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Structure and Thermochemistry of Perrhenate Sodalite and Mixed Guest Perrhenate/Pertechnetate Sodalite Eric M. Pierce, Kristina I. Lilova, David M. Missimer, Wayne W. Lukens, Lili Wu, Jeffrey P. Fitts, Claudia J. Rawn, Ashfia Huq, Donovan Nicholas Leonard, Jeremy R. Eskelsen, Brian F. Woodfield, Carol M. Jantzen, and Alexandra Navrotsky Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b01879 • Publication Date (Web): 05 Dec 2016 Downloaded from http://pubs.acs.org on December 10, 2016

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Environmental Science & Technology

3

Structure and Thermochemistry of Perrhenate Sodalite and Mixed Guest Perrhenate/Pertechnetate Sodalite

4 5 6

Eric M. Piercea‡*, Kristina Lilovab‡, David M. Missimerc, Wayne W. Lukensd, Lili Wub, Jeffrey Fittse, Claudia Rawnf, Ashfia Huqg, Donovan N. Leonardf, Jeremy R. Eskelsena, Brian F. Woodfieldh, Carol M. Jantzeni, and Alexandra Navrotskyb

1 2

7 8 9 10 11 12 13 14 15 16 17 18

a

Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, MS: 6038, Oak Ridge, TN 37831 b

Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California at Davis, Davis, CA 95616 c

Analytical Development Center, Savannah River National Laboratory, Aiken, SC 29808

d

Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720

e

Department of Civil & Environmental Engineering, Princeton University, Princeton, NJ 08544

f

Department of Materials Science & Engineering, University of Tennessee, Knoxville, TN 37996

g

Chemical & Engineering Materials Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831 h i

Chemistry & Biochemistry, Brigham Young University, Provo, UT 84602

Environmental Technology Center, Savannah River National Laboratory, Aiken, SC 29808

19

20 21

KEYWORDS1: sodalite, perrhenate sodalite, pertechnetate sodalite, neutron powder diffraction, x-ray absorption fine structure, high-temperature calorimetry

22

23

1

This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-publicaccess-plan).

1 ACS Paragon Plus Environment


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ABSTRACT: Treatment and immobilization of technetium-99 (99Tc) contained in reprocessed

25

nuclear waste and present in contaminated subsurface systems represents a major environmental

26

challenge. One potential approach to managing this highly mobile and long-lived radionuclide is

27

immobilization into micro- and meso-porous crystalline solids, specifically sodalite. We

28

synthesized and characterized the structure of perrhenate sodalite, Na8[AlSiO4]6(ReO4)2, and the

29

structure of a mixed guest perrhenate/pertechnetate sodalite, Na8[AlSiO4]6(ReO4)2-x(TcO4)x.

30

Perrhenate was used as a chemical analogue for pertechnetate. Bulk analyses of each solid

31

confirm a cubic sodalite-type structure (ܲ4ത3݊, No. 218 space group) with rhenium and

32

technetium in the 7+ oxidation state. High-resolution nanometer scale characterization

33

measurements provide first-of-a-kind evidence that the ReO4- anions are distributed in a periodic

34

array in the sample, nanoscale clustering is not observed, and the ReO4- anion occupies the

35

center of the sodalite β-cage in Na8[AlSiO4]6(ReO4)2. We also demonstrate, for the first time,

36

that the TcO4- anion can be incorporated into the sodalite structure. Lastly, thermochemistry

37

measurements for the perrhenate sodalite were used to estimate the thermochemistry of

38

pertechnetate sodalite based on a relationship between ionic potential and the enthalpy and Gibbs

39

free energy of formation for previously measured oxyanion-bearing feldspathoid phases. The

40

results collected in this study suggest that micro- and mesoporous crystalline solids maybe viable

41

candidates for the treatment and immobilization of

42

streams and contaminated subsurface environments.

43 44

INTRODUCTION Development of a sustainable nuclear fuel cycle, which must include closing the back-end by

45

recycling and/or disposing of used nuclear fuel, is a key component of the nuclear energy

46

renaissance (12% of the electrical energy worldwide1 and 19% in the United States2). Disposition

99

Tc present in reprocessed nuclear waste


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of radioactive waste generated by the nuclear fuel cycle and nuclear weapons production during

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the Cold War era is one of the most pressing environmental challenges facing the United States

49

and the international community.3-4 Furthermore, proposed waste management strategies are

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complicated by the inventory of long-lived radionuclides, such as technetium (99Tc), and the

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time-scales considered for disposal. Since its discovery in 1937 by Perrier and Segre,5-6 the global inventory of 99Tc has increased

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steadily. Technetium-99 (β = 293.7 keV, t1/2 = 2.1 × 105 years), a byproduct of

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fission, comprises a significant component of radioactive waste due to its high fission yield—

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~5%. The world-wide inventory of 99Tc requiring disposition is estimated to have quadrupled to

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~305 MT from 1994 to 2010 because of nuclear energy production.7 Additionally, US weapons

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production sites must dispose of ~5.1 MT of 99Tc (~3.5 MT at the Savannah River Site and ~1.6

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MT at the Hanford Site).8 Treatment and immobilization of

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nuclear waste presents a major challenge because 99Tc volatilizes at the temperatures (~1100 ºC)

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required for vitrification, the preferred international treatment method.8-11 The immobilized

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nuclear waste glass is destined for long-term storage in a geologic repository. The chemistry of

62

99

99

235

U and

239

Pu

Tc contained in reprocessed

Tc suggests that under aerobic environmental conditions, the stable

63

heptavalent Tc 7+ pertechnetate anion (99TcO4-) is dominant. This oxyanion is soluble and

64

readily migrates through the environment because it does not adsorb well onto mineral surfaces,

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soils, or sediments. Because of the long half-life, abundance, and high environmental mobility of

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99

Tc, incorporating it into durable matrices other than glass is an attractive waste management

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strategy.12 For example, recent studies have examined the possibility of incorporating 99Tc in the

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4+ oxidation state into the structure of iron-based minerals.13-19 Although various countries are

69

pursuing vitrification as the primary waste management strategy for other radionuclides (e.g.,



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137

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Cs, 90Sr, U-isotopes, etc.), one approach that has been considered previously but not pursued

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for disposition and remediation of TcO4- is encapsulating the radionuclide into micro- and

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mesoporous crystalline solids, such as the feldsphathoid phase sodalite.

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Micro- and meso-porous solids represent a family of >150 crystalline phases, which support a

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variety of industrial processes (petrochemical cracking, ion exchange for water softening and

75

purification, and gas separation). These porous materials contribute an estimated $350 billion to

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the global economy as part of the world’s chemical industry. The porous structure consists of a

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three-dimensional (3D) framework composed of alternating TO4 (T = Al or Si) tetrahedral units

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that share corner oxygens. The 3D framework structure contains a pore or cavity system that can

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expand (microporous = 2.5 to 20 Å; mesoporous = 20 to 500 Å) to encase various guest anions

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and organic molecules by cooperative changes in the T-O-T bond angle. For example,

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aluminosilicate sodalites, both natural and synthetic, can vary widely in composition but have the

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general formula of M8(Al6Si6O24)X2, where M is a monovalent cation (such as Cs+, K+, Na+, etc.)

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and X can vary between monovalent or divalent anions (such as OH-, Cl-, Br-, I-, MnO42-, ReO4-,

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or theoretically TcO4-).20-31

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Here we use Re as a nonradioactive analogue for

99

Tc, because under oxidizing conditions

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both elements are oxyanions and they have similar metal oxygen bond lengths (Tc–O = 1.702 Å;

87

Re–O = 1.719 Å) and ionic radii (TcO4- = 2.52 Å; ReO4- = 2.60 Å).7,32-34 However, under

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reducing conditions it is easier to reduce Tc in comparison to Re from 7+ to 4+ because of the

89

difference in standard reduction potential of ReO4-/ReO2 = 0.510 V versus TcO4-/TcO2 = 0.738

90

V.8,35-36 Thus, the use of Re as a nonradioactive analogue for

91

oxidizing conditions where both species are expected to remain in the 7+ oxidation state.

99

Tc is only applicable under


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92


Results collected by Dickson et al.

37-39

suggest that the ReO4- anion—and by analogy the

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TcO4- anion—is incorporated into the sodalite β-cage and that anion selectivity for the sodalite

94

β-cage is size-dependent. However, the conclusions are based on bulk characterization results,

95

specifically changes in the chemical composition and bulk X-ray powder diffraction spectra. The

96

data collect by Dickson et al.

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regarding the location and distribution of the ReO4- anion in the crystalline matrix. Additionally,

98

the key question of whether or not the TcO4- anion can be incorporated into the sodalite structure

99

also remains elusive.

37-39

provide key insights, but do not provide definitive evidence

100

The primary objective of the present study is to definitively determine the location and

101

distribution of ReO4- anion in the perrhenate sodalite structure and to demonstrate that the

102

pertechnetate anion can be incorporated into the sodalite structure. An additional objective is to

103

estimate the thermochemistry of pertechnetate sodalite, which is a key data set for evaluating

104

sodalite as a potential host matrix for the highly mobile TcO4- anion. To fulfill the

105

aforementioned objectives, we synthesized and characterized the structure of perrhenate sodalite

106

using a combination of time-of-flight (TOF) neutron powder diffraction (NPD) and aberration-

107

corrected high annular angular dark field (HAADF) scanning transmission electron microscopy

108

(STEM). Additionally, we synthesized and characterized the oxidation state of Re and 99Tc in a

109

mixed guest perrhenate/pertechnetate sodalite using x-ray absorption spectroscopy, extended x-

110

ray absorption fine structure, and x-ray powder diffraction. Lastly, calorimetric measurements

111

for the perrhenate sodalite were used to estimate the thermochemistry of pertechnetate sodalite

112

based on a relationship between ionic potential and the enthalpy and Gibbs free energy of

113

formation for previously measured oxyanion-bearing feldspathoid phases.



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EXPERIMENTAL Synthesis of Perrhenate Sodalite and Mixed Guest Perrhenate / Pertechnetate Sodalite.

116

Perrhenate sodalite was synthesized using hydrothermal methods by treating Zeolite 4A with 8M

117

NaOH in the presence of excess sodium perrhenate at 225°C and 400 psi in an autoclave for 7 d

118

(168 h). The mixed guest perrhenate/pertechnetate sodalite was also prepared hydrothermally

119

using a similar synthesis approach as above with a 11:1 mole ratio of NaReO4 (0.021 moles) to

120

NaTcO4 (0.0019 moles). For additional details on the synthesis see the Supporting Information

121

section.

114

122

X-ray Diffraction. The powder XRD spectrum of the homogenized perrhenate sodalite sample

123

was measured with a Panalytical X’Pert PRO diffractometer using CuKα radiation (λ = 1.54060

124

Å). Data were collected in 0.017° steps over the 2θ range 5–110°. The powder XRD spectrum

125

for the mixed guest perrhenate/pertechnetate sodalite sample was measured with a Bruker D8

126

Advance x-ray diffractometer using CuKα radiation (λ = 1.54060 Å). The samples were ground

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in an agate mortar and pestle, mixed with a 1:10 collodion/amyl acetate mixture, and smeared

128

onto a square glass slide. The XRD data were collected in 0.02° step size and a dwell time of 1 s

129

over the 2θ range 5–70°.

130

X-ray Absorption Spectroscopy. Rhenium x-ray absorption fine structure (XAFS) analysis

131

was conducted by placing approximately 200 mg of sample in a Teflon holder sealed with

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Kapton tape. The bulk Re LII-edge (11,959 eV) X-ray Absorption Near Edge Structure (XANES)

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spectrum of the perrhenate sodalite was collected in transmission at Stanford Synchrotron

134

Radiation Lightsource (SSRL) on beamline 11-2. The beamline configuration consisted of a

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cryogenically cooled Si(220), φ = 90°, double-crystal monochromator with the second crystal

136

detuned by 70% to reduce the harmonic content of the beam. Incident and transmitted beam


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intensity was determined using nitrogen-filled ion chambers. Data were normalized and

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corrected for self-absorption using Athena.40

139

Technetium XAFS analysis was conducted by mixing 100 mg of mixed Re/Tc sodalite with

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100 mg of chloride sodalite and adding the 200 mg mixture to a Teflon holder sealed with

141

Kapton tape. The bulk Tc K-edge (21,047) XANES spectrum of the mixed guest

142

perrhenate/pertechnetate sodalite was collected in fluorescence at the National Synchrotron Light

143

Source on beamline X27A with a HPGe detector. Data were averaged using Athena and are not

144

corrected for detector dead time or self-absorption because neither effect was significant at the

145

detector count rates and pertechnetate concentrations used in this study (1 mol % pertechnetate in

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the mixed guest perrhenate/pertechnetate sodalite).

147

For additional details on the XAS spectrum fitting see Supporting Information.

148

Neutron Powder Diffraction. Time-of-flight powder neutron diffraction (PND) data were

149

collected using 1.312 gram samples of sodium perrhenate [Na8(AlSiO4)6(ReO4)2] contained in an

150

8 mm diameter vanadium sample can at 298 K. The PND patterns were collected using the

151

POWGEN (BL-11A) neutron powder diffractometer at the Spallation Neutron Source (SNS) at

152

Oak Ridge National Laboratory, Oak Ridge, TN. Diffraction profiles were collected using center

153

wavelengths 1.066 Å and 2.665 Å, providing a d-spacing range from 0.57 to 6.18 Å. Rietveld

154

refinements of the data were performed using the GSAS software package along with the

155

EXPGUI interface.41-42 The bound coherent scattering lengths 3.62 ± 0.02 fermi (fm) for sodium,

156

3.449 ± 0.005 fm for aluminum, 4.149 ± 0.001 fm for silicon, 9.2 ± 0.2 fm for rhenium, and

157

5.803 ± 0.004 fm for oxygen. The large bound coherent scattering length of oxygen allows the

158

oxygen positions to be determined using neutron diffraction with more accuracy than with XRD.

159

Additionally, the difference in the bound scattering length for the aluminum, rhenium, and



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silicon atoms allows these elements to be distinguished better using neutron powder diffraction

161

than with XRD. The atomic structure for Na8(AlSiO4)6(ReO4)2 previously reported was used as

162

the starting model for calculating the diffraction patterns.29-30

163

Microscopy imaging. Atomic resolution aberration-corrected STEM images were obtained

164

with a Nion Ultra STEM 60-100 electron microscope. This was equipped with a cold field

165

emission gun and operated at 100kV with a 3rd generation C3/C5 aberration corrector. The

166

aberration-corrected HAADF STEM images were performed with a probe current of 80 pA.

167

Beam damage was readily apparent when imaging in the STEM (see Fig. SI2) and electron dose

168

was minimized by using fast scan speeds at the largest field of view that atomic columns could

169

still be resolved. For additional details on beam damage see Supporting Information. Perrhenate

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sodalite powder was suspended in 50 mL of isopropyl alcohol and a 10 µL droplet was cast onto

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a 3mm copper lacey carbon TEM grid and the solution was allowed to evaporate. The drop cast

172

TEM grid was then prebaked in a vacuum oven station at 160°C for 8 hours at ~10-6 torr and

173

then allowed to cool under vacuum for 10 hours. STEM imaging was performed on a single

174

grain of perrhenate sodalite that was positioned on the lacey carbon in a crystallographic

175

orientation close to [111] zone axis. STEM stage tilts were then used to properly orient the

176

sample into a [111] zone axis for atomic column resolution imaging. The [111] zone axis was

177

selected because it was ideal for observing the ReO4- anion present inside the sodalite β-cage.

178

Additional details on aberration-corrected HAADF—also referred to as Z-contrast imaging—and

179

scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) measurements

180

are provided in the Supporting Information.

181

Calorimetry. High temperature oxide melt solution calorimetry was performed using a Tian

182

Calvet twin calorimeter.43-44 Samples in the form of pellets (between 4 and 6 mg) were dropped


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183

from room temperature (298 K) into the molten 2PbO·B2O3 at the calorimeter temperature in a

184

platinum crucible. Air was flushed over the solvent at 90 mL/min. The calorimeters were

185

calibrated using the heat content of 5 mg α–Al2O3 pellets.

186

A preliminary furnace test was performed before conducting the calorimetry measurements to

187

verify the complete dissolution of the sample. Pellets of approximately 5 mg were prepared and

188

dropped in molten lead borate solvent (2PbO•B2O3), maintained at 973 K in a furnace. The

189

dissolution process started immediately and finished in a minute. After quenching the melt, no

190

undissolved material was found.

191

The drop solution enthalpy, the standard entropies, and the enthalpies of formation from

192

elements for perrhenate sodalite, nepheline, NaReO4, and component oxides are shown in Table

193

SI9. The enthalpies of formation from elements of the component oxides and sodium salt are

194

taken from Robie and Hemingway 45 or calculated from FactSage 46 (NaReO4). The enthalpies of

195

formation of the perrhenate sodalite from components and from elements (reactions 2 and 3) are

196

calculated using the thermodynamic cycles shown in Table SI9:

( ) ( ) +6SiO ( s,298.15K ) → Na  AlSiO  ( ReO )

(

3Na2O s,298.15K + 2Na ReO4 s,298.15K + 3Al2O3 s,298.15K 197

2

(

8

)

(

4 6

)

) (1)

4 2

(

)

(

8Na s,298.15K + 6Al s,298.15K + 6Si s,298.15K + 2Re s,298.15K 198

(

)

(

+16O2 g,298.15K → Na8  Al6 Si6O24  ReO4

) ( s,298.15K )

) (2)

2

199

201

RESULTS AND DISCUSSION Characterization of Perrhenate Sodalite. In this section we discuss the characterization

202

results obtained from perrhenate sodalite synthesized hydrothermally, to confirm the rhenium

203

oxidation state, to determine the crystal structure, and to definitively determine the location and

200



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distribution of ReO4- anions. For additional details on the hydrothermal synthesis, particle size,

205

and chemical composition see Supporting Information Fig. SI1 and Table SI1.

206

The Re L2-edge X-ray absorption near-edge spectroscopy (XANES) spectra of the four

207

standards are shown in Fig. SI3.35 Two major changes are observed in the rhenium standard

208

reference spectra as one proceeds from Re metal (Re [0] oxidation state) to ReO4- (Re [7+]

209

oxidation state). First, the absorption edge shifts to higher energy because the binding energy of

210

the electron increases as the formal oxidation state increases; there are fewer electrons to screen

211

the charge of the nucleus from the 2p electrons. Second, the area of the large peak at the

212

absorption edge—the “white line,” which is associated with the 2p to 5d transition—increases as

213

the rhenium oxidation state increases because the area is proportional to the number of vacancies

214

in the 5d orbitals (Fig. SI3). Analysis of the perrhenate sodalite XANES spectrum indicates that

215

only ReO4- is present (Fig. SI3) but the fit using the standard reference spectrum suggests that

216

KReO4 is less than optimal (Table SI2). The discrepancy is due to the difference between the

217

local environments of ReO4- in perrhenate sodalite and KReO4, as discussed below.

218

In addition to these major differences, the XANES region just above the edge contains features

219

due to extended x-ray absorption fine structure (EXAFS), especially those caused by multiple

220

scattering. The major changes are clearly seen in Fig. SI3 as the spectrum from standard

221

compounds transition through the range of oxidation states from the 4+ (ReO2) to 7+ (KReO4).

222

The smaller EXAFS contributions may be seen in the size and spacing of the features at energies

223

above that of the white line. As noted above, the EXAFS contributions result in slightly different

224

spectra for KReO4 versus perrhenate sodalite. Although both materials contain the tetrahedral

225

coordinated ReO4- anion, in the KReO4, the potassium ion interacts strongly with the ReO4-

226

anion (the only anion present in ReO4-); in perrhenate sodalite, the sodium ions interact with both


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227

the negatively charged sodalite framework and the ReO4- anion. The resulting weakening of the

228

interaction between ReO4- and the sodium ions is reflected in the decrease of the Re–O bond

229

distance in perrhenate sodalite, 1.729(7) Å, versus NaReO4, 1.728(2) Å,47 and in KReO4,

230

1.723(4) Å48-49 (Fig. 1 and Table SI3). The observed shortening of the Re–O bond length in the

231

sodalite crystal structure is consistent with the shortening of the Mn–O bond length in

232

permanganate sodalite.31,50

233

234

235

Fig. 1. Re L2-edge EXAFS spectrum of perrhenate sodalite, Na8[AlSiO4]6(ReO4)2. The EXAFS

236

data and fit are depicted as a solid gray line and black circles, respectively. Fit range: 2 < k < 11

237

(a); 0.8 < R < 2.0 (b); the number of independent points was 8.6, and the number of parameters

238

was 4.

239

A combination of powder x-ray diffraction (pXRD) (not shown) and neutron powder

240

diffraction (NPD) (Fig. 2) measurements were performed on the perrhenate sodalite sample. The

241

crystallography data are provided in Table 1. The refined atomic positions, site occupancies, and

242

atomic displacement parameters are given in Table SI4 for the NPD results. It was possible to

243

refine the anisotropic displacement parameters for all of the atoms with the exception of 11 ACS Paragon Plus Environment


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aluminum with the NPD results (see Table SI5). For the aluminum atom, the atomic

245

displacement parameter was ~5 times smaller than the silicon atom; one explanation for this

246

difference is that portion of the aluminum sites have been replaced by silicon atoms, which has a

247

smaller neutron cross-section. The data were subsequently refined with the aluminum site

248

occupied by both aluminum and silicon atoms, which resulted in site occupancies of 83(7)%

249

aluminum and 17(7)% silicon. The refined value of Uiso only slightly increased to 0.47(9) × 100,

250

and the χ2 decreased slightly to 2.109. The formula obtained by refining the site occupancy of

251

the oxygen atom, labeled as O2 in Table SI4 – SI6, is Na8(AlSiO4)6(ReO3.75)2, compared with

252

Na8(Al0.83Si1.17O4)6(ReO3.75)2 when the aluminum site is shared by both aluminum and silicon.

253

Similar to the NPD, the pXRD results indicate a sodalite-type structure with a P 43n (No. 218)

254

space group and lattice parameter a = 9.15283(8) Å (Table SI6). These bulk measurements are

255

consistent with the results obtained previously by Mattigod and colleagues.29-30

256

257 258

Fig. 2. Rietveld refinement profiles of powder neutron diffraction data for perrhenate sodalite,

259

Na8[AlSiO4]6(ReO4)2. The neutron diffraction data were collected using two different center

260

wavelengths to access different d-spacing ranges (d-spacing from 0.5 to 3.0Å on [a] and d-

261

spacing from 1.1 to 6.2Å [b]). 12 ACS Paragon Plus Environment

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262 263 264 265 266

Table 1. Refinement details and crystal data for perrhenate sodalite, Na8[AlSiO4]6(ReO4)2, determined by neutron and x-ray powder diffraction. Refinement details and crystal data determined from x-ray powder diffraction data collected on mixed perrhenate/pertechnetate sodalite, Na8[AlSiO4]6(ReO4)2-x(TcO4)x.

Refinement wRp Rexp χ2 Variables Crystal Data Crystal system Space Group a, Å Volume, Å3 Z

Na8[AlSiO4]6(ReO4)2 Neutron X-ray 2.40% 7.50% 1.40% histogram 1 1.75% 2.13% histogram 2 2.111 18.4 64 28

Na8[AlSiO4]6(ReO4)2-x(TcO4)x X-ray 11.91% 4.33

Cubic

Cubic

Cubic

P43n , number 218

P43n , number 218

a

a

9.1553(2) 767.40(3)a 1

9.1544(2) 767.18(3)a 1

7.618 23

P43n , number 218 9.155(6)a 767(2)a 1 Na8[AlSiO4]6(ReO4)1.48(TcO4)0.5

Formula Na8[AlSiO4]6(ReO3.75)2 Na8[AlSiO4]6(ReO3.71)2 2 Formula weight 1390.5 1389.4 1339.4 Calculated density, 2.899 g/cm3 3.009 3.007 a Estimated standard deviation for the lattice parameters and volume reported as 3σ. Other results from the NPD and XRD refinements are reported as 1σ. 267



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268

The structure drawn using the refined atomic positions is shown in Fig. SI4. The silicon and

269

aluminum atoms are both tetrahedrally coordinated, and the Al–O bond length is 1.613(2) Å,

270

compared with the Si–O bond length of 1.719(2) Å. The tetrahedra link together to form a

271

framework with the sodium atoms located in channels along the z direction. The rhenium atom is

272

located in the center and at the corners of the unit cell and is surrounded by the partially occupied

273

oxygen (labeled as O2 in Table SI4 – SI6) at a bond distance of 1.655(6) Å. The Re–O bond

274

distance may be compared to previously published values (1.695(7) Å) obtained using a bench-

275

top XRD system.29-30 The Ueq for O2 is large; however, this is most likely due to the dynamic

276

disorder of the site as previously observed in NH4TcO4.51 This disorder, which is caused by

277

circular oscillating movements (libration) of oxygen atoms around Re, artificially shortens the

278

observed Re–O distance. When corrected for the large thermal parameters of O2 using the

279

“riding model,”52 the Re–O bond distance is 1.741 Å, which is within error of the distance

280

determined by EXAFS and 0.01 to 0.02 Å longer than the distances in KReO4 and NaReO4,

281

which are not corrected for libration.

282

To better understand the location and distribution of the ReO4- anion in perrhenate sodalite, a

283

combination of high-resolution nanometer scale characterization techniques were employed (i.e.,

284

SAED, atomic force microscopy [AFM], and aberration-corrected HAADF STEM). A grain of

285

perrhenate sodalite oriented along the [111] crystallographic plane was used to image atomic

286

columns. Fig. 3 shows a wider view of the grain with beam damage, the raw, and processed

287

images. In the acquired raw image, the ReO4- atomic columns are clear with the fainter signal

288

emanating from the Na, Al, Si, O atoms contained in the sodalite framework

289

this aberration-corrected HAADF-STEM image also illustrates that the ReO4- anions are evenly

290

distributed in the sample rather than clustered in certain locations. To further corroborate the 14

ACS Paragon Plus Environment

53-54

. Additionally,

Page 15 of 34


291

aforementioned conclusion, nanometer scale SAED and AFM measurements were also

292

performed to confirm the crystal structure (Fig. SI5 and SI6). Both SAED and AFM

293

measurements showed that the perrhenate sodalite crystals are cubic and have lattice spacings

294

that are consistent with the values measured in the bulk sample (see Supporting Information).

295

Multi-slice frozen phonon model simulations were conducted with the Quantitative STEM

296

(QSTEM) program to provide additional insight into the aforementioned STEM results.55

297

Simulations were performed on an area that was x = 73.235 Å, y = 73.235 Å, and z = 1475.2 Å.

298

Output from the simulations consist of images at varying thicknesses and included 20 nm, 60

299

nm, and 147 nm. The simulation parameters include a box size of 38.98 Å with a scan window

300

105 pixels × 105 pixels, window size of 25.6 Å × 25.6 Å, 8 slabs and 140 slices per slab

301

resulting in a slice thickness of 1.3078 Å. Results illustrate that the background increases with

302

increasing thickness (Fig. 4). However, the ReO4- atomic columns are still clearly visible in a

303

QSTEM simulation image at 147 nm thick with Poison noise added. The results from these

304

simulations compare well with the experimental images collected and provide further indication

305

that the atomic columns observed in Fig. 3 arise from the ReO4- anion.

306

Collectively these results provide clear evidence that the ReO4- anions are uniformly

307

distributed throughout the sample, nanoscale clustering is not observed, and ReO4- occupies the

308

center of the perrhenate sodalite framework. This is consistent with the XAFS and diffraction

309

results.

310

15



Page 16 of 34

311 312

Fig. 3. Aberration-corrected HAADF STEM images showing atomic columns in the perrhenate

313

sodalite along the [111] crystal face. Image (a) wider field of view, (b) is the raw image of scan

314

area, and (c) is the raw image after being cropped and processed using a Gaussian blur and

315

histogram/gamma adjustment.

16


Page 17 of 34


316 317

Fig. 4. Output images from Quantitative STEM simulations of perrhenate sodalite along the

318

[111] crystal face for three different sample thicknesss; (a) = 20 nm, (b) = 60 nm, and (d) = 147

319

nm, with Poisson noise included in each image. For comparison, Poisson noise was both

320

excluded and included in the 147 nm thick images, (c) and (d) respectively.

321 322

17



Page 18 of 34

323

Characterization of Mixed Guest Perrhenate/Pertechnetate Sodalite. A mixed guest

324

perrhenate/pertechnetate sodalite was synthesized (see Supplemental Information) and then was

325

characterized by XAFS, which shows that Tc and Re are both present in the 7+ oxidation state,

326

scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and pXRD.

327

Here we focus the XAFS discussion on technetium; the Re L2-edge XAFS spectra and results

328

are given in Fig. SI1 and Tables SI2 and SI3. Analysis of the XANES spectrum of TcO4- in the

329

mixed guest perrhenate/pertechnetate sodalite is almost identical to that of TcO4- adsorbed on ion

330

exchange resin

331

first peak above the edge is slightly narrower for the mixed guest perrhenate/pertechnetate

332

sodalite. Additionally, the EXAFS fitting showed that the number of neighbors and bond

333

distance are in very good agreement with the TcO4- anion. Furthermore, inclusion of the

334

neighboring sodium atoms did not improve the EXAFS fit, evident by the lack of change in the

335

reduced chi-squared value. Collectively, the XANES and EXAFS measurements confirmed that

336

99

56

(Tc 7+ oxidation state) (Fig. 5 and Table SI7). The main difference is that the

Tc and Re were in the 7+ oxidation state.

337

18


Page 19 of 34


338

339

340 341

Fig. 5. Tc K-edge XANES (a) and EXAFS (b, c) spectra of the Na8[AlSiO4]6(ReO4)1.48(TcO4)0.52

342

sample. The EXAFS data and fit are depicted as a solid grey line and black circles, respectively.

343

Fit range: 2 < k < 14; 1.0 < R < 3.0; the number of independent points was 16.9, the number of

344

parameters was 4, and R factor = 0.003.

345 346

The SEM-EDS measurements confirmed that the structure and size of the crystals were

347

consistent with the perrhenate sodalite sample discussed in the previous section (Fig. SI7). The

348

pXRD data shown in Fig. 6 illustrates a broadening of the diffraction peaks with the addition of

349

TcO4-. The observed peak broadening is most evident at 23.78 °2θ when compared with the 19



Page 20 of 34

350

pXRD spectrum for Na8[AlSiO4]6(ReO4)2 and Na8[AlSiO4]6(ReO4)2-x(TcO4)x. Structural

351

refinement of the mixed guest perrhenate/pertechnetate sodalite pXRD spectrum is consistent

352

with a mixed sodalite sample that contains ~26% TcO4- and 74% ReO4- in the sodalite cage

353

structure, suggesting a stoichiometry of Na8[AlSiO4]6(ReO4)1.48(TcO4)0.52. The refinement and

354

crystal data results are provided in Table 1 and the structural parameters are provided in Table

355

SI8.

356

357 358

Fig. 6. Structural refinements for powder x-ray powder diffraction of mixed guest

359

perrhenate/pertechnetate sodalite, Na8[AlSiO4]6(ReO4)1.48(TcO4)0.52 (a). A comparison of the

360

pXRD

361

Na8[AlSiO4]6(ReO4)1.48(TcO4)0.52 is also provided (b).

spectra

for

perrhenate

sodalite,

Na8[AlSiO4]6(ReO4)2,

and

362 363

20


Page 21 of 34


364

Chemical Stability of Perrhenate and Mixed Guest Perrhenate/Pertechnetate Sodalites.

365

Estimating the thermodynamic stability of pertechnetate sodalite is a key component in

366

evaluating the long-term stability; therefore, the heat capacity and enthalpy of formation were

367

measured for perrhenate sodalite and these results are discussed next. The heat capacity data

368

between 2 and 300 K were fit and used to calculate the thermodynamic functions. The standard

369

molar entropy of both perrhenate sodalite and NaReO4 was calculated from the heat capacity

370

measurements using the following equation: T

Sm =

371

∫ 0

C p,m T

dT

(3)

372

as 1,190.77 and 152.43 J/mol•K (Table 2). Recalculating the enthalpy of formation for

373

perrhenate sodalite from nepheline rather than the components results in a ∆Hneph,comp of–3.76 ±

374

1.55 kJ/mol.

375 376 377

Table 2. Drop solution enthalpies and enthalpies of formation of perrhenate sodalite, recalculated for four oxygen basis. Compound ∆Hds, kJ/mol dehydrated ∆Hf,comp, kJ/mol ∆Hf,el, kJ/mol Na8[AlSiO4]6(ReO4)2 215.35 ± 2.02 –136.17 ± 0.70 –2437.45 ± 2.82 Na2O –112.86 ± 0.97b –414.80 ± 0.30 Al2O3 107.45 ± 0.76c –1675.70 ± 1.30 SiO2 39.70 ± 1.00d –910.70 ± 1.00 NaReO4 126.55 ± 0.55 –1036.00 ± 1.00 a All errors reported are 2σ (i.e., 2 standard deviations from the mean). b Average drop solution enthalpy from Fialips et al. 2001, Kiseleva et al. 2001, and Kiseleva et al. 1996. c Drop solution enthalpy of Al2O3, which is an average of the values measured over 5 years in The Peter A. Rock Thermochemistry Laboratory. d Average drop solution enthalpy from Kiseleva et al. 1996, Chai and Navrotsky 1993, and Trofymluk et al. 2005. e The results are calculated for the stoichiometric compound and for the composition, obtained from the microprobe or elemental analysis. 21



Page 22 of 34

378

The enthalpy of formation from components of perrhenate sodalite is slightly more negative

379

than that of the nepheline: -136.17 ± 0.70 and -132.41 ± 1.34 kJ/mol, respectively. Additionally,

380

the enthalpy of formation of the perrhenate sodalite from the NaReO4 and nepheline can be

381

calculated using the drop solution enthalpies and the following reactions:

382

(

6NaAlSiO4 + 2Na ReO4 ↔ Na8  AlSiO4  ReO4 6

)

2

(4)

383

This results in an enthalpy of reaction of -22.57 ± 9.03 kJ/mol. Recalculated on a 4-oxygen basis

384

(as used for nepheline), the reaction is

385

1 1 NaAlSiO4 + Na ReO4 ↔ Na8  AlSiO4  ReO4 6 3 6

(

)

2

(5)

386

and the drop solution enthalpy is -3.76 ± 1.51 kJ/mol. Thus, the incorporation of NaReO4 into the

387

nepheline structure is slightly exothermic (e.g., stabilizing).

388

The standard entropies of the three compounds were used to calculate the entropy of

389

formation, according to reaction 5 as 23.30 J/mol•K (recalculated to a 4-oxygen basis). The

390

Gibbs Free Energy of formation at 298.15 K was determined to be -10.71 kJ/mol.

391

The data discussed in the previous sections illustrate that TcO4- can be incorporated into the

392

sodalite structure; however, to evaluate the environmental stability of pertechnetate sodalite

393

requires an estimate of the ∆Hf and ∆Gf. To determine the ∆Hf and ∆Gf for pertechnetate

394

sodalite, we use an approach that relates the ionic potential (i.e., ratio of charge to anion radius)

395

with the ∆Hf and ∆Gf for oxyanion-bearing aluminosilicate sodalites. The ∆Hf, ∆Gf, ∆Sf,

396

thermodynamic cycles, ionic radius, and ionic potentials used to develop the estimates are

397

provided in Tables SI10 – SI12.

398

Fig. 7 shows a plot of ∆Hf and ∆Gf as a function of ionic potential for feldspathoids phases.

399

The ionic potential is 0.397 Å-1 for Na8[AlSiO4]6(TcO4)2.00 and resulted in ∆Hf = -815.92 ± 14.20 22


Page 23 of 34


400

kJ/mol at 298 K. This value is similar to ∆Hf = -814.02 ± 10.68 kJ/mol at 298 K measured for

401

Na8[AlSiO4]6(ReO4)2.00. The error in the ∆Hf values for Na8[AlSiO4]6(TcO4)2.00 value is from the

402

errors of the slope and the intercept of the linear fit, which depends on the two standard

403

deviations of the experimental ∆Hf for the anion containing feldspathoids.

404

405

406

Fig. 7. Enthalpy (a) and Gibbs free energy (b) of formation as a function of ionic potential. The

407

line represents a linear regression to the data. The equations of the lines for ∆Hf,comp and ∆Gf,comp

408

are provided in each plot.

409

All Gibbs energies of formation from components are calculated using the standard equation

410

∆Gf,comp = ∆Hf,comp – 298•∆Sf,comp. Based on the ionic potential x = 0.397 Å-1, the Gibbs energy

411

of formation from components at 298 K of the pertechnetate sodalite will be -879.93 ± 10.80

412

kJ/mol (Fig. 7). This value is also similar to that of Na8[AlSiO4]6(ReO4)2.00 (-878.82 ± 10.68

413

kJ/mol). Although the entropy of the Na8[AlSiO4]6(TcO4)2.00 is expected to be similar to that of

414

the Na8[AlSiO4]6(ReO4)2.00 given the similarity in structure, it was not used to calculate the

415

Gibbs energy of formation. The Gibbs free energy of formation value for Na8[AlSiO4]6(TcO4)2.00 23



Page 24 of 34

416

was estimated from the fit of the four Gibbs energies of formation of the anion-based sodium

417

aluminosilicates. It is also important to note that the entropy of formation for nitrate cancrinite

418

was estimated to be ~1,000 J/mol•K, which is similar to the low temperature heat capacity values

419

measured for nosean, Na8[AlSiO4]6SO4, carbonate cancrinite, Na8[AlSiO4]6CO3, and

420

Na8[AlSiO4]6(ReO4)2.00. Lastly, the difference in both enthalpies and entropies of formation

421

originates from the sodium salt values. Because the ReO4- anion has a smaller ionic potential,

422

whereas the other compounds used in the analysis are higher than TcO4- (see Table SI12), the

423

existing data bracket the TcO4- anion, thus this ∆Hf and ∆Gf estimation approach represents an

424

interpolation rather than an extrapolation.

425

In closing, these results conclusively show that both the ReO4- and TcO4- anion are

426

incorporated into the sodalite β-cage. Furthermore, the thermochemical stability is similar for the

427

two solids. On the basis of the present work, we can say that sodalite minerals and more

428

generally micro- and mesoporous materials offer a potentially viable immobilization option for

429

the treatment of complex reprocessed nuclear waste streams that contain 99Tc.

430

Environmental Implications. At former nuclear weapons production sites, such as the

431

Hanford site, technetium represents one of the most problematic contaminants to treat because of

432

its complex chemistry in tank waste, its volatility at the high temperatures required for

433

vitrification, and its high mobility in subsurface systems.57 Currently, a large inventory of

434

technetium is being stored in high-level tank waste or present in subsurface systems as a result of

435

intentional and unintentional discharges. Because high-level tank waste streams contain anions,

436

such as NO3- and NO2-

437

pretreatment process that destroys NO3- or NO2- and concentrates TcO4- may be required prior to

37-38

, which can out compete with TcO4- for the sodalite β-cage, a

24


Page 25 of 34


438

immobilizing TcO4- in a sodalite waste form. Pretreatment options include the application of the

439

Fluidized Bed Steam Reformer Technology12 which directly destroys NO3- and NO2-, or the

440

existing vitrification facilities. For example, the off-gas liquid waste stream downstream of the

441

vitrification melter in the low-activity waste portion of the Hanford Waste Treatment and

442

Immobilization Plant will be enriched in TcO4- and other volatile anions (e.g., SO42-)57, and offer

443

an opportunity to immobilize TcO4- into a sodalite waste form. Additionally, at the Hanford site

444

intentional and unintentional discharges of alkaline tank solutions to the subsurface may have

445

resulted in the formation of pertechnetate-bearing feldspathoid phases. Previous investigations

446

demonstrated that when simulated tank waste reacts with Hanford sediments, a range of

447

feldpathoid phases form including sodalite.28,58 This study provides the data needed to identify

448

the chemical conditions required to maximize TcO4- incorporation into sodalite as well as the

449

ability to predict the long-term stability of this phase in environmental systems.

450

451 452

ASSOCIATED CONTENT Supporting Information

453

The Supporting Information is available free of charge on the ACS Publications website.

454

Details of materials synthesis and characterization (e.g., chemical composition, particle size,

455

and surface area), specifics on the XAFS and EXAFS spectra analysis, supplemental STEM and

456

TEM information, AFM topographic images and height profiles, and thermochemistry details,

457

and list of ionic radii and ionic potentials used for oxyanions.

458

AUTHOR INFORMATION

459

Corresponding Author 25



Page 26 of 34

460

*Corresponding Author: [email protected], Phone: (865) 574-9968, Fax: (865) 576-8646

461

Author Contributions

462

EMP and KL are co-first authors and contributed equally to this study, EMP conceived and

463

organized the research study; DM, EMP, and CMJ synthesized the samples tested; KL, LW,

464

BW, and AN collected and analyzed the thermochemistry data; WWL, JF, and EMP collected,

465

analyzed, and interpreted the x-ray absorption data; EMP, AH, and CR collected, analyzed, and

466

interpreted the neutron powder diffraction data; EMP, DL, and JE collected, analyzed, and

467

interpreted the STEM and QSTEM results; and JE and EMP collected and analyzed the AFM

468

results. The manuscript was written through contributions of all authors. All authors have given

469

approval to the final version of the manuscript.

470

Funding Sources

471

Support was provided by the Subsurface Biogeochemical Research Program under the US

472

Department of Energy (DOE) Office of Biological and Environmental Research, Climate and

473

Environmental Sciences Division. Portions of this research were supported by Heavy Element

474

Chemistry Program under the Office of Basic Energy Sciences (BES) Chemical Sciences,

475

Biosciences and Geosciences Divisions and the Tank Waste Management Technology

476

Development Program under the Office of Environmental Management.

477

ACKNOWLEDGMENT

478

The powder neutron diffraction data was collected on POWGEN (BL-11A) neutron powder

479

diffractometer at Oak Ridge National Laboratory (ORNL) Spallation Neutron Source (SNS)

480

under proposal numbers IPTS 5857 and 7810. The XAFS data was collected on beam line 20-ID-

481

B at the Advanced Photon Source (APS) at Argonne National Laboratory (ANL) under proposal 26


Page 27 of 34


482

number GUP-24070, National Synchrotron Light Source (NSLS) at Brookhaven National

483

Laboratory (BNL) beam line X27A, and at the the Stanford Synchrotron Radiation Lightsource

484

(SSRL). Use of the NSLS, BNL, was supported by the US Department of Energy (DOE), Office

485

of Science, Office of Basic Energy Sciences (BES) under Contract No. DE-AC02-98CH10886.

486

Use of the SSRL, SLAC National Accelerator Laboratory, is supported by the DOE, Office of

487

Science, BES under Contract No. DE-AC02-76SF00515. A portion of this research used

488

resources of the APS, a DOE Office of Science User Facility operated for the DOE Office of

489

Science by ANL under Contract No. DE-AC02-06CH11357. Portions of this work were

490

performed at Lawrence Berkeley National Laboratory under Contract No. DE-AC02-

491

05CH11231. TA portion of this research was performed at ORNL’s SNS was sponsored by the

492

Scientific User Facilities Division, BES, DOE. The ultra STEM imaging was conducted at the

493

Center for Nanophase Material Sciences, which is a DOE Office of Science User Facility. ORNL

494

is managed by UT-Battelle, LLC, for DOE under contract DE-AC05-00OR22725.

495

27



496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548

Page 28 of 34

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23. Weller, M.; Wong, G. Intracage reactions in sodalites. Journal of Chemical Society, Dalton Transactions 1990, 593–597. 24. Weller, M. Where zeolites and oxides merge: Semi-condensed tetrahedral frameworks. Journal of Chemical Society, Dalton Transactions 2000, (23), 4227–4240. 25. Trill, H. Sodalite Solid Solution System. Synthesis, Topotactic Transformations, and Investigation of Framewok-Guest and Guest-Guest Interactions. Westfalische Wilhelms Universitat, Munster, 2002. 26. Trill, H.; Eckert, H.; Srdanov, V. Topotactic transformations of sodalite cages: Synthesis and NMR study of mixed salt-free and salt-bearing sodalites. Journal of the American Chemical Society 2002, 124, 8361–8370. 27. Trill, H.; Eckert, H.; Srdanov, V. Mixed halide sodalite solid solution system. Hydrothermal synthesis and structural characterization by solid state NMR. J. Phys. Chem. B 2003, 107, 8779–8788. 28. Rivera, N.; Choi, S.; Strepka, C.; Mueller, K.; Perdrial, N.; Chorover, J.; O'Day, P. A. Cesium and strontium incorporation into zeolite-type phases during homogeneous nucleation from caustic solutions. American Mineralogist 2011, 96, 1809-1820. 29. Mattigod, S. V.; McGrail, B. P.; McCready, D. E.; Wang, L.; Parker, K. E.; Young, J. S. Synthesis and structure of perrhenate sodalite. Microporous and Mesoporous Materials 2006, 91 (1-3), 139-144. 30. McCready, D. E.; Mattigod, S. V.; Young, J. S.; McGrail, B. P. X-ray powder diffraction data for Na8(AlSiO4)6(ReO4)2. International Center for Diffraction Data: Advances in X-ray Analysis 2004, 47, 297-302. 31. Brenchley, M. E.; Weller, M. T. Synthesis and Structruer of M8[AlSiO4]6 (XO4)2, M = Na, Li, K; X = Cl, Mn Sodalites. Zeolites 1994, 14, 1994. 32. Moyer, B. A.; Bonnesen, P. V., Physical Factors in Anion Separations. In Supramolecular Chemistry of Anions; Bianchi, A.; Bowman-James, K.; Garcia-Espana, E., Eds.; Wiley-VCH: New York, 1997; pp 1-44. 33. Marcus, Y. Ionic-radii in aqueous-solutions. Chemical Reviews 1988, 88, 1475-1498. 34. Marcus, Y. Thermodynamics of solvation of ions. Part 5 - Gibbs free energy of hydration t 298. Journal of the Chemical Society Faraday Transactions 1991, 87, 2995-2999. 35. Lukens, W. Dissimilar behavior of technetium and rhenium in borosilicate waste glass as determined by xray absorption spectroscopy. Chemical Material 2007, 19, 559. 36. Wakoff, B.; Nagy, K. L. Perrhenate uptake by iron and aluminum oxyhydroxides: an analogue for pertechnetate incorporation in Hanford waste tank sludges. Environmental Science and Technology 2004, 38 (6), 1765-1771. 37. Dickson, J. O.; Harsh, J. B.; Flury, M.; Lukens, W. W.; Pierce, E. M. Competitive Incorporation of Perrhenate and Nitrate in Sodalite. Environmental Science and Technology 2014, 48, 12851-12857. 38. Dickson, J. O.; Harsh, J. B.; Lukens, W. W.; Pierce, E. M. Perrhenate incorporation into binary mixed sodalites: The role of anion size and implications for technetium-99 sequestration. Chemical Geology 2015, 395, 138-143. 39. Dickson, J. O.; Harsh, J. B.; Flury, M.; Pierce, E. M. Immobilization and exchange of perrhenate in sodalite and cancrinite. Microporous and Mesoporous Materials 2015, 214, 115-120. 40. Ravel, B. ATHENA and ARTEMIS interactie graphical data analysis using IFEFFIT. Physica Scripta 2005, T115, 1007-1010. 41. Larson, A.; Von Dreele, R. General Structure Analysis System (GSAS). LAUR 86-748; Los Alamos National Laboratory: Los Alamos, New Mexico, 1994. 42. Toby, B. EXPGUI, a graphical user interface for GSAS. Journal of Applied Crystallography 2001, 34, 210–213. 43. Navrotsky, A. Progress and New Directions in High-Temperature Calorimetry. Phys. Chem. Miner. 1977, 2 (1-2), 89-104. 44. Navrotsky, A. Progress and new directions in high temperature calorimetry revisited. Phys. Chem. Miner. 1997, 24 (3), 222-241. 45. Robie, R.; Hemingway, B. Thermodynamic properties of minerals and related substances at 298.15 K and 1 bar (105 pascals) pressure and at higher temperatures. US Geological Survey Bulletin: Denver, Colorado, 1995; p 461. 46. Bale, C. W.; Belisle, E.; Chartrand, P.; Decterov, S. A.; Eriksson, G.; Hack, K.; Jung, I.-H.; Kang, Y.-B.; Melancon, J.; Pelton, A. D.; Robelin, C.; Petersen, S. FactSage thermochemical software and databases - recent developments. Calphad 2009, 33 (2), 295-311. 47. Atzesdorfer, A.; Range, K. J. Sodium Metaperrhenate, NaReO4 - High Pressure Synthesis of SingleCrystals and Structure Refinement. Z.Naturforsch.(B) 1995, 50 (9), 1417-1418.

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Table of Contents:

627 628

Structure and Thermochemistry of Perrhenate Sodalite and Mixed Guest Perrhenate/Pertechnetate Sodalite................................................................................................... 1

629

INTRODUCTION ...................................................................................................................... 2

630

EXPERIMENTAL ...................................................................................................................... 6

631

RESULTS AND DISCUSSION ................................................................................................. 9

632

ASSOCIATED CONTENT ...................................................................................................... 25

633

AUTHOR INFORMATION ..................................................................................................... 25

634

ACKNOWLEDGMENT........................................................................................................... 26

635

REFERENCES ......................................................................................................................... 28

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638

List of Figures:

639 640 641 642

Fig. 1. Extended x-ray absorption fine structure of perrhenate sodalite, Na8[AlSiO4]6(ReO4)2. The EXAFS data and fit are depicted as a solid gray line and black circles, respectively. Fit range: 2 < k < 11 (a); 0.8 < R < 2.0 (b); the number of independent points was 8.6, and the number of parameters was 4.Error! Bookmark not defined.

643 644 645 646

Fig. 2. Rietveld refinement profiles of powder neutron diffraction data for perrhenate sodalite, Na8[AlSiO4]6(ReO4)2. The neutron diffraction data were collected using two different center wavelengths to access different d-spacing ranges (d-spacing from 0.5 to 3.0Å on [a] and d-spacing from 1.1 to 6.2Å [b]). ......................................................................... 12

647 648 649 650

Fig. 3. Aberration-corrected HAADF STEM images showing atomic columns in the perrhenate sodalite along the [111] crystal face. Image (a) wider field of view, (b) is the raw image of scan area, and (c) is the raw image after being cropped and processed using a Gaussian blur and histogram/gamma adjustment. ..................................................................... 16

651 652 653 654

Fig. 4. Output images from Quantitative STEM simulations of perrhenate sodalite along the [111] crystal face for three different sample thicknesss; (a) = 20 nm, (b) = 60 nm, and (d) = 147 nm, with Poisson noise included in each image. For comparison, Poisson noise was both excluded and included in the 147 nm thick images, (c) and (d) respectively................ 17

655 656 657 658

Fig. 5. Tc K-edge XANES (a) and EXAFS (b, c) spectra of the Na8[AlSiO4]6(ReO4)1.48(TcO4)0.52 sample. The EXAFS data and fit are depicted as a solid grey line and black circles, respectively. Fit range: 2 < k < 14; 1.0 < R < 3.0; the number of independent points was 16.9, the number of parameters was 4, and R factor = 0.003. ........... 19

659 660 661 662

Fig. 6. Structural refinements for powder x-ray powder diffraction of mixed guest perrhenate/pertechnetate sodalite, Na8[AlSiO4]6(ReO4)1.48(TcO4)0.52 (a). A comparison of the pXRD spectra for perrhenate sodalite, Na8[AlSiO4]6(ReO4)2, and Na8[AlSiO4]6(ReO4)1.48(TcO4)0.52 is also provided (b).................................................................. 20

663 664 665

Fig. 7. Enthalpy (a) and Gibbs free energy (b) of formation as a function of ionic potential. The line represents a linear regression to the data. The equations of the lines for ∆Hf,comp and ∆Gf,comp are provided in each plot. ........................................................................... 23

666

667

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668

List of Tables:

669 670 671

Table 1. Refinement details and crystal data for perrhenate sodalite, Na8[AlSiO4]6(ReO4)2, determined by neutron and x-ray powder diffraction. Refinement details and crystal data determined from x-ray powder diffraction data collected on mixed perrhenate/pertechnetate sodalite, Na8[AlSiO4]6(ReO4)2-x(TcO4)x. ..................... 13

672 673

Table 2. Drop solution enthalpies and enthalpies of formation of perrhenate sodalite, recalculated for four oxygen basis. ............................................................................................................................................................... 21

674

675

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TABLE OF CONTENT ART

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Structure and Thermochemistry of Perrhenate ... - ACS Publications

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