Mining in focus
Gradually building a stack
at a heap leach operation.
A heap leach operation illustrating the large area
and long train of mobile equipment and conveyors
needed to make the method efficient.
Transverse conveyors feeding a stacker.
including the stacker, is wheel or track
driven. A combination of wheels and
tracks is used to minimise the bearing
pressure on the pad.
The stacker can slew and move backwards
and forwards in a linear fashion.
Heap leach pads require special
preparation in construction. According
to Bundo, a pad should slope by one
or two degrees so that the solution can
gravitate to the pond, and there should
be sufficient aggregates underlying the
surface. Moreover, the high-density
polyurethane (HDPE) liners that cover
the surface are critical to prevent the
chemical solution from seeping into the
groundwater. Special collection pipes
are installed underneath the pad to
direct the solution to the relevant ponds .
Pros and cons
For Breton Scott, managing director of
Bowline Professional Services, the most
important advantage of heap leaching is
that it lowers the capital and operating
expenses relative to other traditional
methods like flotation, agitation, and
vat leaching, especially where low-grade
ores and tailings are present. It also has a
potentially rapid payback period.
“Heap leaching further eliminates
some environmental concerns and
restraints. The main benefit, in terms
of the environmental impact, is that it
requires less energy and water,” says Scott.
Moreover, the method has uncomplicated
design and equipment requirements, and
the construction phase is a lot faster than
other treatment methods.
Although Scott says that the heap
leach method is not seriously affected
by climate, he mentions that a lower
efficiency has been noted at low
temperatures. “High rainfall areas
may also dilute the solution, requiring
additional monitoring,” he says.
The risks associated with heap
leaching are mainly related to
environmental concerns, should
the pad construction process not be
done correctly from the design stage.
Potential issues with the regional
water balance are highlighted as a risk,
along with the possible exposure of
the solutions used to the surrounding
areas. Heap leaching does, however,
have a much lower potential of acid
mine drainage. The costs associated with
pollution control and closure efforts are
one of the main continual expenses in
such operations.
“The drilling of water-monitoring
boreholes and regular testing of
the groundwater by an accredited
water-quality laboratory would be
required if the heap leach method is
used,” says water laboratory analyst, Ben
Steyn. “Tests would generally include
pH, dissolved solids, and heavy metals.”
“The biggest question a mine needs
to ask itself is whether it has an ore
body that is amenable to heap leaching.
Senet prefers to get involved in a
project from the test work phase, which
enables us to prove that heap leaching,
as a processing method, will work for
the project. We not only consider heap
leaching, but also all the other options
available. It is always a trade-off
between the capital investment and
recovery,” Bundo concludes. b
JUNE 2018 MINING MIRROR
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