Rare Earth Elements: A Review of Production, Processing ...

Rare Earth Elements Review Section 6 – Human Health and Environmental Risks
radioactive materials found deeper in the soil column or accumulated sediments are generally shielded by
the top layer of soil. Geometric attenuation generally limits the external radiation from naturally
radioactive materials with no interposed shielding materials to within a few meters (i.e., less than 5 meters
and often less than 1 to 2 meters from the source). Radioactivity can become concentrated in mineral
scales that develop in groundwater recovery wells, holding tanks, aeration ponds, and milling processes
areas. Inhalation of contaminated dusts is generally of greatest concern for naturally occurring radioactive
materials.
Tailings storage facilities typically receive the bulk of processing water, which is normally recycled, but
some of it could be released into the environment through seepage or overflows due to unusually high
rainfall. The tailings storage facilities (TSF), when dry, usually represent the main source of
radon/thorium and dust emissions to the environment. Special containment arrangements are required for
the disposal of tailings generated during chemical and/or thermal processing of uranium and thoriumbearing
minerals to ensure that environmentally mobile radionuclides are not released into the
surrounding environment. The disposal of contaminated equipment and materials also needs to be
controlled. In addition, the possibility of off-site contamination from trucks and equipment moving offsite
needs to be considered.
After milling and concentrating, the mineral is sometimes stockpiled at the mine site prior to transport to
the processing sites, and these stockpiles may contain radioactive minerals in concentrations sufficient to
produce elevated radiation levels and radon. The stockpiles, therefore, need to be protected against
unauthorized access and also against the possibility of the material spreading through wind saltation.
Ideally, stockpiles containing radionuclides in concentrations that require signposting of areas as
“supervised” and/or “controlled” should be located on a concrete slab to simplify the management and
clean-up operations.
The tailings from the separation and downstream processing of minerals may contain radionuclides in
concentrations that could give rise to unacceptable levels of radiation and radon. Appropriate
management is typically required, and the disposal of the waste will depend on the method used to
process the mineral and on the respective levels of radiation and the concentration of radon gas emitted.
The possibility of ground water contamination increases if chemical and/or thermal treatment of the
mineral occurs (e.g., in the case of separating the heavy mineral sands). Otherwise, the radionuclides in
the tailings could be considered as remaining bound in the individual mineral grains; therefore, the
possibility of the contamination of groundwater by radionuclides from tailings is not considered to be less
significant. Radium may be present in the tailings water, which would require removal before being
disposed.
Where any grinding, chemical, and/or thermal treatment of minerals containing radionuclides takes place,
additional safeguards must be implemented due to the fact that secular equilibrium in both uranium and
thorium decay chains may be disrupted. This could result in an increased environmental mobility of
radionuclides, such as radium and radon. Cleaning of certain minerals prior to processing (such as, for
example, the cleaning of the heavy mineral sand grains) may produce finely powdered waste (slimes).
Slime wastes may have significant uranium or thorium content, and the disposal as radioactive waste may
be required.
The equipment used in downstream processing of minerals often becomes contaminated by NORM or
TENORM. Contaminated equipment must either be disposed of properly, or thoroughly decontaminated
prior to any re-use. Scales and sludge build on the inside surfaces of pipes and vessels used in chemical
and thermal processing, and these materials often have elevated levels of radionuclides.
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