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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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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.