Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention
~ THIS invention relates to a froth flotation cell.
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The present invention arose from the requirement of having to separate
mineral particles as large as - 3 mm by means of froth flotation.
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Flotation from - 3 mm feeds is unusual. In fact flotation feeds seldom
exceed 250 microns for metal ores.
Summary of the Invention
According to the invention a method of recovering coarse particles by
froth flotation comprises agitating a conditioned pulp, to which a
suitable frother and collectorhave been added, for turbulent vertical
; flow, injecting air bubbles into the path of pulp flow in such a way
that the only size~ reduction of the bubbles is due to shear~by the pulp,
baffling the pulp flow to ensure a quiescent interface between pulp and
froth, and collecting the froth from the interface.
~ ~ The method also includes the steps of introducing pulp to and withdrawing
;~; the pu1p from the system in d zone of relative pu1p agitation.
According to the invention a flotation cell comprises a tank, a driven
impeller at a low level in the tank, a cover above the impeller minimizing
the entry of fluid from above, and a series of injec~ion points for
co~,pressed air around the axis of the tank and above the level of the
cover.
.0 Further according to the invention the tank is round cylindrical and
over,low of froth is around the entire perimeter of the top of the ta
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The invention also provides that the tank has a series of radial ax;ally
extending ba~fles projecting inwardl~y from the periphery of the tank.
Furthermore the invention provides that pulp be fed into the tank below
the stagnation zone of the radial flow from the impeller and that it be
withdrawn from the t;nk in that zone.
Description of the Drawing
It is a section through a froth flotation cell according to the invention.
Description of a Preferred Embodiment
- The illustrated cell has a round cylindrical tank 10 in the bottom of
which there is a driven impeller 12 rotated by means of a shaft 11. The
. impeller 12 has four radial vanes and is of standard design. However,
above the impeller 12 there is a cover 13 which reduces the entry of
, air into the impeller 12 from above. ~~
The tank 10 has an overflow launder l~ around its entire ~op perimeter
for collecting froth.
, At a 1evel above the cover 13 there is a ring main 15 for injecting com-
pressed air into the tank 10. ~ ~
An inlet pipe 16 leads to a level below the impeller 12 and an outlet 18
leads from the same level as ~he impeller 12. Note that the outlet 18
is from,the annular stagnation zone of the radial flow from the impeller
12 while the inlet 16 leads to a level below that zone.
2Q ~ A series of baffles l7 project radially inwardly -from,the w,all of the
tank 10. The axial extent and the radially inward extent of the baffles
17 require adjustment for various circumstances to ensure that at the top
of the tank there is a quiescent pulp-froth interface. It has been
found beneficial to have the upper parts or the baffles 17 inclined to the
vertical. The angle of inclination may be between 10 and 45. The ``
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direction of inclination is so chosen that, when viewed from above, the
inclined sections of the baffles spiral downwardly in the same direction
as the direction of rotation of the impeller.
Air is injected from the ringmain lS where the turbulence created by the
radial flow from the impeller hitting the wall of the tank 10 provides
some shear to reduce the size of the air bubbles and the rotational flow
created by the impeller helps to ca`rry the air bubbles radially inwards
towards the centre of the tank so that they are reasonably well distribu'ced.
~;~ Sincé the air enters the cell through the ringmain 15 which is situated
-~ l0 above the cover 13,` and since the movement of air is generally up~ards,
;~ there~is little tendency for~air to enter the volume swept by the impeller,
thus ensuring that the impeller performs its primary function of
maintaining the particles-in suspension.
Since the shear forces which produce the bubbles are lower than they are
~ in the conventional cell in which air~is introduced into the impeller zone
with a consequent drop in mixing efficiency, the air bubbles produced~ - -
are~larger and thus better suited to the flotation of particles of a size
for which~the cell is intended.
The circular overflow weir formed by the top of the tank~lO maximlses the
~ potentlal length of~the~weir,
Experimental Results.
Thus far tests on a prototype cell have been restricted to sizes up to
20~ However, gold and~other valuable constituents of a Witwatersrand
ore have been floated successfully from - 2,5 mm~material over pulp
densities ranging from l5 to 55% solids by~mass without sanding out
~ taking place. Varying the pulp density has~been found to have only a very
slight effect on air demand, power requ;remènts and rate of flotation.
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-Example
:~ As an example of the use of the cell, qold and uranium were floated from
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a material grading 100% - 2,36 mm 50% - 150 microns in three different
types of cell. The conditions of flotation were the same in each case,
namely 35% solids, 9 minutes batch flotation, and 100 g of potassium
amyl xanthate and 50 g of AF 55 frother added per ton of solids, the
additions ~e;ng made in the ratios 5:3:2 at the start, after 3 minutes
and after 6 minutes vf flotation respectively. The three cells were a
laboratory Fagergren machine normally of 5~ capacity, but reduced to 1,7
for the purposes of the test, operated at a power density equivalent to
35 kW/m3; a 20Q cell to the design described herein, operated a~ a power
density equivalent to 10 kW/m3 excluslve of the power required for com-
pressing air (30Q/min at a pressure of 25kPa); and a 170 ~ Fagergren cell
operated at a power density equivalent to 15 kW/m3. The 170Q cell
required manual stirring to prevent sands building up to the point where
the impeller stalled. The results may be summarised as follows:-
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Cell 1,7~ 20~ 170
% Solids in feed 35 35 35
Power density kW/m3 35 10 15
% of solids in feed floated 33,1 34,2 18,5
% of gold in feed floated 82,6 86,2 42,7
~ 20 % of uranium in feed floated 68,4 70,8 59,3
(~ ~ It ;s apparent that the novel cell suspends the coarse solids at a far
lower power than conventional cells, and that it can yield at least as
good a récovery of valuable minerals as in conventional cells, when the
conventlonal cells are operated under conditions which suspend the coarse
solids satisfactorily
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