PASTE & TAILINGS 2020
WesTech paste solution successful in heavy rainfall area
An innovative design in China incorporated the benefits of
surface stacking for effective water management
imbalance and minimise process water going
into the pond. The goal of the design was to:
n Provide a safe and effective disposal of the
tailings
n Improve the overall physical characteristics of
the deposits
n Maximise water recovery at the thickener
n Keep rain water separate from process
stream water
The installed 15 m diameter WesTech Deep Bed™ thickener on a hill near the TSF
Agold mine located in a steep mountain solution that would incorporate the benefits of
area of sub-tropical China retrofitted one surface stacking technology to avoid the water
of its slurry ponds to convert it to a
surface stack technology. The tailings storage
facility (TSF) is located in a canyon near the
mine. The narrow canyon is dammed at the
mouth providing about 6.3 ha of area. The TSF
feed is the discharge stream from a process
water treatment plant using Na 2S and CaO to
remove dissolved salts. The metal precipitate
has a fine particle size distribution, PSD, and is
difficult to flocculate and capture. The water
must be recycled as it does not meet discharged
criteria.
The monsoon-influenced climate gives the
heaviest rain in the spring to early summer
(greater than 200 mm per month) with over 1.7
m of rainfall a year. A problem with a slurry
pond operation is that any rain collected from
the pond will overload this process water
balance. An optimisation study focused on a
Recommended solution
The mine site determined that implementing
surface stacking of the underflow from a pastetype
thickener, paste and thickened tailings
(P&TT) would provide a solution for the site
because of the following benefits:
n Dewatering the process stream in a pastetype
thickener recovers significantly more
water, and the water in the underflow
evaporates and does not pool in the TSF like
the slurry pond was pooling. Water balance
control is simplified, recovering the water at
the plant.
The TSF during the first monsoon season
n Without requiring water to be collected from
the pond, the rainwater does not add to the
water balance like with the slurry pond.
n The final tailings density is greater with P&TT,
increasing the TSF capacity.
Day 10 shows the test deposit after two rain events, dried to significant cracking. At this point about
half of the water has evaporated
Issues with drying in a sub-tropical
climate
Though surface stack techniques have been
successful in a variety of climates around the
world, there is still concern about whether the
techniques are effective in heavy rainfall areas.
The mine conducted a pilot-scale deposition
and drying investigation after the installation of
P14 International Mining | SEPTEMBER 2020 Supplement