Note: Descriptions are shown in the official language in which they were submitted.
COLUMN FROTH FLOTATION
BACKGROUND OF THE INVENTION
This invention relates to froth
flotation and, more particularl~, to column froth
flotation for beneficiating mineral ores and the like.
Froth flotation has been used to
beneficiate a variety of mineral o~es and to effect
separation of various other materials for many
years. Froth flotation involve~ the separation of
particles from each other in a liquid pulp based on
differences in hydrophobicity. The pulp is aerated
by introducing a plurality of minute air bubble~ into
it. The air bubble~ tend to attach to the floatable
(hydrophobic) particles and cause those particles ~o
rise to the surface as a froth product which
overflows from the flotation device, leaving behind
the non-floatable thydrophilic) par~icles.
An article entitled "Flotation
Machines" in Mininq Maqazine, January, 1982, page 35,
describes several different types of flotation
devices and proces~es u~ed for benefieiating
minerals. In so-called column flotation, a
conditioned pulp i8 introduced into the midzone of a
rela~ively tall column, pressurized air is introduced
through a diffuser in the bottom of the column, and
wash water is fed into the top of ~he column.
fraction containing the floatable pa~ticles, usually
the mineral values, overflows from the top of the
column and a fraction containing the non-floatable
particles, usually the gangue, is discharged from the
bottom of the column by gravity or a pump. Examples
of p~ior column flotation devices and processes are
described in Canadian Patents 680,576 and 694,547,
Canadian Chemical Processinq. February, 1965, pages
55-58, and E & MW, Volumn 66 No. 1, pages 76-78, 83.
Tha air diffusers in flotation columns
have a tendency to become plugged, particularly when
a lime depressant is used. causing an uneven
distribution of air throughout the pulp. Also, the
small air bubbles generated at the bottom of the
column tend to enlarge as they rise toward the top
due to a change in static pressure within the column,
resulting in a reduced surface contact between the
air and particles. SeveIal differen~ approaches have
been used to alleviate this problem, including the
u~e of hydrophobic materials and, instead of using a
diffuser, introducing the air as a fine `dispersion in
water. The latter approach is disclosed in U.S.
Patent 3,371,779.
SUMMARY OF T~E INVENTION
An ob9ect of the invention is ~o
provide a simple, economical froth flotation device
and process capable of separating floatable particles
from an aqueous pulp of a mixture of floatable and
non-floatable particles with a minimum number of
flotation stages.
Another object o~ the inven~ion i8 to
provide a f~oth flotation device and process which
produces increased air-to-particle contact.
A further object of the invention is to
provide a froth flotation device and process which
reguires mi~imal amounts of water and energy.
A still further object of the inv~ntion
is to provide a froth flotation column which does not
require an air diffuser having a tendency to become
plugged during operation.
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Other objects, aspects and advantages
of the invention will become apparent to those
skilled in art upon reviewing the following detailed
description, the drawing and the appended claims.
The invention provide6 a froth
flotation dsvice including a tubular flotation
column, packing means disposed in the column defining
a large number of small flow passages extending in a
circuitous pattern between the upper and lower
portions o~ the column, pulp feed means for
introducing an aqueous pulp into the column a~ an
intermediate location for flow through the flow
passages, means for introducing wash water into the
upper portion of the column for downward flow through
the flow passages, means for introducing a
pressurized inert gas into the lower portion of the
column for upward flow throu~h the flow passages0
means for discharging a froth fraction containing
floated particles of the aqueous pulp from the upper
portion o~ the co}umn, and means for discharging a
tailing fraction containing unfloated particles of
the agueous pulp from the lower portion of the column.
An aqueous pulp containing a mixtuLe of
floatable and non-floatable particles is introduced
into a column. The iner~ gas, preferably air, is
broken into fine bubbles as it is forced upwardly
through the flow passages in the packing. These
bubbles intimately contact the floatable particles
and form a froth concentrate or float fraction which
contains the floatable particle~ and ovsrflows from
the top portion of the column. The wash water,
flowing through the flow pa~sages in the packing
Gountercurren~ly to the float fraction, removes
entrained non-floatable particles from the float
.
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fraction and a tailing fraction containing the
non-floatable particles is withdrawn from the bottom
of the column.
In one embodiment, ~he packing
comprises a plurality of vertically spaced plates and
spacer means for laterally spacing the plates apact
to define a plurality of small ~low passages between
adjacent plates. The spacer means can comprise rows
of corrugations on each of the plates, preferably
extending diagonally relative ~o the horizontal.
In one embodimen~, separate, vertically
adjacent sections of the plates are provided. These
sections preferably are oriented so that the vertical
planes of the plates in one ~ec~ion are angularly
related ~o the ~ertical planes of She plates in the
adjacent section.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. l is a schematic represen~ation o~
a froth flotation column embodying the invention.
Fig. 2 is an exploded, perspective view
of a portion of the corrugated plates making up one
section of packing for the column illustrated in Fig.
1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The column flotation device and process
of the invention can be used to separate a wide
variety of materials in a broad range of particle
sizes. It is particularly adapta~le for separation
of mineral values from the ganyue i~ fine-grained
ores, such as low-grade, oxidized taconite ores from
the Lake Superior area. T~e invention will be
described in connectior, with that applicatisn.
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The flotation device 10 provided by the
invention includes a tubular column 12 having an
upper portion 14 and a lower portiop 160 a pulp inlet
18 for introducing a conditioned aqueous slurry or
pulp of an oxidized taconite ore into the column at
an intermediate location. a water inlet 20 for
introducing wash water into the upper portion of the
column 12, and a gas inlet 22 for introduGing a
pressurized gas, such as air, into ~he lower portion
16 of the column 12.
The column 12 can be generally upright
or vertical as illustrated in Fig. 1 or inclined at
angle to the vertical. The column 12 is partially
filled with a packing 24 which defines a large number
of small flow passages extending in a circuitous or
tortuous pattern between the upper and lower portions
14 and 16. Wash water introduced into the upper
portion 14 of the column 12 through the water inlet
20 flows downwardly through these flow passages.
Pressurized air introduced into the lower portion ?6
of the column 12 through the gas inlet 22 is forced
upwardly through these flow passages,
countercurrently to the wash water and the portion of
the aqueous pulp descending through these flow
passages.
A~ ~he air passes upwardly through
these flow passages, it is broken into fine bubbles
of relatively,uniform size, These rising bubbles
intimately contact the particl2s of the aqueous pulp
in the flow pa6sages of the packing 24 to produce a
froth concentrat0 or float fraction containing
primarily the floatable particles and a minor amount
of essen~ially non-floatable particles entrained in
the froth. The air bubbles cacry the froth
concentrate 25 upwardly into a froth compartment 26
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in the upper portion of the column 12. The froth
concentrate 25 is discharged from the froth chamber
26 by overflowing therefrom through an outlet 28.
Wash water descending through the flow
passages in the packing 24 induces entrained
non-floatable particles to separate ~rom the froth
concentrate and drop by gravity (i.e.. sink) through
these flow passages. While the wash water can be
introduced into the column 12 in any convenient
manner, it preferably is introduced into the froth
chamber 26 and above the top surface of the froth
concentrate 26 through a spray nozzle 32 centrally
disposed in the top of the column 12. The spray
nozzle 32 distributes multiple streams of wa~e{ over
the froth in the froth chamber 26, thereby insuring a
more uniform contact of the wash water with
non-floatable particles in the froth concentrate 25
and also a more uniform distribution of the wash
water through the flow passage~ in the packing Z4.
A tailing fraction 33 containing the
non-floatable particles in the agueous pulp collects
in a tailing chamber 32 at the bottom of the column
12 and is discharged therefrom through an outlet 34.
Although not particularly critical, the tailing
chambar 32 preferably is conically shaped as
illustrated in Fig. 1 to promote discharge of the
tailing fraction. The tailing fraction preferably is
withdrawn through the outlet 34 by a conventional
variable flow pump 36.
While the colu~n 12 can have various
cross-sectional con~iguratio~s, in the specific
construction illus~rated. it has a square cross
section. The cro s sectional dimensions and length
of the column 12 are governed by the type of aqueous
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pulp being treated, the particular type of packing
used, the desired throughput, and other variables
familiar to those skilled in the art.
The packing 24 can be in a variety of
S different forms capable of providing a substantially
plugged flow condition and defining a large number of
flow passages extending in a circuitous or tortuous
pattern between the upper and lower portions of the
column 12. These flow passages cause the air bubbles
to break up and combine into fine bubble6 of
relatively uniform size, thereby maximizlng intimate
surface area contact with the floatable particles.
Sui~able packiny includes con~entional packing
materials used in ~acked tower for vapor-liquid
trans~er operations, such as Raschig rings, Berl
saddles, partition rings, and the like.
In the preferred embodiment
illustrated, the packing 24 consists of a plurality
of sections 38a-38f of ve~tical extending plates 40.
Each section includes a plurality of the plates ~O
and spacer means for laterally spacing the plates 40
apar~ to define a plurality of relatively small flow
passages between adjacent plates 40. In the specific
construction illustrated, such spacer means comprises
uniformly spaced rows of corLugations 42 on each
plate 40. The corrugations 42 preferably extend
diagonally, e.g., at an angle of approximately 45 to
the hoLizontal, to eliminate vertical flow passages
of subsSantial length. The angular orienSation of
She coIrugations can be varied to control flow
through the flow passage. For instance, this flow
can be increased by increasing the angle of the
corrugations 42 to the horizontal.
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In order to further enhance the
circuitou~ or toLtuous pattern of the flow passages
defined between adjacent plates 40, the corrugations
42 of alternate plates 40 preferably extend in the
opposite direction as illustrated in Fig. 2. That
is, the corrugations on one plate extend at an angle
to the corrugations on the next plate. Also,
alternate sections are positioned so that the
ver~ical planes of the plates in one section are
angularly related (e.g., at about 9O) to the
vertical planes of the plates in the adjacent
section. Referring to Fig. 1, the vertical planes of
the plate~ 40 in sections 38a, 38c, and 38e extend
perpendicularly to the plane of the page and the
vertical planes of the plates in sections 38b, 3~d
and 38~ extend parallel to the plane of the page.
~ he packing ~ections 38c and 38d in the
vicinity of the pulp inlet 38 preferably are spaced
apart to provide a substantially unobstructed feed
compartment OL chamber 44. The packing sections 38a,
38b, and 38c above the feed chamber 44 make up the
primary cleaning section of the column 12 and ~he
packing sections 38d, 38e and 38f below the feed
chamber 44 make up a scavenging section wheLein the
floatable particles are separated from the descending
tailings.
In a typical operation, an iron ore,
such as oxidized taconite~ is comminuted into a
particle size suitable ~or liberation of the mineral
values and for froth flotation. An aqueous slurry or
pulp of the particles i8 intloduced into a stirred
conditioning ve6~el 46 for the addition and admixing
of suitable flo~ation reagents. If silica or gangue
is to be floated (reverse flotation), a cationic
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collector or an anionic collec~or (for calcium
activated silica) is added to and mixed with the
aqueous pulp in the conditioning vessel 4&. If iron
oxide is ~o be floated, a suitable anionic collector,
such as a fatty acid type collector, is added to and
thoroug~ly mixed with the aqueous pulp in the
conditioning vessel 46.
~ arious suitable conditioning reagents
can be used depending primarily on the material being
treated and the type of flota~ion. The conditioning
reagent disclosed in U.S. Patent ~,132,535, is
particularly effective for iron ore6 ~hen ~n anionic
collect~r is used. That conditioning reaqe~t is
formed by mixing a polyvalent metal salt with an
alkali ~etal silicate. The conditioning reagen.~ is
usually added to and thoroughly mixed with ~he pulp
pr;or to the addition of the collector. After the
collector has been added to the conditioning ~essel
46, the pulp is mixed for a suffic;ent time to lnsure
uniform dispersi~n of the collector throughout the
pulp . ~
In some cases, it may be necessary to
add a small amount of fuel oil and/or a conventional
frothing agant to the pulp. When used, the fro~hing
agent can be incorporated into the pulp before,
after, or togethec with the collector. If the
frothing agent is added separa~ely, the pulp is mixed
for a sufficient time to insure uniform dispersion of
the frothing agent throughout the pulp.
Following conditioning, the pulp is
withdrawn ~rom the conditioning vessel 46 by a pump
4~ and introduced into the column through the pulp
inlet 18.
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The flow rates of the ore pulp, the air
and the wash water can be adjusted to ob~ain a
material balance which provides the most effective
separation of the floatable particles (e.g., iron
oxide) from the non-floatable particles (e.g.,
gangue).
The device and proces6 of the invention
have several advantages over conventional flotation
devices and processes. They provide all the
advantages of conventional flotation columnc and
further provide increased air-to-particle contact,
eliminate the need for a pecial device in the bottom
of the column for generating fine air bubbles, and
require less water and energy. More importantly,
floatable particles, such as iron oxide, can be more
effectively separated from non-floatable particles,
such as yangue, with single stage flo~ation. That
is, a conventional Plotation column usually requires
at least two flotation stages to recover the same
amount of iron oxide from a low grade iron ore.
In addition ~o being used for single
stage flotation, the device of ~he in~ention can be
used in combination with conven~ional flotation
machines and two or more can be used in series.
The following examples are presented to
illustrate the invention and are not ~o be construed
as limitations thereof.
EXAMPLE l
A series of laboratory tests were run
on an experimental column consisSing of a 2-inch I.D.
tube, 8 feet long and almost entirel~ packed with
2-inch long conventional brass tower packing
cylinders.
~2~ 6~ .
Samples of -10 mesh oxidized taconite
ore (obtained from the Cascade deposit owned by
Clevel2nd-Cliffs Iron Company) were ground batchwise
at 60 weight % solids in a rod mill in the presence
of water for about 20 minutes to produce a slurry or
pulp o~ about 80 weight % passing 500 mesh. The pulp
was co~ditioned with a conditioning ceagent prepared
in acc~rdance with U.S. Patent 4,132,635 and the pH
was ad~usted to 8.8 by adding soda or sulfuri~ acid.
The resulting pulp samples were separately introduced
- into a stirred container where a fatty acid collector
(PAMAK*~, No. 2 fuel oil, and a frothing agent were
added and mixed into the pulp.
The conditioned pulp samples containing
20% so~ids were continuously pumped from the stirred
contai~er into the mid-section of the column a~ a
rate o~ about 130 cc/min. Water was introduced near
the top of the column at a flow rate of about 50
- cc~min_ and air was introduced near the bottom of the
column at a flow rate of about 8 l/min.
Samples of the concentrate and
tailings, respectively ta~en from the top and bottom
of the column~ were collected and analyzed for iron
conten~. Results from the representative tests are
~ummarized in Table I.
These results demonstrate the superior
separa~ion e~ficiency of a flotation column arranyed
and operated in accordance with the invention, even
though only a single flotation stage is employed.
EXAMPLE 2
A series of pilot plant tests were run
on a column arrangPd generally in the manner
illustrated in Fig. 1 and a conventional 8-stage
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WEM`CG Fagergren flotation machine. The column was 20
feet ~all, had a 7 l/q in. ~ 7 1/~ in. square cross
section, and included six 3-foot sections of packing
plates. Each packing section was packed with 5
layers of corrugated plates. The plate corrugations
were 1/8 inch high and extended a~ about 45 to the
horizontal, and alternate layers or sec~ions were
oriented at 90 to each other.
An oxidized taconite ore was ground to
about 75% -500 mesh and formed into a pulp. A
conditioning reagent prepared in accordance with U.S.
Patent 4,132,635, an anionic collector (PAM~-4), and
No. 2 fuel oil were mixed into the pulp. One stream
of the conditioned pulp containing about 20 weight %
solids was pumped into the ~eed compartment of the
column at a feed rate of about 150 lbsfhr and another
stream of the same pulp was processed in the
conventional flotation machineO Air at a pressure of
about 10-12 psig was introduced into a column through
~0 the gas inlet at a rate of about 300-500 ft3~hr and
wash water was s~rayed into the froth chamher a~ a
rate of about 30-50 gal/hr.
Samples of the froth concentrate and
tailings from the column and the conventional
flotation machine were collected and analyzed for
iIon content. The results from these tests are
summarized in Table II. Under the "Mach7ne Used"
heading in Table II, "A" designates the device of the
invention and "B" designates the conventional
flotation machine.
From these results, it can be seen that
single stage flotation with a column and process of
the invention produces higher grade concentrates
and~or higher recove~ies than eight stages o a
conventional flotation machine.
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From the foregoing description. one .
skilled in the art can easily ascertain the essential
characteristics of the invention, and without
departing from the spirit and scope thereof, make
5 various modif ications and changes to adapt it ~o
variou~ usages and conditions.
