Note: Descriptions are shown in the official language in which they were submitted.
l~ti~ ti ~
CLASSIFICATION OF SOLIDS IN AN A~UEOUS POOL
~Y MEANS OF A MOVING FLOOR
This invention relates to a method for removing coarse
solids from a mixture of particulate gangue, water, and
fine particulat~ metals or minerals. More
particularly, this invention relates ~o a method for
removing lumps, rocks, gravel and coarse sand from a
mixture of tar sand and water or from a mixture -~hat
contains particulate solids and bitumen. The intent of
the present invention is to remove coarse solids from
such mixtures before processing so that in subsequent
processing bitumen or valuable metals or minerals may
be more conveniently recovered. This invention is
particularly suitable for classifying materials into an
overflow feed which is subsequently treated for the
recovery of bitumen, metals or minerals by an
oleophilic sieve.
This invention is primarily concerned with recovering
bitumen from mined tar sands or from the effluent
streams of commercial mined tar sand plants. This
invention is also concerned with recovering metal and
mineral values from low grade ores in which the metal
or mineral values are present in very small particulate
size. Extensive deposits of tar sand~, also known as
oil sands and bituminous sands, are found in Northern
Alberta, Canada. The sands are composed of silicious
m~erial with grains generally having a size greater
than that passing a 325 mesh screen (44 microns) and a
t i ~3 ~
relatively heavy viscous petroleum called bitumen,
which fills the void be-tween the grains in quantities
of from 1 to 21 percent of total composition. (~11
percentages referred to herein are in weight percent
unless noted otherwise.) Generally, the bitumen
content of the sand is between 5 and 15 percent. A
typical bitumen contains about 4.5 percent sulfur, 38
percent aromatics, and has a specific gravity at 16
degrees C. which ranges from about 1.00 to about 1.06.
The tar sands also contain clay and silt. Silt is
defined as silicious material which will pass a 325
mesh screen, but which is larger than 2 microns. Clay
is material smaller than 2 microns, including some
silicious material of that size.
Other tar sands deposits are also found elsewhere is
the world, such as in the Orinoco heavy oil belt of
Venezuela, in many of the African countries, in Russia
and in the United States in the State of Utah. The
mineral and bitumen of these deposits vary from place
to place. For example, compared with the Alberta tar
sands, the Utah tar sands contain a coarser sand, less
clay, less water and an even more viscous bitumen.
Much of the world resource of bitumen and heavy oil is
deeply buried by overburden. For example, it has been
estimated that only about 10 percent of the Alberta tar
sands deposit is close enough to the earth's surface to
be conveniently recovered by mining. The remainder is
buried too deeply to be economically surface mined.
3a Hydraulic mining or tunnel mining has been proposed for
these deeper deposits. Generally, however, it is
considered that enhanced recovery by steam injection,
by injection of aqueous solutions, and/or by in-situ
combustion may possibly be more effective for obtaining
bitumen or heavy oil from deeply buried formations.
~ 3~
Such enhanced recovery methods use one or more oil
wells that penetrate the formation and stimulate or
recover the bitumen resource. Recovery of bitumen from
a well by steam stimulation is described in Canadian
Patent No. 822,985 granted on September 16, 1969 to
Fred D. Muggee. Depending upon the procedure employed,
enhanced recovery methods either produce mixtures of
oil and water, water-in-oil emulsions or produce
oil-in-water emulsions.
There are several well known procedures for separating
bitumen from mined tar sands. One such method is known
as the RHot Water Processn. In a hot water method,
such as disclosed in Canadian Patent No. 841,581 issued
May 12, 1979 to Paul H. Floyd, et al., the bituminous
sands are jetted with steam and mulled with a minor
amount of hot water and sodium hydroxide in a
conditioning drum through a screen, which removes
debris, rocks and oversize lumps, to a sump where it is
diluted with additional water. It is thereafter
carried into a separation cell.
In the separation cell, sand settles to the bottom as
tailings which are discarded. Bitumen rises to the top
of the cell in the form of a bituminous froth which is
called the primary froth product. An aqueous middlings
layer containing some mineral and bitumen is formed
between these layers. A scavenging step is normally
conducted on this middlings layer in a separate
flotation zone. In this scavenging step, the middlings
are aerated so as to produce a scavenger tailings
product which is discarded and a scavenger froth
product. The scavenger froth product is thereafter
combined with the primary froth product for further
treatment. This combined froth product typically
contains about 52 percent bitumen, 6 percent mineral
ti~3t~,4
matter, 41 percent water, and may contain fro~ 20 to 70
volume percent air. It resembles a liquid foam that is
difficult to pump and, for that reason, is usually
treated with steam to improve its flow characteristics.
The high water and mineral contents of the combined
froth product normal]y are reduced by diluting it with
a hydrocarbon diluent such as naptha. It is then
centrifuged to produce a tailings product and a final
bitumen product that typically contains essentially no
water and about 1.3 percent solids and that is suitable
for coking, hydrovisbreaking and other refining
techniques for producing a synthetic crude oil. The
tailings products, containing some naptha, are
discarded.
There are basically four effluent streams from the Hot
Water Process. Each carries with it some bitumen from
the ~eed; thereby reducing the efficiency of the
Process. These include the oversize material, the sand
from the separation cells, the silt and clay from the
scavenger cells and the tailings from the centrifuges.
Up to 30 percent of the bitumen in the original feed
and up to 5 percent of the naptha stream may be lost in
this manner. Much of this bitumen effluent finds its
way into large retention or tailings ponds that are
typical of the Hot Water Process. The bottom of such
ponds may contain up to 50 percent dispersed mineral
matter consisting substantially of clay and silt as
well as up to 10 percent bitumen. As disclosed in
Canadian Patent No. 975,697 issued on October 7, 1975
to Davitt H. James, this part of the pond contents,
referred to as sludge or sediment, is a potential
source of bitumen.
The ~lot Water Proce~s described in the preceeding
paragraphs separates bitumen ~rom a slurry prepared
from mined tar sands. The slurry is hot, contains
finely dispersed air bubbles and the bitumen is in the
form of small flecks. Such a slurry is amenable to
subsequent separation in the Hot Water Process, after
dilution with water, wherein bitumen forms into a roth
that rises to the top of the bath and is skimmed
therefrom. Alkaline reagents such as sodium hydroxide
are normally added in this process to give the slurry
those properties that provide for efficient flotation
of the bitumen in said water. However, in the presence
of sodium nydroxide, fine clay particles in the
effluent streams deposited into the tailings ponds do
not readily settle into a compacted solids layer. For
that reason inordinately large settling ponds are
required to contain the effluents from commercial hot
water tar sands extraction plants.
With some mined tar sands, particularly with Utah tar
2~ sands, the bitumen is so viscous that when a screen is
used to remove debris, rocks and oversize lumps from
the slurry coming from the conditioning drum, this
screen becomes coated with bitumen from the slurry.
The thus coated screen reduces the flow of slurry to
the sump and can result in considerable loss of bitumen
with the oversize discard material. To overcome this
problem inordinately large screens are required for the
removal of this gangue material, or in the alternative,
the aperture size of this screen must be enlarged. The
33 process of the present invention replaces this screen
and eliminates this problem caused by the screen
becoming coated or blinded by bitumen. The present
invention also removes coarse sand from the slurry.
313~
A tar sand separation process, which may be used as a
replacement for the Hot Water Process, has been
developed utilizing an oleophilic sieve. This process,
called the Kruyer Process, relies upon the ability of
an oleophilic sieve to separate hydrophilic material
from oleophilic material. It is described in U.S.
patents 4,224,138, 4,23~,995 and 4,392,949, and
Canadian patents 1,085,760, 1,129,363, 1,132,373,
1,141,318, 1,141,319 and 1,444,498 all of which have
issued to Jan ~ruyer.
The Kruyer Process makes use of an apertured oleophilic
sieve to separate bitumen or other liquid hydrocarbons
from sand and from other particulate solids in an
aqueous medium. In this process, the bitumen and
oleophilic solids are normally captured by the
oleophilic sieve surfaces while the hydrophilic solids
and water pass through the sieve apertures. Prior to
separation by the oleophilic sieve, the mixture to be
separated is normally screened by an oversize rejection
screen or sieve which removes any solids that are too
large to pass through the apertures of the oleophilic
sieve. When the apertures of the oleophilic sieve are
small to efficiently capture the bitumen from the
mixture, the apertures of the oversize rejection sieve
must also be small. The same problems of blinding of
the oversize rejection sieve described above for the
Hot Water Process may also occur in this application,
only more particularly so, because of the need for the
oleophilic sieve to have small apertures for effective
capture of the bitumen of the mixture. The present
invention not only conveniently removes the coarse
solids from the mixture before it reaches the
oleophilic sieve but it also removes coarse sand from
this mixture. Removal of this coarse sand tends to
improve the efficiency of the oleophilic sieve and
reduces the abrasion of this oleophilic sieve and
causes it to last longer.
The oleophilic sieve may also be used for the recovery
of valuable metals and minerals from low grade ores
especially when these metals or minerals are present in
the ores in the form of very small finely dispersed
particles. When this ore is crushed and is mixed with
water and is passed through the process of the present
invention, the fine mineral and metal particles tend to
1~ stay in suspension in the liquid product of the
invention while the coarse gangue particles are removed
as the coarse solids product. Minerals or metals may
then be recovered conveniently from this liquid product
stream through adhesion of these metals or minerals to
the oleophilic sieve by passing the liquid product
through the oleophilic sieve. Removal of the coarse
gangue solids of any mixture, with or without crushing,
prior to passing it to the oleophilic sieve for
recovery of the metal or mineral values, usually
~3 improves the efficiency of the oleophilic sieve
separator and reduces the abrasion of the oleophilic
sieve and causes it to last longer.
It is therefore an object of this invention to provide
a method of separating coarse, dense, particulate
gangue solids from a mixture containing such gangue
with water and recoverable mineral values by
classification means utilizing a moveable floor
contained in an aqueous pool.
It is also an object of this invention to provide a
means of gangue removal which does not require the use
of oversize removal devices such as screens.
~f;'`~
It is a specific object oE the present invention to
remove coarse sand from a mined tar sand ~ixture before
processing the tar sand for bitumen recovery.
Another specific object is to remove coarse solids from
low grade mined ore or placer deposits to improve the
subsequent recovery of metals or minerals from said
ore.
A still different object of this invention is to remove
coarse solids from an aqueous tar sand slurry to
improve subsequent bitumen recovery from said slurry by
oleophilic sieve separation.
Yet another object of this invention is to provide a
method for removing coarse solids from tailings,
middlings or effluents from a Hot Water Process tar
sand separation plant to improve the subsequent removal
of bitumen from these tailings, middlings or effluents
by means of oleophilic separation.
These and other objects may be accomplished by means of
an aqueous pool contained by a moving floor which
cooperate to classify the mixture into a coarse gangue
solids product which is carried away as an underflow
from the pool by the moving floor and an aqueous
suspension containing recoverable minerals, metals or
bitumen that is removed as an overflow from the pool
for subsequent treatment. The mixture to be separated
enters the pool where gangue settles to become the
underflow which is moved out of the pool by the moving
floor. Tbe remaining materials stay in suspension and
are removed from the pool as a continuous liquid
overflow stream.
C~
IN THE DRAWINGS:
Fig. 1 is a side cross sectional view of one embodiment
of a classifier of the present invention showing a
generally horizontal conical drum.
Fig. 2 is a transverse cross sectional view of the
classifier of Fig. 1 showing the contents of the drum
through section A-A of Fig. 1.
Fig~ 3 is a side cross sectional view of a second
embodiment of a classifier of the present invention
showing an inclined conveyor belt.
Fig. 4 is an enlarged sectional view of a broken away
section of the top flight of the belt of Fig. 3.
REFERRING NOW TO THE DRAWINGS:
As used in this description "particulate solids" refers
to any mixture to be classified into coarse solids or
gangue and recoverable minerals. The particulate
solids mixture is first admixed with an aqueous liquid
to form a slurry and is then classifed.
"Classification" refers to the separation of
particulate solids in an aqueous pool into two
fractions, referred to as an overflow and an underflow,
depending on their rate of settling in an aqueous pool.
"Overflow" refers to that portion of the particulate
solids that remain suspended in or floats on the
surface of the aqueous pool during classification which
suspended particulate solids or floating materials are
referred to as "recoverable minerals." nUnderflow"
refers to that portion of the particulate solids that
settle to the bottom or floor of the aqueous pool
during classification which solids are referred to as
"coarse solids" or "ganguen. "Aqueous pool" refers to
a pool of water that contains particulate ~olids
materials being classified and may contain a floating
layer of bitumen. "situmen" refers to a viscous liquid
or semi-solid hydrocarbon with a specific gravity
between 0.9 and 1.5 that is found in tar sands, oil
sands or bituminous sands and having a viscosity that
may range between that of conventional heavy oil and
heavy tar or asphalt. "Liquid" or "aqueous liquid"
refers to any water that is used in the classification
process and may include fresh water, recycle water,
process water that contains some suspended particles.
"Recoverable minerals" refers to metals, mineral ore
concentrates, silt, clay particles, and bitumen having
a particle size and/or density such that such material
will either remain temporarily suspended in or float on
the surface of an aqueous pool for removal as overflow.
"Coarse solids" and "gangue" refers to coarse sand,
gravel, lumps, rocks or any other particulate solids
that will settle to the bottom of the aqueous pool as
underflow.
The present invention is based upon the fact that
coarse gangue solids, such as sand, rocks, gravel,
etc., generally settle more quickly in an aqueous pool
than less coarse solid recoverable mineral particles,
such as silt, clay, or small metallic or mineral
particles, and will also settle more quickly than
bitumen droplets or tar particles in water. In this
manner it is possible to use an aqueous phase to
separate recoverable minerals including bitumen, from
3~ coarse gangue solids on a continuous basis in a pool of
aqueous phase, provided that the coarse gangue solids
are continuously removed from this pool as an underflow
after they have settled to the floor of the pool, and
that the recoverable minerals axe removed from this
pool on a continuous basis in a stream of liquid
overflow. Removal of the underflow from the pool is
l~ti~3~)~"~
achieved by providing a moving floor to the pool to
carry the coarse gangue solids that have settled to the
surface of this floor out of the pool. Removal of the
overflow is achieved by a continuous flow of liquid out
of the pool.
Two separate embodiments of the invention are
disclosed. In one embodiment the pool is formed on the
flight of an inclined conveyor belt. The top flight of
the conveyor belt is either troughed to form a pool or
the belt is provided with sides to contain the pool.
The aqueous particulate solids mixture to be separated
flows into this pool from one or more pipes or chutes
and flows down the incline of the conveyor flight while
the coarse gangue solids settle to the bottom of the
pool towards the surface of the conveyor belt as an
underflow. The conveyor belt is kept in motion and
moves up the incline so that the underflow is carried
up the incline and then falls off the conveyor as it
passes the conveyor endroll at the top of the conveyor
incline. The overflow, containing recoverable
minerals, flows down the conveyor belt decline and
falls off the conveyor at the conveyor endroll at the
bottom of the decline. In this manner the
classification and separation between underflow and
overflow is achieved in an aqueous pool on a moving
inclined conveyor belt. Optimum separation can be
achieved by suitably changing the incline of the
conveyor and/or changing the speed of movement of the
conveyor belt.
A stream of water may be used to wash the underflow
before these leave the conveyor flight to remove
retained overflow out of the underflow. This stream of
water may be supplied from one or more pipes or chutes
that are located higher up the incline than the pipes
or chutes that supply particulate solids mixture for
~i'3
1~
the separation to the conveyor. Small riEfles may be
molded or attached to the floor o~ the conveyor belt to
capture the settled underflow for transport uphill by
the conveyor, or the conveyor belt floor may be
textured or made rough for that same purpose.
Conventionally, sluice boxes are used to classify
particulate placer or ore deposits into two fractions
depending upon their rates of settling through water.
Gold particulates, for example, are denser than sand or
rock particles, and/ if large enough, will settle to
the bottom of the sluice box more readily than the sand
or rock particles. The sand and rock particles are
washed through the sluice box as overflow while the
gold particles settle and remain between the riffles on
the sluice box floor. However, when the gold particles
of an ore or placer deposit are very small, they do not
settle very rapidly in the sluice box but are washed
out of the sluice box with the stream of water intended
for the overflow. The process of the present invention
serves to act as a sluice box in reverse where very
small particles, for example gold, remain suspended in
the water and flow out of the classification apparatus
as overflow while the coarse sand and rock particles
settle to the bottom of the apparatus as underflow. In
the same manner, bitumen flows out of the apparatus
away from the coarse sand and rocks when separating tar
sand. In the present invention these coarse gangue
solids are removed as an underflow from the apparatus
by the conveyor belt floor of the classification
apparatus which moves up the incline in a direction
opposite to the overflow which is down the incline
through the apparatus.
In the second embodiment of the invention, the
classification pool is formed inside a generally
13
horizontal rotating tumbler or drum. The inside of
this drum consists of a forward conical section and a
rear cylindrical section. The cylindrical section
attaches to the large diameter end of the conical
section and has generally the same diameter as that
portion of the conical section, but may also have a
diameter that is larger than that. The particulate
solids mixture for classification enters the drum at
the small diameter end of the conical section as a
slurry into an aqueous pool that is contained in the
drum by one or more endwalls thereof. Aqueous overflow
liquid with suspended recoverable metal, mineral or
bitumen values flows out of the drum through the
endwall of the cylindrical portion of the drum. Due to
the force oE gravity and the centrifugal force and the
tumbling of the drum, the coarse gangue solids settle
in the conical section of the drum as overflow, flow
along the bottom wall thereoE from the small diameter
end to the large diameter end and into the cylindrical
section of the drum. The rate of rotation of this drum
is controlled such that the centrifugal forces on the
underflow solids adjacent to drum wall at the
cylindrical portion of the drum are large enough to
carry these solids out of the pool by the cylindrical
drum wall and deposit them onto a conveyor or chute for
removal. Such a conveyor or chute is mounted through
the endwall of the cylindrical drum section partly into
the drum to permit transport of the underflow, caught
by this conveyor or chute, out of the drum.
The illustrated embodiments will now be described with
reference to the drawings.
Fig. 1 illustrates the rotating drum classifier
embodiment of the invention. The classifier consists
of a generally horizontal conLcal drum 1 supported on
t~i4
14
bearings or on hoops 4, 5 which rest on rollers 20 so
as to permit tumbling oE drum 1 at any desired rate. A
motor and drive (not shown) provide the rotative power.
Drum 1 is made up of a forward conical section 2 and a
rear cylindrical section 3. Front endwall 6 and rear
endwall 7 partially close off the ends of the drum
leaving central openings 9 and 17 to a allow for the
introduction and removal of particulate solids
materials to and from the drum. Forwardly extending
baffles 14 may be mounted in the cylindrical portion of
the drum, if desired, to assist in its operation. A
conveyor, consisting of conveyor endrolls 15, a
conveyor belt 16 and a motor and drive (not shown) is
partly inserted through outlet 17 in the rear endwall 7
of the drum 1. A liquid receiver 18 is mounted under
the outlet 17 of the rear endwall 7 to collect overflow
leaving the drum. A chute or partition 19 is mounted
under the conveyor beyond the rear endwall 7 to catch
the underflow material conveyed out of the drum by the
conveyor belt 16.
Fig. 2 is a transverse view of the drum of Fig. 1 seen
through section A-A of Fig. 1. In addition to the
described items this view also shows a baffle 29 and a
supply pipe 32 for wash water 31 that is used for
washing overflow metals, minerals or bitumen out of the
underflow portion of the mixture. The view also
illustrates the approximate flow of solids and liquid
inside the cylindrical portion of the drum.
The operation of the rotating drum classifier may now
be described with reference to Fig. 1 and 2.
Particulate solids mixture 10 to be classified enters
as an aqueous slurry through opening 9 in the front
wall of the conical section through one or more feed
pipes 8 into the drum interior where it establishes
~ .
and/or adds to an a~ueous pool 12 ha~ing a liquid
leve1 21 th~t is maintained by the outlet 17 in the
rear wall 7 of the drum. The drum revolves at a rate
between 50~ and 120~ of the critical rotation r~te
which is defined as
RPM = ~2936/r] ......... (1)
in revolutions per minute where r is the drum inner
radius in feet of the cylindrical section 3 of the drum
1. The centrifugal orce and the force of gravity at
the apex of the inside wall of the cylindrical section
of the drum are equal and opposite at the critical
rotation rate. When the drum rotation rates begins to
exceed the critical rotation rate, underflow from the
mixture will commence to attach itself to the drum
inside wall at the cylindrical portion of the drum. As
the rate of rotation is increased beyond that, a
progressively thicker layer of underflow will remain
attached to the drum wall. However, in those locations
in the drum that have a small cross section, and hence
a small radius of rotation, such as in the conical
portion 2 of the drum or in the layers of underflow in
the cylindrical portion 3 that are not immediately
adjacent to the interior drum wall, the underflow
particles will only be carried along by the revolving
drum wall for a distance before they fall back into the
drum interior. Large lumps and rocks and gravel in the
cylindrical portion 3 of the drum have a center of
gravity that is some distance away from the drum wall.
This gives them a smaller radius of curvature than
small particles such as sand which can travel closer to
the drum wall. For this reason rocks and other coarse
particles fall back into the drum interior soon after
they are carried out of the li~uid level 21 of the drum
mixture unless baffles 14 are used to lift them higher.
16
The particulate solids mixture 10 to be separated
enters drum 1 via drum inlet 9 at the small end ~ of
its conical portion 2 through opening 9 and classifies
into an underflow layer 11 that settles to the inside
drum wall and moves toward and into the cylindrical
portion 3 while the finer or small particles and/or
bitumen remain in suspension as overflow in aqueous
pool 12. Some or all of the bitumen may float to the
top.
The forces that induce classification of the coarse
solids may be approximated by:
F = M.g. cos o + A.M.g.r. (RPM) ....... (2)
where F is the force on the particle in dynes causing
this particle to flow towards the drum wall, M is the
buoyed mass of the particle in grams, g is a
gravitational conversion factor, A is a conversion
constant, r is the radius of curvature in meters of the
particle moving through the drum, RPM is the value of
rotation of the drum and O is the angle (30) enclosed
in Fig. 2 between a line drawn from the center of the
drum vertically downward and a line drawn from the
center of the drum to the particle under consideration.
The forces that oppose classification of the solids in
the drum are the shear or drag forces on the particles
as they flow in the aqueous pool in the drum. These
drag forces are a function of the surface area of the
settling particle. The net effect is that dense,
large, particles settle more rapidly in the liquid in
the drum than light, small, particles. Generally, for
the mixtures that will be classified in the drum, the
coarse solids of the mixture settle to the wall of the
drum as underflow and leave the metal or mineral values
;9()~i4
in suspension as overflow. Some overflow particles,
though denser than the coarse underflow solids, are
small enough in size that they will not readily settle
to the drum wall in the tumbling mixture in the drum.
In the case of bitumen or tar, these are light enough
S that they will not settle to the drum wall but remain
suspended in the aqueous pool in the drum or float on
top of this pool.
Overflow liquid 13 flowing out of the drum through its
rear wall 7 carries the metal, mineral and bitumen
values out of the drum. The underflow 11 collected at
the inside wall of the cylindrical portion 3 are
carried out of the aqueous pool by this wall under the
combined gravity and centrifugal forces. When the
underflow is finally carried high enough that it falls
down from the drum wall, it falls onto the conveyor
flight 16 which carries the underflow 11 out of the
drum for disposal.
The flow of the liquid and of the solids in the drum 1
may be illustrated in further detail with reference to
Fig. 2. The aqueous pool 12 in the drum 1 has a
constant level 21 dictated by opening 17. Underflow 11
settles in pool 12 as described. In the cylindrical
portion 3 of the drum, the drum wall is roughened,
textured or provided with riffles to give the underflow
11 a suitable surface to attach to after settling.
Baffles 14 may further be provided at this wall to lift
rocks, lumps and gravel 13 out of the aqueous pool.
Under the influence of the centrifugal force this drum
wall carries both some liquid 22 and underflow 11 up
along the drum wall in the direction of rotation.
Howevar, the underflow solids 11 are closer to the drum
wall than the carried up liquid 22 and hence are
influenced to a larger degree by this centrifugal force
.~
~ 3~
than the liquid. As a consequence of the interaction
oE the force of gravity with the centrifugal force in
the drum, the li~uid 22 generally falls back into the
drum interior before the underflow 11 and hence
underflow is carried up higher before it falls back
down. By control of ~he drum rotation rate, at least a
portion of the carried up underflow 11 is delivered
onto the conveyor belt 16 for removal out of the drum
for disposal. Wash water 31 may be added to the drum 1
through a one or more pipes 32 at a suitable location
to wash bitumen or metal or mineral values out of the
underflow 11 before they are deposited onto the
conveyor belt 16. A baffle 29 may be inserted in the
interior of the drum 1 to separate floating bitumen
from wash water 31 or from underflow settling in the
drum. Due to the effect of the radius of curvature on
the centrifugal force in the drum, (see equations 1 and
2) in the conical portion (2) of the drum, the
underflow 11 will be lifted above the aqueous pool 12
surface 21 to a lesser degree than in the cylindrical
portion 3. This allows the mixture in the drum time
for several drum rotations in order to classify the
mixture into underflow solids and into an aqueous
overflow suspension. These underflow solids 11 are
moved axially towards the cylindrical portion 3 before
they are finally lifted out of the liquid and deposited
onto the conveyor belt 16 for removal.
The aqueous overflow suspension containing the metal,
mineral and/or bitumen values flow out of the
cylindrical portion of the drum through opening 17 in
the rear wall 7 of the drum into container 18 as the
product 13 of the classification. This product 13 may
then be withdrawn via hopper 18 for treatment in the
oleophilic sieve separation process.
3t3~
The drum classiEier is here described a~ having a
conical portion and a cylindrical portion. However, it
is also possible to use a mechanically constructed drum
structure that only has a conical portion. When such a
drum is used for classification, the centrifugal forces
on the particles adjacent to the inside wall at the
large end o~ the conical drum, and the adhesive forces
existing between the coarse particles and the drum wall
will, for all practical purposes, collect coarse solids
in the large diameter end of the drum and establish a
cylindrical inside surface for some small distance
adjacent to the rear end wall that will remain there
permanently during operation. Therefore, the
cylindrical portion here described is either part of
the construction of the drum or it establishes itself
by forming a bed of solids at the inside wall at the
large diameter end of the conical drum during operation
of the drum classifier.
The small end of the conical portion 2 may contain an
end wall 6 with a central opening 9. Alternatively,
the central inlet opening 9 may be formed by the
truncated end of the conical section 2 without an end
wall 6.
For a commercial classifier the concepts here described
will work for a very small drum and will also work for
a very large drum provided that the drum speed is
adjusted accordingly to operate between 50% to 120~ of
the critical speed defined above. Therefore, drum
classifiers may be used having diameters from l foot to
50 feet or larger at the large end, 0.1 to lO feet or
larger at the small end and l.0 to 50 feet or longer in
length.
Several of these drum classifiers may be mounted in
series; either to improve the overflow metal, mineral
or bitumen removal out of tùe underflow or to improve
: .
~t;9~3~
the remova1 oE underflow out o~ the overflow liquid
product.
Metal or mineral solids that may be classified from the
coarse particulate solids mixtures in the instant
invention as overflow may vary considerably in size but
preferably are smaller than 100 microns in size and
more preferably smaller than 50 microns.
Fig. 3 illustrates the inclined belt classifier
embodiment of the present invention. It consists of a
generally inclined conveyor belt 34 supported by two
conveyor endrollers 33 that are driven by a motor and a
drive (not shown). Normally one of the conveyor
rollers is driven and the other idles. The conveyor
belt 34 may be troughed at the top flight by the use of
appropriate training rollers (not shown) to permit
liquid on this flight to form an aqueous pool. In the
alternative, flexible sides 35 may be molded or
attached to the conveyor belt for that purpose. The
conveyor revolves such that the top flight moves up the
incline at all times. Particulate solids mixture 10 to
be classified flows onto the top flight surface 37 and
forms an aqueous pool 12 that flows down the inclined
of the conveyor belt 34. By way of illustration the
top flight is broken away and enlarged in Fig. 4 to
illustrate this pool. Underflow solids 11 fro~ the
mixture that may contain rocks, lumps and other coarse
particles settle to the bottom of the pool and onto the
floor of the top belt flight 37 wnich may be textured,
roughened or which may be provided with riffles (not
shown) to hold these solids there. The aqueous pool
portion 13 that contains suspended solids, such as
metal and mineral values and other fine particulate
matter, and/or bitumen flows down the belt incline to
fall off the conveyor near the bottom endroll into a
3t)~
liquid receiver 18 as the product 13 of the
classification. This liquid product 13 i5 then
conveyed, pumped or transported via drain 27 to
subsequent processing to remove the metal, mineral or
bitumen values from the water and from the other
suspended solids. The coarse underflow solids 11 of
the mixture, that have settled to the floor 37 of the
top flight are carried up the incline of the moving
conveyor 34 and fall off the conveyor as they pass the
top conveyor endroll and fall onto a chute or trough 40
for disposal. The coarse solids are normally discarded
as gangue but after disposal, water drained from this
gangue may be reused in the process where suitable.
Baffles 36 are provided to contain the liquid during
separation and a s-tream of wash water 31 from one or
more wash water pipes 32 may be used to wash metal or
mineral or bitumen overflow values out of the coarse
underflow solids 11 before these solids leave the
conveyor for recovery.
Thus, in both embodiments described, a pool of aqueous
liquid is used to classify an aqueous particulate
solids mixture into a coarse underflow solids product
and a liquid overflow product that contains suspended
metal, mineral and/or bitumen values along with other
suspended solids and/or that has bitumen floating on
top of the overflow. The aqueous pool is contained
by a moving floor that carries the settled underflow
and lifts it overhead out of the pool and a wash water
stream may be used to wash this underflow before it
lea~es the classification apparatus. This wash water
becomes part of the aqueous pool. The process is
continuous with particulate solids mixture continuously
entering the aqueous pool and underflow continuously
being carried out of the pool. Overflow continuously
22
Elows out of the pool Eor subsequent treatment as the
desired product.
EXAMPLE 1
A placer deposit that con-tains one ounce of gold for
every 21 tons of ore is classified by the process of
the instant invention to recover the gold values.
Hydraulic jets of water are used to loosen and suspend
the ore and a slurry pump is used to hydraulically
convey the suspension mixture thus produced to the drum
classifier of the instant invention.
The drum is 5 feet long, the conical section has a
minimum diameter of 0.5 feet and a maximum diameter of
5 feet and is 4.5 feet long. The cylindrical portion
of the drum is 5 feet in diameter, 0.5 feet long and is
welded to the large end of the conical section. The
cylindrical portion is closed off with an endwall that
has a 2.0 feet diameter central hole for liquid outlet.
A 4 feet long, 1.0 foot wide, conveyor protrudes 2.0
feet into the interior of the drum through the central
hole in the rear drum endwall and moves at a belt speed
of 2 feet per second. The drum revolves near the
critical rotation rate, which is defined as ~2936/r]
in revolutions per minute where r is the maximum inside
drum radius in feet. For the drum of this example,
this is approximately 34 RPM or about one drum
revolution every 2 seconds.
3~ Thirty tons per hour of placer deposit slurry, composed
of approximately 50% solids and 50% water by weight,
are pumped to the drum for processing. This produces,
by classification in the drum, 18 tons of coarse solids
product per hour that contains 70% solids and 30% water
and also contains one ounce of gold for every 225 tons
of coarse solids product. Five tons per hour of wash
t)~
23
water are introduced simultaneously into the same drum
to wash gold values out oE the coarse solids before
these leave the drum via the conveyor as underflow. A
total liquid product of 17 tons per hour leaves the
drum through the central hole in the rear drum wall.
The liquid overflow product is composed of 86% water
and 14% suspended solids. This product contains one
ounce of gold for every 27 tons of liquid product. The
liquid overflow is piped thereaf-ter to an oleophilic
sieve separator where it is mixed with bitumen to
permit capture of the gold values by the oleophilic
sieve while most of the water and suspended gangue
particles pass through the apertures of the oleophilic
sieve. The gold values are thereafter recovered from
the oleophilic sieve as a bitumen and gold product
after which the gold is recovered by burning this
product in a metallurgical oven with suitable slagging
reagents to produce pure gold and slag that are easily
separated thereafter.
EXAMPLE II
Tailings from an Alberta (Canada) hot water extraction
mined tar sands plant are desanded by the inclined belt
classifier as described above. The classifier is used
as a pilot plant unit for desanding 10 tons per hour of
tailings that contain 64% solids, 35% water and 1.0%
bitumen by weight which are pumped to the belt
classifier. A total of 6.32 tons per hour of coarse
solids product is produced by the belt classifier that
contains 71.2% solids, 28.5% water and 0.3% bitumen and
is disposed off into the tailings pond of the
commercial tar sands plant. Simultaneously with the
tailings, 5 tons of water per hour are introduced from
the top of the same tailings pond through a pipe into
the belt classifier to wash bitumen values out of the
coarse solids product before this leaves the belt for
;90~
disposal as underflow. A total of 8.68 tons per hour
o liquid overflow product leaves the classifier and is
pumped to an oleophilic sieve separator to recover the
bitumen. This liquid product stream con~ains 23.0~
solids 76.0% water and 1.0% bitumen. During subsequent
separation by the oleophilic sieve separator of this
liquid streaml the water and hydrophilic solids pass
through the apertures of the oleophilic sieve while the
bitumen is captured by the sieve and is recovered as
the bitumen product. An equivalent of 0.06 tons per
hour of pure bitumen are produced by the oleophilic
sieve separator.
EXAMPLE III
Mined tar sands from the Asphalt Ridge, Utah deposit
are separated in a pilot plant by mining the tar sand,
conditioning it in a mulling or conditioning drum with
steam and water to produce a tar sand slurry,
classifying this slurry in a drum classifier as
described in Example I above to remove coarse solids
and coarse sand from the slurry, and then separating
the liquid product of this drum classifier by an
oleophilic sieve separator to recover the bitumen while
discarding the other minerals.
In this pilot plant 10 tons per hour of mined tar sands
containing 90% solids, 9~ bitumen and 1~ water by
weight, are mixed with 5 tons of water and steam in the
conditioning drum to produce 15 tons of tar sand slurry
at a temperature of 80 degrees C. This slurry or
mixture is introduced into the drum classifier of
Example I through a feed pipe that introduces the
slurry through the small end of the conical drum
portion into the classifier. The drum revolves at 0.5
revolutions per second or 30 RPM. A stream of recycle
wash water of 5 tons per hour at 45 degrees C. is
: '
~;9S3~,4
introduced through a pipe through the central opening
o the rear drum wall and i9 directed into the
classifier so that it will wash bitumen out of t.he
solids accumlating at the drum wall in the cylindrical
portion of the classifier. A total of 10.02 tons per
hour of coarse solids product leave the classifier via
the conveyor belt as underflow consisting of 79.8%
solids, 20.0~ water, and 0.2% bitumen by weight. The
classifier produces 9.98 tons of liquid product that
spills out of the central opening of the rear drum wall
as overflow consisting of 10.0% solids, 81.2% water and
8.8~ bitumen. This liquid product is pumped to an
oleophilic sieve separator which recovers a bitumen
product that has a pure bitumen content equivalent to
0.85 tons of pure bitumen per hour.
Although the invention as has been described is deemed
to be that which forms the preferred embodiments
thereof, it is recognized that departures may be made
therefrom and still be within the scope of the
invention which is not to be limited to the details
disclosed but is to be accorded the full scope of the
claims so as to include any and all equivalent methods.
For example, after the liquid product leaves the
classifiers of the instant invention it may be
convenient to hydraulically transport this liquid
through a pipe or pipe line for subsequent processing
or separation and there may be an advantage to decant
off some of the water from this liquid product before
it is transported hydraulically for any long distances.
This decanted water may then be reused in the process
of the invention as required. Such refinements will
tend to improve further the economic merit of this
invention for processing ores or for recovering bitumen
from mined tar sands or from other mixtures.
.,
:
26
The process is useful to remove coarse solids from
almost any low grade ore provided that the metal,
mineral or bitumen values of the ore are of a density
or par-ticles size that causes these values to settle in
water less readily than the coarse gangue particles of
the ore.
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