Field Scale Mobility and Transport Manipulation of ... - ACS Publications

Subscriber access provided by University of Sussex Library

Remediation and Control Technologies

Field scale mobility and transport manipulation of carbonsupported nanoscale zero-valent iron (nZVI) in fractured media Meirav Cohen, and Noam Weisbrod Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b01226 • Publication Date (Web): 14 Jun 2018 Downloaded from http://pubs.acs.org on June 16, 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 40

1

Environmental Science & Technology

Manuscript TOC:

2

1 ACS Paragon Plus Environment


3

Field scale mobility and transport manipulation of carbon-supported

4

nanoscale zerovalent iron (nZVI) in fractured media

5

Meirav Cohen1 and Noam Weisbrod*1

6

7

8

Affiliation 1: The Zuckerberg Institute for Water Research, Blaustein

9

Institutes for Desert research, Ben Gurion University of the Negev,

10

Israel

11

12

*Corresponding author (Tel: +972-8-6596979 , Mobile: +972-52-8795756, Fax: +972-8-6596909, Secretary: +972-

13

6596714)

14 15

E-mail addresses: [email protected] (M. Cohen); [email protected] (N. Weisbrod)


Page 2 of 40

Page 3 of 40


16

Abstract

17

In field applications, mostly in porous media, transport of stabilized nano zerovalent iron

18

particles (nZVI) has never exceeded a few meters in range. In the present study, the

19

transport of Carbo-Iron Colloids (CIC), a composite material of activated carbon as a

20

carrier for nZVI stabilized by carboxymethyl cellulose (CMC), was tested under field

21

conditions. The field site lies within a fractured chalk aquitard characterized by moderately

22

saline (~13 mS) groundwater. A forced gradient tracer test was conducted where one

23

borehole was pumped at a rate of 8 L/min and CMC-stabilized CIC was introduced at an

24

injection borehole 47 meters up-gradient. Two CIC-CMC field applications were

25

conducted: one used high 100% wt. CMC (40 g/l) and a second used lower 9% wt. loading

26

(~2.7 g/l). Iodide was injected as a conservative tracer with the CIC-CMC in both cases.

27

The ratio between the CIC-CMC and iodide recovery was 76 and 45% in the high and low

28

CMC loading experiments, respectively. During the low CMC loading experiment, the

29

pumping rate was increased, leading to an additional CIC recovery of 2.5%. The results

30

demonstrate the potentially high mobility of nZVI in fractured environments and the

31

possibility for transport manipulation through the adjustment of stabilizer concentration and

32

transport velocity.



33

Keywords

34

nZVI, Colloid transport, fractured media, groundwater remediation, in situ, CMC.


Page 4 of 40

Page 5 of 40

35


1. Introduction

36

Over the past 20 years, the use of nano zerovalent iron (nZVI) for groundwater

37

remediation has gained much attention. Due to its high reactivity and mobility potential,

38

the application of nZVI is considered a promising technique for contaminated aquifer

39

remediation.1–4 Reactivity of nZVI is reflected in the effective transformation of many

40

contaminants, most notably chlorinated organic compounds.1,4,5 However, nZVI mobility

41

in groundwater is typically very limited and remains a significant constraint for efficient

42

nZVI application in remediation processes.5–7

43

High surface area per mass and magnetic forces between nZVI particles result in

44

agglomeration and deposition, thereby limiting nZVI mobility.8,9 The main approaches

45

for improving nZVI mobility are through the application of stabilizers such as coatings

46

and surface functionalizations like carboxymethyl cellulose (CMC). Such negatively

47

charged polymers can provide electrostatic repulsion between the particles and

48

between the usually charged soil surface.10 Additionally, polymer shear-thinning

49

behavior, where the polymers exhibit decreasing viscosity with increasing shear rate,

50

also can be used for stabilization.11 Another method that has been proven to increase

51

nZVI mobility is through the addition of carrier colloids such as activated carbon (AC).5–

52

7,12–14

53

stability in suspension can be manipulated and consequently their mobility.15,16 CMC is

54

one of the most prevalent and efficient stabilizers used, which functions by inducing

55

electrosteric repulsion between particles.5 One example of an efficient nZVI carrier

56

colloid is “Carbo-Iron Colloids” ((CIC).7,12 CIC are colloidal-sized AC particles,

57

containing nZVI structures within the porous carbon grains. The AC carrier colloids act

In fact, by varying stabilizer concentration and type, nZVIs particle size and



58

as a spacer preventing nZVI interactions. Additionally, CIC lower effective density and

59

decrease zeta potential in comparison to bare nZVI, resulting in the nZVI’s increased

60

stability.7,12,17 When supplemented with CMC, CIC were shown to be highly mobile in

61

porous and fractured environments.7,16,17

62

Laboratory scale experiments, mostly conducted at low ionic strength (IS) (mostly below

63

10 mM though higher IS of up to ~200 mM have been tested) in pure pre-treated silica

64

sand, confirmed the increased mobility and high recoveries of stabilized nZVI in porous

65

media.7,18–20 Nevertheless, stabilized nZVI mobility in natural media was shown to be

66

notably lower due heterogeneities inducing increased surface charge, different type and

67

content of natural organic matter and sorptive clay material encouraging interactions

68

with the media.18,21,22 Additionally, in high IS environments, enhanced particle

69

aggregation and interaction with the aquifer matrix were shown to decrease stabilized

70

nZVI mobility.16,21,23–26

71

The literature is still scarce in field scale studies of stabilized nZVI. In most field studies,

72

nZVI migration is on the order of 1 to 5 m, with an estimated influence radius of 3-30

73

m.3,4,17,27–31 These field studies which explored nZVI transport have mostly been

74

conducted in porous media. Though their applicability to aquifer remediation has been

75

tested,4,27,28

76

Europe, for example, had been conducted in fractured media,32 little attention has been

77

given to nZVI transport potential in naturally fractured systems. It has been suggested

78

that at higher water flow velocities in fractured media, nZVI travel distance will be

79

enhanced.24,33 In many instances, fracturing of porous media is performed in order to

80

increase its permeability and subsequently enhance nZVI mobility.5,29,34 It is well

and despite the fact that by 2012 about 25% of nZVI applications in


Page 6 of 40

Page 7 of 40


81

recognized that fractured systems and preferential flow paths can enable fast migration

82

of solutes and colloids due to higher shear forces and larger conduits.35,36,37 Cohen and

83

Weisbrod (2018)16 in a set of laboratory experiments in a naturally fractured chalk core

84

showed that transport of iron nanoparticles in fractures depended mostly on the particle

85

stability.

86

This study’s objective was to test nZVI mobility potential on a field scale in naturally

87

fractured rock. The study site – a fractured aquitard characterized by moderately saline

88

groundwater (~13 mS) – enabled examination of nZVI transport under saline conditions.

89

Transport potential and manipulation of nZVI were tested through the alteration of

90

stabilizer concentrations and flow velocities, where the distance between the injection

91

and pumping wells was about 50 m. This also enabled examination of the stabilizer

92

loading effect on nZVI transport in-situ. A preliminary conservative tracer test was

93

conducted in the field with uranine and naphthionate, both found to be stable under

94

saline conditions.38 Next, two CIC injections are reported on where scenarios of highly

95

versus slightly stabilized CIC were tested. Together with CIC, Iodide (that in contrast to

96

uranine and naphthionate does not sorb to CIC) was injected as a conservative tracer.

97

98

99

100

101



102 103

Page 8 of 40

2. Materials and Methods 2. 1

Field site

104

The site is located in the Negev desert of Israel within an industrial area (Figure 1). It

105

lies over the Eocene chalk formation ranging from 150 to 285 m thick.

106

formation has in the past been assumed to provide a natural hydrogeological barrier to

107

groundwater flow due to the matrix low permeability.

108

chalk formation is highly fractured, enabling fast migration of water and contaminants

109

from land surface to groundwater and within the saturated system. In the field site,

110

groundwater underlying the industrial complex was found to be contaminated by various

111

volatile and nonvolatile halogenated organic compounds, heavy metals, and halogenide

112

anions.40 As part of later remediation efforts, the site’s fracture system was mapped and

113

studied. It was found that apart from fractures oriented along bedding planes, most

114

fractures are vertical and comprise two main fracture systems. The first dominant

115

fracture system is orientated NE–SW (azimuth 50–600), and the second is oriented

116

NW–SE (310–3400).41 Groundwater flow occurs mostly within the two main fracture

117

systems, the bedding planes and the intersection between the three,41 probably through

118

a network of channels.39

40

39

This chalk

Yet, as later became evident the


Page 9 of 40


119

120 121

Figure 1 – Schematic illustration of the field site: (a) The industrial municipality where the field site lies;

122

The red circle indicates the injection area; (b) Top view of the study site boreholes; blue dashed arrows

123

represent general flow direction; (c) Side view of boreholes' orientation at the injection site. Note that all

124

boreholes are slanted in 68° or 45° normal to the orientation of one of the two prevailing fracture systems

125

and crossing the fractures below the water table.

126

Specifically, the field injection site is located at the convergence of two washes, the

127

Naim and the Hovav ephemeral washes (Figure 1a, b). This location is down-gradient

128

from the industrial center (Figure 1a) and is characterized by brackish water (TDS

129

~8000 mg/L - Table S7) and low organic contaminant concentrations (BTEX ~ 3 µg/L



130

and organic halides ~ 8 µg/L). Seven slanted boreholes were drilled in the test area,

131

crossing the fracture network below the water table (Figure 1b-c). Most boreholes were

132

drilled at an angle of 68° normal to the orientation of the prevailing fracture system.39,41

133

The boreholes are 25-40 m deep, and they are open to the chalk matrix with the

134

exception of casings installed in the upper 2-3 meters of loose, granular media.

135

Previous forced gradient tracer tests conducted in the boreholes at this site showed that

136

transport mostly depends on hydrodynamic dispersion and the concentration decay rate

137

at the injection borehole.39 Tests yielded high recoveries; up to 80% of uranine injected

138

at RH11c and pumped at RH11a39 was recovered.

139

2. 2

Field site characterization

140

A pumping test for groundwater characterization (see Supporting information (SI)) and

141

three sets of independent transport experiments carried out in the field site between

142

December 2014 and May 2016 are described.

143

In experiment I, two different conservative tracers, uranine and naphthionate, were

144

injected into two different boreholes, RH11c and RH11f, respectively (see SI for details),

145

in order to understand the feasibility of injecting CIC into the fracture system.

146

Experiment II, in which CIC were injected with high stabilizer loadings, aimed at

147

exploring the maximum potential migration of CIC in the fractures. Due to the very high

148

CIC recoveries in experiment II, CIC particles with lower stabilizer loading were injected

149

in experiment III. This last experiment aimed at exploring the possibility of manipulating

150

the CIC migration. CMC:CIC ratios explored are in the range of higher and lower

151

stabilizer loadings considered relevant for field applications.17,28,30,42–44


Page 10 of 40

Page 11 of 40


2. 3

152

Experiment II: 1st CIC injection – CMC 100% wt. 2.3.1 The particles

153

154

CIC was manufactured by Scientific Instruments (Dresden GmbH, Germany). The CICs

155

were produced with a mixture of nZVI and iron oxide nanoparticle load of 7 and 13%

156

wt., respectively. Particle size distribution according to the manufacturer was d10= 0.56

157

µm, d50= 1.16 µm, d90= 2.13 µm (nZVI mean cluster size ~0.05 µm). Particle size of

158

selected samples from the field experiment was also tested (section 2.3.3). 2.3.2 Exp. II: Preparation of injection solution on site

159

160

According to the manufacturer7 and sorption tests conducted (SI section S7), the

161

maximum CMC loading on CIC is about 6–9 wt%. Excess stabilizer loadings can

162

contribute to particle stability and subsequent mobility due to increased viscosity and

163

increased CMC layer coverage.43,45 In this experiment, the main goal was to explore the

164

maximum potential CIC mobility. Therefore, in light of the saline environment and long

165

travel distance, a high CMC (90 kg/mol) loading of about 80 wt% on CIC mass (initial

166

injection borehole viscosity of 1.9 cP and density of ~1g/cm3) was used to assure high

167

recovery.



168 169

Figure 2 – Schematic illustration of the experimental setup: (a) The pumping and injection borehole

170

RH11a and RH11c, respectively; (b) Scheme of equipment outside of the RH11c injection borehole; (c)

171

Cross-section of RH11c borehole; (d) Zoom-in of RH11c at around 25 m depth where the packer was

172

installed.

173

CMC 90 kg/mol (Sigma Aldrich) was used as the stabilizer. In preliminary laboratory

174

tests, uranine and naphthionate underwent fast sorption to CIC, while iodide did not.

175

Also, iodide is not found in the local groundwater at high concentrations (unlike Cl and

176

Br – Table S7). Therefore, iodide was used as a soluble conservative tracer, which was

177

added as KI (Sigma Aldrich). The CIC solution was prepared on-site in a 160 L barrel

178

(Figure 2). 120 L groundwater was pumped from RH11a into the barrel situated at


Page 12 of 40

Page 13 of 40


179

RH11c (Figure 2a-b). To maintain nZVI anaerobic and active, the barrel was sealed

180

and nitrogen purged, as has been conducted in field applications where degradation

181

should take place17,30. While purging nitrogen, mixing started with a large customized

182

field mixer. Next, 4.8 kg CMC and 500 g KI were added to the barrel. The solution was

183

mixed for one hour to allow for CMC dissolution, then 6 kg of CIC were added and the

184

solution, and mixing continued for an additional 1.5 hours. Due to the slow solubility, the

185

mixing was continued the next day for 5 additional hours until a homogenous solution

186

was achieved. Eventually, 4.9 Kg were injected, resulting in a CMC loading of ~97 wt%

187

and initial CIC and CMC concentrations of ~41 and 40 g/l, respectively. Next, the 120 L

188

solution was injected, similarly to experiment I (section 2.2.1), by pouring the solution

189

into three pipes positioned inside the borehole (Figure 2c-d). This took a few minutes.

190

Next, the pipes were removed, and circulation and sampling pumps (Figure 2c-d) were

191

initiated. More details can be found in the SI (sections S3 and S2).

192

2.3.3 Experiment. II: Chemical analysis

193

All samples were analyzed for CIC concentration with a UV-VIS spectrophotometer at a

194

wavelength 508 nm.15,20 RH11c samples were analyzed for iodide by EPA Method 30046

195

using a Dionex 4500i ion chromatograph (Sunnyvale, CA USA). RH11a lower

196

concentration (maximum concentration ~3.5 mg/L) iodide samples were analyzed by

197

ICP-MS (Agilent ICP-MS 8800, CA USA) (details in SI section S5).

198

Selected groundwater samples from the two boreholes were tested for particle size,

199

viscosity and density (SI, Tables S2-S5). The solution density was measured using a

200

portable density meter (model DA-130N Kyoto Electronics Manufacturing (Kem) Co.,



201

Shanghai, China). Viscosity was measured using rolling-ball viscometer (Lovis 2000

202

M/ME, Anton Paar GmbH, Gratz, Austria). Particle size was analyzed by dynamic light

203

scattering (DLS) using a particle size analyzer (90plus, Brookhaven Instruments Co.,

204

Holtsville NY, USA).

205

206

2. 4

Experiment III: 2nd CIC injection – CMC 9% wt. 2.4.1 Experiment III: Particle suspension

207

All specifications for the particles were the same as in the previous experiment with the

208

exception that all of the 20% wt. iron loading consisted of nZVI (no iron oxides) due to

209

manufacturer supply issues. According to the manufacturer and to independent tests

210

conducted at the laboratory, this does not affect CIC stability and should subsequently

211

not affect its' mobility.14

212

2.4.2 Experiment III: Particle preparation on site

213

In order to test nZVI mobility manipulation, this experiment was conducted using a lower

214

stabilizer concentration. For that purpose, a low CMC loading of about 5 wt% was

215

applied. 110 L of RH11a solution was pumped into a 120 L barrel situated at RH11c.

216

The barrel was sealed, nitrogen was injected, and mixing was initiated. Following one

217

hour of nitrogen injection, 500 g KI and 300 g CMC were added to the solution.

218

Following 2 more hours of mixing, 6 kg of CIC were added, and the mixing continued for

219

an additional 2.5 hours. As CIC aggregated, thereby clogging the barrel outlet, manual

220

mixing was applied while purging in nitrogen for another 40 minutes. The lower part of

221

the barrel tubing that was blocked by aggregated particles was opened manually, and

222

the removed solution was retuned back into the barrel after removing the aggregated 14 ACS Paragon Plus Environment

Page 14 of 40

Page 15 of 40


223

CIC particles. When the solution was homogenous, the barrel was sealed again and

224

mixed for 20 more minutes. Eventually, 3.2 Kg were injected, which resulted in a CMC

225

loading of ~9 wt% and initial CIC and CMC concentrations of ~29 and 2.7 g/l,

226

respectively. Next, the 110 L solution was injected similarly to experiment II (section

227

2.3.2). The experiment was conducted in the same manner as in experiment II (SI –

228

section S3) with the exception of some equipment changes (SI – section S4). To

229

examine the role of the hydraulic gradient and subsequent flow velocity change, the

230

pumping rate at RH11a was elevated to 17.1 L/min (from 8 L/min) towards the end of

231

the experiment. This was done 61 hours after injection, when the CIC were close to the

232

detection limit at the extraction borehole (RH11a). Samples were analyzed as described

233

in section 2.3.3.

234

2. 5

Data analysis

235

Solutes and particle concentrations at the injection borehole exhibited exponential

236

decay, as previously reported,39 in the form:

237

= (1)

238

where Ct is the concentration at time t (M/L3), C0 is the concentration at the injection

239

borehole immediately following the injection, t is the time (T) and A and α are fitting

240

parameters, where α (1/T) represents the decay rate at the injection borehole. Initial

241

tracer concentration (C0) at the injection borehole was extrapolated from the fitted

242

Equation 1 at t=0. Breakthrough curves (BTCs) were normalized to initial injection

243

concentration (C/C0), and recoveries were calculated according to the extrapolated C0.



Page 16 of 40

244

First arrival time was calculated as C/C0≥0.0001. Uranine BTC (experiment I) modeling

245

is provided in SI, section S7.

246

3. Results 3.1

247

Experiment I: Conservative tracers

248

Conservative tracer BTCs can be observed in Figure 3a-b. At the pumping borehole,

249

uranine was first observed 23 min from its injection, and a high uranine mass recovery of

250

about 83% was recorded (Figure 3a-b, Table 1). A similarly high recovery (~80%) and

251

fast arrival were reported for uranine injected at RH11c and pumped at RH11a by

252

Kurtzman et al (2005).39

253

Table 1: Transport experiment results BTC

Exp. No.

I

Injection borehole

Sampling borehole

First arrival (min)

Main BTC peak (h)

C/C0 max

Uranine

RH11a

23

4

0.014

83.375

RH11c

0.08

2.57

Naphtionate

RH11a

195

17.4

0.145

16.19

RH11f

0.20

1.75

Naphtionate

RH11c

245

26.5

0.006

67.83

RH11f

0.20

0.82

Iodide

RH11a

30

11.7

0.0136

82.66

RH11c

0.05

CIC

RH11a

34.2

6.7

0.0118

62.77

RH11c

0.07

Iodide

RH11a

23

8.2

0.0135

36.1/*38.75

RH11c

0.19

CIC

RH11a

19

8.3

0.0062

16.36/*18.87

RH11c

0.08

Tracer

∆H Exp Mass between Borehole decay recovery (%) boreholes -1 (h ) (m)

II

1.48

III

254

2.89

*Overall mass recovered following increased pumping rate


Page 17 of 40


120

0.025 0.025

a

Naphthionate NaphthionateatRH11c RH11C

120

NaphthionateatRH11a RH11A Naphthionate Concentration (mg/l) Concentration (mg/l)

C/C 0

C/C0

b

6060

0.015 0.015 0.010 0.01

0.01 0.010

0.005 0.005 0.000 0

0.005 0.005

100

8080

0.025 0.025 0.020 0.02

0.015 0.015

Uranine U ranine 1010m m Uranine U ranine 2020m m Naphthionate N aphthionate Uranine Exp. decay U ranine Exp. decay model Naphtionate Exp. decay N aphthionate Exp. decay model

100

Uranineat RH11A Uranine RH11a

0.02 0.020

c

120 120 100 100 80 80 60 60 40 40 20 20 00

4040

0

5

10

15

20

2020

d

0

2

4

6

8

10

00

0 0.000

0

20 20

40 40

60 60

80 80

00

100 100 120 120 140 140

20 20

40 40

60 60

80 80

100 100

120 120

140 140

Time Time(hour) (hour)

TTime ime(ho ur) (hour)

255 256

Figure 3 – Experiment I (Conservative tracers). Note that axes units of the inset figures (b and d) are

257

identical to those of the containing figures (a and c). (a) Conservative tracer BTCs - uranine at RH11a

258

(squares) and naphthionate (circles) at RH11c and (diamonds) at RH11a. Concentration values are

259

normalized to the injection concentration (C/C0) vs. time; (b) Zoom-in on first 20 hours. (c) Concentration

260

of uranine (squares and diamonds at 10 and 20 m depth respectively) and naphthionate (circles) in

261

injection boreholes, RH11c and RH11f, respectively. Dashed black line indicates uranine decay rate and

262

red dashed line indicates naphthionate decay rate; (d) Zoom-in on uranine during the first 10 hours in

263

RH11c injection borehole. Note the different concentrations at the two depths due to the insufficient

264

mixing.

265

During experiment I, the mixing at the injection borehole was insufficient, and thus it

266

took about 3 hours until a uniform concentration along the water column was

267

established (Figure 3c-d). This resulted in an initially higher concentration in the upper

268

part (10 m) of the borehole compared to the bottom part (20 m) (Figure 3d). The initial

269

(

Field Scale Mobility and Transport Manipulation of ... - ACS Publications

Recommend Documents