Field Application of the Stabilization Process for Arsenic-Contaminated Soil - Environmental Contamination: Health Risks and Ecological Restoration - page 460

(Dutre.and.Vandecasteele.1995)..In.addition,.Dutre.et.al..(1999).concluded.
that.oxidation.of.As(III).waste.before.stabilization.into.As(V),.using.H 2 O 2 ,.
decreases.the.leaching.of.arsenic.from.the.stabilized.product.because.the.
calculated.solubility.of.the.Ca 3 (AsO 4 ) 2 .precipitate.is.lower.than.that.of.the.
CaHAsO 3 .precipitate..Arsenic.can.also.be.stabilized.by.other.minor.mech-
anisms,. such. as. physical. encapsulation. and. chemical. inclusion.. Physical.
encapsulation. can. be. achieved. by. creating. a. solidiied. monolith. whereas.
chemical. inclusion. is. the. incorporation. of. arsenic. in. a. binder. hydration.
product. by. isomorphous. substitution. (Dermatas. et. al.. 2004).. Yoon. et. al..
(2010). conducted. a. study. on. the. stabilization. of. arsenic. in. contaminated.
soil.using.Portland.cement.and.cement.kiln.dust..The.Portland.cement.and.
cement. kiln. dust. were. added. into. the. As-contaminated. soil. with. dosed.
ranges. of. 10-30.wt%. and. 20-50.wt%,. respectively.. Stabilized. soils. were.
cured.for.1,.7,.and.28.days,.followed.by.extraction.with.1.N.HCl.to.determine.
if.the.treated.soils.were.suitable.for.disposal..The.results.of.the.stabilization.
using.Portland.cement.and.cement.kiln.dust.are.presented.in.Figure.21.2..
For. arsenic,. as. presented. in. Figure. 21.2a,. the. concentrations. in. contami-
nated.soil.extracted.using.1.N.HCl.gradually.decreased.on.increasing.the.
dose.of.Portland.cement.compared.with.the.control.arsenic.concentration.
of. approximately. 130.mg/L.. When. 30%. Portland. cement. was. added,. the.
arsenic. removal. eficiency. and.inal.pH. were. signiicantly.increased..The.
lowest. arsenic. concentration. with. a. 20.wt%. dose. was. 42.8.mg/L. after. 28.
days.of.curing.and.less.than.2.44.mg/L.after.1.day.of.curing..When.cement.
kiln.dust.was.added.to.the.soil,.a.gradual.decrease.in.the.concentration.of.
arsenic. was. also. observed. (Figure. 21.2b).. In. addition,. when. 50%. cement.
kiln.dust.was.added.to.the.sample,.a.sharp.increase.of.arsenic.removal.was.
observed,.with.a. pH.similar.to.that.with.Portland.cement..Increasing.the.
pH.with.regard.to.the.arsenic.removal.eficacy.indicates.that.pH.has.a.pre-
vailing.inluence.on.arsenic.mobility..The.mechanism.of.stabilization.was.
investigated.using.the.step-scanned.x-ray.diffraction.(XRPD).patterns..The.
XRPD.patterns.from.the.As(III).and.As(V).treated.by.Portland.cement.and.
cement.kiln.dust.are.shown.in.Figure.21.3..From.the.results.of.the.XRPD,.
it.was.concluded.that.the.precipitation.of.As(III).as.calcium.arsenite.(Ca-
As-O).and.As(V).as.NaCaAsO 4 ·7.5H 2 O.signiicantly.controlled.the.immo-
bilizations.of.As(III).and.As(V).
Iron (hydr)oxides
Several.ferric.(hydr)oxides.are.widely.used.as.adsorbents.for.the.removal.
of.arsenic.from.aqueous.solutions.or.contaminated.soils..For.poorly.crys-
talline. iron. oxyhydroxides. and. iron. oxide. minerals. in. aqueous. solution,.
the. kinetics. and. equilibrium. of. arsenic. sorption,. as. well. as. the. factors.
affecting.the.sorption.behavior,.have.been.studied.(Ford.2002,.Zeng.2003,.
Richmond. et. al.. 2004,. Zhang. et. al.. 2004).. In. addition,. iron. salts,. with. or.
without.pH.buffering,.iron.oxyhydroxides,.and.FeOOH.have.been.added.