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
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