he top of the foam. By the visual observation of the penetration time,
one could obtain some additional information on the structure of the
foam.
It was observed that for the foam formed by the DF200-Stypress 504
blend, the hydrophilic pyroxene particles fell through the foam more
easily, while the freshly ground, hydrophobic chalcopyrite stayed on the
surface and only slowly sank into the bulk phase. In the case of the
DF200-Depramin 267 blend, both particle types stayed on the surface
for a longer period than in case of the guar and sank into the bulk phase
much slower. This means that the guar foam sets less resistance against
the penetration of the particles than the CMC foam that could be caused
by the lower liquid content.
3.3. Surface tension measurements
In order to map the possible reasons that cause the difference in
behavior of the two depressants described in the previous sections,
surface tension measurements were performed.
The surface tension is plotted vs. the concentration of the Dowfroth
200 frother in absence and presence of increasing concentration of
Stypress 504 or Depramin 267 depressant in Fig. 8.
The figures clearly show that both depressants have an effect on the
surface tension, even if this effect is not very strong. The largest change
in the surface tension caused by the reagents is only about 1.5 mN/m,
even at the highest depressant concentration. The effect is somewhat
stronger and follows a clearer trend in the case of Depramin 267, while
in the case of Stypress 504 the variation of the data is quite large. It has to
be noted that in the surface tension range close to the surface tension of
water, the surface tension measurement usually shows quite a high
variation in other surfactant systems as well, therefore the variation of
the data in these measurements is not very surprising. Nevertheless it
can be concluded that in the majority of the tested concentration
combinations, the Stypress 504 depressant decreased the surface
tension compared to the pure water or to the case when only frother