5
grade the copper recovery increased by 3.4±1.3 percent,
with greater than 99 percent confidence for Duromax ®U.
Associated with this improvement in copper recovery was
an increase in molybdenum recovery of at least 2.3 per-
cent. Further tests were completed at natural pH (7.7),
which indicated that the high chrome alloy at the lower
pH outperformed forged steel at the elevated pH yielding
improved copper recovery. This result adds credence to the
Red Chris example above whereby lime consumption was
able to be reduced. Reducing the pH significantly increased
molybdenum recoveries (greater than 10 percent) by lower-
ing the calcium concentration in the pulp, as calcium ions
inhibit molybdenite flotation.
Based on the work completed on copper-gold porphyry
deposits where the laboratory result could be discounted by
around 50 percent, it is suggested that the copper recovery
for the Chilean ore could improve by about 1.7 percent if
a plant trial using high chrome grinding media was con-
ducted. The benefits with regard to molybdenum recovery
are not known, however if a lower pH regime was adopted
it is expected that molybdenum recoveries of a similar mag-
nitude to those predicted for copper would be achieved.
A North American Porphyry Copper
This copper-molybdenum porphyry deposit has an aver-
age head grade of 0.25 percent copper (as chalcopyrite and
minor bornite) and 100 g/t of molybdenum. The ore con-
tains nominally 0.2 percent pyrite.
Laboratory test work was completed using the
MagoMill ® and again showed very little difference in the Eh
or dissolved oxygen concentration between for the forged
steel and the high chrome alloys tested. A possible reason
for this was the elevated pH (11.2) employed at this site.
However, it was observed that shifting from forged steel to
high chrome did result in a significant reduction in the oxy-
gen demand (from 1.1 min–1 to 0.7 min–1), and a marked
decrease in the EDTA extractable iron (from 0.85 percent
to 0.49 percent), suggesting that media corrosion was
inhibited when using a more electrochemically inert grind-
ing media. These changes in the pulp chemistry indicated
that a shift from forged steel to Duromax ®T improvement
in the copper grade/recovery curve (Figure 3), with the
copper and molybdenum recoveries improving by 2.1 and
5.1 percent, respectively.
Again, assuming that around half the copper recovery
benefit observed in the laboratory would be realised in the
plant it is expected that utilising high chrome grinding
media in the plant would improve the copper recovery by
at least 1 percent. The molybdenum recovery benefits are
more speculative, but given that it is likely less lime would
be required to achieve the same pH (as per the Red Chris
example) it is highly likely that there would be molybde-
num recovery benefits.
Figure 2. Copper grade/recovery curves for copper rougher flotation tests completed on a
Chilean copper-molybdenum porphyry ore
grade the copper recovery increased by 3.4±1.3 percent,
with greater than 99 percent confidence for Duromax ®U.
Associated with this improvement in copper recovery was
an increase in molybdenum recovery of at least 2.3 per-
cent. Further tests were completed at natural pH (7.7),
which indicated that the high chrome alloy at the lower
pH outperformed forged steel at the elevated pH yielding
improved copper recovery. This result adds credence to the
Red Chris example above whereby lime consumption was
able to be reduced. Reducing the pH significantly increased
molybdenum recoveries (greater than 10 percent) by lower-
ing the calcium concentration in the pulp, as calcium ions
inhibit molybdenite flotation.
Based on the work completed on copper-gold porphyry
deposits where the laboratory result could be discounted by
around 50 percent, it is suggested that the copper recovery
for the Chilean ore could improve by about 1.7 percent if
a plant trial using high chrome grinding media was con-
ducted. The benefits with regard to molybdenum recovery
are not known, however if a lower pH regime was adopted
it is expected that molybdenum recoveries of a similar mag-
nitude to those predicted for copper would be achieved.
A North American Porphyry Copper
This copper-molybdenum porphyry deposit has an aver-
age head grade of 0.25 percent copper (as chalcopyrite and
minor bornite) and 100 g/t of molybdenum. The ore con-
tains nominally 0.2 percent pyrite.
Laboratory test work was completed using the
MagoMill ® and again showed very little difference in the Eh
or dissolved oxygen concentration between for the forged
steel and the high chrome alloys tested. A possible reason
for this was the elevated pH (11.2) employed at this site.
However, it was observed that shifting from forged steel to
high chrome did result in a significant reduction in the oxy-
gen demand (from 1.1 min–1 to 0.7 min–1), and a marked
decrease in the EDTA extractable iron (from 0.85 percent
to 0.49 percent), suggesting that media corrosion was
inhibited when using a more electrochemically inert grind-
ing media. These changes in the pulp chemistry indicated
that a shift from forged steel to Duromax ®T improvement
in the copper grade/recovery curve (Figure 3), with the
copper and molybdenum recoveries improving by 2.1 and
5.1 percent, respectively.
Again, assuming that around half the copper recovery
benefit observed in the laboratory would be realised in the
plant it is expected that utilising high chrome grinding
media in the plant would improve the copper recovery by
at least 1 percent. The molybdenum recovery benefits are
more speculative, but given that it is likely less lime would
be required to achieve the same pH (as per the Red Chris
example) it is highly likely that there would be molybde-
num recovery benefits.
Figure 2. Copper grade/recovery curves for copper rougher flotation tests completed on a
Chilean copper-molybdenum porphyry ore