Microemulsions for stable transport of nanoscale zero va-

lent iron particles (nZVIs)

Heesoo Woo

Ph.D. candidateGeotechnical & Geo-Environmental Engineering Lab.

Seoul National University

Geotechnical and Geo-environmental Engineering Lab., Seoul National University 2Geotechnical and Geo-environmental Engineering Lab., Seoul National University 2

Toxic contaminants, Chlorinated solvents

Chlorinated solvents are frequently found as contaminants of soil and ground-water as a result of their widespread use in various industrial processes.

Among them, the most frequently released are dichloromethane (DM), chloroform (CF), carbon tetrachloride (CT), trichloroethylene (TCE), and tetrachloroethylene (PCE).

TCE CT

Chlorines in their structure cause the toxicity and the most common solventsare classified as known or suspected human carcinogens.

Geotechnical and Geo-environmental Engineering Lab., Seoul National University 3Geotechnical and Geo-environmental Engineering Lab., Seoul National University 3

Toxic contaminants, Chlorinated solvents

Dense NAPL

Deep depth to the cont. sourcein subsurface

The properties of chlorinated sol-vents that make them safely re-mediated include their low degrad-ability and high density.

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Zero valent iron(Fe0)

PCE Ethylene

0 2RCl H Fe RH Fe Cl General form:

ToxicLess toxic or non toxic

Reduction of toxic chlorinated solvents using nZVIs

Applications of nZVI particles

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Treatment of DNAPL contamination by injection of mobile nZVI particles (Tratnyek and Johnson, 2006)

nZVI particles can be transported effectively by the flow of groundwater.

Applications of nZVI particles

Contamination source can be remediated by injection of mobile nZVI particlesin subsurface.

Slurry feeding during treatment (© Aquatest, Czech Re-public)

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Particle agglomeration cause the sedimentation of the nZVI particles.

Fe0 Fe0 Fe0 Fe0

Fe0 Fe0 Fe0 Fe0

Van der WaalsMagnetic force

Limitations of using nZVI particles

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TEM images of nZVI particles

Cluster

Limitations of using nZVI particles

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Sedimentation of nZVI particles

The sedimentation decreases the mobility and reactivity of nZVI particles.

Sedimented nZVI particles

Limitations of using nZVI particles

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Fe0

Ions

IonsDOM

nZVIs’ surface oxidation by non-target constituents in groundwater

Fe0

non reactive

Fe-oxide layer= Reactivity decrease

Cont.

Cont.

Limitations of using nZVI particles

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Fe0

Protective layer in order to prevent agglomeration and reactivity loss in groundwater

Repulsion

Ions

DOM Repulsion

Cont.

Attra

ctio

n

Protective layer coating onto nZVI particles

Fe0

Protective layer

Fe0

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Fe0

Long hydrocarbon chain= steric repulsion= selectivity towards hydrophobic cont. including chlorinated solvents

Anchor to metal surface

Oleic acid main constituent of olive oil

Materials for protective layer

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Emulsion

Microemulsion

Transparent μE

An emulsion is a mixture of two or more liquids that are normally immiscible. In an emulsion, one liquid is dispersed in the other. Examples of emulsions include milk, vinaigrette sauce. Emulsions or macroemulsions are turbid, have droplet size ranging from 0.2 to 10 μm

and may kinetically stable, albeit thermodynamically unstable. Oleic acid and water emulsion can be formed by the aid of appropriate surfactants.

= Droplets of oleic acid were dispersed in water phase in the emulsion.

Microemulsions are emulsions with particle sizes ranging from 5 to 100 nm.

Microemulsions are basically thermodynam-ically stable, isotopically clear dispersions (transparent or translucent) of two immisci-ble liquids.

Emulsion and microemulsion

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100 ~ 200 nm

Oleic acid coated nZVI

Oleic acid (oil phase)

Surfactant

Water phase

Concept of nZVI microemulsion

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Mixing above mixture with surfactants at proper ratiosTweens and spans were used as surfactants which are food grades surfactantswidely used in food industry

nZVI particles in oleic acidHigh temperature heating (> 200) over 1 h in oleic acid and nZVI mixture

1.

Water was added drop by drop until microemulsion was formed.

2.

3.

Preparation of nZVI microemulsion

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Oleic acid with Fe0 particles + Tween 20 + Span 80 + Water

Oil phase Surfactants Water phase

Results and Conclusions

The microemulsions of Fe0 particles were expected to be prepared using oleic acid, tweens and spans series, and water at proper ratios.

Furthermore, the reactivity to chlorinated solvents and transport characteristics in subsurface of the microemulsions have to be confirmed.

However, turbidity, stability, and particle size have to be measured in order toconfirm formulation of the microemulsions.