Technology and innovation
The rake mechanism of a gold
pre-leach thickener.
The underflow system of a tailings thickener.
Bolted thickeners reduce risks
The concept of bolted thickeners is
growing in popularity. Although the
concept has been around for at least a
decade, it is becoming more commonly
used. With a bolted tank, the entire
thickener is constructed inside a
purpose-designed fabrication facility,
with all welding, sandblasting, and
painting taking place under controlled
conditions. This guarantees that
everything fits as it should so there are
no unexpected delays on site.
Thickeners have traditionally been
constructed on site; all rolled and bent
plates are transported to the required
location where they are welded onto
the prefabricated support structure and
radial beams.
This process can take weeks to
complete, as kilometres of welding
runs are required. Moreover, the
considerable weight of the material in
[38] MINING MIRROR MARCH 2018
the finished tank — several thousand
tonnes — means that the weld
quality needs to be high and coded
welders must conduct the work.
These welders must be accommodated
on site for extended periods, which
adds to the cost; cross-border work
often involves the added burden of
obtaining work permits and special
visas for these workers.
Sandblasting of the welding runs is
then necessary, as well as a final coat
of paint. In addition to the extra costs,
the work is highly weather dependent,
and delays can be caused by rain or
excessive dust.
“Weather-related delays can cause
time over-runs for the contractor,
which can then lead to penalty costs,”
says Ricus van Reenen, senior account
manager at FLSmidth. “This sort of
project risk is one of the main reasons
why contractors are choosing bolted
thickeners. As a contractor, your time
on site is where your most significant
risk will lie.”
After the construction of a bolted
thickener in a workshop, the entire
tank can be transported to site where
the bulk of the on-site work can be
undertaken by a mechanical supervisor,
who oversees the lifting and placement,
with the support of a rigger and a
crane driver. Local labour can be used
to fit the necessary bolts into the
structure, and a technical specialist can
come in to torque the bolts.
“Once in place, only touch-up
painting is required, so poor weather
won’t be a serious risk factor,” says Van
Reenen. He adds that bolted thickeners
are a fit-for-purpose, high-quality
dewatering solution with reduced
project construction risk and duration.
A bolted gold pre-leach thickener.