2174 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
This shows that the linear relationship provides a good pre-
diction of the pure mineral values (albite: predicted 10.2,
actual 14.9 mJ/m2 galena: predicted 90.7, actual 95.6 mJ/
m2). These could then be used for modelling the flotation
system where input values for the hydrophobicity of the
component minerals are required. To date it has only been
possible to provide ‘proof of concept’ results for a binary
system. Extrapolating this technique to more complex sys-
tems remains a major challenge.
One further challenge with respect to acquiring heat
of immersion data deserves mention. It was found during
immersion experiments that certain minerals had both an
endothermic and an exothermic peak, and in some cases
only an endothermic peak was observed (Figure 5). This
is unexpected since the wetting interaction is an exother-
mic process. As with all calorimetric measurements, only
a total heat can be measured. The reaction with which this
response is associated may be a single reaction, or multiple
interactions. In the case illustrated in Figure 5 it was found
that two interactions were occurring, viz. the expected exo-
thermic wetting reaction, but also a second endothermic
reaction was also observed to be occurring. It was hypoth-
esized that this was due to dissolution of ions from the min-
eral since when mineral particles are suspended in water,
they undergo dissolution, the extent of which depends
upon the solubility product of the mineral and the type and
concentration of chemicals in solution. The dissolved min-
eral species can undergo further reactions like hydrolysis,
complexation, adsorption and precipitation at the surface
or in the bulk.
The first option to remove dissolution is to measure
the wetting in a saturated solution of the mineral, where
the saturation ions in solution suppress any further dissolu-
tion of the mineral. Surprisingly, this method receives only
the briefest of mentions in two studies (Zimmerman et al.,
1987 Douillard et al., 2002) and no mention at all for
studies with minerals where we have found considerable
overlap between the dissolution and wetting phenomena
(for example, Goncharuk, 2015 Salles et al., 2006 Takei
and Chikazawa, 1998). We have found that the saturation
method was not always successful in suppressing any fur-
ther ionic dissolution.
Another technique that was tested in our laboratory
was to coat the mineral with an adsorbed surfactant to sup-
press dissolution. This proved very effective for minerals
such as galena, where collector coatings above 0.5 mono-
layer coverage prevented the appearance of the endother-
mic peak indicating mineral dissolution. However, this is
not always a desirable solution when the wettability of the
natural, uncoated mineral is required.
The final technique that proved effective to suppress
dissolution of the mineral was to conduct the heat of
immersion measurement in a wetting liquid in which the
mineral is not soluble. This may be a non-polar liquid such
as hexane, however, practical difficulties made this option
unattractive. Finally, hexanol was found to be a good
Time (minutes)
Figure 5. Heat of immersion response for quartz (top, grey) and galena (bottom, blue)
Temperature
Offset
(mK)
This shows that the linear relationship provides a good pre-
diction of the pure mineral values (albite: predicted 10.2,
actual 14.9 mJ/m2 galena: predicted 90.7, actual 95.6 mJ/
m2). These could then be used for modelling the flotation
system where input values for the hydrophobicity of the
component minerals are required. To date it has only been
possible to provide ‘proof of concept’ results for a binary
system. Extrapolating this technique to more complex sys-
tems remains a major challenge.
One further challenge with respect to acquiring heat
of immersion data deserves mention. It was found during
immersion experiments that certain minerals had both an
endothermic and an exothermic peak, and in some cases
only an endothermic peak was observed (Figure 5). This
is unexpected since the wetting interaction is an exother-
mic process. As with all calorimetric measurements, only
a total heat can be measured. The reaction with which this
response is associated may be a single reaction, or multiple
interactions. In the case illustrated in Figure 5 it was found
that two interactions were occurring, viz. the expected exo-
thermic wetting reaction, but also a second endothermic
reaction was also observed to be occurring. It was hypoth-
esized that this was due to dissolution of ions from the min-
eral since when mineral particles are suspended in water,
they undergo dissolution, the extent of which depends
upon the solubility product of the mineral and the type and
concentration of chemicals in solution. The dissolved min-
eral species can undergo further reactions like hydrolysis,
complexation, adsorption and precipitation at the surface
or in the bulk.
The first option to remove dissolution is to measure
the wetting in a saturated solution of the mineral, where
the saturation ions in solution suppress any further dissolu-
tion of the mineral. Surprisingly, this method receives only
the briefest of mentions in two studies (Zimmerman et al.,
1987 Douillard et al., 2002) and no mention at all for
studies with minerals where we have found considerable
overlap between the dissolution and wetting phenomena
(for example, Goncharuk, 2015 Salles et al., 2006 Takei
and Chikazawa, 1998). We have found that the saturation
method was not always successful in suppressing any fur-
ther ionic dissolution.
Another technique that was tested in our laboratory
was to coat the mineral with an adsorbed surfactant to sup-
press dissolution. This proved very effective for minerals
such as galena, where collector coatings above 0.5 mono-
layer coverage prevented the appearance of the endother-
mic peak indicating mineral dissolution. However, this is
not always a desirable solution when the wettability of the
natural, uncoated mineral is required.
The final technique that proved effective to suppress
dissolution of the mineral was to conduct the heat of
immersion measurement in a wetting liquid in which the
mineral is not soluble. This may be a non-polar liquid such
as hexane, however, practical difficulties made this option
unattractive. Finally, hexanol was found to be a good
Time (minutes)
Figure 5. Heat of immersion response for quartz (top, grey) and galena (bottom, blue)
Temperature
Offset
(mK)