9
Because malachite is a hydrophilic carbonate mineral, the
hydrolysis reaction will start when malachite contacts water.
The equivalent diameter of these grains is about 45 nm.
Figures 3 to 8 show that a lot of adsorbate was observed
on malachite surface when it contacts OHA solutions for a
specific time. The change of malachite surface in morphol-
ogy cannot be attributed to the reaction of mineral with
water because the AFM images obtained with the addition
of OHA solutions are totally different from Figure 2, which
is captured during a same time frame, i.e., 10 minutes.
Therefore, the adsorbate shown by Figure 3 to Figure 8
must be due to the adsorption of OHA at the mineral/
liquid interface. It has been reported that hydroxamic acid
can react with heavy metal ions and form a metal complex,
which will adsorb on mineral surface and increase the hydro-
phobicity of the target mineral. The pKa of hydroxamic
acids ranges pH 7–9. (Pradip and Fuerstenau, 1983)
Because the stability constants of the metal- hydroxamic
complexes of alkali earth metals, i.e., Ca2+, Mg2+ and Ba2+,
is comparatively lower than those of heavy metals such as
Cu2+, Fe3+ and rare-earth elements, the hydroxamic acid
collector has a high selectivity for malachite, the source of
Figure 10. ATR-FTIR spectra of a malachite surface before and after it contacts 1×10–4 M
OHA solution at pH 6 for 1 hour
Table 1. The main peaks of the ATR-FTIR spectra of a malachite surface before and after it
contacts 1×10–4 M OHA solution at pH 6 for 1 hour
Sample Wave Number (cm–1) Peaks Assignment
malachite
(bare)
3400, 3300 stretching vibration of hydroxyl group (-OH)
1490, 1384 asymmetric stretching vibration of CO32–
1096 symmetric stretching vibration of CO32–
1043 bending vibration of -OH
868 out-of-plane bending vibration of CO
3
2–
765, 725 in-plane bending vibration of CO32–
malachite
(OHA)
3406, 3308 stretching vibration of hydroxyl group (-OH)
2955, 2871 stretching vibrations of –CH
3 2925, 2850 stretching vibrations of –CH
2 –
1507 Asymmetry bending vibration of -OH
1490, 1385 asymmetric stretching vibration of CO32–
1096 symmetric stretching vibration of CO
3
2–
1046 bending vibration of -OH
868 out-of-plane bending vibration of CO32–
765, 725 in-plane bending vibration of CO32–
Because malachite is a hydrophilic carbonate mineral, the
hydrolysis reaction will start when malachite contacts water.
The equivalent diameter of these grains is about 45 nm.
Figures 3 to 8 show that a lot of adsorbate was observed
on malachite surface when it contacts OHA solutions for a
specific time. The change of malachite surface in morphol-
ogy cannot be attributed to the reaction of mineral with
water because the AFM images obtained with the addition
of OHA solutions are totally different from Figure 2, which
is captured during a same time frame, i.e., 10 minutes.
Therefore, the adsorbate shown by Figure 3 to Figure 8
must be due to the adsorption of OHA at the mineral/
liquid interface. It has been reported that hydroxamic acid
can react with heavy metal ions and form a metal complex,
which will adsorb on mineral surface and increase the hydro-
phobicity of the target mineral. The pKa of hydroxamic
acids ranges pH 7–9. (Pradip and Fuerstenau, 1983)
Because the stability constants of the metal- hydroxamic
complexes of alkali earth metals, i.e., Ca2+, Mg2+ and Ba2+,
is comparatively lower than those of heavy metals such as
Cu2+, Fe3+ and rare-earth elements, the hydroxamic acid
collector has a high selectivity for malachite, the source of
Figure 10. ATR-FTIR spectra of a malachite surface before and after it contacts 1×10–4 M
OHA solution at pH 6 for 1 hour
Table 1. The main peaks of the ATR-FTIR spectra of a malachite surface before and after it
contacts 1×10–4 M OHA solution at pH 6 for 1 hour
Sample Wave Number (cm–1) Peaks Assignment
malachite
(bare)
3400, 3300 stretching vibration of hydroxyl group (-OH)
1490, 1384 asymmetric stretching vibration of CO32–
1096 symmetric stretching vibration of CO32–
1043 bending vibration of -OH
868 out-of-plane bending vibration of CO
3
2–
765, 725 in-plane bending vibration of CO32–
malachite
(OHA)
3406, 3308 stretching vibration of hydroxyl group (-OH)
2955, 2871 stretching vibrations of –CH
3 2925, 2850 stretching vibrations of –CH
2 –
1507 Asymmetry bending vibration of -OH
1490, 1385 asymmetric stretching vibration of CO32–
1096 symmetric stretching vibration of CO
3
2–
1046 bending vibration of -OH
868 out-of-plane bending vibration of CO32–
765, 725 in-plane bending vibration of CO32–