652 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
during the scoping studies for two major composites are
shown in Tables 1 and 2, respectively.
Table 2 shows that the site water resulted in a lower
copper and gold recoveries, which was attributed to a pH
buffering effect leading to very high lime consumption
while depressing pyrite to target a high pH of 11–12 in
the copper cleaner circuit. Also, due to high lime addition,
gypsum precipitation was observed resulting in poor flota-
tion selectivity.
An intensive optimization study was carried out using
different reagent schemes to improve flotation performance
using site water. Of all the schemes tested, an addition of 20
g/t of NaCN in the cleaner circuit improved the flotation
results but still could not replicate the results of tap water.
The cyanide scheme was selected as the best scheme for
carrying out further locked cycle testing on various miner-
alogy composites representing major lithology and altera-
tions. Most of these composites performed well except for
the samples representing Sericite-Clay-Chlorite (SCC) that
showed poor copper recovery of 75%. The proportion of
SCC in the deposit was initially considered low (less than
10%) but this increased to greater than 40% with the re-
categorisation of the ore deposit during the pre-feasibility
study. This meant that the overall life-of-mine metal recov-
ery was significantly lower with the conventional copper
flotation process using site water, resulting in unfavorable
economics and a major setback for the project.
The FLOT-ART Process development steps
Extensive R&D work included detailed mineralogy, water
chemistry evaluation, surface analysis and testing of various
reagent schemes to obtain a deeper understanding of the
challenges with the conventional lime process. The main
conclusions from this optimization work were as follows:
• Addition of lime is detrimental to flotation due to
precipitation of gypsum with site-water
• A low pH chemistry was superior to all other pyrite
depressant reagent schemes tested including cyanide
• Flotation performance improved significantly with
aeration after regrind
• A new reagent scheme was developed that resulted
in significantly better recovery and concentrate grade
with no need for lime and cyanide.
The process also involved a specialized aeration process
after regrinding of rougher concentrates along with recy-
cled cleaner circuit streams for a certain duration without
the need for any pH adjustment. The fundamental reason
for including the aeration step is to improve the kinetics of
copper minerals and not oxidation of pyrite as commonly
believed. The aeration step also provides the optimum elec-
tro-chemical potential (Eh) and slurry chemistry to make
it possible for the low alkaline scheme to depress pyrite
without the need for any lime addition. This combination
of aeration without any addition of lime is a novel way of
separating copper minerals from pyrite at natural pH when
site water poses flotation chemistry problems.
This low alkaline pH flotation process was rigorously
evaluated on various ore types in bench scale test work
using open cleaner and locked cycle tests during the pre-
feasibility study. Table 3 compares the results of the high
lime and low alkaline schemes for three different ore types
that were metallurgically complex. As shown in the table,
the low alkaline scheme gave significantly better flotation
performance than the conventional high lime scheme.
Tables 4 and 5 compare the locked cycle test results
using the conventional lime and the low alkaline processes,
respectively, for 16 different variability samples represent-
ing all major ore types. This was part of a major initiative
Table 1. Head assays for the composites tested using conventional flotation process
Samples
Cu,
%total
Cu,
acid soluble g/t
Au,
g/t
Mo,
g/t
S,
%total
S,
%sulphide
Comp 1 0.58 179 0.61 72 4.3 2.0
Comp 2 0.52 128 0.68 28 3.5 1.6
Table 2. Locked cycle test results using site water and tap water for the composite samples
Concentrate
Mass pull,
%
Final
Concentrate,
Cu %
Recovery %
Cu
Final
Concentrate
Au, g/t
Recovery %
Au
Comp 1 Tap water 2.0 29.4 94.4 13.2 88.5
Comp 1 Site water 1.9 28.4 92.5 12.2 80.5
Comp 2 Tap water 1.7 29.5 94.5 17.3 82.9
Comp 2 Site water 1.7 29.5 90.4 17.4 77.2
during the scoping studies for two major composites are
shown in Tables 1 and 2, respectively.
Table 2 shows that the site water resulted in a lower
copper and gold recoveries, which was attributed to a pH
buffering effect leading to very high lime consumption
while depressing pyrite to target a high pH of 11–12 in
the copper cleaner circuit. Also, due to high lime addition,
gypsum precipitation was observed resulting in poor flota-
tion selectivity.
An intensive optimization study was carried out using
different reagent schemes to improve flotation performance
using site water. Of all the schemes tested, an addition of 20
g/t of NaCN in the cleaner circuit improved the flotation
results but still could not replicate the results of tap water.
The cyanide scheme was selected as the best scheme for
carrying out further locked cycle testing on various miner-
alogy composites representing major lithology and altera-
tions. Most of these composites performed well except for
the samples representing Sericite-Clay-Chlorite (SCC) that
showed poor copper recovery of 75%. The proportion of
SCC in the deposit was initially considered low (less than
10%) but this increased to greater than 40% with the re-
categorisation of the ore deposit during the pre-feasibility
study. This meant that the overall life-of-mine metal recov-
ery was significantly lower with the conventional copper
flotation process using site water, resulting in unfavorable
economics and a major setback for the project.
The FLOT-ART Process development steps
Extensive R&D work included detailed mineralogy, water
chemistry evaluation, surface analysis and testing of various
reagent schemes to obtain a deeper understanding of the
challenges with the conventional lime process. The main
conclusions from this optimization work were as follows:
• Addition of lime is detrimental to flotation due to
precipitation of gypsum with site-water
• A low pH chemistry was superior to all other pyrite
depressant reagent schemes tested including cyanide
• Flotation performance improved significantly with
aeration after regrind
• A new reagent scheme was developed that resulted
in significantly better recovery and concentrate grade
with no need for lime and cyanide.
The process also involved a specialized aeration process
after regrinding of rougher concentrates along with recy-
cled cleaner circuit streams for a certain duration without
the need for any pH adjustment. The fundamental reason
for including the aeration step is to improve the kinetics of
copper minerals and not oxidation of pyrite as commonly
believed. The aeration step also provides the optimum elec-
tro-chemical potential (Eh) and slurry chemistry to make
it possible for the low alkaline scheme to depress pyrite
without the need for any lime addition. This combination
of aeration without any addition of lime is a novel way of
separating copper minerals from pyrite at natural pH when
site water poses flotation chemistry problems.
This low alkaline pH flotation process was rigorously
evaluated on various ore types in bench scale test work
using open cleaner and locked cycle tests during the pre-
feasibility study. Table 3 compares the results of the high
lime and low alkaline schemes for three different ore types
that were metallurgically complex. As shown in the table,
the low alkaline scheme gave significantly better flotation
performance than the conventional high lime scheme.
Tables 4 and 5 compare the locked cycle test results
using the conventional lime and the low alkaline processes,
respectively, for 16 different variability samples represent-
ing all major ore types. This was part of a major initiative
Table 1. Head assays for the composites tested using conventional flotation process
Samples
Cu,
%total
Cu,
acid soluble g/t
Au,
g/t
Mo,
g/t
S,
%total
S,
%sulphide
Comp 1 0.58 179 0.61 72 4.3 2.0
Comp 2 0.52 128 0.68 28 3.5 1.6
Table 2. Locked cycle test results using site water and tap water for the composite samples
Concentrate
Mass pull,
%
Final
Concentrate,
Cu %
Recovery %
Cu
Final
Concentrate
Au, g/t
Recovery %
Au
Comp 1 Tap water 2.0 29.4 94.4 13.2 88.5
Comp 1 Site water 1.9 28.4 92.5 12.2 80.5
Comp 2 Tap water 1.7 29.5 94.5 17.3 82.9
Comp 2 Site water 1.7 29.5 90.4 17.4 77.2