Interaction of NpOþ 2 with Cle in NaeCaeCl-type solutions at ionic strength of 6M: Effect of presence of Ca ion on interaction

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Interaction of NpOþ 2 with Cle in NaeCaeCl-type solutions at ionic strength of 6M: Effect of presence of Ca ion on interaction. The interaction of NpOþ 2 with Cle was studied using visibleenear-infrared spectroscopy in NaCleCaCl2eNaClO4, NaCleNaClO4, and CaCl2eNaClO4 solutions with ionic strength (I) of 6M. The spectra of NpOþ 2 around 980 nm varied with Cle concentration in the NaCleCaCl2eNaClO4 and NaCleNaClO4 solutions at [Cle] 3.5M, but not in the CaCl2eNaClO4 solution. Assuming the 1:1 interaction between NpOþ 2 and Cle, the apparent equilibrium constants at I ¼ 6M were evaluated.
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Contents lists available at ScienceDirect
Nuclear Engineering and Technology
journal homepage: www.elsevier.com/locate/net
Technical Note
Interaction of NpO2 with Cle in NaeCaeCl-type solutions at ionic
strength of 6M: Effect of presence of Ca ion on interaction
Shinya Nagasaki a, *, Takumi Saito b, Satoru Tsushima c, Jared Goguen a, Tammy Yang d
a Department of Engineering Physics, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4L7, Canada
b Department of Nuclear Engineering and Management, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654, Japan
c Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, 01314, Dresden, Germany
d Nuclear Waste Management Organization, 22 St. Clair Avenue East, Sixth Floor, Toronto, Ontario, Canada
a r t i c l e
i n f o
a b s t r a c t
Article history:
Received 12 June 2017
Received in revised form
1 August 2017
Accepted 14 August 2017
Available online 18 August 2017
Keywords:
Cle
Density Functional Theory Calculation
The interaction of NpOþ with Cle was studied using visibleenear-infrared spectroscopy in NaCleCa-
Cl2eNaClO4, NaCleNaClO4, and CaCl2eNaClO4 solutions with ionic strength (I) of 6M. The spectra of
NpOþ around 980 nm varied with Cle concentration in the NaCleCaCl2eNaClO4 and NaCleNaClO4 so-
lutions at [Cle]  3.5M, but not in the CaCl2eNaClO4 solution. Assuming the 1:1 interaction between
NpOþ and Cle, the apparent equilibrium constants at I ¼ 6M were evaluated. The presence of Ca2þ was
found to destabilize overall interaction between NpOþ and Cle. The observations were consistent with
the density functional theory calculation.
© 2017 Korean Nuclear Society, Published by Elsevier Korea LLC. This is an open access article under the
Equilibrium Constants
Ionic Strength
NpO2
Presence of Ca2þ
1. Introduction
the NaCleCaCl2eNaClO4 solutions with I ¼ 6M, as the Na/Ca molar
concentration ratio (Na/Ca ratio) in the solution decreased from
Sedimentary rocks in Canada are being considered as potential
host rocks for a deep geologic repository for radioactive waste.
Some of these rocks in Canada contain NaeCaeCl brine solutions
with total dissolved solid concentrations of up to 350 g/L (e.g.,
Southern Ontario, Michigan Basin [1]).
Sorption of radionuclides onto host rocks surrounding a deep
geologic repository and onto materials comprising the engineered
barrier system is considered an important mechanism for retarding
their transport from the repository to the biosphere [2].
The Nuclear Waste Management Organization has been main-
innity to zero, and this could not be explained solely by the
sorption competition of NpOþ with Ca2þ. Because the sorption
behavior of an element depends, in part, on its speciation, it is
important to investigate the speciation of NpO2 in NaeCaeCl brine
solutions in order to understand the sorption mechanisms.
As Topin and Aupiais [5] pointed out, the reactivity of Cle with
NpO2 is considered to be very low. In the literature [6e14], the
interaction of Cl with NpO is treated as an interaction with one
NpOþ and one Cle (1:1) with an apparent equilibrium constant
taining a database of sorption distribution coefcient values of
many elements including Np for Canadian sedimentary rocks and
bentonite in saline conditions around neutral pH [the sorption
database is targeting for the SR-270-PW reference brine, which is a
½NpO2Cl
NpO2Cl NpO2 Cl
(1)
NaeCaeCl-type with an ionic strength (I) of 6M] [3].
In our previous study [4], we found that the sorption distribu-
tion coefcients of NpO2 for illite, shale, and MX-80 decreased in
The logbNpO Cl values reported are as follows: e0.29 ± 0.05 in
2M HCleHClO4 solution by Gainar and Skyes [6], e0.42 ± 0.04 in
2M NaCleNaClO4 solution by Rao et al [7], 0.48 in 8.5M NaCleNa-
ClO4 solution by Patil et al [8], and e0.05 ±0.02 in 5M NaCleNaClO4
solution by Neck et al [9]. Guillaumont [10] argued that these
* Corresponding author.
studies did not take into account the variations in the medium
E-mail address: nagasas@mcmaster.ca (S. Nagasaki).
when the data were processed, which resulted in bias in the
1738-5733/© 2017 Korean Nuclear Society, Published by Elsevier Korea LLC. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/
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S. Nagasaki et al. / Nuclear Engineering and Technology 49 (2017) 1778e1782
1779
equilibrium constants. The Nuclear Energy Agency (NEA) thermo-
(6) The Np solution prepared in Step 5 was evaporated and
dynamic database [10] selected a logbNpO2Cl ¼ 0.40 ± 0.17 (I ¼ 0M at
298.15 K), based on the studies by Cohen et al. [11] (HClO4 solu-
tions; I ¼ 3M; [Cle] ¼ 0e2.7M), Al-Niaimi et al [12] (HClO4 solu-
tions; I ¼ 0.3M, 0.4M, and 0.5M; [Cle] ¼ 0.01e0.14M), and Danesi
et al [13] (NaCleHClO4eNaClO4 solutions; I ¼ 4M; [Cle]  2.3M).
Recently, Topin et al [14] obtained a logbNpO Cl ¼ e0.40 ± 0.07 at
1M NaCl solution and corrected it to e0.12 ± 0.13 for I ¼ 0M.
dried.
(7) The dry Np prepared in Step 6 was dissolved in 0.01M HClO4
solution.
(8) HONH3Cl was added to the Np solution prepared in Step 7.
(9) The NpO2 solution was stored in the GB.
TheNpoxidationstateswereconrmedbyViseNIRspectroscopy
However, the ionic strength conditions and the concentration range
of Cle adopted by Topin et al [14] and the NEA thermodynamic
(Agilent 8453 UVeViseNIR spectrometer (Agilent Technologies
Canada 6705 Millcreek Dr, Mississauga, ON L5N 8B3, Canada); min-
database [10] may be insufcient for brines.
imumwavelengthdissolution¼1nm).Experimentswereconducted
By contrast, Giffaut [15] and Danesi et al [16] concluded that
there was no NpOþ complexation with Cle in 4M NaCl or in 4M
NaCleHClO4eNaClO4 solutions, respectively. Allen et al [17]
investigated the interaction of NpOþ and Cle in LiCl solution at
pH ¼ 3 by X-ray absorption ne structure spectroscopy and found
that Cle was present in the equatorial region of the NpOþ only in
the solutions with 7e10M Cle and the coordination number of Cle
was 0.6e1.0. Furthermore, Petrov et al [18] illustrated that the
uncomplexed NpOþ aquo ion could be considered to be the main
unhydrolyzed Np(V) species even in 5.0M NaCl at pHm < 10.3. As
such, THEREDA (a German thermodynamic reference database
at 25C. The procedure of pHc [decimal logarithm of proton con-
centration (mol/L)] measurement was described elsewhere [6].
2.2. Interaction of Cle with NpOþ in the presence and absence of
Ca2þ by ViseNIR spectroscopy
The SR-270-PW reference brine solution is NaeCaeCl type,
pH ¼ 6.0, I ¼ 6.0M, [Cle] ¼ 4.8M, and Na/Ca molar concentration
ratio ¼ 2.7 [3]. In this study, NaCleCaCl2eNaClO4 solutions at con-
stant I ¼ 6M and constant Na/Ca molar concentration ratio ¼ 2.7
with various Cle concentrations ([Cle] ¼ 3e4.9M) were prepared.
containing Pitzer ion interaction parameters for brine solutions)
[19] does not include the logbNpO Cl value.
Richmann [20] has recently studied the interaction of NpO
with Cle in NaCl and NaClO4 solutions with ionic strength up to 5M
For comparison, NaCleNaClO4 and CaCl2eNaClO4 solutions with
I ¼ 6M were also prepared. The Cle concentrations were
[Cle] ¼ 3e4.5M for the NaCleNaClO4 solution and [Cle] ¼ 3e5M for
the CaCl2eNaClO4 solution. The upper Cle concentrations (4.9M,
by visibleenear-infrared (ViseNIR) spectroscopy, observed the
NpO2Cl complex at [Cle]  3.5M, and evaluated the logbNpO Cl value
as e1.5 ± 0.5 (I ¼ 5M). The logbNpO Cl value by Richmann [20] is
indeed smaller than previously reported values [6e14]. Although
4.5M,and5M)werelimitedbythesolubilityofNaClandCaCl2$2H2O
compounds. The lower Cle concentration (3M) was from the
experimental results by Richmann [20]. In the CaCl2eNaClO4 solu-
tion, the Na/Ca molar concentration ratio was not kept constant at
many works havebeen conducted, nonnegligible discrepancyexists
concerning the nature of the NpOþeCle interaction. Furthermore,
there is no study on the interaction of NpOþ with Cle in the pres-
ence of Ca2þ in brine solutions. This paper studied the interaction of
NpOþ with Cle in NaeCaeCl-type solutions at the constant high
ionic strength of 6M, and the inuence of Ca2þ on the interaction.
2.7. After we prepared the NaCleCaCl2eNaClO4, NaCleNaClO4, and
CaCl2eNaClO4 solutions, we applied the ltration (Vivaspin 6; 3000
MWCO (GE Healthcare Life Sciences 2300 Meadowvale Blvd., Mis-
sissauga, ON, L5N 5P9, Canada)) for 120 minutes at 8500 g at 25C
(Allegra X-30R; Beckman Coulter, LP. 7075 Financial Drive Mis-
sissauga, Ontario Canada), measured the concentrations of Na and
Ca using inductively coupled plasma atomic emission spectroscopy
2. Experimental
(Varian Vista Pro (Varian Inc. (this company was purchased by Agi-
lent Technologies in 2010.), Corporate Headquarters, 3120 Hansen
2.1. Chemicals and Np solution
Way,PaloAlto,CA94304-1030,USA))priortoandaftertheltration,
All chemicals used for preparing solutions were reagent grade
and supplied from Fisher Scientic (112 Colonnade Road, Ottawa,
and conrmed that there were not any precipitates in all solutions.
A portion of NpO2 stock solution was spiked to the NaCleCa-
Cl2eNaClO4, NaCleNaClO4, and CaCl2eNaClO4 solutions. The pHc of
Ontario, K2E 7L6, Canada). Deionized water from a Milli-Q Direct 8
solutions was adjusted by HCl and NaOH to 7.2 ± 0.5 for NaCle
was used. A Precise Controlled Atmosphere Glove Box (GB) sup-
plied by Labconco (8811 Prospect Avenue, Kansas City, MO 64132-
2696, USA) was lled with N2 gas (>99.999%) to exclude CO2. The
CaCl2eNaClO4, 6.6 ± 0.3 for NaCleNaClO4, and 7.5 ± 0.3 for
CaCl2eNaClO4 solutions. Because NpO2 is dominant at pHc up to 10
in aqueous solution in the absence of ligands [18], the difference of
concentration of O2 in the GB was conrmed to be less than 1 ppm.
The Np-237 solution was purchased from Stuart Hunt & Associates
Ltd (5949 Ambler Drive, Mississauga, Ontario, L4W 2K2, Canada).
Purchased Np in HNO3 solution may contain Np(IV), Np(V), and
Np(VI). Pure NpOþ in HClO4 solution is prepared using the
following procedures [6].
(1) Np in HNO3 solution was fed to an evaporation glass plate.
pHc in this study was considered to be negligible. The concentration
of NpO2 was 1  104 M. How to determine the concentration of
Np is described elsewhere [4].
The principal 5fe5f transition (3H4g to 3P2g) in the electronic
absorption spectrum for NpOþ in aqueous solutions is typically at
around 980 nm[21,22]. Thisband followsa BeereLambert behaviour
and is often used analytically to establish the concentration of NpOþ
in solution and to study its complexation behavior with a ligand as
(2) Np solution was evaporated and dried in the evaporation
glass plate.
(3) The Np dried in Step 2 was dissolved in a mixture of
concentrated HNO3 and concentrated HClO4 solutions
(HNO3/HClO4 ¼ 2:1 by volume ratio).
thebandisaffectedbycomplexation[22,23].Inthisstudy,thespectra
of NpO2 around 980 nm in the NaCleCaCl2eNaClO4, NaCleNaClO4,
and CaCl2eNaClO4 solutions were measured by ViseNIR spectros-
copy. As references, the spectra of NpOþ in 6M NaClO4 solution
([Cle] ¼ 0) at pHc ¼ 6.6, 7.2, and 7.5 were also measured.
(4) The Np solution prepared in Step 3 was evaporated and
dried.
2.3. Density functional theory calculation procedure
(5) The dry Np prepared in Step 4 was dissolved in a mixture of
concentrated HNO3 and concentrated
(HNO3/HClO4 ¼ 2:1 by volume ratio).
HClO4
solutions
In order to theoreticallystudy the effect of chlorine coordination
to NpO2 , we optimized the structures of NpO2ðH2OÞ5 and