Mining in focus
Grasshopper conveyors are mounted on soft wheels to enable the smooth
movement of the equipment over the leach pad. As more agglomerate is added
to the heap and the stack becomes bigger, the whole system has to retract.
Typical Agglomeration Drums
mostly underground operations. The
method is, however, being used on a
large scale in the copper mines of South
America and, according to Bundo, it will
be used more and more on the African
continent in future.
Weighing up the alternatives
Although heap leaching is efficient on its own, the proficiency is greatly improved by adding an
agglomeration drum. Agglomeration drums are based on a rotary drum design that tumbles ore fines in
the presence of leachate, through its interior to promote uniformity and to mix the leachate and fines.
with 90% recovery in an agitated leach
plant. Other metals, such as copper, use
solvent extraction and electrowinning
to extract the target metal from the
solution.
According to Phil Bundo, process
engineering director at Senet, mines
need large reserves, a large resource,
and significant real estate if they want
to employ the heap leach method. “To
build a big heap and accommodate
all the associated equipment, a large
space is required; and to fill that space,
[16] MINING MIRROR JUNE 2018
a mine needs to produce enough ore,”
says Bundo. Bundo adds that climatic
conditions like rain can negatively affect
a heap leach operation, although this
would not ordinarily be enough cause
to discard heap leaching as a processing
method. Resources and reserves play
a much bigger role in determining
whether heap leaching will be viable.
Heap leaching is not that popular
in South Africa because it is more
applicable to shallow opencast mining,
and South African gold mines are
According to Bundo, there are other
recovery methods, besides heap leaching,
to consider when mining gold. These
include gravity concentration, carbon in
pulp (CIP), and carbon in leach (CIL).
“The methodology selected is a function
of the mineralogy of the ore. If the gold is
associated with oxides, for example, it can
be amenable to heap leaching. The grade
also plays a key role. Heap leaching is used
for low-grade oxides, while high-grade ore
(with or without oxides) is better suited to
CIP or CIL methods,” says Bundo.
Bundo explains that while heap
leaching is not as costly as CIL or CIP,
the recovery achieved is also not as
efficient. “CIP and CIL are costlier in
terms of initial capital and operational
costs, but they provide the benefit of high
recovery,” says Bundo. In cases where the
oxides are amenable to heap leaching
and cannot economically justify the
construction of a CIL or CIP plant, then
the operations start off with heap leaching
to generate sufficient capital to finance the
CIP or CIL circuits when mining more
refractory ore.
“It is also important to remember that
if the gold is associated with sulphides