HEAP LEACH – SX-EW_proof 26/10/2016 10:02 Page 7
HEAP LEACH – SX/EW
drilling by Yellow Jacket with a hollow stem
auger. Fine grained material facilitated spreading
in the heap.
n Rinse wells spaced about 90 ft (27 m)
n Phase I designed with four-spot pattern
n Phase II designed with wells in a line
Rinse well screens have started to plug. This
typically happens after about three months of
continual rinsing. Cameras indicate biological
growth.
The SSL program has been operating for well
over two years and has been shown to be
successful at removing inventory. Expansion of
this program will continue for a few more years,
but “there is still much to learn,” says Rucker.
The authors2 expect that “geophysical data
obtained in the future, well into closure and
reclamation, will be used in helping determine
draindown conditions, effective cover design, and
stability of the heap.”
Ore permeability
Michael Milczarek and colleagues at GeoSystems
Analysis (GSA) stress that “ore permeability has
long been recognised as a critical factor in heap
leaching performance. Poor ore permeability
results in decreased metal recovery and
increased leach recovery time.”
Many factors influence leach ore permeability,
including ore/rock behaviour under physical
crushing, chemical decrepitation from acid
agglomeration and raffinate contact (chemical
crushing), the nominal crush size, heap height
and lixiviant irrigation rate. During mine
planning, ore permeability characterisation
programs provide data to characterise the effect
of these factors on permeability and allow for
optimisation of operations methods. During
operations, in-situ monitoring programs can
provide real-time data to determine heap
leaching efficiency.
Permeability characterisation programs should
test the ore material at the designed crush size
(or ROM), and under operating conditions such
as heap height and irrigation rates. GSA
recommends the use of “large diameter
cores/flow cells which can directly measure
solution and air permeability under nominal
irrigation conditions, and the use of flexible wall
(compression) methods which can mimic the
effect of overburden pressure and variable bulk
density which may occur within an operating lift
and also allow unsaturated flow parameters to be
measured. In addition, care should be taken to
use the appropriate lixiviant and simulate the
amount of ore decrepitation (chemical crushing)
that may occur during leaching operations.”
In one such example, a 500,000 t copper
sulphide leach pad was instrumented and
monitored to investigate large-scale heap leach
fluid dynamics under varying i