Field Application of the Stabilization Process for Arsenic-Contaminated Soil - Environmental Contamination: Health Risks and Ecological Restoration - page 458

aluminate.(6%-12%),.and.tetra-calcium.aluminoferrite.(∼8%)..For.cement.sta-
bilization,.wastes.are.mixed.with.cement.and.hydrated.with.water.to.form.a.
crystalline.structure.of.calcium.aluminosilicate..The.hydration.reaction.can.
be.expressed.by.the.following.equations:

. Tri-calcium silicate

: 2 3 ( CaO SiO ⋅ ) + 6 H O → 3 CaO SiO H O Ca O ⋅ ⋅ 3 + 3 ( H) 2

2 2 2 2

. Di-calcium silicate

: 2 2 ( CaO SiO ⋅ ) + 4 H O → 3 CaO SiO H O Ca OH ⋅ ⋅ 3 + ( )

2 2 2 2 2

. Tri-calcium aluminate CaO Al O

: 3 ⋅ + 6 H O → 3 CaO Al O H O heat ⋅ ⋅ 6 +

2 3 2 2 3 2

Cement. is. suitable. for. inorganic. waste. stabilization,. especially. heavy. met-
als.. Increasing. the. pH. of.waste. by. adding. cement.changes. the.form. of.the.
heavy.metals.into.insoluble.hydroxides.or.carbonate.salts..In.addition,.physi-
cal. microencapsulation. is. also. one. of. the. main. mechanisms. for. ixing. the.
contaminants.present.in.waste.

Pozzolans

A.pozzolan. is.a.material. that.produces. cement.by.reacting.with. lime.and.
water. at. ambient. temperature.. Most. general. pozzolanic. materials. are.
obtained.from.ly.ash,.blast.furnace.slack,.and.cement.kiln.dust..Fly.ash.is.
the.most.common.pozzolan,.which.mainly.contains.SiO 2 ,.Al 2 O 3 ,.Fe 2 O 3 ,.CaO,.
and. unburned. carbon.. Like. cement,. pozzolans. can. be. applied. to. the. sta-
bilization. of. inorganic. contaminants. by. creating. a. high-pH. environment..
With. ly. ash,. lime. or. quicklime. can. be. used. to. enhance. the. stabilization.
eficiency.

Lime

Lime,.or.calcium.hydroxide.Ca(OH) 2 ,.is.mainly.obtained.from.the.hydration.
reactions. of. materials. containing. calcium. silicate,. calcium. alumina,. or. cal-
cium.aluminosilicates..Lime.can.be.added.to.increase.the.pH.of.waste,.with.
other. additive,. such. as. ly. ash,. providing. the. main. stabilization. reactions,.
which.is.best.suited.to.inorganic.contaminants.

Leaching Test

A. reduction. in. the. rate. of. migration. from. contaminants. into. the. environ-
ment.is.the.most.important.reason.for.using.stabilization.techniques..There.
are.numerous.leaching.test.methods.available.for.testing.the.leachability.of.
stabilized.materials..Leaching.tests.may.be.conducted. to. provide.the.basis.
for.regulation,.for.the.generation.of.data.to.model.contamination.migration,.