Solid-phase extraction of plutonium(IV) an americium(III) using N-benzoylphenylhydroxylamine and its derivatives

Article abstract of DOI:10.1134/S0036023611110192

The recovery and separation of plutonium(IV) and americium(III) by solid-phase extraction (SPE) on alkylated silica gel S16 modified with N-benzoylphenylhydroxylamine (BPHA) and with its derivatives was studied. BPHA was modified by introducing into the p-position of the phenyl ring of electronactive substituents that differ in their hydrophobicity: CH₃, Ph, Cl, F, and NO₂. The SPE of plutonium(IV) and americium(III) was studied in the range of acidities from pH 8 to 1 M HNO₃. The recovery and separation of these elements was shown to depend on the nature of the substituent, aqueous acidity, and the preparation of S16 to SPE experiments.

Full text of DOI:10.1134/S0036023611110192

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2011, Vol. 56, No. 11, pp. 1839–1846. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © O.M. Petrukhin, B.Ya. Spivakov, V.P. Morgalyuk, G.I. Malofeeva, E.V. Kuzovkina, A.P. Novikov, 2011, published in Zhurnal Neorganicheskoi Khimii,
2011, Vol. 56, No. 11, pp. 1924–1931.
PHYSICAL CHEMISTRY
OF SOLUTIONS
SolidꢀPhase Extraction of Plutonium(IV) an Americium(III) Using
N
ꢀBenzoylphenylhydroxylamine and Its Derivatives
O. M. Petrukhina, B. Ya. Spivakovb, V. P. Morgalyukc,
G. I. Malofeevab, E. V. Kuzovkinab, and A. P. Novikovb
a Mendeleev University of Chemical Technology, Miusskaya pl., 9, Moscow, 125047, Russia
b Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences,
ul. Kosygina 19, Moscow, 119991 Russia
c Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, ul. Vavilova 28, Moscow, 117813 Russia
Received July 15, 2010
Abstract—The recovery and separation of plutonium(IV) and americium(III) by solidꢀphase extraction
(SPE) on alkylated silica gel S16 modified with
atives was studied. BPHA was modified by introducing into the
N
ꢀbenzoylphenylhydroxylamine (BPHA) and with its derivꢀ
ꢀposition of the phenyl ring of electronꢀ
p
active substituents that differ in their hydrophobicity: CH3, Ph, Cl, F, and NO2. The SPE of plutonium(IV)
and americium(III) was studied in the range of acidities from pH 8 to 1 M HNO3. The recovery and separaꢀ
tion of these elements was shown to depend on the nature of the substituent, aqueous acidity, and the prepaꢀ
ration of S16 to SPE experiments.
DOI: 10.1134/S0036023611110192
Solidꢀphase extraction (SPE) is based on the partiꢀ
tion of a material between an aqueous phase and a
grafted organic phase. Metal preconcentration occurs
on account of the formation and recovery of hydroꢀ
phobic metal complexes; in this respect, the method is
close to liquid–liquid extraction. Nonaqueous phases
frequently used in SPE are silica gels with grafted alkyl
groups (S18 and S16) [1]. The method is useful for
recovering and preconcentrating any metals, specifiꢀ
cally radionuclides [2–4].
EXPERIMENTAL
Synthesis of Reagents
The structure of the compounds synthesized was
verified by 1H NMR spectroscopy, elemental analysis,
and melting point measurements (by coincidence with
1
the available literature data). H NMR spectra were
recorded in CDCl3 on a Bruker Avance 300 spectroꢀ
photometer at a working frequency of 300.11 MHz.
ꢀbenzoylphenylhydroxylamine was synthesized
by a modification of the procedure described in [6, 7]
as follows. To 10 g of phenylhydroxylamine dissolved
N
As a result of atmospheric nuclear tests and a numꢀ
ber of manꢀmade disasters, areas contaminated with
plutonium and transplutonium elements appeared in
the region around facilities of the nuclear industry.
There is need to delineate the perimeter of such places
followed by monitoring the distribution of radionuꢀ
in 800 mL of water at 0–5°C, 20 g of NaHCO3 was
added, and then 12 g of benzoyl chloride was added
dropwise under vigorous stirring while the same temꢀ
perature was maintained. After the benzoyl chloride
addition was over, the reaction mixture was stirred for
2 h at 0–5°С. A precipitate was filtered off, crystallized
clides. This requires adequate methods of preconcenꢀ from water/isopropanol, washed with water, and dried
in air. It was again crystallized from heptane/acetone,
filtered, washed with heptane, and dried first in air and
then in a vacuum desiccator over P2O5. As a result, 15.5 g
of BPHA was obtained (yield: 78%) in the form of colꢀ
orless needles with Tm = 122–123°C. The general
scheme of synthesis is found below.
tration and determination of radionuclides. Earlier
[5], we developed SPE to be a method for recovering
neptunium(V), plutonium(IV), and americium(III)
with the use of
Nꢀbenzoylphenylhydroxylamine
(BPHA) as an extractant [5]. This method provides
the recovery of plutonium and transplutonium eleꢀ
ments and an efficient separation of neptunium(V)
from plutonium(IV) and americium(III); however, the
behavior of plutonium(IV) and americium(III) in the
selected conditions was virtually coincident. This
problem was posed for the reason that (as will be
shown below) the incorporation of substituents into a
molecule of the extracting agent can change both the
efficiency and selectivity of the reagent.
H
H
R
O
Cl
O
N
O
N
O
H
+
R
R = H, CH3, Cl, F, Ph, NO2
1839

1840
PETRUKHIN et al.
Table 1. 1H NMR spectroscopy, elemental analysis, melting temperatures, yields, bulk formulas, and formula weights for
the BPHA(R) derivatives synthesized
Elemental analysis, %
(
Calcd. / Found)
Comꢀ
pound
Bulk
formula
Formuꢀ
la weight
1H NMR spectra, δ, ppm (CDCl3)
Tm
,
°
C
Yield, %
78
C
H
N
(Cl, F)
p
ꢀCH3ꢀR 9.12 (s, 1H, –OH), 7.27 (m, 5H,
Ph), 7.20 (d, 2H, ꢀH, Tol), 7.05
(d, 2H, ꢀH, Tol), 2.31 (s, 3H, CH3,
Tol)
73.99/ 5.77/ 6.16/
74.09 5.88 6.11
120–122
[8]
C14H13NO2 227.25
m
o
p
p
ꢀClꢀR 7.32 (m, 5H, Ph), 7.22 (m, 4H,
ꢀH, ClꢀPh)
o
,
63.04/ 4.07/ 5.66/
62.82 4.04 5.71 14.31/
14.24
Cl
16–165
[9]
82
65
C13H10NO2Cl 247.67
C13H10NO2F 231.22
m
ꢀFꢀR
9.28 (s, 1H, –OH), 7.56 (m, 5H,
Ph), 7.12 (t, 2H, ꢀH, F–Ph), 6.96 67.51 4.35
(t, 2H, ꢀH, F–Ph)
67.52/ 4.36/ 6.06/
F
8.22/
8.21
145–147
[10]
m
6.04
o
p
p
ꢀPhꢀR 9.16 (s, 1H, –OH), 7.68–7.25 (w. 78.91/ 5.22/ 4.84/
m, 14H, Ph, Ph–Ph) 79.03 5.24 4.67
182–184
76
61
C19H15NO2 289.32
C13H10N2O4 258.23
ꢀNO2ꢀR 8.17 (d, 2H,
mꢀH, NO2–Ph), 7.65 60.46/ 3.90/ 10.85/
164–166
[9]
(d, 2H, ꢀH, NO2–Ph), 7.40 (t, 3H, 60.71 3.87 10.81
o
m
,
p
ꢀH, Ph), 7.29 (m, 2H, ꢀH, Ph)
o
Analogous procedures with the use of
chloride, ꢀchlorobenzoyl chloride, and ꢀfluorobenꢀ
zoyl chloride were employed to prepare
toluylphenylhydroxylamine ( ꢀCH3ꢀBPHA, colorless
needles), ꢀchlorobenzoylphenylhydroxylamine
ꢀClꢀBPHA, colorless platelets), ꢀfluorobenꢀ
zoylphenylhydroxylamine ( ꢀFꢀBPHA, colorless neeꢀ
dles), ꢀ( ꢀnitrobenzoyl)phenylhydroxylamine
ꢀNO2ꢀBPHA, colorless needles), and ꢀ( ꢀpheꢀ
nylbenzoyl)phenylhydroxylamine ( ꢀPhꢀBPHA, colꢀ
orless platelets). The last compound was synthesized
for the first time. In cases of ꢀPhꢀBPHA and ꢀNO2ꢀ
p
ꢀtoluyl
Procedures
p
p
Solidꢀphase extraction was studied in a batch
mode. The sorbent (100 mg) was shaken for 5 min with
5 mL of ethanol. After settling, ethanol was decanted,
and to the sorbent converted to the work condition,
added was 10 mL of a reagent solution of an adequate
concentration, and the mixture was shaken for 10 min.
After settling, the reagent solution was decanted, to the
Nꢀpꢀ
p
Nꢀp
(
p
Nꢀp
p
N
p
(
p
N p
modified sorbent a test solution was added (V = 10 mL),
p
and the mixture was shaken for the required period of
time. The degree of recovery was determined using
239Pu and 241Am radionuclides as the difference
p
p
BPHA, syntheses were carried out in water/dioxane between their contents in the initial solution and in the
filtrate. Measurements were carried out on an Alpha
Analyst (Canderra) instrument. The metal concentraꢀ
(1 : 1 vol/vol). pꢀPhenylbenzoyl chloride and pꢀnitrobenꢀ
zoyl chloride were used as a 6.5 M solution in dioxane.
tion in a test solution was n × .
10–7
1H NMR spectra, elemental analysis, melting temꢀ
peratures, yields, bulk formulas, and formula weights
of the compounds synthesized (except for BPHA) are
found in Table 1. The results of elemental analysis
coincided with the calculated values no worse than by
98.5%.
RESULTS AND DISCUSSION
BPHA is a representative chelating reagent with a
hard bidentate O,Oꢀchelating group (HA). The liqꢀ
uid–liquid and solidꢀphase extraction constant for the
recovery of metal Mm+ from an aqueous solution to a
nonaqueous phase in the form of a neutral chelate
MAm is written as
Materials
n
m
+
m+
The materials used were ethanol; HNO3 of various
concentration; ethanolic solutions of BPHA and its
CH3, F, Cl, and NO2 derivatives; dimethylamine soluꢀ
tions of BPHA and its Ph, F, and CH3 derivatives; and
Diasorbꢀ100ꢀS16, a sorbent purchased from Bioꢀ
⎡
⎣
⎤
⎦
⎡
⎣
⎤
⎦
Kex = MA
H
M
HA
[
]
[
]
m
nonaq
nonaq
(1)
m
+
⎡
⎤
[
⎦
= KD
H
HA
,
]
(
)
nonaq
⎣
where КD is the metal distribution coefficient, and the
ChimMac (63–200
µ
m, 16.6% C).
“nonaq” subscript denotes the nonaqueous phase,
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 11 2011

SOLIDꢀPHASE EXTRACTION OF PLUTONIUM(IV)
1841
Table 2. Electronic (σ ) and hydrophobic (π ) parameters of
which is organic in liquid–liquid extraction and
pseudoꢀorganic in solidꢀphase extraction by alkylated
silica gel (the latter term is also used since methodꢀ
ologically SPE does not differ from sorption). Kex may
p
ar
substituents [16–18]
Substituent
σ
π
p
ar
also be expressed through the stability constant and
βn
CH3ꢀ
Phꢀ
–0.17
+0.01
+0.06
+0.23
+0.78
+0.56
+1.96
+0.14
+0.71
–0.28
distribution constant
of the complex and the disꢀ
P
MAm
sociation constant KHA and distribution constant PHA
of the chelating agent:
Fꢀ
Kex = βmPMA KHmA PHmA
.
Clꢀ
(2)
m
NO2ꢀ
The feasibility of separating two metals can be
ascertained by the separation constant, which is equal
to the ratio of the / distribution coefficients of the metꢀ
acids (the ratio of the dissociation constant of unsubꢀ
stituted benzoic acid to the dissociation constant of
substituted benzoic acid); this ratio characterizes the
electronic activity of the substituent, namely, the
als:
. Combining Eqs. (1) and (2) for the case
K D K D
1
2
where metals are recovered as MAm and MAn chelates
with constants and , respectively, we obtain an
Kex
Kex
2
expression for the 1separation coefficient:
parameter
will be different depending on whether the substituent
is in the or ꢀposition of an organic molecule: σm
σ
. One should keep in mind that
σ
values
K
K
K
K
P
βm
MA m
m−n n−m
D1
D2
ex1
ex2
(3)
Ks =
=
=
KHA
P
.
mꢀ
p
HA
βn P
MA n
and σp, respectively. Furthermore, these values will be
fundamentally different for aromatic and aliphatic
hydrocarbons.
In interpreting experimental data, it may appear
more convenient to use the ratios of logarithms of the
distribution coefficients:
Tens of electronegativity scales have been proꢀ
posed, and electronegativities for the same substituent
on different scales do not coincide. To date, there are
a number of publications where substituent parameꢀ
ters are given [16–18]. Various values are given to one
parameter for the same substituent, sometimes, conꢀ
siderably depending on the class of compounds and
the reference compound, which is explained by the
contemporary quantumꢀchemical theory.
The concepts of the hydrophobicity of compounds
and separate fragments thereof developed in parallel
[16, 17]. The greatest data set on the distribution conꢀ
stants of organic compounds has been accumulated
for the octanol–water system, which is currently taken
to be a standard system [19]. The distribution constant
log β P
− ml o g P K −1
(
)
(
)
l o g KD
m
MAm
HA HA
1
(4)
=
.
− nlog P K −1
l o g KD
log β P
(
)
(
)
n
MAn
HA HA
2
For possible variations in
and
and in their
KD
2
KD
1
ratio upon the replacement of a substituent in a
reagent molecule to be taken into account, let us conꢀ
sider potential contributions of each rightꢀhandꢀside
term in Eqs. (2) and (3).
The efficiency of a complexing reagent in the sysꢀ
tems under consideration is controlled by both the staꢀ
bilities of metal complexes and their hydrophobicities.
To change the recovery efficiency and selectivity, one
should change, in an adequate manner, the stability
constant and/or the distribution constant. Now we
cannot advise quantitative methods for evaluating a
selective change in these constants. However, there are
many parameters of metal cations, reagents, and
media that are known to control the stability and lipoꢀ
philicity of complexes.
of a compound in this system
(
logPoct/w is considꢀ
)
ered as a measure of hydrophobicity of this compound.
Correlation analysis of these data based on the
assumption of the linearity of free energies [20] allows
us to evaluate the hydrophobicity (hydrophilicity)
parameters of individual groups (πt). The hydrophoꢀ
bicity parameters, as the Hammett constants (σm and
σp), too, depend on the type and structure of the comꢀ
Contemporary theory of atomic electron density in
a molecule regards a chemical compound as a system
of nuclei of chemical elements immersed into a single pound. The parameters of our chosen substituents are
electron cloud [11–13]. The major quantity characꢀ compiled in Table 2.
terizing the electronic structure of a compound is elecꢀ
tronegativity, which characterizes the displacement of
the center of gravity of the valence cloud towards one
atom, which is electronegative in this context [14].
There should be a unique relationship between the
electronic properties of the donor atoms of an analytic
functional group of a chelating reagent and the elecꢀ
tron density on the peripheral atoms of the reagent and
The development of quantitative concepts of the the complex. This relationship can indeed be traced
electronegativity of substituents in organic chemistry for the substituents of interest (Fig. 1). Electronꢀdenꢀ
started with Hammett [15]. Hammett proposed using, sity transfer in a molecule of a metal complex is conꢀ
to characterize the electronic influence of a substituꢀ trolled by the properties of the valence state of the cenꢀ
ent, the ratio of the dissociation constants of benzoic tral atom and by the properties and structure of the
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 11 2011

1842
PETRUKHIN et al.
It is more difficult to predict how the separation
σ
p
factor of two metals will change in going from one subꢀ
stituent to another, although some suggestions are
possible here, too. For coordinatively saturated comꢀ
plexes (where the entire inner sphere of the complex is
occupied by organic ligands), the distribution constant
of the complex should primarily be dictated by the
hydrophobicity and number of ligands in the complex
and not by the nature of the metal. Let us consider two
simple cases of separation of metals that are extractꢀ
able as such complexes. For the first case, let us
assume that pH in an aqueous solution and the
amount of the reagent are so high that the concentraꢀ
tion of the uncomplexed metal in the aqueous phase
1
NO2ꢀ
Clꢀ
CH3
0.1
0
–0.1
Fꢀ
Ph
ꢀ
ꢀ
–1
may be ignored. Of cause, this holds if
β
has suffiꢀ
βn cannot
0
1
π
ar
ciently high values, too. If so, the ratio βm
/
make any significant contribution to Ks, and Eq. (3)
becomes
Fig. 1. Correlation between the electronegativity (σ ) and
p
hydrophobicity (
π
) parameters of substituents.
ar
P
Ks =
KHmA−nPHnA−m
.
MAm
(5)
P
MAn
organic moiety of the molecule; this moiety changes
upon the introduction of an electronꢀactive substituꢀ
ent that has a certain hydrophobicity.
Inasmuch as
mand nvalues cannot differ from each
other considerably, efficient metal separation is not
observed in the aboveꢀindicated conditions. In other
The impossibility to predict the properties of a subꢀ
stituted derivative of the initial complexing compound
explains the methodology adopted today in this field
[21]. Based on own and other data, one selects a comꢀ
pound that approaches, in its properties, the desired
result to the greatest extent, namely, a leader. The
structure of the leader is modified to create a series of
new reagents. As a result of studying this series of
reagents, the next step of synthesis is planned. We
adopt this approach in this work. As the leader, we
selected a BPHA molecule, whose modification sugꢀ
words, when pH is high,
or
l o g KD l o g KD
KD KD
will hardly change noticeably in2going from one subꢀ
1
1
2
stituent to another in the reagent molecule, and even
if it changes, this will occur only for
son that the hydrophobicity ( value) for a metal comꢀ
m > n, for the reaꢀ
P
plex depends not only on the substituent parameter πar
but also on the number of substituents. We will check
this suggestion experimentally.
As the solution acidity increases and the reagent
concentration decreases, we arrive at another case,
where the concentration of the metal uncomplexed to
the reagent cannot be ignored, the more so as there is
additional complexing in the aqueous phase. Then, if
gested introducing, into the pꢀposition of the phenyl
ring, of electronꢀactive substituents that at the same
time differ in their hydrophobicities: CH3, Ph, F, Cl,
and NO2
.
m
and n are close to each other or even equal, we can
In discussing the extraction constants (the extracꢀ
tion efficiency and selectivity) as dependent on the
stability and hydrophobicity of metal complexes, one
should take into account the specifics of extraction by
reagents that contain protonatable nitrogen toms in
their structures. In such complexes, the electron denꢀ
sity of the nitrogen lone pair plays the role of a kind of
depot of the electron density of the compound and is
distributed among all atoms of the compound dependꢀ
ing on their acceptor abilities. It is on account of this
specific feature that such extractants are group extracꢀ
tants. As a result of this situation, the stability conꢀ
stants and the distribution constants of complexes are
interrelated [22]. In a general case, Kex in Eq. (2) might
be expected to increase in going from a reagent with
one substituent to a reagent with another substituent
ignore the last terms of the rightꢀhand part of Eq. (3)
and take that the separation factor depends primarily
on the ratio of stability constants, that is,
We must recall that a rather high value of Ks is necesꢀ
Ks = βm βn .
sary but not sufficient for two compounds to be sepaꢀ
rated. For example, when
and
are equal to 104
KD
2
KD
1
and 102 or 10–4 and 10–2, then in both cases Ks = 100,
but no separation will occur for the reason that in the
former case both compounds in extraction equilibꢀ
rium will appear in the nonaqueous phase, and in the
latter, they appear in the aqueous phase.
Here, we study the recovery and separation of pluꢀ
tonium(IV) and americium(III) with BPHA and its
derivatives as dependent on the initial solution acidity
with the use of ethanol and/or DMAA as solvent for
supporting the reagent on S16 and for conditioning
the sorbent (as in SPE [23]). Table 3 lists data for the
reagent CH3ꢀBPHA, making two inferences possible.
As the aqueous acidity increases, the recovery drops
as βm and
increase, that is, as the contribution of
P
MAm
the parameter σp into the stability of the complex and
that of the parameter πar into its hydrophobicity
increase.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 11 2011

SOLIDꢀPHASE EXTRACTION OF PLUTONIUM(IV)
1843
Table 3. Plutonium and americium percent recovery and the ratio of logarithms of their distribution coefficients with the use of
the CH3ꢀBPHA reagent. The applied reagent concentration: 4 × 10–2 mol/L
Organic solvents
alcohol*–DMAA**
logDPu logDAm
Aqueous
acidity
alcohol*–alcohol**
logDPu logDAm
DMAA*–DMAA**
logDPu logDAm
Pu, % Am, %
/
/
/
Pu, % Am, %
Pu, % Am, %
pH 8.5
81.2
84.0
85.4
72.6
22.0
<2
79.9
65.5
39.2
40.4
8.5
1.0
1.2
1.6
1.8
1.4
–
–
–
–
–
–
–
85.5
81.2
81.4
77.4
81.0
73.3
53.5
54.0
40.5
11.1
2.2
1.4
1.3
1.5
2.5
8.3
pH 3.0
pH 2.0
90.8 47.9
70.7 30.9
57.9 28.5
1.6
1.5
1.4
6.3
pH 1.0
0.5 M HNO3
1 M HNO3
<2
50.4
2.0
<2
>10
Notes: * The solvent for conditioning the sorbent.
** The solvent for applying the reagent.
for both elements; for americium, this drop is in a genꢀ nium(IV) from neutral and weakly acidic solutions is
eral case far stronger, providing for good separation of not interfered with hydrolysis; not only hydrolysis
the two elements in solutions where nitric acid conꢀ would give rise to hydroxo complexes, but it would also
centrations are 0.5–1 mol/L.
cause irreversible transformations of these complexes
to polymeric compounds [25]. For americium(III)
ions, hydrolysis starts only at pH 4.5 [26]. As the nitric
acid concentration increases, nitrate complexes with
−
The separation factor of two elements in the sysꢀ
tems under consideration should primarily depend on
the ratio of the stability constants of the complexes in
which elements are recovered upon liquid–liquid or
solidꢀphase extraction. Indeed, these constants
strongly differ for plutonium(IV) and americium(III)
with hydroxamic acids, specifically with BPHA and its
derivatives. Plutonium in aqueous solutions forms,
with BPHA, coordinatively saturated complexes of
composition PuR4 with the overall stability constant of
the progressively increasing number of
ions are
NO3,
formed consecutively; in the case of plutonium, this
leads to the appearance of a hexanitrate complex [27].
Let us consider how substituents in a BPHA moleꢀ
cule affect the recovery and separation of plutoꢀ
nium(IV) and americium(III) in acid solutions. Table 4
displays data on the recovery the ratios of logarithms of
distribution coefficients of the two elements obtained
under identical conditions. From this data, it follows
that the introduction of substituents is justified in
terms of increasing separation factors in going from
BPHA to its derivatives. In the acidity range from 0.1
to 1 M HNO3, there are conditions (with acidity
slightly differentiated for different substituents) under
2
×
1041 [24, p. 219].
As regards americium, the only we could find in the
literature was the stability constant for the ameriꢀ
cium(III) complex with caprinohydroxamic acid,
equal to
composition AmR3
2 ×
1027 [24, p. 162]. This complex has the
·
2H2R2; this is due to the fact that
tervalent transplutonium elements and rareꢀearth eleꢀ
ments (having similar properties), because of their
high coordination numbers, form coordinatively
unsaturated complexes of composition MeR3, where
the coordination sphere is supplemented with water
molecules, or, when ligands are in excess, MeR3HR2
complexes. This does not change fundamentally anyꢀ
thing in our argumentation; but we may assume that
the hydrophobicities (distribution constants) of extractꢀ
able americium(III) complexes are due to five ligands.
There are data on the stability of rareꢀearth complexes
with BPHA [24, p. 128]. For europium(III), which is
the closest to americium(III) in its properties, the staꢀ
bility constant is known for the complex EuR3, equal
which logDPu/logDAm
≥
6 for the reagents CH3ꢀR,
PhꢀR, and FꢀR, whereas for BPHA itself, the maximal
ratio is 2.8 for extraction from 0.5 M HNO3.
The assumption on the different effects of the
nature of substituents in the reagent molecule on sepꢀ
aration of elements with different acidities is verified
by the data displayed in Fig. 2. For extraction from
acid solutions (1 M HNO3), the separation factors
increase in going from BPHA to its derivatives, and
they change in correlation with the change in elecꢀ
tronegativity substituent parameter σp. For extraction
to 1018
Due to the very high stability of complexes with
.
D1
from solutions with high pH (8.5),
or
K
K
D2
practically does not change in going
l o g KD l o g KD
1
2
BPHA and its analogues, the recovery of plutoꢀ from one substituent in the reagent molecule to
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 11 2011

1844
PETRUKHIN et al.
Table 4. Plutonium and americium percent recovery and the ratio of logarithms of their distribution coefficients with the use of
the BPHA (R) reagent and its derivatives. The solvent for conditioning the sorbent is ethanol; the solvent for applying the reagent
is DMAA. The applied reagent concentration: 4 × 10–2 mol/L
Aqueous acidity
pH 2
pH 1
0.5 M HNO3
1 M HNO3
logDPu /
Agent
logDPu
/
logDPu
/
logDPu
/
Pu, % Am, %
Pu, % Am, %
Pu, % Am, %
Pu, % Am, %
logDAm
logDAm
logDAm
logDAm
CH3ꢀR
PhꢀR
FꢀR
90.8
93.0
84.9
86.5
47.9
18.0
21.1
39.1
1.6
1.8
2.0
1.6
70.7
86.0
82.4
65.2
30.9
11.5
3.2
1.5
2.3
6.6
2.2
57.9
86.0
77.5
67.6
28.5
6.0
3.2
5.0
1.4
4.6
6.0
2.8
50.4
65.0
63.8
30.4
2.0
10.2
6.0
6.3
2.4
3.0
1.4
R
12.6
7.0
another; accordingly, there is no any correlation with tioning the solid phase before the extractant is applied.
either σp or πar. This is what follows from expression (5),
which suggests that the separation of two elements in
the form of complexes with close numbers of ligands
should not be affected by the replacement of substituꢀ
ents.
Table 3 and Figs. 3 and 4 make it clear that there are
some cases where the nature of these solvents considꢀ
erably affects the recovery and separation of elements;
a possible explanation is as follows. The sorbate phase
is formed on the surface of alkylated silica gel. The key
role in the formation of this phase is played by the
alkylated surface; the specifics of this nanometer surꢀ
face consist in that the grafted layer thickness depends
To conclude this section, we will note that the
changing concentration of the reagent supported on
alkylated silica gel in an appropriate organic solvent
should certainly affect the degree of recovery but not
separation factors, which follows from Eqs. (3)–(5)
where the reagent concentration is absent. We have
shown experimentally that variations in reagent conꢀ
centration from 10–4 to 10–2 mol/L do not noticeably
1
2
3
5.0
change Кs
.
4
5
The above arguments and their experimental verifiꢀ
cation should also hold for conventional (liquid–liqꢀ
uid) systems. However, one distinction of SPE consists
of the need to use organic solvents not only at the step
of applying the reagent but also at the step of condiꢀ
6
4.0
3.0
2.0
1.5
1.0
0.5
3.0
2
2.0
1
1.0
8.5
3
2
1
0.5
сHNO , mol/L
1.0
pH
0.5
3
PhꢀR
FꢀR
ClꢀR NO2ꢀR
R
Fig. 3. Ratio of logarithms of plutonium(IV) and ameriꢀ
cium(III) distribution coefficients upon SPE on S16 modiꢀ
Fig. 2. Ratio of logarithms of plutonium(IV) and ameriꢀ
cium(III) distribution coefficients in SPE on S16 modified
with BPHA and its derivatives in extraction from an aqueꢀ
fied with BPHA (R) and with its derivatives: (
) *PhꢀR, ( ) CH ꢀR, ( ) ClꢀR, and ( ) NO ꢀR versus
aqueous acidity. The solvent applying for the reagent is ethaꢀ
1) R, (2) FꢀR,
(3
4
5
6
3
2
–2
ous solution with (
1
) pH 8.5 and (
2
) 1 M HNO .
nol (*DMAA). The reagent concentration:
4 × 10 mol/L.
3
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 11 2011

SOLIDꢀPHASE EXTRACTION OF PLUTONIUM(IV)
1845
apparently be selected so that their introduction to
increase, as greatly as possible, the difference between
the stability constants of the complexes of the metals
to be separated.
Not only does a change in the substituent hydroꢀ
phobicity noticeably increase separation factors, but
certainly it should also change the distribution conꢀ
stants. Therefore, search for reagents with more
hydrophobic substituents is of interest primarily in the
context of increasing recovery of elements from soluꢀ
tions. These inferences may also appear of interest for
selecting extractants in conventional liquid–liquid
extraction, which has much in common with solidꢀ
phase extraction.
7
6
5
4
3
2
1
1
2
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 11 2011