Environmental Engineering Reference
In-Depth Information
particles. tested,. single-walled. carbon. nanotubes. and. fullerols. passed. through. the.
porous.medium.more.rapidly.than.the.colloidal.nano-C60.agglomerates..The.solubi-
lized.forms.of.the.particles.are.more.mobile.than.the.suspended.form..The.research-
ers.identiied.the.need.for.additional.studies.to.evaluate.the.factors.in.natural.systems.
that.may.increase.the.mobility.of.nanoparticles.in.the.environment..These.potential.
factors.include.naturally.occurring.polyelectrolytes.such.as.fulvic.and.humic.acids.
that.might.affect.the.surface.properties.of.the.nanoparticles,.and.light-.or.bio-acti-
vated.functionalization.that.would.alter.the.solubility.of.the.nanoparticles.[17].
Lecoanet. and. Wiesner. [26]. conducted. additional. experiments. to. evaluate. the.
effect.of.low.velocity.on.the.deposition.of.various.nanoparticles.in.a.porous.medium..
They.evaluated.two.types.of.fullerenes.(fullerol.and.nano-C60.agglomerates),.sur-
face-modiied.single-walled.nanotubes,.and.two.mineral.oxides.(silica.and.titanium.
dioxide).. Silica. particles. showed. very. little. removal. and. very. small. variability. in.
changes.in.low.rate..The.passage.of.titanium.dioxide.through.the.porous.medium.
was.proportional.to.the.low.rates..However,.the.afinity.of.the.fullerenes.and.carbon.
nanotubes.was.insensitive.to.low.rate,.which.the.researchers.attributed.to.the.larger.
Hamaker.constants.for.these.nanoparticles..They.also.noted.that.at.the.higher.low.
rates,. the. fullerenes. exhibited. increased. deposition. after. passage. of. the. irst. pore.
volume.. This. suggests. that. previous. fullerene. deposition. can. facilitate. subsequent.
deposition,.most.likely.the.result.of.fullerene-fullerene.interactions.[26].
The. mobility. of. nZVI. and. other. metallic. nanoparticles. in. aquifer. systems.
has. been. widely. studied. because. of. the. potential. application. of. these. materials. in.
groundwater. remediation.. Based. on. its. high. redox. potential,. nZVI. can. facilitate.
reductive. dechlorination. of. organic. contaminants. in. groundwater. and. immobilize.
heavy. metals. through. cation. reduction.. However,. its. effectiveness. in. groundwater.
remediation.depends.on.its.ability.to.remain.dispersed.in.the.groundwater.and.not.
to.agglomerate.with.itself.or.bind.to.soil.particles..A.suspension.of.nZVI.must.resist.
initial.agglomeration.so.it.can.be.delivered.effectively.through.the.porous.medium.
to.the.groundwater.contaminants..As.discussed.in.Chapter.10,.the.fate.and.transport.
of.nZVI.injected.into.an.aquifer.depend.on.the.characteristics.of.the.reagent.and.on.
the.aquifer.characteristics,.including.the.low.of.groundwater,.geochemistry,.and.the.
nature.of.the.aquifer.materials..Oxidation.of.nZVI,.agglomeration,.and.attachment.
to.soil.grains.can.occur.rapidly..Depending.on.the.setting,.nZVI.can.migrate.only.
a.few.meters.to.tens.of.meters.from.the.injection.site,.and.its.reactivity.lasts.on.the.
order.of.weeks.to.months.
Phenrat. et. al.. [27]. performed. laboratory. experiments. to. evaluate. the. effect. of.
dispersion.concentrations.and.magnetic.attractive.forces.on.the.agglomeration.rates.
for. various. aqueous. nZVI. dispersions.. They. concluded. that. because. of. the. rapid.
agglomeration. of. nZVI. into. micrometer-sized. particles,. adsorbed. polymers. are.
required.to.modify.the.surfaces.of.the.nZVI.particles.and.thereby.prevent.agglom-
eration.and.enhance.mobility..A.decrease.in.magnetization.would.also.improve.the.
stability.of.nZVI.dispersion.[27].
Dunphy.Guzman.et.al..[10].conducted.laboratory.experiments.to.evaluate.the.effect.
of.pH.on.the.agglomeration.and.transport.of.titanium.dioxide.in.a.porous.medium..
They.reported.that.pH.affects.the.surface.charge.of.the.titanium.dioxide,.as.well.as.
the.size.of.the.agglomerated.particles..More.than.80%.of.the.suspended.particles.and.
