THE EFFECT OF PARTICLE SIZE ON FROTH STABILITIES OF DIFFERENT ORES
ABSTRACT
Belinda McFadzean*, Innocent Achaye, Jenny Wiese, Tadiwanashe Chidzanira, Martin Harris
*
Corresponding author: Centre for Minerals Research, University of Cape Town, Cape Town, South
Africa, belinda.mcfadzean@uct.ac.za, +27216505528
Froth stability has an overriding effect on metallurgical recovery and grade for many ore types. Froth
recoveries of less than 10% are common for low stability froths such as those in sparsely mineralized ores
or in cells at the back end of flotation circuits. It is well known that, aside from chemical factors such as
frothers and electrolytes, the mineral particles themselves have the dominant influence on froth stability.
The particle properties of size and hydrophobicity are expected to have the greatest effects on froth
stability. The aim of this study was to understand the effects of particle size on froth stability and to
quantify these relationships.
The study compared a synthetic ore of pyrite and quartz, with carefully controlled size ranges and
hydrophobicity, with conventionally milled platinum-bearing UG2 ore and the bulk reverse flotation of
hematite ore. A novel bench-scale continuous column flotation cell and continuous mechanical hybrid cell
with large relative froth volumes, as well as a three-phase froth stability column were used to characterize
the froths.
It was found that froth stability could be related to the concentrate particle surface area by a Langmuir-type
relationship. This is indicative that the mechanism by which particles stabilize the thin films in froths is
similar to the mechanism by which surfactants lower surface tension. Different froth stabilities were found
for different ores and this was thought to be the result of different particle sizes and distributions, which
resulted in different packing densities in the thin films and Plateau borders. Interestingly, there was a clear
relationship between the feed particle size and the froth stability even though froth stability was dependent
on the concentrate particle surface area. It seems that the feed particle size is a good predictor of the
surface area of particles in the concentrate. Concentrate particle size did not show a clear relationship with
froth stability since it was already shown that it is both the size and the amount of the particles in the froth
that contribute to the stability.
80
Synthetic ore
UG2 ore
Synthetic ore model
UG2 ore model
Froth stability (s)
70
60
50
40
30
20
10
0
0
10
20
30
Concentrate surface area (m2)
40
Figure 1 – Froth stability versus concentrate particle surface area. The markers are experimental data
points and the lines are the fitted Langmuir-type model.
KEYWORDS
Froth stability, particle size, particle hydrophobicity