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porphyry copper ores to evaluate the potential benefits a
more electrochemically inert grinding media can provide in
the laboratory as well as the plant.
EXPERIMENTAL
Laboratory Test Methodology
The MagoMill ® was developed11 to allow the researcher
to generate a product in the laboratory that has nominally
the same physical properties (particle size distribution) and
pulp chemical properties (Eh, pH, dissolved oxygen, oxy-
gen demand and EDTA extractable iron) as an equivalent
sample taken from the plant. This is achieved by grinding
an appropriate sample to achieve the particle size distribu-
tion of the flotation feed, and manipulating the pulp chem-
istry, by purging the system with gas (Figure 1), so that it
matches the grinding mill discharge.
The experimental strategy adopted to achieve the
desired outcomes is completed in three phases:
Phase 1—Plant data collection: The collection of
plant data is vital to the success of the test program,
as this data forms the basis of the calibration process
by defining the target parameters. This initial step
involves:
The completion of a pulp chemical and EDTA sur-
vey of the grinding and adjoining flotation circuit
Determination of the oxygen demand at strategic
points within the circuit and
The collection of a bulk sample of the grinding cir-
cuit feed (ore and process water) for further testing.
Phase 2—MagoMill ® calibration: The data col-
lected in Phase 1 essentially describes the circuit
under consideration and provides targets for the
MagoMill ® calibration. The calibration process uses
the same grinding media as the operating plant (the
standard condition). The objective of the calibra-
tion process is to produce a laboratory mill discharge
which has the same particle size distribution as the
conditioned flotation feed, and the pulp chemis-
try of the plant grinding mill discharge. To achieve
this match involves careful manipulation of the dis-
solved oxygen, Eh and grinding time, such that all
the measured parameters line up when grinding the
bulk sample collected during the metallurgical sur-
vey. This task is not trivial. Once the MagoMill ® is
calibrated, oxygen demand and flotation tests are
completed on the ground ore.
Phase 3—Media testing: With the MagoMill ® cali-
brated, alternative grinding media are substituted
into the mill for testing. The procedure determined
for the standard condition is then applied while
grinding the bulk sample employing the alternative
grinding media. In this way, it is possible to measure
changes in pulp chemistry and flotation response.
The changes observed are attributed to the variations
in grinding media composition, as the only inten-
tional parameter being changed in the test is the
grinding media.
If used correctly, this strategy will provide an excellent
screening procedure that will yield valuable information
about the “best” grinding media for the operation. This
should focus subsequent pilot plant and plant trials on only
the most promising of grinding media for that application.
Figure 1. Schematic representation of the MagoMill®
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