Environmental Engineering Reference
In-Depth Information
ratios.was.not.signiicant..The.arsenic.concentration.leached.by.the.TCLP.
solution. (Figure. 21.6b). indicated. relatively. low. arsenic. stabilization. efi-
ciency.compared.with.pH.5.8.DI.water..The.sample.treated.using.magne-
tite. with. a. 0.335%. iron/mine. tailings. ratio. had. 45%. arsenic. stabilization.
eficiency. after. 3. days. and. stable. until. 28. days. of. treatment.. In. the. use.
of. magnetite. with. a. 0.670%. iron/mine. tailings. ratio,. the. eficiency. con-
tinuously.increased.and.reached.60%.after.7.until.28.days..The.maximum.
stabilization.eficiency.was.45%.and.62%.at.the.iron/mine.tailings.ratio.of.
0.335%. and. 0.670%,. respectively.. As. a. result. of. the. ield. application. test,.
synthesized. magnetite. was. shown. to. have. high. As. treatment. eficiency.
and,. therefore,. was. considered. a. good. stabilizing. agent,. especially. from.
the.results.for.extraction.by.pH.5.8.DI.water.
Stabilization of Arsenic in Soil
Stabilization.is.one.of.the.best.remediation.techniques.for.the.reuse.of.contam-
inated.soil..However,.the.application.of.arsenic.stabilization.in.soil.is.harder.
than.that.for.base.metals.due.to.the.unique.geochemical.behavior.of.arsenic..
The.choice.of.additives.is.an.important.factor.for.arsenic.stabilization.in.soil.
In. order. to. measure. the. soil. characteristics,. soil. samples. were. collected.
from.the.Chungyang.area,.where.abandoned.Au-Ag.mines.are.located..The.
pH.of.the.soil.samples.was.5.07,.and.the.soil.texture.was.silt.loam.(sand.33%,.
silt. 63%,. clay. 4%).. The. CEC. value. and. LOI. were. 19.8.meq/100.g. and. 25.6%,.
respectively..From.the.results.of.the.SPLP.and.TCLP.tests,.the.arsenic.con-
centrations.in.the.studied.soil.were.0.23.and.1.14.mg/kg,.respectively..These.
results.show.a.lower.value.for.the.TCLP.than.that.proposed.by.the.U.S..EPA.
(5.mg/kg).. The. total. arsenic. concentration. via. aqua. regia. digestion. of. the.
soil. was. 145.mg/kg,. which. was. signiicantly. higher. than. the. normal. level.
proposed.by.Bowen.(1979)..From.the.sequential.extraction.results,.approxi-
mately. 50%. of. the. arsenic. measured. was. in. the. easily. mobile. fraction. via.
steps.I.and.II..This.result.suggested.that.the.major.forms.of.arsenic.in.the.soil.
samples. would. be. easily. extracted. and. transferred. from. soil. to. the. water-
plant.system..Rice.grain.samples.were.collected.and.the.arsenic.concentra-
tion. measured. to. evaluate. the. correlation. between. the. soil. and. rice. grain.
arsenic.levels..The.arsenic.concentrations.in.the.rice.grains.ranged.from.0.07.
to.0.59.mg/kg,.with.an.average.of.0.19.mg/kg.in.studied.area..The.rice.grains.
cultivated. in. highly. contaminated. soil. contained. higher. concentrations. of.
arsenic..This.result.indicates.that.arsenic.can.move.from.soil.to.rice.grains,.
and.soil.contamination.can.lead.to.plant.contamination.
A.ield.study.on.the.stabilization.of.arsenic.in.contaminated.soil.was.per-
formed. using. two. types. of. additives:. limestone. and. mine. sludge. collected.
from.an.acid.mine.drainage.(AMD).treatment.system..The.mine.sludge.was.
the.by-product.of.AMD.treatment,.for.which.the.oxidized.iron.compounds.
were. identiied. by. XRD. analysis. (Figure. 21.7).. Figure. 21.8. shows. the. pH.
variation. in.the. pore. water.collected.from.the.ield.experimental.plot.after.
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