Environmental Engineering Reference
In-Depth Information
can.eventually.reduce.the.reactivity.of.(or.“passivate”).the.nZVI.particles.[4,.5]..Pas-
sivation.can.begin.immediately.upon.manufacture,.depending.on.how.the.material.is.
stored.and.shipped;.the.oxidation.reaction.continues.after.environmental.application.
The.eficiency.of.treatment.depends.on.the.rate.of.TCE.dechlorination.relative.
to.nonspeciic.corrosion.of.the.nZVI.to.yield.H
2
..In.one.study.with.granular.ZVI,.the.
latter.reaction.consumed.over.80%.of.Fe
0
.[5]..The.solution.pH.and.the.Fe
0
.content.
of.the.particles.may.affect.the.balance.between.nonspeciic.corrosion.and.reduction.
of.TCE.
The.effectiveness.of.
in situ
.treatment.using.nZVI.also.depends.on.the.charac-
teristics.of.the.aquifer..The.pattern.and.rate.of.groundwater.low.affect.the.distribu-
tion.of.nZVI..The.geochemical.characteristics.of.the.groundwater.—.including.pH,.
relative.degree.of.oxygenation,.and.presence.of.naturally.occurring.minerals.—.also.
affect.the.reactivity.and.distribution.of.nZVI.
The. remainder. of. this. section. provides. more. information. on. nZVI. reagents,.
describing.the.size.of.nZVI.particles.and.the.effects.of.particle.size,.other.constitu-
ents.of.nZVI.reagents,.and.factors.that.affect.the.mobility.of.nZVI.in.the.subsurface..
It.describes.how.sites.are.remediated.with.nZVI.and.presents.examples..Finally,.it.
discusses.information.on.the.potential.risks.from.using.nZVI.and.some.of.the.result
-
ing.risk.management.decisions.
10.1.1 F
Orms
OF
n
Zvi
nZVI.can.be.manufactured.using.different.processes.that.convey.different.proper-
ties. to. the. material.. These. properties. include. particle. size. (and. size. distribution),.
surface.area,.and.presence.of.trace.constituents..Reagents.for.environmental.reme-
diation.often.contain.materials.other.than.iron.to.enhance.the.mobility.or.reactivity.
of.nZVI.
In.general,.four.processes.are.used.to.manufacture.nZVI.[7-9]:
.
1.. Heat.iron.pentacarbonyl
.
2.. Ferric.chloride.+.sodium.borohydride.
.
3.. Iron.oxides.+.hydrogen.(high.temperatures).
.
4.. Ball.mill.iron.ilings.to.nano-sized.particles
The.processes.marked.with.an.asterisk.().are.currently.used.in.commercial.produc-
tion.
Researchers. have. modiied. nZVI. particles. to. increase. their. mobility. and/or.
reactivity..Coating.the.nZVI.particles.can.limit.agglomeration.and.deposition,.and.
enhance.their.dispersion..These.particle.treatments.include.emulsiied.nZVI,.poly-
mers,.surfactants,.and.polyelectrolytes.[10].
Bimetallic. nanoscale. particles. (BNPs). have. a. core. of. nZVI. with. a. trace. coat-
ing.of.a.catalyst.such.as.palladium,.silver,.or.platinum.[11]..This.catalyst.enhances.
reduction.reactions..PARS.Environmental.markets.a.BNP.developed.at.Penn.State.
University.. This. BNP. contains. 99.9. wt%. iron. and. 0.1. wt%. palladium. and. poly-
mer.support..The.polymer.is.not.toxic;.the.U.S..Food.and.Drug.Administration.has.
approved.the.use.of.the.polymer.as.a.food.additive..The.polymer.limits.the.ability.
of. the. nZVI. particles. to. agglomerate. and. adhere. to. soils.. Case. studies. presented.
