are presented on Fig. 5a. There is a striking difference in the behavior of
the reagent blends when it comes to the issue of foam stability.
The Dowfroth 200-Stypress504 blend at high frother (50 ppm) and
low polymer (100 ppm) concentration exhibits a far greater stability
than all the other reagent combinations. The relative foam collapse rates
were plotted vs. time at various depressant concentrations on Fig. 5b
and c. The lines are a guide for the eye rather than actual fits of the data.
The figures show an opposite trend in the stabilizing effect of the two
studied depressants: the Stypress 504 modified guar gum enhances the
stability of the foam when used in small concentration (100 ppm), while
the Depramin 267 has a similar effect at high concentration (1000 ppm).
The foam formed by the combination of Dowfroth 200 and Stypress 504
reagents was most stable when only a thin layer of foam, consisting of
very fine bubbles remained on the top of the liquid phase. This thin layer
was stable for several minutes.
The study of the three-phase froth collapse was not possible in the
glass column, because the visibility through the column was hampered
by the particles sticking to the column wall. Therefore the froth collapse
study was done in a laboratory scale flotation cell.
Two sets of experiments were performed, the first with the mixture
of pyroxene and slightly oxidized, less hydrophobic chalcopyrite was
ground earlier (in the figure marked as “solids”), and the second with
the mixture of pyroxene and freshly ground, un-oxidized, hydrophobic
chalcopyrite (in the figure marked as “fresh solids”). The results of these
tests are presented on Fig. 6.
The results show that in frother solution the presence of solids had a
stabilizing effect on the froth. When oxidized and therefore less
hydrophobic solids were added to the system, the stability of the
DF200-Stypress 504 froth decreased considerably, while there was not
any noticeable change for the DF200-Depramin 267 froth compared to
the two phase system.
In the presence of freshly ground, hydrophobic solids, the change in
the froth stability was even more dramatic. The stability of the DF200-
Stypress 504 froth decreased even more than in the previous case, while
an opposite effect was observed in the case of DF200-Depramin 267
solution, with a significant increase in froth stability. Wiese et al. (2007),
have found that neither the Stypress 504 nor the Depramin 267 affected
the recovery of copper from the Merensky ore even at high dosages.
Nevertheless, from the different behavior of the froth in presence of
strongly hydrophobic and less hydrophobic particles, it can be
concluded, that the combined effect of the particle hydrophobicity
and depressant type contributes to the stabilization of the froth.
Therefore the change in froth stability could be attributed mainly to
changes in rheological conditions. The suggested mechanism is described in the Discussion section.