Impact of Redox Reactions on Colloid Transport in Saturated Porous

Sep 21, 2016 - Quartz sand (ultrapure with 99.9% SiO2, Hebei Zhensheng Mining Ltd., China) with a mean diameter (d50) of 0.50 mm was used as granular ...
0 downloads 9 Views 697KB Size
Subscriber access provided by Northern Illinois University

Article

Impact of Redox Reactions on Colloid Transport in Saturated Porous Media: An Example of Ferrihydrite Colloids Transport in the Presence of Sulfide Peng Liao, Songhu Yuan, and Dengjun Wang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b02542 • Publication Date (Web): 21 Sep 2016 Downloaded from http://pubs.acs.org on September 23, 2016

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 free 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 accessible to all readers and 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.

Environmental Science & Technology 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 33

Environmental Science & Technology

TOC art 201x130mm (96 x 96 DPI)

ACS Paragon Plus Environment

Environmental Science & Technology

Page 2 of 33

1

Impact of Redox Reactions on Colloid Transport in Saturated Porous

2

Media: An Example of Ferrihydrite Colloids Transport in the

3

Presence of Sulfide Peng Liao†, Songhu Yuan*,†, Dengjun Wang‡

4

5



6

of Geosciences, 388 Lumo Road, Wuhan 430074, P. R. China

7



8

Science, Chinese Academy of Sciences, 71 East Beijing Road, Nanjing 210008, P. R.

9

China

State Key Laboratory of Biogeology and Environmental Geology, China University

Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil

10 11

* To whom correspondence should be addressed. E-mail: [email protected] (S.

12

Yuan), Phone: +86-27-67848629, Fax: +86-27-67883456.

13 14 15 16 17 18 19 20 21

1 ACS Paragon Plus Environment

Page 3 of 33

Environmental Science & Technology

22

ABSTRACT Transport of colloids in the subsurface is an important environmental

23

process with most research interests centred on the transport in chemically stable

24

conditions. While colloids can be formed under dynamic redox conditions, the impact

25

of redox reactions on their transport is largely overlooked. Taking the redox reactions

26

between ferrihydrite colloids and sulfide as an example, we investigated how and to

27

what extent the redox reactions modulated the transport of ferrihydrite colloids in

28

anoxic sand columns over a range of environmentally relevant conditions. Our results

29

reveal that the presence of sulfide (7.8–46.9 µM) significantly decreased the

30

breakthrough of ferrihydrite colloids in the sand column. The estimated travel

31

distance of ferrihydrite colloids in the absence of sulfide was nearly 7-fold larger than

32

that in the presence of 46.9 µM sulfide. The reduced breakthrough was primarily

33

attributed to the reductive dissolution of ferrihydrite colloids by sulfide in parallel

34

with formation of elemental sulfur (S(0)) particles from sulfide oxidation. Reductive

35

dissolution decreased the total mass of ferrihydrite colloids, while the negatively

36

charged S(0) decreased the overall zeta potential of ferrihydrite colloids by attaching

37

onto their surfaces and thus enhanced their retention in the sand. Our findings provide

38

novel insights into the critical role of redox reactions on the transport of

39

redox-sensitive colloids in saturated porous media.

40 41 42 43

2 ACS Paragon Plus Environment

Environmental Science & Technology

44

Page 4 of 33

INTRODUCTION

45

The transport of naturally-occurring and engineered nanoparticles (NPs) and

46

colloids in porous media has gained great attention over the past decade.1,2 Colloid

47

transport is highly dependent on both the physicochemical conditions of aqueous

48

phase and the properties of the solid surfaces.1‒4 Perturbations of physicochemical

49

conditions (e.g., flow velocity, particle size, ionic strength and composition, pH, and

50

ligands) have long been recognized to affect the aggregation, deposition, and

51

remobilization of colloids in oxic porous media.1,5‒9 Potential mechanisms initiating

52

colloid transport upon varying physicochemical perturbations primarily include the

53

changes in Derjaguin-Landau-Verwey-Overbeek (DLVO) (i.e., electrostatic and van

54

der Waals interactions) and non-DLVO (e.g., Born, hydration, and steric interactions)

55

interactions.1,4,6,10,11

56

Compared to the above perturbation conditions, transport of colloids also occurs

57

in redox oscillation environments that occur naturally or are impacted by human

58

acitivities.12‒14 Mounting evidences have documented that colloidal iron (e.g., goethite

59

and hematite), silver nanoparticles (AgNPs), and carbon nanomaterials (e.g., graphene)

60

could exist in either reducing or oxidizing conditions and play a central role in the

61

mobility of contaminants loaded on them.15‒22 For example, due to the presence of

62

electron donors and microbial population dynamics, transport of Fe(III) hydroxide

63

colloids in anoxic environments may be accompanied by the reduction via biotic or

64

abiotic reactions.12,13,19 Meanwhile, the contaminants that are adsorbed or precipitated

65

onto the Fe(III) hydroxide colloids may be either released from or reduced on the 3 ACS Paragon Plus Environment

Page 5 of 33

Environmental Science & Technology

66

surfaces, depending on the prevailing biogeochemical conditions.3,23 It is therefore

67

logical to anticipate that the transport behavior of colloids under dynamic redox

68

conditions could be different from that under chemically stable environments.4,10

69

However, despite decades of research on the transport of colloids and the associated

70

contaminants,1,3,4,11,24 the effect of redox reactions on the stability and transport of

71

colloids has been largely neglected. It is thus of great importance to incorporate the

72

knowledge of redox chemistry into colloid transport framework.

73

Ferrihydrite colloids are ubiquitous in the subsurface environments and play a

74

significant role in modulating the transport and transformation of nutrients (e.g.,

75

phosphate) and contaminants (e.g., arsenic).3,25‒28 A number of laboratory and field

76

studies have substantiated that the interplay of ferrihydrite (and other Fe(III)

77

(hydro)oxides) and sulfide played a critical role in the redox dynamics of anoxic-oxic

78

interface environments including aquifers, wetlands, and marine sediments, where

79

sulfide was the predominant abiotic reductant for Fe(III) hydroxides.29‒34 While

80

controlled experiments in well-mixed systems have established the mechanistic

81

framework for the reactions between ferrihydrite and sulfide,31,32,35‒37 the effects of

82

these reactions on the transport of ferrihydrite colloids in anoxic porous media remain

83

obscure. It is noteworthy that in addition to the physical transport of ferrihydrite

84

colloids in the presence of sulfide, the colloids could also be subjected to severe

85

chemical alterations that may influence the mobility and stability during transport.17

86

For instance, the transport of ferrihydrite colloids is likely to be accompanied by the

87

reduction-induced transformation, thereby releasing Fe(II) and generating oxidized 4 ACS Paragon Plus Environment

Environmental Science & Technology

Page 6 of 33

88

sulfur products simultaneously.31 The released Fe(II) is likely to accelerate the

89

transformation of ferrihydrite colloids, forming more crystallized Fe oxides.38‒41 The

90

products (e.g., sulfur) from ferrihydrite-sulfide reactions could adsorb or attach onto

91

the ferrihydrite colloids, changing the particle size and surface charge of ferrihydrite

92

colloids and eventually altering their transport. Although recent research advances on

93

the cotransport of different types of colloids/NPs in saturated porous media

94

demonstrated that the transport of primary colloids was strongly influenced by the

95

coexisted secondary colloids,10,42-44 no redox reactions were involved in these

96

processes.

97

The objective of this study was to unravel the role of redox reactions between

98

ferrihydrite and sulfide, as an example, on the transport of ferrihydrite colloids in

99

saturated porous media. To this end, column experiments were designed to understand

100

the transport and retention behavior of ferrihydrite colloids in anoxic quartz sand by

101

monitoring their breakthrough curves (BTCs) and retention profiles (RPs) under

102

environmentally relevant sulfide concentrations (0–46.9 µM) at pH 6.0. Knowledge

103

generated from this study complements the traditional colloid transport research and

104

provide novel insights into understanding the fate of colloid-associated contaminants

105

and nutrients in redox dynamic environments.

106 107

EXPERIMENTAL METHODS

108

Ferrihydrite Colloids. Ferrihydrite colloids used in this study were synthesized

109

following previously published procedures,45 with details provided in Section S1 in 5 ACS Paragon Plus Environment

Page 7 of 33

Environmental Science & Technology

110

the Supporting Information (SI). The ferrihydrite stock suspensions were shown to be

111

stable over a period of two months. Ferrihydrite colloid influent suspensions used for

112

the column transport experiments were prepared by adding aliquots of ferrihydrite

113

stock suspensions to 400 mL of 3 mM NaCl solution at pH 6.0 (described below),

114

stirring for 2 min, and sonicating (100 W, 45k Hz) for 5 min at 25 °C to ensure a

115

homogeneous suspension. The average hydrodynamic diameter and zeta potential of

116

ferrihydrite colloids in the influent suspensions (0.375 mM ferrihydrite, 3 mM NaCl,

117

and pH 6.0) were determined to be 112.5 ± 11.5 nm and 40.5 ± 1.9 mV, respectively,

118

using the dynamic light scattering (DLS, Zetasizer Nano ZS90, Malvern Instruments

119

Ltd., U.K.). The change in particle size of ferrihydrite colloids over the duration of 12

120

h was insignificant (Figure S4), indicating a good stability throughout the column

121

transport experiments.

122

Porous Media. Quartz sand (ultrapure with 99.9% SiO2, Hebei Zhensheng

123

Mining Ltd., China) with a mean diameter (d50) of 0.50 mm was used as granular

124

porous media.6,7,10 Prior to use, the quartz sand was thoroughly cleaned to remove

125

metal oxides, colloids, and clays adsorbed on the surface by soaking sequentially in

126

12 M HCl, 1 M NaOH, and 30% H2O2 for 24 h each, rinsing with deionized (DI)

127

water 20–30 times and drying at 105 °C for 24 h.

128

Column Experiments. The column setup is depicted in Figure S5, and the

129

corresponding experimental parameters are listed in Table S1. Cylindrical Plexiglas

130

columns (2.5 cm inner diameter × 10 cm long) were dry-packed with quartz sand with

131

a porosity of 0.43. The influent ferrihydrite colloid suspensions were continuously 6 ACS Paragon Plus Environment

Environmental Science & Technology

Page 8 of 33

132

stirring on a shaker at 200 rpm. The influent pH was buffered at 6.0 ± 0.1 using 5 mM

133

2-(N-morpholino)ethanesulfonic acid (MES). After packing, the columns were first

134

flushed for 20 min with ultrapure N2 gas (99.999%) to replace O2 in the column. They

135

were then pre-equilibrated with 10 pore volumes (PVs) of O2-free background

136

solution (3 mM NaCl and 5 mM MES). Following pre-equilibration, 11.25 PVs of

137

deoxygenated ferrihydrite colloid suspensions (0.714 mM) and 11.25 PVs of a

138

solution containing different concentrations of sulfide were fed separately and mixed

139

at a volume ratio of 1:1, resulting in an influent ferrihydrite colloids concentration of

140

0.375 mM and the total injected PVs of 22.5. The mixing time of ferrihydrite colloids

141

with sulfide before injecting into the column was less than 1.5 min. According to the

142

reaction kinetics obtained in later batch experiments, approximately 50% of reactions

143

occurred during the initial mixing period before injecting with the remaining reactions

144

occurring during the first 3 cm of transport in the column. Fifteen PVs of background

145

electrolyte solution (3 mM NaCl and 5 mM MES) were ultimately fed to flush the

146

unattached ferrihydrite colloids in the column. Because H2S is the dominant form of

147

sulfide at pH 6.0 (i.e., 91.2% H2S and 8.7% HS-), to ensure the actual concentrations

148

of sulfide in the influent solution are equivalent to those designed for column

149

transport experiments (i.e., 7.8, 15.6, 31.3, and 46.9 µM), the empirical values of

150

~20% higher amount of initial sulfide concentrations than theoretically calculated

151

ones were transferred into the column (Figure S6). Our measurements proved that the

152

concentrations of sulfide in the influent suspension varied by less than 20% over the

153

time frame of the column experiments (Figure S6). All column experiments were run 7 ACS Paragon Plus Environment

Page 9 of 33

Environmental Science & Technology

154

at the room temperature (25 ± 1 °C) in an upward mode using a peristaltic pump (2

155

mL/min or 5.87 m/d). All transport experiments were conducted at least in duplicate.

156

To better understand the mechanisms controlling the transport of ferrihydrite

157

colloids by sulfide, a series of separate experiments with respect to the effects of

158

hydroquinone, dissolved Fe(II), and elemental sulfur (S(0)) particles, instead of

159

sulfide, on ferrihydrite colloids transport, were performed (Table S1). The procedures

160

were the same as those for the transport experiments described above. In addition to

161

the transport of these separate experiments, a transient triple-pulse transport

162

experiment was further performed to more clearly delineate the impacts of sulfide and

163

S(0) particles on the transport of ferrihydrite colloids. This experiment involves the

164

sequential injection of three influents: (i) ferrihydrite colloids alone (13 PVs), (ii)

165

ferrihydrite colloids with sulfide (7 PVs), and (iii) ferrihydrite colloids with sulfide

166

and S(0) (7 PVs) (Table S1).

167

At predetermined time intervals, aliquots (5 mL each time) of suspensions from

168

the column effluents were withdrawn from the sampling port using 5 mL vacuum

169

syringes. The detailed protocol of sampling is provided in Section 2 in SI. Three mL

170

of the sample was analyzed for total Fe, total Fe(II), and S(0) concentrations. The

171

remaining 2 mL sample was filtered through a 0.22 µm nylon membrane for dissolved

172

Fe(II) measurement. All the experimental operations were carefully conducted in the

173

anoxic cabinet to minimize the potential Fe(II) oxidation because ferrihydrite colloids

174

are likely to be reduced by sulfide. The parameters reflecting effluent redox properties

175

including ORP, pH, and DO concentration were monitored with probes installed 8 ACS Paragon Plus Environment

Environmental Science & Technology

Page 10 of 33

176

in-line at the exit of the column. Although the elaborative operations were taken to

177

minimize potential interference of oxygen during the transport experiments, we

178

recognize that a minute amount of oxygen (< 9.4 µM) could still occur in the column.

179

After completion of the transport experiment, the sand was excavated from the

180

column under gravity and dissected into 10 segments (1 cm long each) to obtain

181

spatial distribution of the ferrihydrite colloids retained in the column. The column

182

stayed saturated with background electrolyte solution during the course of dissection

183

in an effort to avoid the remobilization of retained ferrihydrite colloids. This process

184

was conducted in an argon-filled glovebox (O2: 0−10 ppmv). To dissolve the

185

ferrihydrite colloids retained on the quartz sand, 10 mL of 1 M HCl solution was

186

added into each segment (7.5 g sand), and the mixture was continuously shaken at 150

187

rpm for 12 h. In an additional experiment (i.e., in the presence of 31.3 µM sulfide), 10

188

mL of chloroform was transferred into each segment to extract and probe the retained

189

S(0) in the column.

190

Batch Experiments. To quantitatively identify the reaction intermediates of

191

ferrihydrite upon reduction by sulfide, a series of batch experiments were conducted

192

at conditions identical to those used in the transport experiments. All the experiments

193

were operated at the room temperature with oxygen limited conditions (undetectable

194

DO). For each test, 180 mL of 0.375 mM ferrihydrite suspension was transferred into

195

a 190-mL reactor, and different initial sulfide concentrations (0‒46.9 µM) were

196

obtained by diluting 31.3 mM stock Na2S solution. To counteract sulfide partitioning

197

between liquid and gas phases, an empirical value of ~20 % higher initial sulfide 9 ACS Paragon Plus Environment

Page 11 of 33

Environmental Science & Technology

198

concentrations, as described above, was spiked into the solution and the headspace of

199

the reactor was kept at < 8 mL. Three mM NaCl was used as the background

200

electrolyte and the solution pH was buffered at 6.0 ± 0.1 with 5 mM MES. The reactor

201

was immediately sealed and stirred at 600 rpm using a Teflon-coated magnetic

202

stirring bar. All batch experiments were conducted at least in duplicate.

203

Analyses. The concentrations of ferrihydrite colloids collected in column

204

experiments were quantified by measuring Fe(III) concentrations, which are expected

205

to be proportional to the number concentrations of colloids since negligible

206

differences in particle sizes were measured for the column influents and effluents

207

using DLS. Dissolved Fe(II) after filtration and total Fe(II) after digestion by 6 M HCl

208

were measured using a modified 1,10-phenanthroline method at a wavelength of 510

209

nm via a UV-vis spectrophotometer.46 Total Fe was determined after the sample was

210

digested by 6 M HCl and subsequently reduced by 10% hydroxylamine hydrochloride.

211

Fe(III) concentration was calculated by subtracting Fe(II) concentration from the total

212

Fe concentration.

213

The concentration of dissolved sulfide in the stock solution was calibrated with

214

the standard iodometric titration method.47 Dissolved sulfide in filtered (0.22 µm,

215

Nylon) samples during the reaction was quantified by the methylene blue method.48

216

Elemental sulfur (S(0)) was extracted by chloroform for 5 h and then analyzed by an

217

LC-15C high performance liquid chromatography (HPLC, Shimadzu) equipped with a

218

UV detector and an XDB-C18 column (4.6 × 50 mm) after derivatization with

219

triphenyphosphine (TPP) to form triphenyphosphine sulfide (TPPS) in the presence of 10 ACS Paragon Plus Environment

Environmental Science & Technology

Page 12 of 33

220

5% (w/v) phenol.49 The mobile phase consisted of a mixture of acetonitrile and water

221

(80:20, v/v) at 0.6 mL/min, and the detection wavelength was 254 nm.

222

The average hydrodynamic diameter and zeta potential of the ferrihydrite colloids

223

before and after reaction with sulfide in batch experiments were determined by DLS.

224

Solids for characterization were collected from the inlet of column (0–1 cm) after

225

completion of transport experiment as well as from batch experiments after 30 min of

226

reaction. The samples were prepared by placing wet pastes of solid materials onto

227

glass slides and then argon-dried inside the glovebox chamber. The potential phase

228

transformation of ferrihydrite upon reduction by sulfide was examined by X-ray

229

diffraction (XRD) using a Bruker d8 Advance X-ray diffractometer equipped with a

230

Cu Kα radiation source. X-ray photoelectron spectroscopy (XPS) spectra of the solid

231

samples were collected on a Kratos Axis Ultra XPS using a monochromated Al-Ka

232

X-ray source (1486.6 eV). Air exposure time during sample loading into the XPS

233

chamber was less than 1 min, thus potential redox variations of iron and sulfur are

234

regarded as negligible. Transmission electron microscope (TEM, Tecnai TM Spirit)

235

was employed to unravel the interaction between ferrihydrite colloids and sulfide. The

236

samples were prepared by placing a drop of suspension (~20 µL) collected from the

237

column inlet (0–1 cm) after the transport experiments onto a 200-mesh carbon coated

238

copper grid, followed by drying in the glovebox.

239

Mass Recovery Calculation. The effluent mass recovery of ferrihydrite colloids

240

(Meff) was obtained by dividing the mass of ferrihydrite colloids collected in the

241

effluents (all 37.5 PVs) by that injected into the column. Details for the calculation are 11 ACS Paragon Plus Environment

Page 13 of 33

Environmental Science & Technology

242

given in the Section S3 in SI. The mass recovery of ferrihydrite colloids retained in

243

the column (Mret) was calculated by dividing the total mass of ferrihydrite colloids

244

recovered from the dissection experiments by that injected into the column. Summing

245

the percentages of effluent mass and retained mass resulted in the overall mass

246

recoveries of ferrihydrite colloids in the transport experiments.

247 248

RESULTS AND DISCUSSION

249

Effect of Sulfide on Ferrihydrite Colloids Transport. Since ferrihydrite colloids

250

and quartz sands were positively and negatively charged, respectively (Table 1),

251

electrostatic attractions predominate the deposition of ferrihydrite colloids in quartz

252

sand initially. Regardless of sulfide concentrations examined, nearly all of the injected

253

ferrihydrite colloids were retained (C/C0 ≈ 0) during the first 2 PVs (Figure 1a). Once

254

these favorable retention sites of porous media (sand surfaces) are completely

255

occupied, a substantive breakthrough of ferrihydrite colloids starts to occur. For

256

example, in the absence of sulfide (0 µM), the value of C/C0 remained zero within the

257

first 2 PVs, increased sharply with the flushing from 2 to 15 PVs, and reached a

258

steady-state breakthrough (C/C0 = 0.95) at about 15 PVs. When the sand surfaces are

259

occupied by the positively charged ferrihydrite colloids, electrostatic repulsions start

260

to determine the transport of ferrihydrite colloids, resulting in a high breakthrough

261

during later stages of transport (e.g., > 2 PV). Similar findings were reported by

262

Kuhnen et al.6 who observed a nearly complete breakthrough of positively charged

263

hematite colloids (C/C0 ≈ 1) in negatively charged quartz sands under the comparably 12 ACS Paragon Plus Environment

Environmental Science & Technology

264

Page 14 of 33

experimental conditions (3 mM NaNO3 and pH 5.8) with our study.

265

Interestingly, sulfide was found to have a significant impact on the breakthrough

266

of ferrihydrite colloids (Figure 1a). The Meff of ferrihydrite colloids declined from

267

94.7 to 81.6, to 68.5, and to 48.8% when the sulfide concentration was elevated from

268

0 to 15.6, to 31.3, and to 46.9 µM, respectively (Table S2). This is due primarily to

269

the less electrostatic repulsion interaction between positively charged ferrihydrite

270

colloids at higher sulfide concentrations (Table 1). A negative linear correlation (R2 =

271

0.985) existed between the Meff of ferrihydrite colloids and the initial sulfide

272

concentration (Figure S7), suggesting that sulfide concentration controls the transport

273

of ferrihydrite colloids. As expected, the Mret increased from 8.9 to 26.7 and to 37.4%

274

as the concentration of sulfide elevated from 0 to 31.3 and to 46.9 µM, respectively

275

(Figure 1b, Table S2).

276

The presence of sulfide also substantially affected the shapes of BTCs and RPs of

277

ferrihydrite colloids (Figure 1a,b). The BTCs of ferrihydrite colloids were almost

278

symmetrical in shape and exhibited low tailing in the presence of low concentrations

279

(0–7.8 µM) of sulfide. In contrast, the shapes of the BTCs became asymmetrical and

280

the steady-state breakthrough started to disappear when the sulfide concentration was

281

≥ 15.6 µM. In the presence of low concentrations of sulfide, the retention of

282

ferrihydrite colloids in sand decreased linearly (R2 > 0.910, not shown) with the

283

distance from inlet. In the presence of higher sulfide, however, the retention of

284

ferrihydrite colloids exhibited a hyper-exponential decay with greater retention in the

285

section adjacent to the column inlet (0−3 cm) (Figure 1b, Table S2). For example, 13 ACS Paragon Plus Environment

Page 15 of 33

Environmental Science & Technology

286

with an initial 46.9 µM sulfide, the fraction of ferrihydrite colloids deposited in the

287

column inlet (0−3 cm) was about 53.0%, compared to 32.6% in the absence of sulfide

288

(Table S2). The similar type of hyper-exponential retention for colloids was

289

previously

290

conditions.7,24,50,51

encountered

under

both

favorable

and

unfavorable

attachment

291

The overall mass recovery of ferrihydrite colloids, taking the Meff and Mret into

292

account, decreased from 103.7% in the absence of sulfide to 86.2% in the presence of

293

46.9 µM sulfide (Table S2). This unbalance triggered by sulfide reflects that the redox

294

reactions (e.g., reductive dissolution) probably occurred between ferrihydrite colloids

295

and sulfide, decreasing the total mass of ferrihydrite and thus affecting the fate of

296

ferrihydrite colloids. In addition, the increase in Mret with increasing sulfide

297

concentration suggests that sulfide enhanced the retention of ferrihydrite colloids in

298

porous media. Possible mechanisms for these observations may be related to multiple

299

factors such as ionic strength, pH, and the redox reactions along with the products

300

generated. As the ionic strength (3 mM NaCl and 5 mM MES) and pH (6.0) remained

301

constant over the course of the experiments, the influence of these two factors was

302

precluded. Consequently, it is rational to assume that the redox reactions between

303

ferrihydrite colloids and sulfide, as stated above, and the associated reaction products

304

are most likely to be responsible for the reduced breakthrough of ferrihydrite in the

305

column. More details will be discussed later.

306

The effect of sulfide on the transport of ferrihydrite colloids was further evaluated

307

with regard to the travel distance, which is defined as the distance with 99.9% of the 14 ACS Paragon Plus Environment

Environmental Science & Technology

308 309

Page 16 of 33

particles retained in porous medium. The travel distance can be simply evaluated by4 L 0.01 = ln(0.01)

L Cout ln( ) C

(1)

310

where L is the length of the packed bed (m), Cout is the effluent ferrihydrite colloids

311

concentration obtained at 22.5 PVs, and C is the fraction of inlet ferrihydrite colloids

312

concentration that was not suffered from redox reactions, which can be evaluated as C

313

= C0 × (Meff + Mret), where C0 is the concentration of influent ferrihydrite colloids

314

(0.375 mM) . Variation of travel distance exhibited an inverse correlation with sulfide

315

concentration (Figure 1c), showing a remarkable decrease with increasing sulfide

316

concentration. The estimated travel distance of ferrihydrite colloids in the absence of

317

sulfide was nearly 7-fold larger than that in the presence of 46.9 µM sulfide.

318

Redox Reactions and Associated Products during the Transport. The redox

319

reactions between ferrihydrite and sulfide have been proposed to occur through a

320

sequence of reaction steps at the ferrihydrite surface, including surface complex

321

formation, electron transfer, release of the oxidized product, and subsequent

322

detachment of Fe(II).31,32,36 To explicitly decipher the reactions and the associated

323

products in our study, batch experiments were first conducted at solution conditions

324

identical to those used in the transport experiments. In all the cases investigated,

325

dissolved sulfide concentration was completely consumed in the first 5 min (data not

326

shown). Total Fe(II) concentration increased rapidly within the first 5 min and

327

subsequently leveled off during the rest of experiments (Figure 2a). These results

328

suggest a fast kinetics upon reaction of ferrihydrite with sulfide, which agrees well

15 ACS Paragon Plus Environment

Page 17 of 33

Environmental Science & Technology

329

with earlier findings in the same scenarios.31,32 The concentration of total Fe(II)

330

rapidly increased with increasing initial sulfide concentration, with a predominance (>

331

80%) of dissolved Fe(II) (data not shown). An excellent linear correlation (R2 = 0.989)

332

between Fe(II) generation and sulfide consumption was observed with a linear slope

333

of 0.53 (Figure 2b). Given that only one electron was involved in the reduction of

334

ferrihydrite to Fe(II), the slope of 0.53 reveals that each sulfide provided

335

approximately two electrons for ferrihydrite reduction. Thus, elemental sulfur (S(0))

336

was likely the sole sulfur product, consistent with the earlier observations.31,32 Indeed,

337

analysis of the solid phase shows that S(0) constituted most of the reaction products of

338

sulfide oxidation by ferrihydrite colloids (i.e., 92–96%, Table S3).

339

FeS was demonstrated to be another essential sulfur product in addition to the S(0)

340

during ferrihydrite reduction by sulfide.32,33,52,53 However, the production of FeS in

341

our experiments is expected to be at least 10-fold lower compared to that of S(0)

342

(Table S3). It has been established that the production of FeS depended on the molar

343

ratio of initial sulfide concentration to the surface sites of Fe(III) oxides

344

(S(-II)/SS).33,53 Because the consumption of sulfide is much faster than the

345

detachment of Fe(II) from ferrihydrite surfaces, the higher S(-II)/SS ratio is conducive

346

to channel Fe(II) into FeS formation from the remaining sulfide while the lower

347

S(-II)/SS ratio may not be favorable for the production of significant amount of FeS

348

due to the low concentration of remaining sulfide in the solution.33 A recent study

349

showed that the build-up of substantial amount of FeS occurred when the S(-II)/SS

350

ratio was higher than a certain threshold (i.e., ca. 36).33 Assuming the concentration of 16 ACS Paragon Plus Environment

Environmental Science & Technology

Page 18 of 33

351

surface sites of ferrihydrite was 6.3×10-6 mol/m2,54 the S(-II)/SS ratios obtained in our

352

study were 0.26–1.55, much lower than those reported.33 As a result, the formation of

353

FeS in our study is anticipated to be of minor importance.

354

In the column experiments, the generation of Fe(II) and S(0) as a function of

355

sulfide concentration was also observed (Figure 3). Consistent with the results

356

obtained in the batch experiments, Fe(II) concentration increased rapidly in response

357

to the increment in initial sulfide concentration (Figure 3a). The peak concentration of

358

S(0) accounted for ~80% of total sulfur when the initial concentration of sulfide was

359

31.3 µM (Figure 3b). Together with S(0) that was retained in the column (Figure S8),

360

the total of S(0) accounted for 92% of the initial sulfide, suggesting that S(0) was the

361

primary product of sulfide oxidation. To further identify the solid-phase sulfur

362

products, XPS analyses were performed for the samples collected from the column

363

inlet (0‒1 cm). Clearly, the high-resolution XPS spectra of S2s spectra proved that, in

364

the presence of 46.9 µM sulfide, the primary solid-phase sulfur species formed from

365

sulfide oxidation by ferrihydrite was elemental S(0) (Figure S9, Table S4).

366

To sum up, Fe(II) and S(0) are assigned to be the two main products for the

367

reactions between ferrihydrite colloids and sulfide in this study. Therefore, reductive

368

dissolution and formation of these two products are assumed to be accountable for the

369

reduced breakthrough of ferrihydrite colloids in the column in the presence of sulfide.

370

Role of Reductive Dissolution on the Reduced Breakthrough. The reductive

371

dissolution of ferrihydrite with production of Fe(II) unequivocally decreased the

372

overall mass of ferrihydrite, which apparently reduces the breakthrough of colloids in 17 ACS Paragon Plus Environment

Page 19 of 33

Environmental Science & Technology

373

the column (see Mred, Table 1). To evaluate the impact of reductive dissolution on

374

ferrihydrite colloids transport, the transport of ferrihydrite colloids was examined in

375

the presence of hydroquinone, which has been proven to be effective in reducing

376

ferrihydrite colloids with Fe(II) as the sole inorganic product.45 Different from the

377

pronounced decrease caused by 31.3 µM sulfide, the transport of ferrihydrite colloids

378

was only slightly weakened by the same concentration of hydroquinone (Figure 4a).

379

The same extent of ferrihydrite reduction is reflected by the comparable BTCs of

380

Fe(II) in the presence of hydroquinone and sulfide (Figure 4b). As hydroquinone did

381

not result in any detectable alternation in the zeta potential of ferrihydrite colloids

382

(Table 1), the RPs of ferrihydrite colloids in the presence and absence of

383

hydroquinone were similar (Figure 4c). The direct contribution of ferrihydrite

384

reduction by sulfide can be approximately estimated from the difference of

385

ferrihydrite colloids transport with and without hydroquinone. Consequently, the

386

contribution of reduction on the reduced breakthrough of ferrihydrite colloids is

387

essentially attributed to the dissolution of ferrihydrite colloids by sulfide, which

388

decreased the total breakthrough concentration but did not alter the shapes of BTCs

389

and RPs of ferrihydrite colloids.

390

Role of Fe(II) on the Reduced Breakthrough. The dissolved Fe(II), which

391

makes up of a primary fraction of total Fe(II) produced, is expected to catalyze the

392

transformation of ferrihydrite colloids to either goethite or lepidocrocite,38‒41 and thus

393

likely alters the colloids transport in the column. To examine this influence, the sulfide

394

solution fed into the column was replaced by 53.6 µM dissolved Fe(II), which is close 18 ACS Paragon Plus Environment

Environmental Science & Technology

Page 20 of 33

395

to that produced in the presence of 46.9 µM sulfide. Our XRD measurements

396

indicated that the transformation of ferrihydrite triggered by the dissolved Fe(II) was

397

negligible under the tested conditions (data not shown), largely due to the much

398

shorter contact time (~ 12 min) between ferrihydrite and dissolved Fe(II) in our study

399

than those in previous studies (i.e., days). The presence of 53.6 µM dissolved Fe(II)

400

did not significantly affect the transport and retention behaviors of ferrihydrite

401

colloids in quartz sand (Figure 4a), confirming that the influence of dissolved Fe(II)

402

on the transport of ferrihydrite colloids is insignificant.

403

Role of S(0) on the Reduced Breakthrough. The generated S(0) particles that

404

are negatively charged at ambient conditions55 likely affect the transport of positively

405

charged ferrihydrite colloids. Despite the observation of similar BTCs of Fe(II)

406

rendered by sulfide and hydroquinone due to the same number of electrons per mole

407

they donated, the transport and retention of ferrihydrite colloids in the presence of

408

31.3 µM hydroquinone was greater (Meff = 83.8 vs. 68.5%, Figure 4a, Table 1) and

409

lower (Mret = 6.6 vs. 26.7%, Figure 4c, Table 1), respectively, compared to the same

410

concentration (31.3 µM) of sulfide. Moreover, the zeta potential of ferrihydrite

411

colloids (initially 40.5 mV) in the presence of 31.3 µM hydroquinone (40.0 mV) was

412

much higher than that with 31.3 µM sulfide (32.1 mV) (Table 1). The differences in

413

the transport and zeta potential of ferrihydrite colloids collectively imply that, in

414

addition to the effect of direct reductive dissolution, the reaction products, i.e., S(0)

415

particles, play an appreciable role on the reduced breakthrough of ferrihydrite colloids

416

in the column. As the ferrihydrite colloids and sulfide were continuously injected into 19 ACS Paragon Plus Environment

Page 21 of 33

Environmental Science & Technology

417

column, the formed S(0) particles during ferrihydrite colloids transport were likely to

418

adsorb onto ferrihydrite colloids and decreased their overall zeta potentials by

419

electrostatic neutralization effect, thus enhancing the retention of ferrihydrite colloids

420

in quartz sand.

421

To test the above speculation, additional experiments were performed by

422

measuring the transport of ferrihydrite colloids in the presence of 31.3 µM S(0)

423

particles (see preparation in Section S4) instead of sulfide. Considering that the

424

morphology of the synthesized S(0) particles was not identical to that of the S(0)

425

particles produced in the column transport experiments, the results presented here is

426

only for qualitative evaluation of the role of S(0) particles on ferrihydrite colloids

427

transport. Table 1 shows that the zeta potential of ferrihydrite colloids decreased from

428

40.5 to 34.5 mV when S(0) concentration was increased from 0 to 31.3 µM. A close

429

inspection of the BTCs of ferrihydrite colloids obtained with/without 31.3 µM S(0)

430

particles (Figure 4a) revealed that the Meff value was substantially lower in the

431

presence versus absence of 31.3 µM S(0) (73.7% vs. 94.7%). We further performed a

432

transient triple-pulse transport experiment to clearly compare the transport of

433

ferrihydrite colloids in the copresence of sulfide and S(0) particles with that in the

434

absence and presence of sulfide (Table S1, Figure 4d). Results showed that the

435

breakthrough C/C0 value of ferrihydrite colloids dropped from 0.94 in the absence of

436

sulfide to 0.70 in the presence of 31.3 µM sulfide, and further to 0.40 in the

437

concurrent presence of 31.3 µM sulfide and 31.3 µM S(0) particles (Figure 4d). These

438

observations strongly support the proposition that the presence of S(0) particles in the 20 ACS Paragon Plus Environment

Environmental Science & Technology

439

Page 22 of 33

suspension does favor the retention of ferrihydrite colloids (see Mret-sulfide, Table 1).

440

The promotional effect of S(0) particles on retention accounted for the varying

441

shapes of RPs and thus the BTCs of ferrihydrite colloids. The hyper-exponential vs.

442

flat RPs in the presence of lower (0–7.8 µM) vs. higher (15.6–46.9 µM) sulfide

443

concentrations, respectively, may be attributed to the pronounced aggregation of

444

ferrihydrite NPs in the inlet triggered by the fast build-up of larger amount of negative

445

S(0) particles at higher sulfide concentrations. Comparison of the TEM micrographs

446

of suspensions collected from the column inlet (0–1 cm) clearly demonstrates that the

447

larger aggregates occurred at higher sulfide concentration (e.g., 46.9 µM, Figure S10).

448

These large aggregates could narrow down the pore throats of porous media and thus

449

aggravate the physical straining, producing the hyperexponential RPs for the

450

ferrihydrite colloids at high sulfide concentrations. Similarly, recent cotransport study

451

observed that the deposition of positively charged nTiO2 colloids in quartz sand was

452

largely expedited in the copresence of negatively charged nC60 particles.10 The

453

asymmetrical BTCs and lack of steady-state breakthrough for ferrihydrite colloids

454

transport occurring at higher sulfide concentration (Figure 1a) are likely due to the

455

fact that the adsorbed S(0) particles decreased the electrostatic repulsion attraction

456

between ferrihydrite colloids as well as between ferrihydrite colloids and sand (Table

457

1), thereby endowing more favorable sites for ferrihydrite colloids deposition onto

458

sand. This is ascertained by the batch adsorption experiments, demonstrating that the

459

adsorption of ferrihydrite colloids on quartz sand was substantially enhanced by the

460

addition of 31.3 µM S(0) particles (Figure S11). 21 ACS Paragon Plus Environment

Page 23 of 33

Environmental Science & Technology

461

Relative Contributions of Reductive Dissolution and S(0) on the Reduced

462

Breakthrough. Given all the findings described above, we concluded that both the

463

reductive dissolution and the generation of elemental S(0) are responsible for the

464

reduced breakthrough of ferrihydrite colloids in the presence of sulfide. However, the

465

mechanisms for the influence are different. Reductive dissolution, as has already been

466

commented on above, only decreased the total mass of ferrihydrite colloids; whereas

467

elemental S(0) promoted the retention of ferrihydrite colloids in quartz sand, which

468

indirectly decreased their transport. A careful examination of the percentages of

469

ferrihydrite colloids decreased by reductive dissolution (Mred) and retained in column

470

as a result of the presence of sulfide concentration (Mret-sulfide) (Table 1) revealed that

471

the relative contribution of reductive dissolution to the reduced breakthrough of

472

ferrihydrite colloids in the column is similar to that of elemental S(0) over the tested

473

sulfide concentrations.

474

Implications. This work, to our knowledge, is the first study describing the role

475

of redox reactions between ferrihydrite colloids and sulfide on the transport of

476

ferrihydrite colloids in anoxic porous media. The most striking observation is that the

477

presence of sulfide at low concentrations significantly hinders the transport of

478

ferrihydrite colloids due to reductive dissolution and production of elemental S(0)

479

particles. The findings also highlight the distinct fate and transport of ferrihydrite

480

colloids in anoxic aquifers in the presence of low concentrations of sulfide.

481

Specifically, when the ferrihydrite colloids are injected into a contaminated aquifer to

482

elevate the efficiency of in situ bioremediation,56,57 the peculiar effect of sulfide 22 ACS Paragon Plus Environment

Environmental Science & Technology

Page 24 of 33

483

produced from microbial sulfate reduction at organic-rich conditions is worthy of

484

attention because the presence of sulfide weakens the transport distance of ferrihydrite

485

colloids.

486

In contrast to the broad knowledge of colloids transport research,1,2,4,24,58 finding

487

in this study extends our basic understandings on colloid transport processes from

488

steady state redox conditions (i.e., in the absence of chemical reactions) to perturbed

489

redox conditions (i.e., in the presence of chemical reactions). While this study has

490

focused on ferrihydrite transport impacted by sulfide, our results may have a profound

491

implications to the transport of other redox sensitive colloids in other redox dynamic

492

environments, i.e., in the interface of groundwater and surface water interaction,

493

where steep chemical (e.g., sulfur and organic matter) gradients and microbial

494

population dynamics facilitate the redox shifts.59,60 The oxidation/reduction of these

495

colloids and the subsequent formation of secondary solid phase may also affect the

496

final mobility of colloids, which deserves further investigation. Classical DLVO

497

theory and transport models were used to model colloids stability and transport under

498

chemically stable conditions. However, the transport behavior in the presence of

499

redox reactions is more complicated than those previous studies. Thus, further model

500

development is required to gain a deeper understanding on the transport of colloids in

501

redox dynamic systems.

502 503 504

Supporting Information Available Additional information: Sections S1‒S4, Figure S1‒S11, Table S1‒S4. This 23 ACS Paragon Plus Environment

Page 25 of 33

Environmental Science & Technology

505

material is available free of charge via the Internet at http://pubs.acs.org.

506 507

ACKNOWLEDGEMENTS

508

We sincerely thank Dr. Daniel Giammar at the Washington University in St. Louis

509

for his critical comments, constructive suggestion, and editing. Discussions with Dr.

510

Moli Wan at the University of Bayreuth, Dr. Bin Gao at the University of Florida and

511

Dr. Zimeng Wang at the Stanford University were instructive. This work was

512

supported by the Ministry of Education for New Century Excellent Talents Support

513

Plans (NCET-13-1014) and the Natural Science Foundation of China (NSFC, No.

514

41522208, 41521001). Peng Liao acknowledges financial support from Shanghai

515

Tongji Gao Tingyao Environmental Science and Technology Development

516

Foundation (STGEF).

517 518

REFERENCES

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

(1) Ryan, J. N.; Elimelech, M. Colloid mobilization and transport in groundwater. Colloid Surf. A-Physicochem. Eng. Asp. 1996, 107, 1–56. (2) Sen, T. K.; Khilar, K. C. Review on subsurface colloids and colloid-associated contaminant transport in saturated porous media. Adv. Colloid Interface Sci. 2006, 119, 71–96. (3) Puls, R. W.; Powell, R. M. Transport of inorganic colloids through natural aquifer material: Implications for contaminant transport. Environ. Sci. Technol. 1992, 26, 614–621. (4) Tosco, T.; Bosch, J.; Meckenstock, R. U.; Sethi, R. Transport of ferrihydrite nanoparticles in saturated porous media: Role of ionic strength and flow rate. Environ. Sci. Technol. 2012, 46, 4008−4015. (5) Kretzschmar, R.; Sticher, H. Transport of humic-coated iron oxide colloids in a sandy soil: Influence of Ca2+ and trace metals. Environ. Sci. Technol. 1997, 31, 3497−3504. (6) Kuhnen, F.; Barmettler, K.; Bhattacharjee, S.; Elimelech, M.; Kretzschmar, R. Transport of iron oxide colloids in packed quartz sand media: Monolayer and multilayer deposition. J. Colloid Interface Sci. 2000, 231, 32–41.

24 ACS Paragon Plus Environment

Environmental Science & Technology

535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577

Page 26 of 33

(7)

Hong, Y. S.; Honda, R. J.; Myung, N. V.; Walker, S. L. Transport of iron-based nanoparticles: Role of magnetic properties. Environ. Sci. Technol. 2009, 43, 8834–8839. (8) Lin, J. F.; Xie, J. C.; Li, M.; Zhou, G. Q.; Zhang, J. H.; Zhang, H. T.; Yi, X. W. Goethite colloid enhanced Pu transport through a single saturated fracture in granite. J. Contam. Hydrol. 2014, 164, 251–258. (9) Legg, B. A.; Zhu, M. Q.; Comolli, L. R.; Gilbert, B.; Banfield, J. F. Impacts of ionic strength on three-dimensional nanoparticle aggregate structure and consequences for environmental transport and deposition. Environ. Sci. Technol. 2014, 48, 13703–13710. (10) Cai, L.; Tong, M. P.; Ma, H. Y.; Kim, H. J. Cotransport of titanium dioxide and fullerene nanoparticles in saturated porous media. Environ. Sci. Technol. 2013, 47, 5703−5710. (11) Wu, D.; Tong, M. P.; Kim, H. J.Influence of perfluorooctanoic acid on the transport and deposition behaviors of bacteria in quartz sand. Environ. Sci. Technol. 2016, 50, 2381−2388. (12) Liang, L. Y.; Hofmann, A.; Gui, B. H. Ligand-induced dissolution and release of ferrihydrite colloids. Geochim. Cosmochim. Acta 2000, 64, 2027–2037. (13) Hofmann, A.; Liang, L. Mobilization of colloidal ferrihydrite particles in porous media-An inner-sphere complexation approach. Geochim. Cosmochim. Acta 2007, 71, 5847−5861. (14) Sharma, V. K.; Filip, J.; Zboril, R.; Varma, R. S. Natural inorganic nanoparticles–formation, fate, and toxicity in the environment. Chem. Soc. Rev. 2015, 44, 8410−8423. (15) Henderson, R.; Kabengi, N.; Mantripragada, N.; Cabrera, M.; Hassan, S.; Thompson, A. Anoxia-induced release of colloid- and nanoparticle-bound phosphorus in grassland soils. Environ. Sci. Technol. 2012, 46, 11727−11734. (16) Villholth, K. G. Colloid characterization and colloidal phase partitioning of poly-cyclic aromatic hydrocarbons in two creosote-contaminated aquifers in Denmark. Environ. Sci. Technol. 1999, 33, 691−699. (17) Loos, M.; Voegelin, A. Colloid-facilitated contaminant transport in anoxic aquifers.http://www.ibp.ethz.ch/research/aquaticchemistry/teaching/archive_past_lecture s/term_paper_08_09/HS08_Loos_rev_termpaper_ms.pdf, 2009. (18) Thompson, A.; Chadwick, O. A.; Boman, S.; Chorover, J. Colloid mobilization during soil iron redox oscillations. Environ. Sci. Technol. 2006, 40, 5743–5749. (19) Fritzsche, A.; Bosch, J.; Rennert, T.; Heister, K.; Braunschweig, J.; Meckenstock, R. U.; Totsche, K. U. Fast microbial reduction of ferrihydrite colloids from a soil effluent. Geochim. Cosmochim. Acta 2012, 77, 444–456. (20) Garg, S.; Rong. H. Y.; Miller, C. J.; Waite, T. D. Oxidative dissolution of silver nanoparticles by chlorine: Implications to silver nanoparticle fate and toxicity. Environ. Sci. Technol. 2016, 50, 3890−3896. (21) Li, Y.; Zhang, W.; Niu, J .F.; Chen, Y. S. Surface-coating-dependent dissolution, aggregation, and reactive oxygen species (ROS) generation of silver nanoparticles under different irradiation conditions. Environ. Sci. Technol. 2013, 47, 10293−10301. (22) Fu, H.; Qu, X. L.; Chen, W.; Zhu, D. Q. Transformation and destabilization of graphene oxide in reducing aqueous solutions containing sulfide. Environ. Chem. 2014, 9999, 1–7.

25 ACS Paragon Plus Environment

Page 27 of 33

Environmental Science & Technology

578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619

(23) Pederson, 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. (24) Wang, D. J.; Paradelo, M.; Bradford, S. A.; Peijnenburg, W. J. G. M.; Chu, L. Y.; Zhou, D. M. Facilitated transport of Cu with hydroxyapatite nanoparticles in saturated sand: Effects of solution ionic strength and composition. Water Res. 2011, 45, 5905−5915. (25) Jambor, J. L. Occurrence and constitution of natural and synthetic ferrihydrite, a widespread iron oxyhydroxide. Chem. Rev. 1998, 98, 2549–2585. (26) Michel, F. M.; Ehm, L.; Antao, S. M.; Lee, P. L.; Chupas, P.; Liu, G.; Strongin, D. R.; Schoonen, M. A. A.; Phillips,, B. L.; Parise, J. B. The structure of ferrihydrite, a nanocrystalline material. Science 2007, 316, 1726–1729. (27) Wang, X. M.; Li, W.; Harrington, R.; Liu, F.; Parise, J. B.; Feng, X. H.; Sparks, D. L. Effect of ferrihydrite crystallite size on phosphate adsorption reactivity. Environ. Sci. Technol. 2013, 47, 10322−10331. (28) Regelink, I. C.; Weng, L.; van Riemsdijk W. H. The contribution of organic and mineral colloidal nanoparticles to element transport in a podzol soil. Appl. Geochem. 2011, 26, S241–S244. (29) Suter, D.; Banwart, S.; Stumm, W. Dissolution of hydrous iron(III) oxides by reductive mechanisms. Langmuir 1991, 7, 809–813. (30) Peiffer, S.; Dos Santos Afonso, M.; Wehrli, B.; Gaechter, R. Kinetics and mechanism of the reaction of hydrogen sulfide with lepidocrocite. Environ. Sci. Technol. 1992, 26, 2408−2413. (31) Poulton, S. W. Sulfide oxidation and iron dissolution kinetics during the reaction of dissolved sulfide with ferrihydrite. Chem. Geol. 2003, 202, 79– 94. (32) Poulton, S. W.; Krom, M. D.; Raiswell, R. A revised scheme for the reactivity of iron (oxyhydr)oxide minerals towards dissolved sulfide. Geochim. Cosmochim. Acta 2004, 68, 3703–3715. (33) Hellige, K.; Pollok, K.; Larese-Casanova, P.; Behrends, T.; Peiffer, S. Pathways of ferrous iron mineral formation upon sulfidation of lepidocrocite surfaces. Geochim. Cosmochim. Acta 2012, 81, 69−81. (34) Wan, M. L.; Shchukarev, A.; Lohmayer, R.; Planer-Friedrich, B.; Peiffer, S. Occurrence of surface polysulfides during the interaction between ferric (hydr)oxides and aqueous sulfide. Environ. Sci. Technol. 2014, 48, 5076−5084. (35) Dos Santos, A. M.; Stumm, W. Reductive dissolution of iron(III) (hydr)oxides by hydrogen sulfide. Langmuir 1992, 8, 1671−1675. (36) Yao, W.; Millero, F. J. Oxidation of hydrogen sulfide by hydrous Fe(III) oxides in seawater. Mar. Chem. 1996, 52, 1−16. (37) Flynn, T. M.; O’Loughlin, E. J.; Mishra, B.; DiChristina, T. J.; Kemner, K. M. Sulfur-mediated electron shuttling during bacterial iron reduction. Science 2014, 344, 1039–1042. (38) Hansel, C. M.; Benner, S. G.; Fendorf, S. Competing Fe(II)-induced mineralization pathways of ferrihydrite. Environ. Sci. Technol. 2005, 39, 7147−7153.

26 ACS Paragon Plus Environment

Environmental Science & Technology

620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663

Page 28 of 33

(39) Yang, L.; Steefel, C. I.; Marcus, M. A.; Bargar, J. R. Kinetics of Fe(II)-catalyzed transformation of 6-line ferrihydrite under anaerobic flow conditions. Environ. Sci. Technol. 2010, 44, 5469−5475. (40) 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. (41) Li, X. M.; Liu, T. X.; Li, F. B.; Zhang, W.; Zhou, S. G.; Li, Y. T. Reduction of structural Fe(III) in oxyhydroxides by Shewanella decolorationis S12 and characterization of the surface properties of iron minerals. J. Soil. Sediment. 2012, 12, 217–227. (42) Wang, D. J.; Jin, Y. Jaisi, D. P. Effect of size-selective retention on the cotransport of hydroxyapatite and goethite nanoparticles in saturated porous media. Environ. Sci. Technol. 2015, 49, 8461–8470. (43) Nabiul Afrooz, A. R. M.; Das, D.; Murphy, C. J.; Vikeslan, P.; Saleh, N. B. Co-transport of gold nanospheres with single-walled carbon nanotubes in saturated porous media. Water Res. 2016, 99, 7−15. (44) Syngouna, V. I.; Chrysikopoulos, C. V. Cotransport of clay colloids and viruses through water-saturated vertically oriented columns packed with glass beads: gravity effects. Sci. Total Environ. 2016, 545–546, 210–218. (45) Jasmine, J. E.; Gilbert, B.; Penn, R. L. Influence of size on reductive dissolution of six-line ferrihydrite. J. Phys. Chem. C 2008, 112, 12127–12133. (46) Tamura, H.; Goto, K.; Yotsuyanagi, T.; Nagayama, M. Spectrophotometric determination of iron (II) with 1, 10-phenanthroline in the presence of large amounts of iron (III). Talanta 1974, 21, 314−318. (47) Greenberg, A.; Clesceri, L. S.; Eaton, A. D. Standard Methods for the Examination of Water and Wastewater, 18th ed.; American Public Health Association: Washington, DC, 1992. (48) Allen, H.; Fu, G.; Deng, D. Analysis of acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) for the estimation of potential toxicity in aquatic sediments. Environ. Toxicol. Chem. 1993, 12, 1441–1453. (49) Taylor, B. F.; Hood, T. A.; Pope, L. A. Assay of sulfur as triphenylphosphine sulfide by high performance liquid chromatography: application to studies of sulfur bioproduction and sulfur in marine sediments. J. Microbial. Methods 1989, 9, 221–231. (50) Tufenkji, N.; Elimelech, M. Deviation from the classical colloid filtration theory in the presence of repulsive DLVO interactions. Langmuir 2004, 20, 10818–10828. (51) Tong, M. P.; Johnson, W. P. Colloid population heterogeneity drives hyperexponential deviation from classic filtration theory. Environ. Sci. Technol. 2007, 41, 493−499. (52) Peiffer, S.; Behrends, T.; Hellige, K.; Larese-Casanova, P.; Wan, M. L.; Pollok, K. Pyrite formation and mineral transformation pathways upon sulfidation of ferric hydroxides depend on mineral type and sulfide concentration. Chem. Geol. 2015, 400, 44–55. (53) Peiffer, S.; Wan, M. Reductive dissolution and reactivity of ferric (Hydr)oxides: New insights and implications for environmental redox processes, in Iron oxides: From nature to applications. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, 2016.

27 ACS Paragon Plus Environment

Page 29 of 33

Environmental Science & Technology

664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680

doi: 10.1002/9783527691395.ch3. (54) Peiffer, S.; Gade, W. Reactivity of ferric oxides toward H2S at low pH. Environ. Sci. Technol. 2007, 41, 3159–3164. (55) Steudel, R. Aqueous sulfur sols. Top. Curr. Chem. 2003, 230, 153–166. (56) Tobler, N. B.; Hofstetter, T. B.; Straub, K. L.; Fontana, D.; Schwarzenbach, R. P. Iron-mediated microbial oxidation and abiotic reduction of organic contaminants under anoxic conditions. Environ. Sci. Technol. 2007, 41, 7765−7772. (57) Braunschweig, J.; Bosch, J.; Meckenstock, R. U. Iron oxide nanoparticles in geomicrobiology: From biogeochemistry to bioremediation. New Biotechnol. 2013, 30, 793−802. (58) Elimelech, M.; Gregory, J.; Jia, X.; Williams, R. Particle Deposition and Aggregation: Measurement, Modelling and Simulation; Butterworth-Heinemann: Woburn, MA, 1995. (59) Christensen, T.H.; Bjerg, P. L.; Banwart, S. A.; Jakobsen, R.; Heron, G.; Albrechtsen, H. J. Characterization of redox conditions in groundwater contaminant plumes. J. Contam. Hydrol. 2000, 45, 165–241. (60) Killeen, S. A handbook on the groundwater–surface water interface and hyporheic zone for environment managers. EPA Science reports, 2009.

681 682 683

28 ACS Paragon Plus Environment

Environmental Science & Technology

(a)

1.0

Ferrihydrite (C/C0)

Page 30 of 33

0.8 0.6 0.4 0 µM 7.8 µM 15.6 µM 31.3 µM 46.9 µM

0.2 0.0 0

5

10

15

20

25

30

35

40

PV

Retention (µ M/g sand)

3.0

(b) 0 µM 7.8 µM 15.6 µM 31.3 µM 46.9 µM

2.5 2.0 1.5 1.0 0.5 0.0

1

2

3

4

5

6

7

8

9

10

Distance (cm)

(c)

10

L0.01 (m)

8 6 4 2 0 0

684 685 686 687 688 689 690 691 692

10

20

30

40

50

Sulfide (µM)

Figure 1 (a) Breakthrough curves, (b) retention profiles, and (c) predicted maximum travel distance (L0.01) of ferrihydrite colloids as a function of sulfide concentration (0, 7.8, 15.6, 31.3, and 46.9 µM, respectively). C/C0 of ferrihydrite colloids refers to the ratio of effluent concentration of ferrihydrite at a sampling time (C) to the influent concentration of ferrihydrite colloids (C0 = 0.375 mM). Lines in (a-c) are not models fits of data. They are only shown to guide the eye. Experimental conditions are: 0.375 mM initial ferrihydrite colloids concentration, 2 mL/min flow rate, pH 6.0, and 3 mM NaCl. Error bars indicate 95% confidence intervals based on replicate experiments. 29 ACS Paragon Plus Environment

Page 31 of 33

Environmental Science & Technology

100

60 40 20 0

R2=0.989

40 30 20 10 0

0

693 694 695 696 697 698 699 700 701 702 703 704

(b) [S(-II)]consumed=0.53*[Fe(II)] + 0.512

80

Fe(II) (µ M)

50

(a)

15.6 µM 46.9 µM

S(-II)consumed (µ M)

7.8 µM 31.3 µM

5

10

15

20

25

0

30

20

40

60

80

Fe(II)generated (µM)

Time (min)

Figure 2 Identification of reaction products upon ferrihydrite reduction by sulfide in batch experiments. (a) Effect of sulfide concentration (7.8, 15.6, 31.3, and 46.9 µM, respectively) on Fe(II) generation. Fitted curves were derived from first-order equation (Ct = Ceq(1 − e-kt), where Ct and Ceq are the concentration of Fe(II) at time t (min) and equilibrium, respectively, k is a pseudo first-order rate constant). (b) The consumption of sulfide versus the generation of Fe(II) measured at the end of individual experiments (30 min). The initial sulfide concentration for each experiments were 7.8, 15.6, 23.4, 31.3, 39.1, and 46.9 µM, respectively. Batch experimental conditions are: 0.375 mM initial ferrihydrite colloids concentration, pH 6.0, and 3 mM NaCl.

705

0.15

Elemental sulfur (S(0)) (C/C0)

Fe(II)eff (C/C0)

(a)

7.8 µM 15.6 µM 31.3 µM 46.9 µM

0.20

0.10

0.05

0.00 0

706 707 708 709 710 711 712 713

5

10

15

20

25

30

35

40

1.0

(b)

0.8

31.3 µM

0.6 0.4 0.2 0.0 0

5

10

PV

15

20

25

30

35

40

PV

Figure 3 Identification of reaction products upon ferrihydrite reduction by sulfide in column experiments. (a) Production of Fe(II) at different sulfide concentrations in the effluent. (b) Production of elemental sulfur in the presence of 31.3 µM initial sulfide concentration in the effluent. The C/C0 of Fe(II) in (a) and S(0) in (b) refer to the ratio of effluent concentration of Fe(II) and S(0) at a sampling time, respectively, to the influent concentrations of ferrihydrite colloids (C0 = 0.375 mM) and sulfide (C0 = 31.3 µM). The experimental conditions are the same as Figure 1.

714

30 ACS Paragon Plus Environment

Environmental Science & Technology

(a)

0.8 0.6 0.4 no sulfide 31.3 µM sulfide 31.3 µM hydroquinone 31.3 µM S(0) particles 53.6 µM dissolved Fe(II)

0.2 0.0 0

5

10

15

20

25

30

(b)

0.16

Fe(II)eff (C/C0)

Ferrihydrite (C/C0)

1.0

0.12 0.08 0.04 31.3 µM sulfide 31.3 µM hydroquinone

0.00

35

Page 32 of 33

0

40

5

10

15

PV

0.6

716 717 718 719 720 721 722 723 724 725

Ferrihydrite (C/C0)

Retention (µ M/g sand)

0.9

30

35

40

(d)

0.8 0.6

Step 1 no sulfide

0.4

Step 2 31.3 µM sulfide Step 3 31.3 µM sulfide + 31.3 µM S(0)

0.2

0.3 0.0

715

no sulfide 31.3 µM sulfide 31.3 µM hydroquinone 31.3 µM S(0) particles 53.6 µM dissolved Fe(II)

1.2

25

1.0

(c)

1.8 1.5

20

PV

0.0 1

2

3

4

5

6

7

8

9

10

0

5

10

Distance (cm)

15

20

25

30

35

40

PV

Figure 4 Effects of hydroquinone, dissolved Fe(II), S(0) particles, and sulfide on (a) breakthrough curves of ferrihydrite colloids, (b) breakthrough curves of Fe(II) production, and (c) retention profiles of ferrihydrite colloids. The concentration of hydroquinone and S(0) particles are the same as that of the sulfide concentration (31.3 µM). (d) Effect of multiple transport processes on ferrihydrite colloids transport in column. Step 1: 0.375 mM ferrihydrite colloids alone; Step 2: 0.375 mM ferrihydrite colloids + 31.3 µM sulfide; Step 3: 0.375 mM ferrihydrite colloids + 31.3 µM sulfide + 31.3 µM S(0) particles. Experimental conditions are: 0.375 mM initial ferrihydrite colloids concentration, 2 mL/min flow rate, pH 6.0, and 3 mM NaCl. Error bars indicate 95% confidence intervals based on replicate experiments.

726

31 ACS Paragon Plus Environment

Page 33 of 33

727 728

Environmental Science & Technology

Table 1 Electrokinetic potentials of ferrihydrite colloids and quartz sands, average hydrodynamic diameters of ferrihydrite colloids, and mass balance percentages for ferrihydrite colloids transport in column experiments a Conditions

ζferrihydrite b (mV)

ζsand c (mV)

Sizeferrihydrite d (nm)

Meff e (%)

Mred f (%)

Mret g (%)

Mret-inlet h (%)

Mret-sulfidei (%)

Mtot j (%)

0 µM 40.5 ± 1.9 –45.5 ± 0.5 112.5 ± 11.5 94.7 ± 4.5 0.0 ± 0.0 8.9 ± 0.1 32.6 ± 1.1 N.A. 103.7 ± 4.4 sulfide 7.8 µM 38.1 ± 1.1 –45.3 ± 1.3 121.2 ± 2.1 90.0 ± 1.3 5.0 ± 0.6 14.9 ± 1.7 36.2 ± 1.2 6.0 ± 2.4 110.0 ± 5.1 sulfide 15.6 µM 35.6 ± 1.4 –45.5 ± 1.4 137.0 ± 10.5 81.6 ± 3.5 9.3 ± 0.8 19.1 ± 0.5 40.6 ± 2.4 10.2 ± 0.8 110.0 ± 6.7 sulfide 31.3 µM 32.1 ± 3.0 –44.7 ± 0.6 153.4 ± 21.6 68.5 ± 3.7 14.8 ± 0.8 26.7 ± 1.1 45.5 ± 1.4 17.8 ± 1.0 110.0 ± 4.1 sulfide 46.9 µM 29.8 ± 2.9 –43.9 ± 0.8 174.8 ± 13.9 48.8 ± 9.3 18.9 ± 0.7 37.4 ± 2.5 53.0 ± 0.9 28.5 ± 2.2 105.1 ± 11.9 sulfide 31.3 µM S(0) 34.5 ± 0.2 –46.7 ± 1.2 311.0 ± 36.1 73.7 ± 4.1 0.0±0.0 27.4 ± 7.2 45.6 ± 3.2 N.A. 101.1 ± 3.2 particles 31.3 µM 40.0 ± 0.3 –44.2 ± 1.9 108.5 ± 12.6 83.3 ± 0.3 12.8 ± 0.5 6.6 ± 0.7 30.9 ± 0.3 N.A. 102.6 ± 1.5 Hydroquinone 53.6 µM 40.9 ± 1.6 –45.5 ± 0.5 107.9 ± 6.6 95.1 ± 2.4 0.0 ± 0.0 5.2 ± 1.2 33.9 ± 4.9 N.A. 99.9 ± 1.2 dissolved Fe(II) a N.A.: not applicable. b,cζ-potentials of ferrihydrite colloids and quartz sand, respectively. dAverage hydrodynamic diameter of ferrihydrite colloids. b,dThe values were measured by DLS at the end of batch experiments (30 min reaction). eMeff and fMred refer to the mass percentage of ferrihydrite colloids passing through the columns and reduced by sulfide. Details calculation of eMeff and fMred can be found in the SI. gMret refers to the mass percentage of ferrihydrite colloids retained in the columns. hMret-inlet is the mass percentage of ferrihydrite colloids that are retained near the column inlet (0–3 cm). iMret-sulfide (= Mret-with sulfide – Mret-without sulfide (8.9%)), reflects to the mass percentage of retained ferrihydrite colloids caused by sulfide. jMtot (= Meff + Mred + Mret) denotes the total mass percentages of Fe recovered from the columns. 729

32

ACS Paragon Plus Environment