10
Cu2+, in solution, against dolomite and calcite, the source
of Ca2+ and Mg2+ in solution, which at the main deleteri-
ous gangue mineral for oxide copper flotation.
Lenormand et al. (1979) claimed that potassium octyl
hydroxamate chemisorbed on malachite, after the analysis
of the results obtained with UV and IR. It was claimed
that the infrared spectra peak of 1520 cm–1 was due to
the characteristic copper octyl hydroxamate band when
hydroxamate contacted malachite. Figure 10 and Table 1
show that a new IR-ATR spectra peak at 1507 cm–1 appears
after malachite contacts octanohydroxamate, and the result
is in-line with what has been reported by Lenormand et al.
(1979). In addition, because the strong doublet shown at
2955 cm–1 and 2871 cm–1, together with the strong dou-
blet shown at 2925 cm–1 and 2850 cm–1, are due to the
stretching vibrations of – CH3 and –CH2–, it provides a
strong evidence of the adsorption of OHA on malachite
because the aliphatic group of –CH3 and –CH2– come
only from OHA instead of malachite.
Adsorption Time Effect
Figure 3 clearly shows that OHA adsorbs on malachite in a
short contact time, i.e., 10 minutes, in an almost full cover-
age over the whole sample surface. In addition, the grain
size of the adsorbate is larger than that as obtained in water
as shown by Figure 2 for the grains after malachite surface
is hydrolyzed in water. The increase in grain size is clearly
due to the adsorption of OHA, the chemical of which has
8 hydrocarbon atoms in the hydrocarbon chain. Finally,
by comparing Figure 3 to Figure 4 and Figure 5, one can
see that in 5×10–5 M OHA solution, the adsorption kinet-
ics is very fast and the increase in contact time does not
increase the adsorption on malachite surface much. The
results obtained with 5×10–5 M OHA at various contact
time show that OHA adsorbs on malachite in a fast adsorp-
tion kinetics even at a very low collector’s concentration.
The Concentration of OHA
Figure 6 shows the AFM images of a malachite surface
soaked in 1×10–4 M OHA solution for 10 minutes. By com-
paring Figure 6 to Figure 3, when the OHA concentration
increases from 5×10–5 M to 1×10–4 M, a lot of adsorbate
is forming at solid/liquid interface and the mineral surface
is again fully covered by the adsorbate. Because OHA fully
covers malachite surface even at a low concentration, the
increase of the concentration of OHA only show a little bit
increased surface roughness on surface morphology.
Figure 7 shows the AFM images of a malachite surface
soaked in 5×10–4 M OHA solution for 10 minutes. By com-
paring Figure 7 to Figure 3 and Figure 6, when the OHA
concentration increases from 5×10–5 M to 5×10–4 M, a lot
of adsorbate is observed fully covering malachite surface.
Again, because OHA fully covers malachite surface even at
even 5×10–5 M, the increase of the concentration of OHA
collector does not greatly impact the surface morphology.
The above results show that OHA can adsorb on mala-
chite effectively and it can fully cover the mineral surface
even at a low concentration of 5×10–4 M.
The Adhesion Force
Figure 9 shows that when malachite surface contacts 5×10–5
M OHA solution, the detach force value is very low, sug-
gesting a very weak adhesion between malachite surface
and the AFM probe in solution. In addition, because the
“jump-off” point is sharp and the “jump-off” position close
to the “0” separation, it suggests there will be a low adhesion
between the OHA coated malachite surface with bubble
during flotation. Compared to the very large “jump-off”
position as obtained with an oil film coated mineral surface
and a bubble, using OHA only will NOT provide strong
adhesion force between a bubble and malachite, which is
beneficial for a high flotation recovery. That is, an auxil-
iary hydrocarbon oil is needed to add in combination with
OHA for the direct flotation of malachite to achieve a high
recovery.
CONCLUSIONS
AFM surface image measurement has been applied to study
in situ the adsorption of OHA on malachite in aqueous
solution. The AFM images show that malachite surface is
hydrolyze when the mineral contacts water. When mala-
chite contacts OHA, a lot of adsorbate is shown on mineral
surface even at an OHA concentration as low as 5×10–5 M.
The adsorbate covers fully the mineral surface in a short
contact time. Increasing collectors’ concentration from
5×10–5 M to 5×10–4 M does not impact the surface mor-
phology much, because OHA can adsorb on mineral sur-
face completely, leaving little empty spaces. The FTIR-ATR
result confirms that OHA adsorbs on malachite surface.
The AFM force measurement result shows that the adhe-
sion between a OHA coated malachite and a bubble should
be low and an auxiliary hydrocarbon oil should be added
together with OHA. As such, OHA shows a high selec-
tivity with a moderate collectivity will be achieved with a
hydroxamic acid collector for the flotation of malachite.
ACKNOWLEDGMENT
J. Zhang is grateful to Freeport-McMoRan Copper &
Gold, Inc. for sponsoring the Freeport McMoRan Copper
and Gold Chair in Mineral Processing in the Department
Cu2+, in solution, against dolomite and calcite, the source
of Ca2+ and Mg2+ in solution, which at the main deleteri-
ous gangue mineral for oxide copper flotation.
Lenormand et al. (1979) claimed that potassium octyl
hydroxamate chemisorbed on malachite, after the analysis
of the results obtained with UV and IR. It was claimed
that the infrared spectra peak of 1520 cm–1 was due to
the characteristic copper octyl hydroxamate band when
hydroxamate contacted malachite. Figure 10 and Table 1
show that a new IR-ATR spectra peak at 1507 cm–1 appears
after malachite contacts octanohydroxamate, and the result
is in-line with what has been reported by Lenormand et al.
(1979). In addition, because the strong doublet shown at
2955 cm–1 and 2871 cm–1, together with the strong dou-
blet shown at 2925 cm–1 and 2850 cm–1, are due to the
stretching vibrations of – CH3 and –CH2–, it provides a
strong evidence of the adsorption of OHA on malachite
because the aliphatic group of –CH3 and –CH2– come
only from OHA instead of malachite.
Adsorption Time Effect
Figure 3 clearly shows that OHA adsorbs on malachite in a
short contact time, i.e., 10 minutes, in an almost full cover-
age over the whole sample surface. In addition, the grain
size of the adsorbate is larger than that as obtained in water
as shown by Figure 2 for the grains after malachite surface
is hydrolyzed in water. The increase in grain size is clearly
due to the adsorption of OHA, the chemical of which has
8 hydrocarbon atoms in the hydrocarbon chain. Finally,
by comparing Figure 3 to Figure 4 and Figure 5, one can
see that in 5×10–5 M OHA solution, the adsorption kinet-
ics is very fast and the increase in contact time does not
increase the adsorption on malachite surface much. The
results obtained with 5×10–5 M OHA at various contact
time show that OHA adsorbs on malachite in a fast adsorp-
tion kinetics even at a very low collector’s concentration.
The Concentration of OHA
Figure 6 shows the AFM images of a malachite surface
soaked in 1×10–4 M OHA solution for 10 minutes. By com-
paring Figure 6 to Figure 3, when the OHA concentration
increases from 5×10–5 M to 1×10–4 M, a lot of adsorbate
is forming at solid/liquid interface and the mineral surface
is again fully covered by the adsorbate. Because OHA fully
covers malachite surface even at a low concentration, the
increase of the concentration of OHA only show a little bit
increased surface roughness on surface morphology.
Figure 7 shows the AFM images of a malachite surface
soaked in 5×10–4 M OHA solution for 10 minutes. By com-
paring Figure 7 to Figure 3 and Figure 6, when the OHA
concentration increases from 5×10–5 M to 5×10–4 M, a lot
of adsorbate is observed fully covering malachite surface.
Again, because OHA fully covers malachite surface even at
even 5×10–5 M, the increase of the concentration of OHA
collector does not greatly impact the surface morphology.
The above results show that OHA can adsorb on mala-
chite effectively and it can fully cover the mineral surface
even at a low concentration of 5×10–4 M.
The Adhesion Force
Figure 9 shows that when malachite surface contacts 5×10–5
M OHA solution, the detach force value is very low, sug-
gesting a very weak adhesion between malachite surface
and the AFM probe in solution. In addition, because the
“jump-off” point is sharp and the “jump-off” position close
to the “0” separation, it suggests there will be a low adhesion
between the OHA coated malachite surface with bubble
during flotation. Compared to the very large “jump-off”
position as obtained with an oil film coated mineral surface
and a bubble, using OHA only will NOT provide strong
adhesion force between a bubble and malachite, which is
beneficial for a high flotation recovery. That is, an auxil-
iary hydrocarbon oil is needed to add in combination with
OHA for the direct flotation of malachite to achieve a high
recovery.
CONCLUSIONS
AFM surface image measurement has been applied to study
in situ the adsorption of OHA on malachite in aqueous
solution. The AFM images show that malachite surface is
hydrolyze when the mineral contacts water. When mala-
chite contacts OHA, a lot of adsorbate is shown on mineral
surface even at an OHA concentration as low as 5×10–5 M.
The adsorbate covers fully the mineral surface in a short
contact time. Increasing collectors’ concentration from
5×10–5 M to 5×10–4 M does not impact the surface mor-
phology much, because OHA can adsorb on mineral sur-
face completely, leaving little empty spaces. The FTIR-ATR
result confirms that OHA adsorbs on malachite surface.
The AFM force measurement result shows that the adhe-
sion between a OHA coated malachite and a bubble should
be low and an auxiliary hydrocarbon oil should be added
together with OHA. As such, OHA shows a high selec-
tivity with a moderate collectivity will be achieved with a
hydroxamic acid collector for the flotation of malachite.
ACKNOWLEDGMENT
J. Zhang is grateful to Freeport-McMoRan Copper &
Gold, Inc. for sponsoring the Freeport McMoRan Copper
and Gold Chair in Mineral Processing in the Department