HEAP LEACH – SX-EW_proof 26/10/2016 10:00 Page 2
HEAP LEACH – SX/EW
taking apparent short-cuts; you will usually
live to regret it.” Taylor adds the following
advice:
n Adopt a phased approach, with increasing
levels of detail and increasingly large column
tests (e.g. bottle rolls>mini columns>short
columns>tall columns)
n Carry out parallel economic studies and risk
analyses covering all aspects of the project
n Tap water is usually ok for initial work, but
switch to site water as soon as possible.
Water composition can affect leaching and
plant materials (e.g. high chloride)
n Track quality of potential site water. Watch
out as the supply and/or quality can be
seasonable
n Test a range of crush sizes and select the
optimum as early as possible
n Always use realistic commercial leach
conditions for column tests, such as acid
level and irrigation rate
n Test alternative acid addition strategies early,
including strong acid cure. Be aware of the
difference between gross and net acid
consumption. The net figure takes account of
acid regenerated downstream if SX/EW is used
n Ambient temperature, pressure and even
humidity can affect leaching test work,
especially with sulphides. Therefore pay
and the proposed mine site. Sometimes it
may be necessary do test work in an
enclosure under controlled conditions or at
the proposed mine site
n Consider using controlled aeration for
sulphide leach column tests – it is
increasingly used in commercial operations
n If fines and/or clays are present, carry out
percolation tests before committing to
attention to any difference in ambient
column tests. You may need to adopt
conditions between the test work location
agglomeration with strong acid and/or
polymer, blending or
desliming. If
agglomeration is
adopted, stability of
agglomerates during
handling and
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leaching is an issue
to watch
n Build-up of impurities
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during leaching is not
easy to simulate. If
this is an issue, you
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may have to do
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supplementary work
or benchmark against
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similar operations.
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High impurity levels
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can cause viscosity
problems in SX
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during very cold
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weather
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n Final column tests
must be at the full
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projected lift height.
This can lead to long
test duration,
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especially for
sulphides. For
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example, a 6 m high
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secondary sulphide
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column test can take a year to complete.
Primary sulphide leaching can be even slower
n Final test work should be based on
composites representing the final mine plan
n The question of pilot scale tests is always a
thorny issue. It may be determined by
corporate policy or financial institution
requirements. In reality, a well-designed tall
column program with comprehensive
orebody coverage may provide more security
than larger scale pilot work, which is usually
limited to only a portion of the orebody
n If pilot scale tests are necessary, consider
large ‘box’ or large diameter pipe tests as an
alternative to test heaps
n Give early consideration to whether ROM
leaching is an option for part or all of the
orebody. This requires a specially designed
test program and obtaining suitable samples
can be a big challenge
n If ore sorting is included, all leach test work
must be carried out on upgraded material
which poses additional challenges to sample
procurement.
Taylor says to be conservative in scale-up:
n Must apply adequate safety factors to test
figures especially for copper recovery and
leach kinetics. Remember to allow for a
realistic ramp-up time which can be lengthy,
especially for sulphide ores
n The SX circuit has an overriding effect on the
leach curve, and must be taken into account.
Don’t be too optimistic when projecting the
copper level in the SX feed solution. Allow
for dilution with rain or snow and decreasing
ore grades when appropriate
n Include an allowance for ‘catch-up’ in the
SX/EW design, especially for the EW
rectiformer, which is the ultimate bottleneck.