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.
Geotechnical and Geo-environmental Engineering Lab., Seoul National University 4Geotechnical and Geo-environmental Engineering Lab., Seoul National University 4
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
Geotechnical and Geo-environmental Engineering Lab., Seoul National University 5Geotechnical and Geo-environmental Engineering Lab., Seoul National University 5
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)
Geotechnical and Geo-environmental Engineering Lab., Seoul National University 6Geotechnical and Geo-environmental Engineering Lab., Seoul National University 6
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
Geotechnical and Geo-environmental Engineering Lab., Seoul National University 7Geotechnical and Geo-environmental Engineering Lab., Seoul National University 7
TEM images of nZVI particles
Cluster
Limitations of using nZVI particles
Geotechnical and Geo-environmental Engineering Lab., Seoul National University 8Geotechnical and Geo-environmental Engineering Lab., Seoul National University 8
Sedimentation of nZVI particles
The sedimentation decreases the mobility and reactivity of nZVI particles.
Sedimented nZVI particles
Limitations of using nZVI particles
Geotechnical and Geo-environmental Engineering Lab., Seoul National University 9Geotechnical and Geo-environmental Engineering Lab., Seoul National University 9
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
Geotechnical and Geo-environmental Engineering Lab., Seoul National University 10Geotechnical and Geo-environmental Engineering Lab., Seoul National University 10
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
Geotechnical and Geo-environmental Engineering Lab., Seoul National University 11Geotechnical and Geo-environmental Engineering Lab., Seoul National University 11
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
Geotechnical and Geo-environmental Engineering Lab., Seoul National University 12Geotechnical and Geo-environmental Engineering Lab., Seoul National University 12
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
Geotechnical and Geo-environmental Engineering Lab., Seoul National University 13Geotechnical and Geo-environmental Engineering Lab., Seoul National University 13
100 ~ 200 nm
Oleic acid coated nZVI
Oleic acid (oil phase)
Surfactant
Water phase
Concept of nZVI microemulsion
Geotechnical and Geo-environmental Engineering Lab., Seoul National University 14Geotechnical and Geo-environmental Engineering Lab., Seoul National University 14
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
Geotechnical and Geo-environmental Engineering Lab., Seoul National University 15Geotechnical and Geo-environmental Engineering Lab., Seoul National University 15
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.
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