ON SITE
crushed down to a product size that can
be used as roadstone. The mine had their
inaugural blast in June with the aim to
access the bedrock quicker, enabling the
company to diversify its product range.
Having mined the weathered loose top
layers of silica sand, AST decided to drill
and blast making it easier to mine the
more competent sandstone mechanically,
allowing the resource to be mined more
efficiently and in greater quantities.
“At the moment we have three
products that we sell; a run-of-mine
sand that is not screened or washed and
used as a filler sand; a run-of-mine sand
screened to 8mm, that contains 13% by
volume passing 75μ; and our main product
being the 98% silica sand that is produced
after processing through the washplant.
The current installed production capacity
is 30 000 tonnes per month. The mine’s
standard grade of product is delivered at
-8mm /+75μ, carrying an average 2.4% of
sub 75μ material, which allows our clients
to receive a consistently graded product
www.equipmentandhire.co.za
at volume, suitable for making high grade
structural concrete,” says Blackmore.
AST uses a dry mobile screen on site,
a Chieftain CH2100 X power screen, that
produces four distinct sizes. Material larger
than 13mm is ejected as oversize, while
the envelope between 10mm and 13mm
is sold as a G5 screened sand, and the
material between 8mm and 10mm is sold
as a finer screened sand. Everything less
than 8mm is put through the wash plant.
The CDE Evowash plant arrived in
South Africa in seven 40ft containers from
Northern Ireland three years ago. The
plant comprises a hopper, feed conveyor,
washbox, vibrating screen, sump, cyclone,
and an Aquacycle. Micromaterial of
75mm that is ejected from the cyclone
enters the Aquacycle where it is bound
with a biodegradable poly-floculant,
which increases the density, allowing the
material to be disregarded as slimes which
are dried and stored for further processing.
The washplant recycles 90% of the water
used in the washing process, making for
a much more environmentally-friendly
process. The discard from the washing
process contains high concentrations of
Kaolin, which, according to Blackmore, can
also be extracted and sold as a primary
product. However, this process will
require an additional extraction stage and
processing plant.
When the mine initially started moving
sand four years ago, it was a greenfields
project and an earthmoving exercise.
Blackmore says they used a Caterpillar
D10 dozer to push half a metre of
overburden to the perimeters to create
the mine boundaries and the haul roads.
The top three meters of loose sand were
then moved to create four big stockpiles
which was processed over two years.
Today, a Caterplillar 330 LME excavates
the blasted sandstone and a Bell B30 ADT
is used to haul the material to the mobile
screen and wash plant. Other equipment
on site includes two Komatsu WA380
front end loaders and a Mercedes 18000
water bowser.
OCTOBER 2019
17