Uranium tailings are generated as solid and liquid wastes in uranium m
ining/milling operations. Since most of the uranium deposits in the wo
rld have low grades, millions of tonnes of such wastes are produced an
nually. Often, the uranium tailings are locally disposed of, using sit
es with suitable conditions to construct tailings basins. The main con
cern during the operation of a disposal site is the presence of radium
in the liquid phase which overflows from dewatered tailings. This bar
ium is precipitated by adding proper chemical reagent. The potential e
nvironmental hazards of uranium tailings arise when the disposal site
is abandoned after the decommissioning of the uranium mill. Huge amoun
ts of solid waste as small particles of depleted ore remain in place.
Top soils are usually for soil stabilization and for controlling radon
emissions. Hence water infiltration through uranium tailings presents
a potential hazard to underground aquifers. Water plays a dual role b
y triggering a sequence of reactions and by carrying contaminants away
from the wastes sites. The situation is more serious in a country lik
e Canada, where the precipitation rate is higher than the evaporation
rate and the water table is about one metre beneath the ground surface
. For permanent disposal of uranium tailings, either the hazardous con
stituents of these wastes have to be isolated from the percolating wat
er, or the subsoils must have acceptable sealing and sorptive characte
ristics. The first approach is effected by blending proper solidifying
reagents with the tailings in order to totally block them from the le
aching effects of aggressive pore water. Solid waste treatment may pro
ve costly in additive usage and the blending operation. The leaching o
f toxic constituents, however, becomes effective so long as the tailin
gs are in a loose form. This is because of the acid-generating propert
ies of the pyrite, a substantial constituent (up to 8% wt) of the tail
ings. Two types of contaminants tend to leave the solid and migrate to
the pore water. These are the heavy metals and the radioactive elemen
ts, both of which are hazardous for their toxicity and persistence. Th
e sorptive and neutralizing capacities of the underlying soils have to
be carefully examined and measures have to be taken to stop the progr
ession of acidic interstitial water. This paper focuses on three aspec
ts of crucial importance to the permanent disposal of uranium tailings
. These are: leaching in uranium tailings, sorption on natural geologi
cal barriers, and radium immobilization.