2456 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
In the single mineral tests millerite had floated at
potentials above the air-set potential up to +400 mV while
the flotability of pentlandite at these high potentials was
unknown. Two tests were therefore completed at pH 9 and
very high potentials, +650 mV and +750 mV vs SHE, to
determine if a separation could be made. In both tests, the
recovery of millerite was significantly higher than that of
pentlandite and millerite remained readily flotable at such
high potentials whilst pentlandite flotation appeared to be
depressed at +650 and +750 mV vs SHE. The recovery-
time data for the test at +650 mV is shown in Figure 4.
At the high potential, almost 97% of the millerite was
recovered with a concomitant recovery of 24% for pent-
landite. SEM mapping of the combined millerite concen-
trate produced from this test is shown in Figure 5 where
the majority of pentlandite in the concentrate was present
as liberated grains and very little was present as locked par-
ticles with millerite. At the end of the test, the pulp poten-
tial was allowed to return to the air-set potential and an
extra collector addition was made. After 4 minutes of flota-
tion, 50% of the pentlandite was recovered along with the
remainder of the millerite. This demonstrated that the addi-
tion of oxidant did not permanently change the surface of
the pentlandite and that two concentrates, one containing
most of the millerite and the other containing mainly pent-
landite, could be made using pulp potential control.
One further test was done to demonstrate that pulp
potential could be used to separate millerite and pentlandite
in the neat nickel sulfide sample—the results are presented
in Table 3. Fifty grams of the nickel sulphide sample alone
(no quartz) was ground in a small stainless steel rod mill
and floated in a 1 dm3 cell. The pulp potential at pH 9 was
adjusted to +650 mV vs SHE, KeX added, and an 8-min-
ute concentrate taken. The concentrate recovered 82% of
the millerite with a concomitant pentlandite recovery of
9% whilst the tailings contained 91.3% of the pentland-
ite. No effort was taken to match the feed distribution of
the previous tests with quartz or to optimise reagent addi-
tions and pulp densities, but the results demonstrate that
pulp potential in the presence of a xanthate collector could
be used to separate millerite from pentlandite. Separation
of millerite from pentlandite may be advantageous in that
separate high- and low-Ni concentrates may be produced
which may be processed by different means and Grguric et
al. (2006) have suggested that millerite enriched concen-
trates, owing to their high Ni content, could be directly
refined without the need for smelting.
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12
Flotation Time (min)
Millerite
Pentlandite
Air-set potential, extra collector
Figure 4. Recovery-time data for test at +650 mV vs SHE at pH 9. After 7 min, the potential was allowed
to fall back to the air-set potential and an extra 100 g/t KeX added
Mineral
Recovery
(%)
In the single mineral tests millerite had floated at
potentials above the air-set potential up to +400 mV while
the flotability of pentlandite at these high potentials was
unknown. Two tests were therefore completed at pH 9 and
very high potentials, +650 mV and +750 mV vs SHE, to
determine if a separation could be made. In both tests, the
recovery of millerite was significantly higher than that of
pentlandite and millerite remained readily flotable at such
high potentials whilst pentlandite flotation appeared to be
depressed at +650 and +750 mV vs SHE. The recovery-
time data for the test at +650 mV is shown in Figure 4.
At the high potential, almost 97% of the millerite was
recovered with a concomitant recovery of 24% for pent-
landite. SEM mapping of the combined millerite concen-
trate produced from this test is shown in Figure 5 where
the majority of pentlandite in the concentrate was present
as liberated grains and very little was present as locked par-
ticles with millerite. At the end of the test, the pulp poten-
tial was allowed to return to the air-set potential and an
extra collector addition was made. After 4 minutes of flota-
tion, 50% of the pentlandite was recovered along with the
remainder of the millerite. This demonstrated that the addi-
tion of oxidant did not permanently change the surface of
the pentlandite and that two concentrates, one containing
most of the millerite and the other containing mainly pent-
landite, could be made using pulp potential control.
One further test was done to demonstrate that pulp
potential could be used to separate millerite and pentlandite
in the neat nickel sulfide sample—the results are presented
in Table 3. Fifty grams of the nickel sulphide sample alone
(no quartz) was ground in a small stainless steel rod mill
and floated in a 1 dm3 cell. The pulp potential at pH 9 was
adjusted to +650 mV vs SHE, KeX added, and an 8-min-
ute concentrate taken. The concentrate recovered 82% of
the millerite with a concomitant pentlandite recovery of
9% whilst the tailings contained 91.3% of the pentland-
ite. No effort was taken to match the feed distribution of
the previous tests with quartz or to optimise reagent addi-
tions and pulp densities, but the results demonstrate that
pulp potential in the presence of a xanthate collector could
be used to separate millerite from pentlandite. Separation
of millerite from pentlandite may be advantageous in that
separate high- and low-Ni concentrates may be produced
which may be processed by different means and Grguric et
al. (2006) have suggested that millerite enriched concen-
trates, owing to their high Ni content, could be directly
refined without the need for smelting.
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12
Flotation Time (min)
Millerite
Pentlandite
Air-set potential, extra collector
Figure 4. Recovery-time data for test at +650 mV vs SHE at pH 9. After 7 min, the potential was allowed
to fall back to the air-set potential and an extra 100 g/t KeX added
Mineral
Recovery
(%)