1
25-010
An AFM Imaging Study of the Adsorption of Hydroxamic Acid
Collector on Malachite
Jinhong Zhang
Department of Mining and Geological Engineering,
The University of Arizona
Wei Zhang
Department of Mining and Geological Engineering,
The University of Arizona
ABSTRACT
An atomic force microscopy (AFM) image analysis has been
applied to study in situ the adsorption of hydroxamic acid
collector, i.e., octanohydroxamic acid (OHA), on malachite
in aqueous solutions. AFM images show that hydroxamic
acid collector adsorbs strongly on malachite mainly in the
form of insoluble copper hydroxamate complex. Increasing
the collectors’ concentration and the adsorption time both
increase the adsorption of hydroxamic collectors on mala-
chite. Results from the attenuated total reflectance–Fourier
transform infrared spectrometry (ATR-FTIR) also show
that the collector adsorbs strongly onto malachite, with
strong absorbance spectra being detected, and the ATR-
FTIR results confirm those as obtained by AFM. This
specific adsorption mechanism explains that a high selec-
tivity with a moderate collectivity will be achieved with a
hydroxamic acid collector for the flotation of malachite.
The findings of present study also show that AFM image
analysis is a powerful tool for the study of the hydroxamic
acid collectors’ adsorption on malachite surface and it can
help with the development of novel collectors for malachite
flotation.
Keywords: Flotation, AFM, hydroxamic collector, mala-
chite, adsorption, FTIR
INTRODUCTION
For the extractive metallurgy of copper, in general, valu-
able copper sulfide minerals such as chalcopyrite (CuFeS2),
chalcocite (Cu2S) and bornite (Cu5FeS4), which are rela-
tively resistant to acid leaching, are usually selectively sepa-
rated from non-valuable gangue by froth flotation, which
treats the highest throughput and produces the maximum
economic outcome of any surface chemistry process.
(Fuerstenau, 1982) On the other hand, valuable copper
oxide minerals such as malachite [Cu2(CO3)(OH)2] and
azurite [Cu3(CO3)2(OH)2] are treated by acid leaching
because of their high reactivity with sulfuric acid. However,
this general rule of thumb breaks down when a copper oxide
ore feed has a large portion of acid-consuming minerals
such as calcite and dolomite, which make the acid leaching
too expensive to be practical. As such, copper oxide miner-
als are also usually concentrated by using froth flotation.
Unlike the flotation of copper sulfide minerals, for
which the addition of the normal collectors of xanthate and
dithiophosphate can help achieve a satisfying metal recovery
already, (Leja, 1982), the flotation of copper oxide minerals
such as malachite can be much more complicated depend-
ing on the mineralogy and the amount of the gangue min-
erals. Generally, malachite mineral is floated by using either
direct flotation or indirect sulfurization-xanthate flotation
scheme. For the direct flotation, the collectors such as oleic
acid and alkyl hydroxamic acid are added to increase the
hydrophobicity of malachite and therefore directly float
malachite. For the indirect flotation, malachite needs to be
sulfurized firstly by the addition of sulfidizer, commonly
Na2S and NaHS, and then floated by the addition xan-
thate collectors. This sulfurization-xanthate method, how-
ever, requires a careful control of the addition of sulfidizer,
because the chemical is essentially a reducing agent which
can depress the flotation of sulfide mineral when xanthate is
used as a collector and an oxidizing condition is preferred.
For example, the chemicals of Na2S and NaHS have been
used as depressants for chalcopyrite during the Cu-Mo flo-
tation circuit.
Compared to indirect flotation, the flowsheet of direct
flotation of malachite is much simpler and easier for a
process control. However, it can be a little challenging for
the selection and application of an efficient collector to
improve the flotation performance by increasing both selec-
tivity and recovery. For example, during a direct flotation
25-010
An AFM Imaging Study of the Adsorption of Hydroxamic Acid
Collector on Malachite
Jinhong Zhang
Department of Mining and Geological Engineering,
The University of Arizona
Wei Zhang
Department of Mining and Geological Engineering,
The University of Arizona
ABSTRACT
An atomic force microscopy (AFM) image analysis has been
applied to study in situ the adsorption of hydroxamic acid
collector, i.e., octanohydroxamic acid (OHA), on malachite
in aqueous solutions. AFM images show that hydroxamic
acid collector adsorbs strongly on malachite mainly in the
form of insoluble copper hydroxamate complex. Increasing
the collectors’ concentration and the adsorption time both
increase the adsorption of hydroxamic collectors on mala-
chite. Results from the attenuated total reflectance–Fourier
transform infrared spectrometry (ATR-FTIR) also show
that the collector adsorbs strongly onto malachite, with
strong absorbance spectra being detected, and the ATR-
FTIR results confirm those as obtained by AFM. This
specific adsorption mechanism explains that a high selec-
tivity with a moderate collectivity will be achieved with a
hydroxamic acid collector for the flotation of malachite.
The findings of present study also show that AFM image
analysis is a powerful tool for the study of the hydroxamic
acid collectors’ adsorption on malachite surface and it can
help with the development of novel collectors for malachite
flotation.
Keywords: Flotation, AFM, hydroxamic collector, mala-
chite, adsorption, FTIR
INTRODUCTION
For the extractive metallurgy of copper, in general, valu-
able copper sulfide minerals such as chalcopyrite (CuFeS2),
chalcocite (Cu2S) and bornite (Cu5FeS4), which are rela-
tively resistant to acid leaching, are usually selectively sepa-
rated from non-valuable gangue by froth flotation, which
treats the highest throughput and produces the maximum
economic outcome of any surface chemistry process.
(Fuerstenau, 1982) On the other hand, valuable copper
oxide minerals such as malachite [Cu2(CO3)(OH)2] and
azurite [Cu3(CO3)2(OH)2] are treated by acid leaching
because of their high reactivity with sulfuric acid. However,
this general rule of thumb breaks down when a copper oxide
ore feed has a large portion of acid-consuming minerals
such as calcite and dolomite, which make the acid leaching
too expensive to be practical. As such, copper oxide miner-
als are also usually concentrated by using froth flotation.
Unlike the flotation of copper sulfide minerals, for
which the addition of the normal collectors of xanthate and
dithiophosphate can help achieve a satisfying metal recovery
already, (Leja, 1982), the flotation of copper oxide minerals
such as malachite can be much more complicated depend-
ing on the mineralogy and the amount of the gangue min-
erals. Generally, malachite mineral is floated by using either
direct flotation or indirect sulfurization-xanthate flotation
scheme. For the direct flotation, the collectors such as oleic
acid and alkyl hydroxamic acid are added to increase the
hydrophobicity of malachite and therefore directly float
malachite. For the indirect flotation, malachite needs to be
sulfurized firstly by the addition of sulfidizer, commonly
Na2S and NaHS, and then floated by the addition xan-
thate collectors. This sulfurization-xanthate method, how-
ever, requires a careful control of the addition of sulfidizer,
because the chemical is essentially a reducing agent which
can depress the flotation of sulfide mineral when xanthate is
used as a collector and an oxidizing condition is preferred.
For example, the chemicals of Na2S and NaHS have been
used as depressants for chalcopyrite during the Cu-Mo flo-
tation circuit.
Compared to indirect flotation, the flowsheet of direct
flotation of malachite is much simpler and easier for a
process control. However, it can be a little challenging for
the selection and application of an efficient collector to
improve the flotation performance by increasing both selec-
tivity and recovery. For example, during a direct flotation