10ο ΠΑΝΕΛΛΗΝΙΟ ΕΠΙΣΤΗΜΟΝΙΚΟ ΣΥΝΕΔΡΙΟ ΧΗΜΙΚΗΣ ΜΗΧΑΝΙΚΗΣ, ΠΑΤΡΑ, 4-6 ΙΟΥΝΙΟΥ, 2015.

AN EXPERIMENTAL STUDY OF THE FATE AND REACTIVITY OF ZERO-VALENT IRON

NANOPARTICLES DURING THE INJECTION OF NANOFLUIDS IN SATURATED POROUS

MEDIA POLLUTED WITH CHLORINATED HYDROCARBONS

K. Terzi1,2, K. Hajdu1, A. Sikinioti-Lock1,2, Th. Asimakopoulos2, C.A. Aggelopoulos1, G. Staikos2,

C.D. Tsakiroglou1,*

1Foundation for Research and Technology Hellas-Institute of Chemical Engineering Sciences, Stadiou street,

Platani, 26504 Patras

2Department of Chemical Engineering, University of Patras, 26504 Patras

ABSTRACT

Aqueous suspensions of nZVI (nanofluids) are prepared by adding NaBH4 solution under anoxic conditions in an

aqueous solution of FeSO4 7H2O pre-grafted with two polymers acting as coatings: CMC (carboxymethyl

cellulose) and CMC-g-PDMAM (carboxymethyl cellulose-g-polydimethylacryl amide). The size distribution of

nanoparticles (NP) is measured with dynamic light scattering (DLS) and transmission electron microscopy (TEM),

whereas their stability is evaluated with sedimentation tests and measuring the ζ-potential. Per-chloro-ethylene

(PCE) is used as model non-aqueous phase liquid (NAPL). To assess the nZVI reactivity with respect to dissolved

NAPL, tests are performed in batch reactors to determine the rate of PCE dechlorination. Visualization studies of

the flow of nZVI suspension through a glass-etched pore network enable us to assess the nanoparticle mobility

and identify the mechanisms of nZVI attachment/detachment and deposition in the pore-walls.

INTRODUCTION

Nanotechnology has special relevance to the in situ soil and groundwater remediation, due to the combination of

nanoparticles properties with fluid characteristics and thus the potential for injecting nano-sized (reactive or

adsorptive) particles into contaminated porous media (e.g. soils, sediments, and aquifers). Among the various

nano-materials explored for remediation (e.g. zeolites, metal oxides, carbon nanotubes, etc) nanoscale zero-valent

iron (nZVI) is currently the most widely used for the in situ remediation of soils from a variety of toxic pollutants

(e.g. chlorinated solvents, hexavalent chromium, nitroaromatics, etc) [1]. The advantages of nZVI may be

summarized as follows [2,3]: (a) fast reaction; (b) complete reduction pathway to non-toxic byproducts; (c) in situ

treatment. Particles of nZVI may range from 10 nm to 100 nm in diameter or slightly larger. Macroscale ZVI has

been shown to be effective for treating groundwater contaminants within Permeable Reactive Barriers [1]. The

main drawback of PRBs is that they can only address contaminants that flow through the barrier

A case study cost comparison of a manufacturing site (groundwater) remediation from tetrachloroethylene

(PCE) and trichloroethylene (TCE) indicated the following costs: pump-and-treat~4,160,000 US$; permeable

reactive barriers~ US$ 2,200,000; nZVI (nanoparticles) ~ US$ 450,000 representing a cost saving of 80-90% over

the pump and treat method [4]. The cost and treatment time of in situ soil and groundwater remediation could be

reduced by: (i) specifying the factors that maximize the longevity/ stability/ reactivity of nanoparticles without any

losses of materials or waste of treatment time; (ii) adjusting the nanofluid composition to soil properties and

hydrodynamic/physicochemical conditions; (iii) improving the cost-efficiency of technology even to very difficult

to reach sites (e.g. below buildings); (iv) improving the delivery of nanoparticles at deeper soil layers and pollutant

targeting, increasing the overall rate of reactive processes, and contributing to shorter cleanup times; (v)

stimulating anaerobic microbial growth and natural biological degradation as a concurrent or post-treatment

process, increasing the overall process efficiency, and enhancing the technology eco-safety.

In spite of the great deal of work done for the in situ remediation of dissolved pollutants with nZVI [4,5], little

progress has been made toward delivery of nZVI to NAPL source zones. Delivering nZVI to the DNAPL/water

interface, where the DNAPL concentration in aqueous phase is at its highest value, can potentially increase the

rate of DNAPL reduction and the efficient usage of Fe0 for reductive dechlorination. It would increase the amount

of Fe0 in the nZVI particles that is used for transformation (e.g. dechlorination) rather than for reducing water to

H2 or reducing other groundwater constituents that may be present (e.g. nitrates) [6]. The dechlorination rate is

typically first order with respect to pollutant concentration, and hence the rate of DNAPL dechlorination can also

be limited by the availability of dissolved contaminant. This potentially limits the prospects of rapid and substantial

* Corresponding author (e-mail: ctsakir@iceht.forth.gr)

10ο ΠΑΝΕΛΛΗΝΙΟ ΕΠΙΣΤΗΜΟΝΙΚΟ ΣΥΝΕΔΡΙΟ ΧΗΜΙΚΗΣ ΜΗΧΑΝΙΚΗΣ, ΠΑΤΡΑ, 4-6 ΙΟΥΝΙΟΥ, 2015.

DNAPL mass depletion [7]. Nonetheless, the regions of maximum dissolved contaminants that are most amenable

to nZVI targeting are found in the DNAPL source zone (trapped ganglia) as well as directly downgradient of the

capture zone. One of the first ideas proposed on NAPL targeting was the use of nZVI modified by an amphiphilic

triblock copolymer that contained polyanionic blocks to stabilize nZVI in suspension and a hydrophobic poly

(methyl methacrylate) block to drive nanoparticle adsorption to the NAPL/water interface [8]. In another study

[9] water-in-oil emulsions were suggested, where nZVI was suspended in the water droplets stabilized by food-

grade surfactants. More recently, multifunctional nZVI-silica nanocomposites were found capable to adsorb to a

DNAPL/water interface [10]. Limited attention was paid on NAPL targeting by nZVI under flow-through

conditions in real porous media [11,12].

In the present study, nZVI suspensions are prepared with wet chemistry techniques. For the stabilization of

nanoparticles and prevention of undesirable reactions (e.g. fast oxidation of nZVI), the NPs are coated by a

qualified selection of polymers and the coatings ensuring the longest stability, longevity and reactivity are

identified by combining NP characterization tests with batch reactivity tests, and flow-through studies in a glass-

etched pore network.

SYNTHESIS OF POLYMERS

Preparation of carboxyl-methyl-cellulose (CMC) solution. 20g of CMC was dissolved in 200 mL of deionized

water under stirring for a period of 3 days. Then, the solution was purified with membrane 30 kDa, and condensed

by freeze drying for 48 hrs [13].

Preparation of poly-dimethyl-acryl-amide (PDMAM). 20 mL of dimethyl-acryl-amide (DMAM) of purity 99%

was dissolved in 160 mL of deionized water under stirring for 30 min, and then the following solutions were added

in it: (a) 4 mM of ammonium persulfate (APS) dissolved in 5 mL of deionized water using a sonicator; (b) 8 mM

of 2-aminoethanethiol (AET) dissolved in 5 mL water with the use of sonicator. The whole solution was stirred

for 24 hrs. Then, 6.25 mL NaOH 4M was added for neutralization. The solution was purified by permeation

through a membrane for 24 hrs, and condensed by freeze drying.

Preparation of grafted polymer CMC-g-PDMAM. Initially, 2.5 g of the CMC was added in 150ml of deionized

water along with 5g of PDMAM and 2.32 g of 1- (3- (dimethylaminopropyl) -3-ethylcarbodiimide (EDC)

dissolved in 5mL of deionized water, acting as condensing agent. The grafter polymer CMC-g-PDMAM was

obtained after purification and freeze drying for 48 hrs.

SYNTHESIS AND CHARACTERIZATION OF nZVI SUSPENSIONS

Figure 1. Synthesis of polymer coated nZVI suspension.

Aqueous suspensions of nZVI were prepared by adding 𝑁𝑎𝐵𝐻4 solution under anoxic conditions in an aqueous

solution of 𝐹𝑒𝑆𝑂4. 7𝐻2𝑂 pre-grafted with the above-mentioned polymers acting as stabilizing coatings: (1) CMC

(MWCMC=90000 g/mol); (2) CMC-g-PDMAM (MWCMC-g-PDMAM=140000 g/mol). The protocol of He and Zhao

[14] was followed by keeping the w/w ratios 𝑃𝑜𝑙𝑦𝑚𝑒𝑟/𝐹𝑒 = 0.003, and of 𝑁𝑎𝐵𝐻4/𝐹𝑒 = 2. A 250 𝑚𝐿 three-

neck flask (Fig.1) was placed inside a cold bath at ~4𝑜𝐶, and two sensors measuring the pH, and redox potential,

were inserted in the two necks. First, the flask was filled with 100 𝑚𝐿 of the polymer solution of concentration

10g/L, and 40 𝑚𝐿 of deionized and degased water. In order to keep anoxic conditions, a steady flow of nitrogen

was injected in the solution during the entire procedure. The solution was stirred steadily at ~800 rpm, and 10 𝑚𝐿

of deionized and degased 𝐹𝑒𝑆𝑂4. 7𝐻2𝑂 solution of concentration 100 g/L were added in it. After 15 min, a

yellowish or green solution evolved depending on whether CMC or CMC-g-PDMAM was used. Afterwards,

50 𝑚𝐿 of a fresh 𝑁𝑎𝐵𝐻4 solution of concentration 5.4 g/L was added in the flask at flow rate 5 𝑚𝐿/𝑚𝑖𝑛.

10ο ΠΑΝΕΛΛΗΝΙΟ ΕΠΙΣΤΗΜΟΝΙΚΟ ΣΥΝΕΔΡΙΟ ΧΗΜΙΚΗΣ ΜΗΧΑΝΙΚΗΣ, ΠΑΤΡΑ, 4-6 ΙΟΥΝΙΟΥ, 2015.

Gradually, the solution became black indicating the generation of nZVI suspension. The stirring continued for 10

min to allow all bubbles of evolved hydrogen to release. Then, the suspension was undergone vacuum filtration,

degassed and finally stored in amber glass vials which were filled with N2 on top and closed tightly. The variation

of pH and Eh during the synthesis process is shown in Table 1. A series of tests confirmed the results of [14] that

the average size of nanoparticles decreases with the temperature decreasing, and this was attributed to the very

slow reaction rate at the lowest temperature tested (~4𝑜𝐶).

Table 1. pH and redox potential measurements during the production of polymer coated nZVI

Polymer solution Polymer and iron salt

solution

Polymer coated-nZVI

suspension

CMC CMC-g-

PDMAM

CMC CMC-g-

PDMAM

CMC CMC-g-

PDMAM

pH 7.66 8.75 6.6 7.15 8.34 8

Eh (mV) 113.7 73.3 -239.8 -363.3 -498 -433.3

The hydrodynamic diameter distribution and ζ-potential of nanopartricles were measured with Dynamic Light

Scattering (DLS) in a Zetasizer Nano-Instrument (Nano ZS, MALVERN) with dilution of the nZVI concentration

by several orders of magnitude. The characteristics of CMC-coated nZVI suspensions prepared at concentrations

0.1 g/L, and 1.0 g/L are shown in Table 2. It is worth mentioning that the actual Fe concentration in synthesized

suspensions (0.095 and 0.95 g/L), as measured with dissolution in dense HNO3 and flame atomic absorption

spectroscopy, is ~5 % less than its target value (0.1 and 1 g/L). The variation of ζ-potential with pH (Fig.2) shows

that the isoelectric point is close to 1 [5,6]. The transient evolution of the average size of CMC-coated nZVI of

concentration 1.0 g/L is shown in Fig.3. Evidently, the suspensions are stable for a couple of days, and

progressively their agglomeration leads to micro-particles (Fig.3). However, when a tightly sealed bottle of CMC-

coated nZVI was opened after 18 days, the average size was almost identical to that measured on the day of

production (Fig.3), indicating the effect of storage conditions on nanoparticle stability.

Table 2. Physicochemical properties of CMC-coated nZVI suspensions

Iron concentration 0.1 g/L 1.0 g/L

pH 8.45 8.34

Eh (mV) -500 -498

Size (nm) 33.0 104.3

Particle Dispersion Index (PDI) 0.44 0.513

Zeta Potential (mV) -43.1 -38.1

Figure 2. ζ-potential as a function of pH (a) 0.1 g/L nZVI, (b) 1.0 g/L nZVI.

0 2 4 6 8 10 12

-60

-50

-40

-30

-20

-10

0

ζ-p

ote

nti

al (m

V)

pH

0.1g/L CMC-coated nZVI(a)

0 2 4 6 8 10 12

-60

-50

-40

-30

-20

-10

0

10

ζ-p

ote

nti

al

(mV

)

pH

1.0 g/L CMC-coated nZVI(b)

10ο ΠΑΝΕΛΛΗΝΙΟ ΕΠΙΣΤΗΜΟΝΙΚΟ ΣΥΝΕΔΡΙΟ ΧΗΜΙΚΗΣ ΜΗΧΑΝΙΚΗΣ, ΠΑΤΡΑ, 4-6 ΙΟΥΝΙΟΥ, 2015.

Figure 3. Transient variation of the average size of CMC-coated nZVI

A parametric study of nZVI synthesis conditions was done and the results are shown in Table 3.

The average particle size increases as the polymer to iron ratio goes to high or low values indicating that

there is an optimum ratio generating the smallest nanoparticles.

The average particle size increases profoundly as the sodium borohydride to iron ratio increases.

The molecular weight of polymers (CMC, CMC-g-PDMAM) had no visible effect on particle sizes or ζ-

potential.

Increasing the temperature to ~18𝑜𝐶, the average size of the polymer coated nZVI increases.

If a powder of CMC is used by skipping the lyophilization process, instantaneous sedimentation takes

place.

Table 3. Parametric analysis of nZVI synthesis

Polymer

/Fe

NaBH4

/Fe

CMC

(g/L)

CMC-g-

PDMAM

(g/L)

CMC-

Powder

(g/L)

pH Eh

(mV)

Size

(nm)

Zeta

Potential

(mV)

Sedimentation

0.003 2 10 7.99 -750 165 -41.7

0.006 2 20 7.95 -744 158 -49.6 Mud

0.003 2 15.6 7.96 -636 192 -26.2

0.003 2 10.0 7.8 -783 181 -27.5

0.003 2 10 7.87 -868 237 -27.5 Instantaneous

0.03 0.2 10 8.02 -877 201 -27.9

0.03 2 10 9.44 -863 887 -47 Instantaneous

0.0005 2 1.7 8.02 -480 218 -27.2 Instantaneous

It seems that the suspension is dominated by nanoparticles with sizes less than 50 nm (Fig.4a,b) which may

be enlarged by the presence of polymer coatings (Fig.4c). Moreover, the reported particle size distributions (Fig.3,

Tables 2, 3) are intensity-based and given that the scattering intensity is proportional to the 6th power of particle

size whereas the particle volume is proportional to the 3rd power of particle size, the size distribution shifts to lower

sizes as one goes from intensity-based to volume-based and to number-based frequency distribution functions.

Subsequently, the volume-based and number-based average particle diameters are expected to be lower than the

intensity-based average particle used in quantifying the suspension characteristics.

Figure 4. TEM images of (a) uniform (~5 nm) nZVI coated by CMC, (b) dispersed nZVI coated by CMC, (c)

CMC-g-PDMAM-coated nZVI.

0 5 10 15 20

0

100

200

300

400

500

Siz

e (

nm

)

Time (Days)

CMC-coated nZVI

(a) (b) (c)

10ο ΠΑΝΕΛΛΗΝΙΟ ΕΠΙΣΤΗΜΟΝΙΚΟ ΣΥΝΕΔΡΙΟ ΧΗΜΙΚΗΣ ΜΗΧΑΝΙΚΗΣ, ΠΑΤΡΑ, 4-6 ΙΟΥΝΙΟΥ, 2015.

TESTS IN BATCH REACTORS

Tetrachlorethylene (PCE) was used as model pollutant. Its solubility in water is 0.15g/L at 25oC. The upper safety

limit of PCE concentration in water was set equal to 0.005 mg/L by the Environmental Protection Agency (EPA).

A stock PCE solution of concentration 100 ppm was prepared in deionized and degased water. From that stock

solution, PCE concentrations at 100, 75, 50, 20, 10, 5 ppm were prepared. Suspensions of nZVI were used at three

concentrations: 1.0, 0.1, 0.01 g/L. For each PCE concentration, 1 mL of the PCE stock solution and 1 mL of the

synthesized nZVI suspension was injected into five different extraction bottles without opening them, by using a

syringe. The bottles were filled with N2 gas in the top to prevent the oxidation of the iron particles. The five

samples were rotated for different time spans (2 min-2 hrs). The PCE extraction from the aqueous phase into

hexane was performed by (1) adding 400 μL of the PCE/nZVI suspension in 4 mL of hexane in extraction bottles

and (2) shaking the mixture for 20 min at 20 Hz. After the extraction has been completed, the polar and non-polar

phases were separated. Liquid samples were collected from the (upper) hexane phase. Chemical analyses were

performed on a Shimadzu GC-2010 gas chromatograph, equipped with an Electron Capture Detector (ECD) and

auto-sampler. A capillary column of dimensions 30 m x 0.25 mm x 0.52 μm was used. The carrier gas was He

injected at constant flow rate of 24.7 ml/min and split ratio 10. The injector temperature was set to 220 oC. The

column temperature was kept at 35 oC for 5 min and increased to 150 oC at a rate 10 oC/min, whereas the detector

was operating at 300 oC with N2 injected at flow rate 30 ml/L.

Figure 5. Transient variation of dissolved PCE concentration, Cp, in batch reactors for various initial PCE

concentrations, Cp0, and three nZVI concentrations: (a) 1.0 g/L, (b) 0.1 g/L, (c) 0.01 g/L.

The dissolved PCE concentration as a function of time is illustrated in Fig.5 for three nZVI suspensions. It is

evident that PCE is dechlorinated and nZVI is oxidized very fast in agreement with analogous results of He et al.

[15]. This is attributed to the use of distilled water, and the absence of any other species that might oxidize nZVI,

acting competitively to PCE (Fig.5). It is worth mentioning that the kinetics of the dechlorination of produced

intermediates (e.g. TCE, DCE, VCD) to ethene, which is the final product of PCE reduction, is under investigation.

MOBILITY TESTS IN A GLASS-ETCHED PORE NETWORK

The mobility of nZVI was tested with visualization experiments performed on a glass-etched pore network used

in earlier multiphase transport studies [16,17]. A schematic diagram of the experimental apparatus along with the

characteristics of the glass-etched pore network are shown in Fig.6. The entire system was placed in a thermostatted

chamber to keep constant temperature and avoid any undesired changes in fluid properties. The suspension was

injected in the pore network through four inlet ports and expelled from it through four outlet ports. A syringe pump

(HARVARD PHD 2000) was used for the injection of nZVI suspension, and a CCD camera (PANASONIC AW-

E300), connected through an image USB stick grabber to the host computer, was used to capture images and store

them directly on the hard disk of the PC (Fig.6). The micro-model was illuminated by a transmitted light source

placed beneath it. The effluent was collected automatically in the tubes of a fractional collector (ELDEX).

Initially, the pore network was fully saturated with distilled and degased water, and a nZVI suspension of

concentrtation 0.85 g/L was injected for 3 hrs. Afterwards, the feed solution was replaced by distilled and degased

water and the injection was continued for 2 hrs. The total flow rate was 𝑄𝑡 = 0.025 𝑚𝐿/𝑚𝑖𝑛 which corresponds

to a pore velocity 𝑢𝑝 = 7.0𝑥10−5 𝑚/𝑠. The collection of each effluent sample lasted for 1 hr. Each sample was

digested by adding 0.1 𝑁 𝐻𝑁𝑂3 solution and analyzed by atomic absorption spectroscopy (AAS). In Table 4,

sample “0” denotes the initial feed solution, sample “7” denotes the residual solution in the syringes after 3 hrs,

sample “6” denotes the residual solution in the glass micro-model at the end of experiment, and all other numbers

correspond to the effluent sampled every 1hr. The nZVI concentration refers to the time-averaged value over the

sampling interval (Table 4).

Gradually the pore network tends to be saturated completely with nZVI (Fig.7a-c), and a fraction of

nanoparticles is attached to the pore-walls (Table 4). Then, as the clean distilled water is injected, a significant

fraction of nZVI is expelled from the pore network after 2 hrs (~ 4PV) (Fig.8a-c, Table 4).

0 20 40 60 80 100 120 14010

-3

10-2

10-1

100

Cp/C

p0

Time, t (min)

Cp0

=100 ppm

Cp0

=75 ppm

Cp0

=50 ppm

Cp0

=20 ppm

Cp0

=10 ppm

Cp0

=5 ppm

[nZVI]=1.0 g/L(a)

0 20 40 60 80 100 120 14010

-3

10-2

10-1

100

Cp/C

p0

Time, t (min)

Cp0

=100 ppm

Cp0

=75 ppm

Cp0

=50 ppm

Cp0

=20 ppm

Cp0

=10 ppm

Cp0

=5 ppm

[nZVI]=0.1 g/L(b)

0 20 40 60 80 100 120 14010

-3

10-2

10-1

100

Cp/C

p0

Time, t (min)

Cp0

=100 ppm

Cp0

=75 ppm

Cp0

=50 ppm

Cp0

=20 ppm

[nZVI]=0.01 g/L(c)

10ο ΠΑΝΕΛΛΗΝΙΟ ΕΠΙΣΤΗΜΟΝΙΚΟ ΣΥΝΕΔΡΙΟ ΧΗΜΙΚΗΣ ΜΗΧΑΝΙΚΗΣ, ΠΑΤΡΑ, 4-6 ΙΟΥΝΙΟΥ, 2015.

Figure 6. Schematic diagrma of experimental setup and pore network pattern

Table 4. pH, redox potential, size distribution, zeta potential and and concentration of the outflow samples of the

experiment inside porous network.

Sample Time

(min) PV

Total

PV pH

Eh

(mV)

Size

(nm) PDI

Zeta

Potential

(mV)

Concentration

(g/L)

0 0 0 0 8.28 -475 156.6 0.389 -51.9 0.85

1 60 3.69 3.69 5.79 -132 190.9 0.48 -44.5 0.023

2 120 7.44 7.44 7.9 -462 151.8 0.388 -30.2 0.305

3 180 10.3 10.3 7.88 -380 194.7 0.368 -25.3 0.514

4 240 2.62 12.9 8.05 -426 161.2 0.423 -52.2 0.533

5 300 4.52 17.4 7.3 -55.1 186.2 0.419 -64 0.161

6 300 4.52 17.4 6.35 4.4 239.1 0.431 -49.5 0.061

7 180 10.3 10.3 8.39 -480 193.6 0.419 -49.8 0.697

Figure 7. Successive snap-shots of the injection of nZVI suspension in the pore network at times: (a) t=68 min,

(b) t=86 min, (c) t=134 min

Figure 8. Successive snapshots of the injection of distilled water in the pore network at times: (a) t=248 min

(ts=68 min after initiating the water injection), (b) t=263 min (ts=83 min), (c) t=294 min (ts=114 min).

Pore cross-section

14.5 cm

10.3 cm

Pore network

morphology

1840 μm

syringe pump

glass

model

CCD

camera

pressure

transducer

fractional

collector

host computer

light

(a) (b) (c)

(a) (b) (c)

10ο ΠΑΝΕΛΛΗΝΙΟ ΕΠΙΣΤΗΜΟΝΙΚΟ ΣΥΝΕΔΡΙΟ ΧΗΜΙΚΗΣ ΜΗΧΑΝΙΚΗΣ, ΠΑΤΡΑ, 4-6 ΙΟΥΝΙΟΥ, 2015.

Figure 9. Dynamic changes of the average size of CMC-coated nZVI and ζ-potential during an injection test.

In order to assess the dynamics of nanoparticles stability, the average particle size and ζ-potential of effluents were

measured as a function of injected pore volumes (PV). The average particle diameter increases sensibly and the

agglomeration of nanoparticles becomes evident only at late times (Fig.9a) where the nZVI concentration of nZVI

has greatly decreased (Table 4). On the other hand, the ζ-potential increases with the nZVI concentration in effluent

increasing, and it decreases when the injection of nZVI suspension ceases (Fig.9b, Table 4).

Figure 10. Focusing on a small area of the glass-etched pore network during the injection of CMC-coated nZVI.

(a) Initiation of nZVI injection; (b) 40 PV of nZVI suspension has been injected; (c) 47 PV of nZVI suspension

has been injected (the generation of very large aggregates flowing through the pores is evident).

Figure 11. (a) Dimensionless nZVI concentration in the effluent of the glass-etched pore network (breakthrough

curve). (b) Pressure drop measured across a central area (Fig.6) of the pore network.

In another mobility experiment which lasted for 30 hrs (Fig.10), during the injection of 10 PV of nZVI

suspension, almost the 90% of injected nZVI was recovered at the outlet (Fig.11a) and no significant deposition

of nZVI occurred in the pore network as reflected in the pressure drop measured across a central area of the micro-

model (Fig.11b). Afterwards, during the injection of the next 10 PV of suspension, the dimensionless nZVI

concentration in the effluent was almost constant, fluctuating between 0.7 and 0.9 (Fig.11a). During the same

period, the nearly linear increase of the pressure drop is indicative of the gradual nZVI deposition on the pore-

0 2 4 6 8 10 12 14 16 18

120

140

160

180

200

220

240

7

6

5

4

3

2

1

0

Av

era

ge

na

no

pa

rtic

le d

iam

ete

r (n

m)

Total PV

Injection of CMC-coated nZVI

Injection of distilled water

(a)

0 2 4 6 8 10 12 14 16 18

-70

-60

-50

-40

-30

-20

-10

0

Total PV

(b) Injection of CMC-coated nZVI

Injection of distilled water

5

64

7

32

1

0

ζ-p

ote

nti

al

(mV

)

Flow of nZVIaggregates

(a) (b) (c)

0 5 10 15 20 25 30 35 40 45 500.0

0.2

0.4

0.6

0.8

1.0(a)

[Fe]inj,0

=0.85 g/L[Fe]/

[Fe] in

j,0

Number of pore volumes injected, PV

0 2 4 6 8 10 12 14 16 180

20

40

60

80

100

Pre

ss

ure

Dro

p, Δ

P (

Pa)

Number of pore volumes injected, PV

(b)

10ο ΠΑΝΕΛΛΗΝΙΟ ΕΠΙΣΤΗΜΟΝΙΚΟ ΣΥΝΕΔΡΙΟ ΧΗΜΙΚΗΣ ΜΗΧΑΝΙΚΗΣ, ΠΑΤΡΑ, 4-6 ΙΟΥΝΙΟΥ, 2015.

walls (Fig.11b). In advanced stages of nZVI injection process, hydrogen bubbles produced by the anaerobic

corrosion of the nZVI [18] occupied a significant fraction of the pore space displacing the nano-iron suspension

and preventing the measurement of the pressure drop. It is worth mentioning that in analogous experiments of

micro-sized ZVI injection in a glass-etched pore network, the fast deposition of micro-sized ZVI caused clogging

of the porosity after the injection of several pore volumes (3-5 PV) of suspensions at low iron concentration (<0.2

g/L) [19].

CONCLUSIONS

CMC-coated nZVI suspensions were prepared from 𝑁𝑎𝐵𝐻4 and CMC pre-grafted 𝐹𝑒𝑆𝑂4. 7𝐻2𝑂 solutions by

controlling carefully the conditions of the conventional wet-chemistry technique, and selecting the protocol that

ensures the optimization of the nano-colloid properties for soil remediation studies: stability, longevity, reactivity,

and mobility. The stability and longevity of suspensions was evaluated with physicochemical and morphological

characterization on nanoparticles. The reactivity of nanoparticles was assessed with batch tests in aqueous

solutions of per-chloro-ethylene (PCE). The mobility of nanoparticles was tested with flow-through experiments

in a glass-etched pore network. In the next step, the nano-colloid will be tested as an agent for the dechlorination

of PCE source zone under flow-through conditions.

ACKNOWLEDGEMENTS

The research is co-financed by the European Union (European Social Fund-ESF) and Greek national funds in the

context of the action “EXCELLENCE II” of the Operational Program “Education and Lifelong Learning” (project:

“Optimizing the properties of nanofluids for the efficient in situ soil remediation-SOILREM”).

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