XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2381
The minus 25 micron material was stored away from light
and under vacuum until required.
Zeta Potential Determinations
Zeta potential measurements were carried out using
Malvern Zetasizer Nano Z. Mineral samples (minus 25
micron) were dispersed in 10–4 mol/L NaCl background
electrolyte solution at 0.2% solids. Samples were sonicated
for 4 minutes prior to conditioning for 5 minutes at the
desired pH. Collector was then added and conditioned
for 2 minutes. The pH was adjusted with HCl and NaOH
solutions.
Potassium amyl xanthate (PAX) commercial grade
(90%) was prepared using ultrapure water (resistivity
greater than 18Mohm cm). All other reagents used for zeta
potential measurements were analytical grade and prepared
using ultrapure water.
The standard deviation for zeta potential measure-
ments was 1.4 mV, 1.3 mV and 2.4 mV for pH 4, 6 and 8
respectively.
Microflotation Test Work
A modified Partridge and Smith flotation column (Partridge
&Smith, 1971) was used for all microflotation test work.
The 110 mL borosilicate glass cell featured a magnetic stir-
rer at the bottom of the cell to maintain solids in suspen-
sion. Air was introduced through a glass frit at a rate of
25 mL/min for all tests.
Prior to flotation, a 1% mineral suspension was
conditioned in a beaker then transferred to the column.
Conditioning included an initial 4 minute sonication step
in an ultrasonic bath to ensure dispersion of solids. This
was followed by conditioning periods of 2 minutes for ini-
tial stabilisation, 2 minutes for collector (when added) and
2 minutes for frother. Froth products were continuously
removed over a period of 3 minutes and for an additional 5
minutes for selected tests. Concentrate and tailings samples
were filtered and dried in a desiccator. Each test was con-
ducted in duplicate with a maximum error of 3.5%.
The pH was allowed to vary naturally but was mea-
sured at approximately 6 for all microflotation tests. This is
consistent with pH values observed in Kalgoorlie flotation
operations.
Microflotation tests were conducted in ultrapure water.
Frother reagents used included methyl isobutyl carbinol
(MIBC, 99% purity) and polypropylene glycol frother
(Teric 407/Polyfroth H57). Flotation collectors included
potassium amyl xanthate (PAX, 90% commercial grade)
and kerosene (commercial grade). A 1% kerosene emulsion
was prepared using a blender at high speed for 30 seconds
immediately prior to conditioning. Reagents used for
microflotation were prepared using ultrapure water.
RESULTS
Zeta Potential of Hessite and Calaverite
Zeta potential studies were conducted to investigate the of
interaction of PAX with calaverite and hessite surfaces in
addition to the stability of the telluride particles in suspen-
sion. Figure 1 shows the resultant curves for hessite (a) and
calaverite (b). No previous data is available for silver and
gold telluride minerals however the values for hessite at pH
6 are similar when compared with data for platinum and
palladium tellurides (Shackleton et al., 2007). The values at
pH 8 are more negative for both hessite and calaverite when
compared with platinum and palladium tellurides however
this may be attributed to the buffering effect of synthetic
water for the platinum and palladium tellurides.
The observed zeta potential in Figure 1 is negative
across the measured range for both telluride minerals.
Aggregation of particles has been observed to occur at
–15 mV with maximum agglomeration occurring at 0 mv
(Farrokhpay et al., 2021 Salopek et al., 1992). The ten-
dency of both hessite and calaverite particles to agglomerate
during measurements at pH 4 was observed.
The implication of the results in Figure 1 is the poten-
tial for aggregation of fine particles to occur at pH 4, with
an increased likelihood with the addition of PAX. In con-
trast, observations at pH 8 indicate the greater likelihood
for no aggregation to occur with the solids remaining in
suspension. For calaverite at pH 8 (Figure 1b), the increased
stability with the addition of PAX may result in reduced
flotation recovery due to the low collision and attachment
with bubbles for fine particles (Farrokhpay et al., 2021).
The implication for microflotation at pH 6 is that hess-
ite is more likely to exhibit aggregation than calaverite. Zeta
potential results also indicate PAX addition may increase
the likelihood of aggregation, thereby increasing flotation
recovery.
Previous test work on tellurides has indicated that the
optimum range for flotation is pH 6 to 8 (Padmanaban &
Lawson, 1991 Yan &Hariyasa, 1997). Results in Figure 1
indicate further test work conducted at pH 4 with and
without collector should be investigated.
Microflotation
Natural Floatability of Hessite and Calaverite
A lower strength alcohol (MIBC) and a polypropylene
glycol (H57) were used as frothers for this stage of micro-
flotation test work. H57 is the frother previously used in
The minus 25 micron material was stored away from light
and under vacuum until required.
Zeta Potential Determinations
Zeta potential measurements were carried out using
Malvern Zetasizer Nano Z. Mineral samples (minus 25
micron) were dispersed in 10–4 mol/L NaCl background
electrolyte solution at 0.2% solids. Samples were sonicated
for 4 minutes prior to conditioning for 5 minutes at the
desired pH. Collector was then added and conditioned
for 2 minutes. The pH was adjusted with HCl and NaOH
solutions.
Potassium amyl xanthate (PAX) commercial grade
(90%) was prepared using ultrapure water (resistivity
greater than 18Mohm cm). All other reagents used for zeta
potential measurements were analytical grade and prepared
using ultrapure water.
The standard deviation for zeta potential measure-
ments was 1.4 mV, 1.3 mV and 2.4 mV for pH 4, 6 and 8
respectively.
Microflotation Test Work
A modified Partridge and Smith flotation column (Partridge
&Smith, 1971) was used for all microflotation test work.
The 110 mL borosilicate glass cell featured a magnetic stir-
rer at the bottom of the cell to maintain solids in suspen-
sion. Air was introduced through a glass frit at a rate of
25 mL/min for all tests.
Prior to flotation, a 1% mineral suspension was
conditioned in a beaker then transferred to the column.
Conditioning included an initial 4 minute sonication step
in an ultrasonic bath to ensure dispersion of solids. This
was followed by conditioning periods of 2 minutes for ini-
tial stabilisation, 2 minutes for collector (when added) and
2 minutes for frother. Froth products were continuously
removed over a period of 3 minutes and for an additional 5
minutes for selected tests. Concentrate and tailings samples
were filtered and dried in a desiccator. Each test was con-
ducted in duplicate with a maximum error of 3.5%.
The pH was allowed to vary naturally but was mea-
sured at approximately 6 for all microflotation tests. This is
consistent with pH values observed in Kalgoorlie flotation
operations.
Microflotation tests were conducted in ultrapure water.
Frother reagents used included methyl isobutyl carbinol
(MIBC, 99% purity) and polypropylene glycol frother
(Teric 407/Polyfroth H57). Flotation collectors included
potassium amyl xanthate (PAX, 90% commercial grade)
and kerosene (commercial grade). A 1% kerosene emulsion
was prepared using a blender at high speed for 30 seconds
immediately prior to conditioning. Reagents used for
microflotation were prepared using ultrapure water.
RESULTS
Zeta Potential of Hessite and Calaverite
Zeta potential studies were conducted to investigate the of
interaction of PAX with calaverite and hessite surfaces in
addition to the stability of the telluride particles in suspen-
sion. Figure 1 shows the resultant curves for hessite (a) and
calaverite (b). No previous data is available for silver and
gold telluride minerals however the values for hessite at pH
6 are similar when compared with data for platinum and
palladium tellurides (Shackleton et al., 2007). The values at
pH 8 are more negative for both hessite and calaverite when
compared with platinum and palladium tellurides however
this may be attributed to the buffering effect of synthetic
water for the platinum and palladium tellurides.
The observed zeta potential in Figure 1 is negative
across the measured range for both telluride minerals.
Aggregation of particles has been observed to occur at
–15 mV with maximum agglomeration occurring at 0 mv
(Farrokhpay et al., 2021 Salopek et al., 1992). The ten-
dency of both hessite and calaverite particles to agglomerate
during measurements at pH 4 was observed.
The implication of the results in Figure 1 is the poten-
tial for aggregation of fine particles to occur at pH 4, with
an increased likelihood with the addition of PAX. In con-
trast, observations at pH 8 indicate the greater likelihood
for no aggregation to occur with the solids remaining in
suspension. For calaverite at pH 8 (Figure 1b), the increased
stability with the addition of PAX may result in reduced
flotation recovery due to the low collision and attachment
with bubbles for fine particles (Farrokhpay et al., 2021).
The implication for microflotation at pH 6 is that hess-
ite is more likely to exhibit aggregation than calaverite. Zeta
potential results also indicate PAX addition may increase
the likelihood of aggregation, thereby increasing flotation
recovery.
Previous test work on tellurides has indicated that the
optimum range for flotation is pH 6 to 8 (Padmanaban &
Lawson, 1991 Yan &Hariyasa, 1997). Results in Figure 1
indicate further test work conducted at pH 4 with and
without collector should be investigated.
Microflotation
Natural Floatability of Hessite and Calaverite
A lower strength alcohol (MIBC) and a polypropylene
glycol (H57) were used as frothers for this stage of micro-
flotation test work. H57 is the frother previously used in