3048 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Cu Depression
In conventional Cu-Mo flotation systems, xanthates are
predominantly used where the xanthate organic tail is
commonly ethyl, isopropyl or butyl. Xanthates are proven
to be effective collectors for refractory ore separation.
Chalcopyrite flotation kinetics increase significantly in the
presence of butyl xanthate and can be attributed to the high
collector adsorption as well as the longer chain length [2] .
However, the interaction mechanism of Orfom ® D8 has
only been established for ethyl xanthate. Furthermore,
other collectors are used for Cu-mineral flotation and
include dithiophosphate, thiocarbamate, and mercapto-
benzothiazole [16] .Consequently, the ability of Orfom ® D8
to co-adsorb in their presence is yet to be established as
well.
EXPERIMENTAL DETAILS
Materials
Chalcopyrite and molybdenite concentrate samples were
obtained from a North American mine for this project.
As received particle sizes were -106 mm but were pulver-
ized to -38 mm fines with a benchtop ceramic ball mill.
Using the Rigaku Ultima IV, X-ray Diffraction (XRD)
patterns were collected and processed with the JADE char-
acterization Software. Results demonstrated mineral com-
position for copper concentrate were 37.3%, 36.4%, and
26.4% for pyrite, covellite, and chalcopyrite, respectively.
Molybdenum concentrate contained 87.2% molybdenite.
Orfom ® D8 depressants were obtained from Chevron
Phillips Chemical Company at 38 wt%.
Methods
Zeta Potential
Chalcopyrite and molybdenite surface potential were deter-
mined using the Malvern Zeta Sizer Nano ZS which employs
Dynamic Light Scattering (DLS) and Electrophoretic Light
Scattering (ELS) characterization to measure size and zeta
potential, respectively. The Orfom ® D8 was dosed at 100
lbs/t to slurries of 10% solids by wgt. which were then ana-
lyzed. Experiments were conducted at room temperature
near 20°C at variable pH ranging from 2 to 12. The slurry
was filtered so that the solution and only -0.5um particles
were loaded into a DTS1070 capillary cell for zeta poten-
tial measurement. Because Orfom ® was already at pH 13.2,
the solution pH typically needed adjusting only with acid,
either H2SO4 or HCl
FT-IR Spectroscopy
FT-IR measurements were made with a SHIMADZU IR
Tracer-100 using the diffuse reflectance (DRIFTS) IR tech-
nique. DRIFTS evaluates non-transparent, highly absor-
bent materials to identify minute variations on surfaces.
For these determinations, 0.1M Orfom ® D8 and/or KEX
reagent concentrations were prepared equilibrating 10%
solids at pH 9.5 for 60 minutes to insure adsorption. The
slurry was subsequently filtered and dried. KBr diluent was
mixed with a dried sample in a ratio of 98:2 and pulver-
ized to obtain a consistent texture. Infrared spectra were
collected from 400-4000 cm–1 at a resolution of 4 cm–1 so
that both the fingerprint and the functional group regions
were obtained however, most analyses focused on the fin-
gerprint region of 400-2000 cm –1 .
Source: S. Timbillah, 2019
Figure 2. Orfom® D8 Interaction with Chalcopyrite (a) and Pyrite (b)

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Extracted Text (may have errors)

3048 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Cu Depression
In conventional Cu-Mo flotation systems, xanthates are
predominantly used where the xanthate organic tail is
commonly ethyl, isopropyl or butyl. Xanthates are proven
to be effective collectors for refractory ore separation.
Chalcopyrite flotation kinetics increase significantly in the
presence of butyl xanthate and can be attributed to the high
collector adsorption as well as the longer chain length [2] .
However, the interaction mechanism of Orfom ® D8 has
only been established for ethyl xanthate. Furthermore,
other collectors are used for Cu-mineral flotation and
include dithiophosphate, thiocarbamate, and mercapto-
benzothiazole [16] .Consequently, the ability of Orfom ® D8
to co-adsorb in their presence is yet to be established as
well.
EXPERIMENTAL DETAILS
Materials
Chalcopyrite and molybdenite concentrate samples were
obtained from a North American mine for this project.
As received particle sizes were -106 mm but were pulver-
ized to -38 mm fines with a benchtop ceramic ball mill.
Using the Rigaku Ultima IV, X-ray Diffraction (XRD)
patterns were collected and processed with the JADE char-
acterization Software. Results demonstrated mineral com-
position for copper concentrate were 37.3%, 36.4%, and
26.4% for pyrite, covellite, and chalcopyrite, respectively.
Molybdenum concentrate contained 87.2% molybdenite.
Orfom ® D8 depressants were obtained from Chevron
Phillips Chemical Company at 38 wt%.
Methods
Zeta Potential
Chalcopyrite and molybdenite surface potential were deter-
mined using the Malvern Zeta Sizer Nano ZS which employs
Dynamic Light Scattering (DLS) and Electrophoretic Light
Scattering (ELS) characterization to measure size and zeta
potential, respectively. The Orfom ® D8 was dosed at 100
lbs/t to slurries of 10% solids by wgt. which were then ana-
lyzed. Experiments were conducted at room temperature
near 20°C at variable pH ranging from 2 to 12. The slurry
was filtered so that the solution and only -0.5um particles
were loaded into a DTS1070 capillary cell for zeta poten-
tial measurement. Because Orfom ® was already at pH 13.2,
the solution pH typically needed adjusting only with acid,
either H2SO4 or HCl
FT-IR Spectroscopy
FT-IR measurements were made with a SHIMADZU IR
Tracer-100 using the diffuse reflectance (DRIFTS) IR tech-
nique. DRIFTS evaluates non-transparent, highly absor-
bent materials to identify minute variations on surfaces.
For these determinations, 0.1M Orfom ® D8 and/or KEX
reagent concentrations were prepared equilibrating 10%
solids at pH 9.5 for 60 minutes to insure adsorption. The
slurry was subsequently filtered and dried. KBr diluent was
mixed with a dried sample in a ratio of 98:2 and pulver-
ized to obtain a consistent texture. Infrared spectra were
collected from 400-4000 cm–1 at a resolution of 4 cm–1 so
that both the fingerprint and the functional group regions
were obtained however, most analyses focused on the fin-
gerprint region of 400-2000 cm –1 .
Source: S. Timbillah, 2019
Figure 2. Orfom® D8 Interaction with Chalcopyrite (a) and Pyrite (b)

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XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3047
which include toxicity, strong odor, explosion potential,
and high consumption. Because the latter can be caused by
oxidation in air, flotation can be conducted with inert gases
such as nitrogen, making the process even more expensive.
To remedy these mining sustainability challenges, the flo-
tation industry is switching to organic depressants. While
disodium carboxymethyl trithiocarbonate (Orfom ® D8) is
a leading candidate for Cu-Mo separation, other organic
depressants have also gained attention: dextrin, pseudo
glycol thiourea (PGA), thioglycolic acid (TGA), and
chitosan, to name a few. Research by Chen et al., Lui et
al., and Bruke et al. [5,6,9,12,14] have shown these organic
depressants have potential but the effect of Orfom ® D8 is
much greater. Specifically, Orfom ® D8 has been success-
fully used to replace sodium bisulfide (NaSH), sodium
sulfide (Na2S), Nokes reagent (sodium dithiophosphate,
Na3PS2O2), sodium cyanide (NaCN) and sodium ferrocy-
anide (Na4FeCN6) for depressing Cu in Cu-Mo separation
of bulk concentrates [9,17,20].
As discussed by Ma and Bagci et al., the conventional
Cu-Mo flotation separation system employs xanthate as
the Cu-collector and diesel fuel for Mo [1,14,15]. According
to Young and Timbillah [17–20], Orfom ® D8 works well in
this system for depressing copper-iron sulfide minerals such
as chalcocite, chalcopyrite and pyrite and has little to no
impact on molybdenite flotation, making the depressant
highly selective. For this paper, research was conducted to
verify the mechanism that Young and Timbillah determined
[18–20]. However, additional research is also presented with
a focus on examining Orfom ® D8 performance with other
mineral and collector systems to see if the mechanism still
applied.
Orfom® D8 Depressant
As shown in Figure 1, Orfom ® D8 is a homopolar mol-
ecule with two polar groups, one on each end of its struc-
ture: carboxylate (CO2–) and trithiocarbonate (SCS2–).
Sodium cations are needed to offset the anionic charges.
Its structural core is methylene [17]. Bresson et al., explain
that Orfom ® D8 is synthesized from a reaction between
mercapto polycarboxylic acid, carbon disulfide (CS2), and
NaOH while simultaneously producing water [3,4,17,19].
When the molecule is attached to a mineral surface at one
end, the other end protrudes into the bulk solution mak-
ing the surface charged and hydrophilic which, of course,
causes the mineral to be depressed [17]. As explained by
Laskowski et al.[9], a depressant imparts strong hydrophilic
characteristics onto a mineral surface or inhibits collector
action by preventing surface adhesion. According to Young
and Timbillah [18–20], Orfom ® D8 does both.
Theoretical Modelling
According to Timbillah et al., Orfom ® D8 is significantly
more interactive with chalcopyrite than it is with molyb-
denite creating conditions for depressing chalcopyrite.
Experimental observations made on electrophoretic mobil-
ity studies between the abovementioned minerals reflect
its reactivity descriptors, frontier orbital energies, and
quantum chem-molecular properties giving rise to the
highest occupied molecular orbital (HOMO) and Lowest
Unoccupied Molecular Orbital (LUMO) of -3.0 eV and
0.1 eV, respectively. A total energy (ET) of -1460.4485 is
negative enough to polarize chalcopyrite up to -150 mV
potential as obtained from zeta potential studies [8,17,18].
As shown in Figure 2, Orfom ® D8, chalcopyrite,
and pyrite molecules show that the two sulfides can form
complexes. Binding energies reveal a strong interaction.
The focus of most work has been on chalcopyrite inter-
action, while pyrite promises to better interact with the
reagent. Interaction energy data yielded values of -239.4
and -540.6 kJ/mol for chalcopyrite and pyrite, respectively.
The reagent is highly alkaline because it is stored at 13.2
pH. To establish the best pH regime for optimal depres-
sant performance, the pKa values were determined. Due to
the diprotic nature of Orfom ® D8 with two functionalities,
two pKa values of 4.20 and 5.06 can be attributed to the
successive protonation of the trithiocarbonate and carbox-
ylate functional groups. The lower pKa value [18] suggests
that Orfom ® D8 likely bonds with the metal atoms at the
sulfide mineral surface indicating the carboxylates cause the
minerals to become hydrophilic and therefore depressed
[10,11]. This chemisorption behavior was confirmed using
cyclic voltammetry due to the appearance of peaks similar
to xanthate chemisorption as well as FT-IR spectroscopy
due to -CS vibrations shifting to different wavenumbers
following adsorption [17–20].
Source: S Timbillah, 2019
Figure 1. Two-Dimensional Structure of Orfom D8

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Extracted Text (may have errors)

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3047
which include toxicity, strong odor, explosion potential,
and high consumption. Because the latter can be caused by
oxidation in air, flotation can be conducted with inert gases
such as nitrogen, making the process even more expensive.
To remedy these mining sustainability challenges, the flo-
tation industry is switching to organic depressants. While
disodium carboxymethyl trithiocarbonate (Orfom ® D8) is
a leading candidate for Cu-Mo separation, other organic
depressants have also gained attention: dextrin, pseudo
glycol thiourea (PGA), thioglycolic acid (TGA), and
chitosan, to name a few. Research by Chen et al., Lui et
al., and Bruke et al. [5,6,9,12,14] have shown these organic
depressants have potential but the effect of Orfom ® D8 is
much greater. Specifically, Orfom ® D8 has been success-
fully used to replace sodium bisulfide (NaSH), sodium
sulfide (Na2S), Nokes reagent (sodium dithiophosphate,
Na3PS2O2), sodium cyanide (NaCN) and sodium ferrocy-
anide (Na4FeCN6) for depressing Cu in Cu-Mo separation
of bulk concentrates [9,17,20].
As discussed by Ma and Bagci et al., the conventional
Cu-Mo flotation separation system employs xanthate as
the Cu-collector and diesel fuel for Mo [1,14,15]. According
to Young and Timbillah [17–20], Orfom ® D8 works well in
this system for depressing copper-iron sulfide minerals such
as chalcocite, chalcopyrite and pyrite and has little to no
impact on molybdenite flotation, making the depressant
highly selective. For this paper, research was conducted to
verify the mechanism that Young and Timbillah determined
[18–20]. However, additional research is also presented with
a focus on examining Orfom ® D8 performance with other
mineral and collector systems to see if the mechanism still
applied.
Orfom® D8 Depressant
As shown in Figure 1, Orfom ® D8 is a homopolar mol-
ecule with two polar groups, one on each end of its struc-
ture: carboxylate (CO2–) and trithiocarbonate (SCS2–).
Sodium cations are needed to offset the anionic charges.
Its structural core is methylene [17]. Bresson et al., explain
that Orfom ® D8 is synthesized from a reaction between
mercapto polycarboxylic acid, carbon disulfide (CS2), and
NaOH while simultaneously producing water [3,4,17,19].
When the molecule is attached to a mineral surface at one
end, the other end protrudes into the bulk solution mak-
ing the surface charged and hydrophilic which, of course,
causes the mineral to be depressed [17]. As explained by
Laskowski et al.[9], a depressant imparts strong hydrophilic
characteristics onto a mineral surface or inhibits collector
action by preventing surface adhesion. According to Young
and Timbillah [18–20], Orfom ® D8 does both.
Theoretical Modelling
According to Timbillah et al., Orfom ® D8 is significantly
more interactive with chalcopyrite than it is with molyb-
denite creating conditions for depressing chalcopyrite.
Experimental observations made on electrophoretic mobil-
ity studies between the abovementioned minerals reflect
its reactivity descriptors, frontier orbital energies, and
quantum chem-molecular properties giving rise to the
highest occupied molecular orbital (HOMO) and Lowest
Unoccupied Molecular Orbital (LUMO) of -3.0 eV and
0.1 eV, respectively. A total energy (ET) of -1460.4485 is
negative enough to polarize chalcopyrite up to -150 mV
potential as obtained from zeta potential studies [8,17,18].
As shown in Figure 2, Orfom ® D8, chalcopyrite,
and pyrite molecules show that the two sulfides can form
complexes. Binding energies reveal a strong interaction.
The focus of most work has been on chalcopyrite inter-
action, while pyrite promises to better interact with the
reagent. Interaction energy data yielded values of -239.4
and -540.6 kJ/mol for chalcopyrite and pyrite, respectively.
The reagent is highly alkaline because it is stored at 13.2
pH. To establish the best pH regime for optimal depres-
sant performance, the pKa values were determined. Due to
the diprotic nature of Orfom ® D8 with two functionalities,
two pKa values of 4.20 and 5.06 can be attributed to the
successive protonation of the trithiocarbonate and carbox-
ylate functional groups. The lower pKa value [18] suggests
that Orfom ® D8 likely bonds with the metal atoms at the
sulfide mineral surface indicating the carboxylates cause the
minerals to become hydrophilic and therefore depressed
[10,11]. This chemisorption behavior was confirmed using
cyclic voltammetry due to the appearance of peaks similar
to xanthate chemisorption as well as FT-IR spectroscopy
due to -CS vibrations shifting to different wavenumbers
following adsorption [17–20].
Source: S Timbillah, 2019
Figure 1. Two-Dimensional Structure of Orfom D8

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3049
RESULTS AND DISCUSSIONS
FT-IR Spectroscopy
High-resolution spectra were collected to ascertain the
mechanism by which Orfom ® D8 adsorbs on the chalco-
pyrite surface. From Figure 3, untreated chalcopyrite (blue)
demonstrated two distinct bands at 1039.63 and 1369.45
cm–1. Chalcopyrite treated with Orfom ® D8 (orange)
shows new peaks which can only be attributed to adsorbed
Orfom ® D8 on chalcopyrite that exhibited band vibrations
that changed from 1118.51 and 1233.25 cm–1 to 1101.35
and 1205.51 cm–1, respectively. These are attributed to
C=S vibration of the SCS2– functionality. The interaction
outcome indicates adsorption occurs through the SCS2–
functionality and not through CO2– functionality. Band
vibrations with the chalcopyrite itself are also observed to
shift slightly from 1039.63 and 1369.45 to 1033.84 and
1371.33, respectively, indicating chemical bonds formed
further suggesting that Orfom ® D8 is chemisorbed. Because
this shows Orfom ® D8 chemisorbs through its SCS2– func-
tionality, these results support the mechanism proposed by
Young and Timbillah’s findings that also suggested that, the
carboxylate end pulls chalcopyrite into solution due to its
highly negative polarity [17–20].
Chalcopyrite was treated with potassium ethyl xanthate
(KEX) and Orfom ® D8 to ascertain the adsorption mech-
anism between the reagents and the mineral in Figure 4.
Chalcopyrite treated with KEX (yellow) exhibited three
significant vibrations at 1033.84, 1124.49 and 1199.79
cm–1. Similar to Orfom ® D8 treated chalcopyrite, 1033.84
cm–1 band vibration occurs at the same wave number as
the KEX treated chalcopyrite, and the 1205.51 cm–1 band
shifted to 1199.79 cm–1 with KEX combined with chalco-
pyrite. The Peak vibration 1124.49 cm–1 is specific to KEX
in the fingerprint region indicating that KEX is present
on the chalcopyrite surface. Both KEX and Orfom ® D8
treated chalcopyrite (grey) appears to have nearly similar
vibrations as the individual reagents on chalcopyrite. Bands
of both reagents, 1033.84 and 1205.51 for Orfom ® D8
and 1124.49 for KEX, are observed on the chalcopyrite
surface indicating both reagents are present on the chalco-
pyrite surface. Because these results show Orfom ® D8 does
not cause xanthate desorption, they suggest it masks the
hydrophobicity caused by xanthate thereby supporting the
mechanism proposed by Young and Timbillah [17–20].
Molybdenite interaction with the reagents under same
conditions as collected for chalcopyrite. Untreated molyb-
denite (Mo) exhibited three band vibrations at 468.70,
781.17 and 1093.63 cm–1. Molybdenite when treated with
Orfom ® D8 (Mo+D8), revealed band vibrations occurring
at the same wave number as the untreated mineral because
no new vibrations appeared. Unlike chalcopyrite, no
noticeable Orfom ® D8 adsorption occurred on the molyb-
denite surface. Again, these results support the mechanism
proposed by Young and Timbillah [17–20].
Zeta Potential
Chalcopyrite
It has been confirmed that Orfom ® D8 chemisorbs through
its SCS2– functionality but does not cause xanthate to
desorb so its depressant effect must mask the hydropho-
bicity caused by xanthate. This means the CO2– function-
ality on Orfom ® D8 must protrude into solution thereby
creating surface charge. Zeta potential measurements were
400 900 1400 1900
Wave Number (cm-1)
CuFeS2
CuFeS2 +D8
Figure 3. FT-IR of Chalcopyrite with and without Orfom® D8
Transmit
(%)1039.63
1033.84 1101.35
1369.45
1205.51 1371.33

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Extracted Text (may have errors)

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3049
RESULTS AND DISCUSSIONS
FT-IR Spectroscopy
High-resolution spectra were collected to ascertain the
mechanism by which Orfom ® D8 adsorbs on the chalco-
pyrite surface. From Figure 3, untreated chalcopyrite (blue)
demonstrated two distinct bands at 1039.63 and 1369.45
cm–1. Chalcopyrite treated with Orfom ® D8 (orange)
shows new peaks which can only be attributed to adsorbed
Orfom ® D8 on chalcopyrite that exhibited band vibrations
that changed from 1118.51 and 1233.25 cm–1 to 1101.35
and 1205.51 cm–1, respectively. These are attributed to
C=S vibration of the SCS2– functionality. The interaction
outcome indicates adsorption occurs through the SCS2–
functionality and not through CO2– functionality. Band
vibrations with the chalcopyrite itself are also observed to
shift slightly from 1039.63 and 1369.45 to 1033.84 and
1371.33, respectively, indicating chemical bonds formed
further suggesting that Orfom ® D8 is chemisorbed. Because
this shows Orfom ® D8 chemisorbs through its SCS2– func-
tionality, these results support the mechanism proposed by
Young and Timbillah’s findings that also suggested that, the
carboxylate end pulls chalcopyrite into solution due to its
highly negative polarity [17–20].
Chalcopyrite was treated with potassium ethyl xanthate
(KEX) and Orfom ® D8 to ascertain the adsorption mech-
anism between the reagents and the mineral in Figure 4.
Chalcopyrite treated with KEX (yellow) exhibited three
significant vibrations at 1033.84, 1124.49 and 1199.79
cm–1. Similar to Orfom ® D8 treated chalcopyrite, 1033.84
cm–1 band vibration occurs at the same wave number as
the KEX treated chalcopyrite, and the 1205.51 cm–1 band
shifted to 1199.79 cm–1 with KEX combined with chalco-
pyrite. The Peak vibration 1124.49 cm–1 is specific to KEX
in the fingerprint region indicating that KEX is present
on the chalcopyrite surface. Both KEX and Orfom ® D8
treated chalcopyrite (grey) appears to have nearly similar
vibrations as the individual reagents on chalcopyrite. Bands
of both reagents, 1033.84 and 1205.51 for Orfom ® D8
and 1124.49 for KEX, are observed on the chalcopyrite
surface indicating both reagents are present on the chalco-
pyrite surface. Because these results show Orfom ® D8 does
not cause xanthate desorption, they suggest it masks the
hydrophobicity caused by xanthate thereby supporting the
mechanism proposed by Young and Timbillah [17–20].
Molybdenite interaction with the reagents under same
conditions as collected for chalcopyrite. Untreated molyb-
denite (Mo) exhibited three band vibrations at 468.70,
781.17 and 1093.63 cm–1. Molybdenite when treated with
Orfom ® D8 (Mo+D8), revealed band vibrations occurring
at the same wave number as the untreated mineral because
no new vibrations appeared. Unlike chalcopyrite, no
noticeable Orfom ® D8 adsorption occurred on the molyb-
denite surface. Again, these results support the mechanism
proposed by Young and Timbillah [17–20].
Zeta Potential
Chalcopyrite
It has been confirmed that Orfom ® D8 chemisorbs through
its SCS2– functionality but does not cause xanthate to
desorb so its depressant effect must mask the hydropho-
bicity caused by xanthate. This means the CO2– function-
ality on Orfom ® D8 must protrude into solution thereby
creating surface charge. Zeta potential measurements were
400 900 1400 1900
Wave Number (cm-1)
CuFeS2
CuFeS2 +D8
Figure 3. FT-IR of Chalcopyrite with and without Orfom® D8
Transmit
(%)1039.63
1033.84 1101.35
1369.45
1205.51 1371.33