Environmental Engineering Reference
In-Depth Information
FIGURE 20.4
Downward.extension.of.oxidation.in.the.proile.from.TERF.exhibited.in.cores.taken.at.time.of.
irst.planting.in.2003,.and.again.in.2006.
quickly.evolved.to.the.higher.pH,.suggesting.initial.effects.of.organic.acids.
and/or.microbial.activity..On.TERF,.the.geochemically.open.systems.to.0.5.m.
allowed.ingress.of.oxygen.and.water.but.did.not.result.in.elevated.soil.acid-
ity,. nor. was. there. an. increase. in. the. concentrations. of. labile. As. and. toxic.
metals.. Progressive. oxidation. of. the. tailings. occurred. beneath. the. amend-
ments.(Figure.20.4).either.uniformly,.or.preferentially.along.layers.of.coarser.
tailings.that.resulted.from.the.original.settling.
Chemical.changes.in.the.tailings.cover.were.monitored.over.two.summers..
Soil. sampling. of. the. experimental. plots. was. regularly. performed. and. pH.
and. electrical. conductivity. measured.. After. two. summers,. the. pH. of. tail-
ings.ranged.from.6.4.to.6.7,.and.oxide.covers.pH.5.8.were.still.slightly.acidic.
(Figure.20.4)..The.surface.of.exposed.tailings.was.observed.to.have.changed.
in.color.from.dark.gray.to.light.red.in.different.sections.of.the.experimen-
tal. plots.. Biosolid. amended. tailings. or. oxide. cover. were. acidic. (pH. 4-6)..
Unamended.oxide.cover.had.electrical.conductivity.levels.which.could.only.
be. tolerated. by. very. salinity-tolerant. plant. species.. Biosolid. incorporation.
into. oxide. material. reduced. salinity. levels. by. increasing. water. iniltration.
and.reducing.capillary.movement.of.saline.tailings.water..Sequential.extrac-
tion.procedures.has.shown.that.as.tailings.particles.weather.and.decompose.
the.predominant.form.in.which.it.is.associated.is.in.the.amorphous.colloidal.
phase.and.minimal.contribution.to.bioavailable.forms.(Figure.20.5).
Recent.excavation.of.root.proiles.through.the.test.plots.have.shown.that.
shrinkage.and.desiccation.cracks.have.formed.in.the.covered.tailings..These.
form.preferential.pathways.for.water.to.percolate.through.as.well.as.allow-
ing.proliferation.of.plant.roots.to.the.deeper.levels.of.the.tailings..The.for-
mation. of. oxidized. cutans. or. skins. was. also. pronounced. where. there. was.
extensive.cracking.of.the.tailings..Geochemical.analysis.of.these.boundary.
layers.is.currently.identifying.components.of.the.secondary.minerals.formed.
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