Environmental Engineering Reference
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removed little or no
131
I.
52
The sorbed radioisotopes were not eluted by water or 4
N
ammonia.
Vermiculite ranked first for cesium sorption in the following ranking of natural
clays and minerals:
53
Vermiculite > phillipsite > mordenite ≈ montmorillonites ≈ clinoptilolite >
illite ≈ salona shale > labradorite basalt ≈ mica > conasauga shale ≈ kaolinite
> chlorite
Under hydrothermal conditions, vermiculite, tobermorite, and zirconium phos-
phate were best for cesium immobilization. Tobermorite and hydroxyapatite were
best for strontium, lead, and cadmium immobilization.
54
Vermiculite from South Africa was used as a comparative base for sorption of
Cs, Sr, and Ca by Polish minerals.
55
The relative rankings of Cs distribution ratios
(from 900 for vermiculite to 1.6 for shales) follow:
Vermiculite > bentonites > silica > sand > iron sands > iron and silty sands
> phosphorites > halloysite ≈ bog iron ore > chlorite detritus > shales
Another study ranked the effect of additives on the cesium effective diffusion
coefficient in the following order:
56
Ca-bentonite (Karlich) > Na-bentonite (U.S. & Geisenheim) ≈ H-bentonite
> Ca-bentonite (Neiderbayern) ≈ Na-bentonite (Karlich) ≈ vermiculite ≈
kaolin ≈ illite > zeolite > attapulgite
The equivalent leachability indices ranged from 11.2 for the Karlich Ca-bento-
nite down to 7.4 for attapulgite, with a value of 8.6 for illite, significantly below
that measured at ORNL (> 10). The value for vermiculite was 8.8. As the bentonite
increased from 0 to 20 wt% in steps of 5 wt%, the effective diffusion coefficient
decreased with each addition from about 10
-1
to about 10
-5
cm
2
/d (leachability index
of 6 to 10) for cesium, but slightly increased with each addition around a value of
10
-3
cm
2
/d (leachability index of 8) for strontium.
Higher salt concentrations of sodium or calcium nitrate suppressed sorbent
selectivity for
137
Cs and
85
Sr.
57
Of the agents tested, ferrocyanides had the highest
selectivity for
137
Cs (distribution ratio > 10,000 cm
3
/g). At low salt concentrations,
high distribution ratios for
137
Cs were also observed for natural aluminosilicates
(vermiculite and clinoptilolite), synthetic zeolites, and phosphates. The lowest
137
Cs
ratios were observed for ion exchange resins, hydrous metal oxides, and carbon
adsorbents. Synthetic shabazite had the highest selectivity for
85
Sr in sodium nitrate
solutions (distribution ratio > 43,000 cm
3
/g). Efficient Sr sorption also occurred for
ion exchange resins, some synthetic zeolites, and modified manganese dioxide.
85
Vermiculite, clinoptilolite, other synthetic zeolites, phosphates, ferrocyanides, and
carbon adsorbents showed relatively low selectivity for
85
Sr. Clinoptilolite and mod-
ified manganese dioxide had the highest selectivity for
85
Sr in calcium nitrate solu-
tions (distribution ratio > 500 cm
3
/g), though synthetic shabazite was still efficient
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