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2015/2/5
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Decontamination of radioactive-contaminated soils
A PRESENTATION TO Jubail International Environment Conference (5-6 June 2011)
By Prof. Dr Mamdouh F. Abdel-Sabour Head of Environmental Studies Department Saudi ASMA Environmental Solution (SAES)
Naturally occurring radioactive
materials (NORM) U238, 235,
228, 230, 232Th, 226, 228Ra, 210Pb, 210Po, 231Pa, 227Ac
Sources of NORM contamination
1- Milling metal mining and smelting
2- Phosphate ore processing
3- Coal mining
4- Fossil fuel power production
5- Oil gas drilling
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Sources of contamination 7- Rare earth extracting and processing
8- Titanium oxide industry
9- Zirconium and ceramic industries
10- Application of radium and thorium
11- Heavy metals
Rare earth Titanium oxide sources of heavy metals
Sources of contamination 12- Building materials
13- Depleted uranium (DU) alpha-radiation, toxicity, Depleted
Uranium as ammunition, ranges and average
concentrations of natural U.
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The widespread occurrence of NORM means that :
sands, clays, soils and rocks,
many of the ores and minerals (e.g. coal, oil and gas,
bauxite, rock phosphate, ores containing tin, tantalum,
niobium, rare earths, and some copper and gold
deposits),
supplies (e.g. water, building materials)
products (e.g. ceramics, phosphate fertilizer),
by-products (e.g. phospho-gypsum),
recycled residues (e.g. fly ash from coal burning, red
mud from alumina production and slags from mineral
processing), and
devices used by humans (e.g. welding rods and
electronic components) can contain NORM.
The processing of these naturally
occurring radioactive materials (NORM) can
lead to the enhancement of the
concentrations of the radio-nuclides either
within the products, or in the wastes from
the processes.
The radio-nuclides which are of most
interest are 235U, 238U and 232Th because
they can undergo a series of radioactive
decays and give rise to daughters which
may also be found in NORM.
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7
Uranium-238
Decay Series
Radium-226
Thorium-230
Uranium-234
Protactinium-234
Thorium-234
Uranium-238
Lead-206
(Stable)
Polonium-210
Lead-210
Polonium-214
Bismuth-214
Lead-214
Polonium-218
Radon-222 Bismuth-210
a,g
b,g
b,g
a,g
a,g
a,g
b,g
a,g
a,g
a,g
b,g
b,g
a,g
b,g
Radioactive Decay Chains of Naturally occurring
radioactive materials (NORM)
natural decay
237Np Decay Series 209Pb
232Th Decay Series 208Pb
235U Decay Series 207Pb
Alarming Situation There is widespread of U contamination
of soils throughout the world. Soils
contamination results from improper U
waste-storage practices (Liator, 1995; Jones and
Serne, 1995) and from the mining and
milling of U-Large quantities of waste
material from milling facilities contain
sufficient amounts of radio-nuclides to
demand concern over environmental
health (Johnson et al., 1980; Sheppard and Thibault, 1984).
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The carcinogenic
nature (mutation &
genetic impact) and
long half-lives of these
radio-nuclides make
them a potential threat
to human health.
Moreover, there is
an increasing trend of
uranium accumulating
in soils due to a
number of deliberate
or wrong practices.
It is suggested that our knowledge of the
mechanisms that control the behaviour of
such radionuclide in soil must be
improved and can be used for risk
assessment and proposition of remediation
treatments.
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Remediation technologies may be divided into five major
categories:-
1- Removal of source - where the contaminated material is collected
and removed to a more secure location.
2- Containment - where barriers are installed between contaminated
and uncontaminated media to prevent the migration of contaminants,
i.e. capping and sub-surface barriers.
3- Immobilization - where materials are added to the contaminated
medium, in order to bind the contaminants and reduce their mobility,
i.e. cement-based solidification and chemical immobilization.
4- Separation - where the contaminating radio-nuclides are separated
from the bulk of the material, i.e. soil washing, flotation and
chemical/solvent extraction.
5- Phyto-remediation - The bio-reduction and immobilization of
soluble U(VI) to insoluble U(IV) minerals is a promising strategy for
the remediation of uranium-contaminated soil and groundwater.
Phytoremediation has been used to extract
radio nuclides and other pollutants from
contaminated sites.
The accuracy and success of these applications
depend on an understanding of the processes
involved in plant uptake of radio nuclides.
This presentation reviews the recent advances
in uranium removal from contaminated soils,
using
hyper-accumulator plants, or
high biomass crop species after soil treatment
with chelating compounds.
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Phytoremediation Phytoremediation, an emerging cleanup
technology for contaminated soils,
groundwater, and wastewater, is both low-
tech and low-cost.
Phytoremediation is the engineered use of
green plants, including grasses, shrubs, and
woody tree species, to remove, contain, or
render pollutant such as heavy metals,
organic compounds, and radioactive
compounds in soil or water ((Raskin et al.,
1997and Salt et al., 1998).
Plant-based soil remediation systems can be
viewed as biological, solar driven, pump-and-treat
systems (the root system) that enhances the
below-ground ecosystem for subsequent reductive
use (Wenger et al., 2002; Liphadzi et al., 2003; Dickinson and Pulford,
2005).
This function of the plant includes biological, chemical,
and physical processes either by plants or by the free-
living organisms (bacteria or fungi) that constitute the
plant's rhizosphere such as:
uptake & extraction,
Sequestration & immobilization,
degradation, and
metabolism of the contaminants, (Baker et al., 1995; McGrath, 1998).
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Fig. (1) Phyto-remediation technologies
Plants can help us in finding uranium
Astraqualus Sp Aster venusta Sp.
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Higher plants as indicators of uranium
occurrence in soil.
Shahandeh and Hossner, (2002a,b) evaluated 34 plant
species for uranium accumulation from U contaminated soil.
Results indicated that sunflower (Helianthus annuus) and
Indian mustard (Brassica juncea) accumulated more U than
other plant species.
Helianthus annuus Atriplex canescens Brassica juncea
Kochia scoparia barley lucerne
Melilotus officinalis
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Conclusion
Metal hyper-accumulator for radionuclide phyto-remediation includes the following character:
1)Highly efficient root uptake,
2)Enhanced root to shoot transport,
3)Hyper-tolerance of metal(s), involving internal complexation and sequestration
4)Crops like willow (Salix viminalis L.), Indian mustard [Brassica juncea (L.) , and sunflower (Helianthus annuus L.) were reported as successful hyper accumulator.
Salix viminalis L Brassica juncea Zea mays Helianthus annuus L.