Lithium, rubidium and cesium ion
removal using potassium iron(III)
hexacyanoferrate(II) supported on
polymethylmethacrylate
Journal of Radioanalytical
and Nuclear Chemistry
An International Journal
Dealing with All Aspects
and Applications of Nuclear
Chemistry
ISSN 0236-5731
Volume 288
Number 1
J Radioanal Nucl Chem (2011)
288:79-88
DOI 10.1007/
s10967-010-0873-1
1 23
Your article is protected by copyright and
all rights are held exclusively by Akadémiai
Kiadó, Budapest, Hungary. This e-offprint is
for personal use only and shall not be selfarchived in electronic repositories. If you
wish to self-archive your work, please use the
accepted author’s version for posting to your
own website or your institution’s repository.
You may further deposit the accepted author’s
version on a funder’s repository at a funder’s
request, provided it is not made publicly
available until 12 months after publication.
1 23
Author's personal copy
J Radioanal Nucl Chem (2011) 288:79–88
DOI 10.1007/s10967-010-0873-1
Lithium, rubidium and cesium ion removal using potassium
iron(III) hexacyanoferrate(II) supported
on polymethylmethacrylate
Shabana Taj • Din Muhammad •
M. Ashraf Chaudhry • Muhammad Mazhar
Received: 27 September 2010 / Published online: 26 October 2010
Ó Akadémiai Kiadó, Budapest, Hungary 2010
Abstract Potassium iron(III) hexacyanoferrate(II) supported on poly methyl methacrylate, has been developed
and investigated for the removal of lithium, rubidium and
cesium ions. The material is capable of sorbing maximum
quantities of these ions from 5.0, 2.5 and 4.5 M HNO3
solutions respectively. Sorption studies, conducted individually for each metal ion, under optimized conditions,
demonstrated that it was predominantly physisorption in
the case of lithium ion while shifting to chemisorption with
increasing ionic size. Distribution coefficient (Kd) values
followed the order Cs? [ Rb? [ Li? at low concentrations of metal ions. Following these findings Cs? can
preferably be removed from 1.5 to 5 M HNO3 nuclear
waste solutions.
Keywords Lithium ion Rubidium ion Cesium ion Sorption Supported hexacyanoferrate
Introduction
Industrial developments in domestic, defense and energy
sectors employing chemical and nuclear processes, more
often, lead to subsequent environmental problems. Use of
lithium may be cited as one of such area due to its frequent
application in atomic power, alloy making, hydrogen
S. Taj D. Muhammad M. A. Chaudhry
Department of Chemistry, Quaid-I-Azam University,
Islamabad 45320, Pakistan
M. Mazhar (&)
Department of chemistry, Faculty of Science,
University of Malaya, 50603 Kuala Lumpur, Malaysia
e-mail: [email protected]
storage, heat-resistant ceramic technologies, pharmaceutical industry and power sources including the storage batteries. This demonstrated its importance and envisaged
environmental induction leading to deterioration of the
latter. Wastes thus generated presented a serious threat to
health issues highlighting an element of essentiality for
remedial measures accompanied by its recovery [1–3].
With the present energy production scenario using fossil
fuels, adaptation of nuclear power production looks inevitable as an essential and viable alternate. Thus the future
may result in the production of more than 40 radioactive
nuclei by-products including Rb86, 87 and Cs134,137. Such
radioactive contaminants with high transport abilities are
expected to find their way to water bodies and soils and
finally may end up in plant materials, incorporation into
food chain and ultimately becoming a part of the animals
and human beings [4–9].
Separation of such radioactive metal ions from the
nuclear effluents and thus environmental remedial mitigation may be followed by direct solvent extraction and ion
exchange techniques or indirect application of membranes
and emulsion liquid membranes [10]. Similarly composite
and supported materials, which help to increase the effective surface area could be employed to improve sorption
and ion exchange leading to meaningful separations.
Therefore certain oxides, silica gels and polyacrylonitrile supported materials have been successfully used for
removal of such radio nuclides [11–25]. Insoluble Prussian
blue (PB) Fe4[Fe(CN)6]3xH2O, has been reported as an
excellent scavenger for radioactive cesium and applied for
its removal from gastrointestinal tract of animals by oral
applications [26].
Polymethylmethacrylate (PMMA) supported iron(III)
hexacyanoferrate(II) has been synthesized and reported for
removal of Sr2? [27] and its possible application for the
123
Author's personal copy
80
separation of alkali metal ions from acidic industrial and
nuclear wastes.
In the present study, removal of Li, Rb and Cs metal
ions using PMMA supported potassium iron(III) hexacyanoferrate(II) has been presented. The results suggest
application of the system for removal of Li?, Rb? and Cs?
from the waste solutions.
Experimental
Synthesis of material and characterization
PMMA supported potassium iron(III) hexacyanoferrate(II)
was synthesized and characterized for its solubility measurement in water and mineral acids, FTIR, XRD, EDX
spectral analysis and SEM scans conducted following the
earlier reported instrumental procedures [27]. Similarly
surface area measurement methods leading to total pore
volume, micro pore volume, BET and Langmuir surface
area were followed as reported earlier [27].
The synthesized material consisting of hydrated potassium iron(III) hexacyanoferrate(II) and iron(III) hexacyanoferrate(II) was further subjected to thermo gravimetric
analysis (TGA) under nitrogen, along with PMMA using
Perkin-Elmer thermo gravimetric analyser TGA-7 and
following heating rates of 20 °C min-1
The metallic contents of the material were also determined following atomic absorption spectrometric (AAS)
and inductively coupled plasma atomic emission spectrometric (ICP-AES) techniques after proper destruction of
the organic matter.
Metal ion sorption, equipment, conditions
and procedures
All the optimization studies were conducted by batch
method using polyethylene bottles. However for some
parameters column technique was also followed. Separation columns were prepared using 30 cm long doublejacketed Pyrex tubing of internal diameter 1.0 cm, having
sintered glass disc at one end with an appropriate amount
of the material loaded on it as reported earlier [27].
Optimization and separation procedures
(a) Aqueous solutions of HNO3 (0.5–5 M) were used to
find out the optimum acid concentration for the maximum
sorption of metal ions. 0.5 g of the ion exchange material
was equilibrated in polyethylene bottles with 10 cm3 of the
HNO3 solution for 24 h in each particular acid concentration. After sufficient contact time the acid was filtered off
and the resin was further equilibrated for 24 h separately
123
S. Taj et al.
with 100 cm3 solution of 100 mg dm-3 of Li?and 200 cm3
solution of 200 mg dm-3 in each case of the Rb? and Cs?
in the appropriate optimized HNO3 concentration. The
mixtures were further filtered and metal ion concentration,
in each case, was determined in the filtrate by atomic
absorption spectrometry. Amount of metal ion sorbed was
estimated, by the difference of the initial and final concentrations. Optimized concentrations of the HNO3 solutions for the maximum sorption of Li?, Rb? and Cs? were
determined.
(b) For study of the effect of other parameters such as
the particle size of the sorbent, soaking time and contact
time on uptake, in each metal ion case, the procedures
followed were the same as reported for Sr(II) [27].
Similarly the experimental details of the methods followed for the determination of sorption capacity, extent of
ion exchange and sorption temperature relationship were
on the similar lines [27].
Results and discussion
Synthesis and characterization of the PMMA supported
potassium iron(III) hexacyanoferrate(II) as reported [27]
confirmed that the material was deposited on the polymeric
support, due to the electrostatic interactions operative
between the reactants and the polar sites of the polymeric
chain and possessed ion exchange properties along with
adsorption behavior.
The three different fractions of the materials, as
described in proceeding section, tested for the solubility in
aqueous nitric acid solutions of different concentrations,
have shown that material with larger particle size was
relatively more stable over a wider range of nitric acid
concentrations as compared to the finest fraction which was
stable only in a narrow range. Thus stability ranges were
1.0–5.0 M, 1.5–5.0 M and 1.5–4.0 M HNO3 for 30–50 (a),
50–115 (b) and [115 (c) mesh sizes respectively.
The material was subjected to XRD and EDX analysis and the data confirmed presence of a mixture
of stoichiometric polycrystalline insoluble Prussian blue
Fe4[Fe(CN)6]3xH2O and non-stoichiometric KFe3.5C12.25
N10.56O5.18. Further the analysis data of AAS and ICPAES confirmed the general stoichiometry of the material
with reference to the elements which could be determined using these techniques.
Scanning electron micrographs of fractions a, b and c
(Fig. 1a–c) depicted that the materials consisted of the
particles, formed by irregular deposition of the potassium
iron(III) hexacyanoferrate(II) on the support. The particle
sizes calculated from SEM pictures range from 0.62–10.26,
0.55–5.77 and 0.3–3.33 lm for a, b and c respectively. The
non-stoichiometric material KFe3.5C12.25N10.56 O5.18, may
Author's personal copy
Lithium, rubidium and cesium ion removal using potassium iron(III) hexacyanoferrate(II)
81
Fig. 1 a Scanning electron
micrograph of PMMA
supported potassium iron(III)
hexacyanoferrate(II) at
10.0 kV 9 42 (particle size
0.62–10.263 lm). b Scanning
electron micrograph of PMMA
supported potassium iron(III)
hexacyanoferrate(II) at
10.0 kV 9 52(particle size
0.55–5.77 lm) c. Scanning
electron micrograph of PMMA
supported potassium iron(III)
hexacyanoferrate(II) at
10 kV 9 50(particle size
0.3–3.33 lm)
Sorption of M + mol g-1 × 10-4
30
110
Cs+
24
+
Li
+
Rb 105
21
+
Cs
27
Li
+
100
18
15
95
12
9
+
90
Rb
6
3
85
0
-3
0
1
2
3
4
5
6
7
8
Sorption of Cs+ mol g-1 × 10-4
be responsible for presence of some irregular defects in the
packing and influencing changes in the sorption properties.
Reduction in the particle size may increase the surface
area, total pore volume and micro pore volume of the
sorbent thus resulting into an enhancement of the sorption
properties of the sorbent. The metal ions sorption data
presented in Fig. 2 depicted that the most active fraction of
the material was ‘b’ with average particle size in the
0.55–5.77 lm range possessing 3.37 mm3 g-1 micro pore
volume. The maximum sorption capacity of the material
with intermediate size may be attributed primarily to the
increase of surface area followed by a size compatibility
factor leading to an overall decrease with further increase
of the pore volume. This aspect may need a separate
treatment. However further studies were carried out using
the fraction ‘b’.
The selected material size and blank PMMA were subjected to TGA and the thermograms taken are depicted in
Fig. 3a, b. It is evident from these thermograms that
maximum weight loss of the PMMA commenced at 311 °C
and completed at 439 °C with maximum weight loss at
348 °C, whereas thermogram of the PMMA supported ion
exchange material has shown that a slow weight loss
starting at about 21 °C proceeding to a 12.25% weight loss
up to 300 °C. This could be due to loss of the water
80
Micro pore volume mm3 g-1
Fig. 2 Sorption dependence of metal ions versus micropore volume
molecules present in the sample as adhered moisture and
water of crystallization [27, 28]. A steep change in weight
showing maximum weight loss of 56.07% started at 300 °C
with average decomposition temperature of 332.4 °C. Thus
a minimum of 43.93% residual weight was observed. It is
evident that decomposition of PMMA present as a support
in the ion exchange material has taken place on the same
pattern as pure PMMA. However slight change in the
decomposition temperature and position of the curve may
be attributed to a difference in the heating rates of the two
123
Author's personal copy
82
S. Taj et al.
(a)
Residual weight %
60
Li
64.105%(332.36°C)
43.93%(352.32°C)
ST100
42.97%(347.16°C)
20
PMMA
0
-0.85%
-20
100
200
300
400
600
Air
N2
100
weight %
80
N2
Residue
Air = 40.0745%
Nitrogen = 40.8639%
40
20
400
600
800
1000
1200
Temperature°C
Fig. 3 a Thermograms for PMMA and PMMA supported potassium
iron(III) hexacyanoferrate(II) showing change in weight (wt%) with
respect to the change in temperature (heating rate 20 °C min-1).
b Thermograms for PMMA supported potassium iron(III) hexacyanoferrate(II) showing change in weight (wt%) with respect to the
change in temperature in air and nitrogen atmosphere (heating rate
20 °C min-1)
samples [29, 30]. As no further weight loss was observed
the 43.93% residual weight could be due to the stable
inorganic component of the synthesized material, a combination of non-stoichiometric KFe3.5C12.25N10.56O5.18 and
stoichiometric entity of the polycrystalline Fe4[Fe(CN)6]3
xH2O [27]. The 43.93% residual mass indicated that
&0.44 g g-1 of the material could be part of the active
component capable of ion exchange and sorption behavior
limited to a few lm depth only.
The data on uptake of metal ions by PMMA supported
iron(III) hexacyanoferrate(II) for different HNO3 concentrations has been given in Fig. 4. Optimum acid concentrations for maximum sorption values showing 12.87 9
10-5 mol g-1 for Li?, 53.5 9 10-5 mol g-1 for Rb?
and 55.07 9 10-5 mol g-1 of Cs? were recorded at 5.0,
2.5 and 4.5 M HNO3 respectively. Increase in HNO3
123
40
30
+
Rb
20
Li
0
Air
200
+
Cs
+
Cs
+
700
(b)120
0
Rb
50
10
500
Temperature°C
60
+
+
Sorption of Li+ mol g-1 × 10-5
88.42% 89.68%
80
40
60
91.23% 96.62%(286.7°C)
87.75%
100
0
1
2
3
4
5
6
[HNO3]
Fig. 4 Metal ion sorption versus molar concentration of acids
concentration recorded a gradual increase in the Li?
uptake, while Rb? sorption increased sharply to a maximum value at 2.5 M and then decreased with further
increase in the acid concentration. While in case of Cs?
increase of HNO3 concentration resulted in gradual
enhancement of the Cs? sorption to a maximum in the
3.0–4.5 M range and then a decrease with further increase
of acid concentration.
Soaking of material in the acidic solution converts it into
protonated form. Figure 5 shows that in case of Li? and
Cs? protonation occurred in 1.0 h which may be due to the
higher concentrations (5.0 and 4.5 M respectively) of the
nitric acid solutions employed. The optimum soaking time
determined for maximum sorption of Rb? was 24 h using
2.5 M HNO3 solution. Sorption of Li? in this case
decreased from 211 9 10-5 to 0.115 9 10-5 mol g-1
beyond 1 h soaking. The anomalous trend in the Li?
sorption with the increase of the soaking time of the
material may be due to increased protonated form of sorbent sites. Due to possession of closer charge densities H?
ion may be successfully competing with Li? ion sorption
rate and this may further suggest relatively more mobility
of the (H?) as compared to Li?. Thus the sorbent having its
all sites occupied by H? may have been incapable to accept
Li?.
Impact of the equilibration time on sorption was
observed under optimized conditions of acid concentration
and soaking time. It has been shown in Fig. 6 that maximum sorption of Li? was attained within 30 min which
remained more or less constant with the further increase of
equilibration time. A slow increase in uptake of Rb? and
Cs? was observed up to 24 h with the passage of time,
which may suggest diffusive penetration of the ions into
the core of the sorbent particles.
Author's personal copy
Lithium, rubidium and cesium ion removal using potassium iron(III) hexacyanoferrate(II)
+
Cs
200
100
+
Cs
50
+
0
-50
100
+
150
-5
+
Rb
+
Li
120
-1
250
+
Sorption of M ions molg ×10
Li
-1
Sorption of metal ion mol g ×10
-5
300
Rb
83
Li
80
+
Rb
60
40
Cs+
20
0
0
0
5
10
15
20
+
Li
+
Rb
+
Cs
+
200
400
600
800
1000
+
25
Initial Conc. of M ions mg dm-3
Soaking Time(hours)
Fig. 7 Metal ion Sorption in mol g-1 versus initial concentration of
metal ion
250
+
Li
-1
Sorption of metal ion mol g × 10-5
Fig. 5 Metal ions sorption versus soaking time
+
Li
+
200
Rb
+
Cs
150
100
50
+
Cs
+
Rb
0
0
5
10
15
20
25
Contact Time (hours)
Fig. 6 Sorption of metal ions versus contact time of ion exchanger
and metal ion solution
Metal ion concentration dependent sorption results shown
in Fig. 7 indicated a regular increase in the Li? sorption
which increased significantly at higher initially applied
concentration showing up to 113.44 9 10-5 mol g-1
uptake. A regular increase in the sorption of Rb? and Cs?
was also observed with increase in the initial concentration
of the respective metal ion. Amounts of Rb? and Cs?
extracted from the maximum initial concentration were
54.28 9 10-5 and 13.02 9 10-5 mol g-1 respectively.
Sorption increased with the increase of the concentration in
each ion case. However as evident from the data of Fig. 7 this
increase has been indirectly related to the ionic size of the
ions.
Distribution coefficient (Kd) values for each metal ion at
each applied concentration used in the dynamic mode were
calculated employing the following Eq. 1:
Ci
Kd ¼
1 V=M
ð1Þ
Cf
where Ci is the initial concentration of the metal ion in
solution, Cf the final concentration of the metal ion in
solution, V the volume of the solution and M is the mass of
the ion exchanger in gram.
Distribution coefficient (Kd) versus initial concentration
plots, shown in Fig. 8, indicated that distribution coefficient
values at the onset of the process were the lowest in the case
of Li? ion and intermediate for the Rb? while maximum
distribution occurred in case of the Cs?. Further the Kd
values recorded a slow but gradual increase in case of Li?
with the increase in the initial applied concentration. However a change in the Kd values for Rb? has shown initially a
sharp decrease and then a gradual decrease with the increase
in the initially applied concentration of Rb?. Similarly a
sharp decrease in the distribution coefficient with the
increase in the applied concentration of the Cs? indicated
attainment of maximum distribution of the Cs? between the
solid sorbent and the solution at this stage. By the comparison of the distribution coefficient values for all the three
metal ions at similar initial concentrations it was determined
that Kd values were the minimum for Li?, intermediate for
Rb? and maximum for Cs? showing the greatest affinity of
the material for Cs?. This may be related to the ionic volume
of these ions as pointed in proceeding paragraphs.
Decontamination factor (Df), a ratio of the initially
applied metal ion concentration to its concentration after
the completion of the equilibration process, was calculated
using the following Eq. 2:
Df ¼
Ci
Cf
ð2Þ
Decontamination factor (Df) as shown in Fig. 9 was initially low for Li? at lower concentration and increased
when initially applied ion concentration was raised. Rb?
and Cs? have been decontaminated to a greater extent at
low initially applied concentrations, while decontamination
123
Author's personal copy
84
S. Taj et al.
10
8
6
4
2
+
Rb
+
Li
0
0
200
400
600
800
+
1000
-3
Initial Conc. of M ions mg dm
Fig. 8 Distribution coefficient (Kd) versus initial concentration of
metal ion
factor decreased at high concentrations for both these metal
ions. It was observed that the Df values were maximum
(Df = 25) in the case of Cs?, lower for Rb? (Df = 2.5) at
low initial concentrations of 25 mg dm-3 and the lowest
(Df = 1.27) for Li? at the same initial concentration
which, however, increased up to 4.7 at the concentration
level of 500 mg dm-3 of Li?. It can be inferred from these
observations, that sorbent was capable of extracting Li?
from the concentrated solutions while it can be applied
more successfully for low concentrations of the Rb? and
Cs? solutions.
Percent removal (%R) of the metal ions was calculated
using Eq. 3:
%R ¼
Ci Cf
100
Ci
ð3Þ
Decontamination Factor (Df )
A plot of percent removal (%R) of metal ion versus
initial applied concentration of metal ions, shown in
Cs
25
Fig. 10, indicated that 21% of the Li? has been removed
when initially applied concentration was low, but there was
an increase in the percentage removal up to &79% of the
Li? with the increase in initial concentration of the metal
ion. Rb? and Cs? were removed up to 60% and 96%
respectively at 25 mg dm-3 solution concentration level
which decreased at higher concentrations of the metal ions
contrary to that of Li?.
Sorption capacity of the material for these metal ions,
determined by the batch method until no further sorption of
a metal ion was taking place, was found to be 2.69 9 10-3
mol g-1 for Li? ion from 5.0 M HNO3. The sorption
capacity values were 1.66 9 10-4 mol g-1 from 2.5 M
HNO3 and 4.89 9 10-4 mol g-1 from 4.5 M HNO3 for
Rb? and Cs? respectively. Distribution coefficient (Kd)
values calculated using data presented in the preceding
section are 22.11, 16.05 and 141.44 cm3 g-1 for Li?, Rb?
and Cs? ions respectively showing the maximum distribution of Cs? on the PMMA supported potassium iron(III)
hexacyanoferrate(II).
Nature of the sorption process was investigated by
applying Langmuir sorption model represented by Eq. 4 to
the sorption data obtained at different concentrations of the
metal ions in the dynamic mode.
KQmax Ceq
1 þ KCeq
Ceq
1
1
¼
Ceq þ
Qmax
KQmax
Qeq
Qeq ¼
+
+
Li
+
20
15
10
+
Li
5 Rb+
ð5Þ
100
Li
Rb
+
Cs
ð4Þ
where Ceq is the equilibrium concentration in liquid phase
(mol dm-3), Qeq the sorbed concentration (mol g-1) in
solid phase at equilibrium, Qmax the maximum amount
taken up (mol g-1) and K is the Langmuir adsorption
constant.
% Removal of metal ions
Kd × 102cm3 g-1of M+ ions
+
Li
+
Rb
+
Cs
+
Cs
12
90
Li
80
+
+
Rb
Cs
+
+
70
60
50
40
Rb
Cs
+
+
30
20
0
0
200
400
600
800
Initial Conc. of metal ions mgdm
1000
-3
Fig. 9 Decontamination factor (Df) versus initial concentration of
metal ion
123
10
0
200
400
600
800
1000
-3
Initial Conc. metal ion mg dm
Fig. 10 % Removal of M? ions versus initial concentration of the
metal ion
Author's personal copy
Lithium, rubidium and cesium ion removal using potassium iron(III) hexacyanoferrate(II)
Langmuir mode of adsorption in general is followed by
the systems operating through chemisorption involving
the bond dissociation and bond formation. Energy involved
in the chemisorption process is higher than that of the
physical adsorption. Following Eq. 4 a plot of the ratio
(Ceq/Qeq) versus Ceq in a system following Langmuir
adsorption should appear as a linear relationship having
slope 1/Qmax and intercept 1/KQmax.
Application of the Langmuir model to Li?, Rb? and Cs?
sorption systems has been shown in Fig. 11. Using the data
of slope and intercept of plots representing Li?, Rb? and
Cs?, the Qmax and K (constant) values calculated in each
case are given in Table 1.
A successful application of Langmuir model as indicated by the value of K may suggest that, the adsorption
phenomenon operating at the surface of the adsorbent
following the trend Cs? [ Rb? [ Li? could be characterized as physisorption followed by chemisorption.
Extent of the ion exchange process between univalent metal ion (M?) and non-stoichiometric sorbent
(KFe3.5C12.25N10.56O5.18) was determined by treatment of
solution of fixed volumes of known concentration of a
metal ion with different amounts of adsorbent in a similar
fashion as reported [27]. From the amount of the M?1
retained on the material and concentration of the K?1
35
+
Cs
180
30
150
25
+
Cs
y = 6617x+3.94
120
Li
+
20
y = 1125x+52.9
90
+
Li
60
15
10
+
30
Rb
+
Ceq/Qeq gdm-3 (Cs+)
Ceq/Qeq gdm-3 (Rb+and Li+)
210
85
eluted into the solution a relationship has been established
for the ion exchange process, considering the ion exchange
mechanism given as under:
Mþ þ KFe FeðCNÞ6 ! MFe FeðCNÞ6 þ Kþ
ðAÞ
þ
þ
M þ nKFe FeðCNÞ6 ! M Fe FeðCNÞ6 n þnK
ðBÞ
Supposing Fe[Fe(CN)6] as X
Keq ¼
½MX½Kþ n
½Mþ ½KXn
ð6Þ
Keq ¼
D½K þ n
½KXn
ð7Þ
where D represents the distribution coefficient.Now taking
K = 1 since KX is a solid specie its concentration is not
effecting the equilibrium reaction, the Eq. 7 can be written
as:
Keq ¼ D½Kþ n
D¼
ð8Þ
Keq
½Kþ n
ð9Þ
log D ¼ log Keq n log ½Kþ ð10Þ
The chemical reaction (B) indicates that there should be
an equimolar exchange reaction between M? and K? ions
during the ion exchange process. Equation 10 is a
mathematical representation of the ion exchange process
in which value of slope ‘n’ corresponds to the number of
moles of the K? involved in the exchange process.
Data regarding plot of log D versus log [K?] for Li?,
Rb? and Cs? have been depicted in Fig. 12. Information
extracted from these plots for the slope in each case has
been given in Table 2, which suggests a preferable
exchange of the adsorbate ionic species with K?. The
relationship of the extent of the ion exchange process to
5
Rb
y = 1069x+5.99
0
0
0
50
100
150
200
250
300
+
−4
-3
2.6
Ceqmol dm × 10
Fig. 11 Ceq/Qeq versus equilibrium concentration (Ceq) of metal ion
in solution
Cs
Li+
+
y = 0.758x + 2.42 → Cs
2
R = 0.996
Rb+
Cs+
2.4
Table 1 Maximum sorption and Langmuir constant data obtained
from slope and intercept values of Langmuir plots for lithium,
rubidium, cesium and strontium ions
Metal ion (M?)
Qmax (mol g-1)
K (dm3 g-1)
Li?
8.89 9 10–
4
21.3
Rb?
9.35 9 10–
4
1.785 9 102
Cs?
Sr2?
1.51 9 10–
2.89 9 10–
4
1.682 9 103
4.56 9 102a
logD
2.2
+
Li
+
y = 0.179x + 2.42 → Li
2
R = 0.839
2.0
1.8
+
a
Data from [27]
4
y = 0.487x + 3.12 → Rb
2
R = 0.99
+
1.6
-3.4
Rb
-3.2
-3.0
-2.8
-2.6
-2.4
-2.2
-2.0
+
log[K ]
Fig. 12 Log D of the M? ion versus log [K?]
123
Author's personal copy
86
S. Taj et al.
Table 2 Slope values data obtained from the ion exchange studies of the for lithium, rubidium, cesium and Strontium ions on PMMA supported
potassium iron(III) hexacyanoferrate(II)
Crystal ionic Slope Expected
% Ion
Reason
Metal
slope value exchange
ion (M?) radii (pm)
Li?
65
0.179 1
17.9
Small sized Li? with high charge density is acting as hard acid has least capability
of binding with large sized soft base of the anion
Rb?
148
0.487 1
48.7
Rb? with intermediate ionic size with the same charge, have medium charge density
and capable of exchange to the greater extent than that of Li?
Cs?
169
0.754 1
75.4
Cs? being the largest of the alkali metal ions with same charge possessing low
charge density is the softest acid capable of ionic binding with large sized small
charge anion of the exchanger.
Sr2?
115
0.6a
30
Sr2? a divalent ion with its size falling between that of the Li? and Rb? ions. The
percentage ion exchange mechanism operative in its sorption is 30% which lies
between those of the Li? and Rb? percentage
Data from [27]
Li +
Rb+ 6.5
Cs+ 6.4
40
38
36
6.3
Li+
34
6.2
32
6.1
30
6.0
28
Rb+
24
290
5.9
+
Cs
26
300
310
320
330
340
+
123
6.6
42
Cs Sorption mol g-1×10-5
that of the ionic radii [31] of the hydrated ions as evident
from data of Table 2 suggested it as one of the operative
parameters. It may be elucidated from the data, given here
that, the anion of the ion exchanger, being larger in size
and possessing low charge density, could be considered as
‘soft base’. The metal ion present in the hydrated form if
arranged in order of the increasing ionic size are
Li? \ Sr2? \ Rb? \ Cs? appeared to be capable of ion
exchange in the same order. This indicated that increasing
size of these ions with similar charges would reduce charge
to size ratio and enhancement of the ‘soft acid’ behavior
going from Li? to Cs?. This indicated that increasing
extent of the ion exchange process might be explained on
the bases of soft and hard acid base concept. Li? being the
hardest of all is showing the least capability of ion
exchange, while the softest of all Cs? was appearing as the
most favorite for the exchange with K? ions of the
material.
However taking data of Table 2 into further consideration the process seemed to be very complicated in view
of the fact that the base material has already been protonated. The sites available for adsorption plus exchange
process would certainly compete depending upon the
ionic size and availability even if having the same charge.
This particular aspect may need further in depth study to
resolve the issue.
Temperature dependent sorption studies were conducted
at different temperatures ranging from 298 to 343 K
(25–70 °C). Sorption versus temperature data have been
shown in Fig. 13. It indicated a gradual decrease in the
sorption occurring with the increase of the temperature in
all the three cases of metal ion separation under specified
experimental conditions.
The enthalpy change associated with adsorption was
determined by subjecting sorption and temperature data to
Eq. 11
Sorption of Li+and Rb+mol g-1×10-5
a
2
5.8
5.7
350
Temperature (K)
Fig. 13 Sorption of metal ion versus temperature
ln C ¼
DHad
þ constant
RT
ð11Þ
where C is the concentration (mol dm-3), Had the heat of
adsorption, R the universal gas constant, and T is the
temperature in Kelvin.The plots of the natural logarithm of
the sorbed molar concentration (ln C) at any particular
temperature versus 1/T shown in Fig. 14, were straight
lines for Li?, Rb? and Cs? with slope = DHad/R giving an
enthalpy change (DHad) & 1.3 9 10-1, 3.91 9 10-1 and
8.97 9 10-2 kJ mol-1 respectively. The calculated
slightly positive values of the enthalpy change may indicate a contribution of the chemisorption processes as well
with overall sorption process of Li?, Rb? and Cs? of
physical nature besides the ion exchange processes, all
operating at different levels depending upon the nature of
both the adsorbent and the adsorbate materials. The difference of the DHad values of the sorption process of Li?,
Rb? and Cs? was supported by extent of the ion exchange
process which has been already discussed. For Rb? ion
exchange the chemical process was taking place to a lesser
Author's personal copy
Lithium, rubidium and cesium ion removal using potassium iron(III) hexacyanoferrate(II)
extent as compared to that of Cs? ion. Cs? being the softest
specie having low charge density and capable of interacting
chemically with large sized (KFe3.5C12.25N10.56O5.2) unit,
which by releasing K?, may bear a single negative charge
on the complex ion behaving as a soft base. This may
be explained with respect to the nature of the material
being a mixture of non-stoichiometric potassium iron(III)
hexacyanoferrate(II) possessing (KFe3.5C12.25N10.56O5.2)
and stoichiometric polycrystalline iron(III) hexacyanoferrate(II), Fe4[Fe(CN)6]3xH2O. The non-stoichiometric
component, KFe3.5C12.25N10.56O5.2 of the supported ion
exchanger has the site for the ion exchange. The polycrystalline Prussian blue Fe4[Fe(CN)6]3xH2O possess
water molecules and K? ions intercalated in the structure
[28], which may provide spaces to scavenge the Cs? ion
suggesting that physical adsorption and diffusion may also
be the processes taking place along with the chemisorption.
In Table 3 DHad values for Li?, Rb?, Cs? and Sr2? are
presented. It was indicating that in case of each of the
alkali metal ion the process was endothermic contrary to
that of Sr2?, though associated with very small enthalpy
changes. The process involved in this case could thus be
attributed as physisorption accompanied by chemisorption,
ion exchange and capillary diffusion phenomenon due to
mesoporous nature of the material.
Thus the overall process involved could be attributed as
predominantly physical in nature with monolayer formation and simultaneously shifting to chemisorption as
-7.8
-7.9
+
Li
y= 373.63x -9.12
2
R =0.968
-9.64
+
-8.0
Li
-9.68
-8.1
+
Cs
y = 261.54 -10.52
2
R = 0.998
-8.2
+
Rb
y = 1139.1x-11.7
2
R = 0.9902
+
Cs
-8.3
+
Rb
-8.4
-9.72
lnC (Cs+)
lnC( Li+ and Rb+)
-9.60
+
Li
+
Rb
Cs+
2.9
3.0
3.1
3.2
-3
-9.76
3.3
-9.80
3.4
Table 3 Slope and enthalpy change values
Metal ion (M?)
Slope = DHad/R
DHad (kJ mol-1)
Li?
373.63
1.3910-1
-1
Rb
1139.1
3.91910
Cs?
Sr2?
261.54
-2.701
8.97910-2
-5.3910-5a
Data from [27]
Conclusions
The material, PMMA supported potassium iron(III) hexacyanoferrate(II) has been tested for its ion exchange and
sorption applications for removal of the Li?, Rb? and Cs?.
It has been found suitable for Li? removal from concentrated Li? solutions in 5.0 M HNO3. Efficient removals of
Rb? and Cs? could also be carried out under optimized
conditions, at low concentration of these metal ions from
2.5 and 4.5 M HNO3 solution respectively. The separation
mechanism, taking place at the surface of the sorbent,
could be predominantly suggested as physisorption, followed by chemisorption phenomenon going from Li?, Rb?
and Cs? in combination with the ion exchange and capillary diffusion processes. PMMA has provided a sound
support for the sorbent. For a high efficiency application
process using the proposed material high concentration and
low temperature would be needed for Li?, while Rb? and
Cs? could be removed from low initial concentrations of
these ions at low temperatures. Ionic size has been postulated to be playing an important role in the sorption of Li?,
Rb? and Cs?. Distribution coefficient (Kd) values, depicted
the metal removal efficiency of the material following the
order Cs? [ Rb? [ Li?. Temperature dependent studies
and enthalpy of adsorption (DHad) values indicated that
sorption process in each case was endothermic associated
with very small energy changes. Over all the material is
considered to be more suitable for Cs? removal, as
75–96% Cs? could be removed from 0 to 300 mg dm-3 of
Cs? solutions in 4.5 M HNO3 suggesting its application for
the removal of Cs137 and Cs134 radio nuclides from low
level aqueous wastes.
Acknowledgment S. Taj is grateful to Higher Education Commission of Pakistan for funding this research work.
Fig. 14 Ln C versus reciprocal temperature (1/T)
a
concluded from the application of Langmuir model and
enthalpy data. Further the ion exchange process operative
in the system as a final consequence of the earlier effects of
the Vander Waal forces followed by a complexity of
physico-chemical sorption leading to development of multi
layers with diffusion phenomenon may also be playing
some role.
-1
1/T × 10 (K )
?
87
References
1. Tsuchiya S, Nakatani Y, Ibrahim R, Ogawa S (2002) Highly
efficient separation of lithium chloride from seawater. J Am
Chem Soc 124:4936–4937
2. Tasuruta T (2005) Removal and recovery of lithium using various
microorganisms. J Biosci Bioeng 100:562–566
3. Sun H, Tabata M (1999) Separation and trans port of lithium of
10–5 M in the presence of sodium chloride higher than 0.1 M by
123
Author's personal copy
88
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
S. Taj et al.
2, 3, 7, 8, 12, 13, 17, 18-Octabromo-5, 10, 15, 20-tetrakis
(4-sulfonatophenyl) porphyrin. Talanta 49:603–610
Laddicotte GW (1962) The radiochemistry of rubidium. Oak
Ridge National Laboratory, National Academy of Sciences,
Nuclear Research Council, Nuclear Research Series, NAS-NS,
3053, U.S. Atomic Energy Commission, Los Alamos Scientific
Laboratory, May 4, pp 1–31
Murhy GK (1967) Rubidium-87 concentration in market milk.
J Dairy Sci 50:818–820
Wang X, Du J, Tao Z, Fan Z (2003) Migration characteristics of radio
nuclides 85?89Sr2?, 134Cs?, 125I1–, 75SeO32- and 152?154 Eu(III) in
Chinese soils column investigation. J Radioanal Nucl Chem
258:133–138
Jabbar T, Subhani MS, Khan K, Rashid A, Orfi SD, Khan AY
(2003) Natural and fallout radionuclide concentrations in the
environment of Islamabad. J Radioanal Nucl Chem 258:143–149
Peterson J, Macdonell M, Haroun L, Monette FR, Hildebrand
RD, Taboas A (2007) Human health fact sheet 2005., Radiological and chemical fact sheets to support health risk analyses
for contaminated areas. Argonne National Laboratory Environmental Science Division
Chibowski S, Gładysz A (1999) Examination of radioactive
contamination in the soil-plant system and their transfer to
selected animal tissues. Pol J Environ Studies 8:19–23
El-Said N, El-Sheref E, Borai E (2003) Modeling of transport of
Cs (137) by emulsion liquid membrane (18C6) in xylene promoted by ephedrine hydrochloride in stripping phase. J Membr
Sci 211:183–191
Clearfield A (2000) Inorganic ion exchangers, past, present, and
future. Sol Extr Ion Exch. 18:655–678
Ganzerli-Valentini MT, Meloni S, Maxia V (1972) Adsorption of
monovalent ions on zinc ferrocyanide. J Inorg Nucl Chem 34:
1427–1436
Jain AK, Singh R, Bala C (1963) On the sorption behaviour of
some cations on cobalt hexacyanoferrate(III) exchanger binary
separation of Rb? and Cs? on columns. Bull Chem Soc Jpn 56:
1269–1270
Konecny C (1973) Adsorption properties of insoluble hexacyanoferrates(II) supported on silica gel. J Radioanal Nucl Chem
14:255–266
Mimura H, Lehto J, Harjula R (1997) Selective removal of
cesium from simulated high- level liquid wastes by insoluble
ferrocyanides. J Nucl Sci Technol 34:607–609
Lehto J, Harjula R, Wallace J (1987) Absorption of cesium on
potassium cobalt hexacyanoferrate(II). J Radioanal Nucl 111:
297–304
Mimura H, Lehto J, Harjula R (1997) Ion exchange of cesium on
potassium nickel hexacyanoferrate (II). J Nucl Sci Technol 34:
484–489
123
18. Singh IJ, Misra BM (1996) Studies on sorption of radiocesium on
copper hexacyanoferrate loaded resins. Sep Sci Technol 31:
1695–1705
19. Mimura H, Kimura M, Akiba K, Onodera Y (1999) Separation of
cesium and strontium by potassium nickel hexacyanoferrate(II)–
loaded zeolite A. J Nucl Sci Tech 36:307–310
20. Mimura H, Kimura M, Akiba K, Onodera Y (1999) Selective
removal of cesium from highly concentrated sodium nitrate
neutral solutions by potassium nickel hexacyanoferrate(II) loaded
silica gel. Sol Extr Ion Exch 17:403–417
21. Mimura H, Kimura M, Akiba K, Onodera Y (1999) Selective
removal of cesium from sodium nitrate solutions by potassium
nickel hexacyanoferrate-loaded chabazites. Sep Sci Technol
34:17–28
22. Field D, Etal K (1999) Cesium removal from fuel pond water
using a composite ion exchanger containing nickel hexacyanoferrate supported on polyacrylonitrile. Czech J Phys 49 Suppl S1
part II 965–969
23. Rajec P, Orechovska J, Novak I (2000) NIFSIL: A new composite sorbent for cesium. J Radioanal Nucl Chem 245:317–321
24. Chang C-Y, Chau L-K, Hu W-P, Wang C-Y, Liao J-H (2008)
Nickel hexacyanoferrate multilayers on functionalized mesoporous silica supports for selective sorption and sensing of cesium.
Micropor Mesopor Mater 109:505–512
25. Valsala TP, Joseph A, Shah JG, Raj K, Venugopal V (2009)
Synthesis and characterization of cobalt ferrocyanides loaded on
organic anion exchanger. J Nucl Mater 384:146–152
26. RadiogardaseTM Cs, Insoluble prussian blue(ferrichexacyanoferrate) Fe4[Fe(CN)6]3) Informational Material (2007) Oak
Ridge Institute for Science and Education (ORISE), November
9, 2007
27. Taj S, Chaudhry MA, Mazhar M (2009) Potassium iron(III)
hexacyanoferrate(II) supported on polymethylmethacrylate ion
exchanger for removal of strontium (II). J Radioanal Nucl Chem
281:393–403
28. Bueno PR., Ferreira FF, Gimenez-Romero D, Setti GO, Faria RC,
Gabrielli C., Perrot H, Garcia-Jareno J, Vicente F (2008) Synchrotron structural characterization of electrochemically synthesized hexacyanoferrates containing K?: a revisited analysis of
electrochemical redox. J Phys Chem C 112: 13264–13271
29. Katsikas L, Avramovic M, Cortés RDB, Milovanovic M, Melina
T, Kalagasidis-Krusic MT, Popovic IG (2008) The thermal stability of poly (methylmethacrylate) prepared by RAFT polymerization. J Serb Chem Soc 73:915–921
30. Lopeargolo LC, Catalani LH, Machado LDB, Rela PR, Lugaao
AB (2000) Development of reinforced hydrogels–I Radiation
induced graft copolymerization of methylmethacrylate on nonwoven poly-propylene fabric. Radiat Phys chem 57:451–454
31. Stern HK, Amis SE (1959) Ionic size. Chem Rev 59:1–64