654 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
The low alkaline flotation process has now been vali-
dated for several ore types. The key feature of this process is
that the depression of pyrite in cleaner flotation is possible
at a natural pH of the ore without the need for conventional
pyrite depressants such as cyanide and high lime addition.
This process was effective even for complex copper, copper-
gold and copper-gold-silver ores with a high iron to copper
ratios. Importantly, the process also works well when poor
quality water, such as brackish or high salinity water, is used
in the flotation process. In poor-quality water, the conven-
tional high lime scheme is not effective in depressing pyrite
as obtaining a high slurry pH of 10 to 11 is difficult due to
pH buffering effects.
Commercial Applications of the Low Alkaline Process
(now FLOT-ART)
The low alkaline process has been commercially used suc-
cessfully by a mining company in Chile with raw seawa-
ter since 2012. This company encountered difficulties in
upgrading the copper concentrate in the cleaner circuit
when seawater was used with a conventional lime-based
process. With the low alkaline, however, no such detrimen-
tal effect was observed even at natural pH in the cleaner
circuit. In addition, higher recoveries of molybdenum were
observed using this process.
This process is also commercially used in a major cop-
per-gold operation based in Saudi Arabia. The motivation
for using the low-alkaline process here was to replace cya-
nide and lime in depressing pyrite. The use of cyanide was
a significant risk for the project due to permitting issues.
Since the only water available for the operation was munici-
pal sewage water, which meant that the use of lime would
quickly result in scaling issues because of the requirement
for recycling the concentrate and tailing thickener overflow
water. This would also be problematic, especially in the
concentrate and tailings filtration areas requiring washing
with weak acid instead of just water. Also obtaining large
steady volumes of limestone was seen as a risk in the coun-
try where this operation is located.
Table 5. Locked cycle test results for the 16 different variability samples using the low alkaline scheme
Comp No Lith -Alt
%of Ore
Deposit
Head
Cu %
Concentrate
Cu %
Mass Pull
%
Recovery,
Cu %
1 PFB1 -POT 5.0 0.60 33.7 1.66 93.6
2 PFB1 -MIX 2.0 0.44 33.6 1.20 92.1
3 PFB2 -POT 5.0 0.63 36.6 1.66 92.2
4 PFB2 -MIX 3.0 0.51 34.4 1.38 93.3
5 VIN -POT 3.0 0.70 34.0 1.98 93.8
6 VIN -MIX 4.0 0.44 34.7 1.09 91.3
7 VIN -SCC 6.0 0.41 29.0 1.32 92.6
8 VFL -POT 5.0 0.75 37.6 1.09 87.6
9 VFL -MIX 7.0 0.60 37.4 1.49 91.0
10 VFL -SCC 9.0 0.57 33.3 1.65 90.4
11 PFB1 -SCC 4.0 0.60 34.7 1.58 91.7
12 PFB1 -SCC 11.0 0.48 33.2 1.44 92.4
13 PFB2 -SCC 5.0 0.56 24.8 2.11 90.6
14 VIN – MIX 2 1.0 0.60 33.7 1.78 93.5
15 VIN –SCC 2 8.0 0.51 32.0 1.43 90.3
16 VFL – MIX 2 4.0 0.53 36.8 1.30 90.1
Weighted average 100.0 0.55 33.6 1.50 91.4
Table 6. Flotation results of the low alkaline and conventional high lime schemes using site and seawater
Water Type
Conventional high lime scheme Low alkaline scheme
Concentrate
Cu%
Recovery%
Cu
Recovery%
Au
Concentrate
Cu%
Recovery%
Cu
Recovery%
Au
Site water (locked cycle) 27.6 79.5 62.0 31.2 87.3 62.0
Sea water (locked cycle) poor flotation 30.2 86.6 58.7
The low alkaline flotation process has now been vali-
dated for several ore types. The key feature of this process is
that the depression of pyrite in cleaner flotation is possible
at a natural pH of the ore without the need for conventional
pyrite depressants such as cyanide and high lime addition.
This process was effective even for complex copper, copper-
gold and copper-gold-silver ores with a high iron to copper
ratios. Importantly, the process also works well when poor
quality water, such as brackish or high salinity water, is used
in the flotation process. In poor-quality water, the conven-
tional high lime scheme is not effective in depressing pyrite
as obtaining a high slurry pH of 10 to 11 is difficult due to
pH buffering effects.
Commercial Applications of the Low Alkaline Process
(now FLOT-ART)
The low alkaline process has been commercially used suc-
cessfully by a mining company in Chile with raw seawa-
ter since 2012. This company encountered difficulties in
upgrading the copper concentrate in the cleaner circuit
when seawater was used with a conventional lime-based
process. With the low alkaline, however, no such detrimen-
tal effect was observed even at natural pH in the cleaner
circuit. In addition, higher recoveries of molybdenum were
observed using this process.
This process is also commercially used in a major cop-
per-gold operation based in Saudi Arabia. The motivation
for using the low-alkaline process here was to replace cya-
nide and lime in depressing pyrite. The use of cyanide was
a significant risk for the project due to permitting issues.
Since the only water available for the operation was munici-
pal sewage water, which meant that the use of lime would
quickly result in scaling issues because of the requirement
for recycling the concentrate and tailing thickener overflow
water. This would also be problematic, especially in the
concentrate and tailings filtration areas requiring washing
with weak acid instead of just water. Also obtaining large
steady volumes of limestone was seen as a risk in the coun-
try where this operation is located.
Table 5. Locked cycle test results for the 16 different variability samples using the low alkaline scheme
Comp No Lith -Alt
%of Ore
Deposit
Head
Cu %
Concentrate
Cu %
Mass Pull
%
Recovery,
Cu %
1 PFB1 -POT 5.0 0.60 33.7 1.66 93.6
2 PFB1 -MIX 2.0 0.44 33.6 1.20 92.1
3 PFB2 -POT 5.0 0.63 36.6 1.66 92.2
4 PFB2 -MIX 3.0 0.51 34.4 1.38 93.3
5 VIN -POT 3.0 0.70 34.0 1.98 93.8
6 VIN -MIX 4.0 0.44 34.7 1.09 91.3
7 VIN -SCC 6.0 0.41 29.0 1.32 92.6
8 VFL -POT 5.0 0.75 37.6 1.09 87.6
9 VFL -MIX 7.0 0.60 37.4 1.49 91.0
10 VFL -SCC 9.0 0.57 33.3 1.65 90.4
11 PFB1 -SCC 4.0 0.60 34.7 1.58 91.7
12 PFB1 -SCC 11.0 0.48 33.2 1.44 92.4
13 PFB2 -SCC 5.0 0.56 24.8 2.11 90.6
14 VIN – MIX 2 1.0 0.60 33.7 1.78 93.5
15 VIN –SCC 2 8.0 0.51 32.0 1.43 90.3
16 VFL – MIX 2 4.0 0.53 36.8 1.30 90.1
Weighted average 100.0 0.55 33.6 1.50 91.4
Table 6. Flotation results of the low alkaline and conventional high lime schemes using site and seawater
Water Type
Conventional high lime scheme Low alkaline scheme
Concentrate
Cu%
Recovery%
Cu
Recovery%
Au
Concentrate
Cu%
Recovery%
Cu
Recovery%
Au
Site water (locked cycle) 27.6 79.5 62.0 31.2 87.3 62.0
Sea water (locked cycle) poor flotation 30.2 86.6 58.7