Mechanisms of Se(IV) Co-precipitation with Ferrihydrite at Acidic and

Subscriber access provided by UNIVERSITY OF TOLEDO LIBRARIES

Remediation and Control Technologies

Mechanisms of Se(IV) co-precipitation with ferrihydrite at acidic and alkaline conditions, and its behavior during aging Paul Clarence M. Francisco, Tsutomu Sato, Tsubasa Otake, Takeshi Kasama, Shinichi Suzuki, Hideaki Shiwaku, and Tsuyoshi Yaita Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b00462 • Publication Date (Web): 28 Mar 2018 Downloaded from http://pubs.acs.org on March 28, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32

Environmental Science & Technology

1

Mechanisms of Se(IV) co-precipitation with ferrihydrite at acidic and alkaline

2

conditions, and its behavior during aging

3

Paul Clarence M. Francisco †§*, Tsutomu Sato †*, Tsubasa Otake †, Takeshi Kasama ‡, Shinichi

4

Suzuki ‖, Hideaki Shiwaku ‖, Tsuyoshi Yaita ‖

5

† Environmental Geology Laboratory, Graduate School of Engineering, Hokkaido University, Kita 13

6

Nishi 8, Sapporo, Hokkaido 060-8628, JAPAN

7

‡ Center for Electron Nanoscopy, Technical University of Denmark, DK-2800 Kongens Lyngby,

8

DENMARK

9

‖ Actinide Chemistry Group, Materials Sciences Research Center, Japan Atomic Energy Agency, 2-4

10

Shirakata, Tokai-mura, Ibaraki 319-1195, JAPAN

11

§ Present Address: Radionuclide Migration Research Group, Nuclear Fuel Cycle Engineering

12

Laboratories, Japan Atomic Energy Agency, 4-33 Muramatsu, Tokai-mura, Ibaraki 319-1194, JAPAN

13

([email protected])

14

*Correspondence: [email protected]; [email protected]

15 16 17 18 19 20 21 22 23 24

Contact Information: P.C.M. Francisco: [email protected]; [email protected] T. Sato: [email protected] T. Otake: [email protected] T. Kasama: [email protected] S. Suzuki: [email protected] H. Shiwaku: [email protected] T. Yaita: [email protected]

25 26 27 28 29 30 31 1 ACS Paragon Plus Environment


32

Page 2 of 32

ABSTRACT

33

34 35

Understanding the form of Se(IV) co-precipitated with ferrihydrite, and its subsequent behavior

36

during phase transformation, is critical to predicting its long-term fate in a range of natural and

37

engineered settings. In this work, Se(IV)-ferrihydrite co-precipitates formed at different pH were

38

characterized with chemical extraction, transmission electron microscopy (TEM) and x-ray absorption

39

spectroscopy (XAS) to determine how Se(IV) is associated with ferrihydrite. Results show that despite

40

efficient removal, the mode and stability of Se(IV) retention in the co-precipitates varied with pH. At pH

41

5, Se(IV) was removed dominantly as a ferric selenite-like phase intimately associated with ferrihydrite,

42

while at pH 10, it was mostly present as a surface species on ferrihydrite. Similarly, the behavior of

43

Se(IV) and the extent of its retention during phase transformation varied with pH. At pH 5, Se(IV)

44

remained completely associated with the solid phase despite phase change, whereas it was partially

45

released back into solution at pH 10. Regardless of this difference in behavior, TEM and XAS results 2 ACS Paragon Plus Environment

Page 3 of 32


46

show that Se(IV) was retained within the crystalline post-aging products, possibly occluded in nanopore

47

and defect structures. These results demonstrate a potential long-term immobilization pathway for Se(IV)

48

even after phase transformation. This work presents one of the first direct insights on Se(IV) co-

49

precipitation, and its behavior in response to iron phase transformations.

50 51

INTRODUCTION

52

Selenium (Se) is a naturally occurring element that is both essential and hazardous for biological

53

organisms (1). Se exists in four main oxidation states (-II, 0, IV, and VI). Of these, Se(IV) and Se(VI)

54

are the most mobile, with Se(IV) being the more toxic (2). While commonly found as a trace element in

55

most rocks, it can be released into the wider environment by chemical weathering (3) or by anthropogenic

56

activities such as mining, excavation, mineral processing, and energy generation (4-6), which produce

57

acidic wastewaters and process solutions. In addition, in the geologic disposal of high-level radioactive

58

wastes, 79Se is one of the long-lived fission products that can be released from vitrified waste (7) or spent

59

fuels (8). The development of partially oxidizing conditions, arising from microbial activity or

60

groundwater penetration into the repository (9, 10), could result in the release of oxidized Se species. Se

61

thus presents environmental challenges in a diverse range of settings.

62

Se(IV) can be sequestered from aqueous solutions and immobilized by adsorption on the surfaces

63

of iron phases such as magnetite, maghemite, hematite, and goethite (11-19). However, in many natural

64

and engineered environments, more dynamic processes, such as co-precipitation are also likely to occur.

65

Co-precipitation proceeds when aqueous Se(IV) species are present in the same solution during the

66

hydrolysis of Fe(II) and Fe(III) ions, which result in the precipitation of poorly crystalline iron phases

67

such as ferrihydrite (20). Previous studies on contaminants such as Ni(II), Cr(III) and As(V), have

68

demonstrated that co-precipitation with Fe(III) was found to be more effective at sequestering these

69

elements from solutions than adsorption on pre-existing iron phases over a wide range of pH conditions 3 ACS Paragon Plus Environment


Page 4 of 32

70

(21-23). In the case of Se(IV), co-precipitation with Fe(III) has been used to sequester Se(IV) from acidic

71

wastewaters (4). Despite its potential as an effective immobilization pathway for Se(IV), there is little

72

information on the form of Se(IV) in Fe(III) co-precipitates. For example, it is uncertain whether Se(IV)

73

is associated with ferrihydrite co-precipitates as a surface complex, is structurally incorporated into

74

ferrihydrite or forms discrete Se-bearing precipitates. Depending on its association, the long-term

75

behavior of sequestered Se(IV) may become more or less sensitive to factors such as changes in solution

76

chemistry or the presence of strongly competitive species. Recent co-precipitation studies at neutral

77

conditions (pH ~7.5) show that Se(IV,VI) exist as sorption complexes on ferrihydrite surfaces (24). With

78

the wide operative pH range of co-precipitation, it is unclear if this sequestration mechanism operates

79

across different pH conditions.

80

Another issue that is directly relevant in predicting the long-term fate of Se(IV) is its behavior

81

during thermal aging of precipitates and phase transformation. Sludge resulting from co-precipitation are

82

typically aged at elevated temperatures (45-200°C) to reduce waste volume (25, 26). Similarly, increased

83

temperatures (45-100°C) due to the geothermal gradient and radioactive decay may induce a similar

84

process in geological disposal environments for radioactive wastes (27). Rapidly precipitated phases such

85

as ferrihydrite are metastable and transform into thermodynamically stable phases during aging over a

86

broad range of conditions (28).This conversion, which involves structural changes, can modify the

87

retention of contaminants associated with it. In studies on As(V) co-precipitated with ferrihydrite, various

88

behaviors during aging have been reported, such as the expulsion of structurally incompatible As(V) (25,

89

29), occlusion in defect sites (30) or the precipitation of ferric arsenate phases (31). Others, such as Sb(V)

90

(32), have been shown to be crystallographically incorporated in the transformation products such as

91

goethite and hematite. These studies show that aging of the precipitates may either enhance or limit the

92

long-term mobility of contaminants. At present, there is limited information on whether Se(IV) is

93

retained or remobilized during aging of co-precipitates, what processes control its behavior, and the 4 ACS Paragon Plus Environment

Page 5 of 32


94

extent to which it is retained/remobilized. Recent studies at neutral conditions show that Se(IV, VI)

95

oxyanions are retained as adsorbed species occluded within hematite (24). It is, however, not clear

96

whether a similar retention mechanism operates under different pH conditions.

97

In this work, Se(IV) was co-precipitated with ferrihydrite at pH 5 and 10 and the co-precipitates

98

were aged for up to 190 hours at 80°C. The objectives of this work are (1) to obtain fundamental

99

information on the partitioning and speciation of Se(IV) co-precipitated with ferrihydrite, (2) to

100

understand its behavior during aging of the co-precipitates and (3) to identify the underlying processes

101

governing its behavior. By observing the changes in the concentration of Se(IV) in solution, we

102

determined whether co-precipitated Se(IV) is released or retained in the solid phase during aging. Using

103

a combination of chemical extraction, transmission electron microscopy and X-ray absorption

104

spectroscopy, we investigated the form of Se(IV) in the initial co-precipitates as well as how it changes

105

after aging. The information obtained in this study have broad implications on the behavior of Se(IV) in

106

both natural (e.g. soils and contaminated streams) and engineered environments (e.g. radionuclide

107

transport in geological disposal of radioactive wastes, wastewater treatment and management).

108 109

MATERIALS AND METHODS

110

Co-precipitation and Transformation Experiments

111

Co-precipitation of Se(IV) and Fe(III)-hydroxides/oxides was carried out by preparing Fe(III)

112

solution by dissolving reagent grade Fe(NO3)3•9H2O (Kanto, 99%) and mixing this solution with selenite

113

solution prepared by dissolving Na2SeO3 (Kanto, 96%) to achieve concentrations of 5 x 10-2 M for Fe

114

(III) and ~6.3 x 10-4 M (50 ppm) for Se(IV). In this study, the concentration of Se(IV) is higher than

115

typically observed in natural waters (~0.2 ppb; 1), or waste and process solutions (~12-33 ppm; 5) to

116

facilitate the detection of Se in the samples. All solutions were prepared using ultrapure water (18

117

MΩ•cm) that was first boiled and equilibrated with an N2 atmosphere for ~1 week to remove dissolved 5 ACS Paragon Plus Environment


Page 6 of 32

118

O2. The dissolved O2 concentration was less than 0.1 ppm. The solutions (initial pH: ~1.85 at 24°C) were

119

then titrated with NaOH (Kanto, 97%) to increase the pH to 5 and 10. During base titration, the initially

120

clear, orange-colored solutions changed into dark brown-colored slurries, indicating the formation of

121

poorly crystalline iron (oxyhydro)xides. The pH of the slurries was allowed to stabilize for about 30

122

minutes under constant stirring before the slurries were transferred into sealed, metal-jacketed, PTFE-

123

lined bombs (100 mL; Parr). The slurries were aged in an oven at 80°C for up to 190 hours to promote

124

transformation to stable phases. This temperature is well within the range of temperatures typically used

125

in sludge heat treatments and the expected temperatures in radioactive waste disposal. Except for this

126

aging step, all the experiments were conducted inside a glove box with N2 atmosphere.

127

Samples in separate containers were taken at specified time intervals. Solid and liquid samples

128

were then taken after centrifugation (1650 g, 40 minutes). Supernatants were passed through 0.20 μm

129

PTFE membrane filters and acidified with ultrapure HNO3 (Kanto, 60%) for solution analyses. Solids

130

were rapidly washed with deionized water to remove excess dissolved species and freeze-dried under

131

vacuum for at least 24 hours. The washing solutions were also collected for solution analyses.

132 133

Sample Analyses and Characterization

134

The procedures for the analyses of solid and liquid samples are briefly described here. Details for

135

all analyses and data processing procedures are given in the Supporting Information. Se concentrations

136

in solution were determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES;

137

Shimadzu ICPE-9000). The amount of Se taken up or retained by the solids was determined from the

138

difference between the initial concentration of the initial liquid and the concentrations after co-

139

precipitation/crystallization. To check the oxidation state of Se species in solution, non-acidified solution

140

fractions were analyzed using the hydride-vapor generation method coupled with ICP-AES (33).

6 ACS Paragon Plus Environment

Page 7 of 32


141

Solid phase compositions were determined using X-ray diffraction (XRD; Rigaku RINT2000

142

with Cu target). The proportion of crystalline phases was estimated by Rietveld refinement of XRD data

143

using the SIROQUANT software (34). The proportion of amorphous-like or poorly crystalline phases

144

was estimated from the Rietveld refinement based on the internal standard method (35).

145

Particle morphologies were examined using transmission electron microscopy (TEM; FEI Titan

146

80-300ST, 120 kV). Freeze-dried powders were directly mounted onto Cu TEM grids for observation.

147

Elemental distribution was analyzed in scanning TEM mode by high-angle annular dark-field (HAADF)

148

imaging and energy dispersive X-ray spectroscopy (EDS) with an X-MaxN silicon drift detector (Oxford

149

Instruments) TEM attachment. Elemental maps were processed by principal component analysis and

150

pixel-by-pixel background subtraction (36). Minimally rinsed samples loaded with ~3.2 x 10-3 M (250

151

ppm) Se(IV) were used for (S)TEM characterization.

152

Se partitioning was determined by chemical extraction experiments on finely powdered (95%) (Table S2). TEM observation shows that the hematite particles assume a spherical morphology

175

(~100 nm in diameter), with each particle consisting of smaller (~5 nm) hematite nanocrystals oriented

176

along the same crystallographic direction (Fig. 1B). SAED patterns (Fig. S2) show that each spherical

177

aggregate behaves as a single crystal. The morphology of the hematite particles strongly suggests that

178

phase transformation involved mainly solid-state processes, dominated by ferrihydrite particle

179

aggregation and solid-state recrystallization followed by growth via oriented attachment (45, 46). These

180

mechanisms are generally favored at mildly acidic (pH 4-5) to circum-neutral conditions (47). In addition

181

to hematite, small amounts ( 7, initially formed

341

ferric selenite likely dissolved as pH increased to more alkaline conditions. This may have liberated

342

soluble Se(IV) species that can adsorb on the surfaces of the more dominant ferrihydrite particles. This

343

behavior is analogous to that observed for As(V), which was found to precipitate as ferric arsenate at pH

344

3-5, while it exists mainly as a surface complex at pH 8 (23, 58). These results thus imply that beyond a

345

certain pH (i.e. the maximum pH at which ferric selenite is stable), Se(IV) co-precipitation mechanism

346

shifts from dominantly ferric selenite precipitation to dominantly adsorption on ferrihydrite.

347

Although this study was carried out at relatively higher Se(IV) loadings, it is conceivable that the

348

mechanisms described are valid at lower concentrations. Based on the thermodynamic data given by Rai

349

et al. (57), ferric selenite may be saturated in solutions at concentrations representative of waste water or

350

process effluents (~12-33 mg/L; 5, Table S5). Moreover, solution properties at ferrihydrite surfaces may

351

also produce localized supersaturation effects that may promote ferric selenite precipitation even if the

352

bulk solution is nominally undersaturated with respect to ferric selenite. This was demonstrated in the

353

study of Duc et al. (16) and Missana et al. (17), which showed ferric selenite precipitation on hematite 15 ACS Paragon Plus Environment


Page 16 of 32

354

and magnetite surfaces, respectively, at acidic conditions even at very low Se(IV) concentrations (~10-10

355

to ~10-4 M).

356 357

Se(IV) Retention Mechanisms During Aging

358

The results of the chemical extraction experiments and STEM-EDS mapping that Se(IV) is

359

retained within the crystalline aging products. It is not clear, however, whether it is incorporated in the

360

post-aging solids. One possible mechanism for retention is via substitution of Se(IV) for Fe(III). A similar

361

mechanism has been suggested for Sb(V) (32), which was incorporated in goethite and hematite during

362

ferrihydrite transformation at pH ~7. Results of the EXAFS, however, explicitly rule out this possibility

363

since Se(IV) retains its pyramidal geometry, making it incompatible with crystallographic sites in either

364

goethite or hematite, both of which are characterized by Fe(III) in octahedral coordination (28).

365

Tetrahedral vacancies in hematite, which arise from the hexagonal closest packing of octahedral units,

366

have been shown to be capable of accommodating foreign species such as P(V) (59). Incorporation in

367

such sites would require the Se(IV) to share edges with multiple surrounding Fe(III) octahedra, resulting

368

in a dominant configuration consisting of ~3 Se-Fe linkages at average distances of ~2.8-2.9 Å. This is,

369

however, unlikely since the edge-sharing linkage in the pH 5 solids has only ~0.9 Fe atoms, while it is

370

absent in the pH 10 solids. Furthermore, incorporation of a small ion in such sites would likely result in

371

the distortion of the hematite lattice. Comparison of the calculated lattice parameters of hematite in this

372

study with published values, however, shows no evidence of lattice distortion (Table S4), which further

373

rules out crystallographic incorporation.

374

It is more likely that Se(IV) was occluded in defect or nanopore structures, where it may attach

375

to exposed crystal terminations of multiple surrounding crystals. This may explain the high number of

376

Fe neighbors, while not being located in a crystallographic site. Such features are known to form along

377

nanocrystal grain boundaries during oriented attachment (60) as well as within nanocrystals themselves 16 ACS Paragon Plus Environment

Page 17 of 32


378

(61), as a result of particle aggregation. The presence of such features is evident in the STEM-HAADF

379

images, which show the hematite particles having "grainy" and rough characteristics. At pH 5, in which

380

transformation was dominated by aggregation and solid-state transformation processes, the ferric

381

selenite-like phase that were initially associated with the ferrihydrite may have been trapped between

382

particles as they aggregated during oriented attachment and subsequently occluded during solid-state

383

transformation to hematite. Moreover, given that there was limited dissolution, there was also limited

384

release of Se(IV) into the solution, such that Se(IV) was effectively retained in the solid phase. Following

385

occlusion, there is no evidence of localized Se(IV) accumulation within the hematite crystals (Fig. 4),

386

indicating the disappearance of the ferric selenite-like phase that initially existed in the co-precipitates.

387

This aggregation-based retention mechanism into defect structures has been proposed for As(V) (30),

388

which, like Se(IV), does not assume an octahedral coordination that is structurally compatible with

389

crystalline iron (oxyhydr)oxides.

390

Aging at pH 10 involves likely two simultaneous processes: Se(IV) release and retention. As a

391

surface species, Se(IV) is sensitive to the solubility of its substrate. Due to increased ferrihydrite

392

solubility at high pH, the partial dissolution of ferrihydrite resulted in a net release of surface-bound

393

Se(IV). At the same time, some Se(IV) may have been occluded during the initial aggregation of

394

undissolved ferrihydrite particles and subsequent transformation to hematite nuclei. Close to the surface

395

of ferrihydrite, the concentration of Se(IV) is likely higher than in the bulk solution, allowing at least a

396

fraction of the released Se(IV) to be occluded into the hematite, as well as goethite, crystals by being

397

adsorbed and trapped on the surfaces of growing crystals during solution-mediated crystal growth. Since

398

Se(IV) adsorption onto crystalline iron (oxyhydr)oxides is not generally favored at high pH, only a

399

fraction of the Se(IV) could be retained via this mechanism, which may explain the lower concentration

400

of Se in hematite crystals from pH 10 compared to those from pH 5. This mechanism is similar to that



Page 18 of 32

401

described for the repartitioning of Pb(II) during crystallization of goethite from ferrihydrite (62). These

402

processes provide a stable retention pathway for Se(IV) at alkaline conditions.

403

It is important to note that ferrihydrite phase transformation is also dependent on the aging

404

temperature. Higher temperatures enhance hematite crystallization while lower temperatures tend to

405

favor goethite formation (35). Given that the primary host for Se(IV) in the post-aging products was

406

identified to be hematite, enhanced formation of hematite, brought about by higher aging temperatures,

407

may theoretically lead to increased Se(IV) retention.

408 409

ENVIRONMENTAL SIGNIFICANCE

410

In this work, the partitioning and speciation of Se(IV) co-precipitated with Fe(III) at pH 5 and 10

411

and its behavior during aging at 80°C was examined. The results described above show that although co-

412

precipitation with Fe(III) effectively sequesters Se(IV) from solutions under a broad pH range, the

413

underlying mechanisms by which it is immobilized is different, which may affect the stability of retention.

414

The findings of this work has important implications in understanding the long-term behavior of Se(IV)

415

in a variety of settings. For example, in the treatment of acidic wastewater, co-precipitation with Fe(III)

416

likely results in the precipitation of ferric selenite that is interspersed with more Fe(III) phases like

417

ferrihydrite. As a discrete precipitate, Se(IV) is less likely to be remobilized from the co-precipitates by

418

leaching or by the presence of competitive ligands that could exchange with surface-bound Se(IV), which

419

ensures stable retention of Se(IV). Moreover, understanding the thermodynamic properties of ferric

420

selenite phases may also open up potential ways to optimize the co-precipitation process. During aging

421

of sludges at elevated temperatures, commonly practiced to reduce waste volume (24), Se(IV) remains

422

completely associated with aging products, completely inhibiting its remobilization.

423

Co-precipitation is also one of the major near-field processes expected to regulate radionuclide

424

mobility in radioactive waste disposal environments (27). The development of partially oxidizing 18 ACS Paragon Plus Environment

Page 19 of 32


425

conditions (9, 10), may result in the interaction and co-precipitation of Se(IV) with iron (oxyhydr)oxides

426

such as ferrihydrite. Under alkaline conditions predicted in such environments (pH ~9-10 due to

427

bentonite buffering; 63), Se(IV) originating from nuclear waste may be sequestered by co-precipitation

428

with Fe(III) derived from the surrounding host rock or the corrosion of the steel overpack. In these

429

conditions, surface adsorption on phases like ferrihydrite plays a larger role in the initial immobilization

430

of Se(IV). Surface-bound Se(IV) species are, however, susceptible to remobilization due to changes in

431

the chemistry of the fluids in contact with the precipitates or the presence of ligands that may exchange

432

with Se(IV). Furthermore, phase transformation likely to be induced by heat generated by high-level

433

wastes (27) may influence the retention of Se(IV). In particular, the enhanced dissolution of ferrihydrite

434

at alkaline conditions may result in the partial remobilization of Se(IV). The dependence of Se(IV)

435

release on ferrihydrite dissolution, however, suggests a kinetic control, and implies that Se(IV) release

436

may be retarded by species that inhibit the dissolution of ferrihydrite, such as Si (e.g. 35), which are

437

likely to be present in disposal environments. At the same time, partial retention of Se(IV) may still be

438

achieved via occlusion in hematite. Due to the thermodynamic stability of hematite, Se(IV) is unlikely

439

to be immobilized by phase dissolution or transformation. At conditions in which surface adsorption of

440

oxyanions is limited, occlusion in hematite presents a potentially stable immobilization pathway for

441

Se(IV). Thus, the remobilization and retention of Se(IV) as a result of phase transformation, as well as

442

the role of possible inhibitors, must be taken into account in developing safety cases for waste disposal.

443 444

ACKNOWLEDGEMENTS

445

We acknowledge the Nuclear Safety Research Association, in the framework of “Study on

446

Confidence in Assessment of Evolution of the Near-field of Geological Disposal System over Ultra

447

Long-term (Phase II)” under contract with the Nuclear Waste Management Organization of Japan, for

448

technical and financial support. The synchrotron radiation experiments in this study were performed at 19 ACS Paragon Plus Environment


Page 20 of 32

449

the SPring-8 beam line BL11XU under Proposal Nos. 2015B3504 and 2016A3504 with approval from

450

the Japan Atomic Energy Agency. We acknowledge C. Tabelin and C. Walker for valuable discussions;

451

and S. Dei, K. Kinoshita and T. Kobayashi for experimental assistance. We also thank four anonymous

452

reviewers for their thoughtful reviews and comments, and D. Giammar for his comments and editorial

453

handling.

454 455

SUPPORTING INFORMATION. Detailed sample characterization and data processing procedures;

456

tables showing Se oxidation state in solution, results of Rietveld refinement, EDS analyses of Se in post-

457

aging solids and lattice parameters for crystalline phases observed in the post-aging solids; additional

458

TEM images, XRD and ED profiles, elemental ratio maps, Se K-edge XANES results and solubility

459

diagram for ferric selenite.

460 461 462 463

REFERENCES 1. Lemly, A.D. Aquatic selenium pollution is a global environmental safety issue. Ecotoxicol. Environ. Saf. 2004, 59, 44-56.

464

2. Fernandez, C.M.G.; Palacios, M.A.; Camara, C. Flow-injection and continuous-flow systems for

465

the determination of Se(IV) and Se(VI) by hydride generation atomic absorption spectrometry

466

with on-line prereduction of Se(VI) to Se(IV). Anal. Chim. Acta, 1993, 283, 386-392.

467

3. Ihnat, M. Occurrence and distribution of selenium. CRC Press, Boca Raton, FL., 1989

468

4. Merrill, D.T.; Manzione, M.A.; Parker, D.S.; Petersen, J.J.; Chow, W.; Hobbs, A.O. (1987) Field

469

evaluation of arsenic and selenium removal by iron coprecipitation. Environ. Prog. Sustain

470

Energy 1987, 6, 82-90.


Page 21 of 32


471

5. Adams, D.J.; Pickett, T.M. Microbial and cell-free selenium bioreduction in mining waters. In

472

Environmental Chemistry of Selenium; Frankenberger, Jr., W.T., Engberg, R.A., Eds.; CRC

473

Press: Boca Raton, FL 1998, pp. 479.

474

6. Tabelin, C.B.; Hashimoto, A.; Igarashi, T.; Yoneda, T. Leaching of boron, arsenic and selenium

475

from sedimentary rocks: II. pH dependence, speciation and mechanisms of release. Sci. Total

476

Environ. 2014, 473, 244-253.

477

7. De Canniere, P.; Maes, A.; Williams, S.; Bruggeman, C.; Beauwens, T.; Maes, N.; Cowper, M

478

(2010) Behaviour of Selenium in Boom Clay. SCK•CEN External Report. Belgium.

479

http://publications.sckcen.be/dspace/bitstream/10038/7079/1/er_120.pdf

480

8. Asai, S.; Hanzawa, Y.; Okumura, K.; Shinohara, N.; Inagawa, J.; Hotoku, S.; Suzuki, K.; Kaneko,

481

S. (2012) Determination of 79Se and 135Cs in spent nuclear fuel for inventory estimation of high-

482

level radioactive wastes. J. Nucl. Sci. Technol. 2012, 48 (5), 851-854.

483 484

9. Yoshida, H.; Ohnuki, T.; Naganuma, T. (2007) Microbes in geological disposal system of highlevel radioactive waste in Japan. J. Nucl. Fuel Cycle Environ. 2007, 14 (1), 31-42.

485

10. Iwatsuki, T.; Hagiwara H.; Ohmori, K.; Munemoto, T.; Onoe, H. Hydrochemical disturbances

486

measured in groundwater during the construction and operation of a large-scale underground

487

facility in deep crystalline rock in Japan. Environ. Earth Sci. 2015, 74 (4), 3041-3057.

488 489 490 491 492 493

11. Balistrieri, L.; Chao, T.T. Selenium adsorption by goethite. Soil Sci. Soc. Am. J. 1987, 51 (5), 1145-1151. 12. Balistrieri, L.; Chao, T.T. Adsorption of selenium by amorphous iron oxyhydroxide and manganese-dioxide. Geochim. Cosmochim. Acta 1990, 54 (3), 739-751. 13. Zhang, P.; Sparks, D.L. Kinetics of selenate and selenite adsorption/desorption at the goethite/water interface. Environ. Sci. Technol. 1990, 24, 1848-1856.



494 495

Page 22 of 32

14. Su, C.; Suarez, D.L. Selenate and selenite sorption on iron oxides: An infrared and electrophoretic study. Soil Sci. Soc. Am. J. 2000, 64, 101-111

496

15. Rovira, M.; Gimenez, J.; Martinez, M.; Martinez-Llado, X.; de Pablo, J.; Marti, V.; and Duro, L.

497

Sorption of selenium(IV) and selenium(VI) onto natural iron oxides: Goethite and hematite. J.

498

Hazard. Mater. 2008, 150 (2), 279-284.

499 500

16. Duc, M.; Lefevre, G.; Fedoroff, M. Sorption of selenite ions on hematite. J. Colloid Interface Sci. 2006, 298, 556-563.

501

17. Missana, T.; Alonso, U.; Scheinost, A.C.; Granizo, N.; Garcia-Gutierrez, M. Selenite retention

502

by nanocrystalline magnetite: Role of adsorption, reduction and dissolution/co-precipitation

503

processes. Geochim. Cosmochim. Acta 2009, 73, 6205-6217.

504 505

18. Jordan, N.; Ritter, A.; Schenoist, A.C.; Weiss, S.; Schild, D.; Hubner, R. Selenium(IV) uptake by maghemite (γ-Fe2O3). Environ. Sci. Technol. 2014, 48, 1665-1674.

506

19. Hayes, K.F.; Roe, A.L.; Brown, G.E. Jr.; Hodgson K.O.; Leckie, J.O.; Parks G.A. In situ x-ray

507

absorption study of surface complexes: Selenium oxyanions on α-FeOOH. Science 1987,

508

238(4828), 783-786.

509 510 511 512

20. Cudennec, Y.; and Lecerf, A. The transformation of ferrihydrite into goethite or hematite, revisited. J. Solid State Chem. 2006, 179 (3), 716-722. 21. Crawford, R.J.; Harding, I.H.; Mainwaring, D.E. Adsorption and coprecipitation of single heavy metal ions onto the hydrated oxides of iron and chromium. Langmuir 1993, 9, 3050-3056.

513

22. Charlet, L.; Manceau, A. X-ray absorption spectroscopic study of the sorption of Cr(III) at the

514

oxide water interface. 2. Adsorption, coprecipitation, and surface precipitation on hydrous ferric-

515

oxide. J. Colloid Interface Sci. 1992, 148, 443-470.


Page 23 of 32


516

23. Waychunas, G.A.; Rea, B.A.; Fuller, C.C.; Davis, J.A. Surface chemistry of ferrihydrite: Part 1.

517

EXAFS studies of the geometry of coprecipitated and adsorbed arsenate. Geochim. Cosmochim.

518

Acta 1993, 57, 2251-2269.

519

24. Börsig, N.; Schenoist, A.C.; Shaw, S.; Schild, D.; Neumann, T. Uptake mechanisms of selenium

520

oxyanions during the ferrihydrite-hematite recrystallization. Geochim. Cosmochim. Acta 2017,

521

206, 236-253.

522 523 524 525

25. Paige, C.R.; Snodgrass, W.J. Nicholson, R.V.; Scharer, J.M. The crystallization of arsenatecontaminated iron hydroxide solids at high pH. Water Environ. Res. 1996, 68, 981-987. 26. Neyens, E.; Baeyens, J. A review of thermal sludge pre-treatment processes to improve dewaterability. J. Hazard. Mater. 2003, B98, 51-67.

526

27. JNC (2000) H12: Project to Establish the Scientific and Technical Basis for HLW Disposal in

527

Japan, Supporting Report 2, Repository Design and Engineering Technology. JNC TN1410 2000-

528

003, D38-D42

529 530 531 532 533 534

28. Cornell, R.M.; Schwertmann, U. The Iron Oxides: Structure, Properties, Reactions, Occurrences and Uses, 2nd ed. Wiley-VCH: Weinheim, 2003. 29. Fuller, C.C.; Davis, J.A.; Waychunas, G.A. Surface chemistry of ferrihydrite: Part 2. Kinetics of arsenate adsorption and coprecipitation. Geochim. Cosmochim. Acta 1993, 57, 2271-2282. 30. Ford, R.G. Rates of hydrous ferric oxide crystallization and the influence on coprecipitated arsenate. Environ. Sci. Technol. 2002, 26, 2459-2463.

535

31. Bolanz, R.M.; Wierzbicka-Wieczorek, M.; Caplovicova, M.; Uhlik, P.; Gottlicher, J.; Steininger,

536

R.; Majzlan, J. Structural incorporation of As5+ into hematite. Environ. Sci. Technol. 2013, 47,

537

9140-9147.



Page 24 of 32

538

32. Mitsunobu, S.; Muramatsu, C.; Watanabe, K.; Sakata, M. Behavior of antimony(V) during the

539

transformation of ferrihydrite and its environmental implications. Environ. Sci. Technol. 2013,

540

47, 9660-9667.

541

33. Tamari, Y. Methods of analysis for the determination of selenium in biological, geological, and

542

water samples. In Environmental Chemistry of Selenium; Frankenberger, Jr., W.T., Engberg, R.A.,

543

Eds.; CRC Press: Boca Raton, FL 1998, pp. 27.

544

34. Taylor, J.C.; and Clapp, R.A. New features and advanced applications of Siroquant: A personal

545

computer XRD full profile quantitative analysis software package. Adv. X-ray Anal. 1992, 35,

546

49-55.

547 548

35. Francisco, P.C.M.; Sato, T.; Otake, T.; Kasama, T. Kinetics of Fe(III) mineral crystallization in the presence of Si at alkaline conditions. Am. Mineral. 2016, 101, 2057-2069.

549

36. Kasama, T.; Thuvander, M.; Siusys, A.; Gontard, L.C.; Kovacs, A.; Yazdi, S.; Duchamp, M.;

550

Dunin-Borkowski, R.E.; and Sadowski, J. Direct observation of doping incorporation pathways

551

in self-catalytic GaMnAs nanowires. J. Appl. Phys. 2015, 118, 054302.

552 553 554 555

37. Ryden, J.C.; Syers, J.K.; Tillman, R.W. Inorganic anion sorption and interactions with phosphate sorption by hydrous ferric oxide gel. J. Soil Sci. 1987, 38, 211-217. 38. Jackson, B.P.; Miller, W.P. Effectiveness of phosphate and hydroxide for desorption of arsenic and selenium species from iron oxides. Soil Sci. Soc. Am. J. 2000, 64, 1616-1622.

556

39. Yokoyama, T.; Makishima, A.; Nakamura, E. Evaluation of the coprecipitation of incompatible

557

trace elements with fluoride during silicate rock dissolution by acid digestion. Chem. Geol. 1999,

558

157, 175-187.

559

40. Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: Data analysis for x-ray

560

absorption spectroscopy using IFEFFIT. J. Synchrotron Rad. 2005, 12, 537-541.

561

41. Wickleder, M.S. Sodium selenite, Na2SeO3. Acta Cryst. E 2002, E58, i103-i104. 24 ACS Paragon Plus Environment

Page 25 of 32


562

42. Zhang, S.-Y.; Hu, C.L.; Li, P.-X.; Jiang, H.-L.; Mao, J.-G. Syntheses, crystal structures and

563

properties of new lead(II) or bismuth(III) selenites and tellurite. J. Chem. Soc., Dalton Trans.

564

2012, 41, 9532-9542.

565

43. Giester, G. The crystal structure of Fe2(SeO3)3•H2O. J. Solid State Chem. 1993, 103, 451-457.

566

44. Xiao, D.; Hou, Y.; Wang, E.; An, H.; Lue, A.; Li, Y.; Hu, C.; Xu, L. Hydrothermal synthesis and

567

crystal structure of a three-dimensional metal selenite containing double helical chains:

568

Fe3(SeO3)3·H2O. J. Solid State Chem. 2004, 177, 2699-2704.

569 570

45. Penn, R.L.; Soltis, J.A. Characterizing crystal growth by oriented aggregation. CrystEngComm 2014, 14, 1409-1418.

571

46. Soltis, J.A.; Feinber, J.M.; Gilber, B.; Penn, R.L. Phase transformation and particle-mediated

572

growth in the formation of hematite from 2-line ferrihydrite. Cryst. Growth Des. 2016, 16, 922-

573

932.

574 575 576 577 578 579

47. Yuwono, V.M.; Burrows, N.D.; Soltis, J.A.; Do, T.A.; Penn, R.L. Aggregation of ferrihydrite nanoparticles in aqueous systems. Faraday Discuss. 2012, 159, 235-245. 48. Schwertmann, U.; Friedl, J.; Stanjek, H. From Fe(III) ions to ferrihydrite and then to hematite. J. Colloid Interface Sci. 1999, 209, 215-223. 49. Schwertmann, U.; and Murad, E. Effect of pH on the formation of goethite and hematite from ferrihydrite. Clays Clay Miner. 1983, 31 (4), 277-284.

580

50. Nagano, T.; Nakashima, S.; Nakayama, S.; and Senoo, M. The use of color to quantify the effects

581

of pH and temperature on the crystallization kinetics of goethite under highly alkaline conditions.

582

Clays Clay Miner. 1994, 42 (2), 226-234.

583 584

51. Sugimoto, T.; Muramatsu, A.; Sakata, K.; Shindo, D. Characterization of hematite particles of different shapes. J. Colloid Interface Sci. 1993, 158, 420-428.



Page 26 of 32

585

52. Sugimoto, T.; Waki, S.; Itoh, H.; Muramatsu, A. Preparation of monodisperse-platelet type

586

hematite particles from a highly condensed β-FeOOH suspension. Colloids Surf. A 1996, 109,

587

155-165.

588 589

53. Bao, H.M.; and Koch, P.L. Oxygen isotope fractionation in ferric oxide-water systems: Low temperature synthesis. Geochim. Cosmochim. Acta 1999, 63 (5), 599–613.

590

54. Kukkadapu, R.K.; Zachara, J.M.; Fredrickson, J.K.; Smith, S.C.; Dohnalkova, A.C. (2003)

591

Transformation of 2-line ferrihydrite to 6-line ferrihydrite under oxic and anoxic conditions. Am.

592

Mineral. 2003, 88, 1903-1914.

593 594 595 596

55. Eklund, L. Persson, I. Structure and hydrogen bonding of the hydrated selenite and selenate ions in aqueous solution. J. Chem. Soc., Dalton Trans. 2014, 43 (17), 6315-6321. 56. Peak, D. Adsorption mechanisms of selenium oxyanions at the aluminum oxide/water interface. J. Colloid Interface Sci. 2006, 303, 337-345.

597

57. Rai, D.; Felmty, A.R.; Moore, D.A. (1995) The solubility product of crystalline ferric selenite

598

hexahydrate and the complexation constant of FeSeO3+. J. Solution Chem. 1995, 24 (8), 735-752.

599

58. Jia, Y.; Xu, L.; Fang, Z.; Demopoulos, G.P. Observation of surface precipitation of arsenate on

600 601 602

ferrihydrite. Environ. Sci. Technol. 2006, 40, 3248-3253. 59. Galvez, N. Barron, V.; Torrent, J. Preparation and properties of hematite with structural phosphorus. Clays Clay Mineral. 1999, 47 (3), 375-385.

603

60. Banfield, J.F.; Welch, S.A.; Zhang, H.; Ebert, T.T.; Penn, R.L. Aggregation-based crystal growth

604

and microstructre development in natural iron oxyhydroxide biomineralization products. Science

605

2000, 289, 751-754.

606

61. Echigo, T.; Monsegue, N.; Aruguete, D.M.; Murayama, M.; Hochella, M.F.; Jr. Nanopores in

607

hematite (α-Fe2O3) nanocrystals observed by electron tomography. Am. Mineral. 2013, 98 (1),

608

154-162. 26 ACS Paragon Plus Environment

Page 27 of 32


609

62. Vu, H.P.; Shaw, S.; Brinza, L.; Benning, L.G. Partitioning of Pb(II) during goethite and hematite

610

crystallization: Implications for Pb transport in natural systems. Appl. Geochem. 2013, 39, 119-

611

128.

612 613

63. Savage, D; Noy, D.; Mihara, M. Modelling the interaction of bentonite with hyperalkaline fluids. Appl. Geochem. 2002, 17 (3), 207-223.

614 615 616 617 618 619 620 621 622 623 624 625 626 627 628



629 630 631 632

TABLES TABLE 1. Partitioning of Se in solid samples.

Extractant Watera Phosphate HCl Total 633 634 635 636 637 638

639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656

Page 28 of 32

Se concentration in solid (mg/g) pH 5 pH 10 Initial Aged Initial Aged n.d. n.d. 4.1±0.5 n.d. 1.5±0.7 0.5±0.1 1.9±0.1 0.4±0.03 7.4±0.9 7.7±0.5 1.3±0.2 3.1±0.6 8.9±1.2

8.3±0.5

7.4±0.6

3.5±0.6

a Calculated

from concentrations in washing solutions (ultrapure water) n.d.: Not detected Uncertainties represent 1σ calculated from replicate samples

TABLE 2. Fitting results for the Se K-edge EXAFS spectra.

a

Fourier back-transform window: 1.0-2.0 Å Fourier back-transform window: 2.0-3.3 Å c Synthesized following Duc et al. (16) CN: coordination number; R: interatomic distance; σ2: disorder parameter; S0: amplitude reduction factor; ΔE0: energy shift. b


Page 29 of 32

657 658


FIGURES

659 660 661 662 663 664 665 666

FIGURE 1. (A) TEM image and SAED pattern of initial co-precipitates from pH 5, showing the solids to be composed of amorphous/poorly crystalline ferrihydrite. (B) TEM image of goethite and hematite formed during aging at pH 5; inset (top; scale: 20 nm) shows a spherical hematite particle, consisting of ~5 nm hematite nanocrystals (bottom; scale 5 nm). (C) TEM image of initial, amorphous/poorly crystalline ferrihydrite from pH 10. (D) TEM image of post-aging solids from pH 10, consisting of disk/spindle-shaped hematite and lath goethite. (Gt: Goethite; Hm: Hematite)



667 668 669 670 671 672

673 674 675 676 677 678

Page 30 of 32

FIGURE 2. Change in the concentration of Se in solution, along with the change in the proportion of ferrihydrite (estimated by Rietveld refinement) in the solid phase, during aging. Error bars for the Se(IV) concentrations, representing 1σ calculated from replicate samples, are smaller than the symbols. Data for solid phase composition are given in Table S2.

FIGURE 3. Normalized Se/Fe intensity ratio maps of initial co-precipitates from pH 5 (A) and pH 10 (B) measured by STEM-EDS. The pH 5 co-precipitates exhibit significant variations in Se/Fe ratios, while those from pH 10 show a uniform distribution.


Page 31 of 32

679 680 681 682 683 684 685


FIGURE 4. STEM-HAADF and the corresponding STEM-EDS maps for Se and Fe in post-aging solids from pH 5 (top) and 10 (bottom). The images from pH 5 show only the spherical hematite crystals; Se was not detected in the goethite crystals. (Gt: Goethite; Hm: Hematite)



Page 32 of 32

686

687 688 689 690 691 692

FIGURE 5. Se K-edge EXAFS spectra (A) of solid products and the corresponding Fourier Transforms (B). The Fourier Transforms (not corrected for phase shift) exhibit a strong first-shell contribution corresponding to Se-O backscattering and a weaker second-shell contribution corresponding to Se-Fe backscattering.


Mechanisms of Se(IV) Co-precipitation with Ferrihydrite at Acidic and

Recommend Documents