volume Capacity Units: eq/liter packed bed in H+ or Cl− form and fully
water-swollen
• 4. Apparent Capacity (Effective Capacity) Definition : Number of exchangeable
counter ions per specified amount of ion exchanger. Units : meq/g dry H+ or Cl
form (apparent weight capacity). Apparent capacity is lower than maximum
capacity when inorganic groups are incompletely ionized ; depends on
experimental conditions (pH, conc. ,etc)
• 5. Sorption Capacity. Definition : Amount of solute , taken up by sorption rather
than by exchange, per specified amount of ion exchanger
• 6. Useful Capacity Definition : Capacity utilized when equilibrium is not attained
Used at low ion exchange rates Depends on experimental conditions (ion-
exchange rate, etc.)
• 7. Breakthrough Capacity ( Dynamic Capacity) Definition : Capacity utilized in
column operation, Depends on operating conditions
11
12. Characteristics of a
chromatographic column
• Diameter: Φ
• Height H
• Optimal ratio H/ Φ ~ 10
• Interstitial volume or dead volume which
corresponds to the volume around the
resin grains.
12
13. 2 paths for separation by
chromatography
• Development by elution for small amount
of metallic ions to be separated
• Development by displacement in the case
of important quantity of matter to be
separated
13
14. Cationic Resins
• Actinides elements are absorbed onto the
cationic exchange resins (sulfonic, strong acid)
as a function of the charge. The affinity of the
cationic resin is:
MO2+<MO2 2+ <M 3+ <M 4+
The reaction equation is
Kex
n + + nHR ← → MR + nH +
M n
With M n+ = actinide ion, HR: resin under acidic
form, MRn is the metallic compound formed in
the resin
14
15. • In the case of the absorption of tetravalent
actinides or trivalent actinides, we observe an
extreme sensibility of the partition coefficient
KD to the pH of the aqueous solutions.
• Consequently, to master the partition of ions
between the 2 phases, the resin is often used
under the form NH4+, the equilibrium is no
more dependent on the pH:
n + + nNH R ← +
M 4 → MRn + nNH 4
15
16. • The used of cationic resins is used
especially for the investigation of An(III)
behavior.
• This method is at the origin of the
discovery of the transplutonium elements
which exist exclusively in aqueous solution
as ions M(III).
• This method also is used to study the
formation of complexes between M n+ and
ligands in aqueous solution.
16
17. Absorption characteristics of Am(III) and Cm(III) and
Lanthanides (III) towards the resin DOWEX 50X4 (under
H+ form)
17
18. • One can notice that the reactions occur
because of the strong associated entropic
variations.
• Two actinides (III) have the same affinity
towards the resin (∆G is quite similar).
18
19. Distribution of
Am(III), Pu(III)
and Pm(III) with
cationic resins.
Influence of the
acid
concentration
on KD
a,c = Resin
DOWEX
b= resin C 50
19
20. • For acidic concentration
<3M, the increase of the
acidity implies a decrease
in KD (exchange
M3+/3H+)
• The KD values for a
metal are very close and
are independent of the
nature of the acid. This is
du to the fact that the
nitrato and chloro
complexes of actinides
(III) have a weak stability.
• Furthermore the KD do
not depend on the Z of
the element
20
21. • These systems are not favorable for a
separation of actinides between
themselves or the separation of actinides
and lanthanides.
21
23. Separation factor for the An(III) from
transplutonium (Am to Md) elements for the
system resin DOWEX 50 * 12 with
ammonium hydroxycarboxylate solutions
23
25. Anionic Resin
• The absorption of metallic ions by a
anionic resin is possible if the metallic ion
M n+ forms with the anionic ligand X- one or
several anionic complexes MXn (m-n)- . The
anion X- is often = Cl-, SCN-, NO3-, SO42-.
• Since only few metallic ions can form such
complexes, extremely selective separation
can be realized.
25
26. -Not Absorbed
+ Absorbed
++ Strongly Absorbed
Medium Chloride Nitrate Sulfate
Actinide HCl MCl HNO3 MNO3 H2SO4 M2SO4
M(III) - ++ - ++ - -
M(IV) ++ ++ ++ - + +
M(V) - - _ ++ - -
M(VI) ++ ++ _ ++ + ++
Affinity of actinides for anion exchange resin as a function 26
of the oxidation state and acid or acid salt
27. • From the previous table we wee that:
– Actinides M(IV) and M(VI) are the most
susceptible to be sorbed as anionic
complexes.
– The absorption of M 3+ ions is not possible
from solution HCl, HNO3 and H2SO4, on the
other side actinides M 3+ can be sorbed by the
salts MCl and MNO3 in concentrated solutions.
27
28. • Among the most important systems, the
absorption of U(VI) from sulfate medium or
Pu(IV) from concentrated HNO3 are going
to be presented because they present an
industrial interest
• U(VI), purification of U from the sulfuric
liquors used to attack the minerals
• Pu(IV), final purification of Pu in certain
reprocessing plants
28
29. U(VI) in sulfate medium (1)
• U(VI) can exits in sulfate medium as
• Find the complexes of U sulfate.
• The 2 anionic forms of U(VI) sulfate can be
absorbed on an anionic resin as:
K1
2 − ←→ R UO ( SO ) + SO 2 −
R2 SO4 + UO2 ( SO4 )2 2 2 4 2 4
4 − ←2 → R UO ( SO ) + 2 SO 2 −
2 R2 SO4 + UO2 ( SO4 )3
K
4 2 4 3 4
• For a ionic strength of 0.3,
• K1 = 230 and K2 = 262
29
30. U(VI) in sulfate medium (2)
• A reaction is competing and is not in favor for
the formation of the sulfato U(VI) complexes,
the absorption of the bisulfate ions HSO4- whose
the quantity increases with the increase of H 2SO4
concentration:
K
− ←3 → 2 RH ( SO ) + SO 2 −
R2 SO4 + 2 HSO4 4 4
• With K3 = 17.5 (for ionic strength of 0.3)
30
32. • In H2SO4, the increase of the
acidity of the medium,
corresponds to a decrease
of KDU(VI).
• If the absorption of U(VI) is
excellent for H2SO4 = 0.1M
(KD = 103 mL/g) , it
becomes mediocre for
H2SO4 = 1M (KD = 6 mL/g).
• This is due to the
competition with the HSO4-
ions for the resin sites.
• For (NH4)2SO4, the effect is
not as strong.
32
33. • The behavior of Th(IV)
is quite similar to U(VI)
but displaced with 2
order of magnitudes
for KD values.
• Separation of
U(VI)/Th(IV) are
consequently possible
with a selective
absorption of U(VI).
33
34. • The extraction of U(VI) by anion resins in sulfate
medium is a very selective method which
separates U(VI) from numerous metallic ions:
M+ (alkalines), Tl+, Be 2+ , Mg 2+ , Mn 2+ , Fe 2+ , Co 2+
, Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ , Al 3+ , Sb 3+ , Ln 3+ (rare
earth)…
• After its absorption on the anionic resin (SO4 2- ),
uranium can be eluted from the chromatographic
column by the seepage of an aqueous solution
that contains anions which have a bigger affinity
for the resin than the ions SO4 2- have.
• The ions are Cl-, NO3-, ClO4-
34
35. Elution of U(VI) from an anionic resin (SO 42- )
Eluent: 0.9M NaCl, 0.1M HCl
Flow: 8.4 mL/cm2/mn
Column diameter = 5cm, H = 122 cm
35
36. • The elution peak of SO42-
ions is obtained for a
volume of eluent = 1V
while the elution peak for
U(VI) is obtained for a
volume of eluent = 2.5V.
• The elution peak of the
U(VI) is large, which is
probably due to the
greater eluent speed onto
the column
36
37. Pu(IV) in HNO3 medium (1)
• Tetravalent Pu has a tendency to form
anionic complexes with NO3- ions in very
concentrated HNO3 solutions or in
concentrated nitrates solutions (LiNO 3,
Ca(NO3)2, Al(NO3)3
• Important ions NO3- concentrations are
necessary because the stability constants
of Pu(IV) nitrate complexes are generally
weak.
37
38. Pu(IV) in HNO3 medium (2)
Pu( NO3 ) 3+ , K = 10
1
Pu( NO3 )2 2 + , K = 100.36
2
This property (weak stability constant)
is unique for M(IV) in concentrated
HNO3 medium
38
39. Pu(IV) in HNO3 medium (3)
• The absorption reaction of Pu(IV) by anion
resins (NO3- form) can be written as:
2 RNO3 + Pu 4 + + 4 NO − ←
3 → R2 Pu ( NO3 )6
• Which means that the anionic nitrato complex of
Pu(IV) is formed in the resin
39
40. Influence of [NO3-] on the extraction of Pu(IV)
by the resin DOWEX 1X4 (50 to 100 mesh)
40
41. • In every cases, we observe a
strong increase of KD with
NO3-, the curves have a
maximum for NO3- = 7 to 7.5M
• Ca(NO3)2 is a more favorable
medium for the extraction of
Pu(IV) than HNO3 medium,
because of the formation of
compounds such as
HPu(NO3)6- and H2Pu(NO3)6 in
the aqueous solutions
• Increase of temperature does
not favor a good absorption of
Pu onto DOWEX 1X4
41
42. Pu(IV) in HNO3 medium (4)
• The absorption of Pu(IV) by anion resins is an
extreme slow process, it can take several
months at ambient temperature to reach the
equilibrium.
• The desorption of Pu absorbed on anionic resins
column can take place by
– Seepage of diluted HNO3
– Reduction of Pu(IV) by hydroxylammonium nitrate
(NH3OHNO3)
– Displacement of anions by percolation of HClO4
solutions
42
43. Pu(IV) in HNO3 medium (5)
• By an absorption/desorption cycle on
anionic resins (NO3-), Pu can be separated
from a big variety of contaminants.
• Next table is presenting the performances
of a cycle of purification
43
44. Separation of Pu from impurities by anionic exchange at 60°C
element Initial Pu in ppm Final Pu in ppm Decontamination
Factor
Ag 105 <2 >5*104
Al 105 <13 >7.7*103
Ca 105 <5 >2*104
Cr 105 5 2*104
Cu 105 10 104
Fe 2*106 45 4.4*104
K 105 <5 >2*104
Li 105 <1 >105
Mg 105 20 5*103
Mn 104 2 5*103
Na 104 20 5*102
Ni 105 <10 >104
Column: 0.28 cm2, H = 90cm, Resin DOWEX 1X4, 44
Wash: 15 volumes, 7.2M HNO Flow: 10 mL/cm2/mn
