Environmental Engineering Reference
In-Depth Information
FIGURE 13.18
Uranium Mill Tailings Hazards
Radon-exhalation
Gamma-radiation
Dust Blowing
Source:
based on Diehl 2004
Dam Failure
Water
Seepage
Erosion
Flood
Earthquake
Heavy Rain
Tailings
Dam Wall
Seepage
Groundwater
the ground rock into the atmosphere and is spread over long distances by the air. However,
radon is easily soluble in water and, thus, is usually retained in any aqueous phases. Chemical
reagents used in the uranium extraction together with the waste from the uranium process-
ing are also deposited in the tailings ponds. Consequently tailings as a whole are a complex
system containing inert rock matter ground to small grain sizes, radionuclides from the ura-
nium and thorium decay series, chemical substances, mainly sulphates, carbonates, nitrates
and complex salts of metals and alkali-earth elements, as well as heavy and rare metals.
During the operational life of an on-land tailings storage facility, tailings are usually cov-
ered by water to reduce surface radioactivity and radon emission (though with lower-grade
ores neither pose a major hazard at these levels). On completion of the mining operation, tail-
ings storage areas are commonly covered with some two metres of clay and topsoil to reduce
radiation levels to natural background levels at the mine site. At underground mines, tailings
may be used for underground i ll, reducing the risk of radon exposure at the ground surface.
Figure 13.18
illustrates the various hazards associated with radioactive tailings stor-
age facilities (Diehl 2004). The greatest risks to the environment are (1) contamination of
groundwater and river systems with dissolved radioactive materials; (2) catastrophic fail-
ures of tailings containment; (3) the dispersal of radioactive dust, which i nds its way into
water, plants, animals, i sh and humans; (4) releases of radon gas into the air, which will
deposit radon progeny on the ground for hundreds of kilometres around; (5) pollution of
surface and groundwater by chemical pollutants in tailings, notably heavy metals, acids,
ammonia and salts. Radionuclides contained in uranium tailings also emit 20 to 100 times
as much gamma-radiation as natural background levels on deposit surfaces but gamma
radiation levels decrease rapidly with distance.
In the short term, chemical pollution is of most concern. Radiation hazards are more
subtle and will take longer to be manifested. However, unless the tailings are properly dis-
posed of, these hazards will continue unabated for thousands of years. Arguably tailings
hazards will get worse as time goes on because of erosion, neglect and climatic change.
Water Management
Runoff from mine stockpiles and waste liquors from the milling operation are collected
in secure retention ponds for isolation and recovery of any heavy metals or other con-
taminants. The liquid portion is disposed of either by natural evaporation or recirculation
to the milling operation. Most Australian mines adopt a 'zero discharge' policy for any
pollutants. Process water discharged from the mill contains traces of radium and some
other metals which would be undesirable in biological systems downstream. This water is
Most Australian mines adopt a
'zero discharge' policy for any
pollutants.
Search WWH ::
Custom Search