Environmental Engineering Reference
In-Depth Information
perhaps. the. most. widely. used. nanomaterial. in. environmental. remediation. and. is.
described. in. some. detail. below.. This. chapter. also. includes. information. on. other.
nanomaterials.under.development.or.currently.in.use.to.treat.groundwater.or.waste-
water,.or.in.other.pollution-control.applications.
The.information.presented.in.this.chapter.originated.from.a.combination.of.peer-
reviewed.literature,.“gray”.literature.such.as.conference.proceedings,.and.informa-
tion. from. vendors.. Readers. should. consult. the. references. section. for. the. basis. for.
information.presented.in.this.chapter.
Due.to.the.rapid.developments.in.the.ield,.and.
at.times.to.the.need.to.protect.conidential.business.information,.supporting.data.for.
some.of.the.referenced.information.are.not.always.available..Mention.of.a.speciic.
product.or.brand.name.does.not.constitute.endorsement.
0. zeRo-Valent iRon (zVi)
Zero-valent.iron.(ZVI).is.used.to.treat.recalcitrant.and.toxic.contaminants.such.as.
chlorinated.hydrocarbons.and.chromium.in.groundwater.[2]..The.initial.applications.
used.granular.iron,.alone.or.mixed.with.sand.to.make.“magic.sand,”.to.treat.extracted.
groundwater..Later,.engineers.installed.low-through.ZVI.cells.in.the.ground,.using.
slurry.walls.or.sheet.piling.to.direct.the.low.of.groundwater.through.the.treatment.
cells.
However,.these.walls.were.expensive.and.sometimes.dificult.to.construct,.and.
often.incurred.long-term.costs.for.maintenance.and.monitoring..Injectable.forms.of.
ZVI,.most.recently.nano.zero-valent.iron.(nZVI).and.its.variations,.were.developed.to.
surmount.these.problems..In.these.applications,.nanoscale.iron.particles.are.injected.
directly.into.an.aquifer.to.effect.treatment.
in situ
..As.described.below,.nZVI.is.com-
mercially.available.and.has.been.used.on.more.than.30.sites.as.of.this.writing.
Zero-valent.iron.(Fe
0
).enters.oxidation-reduction.(redox).reactions.that.degrade.
certain. contaminants,. particularly. chlorinated. hydrocarbons. such. as. trichloroeth-
ylene. (TCE). and. tetrachloroethylene.. ZVI. also. has. been. used. to. treat. arsenic. and.
certain.metals.[3]..In.the.presence.of.oxygen,.nZVI.can.oxidize.organic.compounds.
such.as.phenol.[4]..Much.of.the.discussion.in.this.chapter.pertains.to.the.treatment.
of. chlorinated. hydrocarbons. because. of. the. prevalence. of. those. contaminants. and.
resulting.focus.on.their.remediation.using.nZVI.
Reductive.dehalogenation.of.TCE.generally.occurs.as.follows.[5]:
.
Fe
0
.→.Fe
2+
.+.2e
−
.
3Fe
0
.+.4H
2
O.→.Fe
3
O
4
.+.8H
+
.+.8e
−.
(10.1)
.
TCE.+.
n
∙e
−
.+.(
n
-3)∙H
+
.→.Products.+.3Cl
−
.
.
H
+
.+.e
−
.→.H.
∙
→.½.H
2
↑
where. the. value. of.
n
. depends. on. the. products. formed.. As. indicated. by. these. half-
reactions,.nZVI.can.be.oxidized.to.ferrous.iron.or.to.Fe
3
O
4
.(magnetite);.the.latter.is.
more.thermodynamically.favored.above.pH.6.1..As.reaction.proceeds,.ZVI.particles.
can.become.coated.with.a.shell.of.oxidized.iron.(i.e.,.Fe
3
O
4
.and.Fe
2
O
3
)..This.coating.
