XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3107
into unique flotation outcomes at the macro level from ores
and tailing. There is almost no information in the litera-
ture on the nature of the interaction of AIBTC with metals
and metal sulfides. The traditional electrostatic interac-
tion driven by a charge on the mineral surface and/or the
ligand can be ruled out because AIBTC is charge-neutral
and oily (almost insoluble in water). Collector oxidation
(similar to that of xanthate to dixanthogen) is ruled out
as part of the adsorption process and surface site binding
because AIBTC does not undergo any oxidation/reduction
in the pulp potential range of relevance to practical ore flo-
tation system. We believe that the ligand surface binding
on metals and metal sulfides is via Lewis acid-base interac-
tions, which result in electron delocalization and redistri-
bution within the metal-ligand surface complex. However,
the exact mechanism and, more importantly, the critical
role of the allylic double bond in modifying the electron
donor-acceptor interactions and the consequent significant
increase in the hydrophobicity of the adsorbed layer, which
in turn translates to the flotation rates of value minerals, is
not well known (Figure 1).
Most existing literature focuses on N-ethyl
O-isopropyl thionocarbamate (IPETC) and O-isobutyl
N-ethoxycarbonyl thionocarbamate (IBECTC). In a study
using surface-enhanced Rama spectroscopy and potentiom-
etry (open circuit potential) at a Cu electrode, Woods and
Hope (1999) found that the formal potential of forming
bulk Cu-IPETC complexes was 0.131 V vs. SHE. IPETC
interacted with copper electrodes via a charge transfer pro-
cess in which the sulfur atom bonded to a copper atom on
the metal surface while the N-H bond dissociates, releasing
a proton to the solution. Fairthorne et al. (1996) investi-
gated the solution properties of IPETC and IBECTC and
concluded that the pH-dependent behavior of IBECTC
suggested a stronger electron-withdrawing effect of the eth-
oxy carbonyl substituent than the ethyl group of IPETC.
The pKa of IBECTC was reported to be around 8, while
that of IPETC was larger than 12. This study also revealed
that chalcopyrite recovery with IPETC exhibits minimal
dependence on pH within the range of 5 to 9.5, below
its pKa. Mielczarski and Yoon (1991) studied the adsorp-
tion of IBECTC on cuprous sulfide using FTIR and XPS
spectroscopies. The reported results suggested that a six-
membered chelate formed during the complexation of cop-
per and IBECTC, and the N-H bond dissociated. In an
FTIR study of the adsorption of IPETC and IBECTC on
sulfides, Leppinen et al. (1988) found that Cu(II) did not
form precipitates with either IPETC or IBECTC. The pre-
cipitate formed only when Cu(II) was reduced to Cu(I) by
adding a reducing agent. Their studies implied that IPETC
bonded through sulfur when adsorbing on the surface of
chalcocite, and it was likely that at low pH values, IPETC
coordinated with the surface copper through sulfur, while
both sulfur and oxygen were involved in the adsorption at
high pH values. IBECTC reacted with Cu(I) via the bond-
ing of sulfur and oxygen.
Research on AIBTC is scarce, with very few studies
conducted thus far. Based on spectroscopic and wettability
studies of the interaction of N-allyl isobutyl thionocarba-
mate (AIBTC) and the saturated analog N-propyl isobutyl
thionocarbamate (NPIBTC) copper at pH 9, Farinato et
al. (1993) proposed that AIBTC and NPIBTC adsorbed
onto Cu surface through the sulfur of C=S. AIBTC, how-
ever, increased surface hydrophobicity and exhibited faster
adsorption kinetics, which could explain its better flotation
performance. This study did not shed light on the role of the
double bond. Liu et al. (2008) used ab initio calculations to
investigate the effect of N-substituents in thionocarbamates
on their performance as collectors for copper sulfides. The
highest occupied molecular orbital energies indicated that
sulfur was the reactive atom and could donate its frontier
electrons to a metal atom on the mineral surface, forming
a s-bond. This electron donating ability was classified in
the order of IPETC O-isobutyl N-ethyl thionocarbamate
(IBETC) O-isobutyl N-allyl thionocarbamate (IBALTC
or AIBTC) O-isobutyl N-acetyl thionocarbamate
(IBACTC) O-isobutyl N-ethoxycarbonyl thionocarba-
mate (IBECTC). The lowest occupied molecular orbital
energies suggested these collectors could also overlap with
d-orbitals of metal atoms to form a dative p-bond, with
Figure 1. a) N-allyl O-isobutyl thionocarbamate (AIBTC), b) N-ethyl O-isopropyl thionocarbamate (IPETC)
into unique flotation outcomes at the macro level from ores
and tailing. There is almost no information in the litera-
ture on the nature of the interaction of AIBTC with metals
and metal sulfides. The traditional electrostatic interac-
tion driven by a charge on the mineral surface and/or the
ligand can be ruled out because AIBTC is charge-neutral
and oily (almost insoluble in water). Collector oxidation
(similar to that of xanthate to dixanthogen) is ruled out
as part of the adsorption process and surface site binding
because AIBTC does not undergo any oxidation/reduction
in the pulp potential range of relevance to practical ore flo-
tation system. We believe that the ligand surface binding
on metals and metal sulfides is via Lewis acid-base interac-
tions, which result in electron delocalization and redistri-
bution within the metal-ligand surface complex. However,
the exact mechanism and, more importantly, the critical
role of the allylic double bond in modifying the electron
donor-acceptor interactions and the consequent significant
increase in the hydrophobicity of the adsorbed layer, which
in turn translates to the flotation rates of value minerals, is
not well known (Figure 1).
Most existing literature focuses on N-ethyl
O-isopropyl thionocarbamate (IPETC) and O-isobutyl
N-ethoxycarbonyl thionocarbamate (IBECTC). In a study
using surface-enhanced Rama spectroscopy and potentiom-
etry (open circuit potential) at a Cu electrode, Woods and
Hope (1999) found that the formal potential of forming
bulk Cu-IPETC complexes was 0.131 V vs. SHE. IPETC
interacted with copper electrodes via a charge transfer pro-
cess in which the sulfur atom bonded to a copper atom on
the metal surface while the N-H bond dissociates, releasing
a proton to the solution. Fairthorne et al. (1996) investi-
gated the solution properties of IPETC and IBECTC and
concluded that the pH-dependent behavior of IBECTC
suggested a stronger electron-withdrawing effect of the eth-
oxy carbonyl substituent than the ethyl group of IPETC.
The pKa of IBECTC was reported to be around 8, while
that of IPETC was larger than 12. This study also revealed
that chalcopyrite recovery with IPETC exhibits minimal
dependence on pH within the range of 5 to 9.5, below
its pKa. Mielczarski and Yoon (1991) studied the adsorp-
tion of IBECTC on cuprous sulfide using FTIR and XPS
spectroscopies. The reported results suggested that a six-
membered chelate formed during the complexation of cop-
per and IBECTC, and the N-H bond dissociated. In an
FTIR study of the adsorption of IPETC and IBECTC on
sulfides, Leppinen et al. (1988) found that Cu(II) did not
form precipitates with either IPETC or IBECTC. The pre-
cipitate formed only when Cu(II) was reduced to Cu(I) by
adding a reducing agent. Their studies implied that IPETC
bonded through sulfur when adsorbing on the surface of
chalcocite, and it was likely that at low pH values, IPETC
coordinated with the surface copper through sulfur, while
both sulfur and oxygen were involved in the adsorption at
high pH values. IBECTC reacted with Cu(I) via the bond-
ing of sulfur and oxygen.
Research on AIBTC is scarce, with very few studies
conducted thus far. Based on spectroscopic and wettability
studies of the interaction of N-allyl isobutyl thionocarba-
mate (AIBTC) and the saturated analog N-propyl isobutyl
thionocarbamate (NPIBTC) copper at pH 9, Farinato et
al. (1993) proposed that AIBTC and NPIBTC adsorbed
onto Cu surface through the sulfur of C=S. AIBTC, how-
ever, increased surface hydrophobicity and exhibited faster
adsorption kinetics, which could explain its better flotation
performance. This study did not shed light on the role of the
double bond. Liu et al. (2008) used ab initio calculations to
investigate the effect of N-substituents in thionocarbamates
on their performance as collectors for copper sulfides. The
highest occupied molecular orbital energies indicated that
sulfur was the reactive atom and could donate its frontier
electrons to a metal atom on the mineral surface, forming
a s-bond. This electron donating ability was classified in
the order of IPETC O-isobutyl N-ethyl thionocarbamate
(IBETC) O-isobutyl N-allyl thionocarbamate (IBALTC
or AIBTC) O-isobutyl N-acetyl thionocarbamate
(IBACTC) O-isobutyl N-ethoxycarbonyl thionocarba-
mate (IBECTC). The lowest occupied molecular orbital
energies suggested these collectors could also overlap with
d-orbitals of metal atoms to form a dative p-bond, with
Figure 1. a) N-allyl O-isobutyl thionocarbamate (AIBTC), b) N-ethyl O-isopropyl thionocarbamate (IPETC)