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Geotechnical News • December 2014
47
WASTE GEOTECHNICS
estimates of the rate of evaporation
from a freshly deposited tailings lift
(1st lift), the degree of surface drying
of this lift as a function of drying
time (exposure time) and the associ-
ated rewetting losses upon deposition
of additional tailings (2nd lift) over
previously dried areas (as shown in
Figure 5b). Ultimately, the modelled
results for evaporative drying and
rewetting losses are combined with
tailings lift exposure times provided
by the deposition plan to determine
the overall water recoveries that result
from the selected tailings deposition
sequence during the life of the facility.
Conclusion
Estimates of the evaporation, drying
and rewetting of tailings under field
conditions are generally addressed
using unsaturated soils theory and
models. The accuracy of such models
can be difficult to judge in the absence
of information that can serve as basis
for comparison and validation. Col-
umn tests have been developed to fill
this gap and support the assessment
of evaporation, drying and rewetting
losses during the planning and design
stages of a tailings deposition plan,
when field scale data is not available.
The approach involves measuring
water losses from the tailings under
controlled laboratory conditions and
comparing them to those predicted
by unsaturated models. Data obtained
from the laboratory tests are used to
calibrate the models by adjusting the
tailings material properties and input
parameters required to assess evapora-
tion and drying. The tests are intended
to increase confidence in the represen-
tativeness of numerical model results
and to support estimates of water
recovery from tailings under field con-
ditions during the early stages of proj-
ect development. Refinement of water
recovery predictions and adjustments
to the deposition plan should continue
during all stages of design and most
importantly into operations when
measurements of evaporation from the
tailings surface become possible.
Acknowledgements
The author would like to thank G.
Ward Wilson for reviewing it prior to
publication.
Eduardo Salfate
Geotechnical Engineer with Golder
Associates S.A.
esalfate@golder.com