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Colloids and Surfaces A: Physicochemical and Engineering Aspects, 74 (1993) 31 l-312 0927-7757/93/$06.00 0 1993 ~ Elsevier Science Publishers B.V. All rights reserved.
Brief Note
311
Selective flocculation of coarse particles
Brij M. Moudgil*, Sanjay Behl, T.S. Prakash Mineral Resources Research Center, Department of Materials Science and Engineering, University of Florida, 161 Rhines Hall, Gainesville, FL32611, USA
(Received 5 October 1992; accepted 23 November 1992)
Key words: Coarse particles; Selective flocculation
Selective flocculation using polymeric flocculants
has shown promise in the benefication of mineral
fines. However it has been limited in practice
because the single mineral selectivity often does
not translate to the mixed mineral system. A
number of reasons have been suggested for this
loss in selectivity namely heterocoagulation,
entrapment and entrainment, and hetero-
flocculation.
The difficulty in flocculating submicron size par-
ticles has been reported previously [l]. However
the effect of particle size on selective flocculation
efficiency has not been systematically examined. In
preliminary experiments conducted in our labora-
tory, it was observed that the coarser size fraction
of apatite could be flocculated with polyacrylic
acid rather easily. Apatite and silica were ground
separately in a ceramic ball mill and various size
fractions such as -65 + 100, -100 + 150, - 150
+200, -200 +270, -270 +325, -325 +400 and
- 400 mesh were collected. A standard mixing unit
consisting of 150-ml beakers fitted with removable
plexiglass baffles of appropriate dimensions was
employed for flocculation in this investigation. The
sample was agitated by a stainless steel turbine
impeller driven by a variable speed motor at a
speed of 100 rev min- ’ such that the entire slurry
was in suspension.
A 2 wt.% suspension of synthetic mixture (50:50
apatite and silica) of various size fractions was
prepared in beakers. Sodium silicate (2 kg t ~’ of
solids) was added as a dispersant and the slurry
was aged for about 1 h. The pH was adjusted to
9.5 and the slurry was sonicated for 30 s. At this
stage the flocculant was added and the suspension
was agitated for 2 min at 1100 rev min-‘. The
floes were separated form the suspended fines by
sieving. It can be seen from Fig. 1 that at a constant
flocculant dosage of 1 kg t ’ higher selectivity is
observed for coarser size fractions.
The possible reasons for improved selectivity in
coarser particles are as follows:
(i) less physical entrapment of coarser size
particles;
(ii) relatively higher surface coverage of coarse
100.0 f p 90.0..
g
2 60.0~-
g ‘O.O ii 60.0 -.
A’ RECOVERY
O-O mixed mjnsrol
A 0-O single tfiffl
A-A mixed mineral
90.0 o
g 60.0 .”
: 70.0 3
=i m
60.0
40.0 60.0 120.0 160.0 PARTICLE SIZE. pM
*Corresponding author. Fig. 1. Recovery and grade as a function of particle size.
particles affecting the floe characteristics, e.g. higher
floe density;
(iii) less adsorption of flocculant on coarser silica
particles, hence less heteroflocculation.
The results obtained so far prove that not only
is it possible to flocculate coarser particles, but
that it may also lead to higher selectivity.
References
I S. Yu and Y.A. Attia, Review of selective flocculation in
mineral processing. in Y.A. Attia (Eds.) Flocculation in Biotechnology and Separation Systems, Elsevier,
Amsterdam, 1988, pp. 60 I-638.
Acknowledgements
Financial support for this work by the Mineral
Resources Research Center, University of Florida
is acknowledged.