3108 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
the order as follows: IBACTC IBECTC IBALTC
IBETC IPETC. These observations were based on ab ini-
tio calculations, and no attempt was made to validate any
of these in ore flotation systems, as happens with most such
studies.
The present study attempts to understand the details
of the Lewis acid-based interactions of AIBTC (N-allyl
O-isobutyl thionocarbamate) with copper and copper min-
erals. Its alkyl analog IPETC (N-ethyl O-isopropyl thiono-
carbamate), without the double bond, was also studied for
comparison and to understand the role of the allylic double
bond. This preliminary investigation encompasses real ore
flotation tests, solubility and surface tension measurements,
and voltammetry. Using copper as a model system, the
electrochemical assessment involved open circuit poten-
tial measurements, linear sweep voltammetry, and cyclic
voltammetry.
MATERIALS AND METHODS
The ligands and other flotation reagents used in this study
were AIBTC (87% purity, most impurity is isobutanol) and
IPETC (95% purity), obtained from SYENSQO. Milli-Q
water with a resistivity of 18.2 mΩ∙cm at 25°C was used
throughout the work, except for real ore flotation experi-
ments, where tap water was used. Sodium borate and lime
of analytical grade from Sigma-Aldrich were used as the pH
buffer and regulator. Low-grade copper ore for flotation
tests originated from stockpiles in South Africa, with the
main value minerals being chalcopyrite (~0.5% Cu) and
molybdenite (~300 g/t Mo). 10-minute bench-scale flota-
tion tests were carried out using 0.5 kg charges of ore sam-
ples of P80 =212 μm at 60 wt.% solids. pH was adjusted to
10.5 by adding lime to the mill, after which 5 g/t of mixed
frother (MIBC +DowFroth 250A ratio of 1:1) was added
during the conditioning, followed by test-specific collec-
tors. Six concentrates were collected at a cumulative flota-
tion time of 30th sec, 1st, 2nd, 4th, 7th, and 10th min. All
concentrates and tailings were assayed for elemental con-
tent (Cu and Mo) by Base Metallurgical Labs at Kamloops,
BC, Canada. Lambda 25 UV/Vis spectrometer from
PerkinElmer was used for solubility measurements. The
calibration curves were generated for AIBTC and IPETC in
sodium borate buffer solutions. The characteristic peaks for
AIBTC-borate, AIBTC-water, IPETC-borate, and IPETC-
water were decided at 241.7, 241.7, 241.4, and 241.4 nm,
respectively.
For solubility tests, an excessive amount of AIBTC or
IPETC (about 1.8 g) sample was added to 100 mL borate
buffer or Milli-Q water (equivalent to over 0.1 M ligand),
and the suspensions were rigorously stirred over 40 hours.
Then, the suspensions were centrifuged for 4 hours. A clear
solution was collected using a syringe with a needle from the
bottom and diluted to achieve a concentration range suit-
able for UV/Vis measurements. The absorbance of diluted
saturated solutions was measured at least five times with
a standard deviation of less than 0.08%, and the average
was used to calculate the concentration. The absorbances
of AIBTC were determined at a wavelength of 241.7 nm
for both borate and water solutions, nearly the same as the
absorption peaks for IPETC in borate and water solutions,
which were 241.4 and 241.1 nm. Equilibrium aqueous-air
surface tension of AIBTC and IPETC in Milli-Q water (pH
5.6) at 23°C was measured as a function of concentration
using a bubble pressure tensiometer (KRUSS BPT mobile).
The maximal measured concentrations of the ligands were
at their solubility limits in water. The tensiometer was cali-
brated with Milli-Q water, assuming its surface tension to
be 72.3 mN/m.
Electrochemical studies, including open circuit poten-
tial (OCP) measurements, Linear sweep voltammetry
(LSV), and cyclic voltammetry (CV), were conducted at
pH 9.2 (0.1 M sodium borate buffer solution) and open
atmosphere, using AUT 58430 potentiostat from Metrohm
America. The electrochemical cell employed in this study
comprised three electrodes and incorporated a Luggin
capillary. Specifically, the working electrode was a copper
disk, the reference electrode was a platinum plate, and the
reference electrode was Ag/AgCl (with 3 M NaCl filling
solution). The working copper electrode was polished with
alumina powder on a polishing cloth before each trial for
2 minutes, ultrasonicated for two minutes, and promptly
transferred to the electrochemical cell. OCP measurements,
LSV, and CV were measured at various concentrations,
including 0, 10–6, 10–5, 10–4, and 10–3 M of AIBTC or
IPETC. The potential values in this study were referenced
and reported versus an Ag/AgCl electrode (+0.209 V vs.
the normal hydrogen electrode) unless stated otherwise.
During measurements, solutions were moderately stirred.
RESULTS AND DISCUSSION
Real Ore, Bench-Scale Flotation
Cumulative Cu and Mo recovery versus cumulative flota-
tion time was plotted in Figure 2. First, the conditions where
AIBTC and IPETC were introduced as neat products were
compared. In the first 30 seconds of flotation, IPETC direct
addition achieved greater Cu and Mo recovery of about
42% and 11%, respectively, compared to AIBTC, which
resulted in a Cu recovery of 35% and Mo recovery of 9%.
This is believed to be due to the higher solubility of IPETC,
measured and reported in the next section, and, therefore,
the order as follows: IBACTC IBECTC IBALTC
IBETC IPETC. These observations were based on ab ini-
tio calculations, and no attempt was made to validate any
of these in ore flotation systems, as happens with most such
studies.
The present study attempts to understand the details
of the Lewis acid-based interactions of AIBTC (N-allyl
O-isobutyl thionocarbamate) with copper and copper min-
erals. Its alkyl analog IPETC (N-ethyl O-isopropyl thiono-
carbamate), without the double bond, was also studied for
comparison and to understand the role of the allylic double
bond. This preliminary investigation encompasses real ore
flotation tests, solubility and surface tension measurements,
and voltammetry. Using copper as a model system, the
electrochemical assessment involved open circuit poten-
tial measurements, linear sweep voltammetry, and cyclic
voltammetry.
MATERIALS AND METHODS
The ligands and other flotation reagents used in this study
were AIBTC (87% purity, most impurity is isobutanol) and
IPETC (95% purity), obtained from SYENSQO. Milli-Q
water with a resistivity of 18.2 mΩ∙cm at 25°C was used
throughout the work, except for real ore flotation experi-
ments, where tap water was used. Sodium borate and lime
of analytical grade from Sigma-Aldrich were used as the pH
buffer and regulator. Low-grade copper ore for flotation
tests originated from stockpiles in South Africa, with the
main value minerals being chalcopyrite (~0.5% Cu) and
molybdenite (~300 g/t Mo). 10-minute bench-scale flota-
tion tests were carried out using 0.5 kg charges of ore sam-
ples of P80 =212 μm at 60 wt.% solids. pH was adjusted to
10.5 by adding lime to the mill, after which 5 g/t of mixed
frother (MIBC +DowFroth 250A ratio of 1:1) was added
during the conditioning, followed by test-specific collec-
tors. Six concentrates were collected at a cumulative flota-
tion time of 30th sec, 1st, 2nd, 4th, 7th, and 10th min. All
concentrates and tailings were assayed for elemental con-
tent (Cu and Mo) by Base Metallurgical Labs at Kamloops,
BC, Canada. Lambda 25 UV/Vis spectrometer from
PerkinElmer was used for solubility measurements. The
calibration curves were generated for AIBTC and IPETC in
sodium borate buffer solutions. The characteristic peaks for
AIBTC-borate, AIBTC-water, IPETC-borate, and IPETC-
water were decided at 241.7, 241.7, 241.4, and 241.4 nm,
respectively.
For solubility tests, an excessive amount of AIBTC or
IPETC (about 1.8 g) sample was added to 100 mL borate
buffer or Milli-Q water (equivalent to over 0.1 M ligand),
and the suspensions were rigorously stirred over 40 hours.
Then, the suspensions were centrifuged for 4 hours. A clear
solution was collected using a syringe with a needle from the
bottom and diluted to achieve a concentration range suit-
able for UV/Vis measurements. The absorbance of diluted
saturated solutions was measured at least five times with
a standard deviation of less than 0.08%, and the average
was used to calculate the concentration. The absorbances
of AIBTC were determined at a wavelength of 241.7 nm
for both borate and water solutions, nearly the same as the
absorption peaks for IPETC in borate and water solutions,
which were 241.4 and 241.1 nm. Equilibrium aqueous-air
surface tension of AIBTC and IPETC in Milli-Q water (pH
5.6) at 23°C was measured as a function of concentration
using a bubble pressure tensiometer (KRUSS BPT mobile).
The maximal measured concentrations of the ligands were
at their solubility limits in water. The tensiometer was cali-
brated with Milli-Q water, assuming its surface tension to
be 72.3 mN/m.
Electrochemical studies, including open circuit poten-
tial (OCP) measurements, Linear sweep voltammetry
(LSV), and cyclic voltammetry (CV), were conducted at
pH 9.2 (0.1 M sodium borate buffer solution) and open
atmosphere, using AUT 58430 potentiostat from Metrohm
America. The electrochemical cell employed in this study
comprised three electrodes and incorporated a Luggin
capillary. Specifically, the working electrode was a copper
disk, the reference electrode was a platinum plate, and the
reference electrode was Ag/AgCl (with 3 M NaCl filling
solution). The working copper electrode was polished with
alumina powder on a polishing cloth before each trial for
2 minutes, ultrasonicated for two minutes, and promptly
transferred to the electrochemical cell. OCP measurements,
LSV, and CV were measured at various concentrations,
including 0, 10–6, 10–5, 10–4, and 10–3 M of AIBTC or
IPETC. The potential values in this study were referenced
and reported versus an Ag/AgCl electrode (+0.209 V vs.
the normal hydrogen electrode) unless stated otherwise.
During measurements, solutions were moderately stirred.
RESULTS AND DISCUSSION
Real Ore, Bench-Scale Flotation
Cumulative Cu and Mo recovery versus cumulative flota-
tion time was plotted in Figure 2. First, the conditions where
AIBTC and IPETC were introduced as neat products were
compared. In the first 30 seconds of flotation, IPETC direct
addition achieved greater Cu and Mo recovery of about
42% and 11%, respectively, compared to AIBTC, which
resulted in a Cu recovery of 35% and Mo recovery of 9%.
This is believed to be due to the higher solubility of IPETC,
measured and reported in the next section, and, therefore,