Fe(II)–Induced Mineral Transformation of Ferrihydrite-Organic Matter

of Fe(II)-induced transformation of (As(III)-adsorbed) OM-Fh adsorption and .... 92 impact many biogeochemical processes. 93. 94. Materials and Method...
0 downloads 0 Views 713KB Size
Subscriber access provided by University of South Dakota

Letter

Fe(II)–Induced Mineral Transformation of FerrihydriteOrganic Matter Adsorption and Coprecipitation Complexes in the Absence and Presence of As(III) Chunmei Chen, and Donald L. Sparks ACS Earth Space Chem., Just Accepted Manuscript • DOI: 10.1021/ acsearthspacechem.8b00041 • Publication Date (Web): 13 Sep 2018 Downloaded from http://pubs.acs.org on September 14, 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 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Earth and Space Chemistry

1

2

3

4

Fe(II)–Induced Mineral Transformation of Ferrihydrite-Organic Matter Adsorption and

5

Coprecipitation Complexes in the Absence and Presence of As(III)

6

Chunmei Chen* and Donald L. Sparks

7 8 9

Department of Plant and Soil Sciences

10

Delaware Environmental Institute

11

University of Delaware, Newark, DE, USA 19711

12 13 14 15 16 17 18 19

Corresponding Author

20

*Phone: (302)8318345. Fax: (302)8310605. E-mail: [email protected]

21 22

1 ACS Paragon Plus Environment

ACS Earth and Space Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

23 24

Abstract The poorly crystalline ferrihydrite (Fh) is often associated with organic matter (OM) and

25

metal(loid)s like arsenic (As). The transformation of Fh to more stable and hence less reactive

26

phases is catalyzed by surface reaction with Fe(II). However, little is known regarding the impact

27

of various specific OM types and the co-existence of OM and As on the secondary

28

mineralization of Fh. Accordingly, we explored the extent and the resulting secondary minerals

29

of Fe(II)-induced transformation of (As(III)-adsorbed) OM-Fh adsorption and coprecipitation

30

complexes, which were synthesized using two types of OM (DOM extracted from the O horizon

31

of an Ultisol and polygalacturonic acid (PGA) as a proxy for polysaccharides. Regardless of OM

32

type, increased contents of the coprecipitated or adsorbed OM led to a decrease in Fh

33

transformation in both the absence and presence of As(III). Adsorbed As(III) caused a decrease

34

in Fh conversion for both pure Fh and OM-Fh complexes. We observed only small differences in

35

Fe(II)-induced transformation of OM-Fh coprecipitates vs. adsorptive complexes. However,

36

without adsorbed As(III), OM types strongly influenced the secondary mineral products: DOM

37

impeded goethite (Gt) and stimulated lepidocrocite (Lp) formation, while only Gt was formed for

38

PGA. When As(III) and OM coexists, As (III) favored Lp over Gt formation for both DOM- and

39

PGA-Fh complexes. These findings provide evidence that the mineral evolution of Fh largely

40

depends on the potential additive/competing influence of coexisting constituents.

41 42

Keywords: EXAFS; iron oxides; crystallization; dissolved organic matter; polysaccharides; arsenic

43 44 45

2 ACS Paragon Plus Environment

Page 2 of 20

Page 3 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

46 47

ACS Earth and Space Chemistry

Introduction Fe(III) (oxyhydr)oxides (hereafter termed Fe oxides) are ubiquitous in soils and

48

sediments and can be strong sorbents for soil nutrients, contaminants and organic matter (OM).1-6

49

Fe oxides are present in the environment as a wide range of minerals with different

50

characteristics such as stability, specific surface area, and reactivity.1, 7-8 Fe oxides can undergo

51

reductive dissolution in anoxic environments, releasing Fe(II)3, 9, 10. The adsorption of Fe(II) onto

52

Fe(III) oxides induces electron transfer from Fe(II) to the host Fe oxides with accompanying

53

recrystallization of the Fe oxides to thermodynamically more stable forms.11-16 This

54

transformation process has wider implications than just the cycling of Fe alone, as the varying

55

properties of Fe phases, such as surface area and crystallinity and their interaction with Fe(II),

56

can affect the cycling of metal(loid)s and OM that are either adsorbed to or coprecipitated with

57

Fe oxides17-19. Mineralogical changes are particularly dramatic when the initial Fe(III) oxide

58

phase is ferrihydrite (Fh), a poorly-crystalline/amorphous Fe mineral, which readily undergoes

59

Fe(II)-catalyzed crystallization to lepidocrocite (Lp), goethite (Gt) and magnetite11, 12-16.

60

The rate and extent of Fe(II)-catalyzed Fh transformation, as well as the mineralogy and

61

physicochemical properties of the products, may be affected by the presence of surface-

62

associated or structurally incorporated elements. In nature, Fe oxides like Fh are often associated

63

with OM20-22, via adsorption and/or coprecipitation23-26. OM was shown to hinder Fe(II)-induced

64

Fh transformation by surface-site blockage and/or organic Fe(II) complexation.19, 27, 28 With

65

respect to OM adsorption on pre-existing Fe oxides, OM coprecipitation with Fh results in

66

smaller crystal sizes and greater structural disorder19, 28-30, and may subsequently affect the

67

reactivity and stability of Fh. Chen et al. showed that Fh coprecipitated with OM extracted from

68

forest litter samples, displayed a linear decrease in mineral transformation rates with increasing

3 ACS Paragon Plus Environment

ACS Earth and Space Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

69

OM contents following reaction with Fe(II), and favored Lp formation over Gt and magnetite.19

70

Recently, it was observed that, at similar OM loadings, coprecipitated Fh was more reactive

71

towards microbial reduction than Fh with adsorbed OM.31-32 However, the impact of adsorbed vs.

72

copecipitated OM on abiotic Fh transformation induced by Fe(II) has not been directly compared.

73

In addition, OM composition in natural environments is very complex, comprising a collection

74

of simple and macromolecular organic groups33-35. However, the impact of varying specific

75

organic compounds on Fh transformation and the nature of the resulting products is rarely

76

investigated36, 37.

77

OM-rich soil and sediments tend to show high affinities for trace metal(loid)s like arsenic

78

(As).38-41 As(V) has a strong affinity for both Al and Fe oxides, while As(III) adsorption is

79

largely limited to Fe oxides.42-45 The As content of naturally occurring iron oxides shows great

80

variation ranging from an As/Fe molar ratio of 2.4 × 10−6 to 0.146-49, with As speciation primarily

81

As(III) in some cases49. Although low As(V) concentrations (As/Fe 1.1), a complete suppression of Fh transformation was

168

observed following 7 days of reaction (Figure 1; SI Figure S6 and S7). The impaired Fh

169

transformation by OM, which is consistent with previous studies19, 27, 28, 60, could be attributable

170

to the decreased Fe(II) adsorption (SI Table S3), the surface blockage as indicated by surface

171

area measurement (SI Table S1), and organic complexation of Fe(II). This could reduce the

172

direct contact between Fe(II) and the mineral surface, and hence inhibit/slowdown mineral

173

transformation19, 28. Previous studies have also demonstrated that OM can retard transformation

174

of Fh to more crystalline minerals by blocking dissolution sites or hindering nucleation of more

175

stable minerals even in the absence of Fe(II).61, 62

176

Apart from the amount of Fh-associated OM, we demonstrated for the first time that the

177

type of OM is a another key factor in determining the products of the Fe(II)-catalyzed Fh

178

transformation in the absence of As(III). Although the extent of Fh preservation was greater for

179

DOM than for PGA at a C/Fe ratio of ~0.85, a similar degree of Fh preservation between PGA

180

and DOM was observed at all the other C/Fe ratios (SI Figure S11). The reaction products of

181

Fe(II)-catalyzed transformation of Fh are primarily a function of Fe(II)/Fh ratio, pH and ligand

182

type. The Fe(II) concentration (~0.5 mmol/g Fh) used in this study was below the threshold

8 ACS Paragon Plus Environment

Page 8 of 20

Page 9 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Earth and Space Chemistry

183

required for magnetite precipitation (~1.0 mmol Fe(II)/g Fh) at circumneutral pH 11. Consistent

184

with previous studies11, 16, 19, FeSO4 (~0.5 mmol/g Fh) favored the conversion of pure Fh to Gt at

185

pH 7 (buffered with PIPES). In contrast to only Gt formation for pure Fh, DOM resulted in more

186

Lp formation with less Gt (Figure 1a; SI Figure S6), as observed previously19. However,

187

interestingly, only Gt formation was observed for PGA (Figure 1b; SI Figure S7). These results

188

indicate a strong role of OM composition in Fh transformation products. Lp is

189

thermodynamically unstable with respect to Gt, and thus Lp may serve as a precursor to Gt

190

formation.1 Transformation of Lp to Gt was noticed in our previous study of reaction of pure Fh

191

with Fe(II)19. However, mineral-associated DOM stabilized Lp from further transformation19. In

192

contrast, only Gt formation with PGA may suggest that unlike DOM, polysaccharides may be

193

unable to hinder the transformation of Lp to Gt. However, future studies on temporal mineral

194

evolution are needed to unravel if Lp is formed as an intermediate product, or if Fh is directly

195

converted to Gt during reaction of PGA-Fh with Fe(II). The amount of Fe(II) removed from

196

solution following 1 hour of reaction is nearly equivalent for DOM- and PGA-Fh complexes (SI

197

Table S3). This implies that the difference in the transformation products between DOM and

198

PGA is unlikely due to Fe(II) sorption, although it is currently unknown if the amount of electron

199

transfer from adsorbed Fe(II) to bulk Fe(III) differed between PGA- and DOM-Fh complexes. It

200

was suggested that the effectiveness in suppressing crystallization depends on how strongly the

201

organic compounds sorb onto Fe oxides36, 37. Although the solid-phase C content in all samples

202

before and after reaction with Fe(II) indicates no significant loss of solid-phase OM (SI Table

203

S2), DOM appeared to bind more strongly with Fe oxides than PGA (SI Figure S10). Thus, the

204

displacement of DOM on oxides by the Fe(II) ions may be more difficult than that for PGA.

205

Therefore, DOM could more effectively stabilize meta-stable oxides like Lp from

9 ACS Paragon Plus Environment

ACS Earth and Space Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

206

recrystallization than extracellular organic compounds from plant root exudates or microbial EPS.

207

In addition, DOM contains aromatic and phenolic C in addition to carboxyl groups, while PGA

208

only has carboxylic C (SI Figure S1). The aromatic and phenolic C may hinder the nucleation of

209

more stable minerals like Gt. Considering the common associations of OM and oxides in nature6,

210

21, 23

211

, the influence of varying OM types on mineral evolution needs to be fully explored. The FTIR spectra of the adsorbed and coprecipitated OM were similar for both PGA and

212

DOM (SI Figure S2). In addition, we observed no difference in the extent or products of Fh

213

transformation between coprecipitates and adsorption complexes at the lowest and highest OM

214

contents for both DOM and PGA (Figure 1 and SI Figure S11). With intermediate OM contents

215

(C/Fe=0.52-0.88), the coprecipitated OM resulted in slightly more Fh transformation (5-10% of

216

total Fe) to Gt than the adsorbed OM for both DOM and PGA. This might be due to the smaller

217

particle size and lower crystallinity of the coprecipitated Fh, based on Mössbauer analysis from

218

previous studies19, 29. Overall, the reactivity of OM-Fh adsorption and coprecipitation complexes

219

did not display large differences in the reactivity towards Fe(II). Similarly, a previous study,

220

which compared microbial Fe(III) reduction of DOM-Fh complexes, showed Fe(III) reduction

221

rates was only slightly higher for DOM-Fh coprepitates (0.038-0.058 mmol h-1) compared to the

222

adsorption complexes (0.02-0.05 mmol h-1).32 In addition, it was previously reported that the

223

differences in the degradability of the adsorbed and coprecipitated DOM and lignin were small 63.

224

Collectively, we may not expect dramatic differences in the stability, transformation and

225

composition of both organic and mineral components of OM-Fh complexes formed via

226

coprecipitation vs. adsorption in natural environments.

227

Fe(II)-induced transformation of As(III)-bearing (OM-)Fh

10 ACS Paragon Plus Environment

Page 10 of 20

Page 11 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

228

ACS Earth and Space Chemistry

Following reaction with Fe(II), the oxidation state of the adsorbed As(III) remained

229

unchanged based on As K-edge XANES analysis (SI Section 8). Similar to As(III)-free systems,

230

the extent of Fh preservation also increased with increasing OM contents when As(III) was

231

adsorbed. Adsorbed As(III) resulted in a decrease in Fh conversion and hence the preservation of

232

Fh, compared to the corresponding As-free treatment for both pure- and OM-Fh (Figure 2 and SI

233

Figure S11), as determined by EXAFS LCF. Previous studies have found that adsorbed As(V)

234

can inhibit Fe(II)-catalyzed Fh transformation.18, 51 We showed here that this is true for As(III)

235

with an As(III)/Fe ratio of 0.03, and the co-existence of As(III) and OM resulted in less Fh

236

transformation than OM-free and As-bearing systems following short-term (≤ 7 days) exposure

237

to Fe(II). Such inhibition of phase transformation has been reasoned to result from As covalently

238

bonded to the surface of Fh64, which can reduce the extent of electron exchange between Fe(II)

239

and Fe(III) required for Fe(II)-catalyzed transformation 51, 65. Arsenic is also believed to retard

240

Fh transformation in a similar way as hydroxyl-carboxylic acids 66. Cornell and Schwertmann

241

suggested that the anion linkage of two or more units of Fh forms a network of particles resistant

242

to dissolution 37.

243

Adsorbed As(III) also alters the secondary products of Fh transformation—for both pure-

244

and OM-Fh (Figure 2). Unlike pure Fh, reaction of As(III)-bearing Fh with Fe(II) produced

245

primarily Lp with much less Gt following 7 days of reaction (Figure 2; SI Figure S5b). The

246

preferential formation of Lp during abiotic As(V)-bearing Fh transformation has also been noted

247

previously 18, 51. A previous study showed that Lp could be slowly converted to Gt in the absence

248

of other constituents at the longer reaction time scale (e.g. months), however no transformation

249

of Lp was observed in the presence of DOM even following 3-month reaction with Fe(II).19

250

Therefore similar to what was observed for DOM, As could inhibit or at least slow down the

11 ACS Paragon Plus Environment

ACS Earth and Space Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

251

transformation of the relatively unstable Fe oxides like Lp to more stable Gt, possibly by

252

blocking dissolution sites or by preventing polymerization of thermodynamically stable Fe(III)

253

minerals 67, 68.

254

An interesting and important finding is that adsorbed As(III) minimizes the impact of

255

OM types on the secondary products of Fe(II)-catalyzed OM-Fh complex transformation with an

256

As/Fe ratio of 0.03 (Figure 2). The co-existence of DOM and As(III) on Fh increased Lp

257

formation by inhibiting Gt formation, relative to As-free DOM-Fh complexes (Figure 2; SI

258

Figure S8). This favored Lp over Gt formation by adsorbed As(III), was much more dramatic

259

for PGA-Fh complexes, compared to DOM-Fh complexes (Figure 2; SI Figure S9).

260

Consequently, in the presence of adsorbed As(III), nearly identical secondary products were

261

observed between DOM- and PGA-Fh complexes (Figure 2). While As(III) (As/Fe = 0.03) and

262

OM (C/Fe = 0.3-0.6) co-occur in the systems with ~0.5 mmol FeSO4/g Fh and pH 7, Lp

263

formation was much more pronounced relative to Gt, regardless of OM types. Therefore, with

264

adsorbed As(III), the concentrations of Fh-associated OM and As(III) are critical in determining

265

the mineral evolution. Owing to the significant co-occurrence of As and OM in contaminated

266

sites, the observed less-crystalline (and hence more reactive) Fe oxides including Fh and Lp in

267

the presence of As and OM, has to be considered when evaluating the reactivity of Fe minerals

268

and the subsequent impact on the fate of OM and metal(oids) associated with these minerals in

269

the environment.

270 271 272 273

Environmental Implications In soils and sediments, where Fe oxides are impure, alteration of mineral transformation by impurities may influence the dynamics of OM, metals and nutrients associated with Fe oxides.

12 ACS Paragon Plus Environment

Page 12 of 20

Page 13 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Earth and Space Chemistry

274

Here, we note that the adsorbed or coprecipitated OM and the adsorbed As(III) decreased the

275

extent of Fh transformation. These findings may provide an explanation for the preservation of

276

Fh-like phases in natural environments 49, 69, 70. Transformation of Fh to presumably less-reactive

277

Gt is expect to preferentially occur in environments lacking of DOM and As(III) (i.e.

278

uncontaminated subsurface environments). In addition, the decreased Fh transformation, as well

279

as the favored Lp over Gt formation in the presence of DOM and As(III), has important

280

implications for predicting the fate of Fe minerals and their associated species such as As and

281

OM. The persistence of Fh/Lp in OM-rich and As-contaminated fields may provide reactive

282

surface area for OM, metals or nutrients, as well as electron transfer reactions. For example,

283

rapid reductive dissolution of these presumably more bioavailable oxides such as Fh and Lp,

284

may consequently drive OM 71, 72 and As mobilization 73, 74 to the aqueous phase under anoxic

285

conditions.

286 287

Supporting Information

288

Additional details on Fe EXAFS analysis, XRD data, FTIR measurements, and As XANES

289

analysis.

290 291

Acknowledgements This research is a part of the Christina River Basin Critical Zone Observatory (CRB-CZO)

292

project that was supported by the National Science Foundation (EAR 0724971). XAS analysis

293

was carried out at the Stanford Synchrotron Radiation Lightsource, a Directorate of SLAC

294

National Accelerator Laboratory and an Office of Science User Facility operated for the U.S.

295

Department of Energy Office of Science by Stanford University. We are also grateful to the

13 ACS Paragon Plus Environment

ACS Earth and Space Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

296

Shanghai Synchrotron Radiation Facility for use of the synchrotron radiation facilities at

297

beamline 14W.

298

References

299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342

1) Cornell, R. M.; Schwertmann, U. The Iron Oxides: Structure, Properties, Reactions, Occurrences, and Uses. Wiley-VCH, 2003. 2) Hochella, M. F.; Lower, S. K.; Maurice, P. A.; Penn, R. L.; Sahai, N.; Sparks, D. L.; Twining, B. S. Nanominerals, mineral nanoparticles, and earth systems. Science 2008, 319 (5870), 1631– 1635. 3) Borch, T.; Kretzschmar, R.; Kappler, A.; Van Cappellen, P.; Ginder-Vogel, M.; Voegelin, A.; Campbell, K. Biogeochemical redox processes and their impact on contaminant dynamics. Environ. Sci. Technol. 2010, 44 (1), 15–23. 4) Kaiser, K.; Guggenberger, G. Mineral surfaces and soil organic matter. Eur. J. Soil Sci. 2003, 54 (2), 219–236. 5) Taylor, K. G.; Konhauser, K. O. Iron in earth surface systems: a major player in chemical and biological processes. Elements 2011, 7, 83–88. 6) Lalonde, K.; Mucci, A.; Ouellet, A.; Gélinas, Y. Preservation of organic matter in sediments promoted by iron. Nature 2012, 483(7388), 198 –200. 7) Larsen, O.; Postma, D. Kinetics of reductive bulk dissolution of lepidocrocite, ferrihydrite and goethite. Geochim. Cosmochim. Acta 2001, 65, 1367–1379. 8) Bonneville, S.; Behrends, T.; Van Cappenllen, P. Solubility and dissimilatory reduction kinetics of iron(III) oxyhydroxides: A linear free energy relationship. Geochim. Cosmochim. Acta 2009, 73, 5273–5282. 9) Lovley, D. R.; Phillips, E. J. Organic matter mineralization with reduction of ferric iron in anaerobic sediments. Appl. Environ. Microbiol. 1986, 51(4), 683–689. 10) Melton, E. D.; Swanner, E. D.; Behrens, S.; Schmidt, C.; Kappler, A. The interplay of microbially mediated and abiotic reactions in the biogeochemical Fe cycle. Nat. Rev. Microbiol. 2014, 12, 797–808. 11) Hansel, C. M.; Benner, S. G.; Fendorf, S. Competing Fe(II)-induced mineralization pathways of ferrihydrite. Environ. Sci. Technol. 2005, 39, 7147–7153. 12) Pedersen, H. D.; Postma, D.; Jakobsen, R.; Larsen, O. Fast transformation of iron oxyhydroxides by the catalytic action of aqueous Fe(II). Geochim. Cosmochim. Acta 2005, 69, 3967–3977. 13) Yee, N.; Shaw, S.; Benning, L. G.; Nguyen, T. H. The rate of ferrihydrite transformation to goethite via the Fe(II) pathway. Am. Miner. 2006, 91, 92–96. 14) Hansel, C. M.; Learman, D. R.; Lentini, C. J.; Ekstrom, E. B. Effect of adsorbed and substituted Al on Fe(II)-induced mineralization pathways of ferrihydrite. Geochim. Cosmochim. Acta 2011, 75, 4653–4666. 15) Liu, H.; Guo, H.; Li, P.; Yu, W. The transformation of ferrihydrite in the presence of trace Fe(II):The effect of the anionic media. J. Solid State Chem. 2008, 181, 2666–2671. 16) Boland, D. D.; Collins, R. N.; Miller, C. J.; Glover, C. J.; Waite, T. D. Effect of solution and solid-phase conditions on the Fe(II)-accelerated transformation of ferrihydrite to lepidocrocite and goethite. Environ. Sci. Technol. 2014, 48, 5477–5485. 17) Amstaetter, K.; Borch, T.; Larese-Casanova, P.; Kappler, A. Redox Transformation of Arsenic by Fe(II)-Activated Goethite (α-FeOOH). Environ. Sci. Technol. 2010, 44, 102–108. 18) Masue-Slowey, Y.; Loeppert, R. H.; Fendorf, S. Alteration of ferrihydrite reductive dissolution and transformation by adsorbed As and structural Al: Implications for As retention. Geochim. Cosmochim. Acta 2011, 75, 870–886. 14 ACS Paragon Plus Environment

Page 14 of 20

Page 15 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392

ACS Earth and Space Chemistry

19) Chen, C.; Kukkadapu, R.; Sparks, D. L. Influence of coprecipitated organic matter on Fe2+(aq) catalyzed transformation of ferrihydrite: implications for carbon dynamics. Environ. Sci. Technol. 2015, 49, 10927–10936. 20) Mcknight, D. M.; Bencala, K. E.; Zellweger, G. W.; Aiken, G. R.; Feder, G. L.; Thorn, K. A. Sorption of dissolved organic carbon by hydrous aluminum and iron oxides occurring at the confluence of Deer Creek with the Snake River, Summit County, Colorado. Environ. Sci. Technol. 1992, 26, 1388–1396. 21) Wagai, R. Mayer, L. M. Sorptive stabilization of organic matter in soils by hydrous iron oxides. Geochim. Cosmochim. Acta 2007, 71(1), 25–35. 22) Chen, C.; Dynes, J.J.; Wang, J.; Karunakaran, C.; Sparks, D.L. 2014. Soft X-ray Spectromicroscopy Study of Mineral-Organic Matter Associations in Pasture Soil Clay Fractions. Environ. Sci. Technol. 2014, 48(12), 6678–6686. 23) Riedel, T.; Zak, D.; Biester, H.; Dittmar, T. Iron traps terrestrially derived dissolved organic matter at redox interfaces. Proc. Natl. Acad. Sci. USA 2013, 110(25), 10101–10105. 24) Eusterhues, K.; Rennert, T.; Knicker, H.; Kögel-Knabner, I.; Totsche, K. U.; Schwertmann, U. Fractionation of Organic Matter Due to Reaction with Ferrihydrite: Coprecipitation versus Adsorption. Environ. Sci. Technol. 2011, 45, 527–533. 25) Chen, C.; Dynes J.; Wang, J.; Sparks, D.L. Properties of Fe-organic matter associations via coprecipitation versus adsorption. Environ. Sci. Technol. 2014, 48 (23), 13751–13759. 26) Mikutta, R.; Lorenz, D.;Guggenberger, G.; Haumaier, L.; Freund, A. Properties and reactivity of Fe-organic matter associations formed by coprecipitation versus adsorption: Clues from arsenate batch adsorption. Geochim. Cosmochim. Acta 2014, 144, 258–276. 27) Jones, A. M.; Collins, R. N.; Rose, J.; Waite, T. D. The effect of silica and natural organic matter on the Fe(II)-catalysed transformation and reactivity of Fe(III) minerals. Geochim. Cosmochim. Acta 2009, 73(15), 4409–4422. 28) ThomasArrigo, L. K.; Mikutta, C.; Byrne, J.; Kappler, A.; Kretzschmar, R. Iron(II)-Catalyzed Iron Atom Exchange and Mineralogical Changes in Iron-rich Organic Freshwater Flocs: An Iron Isotope Tracer Study. Environ. Sci. Technol. 2017, 51 (12), 6897–6907. 29) Mikutta, C.; Mikutta, R.; Bonneville, S.; Wagner, F.; Voegelin, A.; Christl, I.; Kretzschmar, R. Synthetic coprecipitates of exopolysaccharides and ferrihydrite. Part I: Characterization. Geochim. Cosmochim. Acta 2008, 72, 1111–1127. 30) Eusterhues, K.; Wagner, F. E.; Häusler, W.; Hanzlik, M.; Knicker, H.; Totsche, K. U.; KögelKnabner, I.; Schwertmann, U. Characterization of ferrihydrite-soil organic matter coprecipitates by X-ray diffraction and Mössbauer spectroscopy. Environ. Sci. Technol. 2008, 42, 7891–7897. 31) Eusterhues, K.; Hädrich, A.; Neidhardt, J.; Küsel, K.; Keller, T. F.; Jandt, K. D., Totsche K. U. Reduction of ferrihydrite with adsorbed and coprecipitated organic matter: microbial reduction by Geobacter bremensis vs. abiotic reduction by Na-dithionite. Biogeosci. Discuss. 2014, 11, 6039–6067. 32) Cooper, R. E.; Eusterhues, K.; Wegner, C. E.; Totsche, K. U.; Küsel, K. Ferrihydrite-associated organic matter (OM) stimulates reduction by Shewanella oneidensis MR-1 and a complex microbial consortia. Biogeosciences 2017, 14, 5171–5188. 33) Krull, E.S.; Baldock, J. A.; Skjemstad, J. O. Importance of mechanisms and processes of the stabilization of soil organic matter for modeling carbon turnover. Funct. Plant Biol. 2003, 30(2), 207–222. 34) Sollins, P.; Homman, P.; Caldwell, B. A. Stabilization and destabilization of soil organic matter: mechanisms and controls. Geoderma 1996, 74, 65–105. 35) Lehmann, J.; Kleber, M. The contentious nature of soil organic matter. Nature 2015, 528, 60– 68. 36) Cornell, R. M. Effect of simple sugars on the alkaline transformation of ferrihydrite into goethite and hematite. Clays Clay Miner. 1985, 33(3), 219–227.

15 ACS Paragon Plus Environment

ACS Earth and Space Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442

37) Cornell, R. M.; Schwertmann, U. Influence of organic anions on the crystallization of ferrihydrite. Clays Clay Miner. 1979, 27(6), 402–410. 38) Elliott, A. V. C.; Plach, J. M.; Droppo, I. G.; Warren, L. A. Comparative floc-bed sediment trace element partitioning across variably contaminated aquatic ecosystems. Environ. Sci. Technol. 2012, 46, 209–216. 39) ThomasArrigo, L. K.; Mikutta, C.; Byrne, J.; Barmettler, K.; Kappler, A.; Kretzschmar, R. Iron and arsenic speciation and distribution in organic flocs from streambeds of an arsenic-enriched peatland. Environ. Sci. Technol. 2014, 48, 13218–13228. 40) ThomasArrigo, L. K.; Mikutta, C.; Lohmayer, R.; Planer-Friedrich, B.; Kretzschmar, R. Sulfidization of organic freshwater flocs from a minerotrophic peatland: Speciation changes of iron, sulfur, and arsenic. Environ. Sci. Technol. 2016, 50, 3607–3616. 41) Shimizu, M.; Arai, Y.; Sparks, D. L. Multiscale Assessment of Methylarsenic Reactivity in Soil. 2. Distribution and Speciation in Soil. Environ. Sci. Technol. 2011, 45, 4300–4306. 42) Manning, B. A.; Goldberg, S. Arsenic(III) and arsenic(V) adsorption on three California soils. Soil Sci. 1997, 162, 886–895. 43) Arai, Y.; Elzinga, E. J.; Sparks, D. L. (2001) X-ray absorption spettroscopy investigation of arsenite and arsenate adsorption on the aluminium oxide-water interface. J Colloid Interf. Sci. 2001, 235, 80–88. 44) Dixit, S. I. Hering, J. G. Comparison of arsenic(V) and arsenic(III) sorption onto iron oxide minerals: implications for arsenic mobility. Environ Sci. Technol. 2003, 37(18), 4182–4189. 45) Masue, Y.; Loeppert, R. H.; Kramer, T. A. Arsenate and arsenite adsorption and desorption behavior on coprecipitated aluminum: iron hydroxides. Environ. Sci. Technol. 2007, 41 (3), 837–842. 46) Pedersen, H. D.; Postma, D.; Jakobsen, R. Release of arsenic associated with the reduction and transformation of iron oxides. Geochim. Cosmochim. Acta 2006, 70, 4116–4129. 47) Bowell, R. J. Sorption of arsenic by iron oxides and oxyhydroxides in soils. Appl. Geochem. 1994, 9, 279–286. 48) Pichler, T.; Veizer, J.; Hall, G. E. M. Natural input of arsenic into a coral-reef ecosystem by hydrothermal fluids and its removal by Fe(III) oxyhydroxides. Environ. Sci. Technol. 1999, 33, 1373–1378. 49) LeMonte, J. J.; Stuckey, J. W.; Sanchez, J. Z. Tappero, R. V.; Rinklebe, J.; Sparks, D. L. Sea level rise induced arsenic release from historically contaminated coastal soils. Environ. Sci. Technol. 2017, 51(11), 5913–5922. 50) Ford, R. G. Rates of hydrous ferric oxide crystallization and the influence on coprecipitated arsenate. Environ. Sci. Technol. 2002, 36, 2459–2463. 51) Gomez, M. A.; Hendry, M. J.; Hossain, A.; Das, S.; Elouatik, S. Abiotic reduction of 2-line ferrihydrite: effects on adsorbed arsenate, molybdate, and nickel. RSC Adv. 2013, 3, 25812– 25822. 52) Kocar, B. D.; Fendorf, S. Thermodynamic constraints on reductive reactions influencing the biogeochemistry of arsenic in soils and sediments. Environ. Sci. Technol. 2009, 43 (13), 4871– 4877. 53) Stuckey, J. W.; Schaefer, M. V.; Benner, S. G.; Fendorf, S. Reactivity and speciation of mineral-associated arsenic in seasonal and permanent wetlands of the Mekong Delta. Geochim. Cosmochim. Acta 2015, 171, 143–155. 54) Knee, E. M.; Gong, F. C.; Gao, M.; Teplitski, M.; Jones, A. R.; Foxworthy, A.; Mort, A. J.; Bauer, W. D. Root mucilage from pea and its utilization by rhizosphere bacteria as a sole carbon source. Mol. Plant Microbe Interact. 2001, 14, 775–784. 55) Cheshire, M. V. Nature and Origin of Carbohydrates in Soils Academic Press, London, 1979. 56) Brunauer, S.; Emmett, P. H.; Teller, E. Adsorption of gases in multimolecular layers. J. Am. Chem. Soc. 1938, 60, 309–319.

16 ACS Paragon Plus Environment

Page 16 of 20

Page 17 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490

ACS Earth and Space Chemistry

57) Stookey, L. L. Ferrozine-A new spectrophotometric reagent for iron. Anal. Chem. 1970, 42(7), 779–781. 58) Webb, S. M. SIXPack a graphical user interface for XAS analysis using IFEFFIT. Phys. Scr. 2005, T115, 1011–1014. 59) Hansel, C. M.; Benner, S. G.; Neiss, J.; Dohnalkova, A.; Kukkadapu, R. K.; Fendorf S. Secondary mineralization pathways induced by dissimilatory iron reduction of ferrihydrite under advective flow. Geochim. Cosmochim. Acta 2003, 67, 2977–2992. 60) Henneberry, Y. K.; Kraus, T. E. C.; Nico, P. S.; Horwath, W. R. Structural stability of coprecipitated natural organic matter and ferric iron under reducing conditions. Org. Geochem. 2012, 48, 81–89. 61) Cornell, R. M.; Schwertmann, U. Influence of organic anions on the crystallization of ferrihydrite. Clays Clay Miner.1979, 27, 402−410. 62) Xiao, W.; Jones, A. M.; Li, X.; Collins, R. N.; Waite, T. D. Effect of Shewanella oneidensis on the kinetics of Fe(II)-catalyzed transformation of ferrihydrite to crystalline iron oxides. Environ. Sci. Technol. 2018, 52 (1), 114–123. 63) Eusterhues, K.; Neidhardt, J.; Hädrich, A.; Küsel, K; Totsche K. U. Biodegradation of ferrihydrite-associated organic matter. Biogeochem. 2014, 119, 45–50. 64) Waychunas, A.; Rea, B.A.; Fuller, C. C.; Davis, J. A. Surface chemistry of ferrihydrite: 1. EXAFS studies of the geometry of coprecipitated and adsorbed arsenate. Geochim. Cosmochim. Acta 1993, 57, 2251–2269. 65) Katz, J. E.; Zhang, X.; Attenkofer, K.; Chapman, K. W.; Frandsen, C.; Zarzycki, P.; Rosso, K. M.; Falcone, R. W.; Waychunas, G. A.; Gilbert, B. Electron small polarons and their mobility in iron (oxyhydr)oxide nanoparticles. Science 2012, 337, 1200–1203. 66) Sun, T.; Paige, C. R.; Snodgrass, W. J. Combined effect of arsenic and cadmium on the transformation of ferrihydrite onto crystalline products. J. Univ. Sci. Technol. B 1999, 3, 168– 173 67) Schwertmann, U.; Cornell, R. M. Iron Oxides in the Laboratory – Preparation and Characterization. VCH Verlagsgesellschaft mbH, Weinheim, Germany 1991. 68) Schwertmann, U.; Taylor, R. M. Natural and synthetic poorly crystallised lepidocrocite. Clay Miner. 1979, 14, 85–293. 69) Schwertmann, U.; Murad, E. The nature of an iron oxide: Organic iron association in a peaty environment. Clay Miner. 1988, 23 (3) 291–299 70) Chen, C.; Kukkadapu, R. K.; Lazareva, O.; Sparks, D. L. Solid-phase Fe speciation along the vertical redox gradients in floodplains using XAS and Mössbauer spectroscopies. Environ. Sci. Technol. 2017, 51 (14), 7903–7912. 71) Adhikari,D.; Zhao, Q.; Das, K.; Mejia, J.; Huang, R.; Wang, X.; Poulson, S. R.; Tang, Y.; Roden, E. E.; Yang, Y. Dynamics of ferrihydrite-bound organic carbon during microbial reduction. Geochim. Cosmochim. Acta 2017, 212, 221–223. 72) Pan, W.; Kan, J.; Inamdar, S.; Chen, C.; Sparks, D. L. Dissimilatory microbial iron reduction release DOC (dissolved organic carbon) from carbon-ferrihydrite association. Soil Biol. Biochem. 2016, 103, 232–240. 73) Horneman, A.; van Geen, A.; Kent, D.; Mathe, P. E.; Zheng, Y.; Dhar, R. K.; O’Connell, S.; Hoque, M.; Aziz, Z.; Shamsudduha, M.; Seddique, A.; Ahmed, K. M. Decoupling of As and Fe release to Bangladesh groundwater under reducing conditions. Part I: Evidence from sediment profiles. Geochim. Cosmochim. Acta 2004, 68, 3459–3473. 74) Tufano, K. J.; Fendorf, S. Confounding impacts of iron reduction on arsenic retention. Environ. Sci. Technol. 2008, 42(13), 4777–4783.

491

17 ACS Paragon Plus Environment

ACS Earth and Space Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510

Figure 1 Secondary minerals formed following 7 days of reaction of 1 mM Fe(II) with

511

ferrihydrite (C/Fe = 0) as well as (a) DOM- and (b) PGA-ferrihydrite adsorption vs.

512

coprecipitation complexes, as a function of C/Fe molar ratios. Mineral percentages were obtained

513

via linear combination fitting of k3-weighted Fe EXAFS spectra with reference minerals. The k3-

514

weighted EXAFS spectra and linear combination fits are shown in Supporting Information (SI

515

Figure S13 and S14).

516 517 518 18 ACS Paragon Plus Environment

Page 18 of 20

Page 19 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Earth and Space Chemistry

519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537

Figure 2 Secondary minerals formed following 7 days of reaction of 1 mM Fe(II) with As(III)-

538

bearing ferrihydrite, as well as As(III)-bearing (a) DOM- and (b) PGA-ferrihydrite adsorption vs.

539

coprecipitation complexes, as a function of C/Fe molar ratios. Mineral percentages were obtained

540

via linear combination fitting of k3-weighted Fe EXAFS spectra with reference minerals. The k3-

541

weighted EXAFS spectra and linear combination fits are shown in Supporting Information (SI

542

Figure S15 and S16).

543 544 545 19 ACS Paragon Plus Environment

ACS Earth and Space Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

546

TOC Art

547 548 549

20 ACS Paragon Plus Environment

Page 20 of 20