Environmental Engineering Reference
In-Depth Information
or.to.understand.the.basic.mechanism.of.stabilization..Due.to.these.different.
purposes,.different.test.methods.have.been.developed..There.are.several.fac-
tors.that.can.affect.the.concentration.of.leachate:
•. Speciic.surface.area.of.waste
•. Volumetric.ratio.of.leachant.to.waste
•. Type.and.properties.of.leachant
•. Contact.time
•. Agitation
•. Temperature
The. extraction. procedure. toxicity. test. (EP. TOX),. toxicity. characteristic.
leaching. test. (TCLP),. synthetic. precipitation. leaching. procedure. (SPLP),.
equilibrium.leach.test,.sequential.leach.test,.and.multiple.extraction.proce-
dure.are.widely.used.to.test.leachability.
Arsenic Stabilization
Cement/Lime/Fly Ash
In. soil. treated. by. a. stabilizing. agent. containing. Ca. ions,. such. as. Portland.
cement,.lime,.or.ly.ash,.As.stabilization.is.mainly.controlled.by.the.forma-
tion.of.insoluble.Ca-As.precipitates..It.is.suggested.that.the.precipitation.of.
Ca
3
(AsO
4
)
2
.As.(V).and.CaHAsO
3
.controls.the.stabilization.of.As.in.contami-
nated.soils.(Dutre.and.Vandecasteele.1995,.1998,.Dutre.et.al..1999).
As(V).precipitation.can.be.expressed.by.the.following.equations:
2
+
+
3
Ca
+
2
H AsO
+
4
H O Ca AsO
→
(
)
⋅
4
H O
+
6
H
.
3
4
2
3
4 2
2
( )
s
2
+
+
5
Ca
+
3
H AsO H O Ca AsO
+
→
(
) (
OH
)
( )
+
10
H
.
3
4
2
5
4 3
s
2
+
+
Ca
+
H AsO H O CaHAsO H O
+
→
⋅
+
2
H
.
3
4
2
4
2
( )
s
As(III).precipitation.can.be.expressed.by.the.following.equation:
2
+
+
Ca
+
H AsO H O CaHAsO H O
+
→
⋅
+
2
H
.
3
3
2
3
2
( )
s
The.oxidation.state.of.arsenic.is.an.important.factor.in.controlling.the.leach-
ability.of.arsenic.from.stabilized.waste.because.As(III).is.more.mobile.and.
toxic.than.As(V)..Due.to.its.higher.mobility,.As(III).is.easily.leached.from.
stabilization-treated. waste.. For. example,. 95%. of. the. total. leached. arse-
nic. fraction. after. stabilization. of. arsenic. baring. ly. ash. waste. was. As(III).
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