111111111111111111111111111111111111111111111111111111111111111111111111111
US006199779Bl
(12) United States Patent
Mosher
(10) Patent No.:
(45) Date of Patent:
US 6,199,779 Bl
Mar. 13,2001
(54) METHOD TO RECOVER METAL FROM A
METAL-CONTAINING DROSS MATERIAL
5,192,359 3/1993 Bourcier et al. .
OTHER PUBLICATIONS
(75) Inventor: John Mosher, Golden, CO (US)
(73) Assignee: Alcoa Inc., Alcoa Center, PA (US)
( *) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.c. 154(b) by 0 days.
Heath, R.A., "The Aerofall Mill Applied to Industrial Materials",
Aerofall Mills (U.S.), Inc.
* cited by examiner
Primary Examiner-Mark Rosenbaum
(74) Attorney, Agent, or Firm---8heridan Ross pc.; Edward
L. Lavine
References Cited
Appl. No.: 09/345,332
Filed: Jun. 30, 1999
Int. CI? B02C 19/12
U.S. Cl. 241/19; 241/24.13
Field of Search 241/19, 24.13,
241/24.14,24.15,80, 97
U.S. PATENT DOCUMENTS
22 Claims, 2 Drawing Sheets
(57) ABSTRACT
A process is provided for recovering metal from metalcontaining
waste or dross. The process generally includes
the steps of comminuting the dross, and then classifying the
comminuted dross into a metal enriched large size fraction
and salt enriched small size fraction. The process further
involves the classification of the large size fraction into a
metal-containing product stream and a recycle stream.
According to the method, the portion characterized as
recycle may then be conducted to the comminution device
for further comminution. The salt enriched fraction may be
classified on the basis of size, and that portion having a
larger size may be conducted to the comminution device for
further processing. Additional steps of size classification
may also be beneficially utilized according to the process.
The disclosed process allows the efficient recovery of metal
from metal-containing dross while significantly reducing the
amount of waste salts that must be disposed of in landfills.
Williams.
Floyd et al. 241/24.13
Lance et al. .
Watanabe et al. .
Morey et al. .
Roth et al. .
Howell.
Peterson.
Brassinga et al. .
Walker.
5/1972
* 11/1973
7/1977
8/1978
1/1979
6/1983
12/1983
6/1988
10/1991
4/1992
3,660,076
3,770,424
4,033,760
4,106,627
4,137,156
4,386,956
4,418,892
4,752,328
5,060,871
5,108,587
(56)
(21)
(22)
(51)
(52)
(58)
DROSS
-- - -- - -- - -- - - --- --- - -- ---- ------ --- ---.
COMMINUTION
SIZE SEPARATION SMALL
FRACTION
L. ___________________
- ---- --- - --- - ---- ---
LARGE
FRACTION
WASTE SECONDARY SEPARATION
PRODUCT
METAL
PRODUCT
METAL PROCESSING
u.s. Patent Mar. 13, 2001 Sheet 1 of 2
DROSS
"
.....
COMMINUTION
US 6,199,779 Bl
WASTE
PRODUCT
SIZE SEPARATION
______________________________________ J
LARGE
FRACTION
"
SECONDARY SEPARATION
METAL
PRODUCT
METAL PROCESSING
FIG. 1
SMALL
FRACTION
...
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US 6,199,779 B1
2
SUMMARY OF THE INVENTION
The present invention includes a method to recover metal
from a metal-containing dross material. In preferred
embodiments, the metal in the metal-containing dross can
include aluminum, magnesium, nickel, tin, copper, brass,
zinc, gold, silver, and platinum. In a further preferred
embodiment, the metal is aluminum.
The method includes comminuting the dross in a com-
10 minution device. A salt enriched small size fraction is
removed from the comminuted dross on a size separation
basis. A metal-enriched, large size fraction is removed from
the comminuted dross on a size separation basis. Metal from
the metal enriched fraction of material is recovered using a
15 method selected from the group consisting of eddy current
separation, magnetic separation, electromagnetic separation,
density separation, electrostatic separation, electrodynamic
separation, size separation, shape separation and color separation
to form a metal product and a recycle product. The
20 metal product from this separation is preferably of high
grade. Thus, the separation is made so that the recycle
product contains particles which are substantially mixed
quality. Therefore, the recycle product contains particles
having significant amounts of metal, in addition to particles
25 which are of substantially only waste material. Typically, the
recycle product comprises between about 30% and about
75% by weight metal. The method further includes conducting
the recycle product to the comminution device for
further processing. In this manner, the mixed quality par-
30 ticles can be further comminuted to liberate the metal
portions of the particles for separation as a high quality
metal product.
In a preferred embodiment, the comminution device is a
mill, and in a further preferred embodiment, the comminu-
35 tion device is a semi-autogenous mill. According to one
embodiment, the step of removing a salt enriched small size
fraction from the comminuted dross material comprises
removing that fraction using an air sweep.
The metal in the metal-containing dross material can be of
40 any type. According to one embodiment of the invention, the
metal is selected from the group consisting of aluminum,
magnesium, nickel, tin, copper, brass, zinc, gold, silver, and
platinum. Further, the metal-containing dross material may
be an aluminum dross, a copper slag, or a brass dross.
45 According to one embodiment, the metal-containing dross
material comprises between about 50% and about 65%
metal.
In a further preferred embodiment, the described method
is conducted continuously. In an additional preferred
50 embodiment, the step of recovering metal from the metal
enriched large size fraction comprises eddy current separation.
In yet another preferred embodiment, the metal
enriched fraction comprises greater than about 65% by
weight aluminum. In a more preferred embodiment, the
55 recovered metal comprises greater than about 70% by
weight aluminum.
In another preferred embodiment, the salt enriched small
size fraction is processed by a vertical vortex classifier.
Larger and/or heavier particles from a vertical vortex clas-
60 sifier can be returned to the comminution device for further
processing. In yet another preferred embodiment, the salt
enriched small size fraction is additionally processed by
cyclone classifiers. The heavier fraction from the cyclone
classifiers can be screened to produce a metal concentrate
65 and a waste product.
According to an additional embodiment of the present
invention, the method for recovering metal from a metal-
1
METHOD TO RECOVER METAL FROM A
METAL-CONTAINING DROSS MATERIAL
FIELD OF THE INVENTION
The present invention relates generally to the recovery of 5
metal or metal concentrate from a metal-containing thermal
processing by-product or dross.
BACKGROUND OF THE INVENTION
Used aluminum beverage cans and other products made
from aluminum are often recycled to recover the aluminum
they contain for use in other products. Typically, aluminum
scrap is recycled in reverberatory furnaces. Flux is used in
these furnaces to promote the melting of the aluminum. This
flux, together with oxides, dirt, and other materials, forms a
viscous mass of dross, which floats on top of the molten
aluminum. This dross impedes the assimilation of additional
metal to the molten aluminum, and therefore must be
skimmed off of the liquid aluminum before additional solid
material may be melted in the furnace. The dross solidifies
after cooling into a mass that typically contains about 65%
aluminum metal.
Methods to recover aluminum from furnace dross include
grinding and screening the metallic dross. Grinding achieves
some separation of the metal from the portions having a high
salt and oxide content because the waste products are more
friable than the portions having a relatively high metal
content. Therefore, after grinding, the portions of the dross
constituting waste are reduced to fine particles, while those
portions having a higher aluminum content tend to resist
reduction by the mill. Accordingly, a screening operation
can achieve some separation between metal enriched and
waste products. However, previous methods for recovering
aluminum values from dross that rely on grinding processes
either do not produce a high enough grade product because
efficient separation of aluminum from waste is not effected
or have poor recoveries if sufficient size reduction is conducted
because aluminum fines are produced which are lost
with waste product.
Another method for directly recovering metal from metalcontaining
dross, used alone or in combination with
grinding, is the melting of metal-containing dross in a rotary
furnace. According to such a method, the dross is fed into a
rotary furnace, together with a large amount of salt flux. The
flux is necessary to enable the release of the aluminum metal
from the other constituents. This salt flux reports to salt cake
upon cooling, which must be landfilled. Therefore, such
methods have associated drawbacks, such as environmental
concerns.
An additional method for recovering metal from dross,
disclosed in U.S. Pat. No. 5,192,359, involves the separation
and classification of dross particles based on the electrical
conductivity of each particle. According to this method, size
separation is conducted and large particles are processed in
a furnace and small particles are subjected to a linear
electromagnetic force field provided by an inclined linear
induction motor. Particles that are dropped generally along
the length of the inclined linear motor are levitated if they
are conductive. A separator then allows the conductive,
metal-containing particles to be collected separately from
the waste particles.
Accordingly, there is a need for an economical process
that is capable of recovering high grade metal from metalcontaining
dross, and which is capable of processing large
amounts of dross. Furthermore, there is a need for a process
that reduces the amount of waste material remaining after
the metal has been removed from the metal-containing
dross.
3
US 6,199,779 B1
4
containing dross material comprises comminuting the dross
in a semi-autogenous mill having a peripheral port. A salt
enriched fraction is continuously removed from the comminuted
dross material using an air sweep. A metal enriched
fraction comprising greater than about 65% by weight metal
is continuously removed from the comminuted dross
through the peripheral port of the semi-autogenous mill. An
enriched product, comprising greater than about 70% by
weight metal, and a recycle product comprising between
about 30% by weight and about 75% by weight metal, are
formed by conducting eddy current separation on the metal
enriched fraction. The recycle product is then conducted to
the comminution device.
According to a further embodiment of the present
invention, a method for recovering aluminum from an
aluminum-containing dross is provided. According to this
method, a continuous flow of aluminum-containing dross is
provided to a semi-autogenous mill having at least one
peripheral port. The particle size of this dross is less than
about 150 mm and comprises between about 50% and about
65% by weight aluminum. The size of the aluminumcontaining
dross is reduced in the semi-autogenous mill. A
flow of air is directed through the mill to remove a salt
enriched fraction having an 80% passing particle size of
about 2000 ,um. An aluminum enriched fraction, having an
80% retained particle size of greater than about 1.0 mm and
comprising greater than about 65% by weight aluminum, is
removed from the semi-autogenous mill through the peripheral
port. Eddy current separation is then conducted on the
aluminum enriched fraction to form an enriched product
comprising greater than about 70% by weight aluminum and
a recycle product. The recycle product of the aluminum
enriched fraction is then returned to the semi-autogenous
mill for further comminution.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flow chart of the process of the present
invention;
FIG. 2 is an illustration of a preferred embodiment of
equipment used in the process of the present invention.
DETAILED DESCRIPTION
The present invention concerns a method to recover metal
from a metal-containing dross material. The method of the
present invention provides a high grade metal product, using
a continuous process. This process employs a variety of
separation methods to improve the quality of the product.
Generally, the separation steps include separation on the
basis of differences in density and separation by a secondary
separation process as described fully below.
The present invention is effective at removing metal from
a metal-containing dross material. As used herein, the term
"dross" generally refers to any waste material taken from
molten metal during processing. Thus, the process of the
present invention is suitable for any metal-containing dross.
For example, the dross can be aluminum dross (black or
white), copper slag or brass dross. Preferably, the dross
processed by the present invention is aluminum dross. As
used herein, the term "dross material" refers to not only
dross, but also to by-products of processing dross, such as a
salt cake produced by processing dross in a rotary furnace.
Moreover, the metal removed from the dross material can be
any metal in the dross material and is not limited to the metal
being processed to produce the dross. Thus, the recovered
metal can be aluminum, magnesium, nickel, tin, copper,
brass, zinc, gold, silver, and platinum. Preferably, the recovered
metal is aluminum. The dross material typically has
between about 5% by weight and about 85% by weight
metal, more typically, between about 40% and about 70%
metal, and most typically, between about 50% and about
5 65% metal.
It should be appreciated that the present invention can be
conducted to recover metals from other metal containing
materials as well. For example, the present process can be
used to recover metal from recycled refractory bricks which
10 contain significant amounts of various metals, such as copper
or platinum.
The dross material at the outset of the process can be
processed so that it has an appropriate size for handling in
the process of the present invention. Typically, the dross has
15 a particle size of less than about 150 mm.
With reference to FIG. 1, the basic steps of the process of
the present invention are illustrated. Dross material is introduced
to a comminution device in which the dross material
20 is reduced in size to liberate metal particles from waste
material. The comminuted dross material is then divided into
a salt enriched small size fraction and a metal enriched large
size fraction on a size separation basis. The metal enriched
large size fraction is conducted to a secondary separation
25 device. The metal enriched fraction is then further separated
into a metal product and a recycle product by a secondary
separation method. The metal product from this separation is
preferably of high grade and can be conducted to further
processing. Thus, the secondary separation is made so that
30 the recycle product contains particles which are of substantially
mixed quality. Therefore, the recycle product contains
particles having significant amounts of metal, in addition to
particles which are substantially only waste material. The
method further includes conducting the recycle product to
35 the comminution device for further processing. In this
manner, the mixed quality particles can be further comminuted
to liberate the metal portions of the particles for
separation as a high quality metal product.
Comminution of the dross material serves to break the
40 dross material into particles having a relatively high metal
content and particles having a relatively low metal content.
This is because particles consisting primarily of metal are
less friable. Conversely, particles having a lower metal
content, and thus a higher relative content of oxides and
45 impurities, are more friable. Therefore, the brittle lower
metal content particles are more prone to being reduced in
size by the comminution process than are the relatively
metal enriched portions. Thus, comminution reduces the
dross material to a portion having a relatively large particle
50 size characterized by having a relatively high metal content,
and a small size fraction characterized by having a relatively
lower metal content.
According to the present invention, the comminution of
the dross may be achieved in a mill. As discussed below, in
55 addition to comminution, a semi-autogenous mill can function
to make a size separation. Thus, in FIG. 1, the comminution
step and the size separation steps are enclosed by a
dashed line to indicate that these steps can be accomplished
by a single apparatus. Preferably, the mill is a semi-
60 autogenous mill. A semi-autogenous mill breaks the feed
material into smaller particles through impact and abrasion.
In such a mill, this impact and abrasion is the result of
contact with a charge of steel balls resident in the mill, and
of the interaction of particles of the material being milled.
65 Semi-autogenous mills are particularly effective in the
recovery of metal from dross material because the particle to
particle abrasion breakage of the dross particles promotes
US 6,199,779 B1
5 6
more preferably, about 1000,um, and even more preferably,
about 750 ,um. By "80% passing particle size," it is meant
that 80% by weight of the particles in the fraction would
pass through a screen of the referenced size.
The fine particles classified by a first density and size
separation, such as by a vertical vortex classifier, as having
a low density and small size may be subjected to further
processing by a density separator. This material so classified
is characterized as having a metal content lower than the
10 starting dross material. For example, the particles may be
processed by a size separation such as by one or more
cyclone classifiers, which separate the lighter (i.e. smaller
and/or less dense) particles from heavier (i.e. larger and/or
denser) particles. The heavier fraction may be screened to
15 produce a metal concentrate and a waste product. The lower
density particles may be removed as waste.
The metal enriched, large size fraction from the first size
separation is removed from the mill through a peripheral
port or ports. The removal of the metal enriched portion
20 through peripheral ports eliminates the need to periodically
stop the mill to empty it. Accordingly, the present invention
allows the milling process to be conducted continuously,
thereby enhancing efficiency. It will be appreciated that to
conduct the process continuously, without buildup of mate-
25 rial in the mill, the total inflow from the feed and any recycle
streams must be balanced against the total outflow through
the air sweep and the peripheral ports. More particularly, the
outflow through the air sweep is a function of the airflow and
the size of the airflow outlet. The outflow through the
30 peripheral ports is a function of the aperture of the ports.
Both outflows are also affected by the rate of size reduction
which is a function of the volume of steel charge and the rate
of rotation of the steel shell.
The metal enriched fraction being removed from the mill
35 has a metal content greater than the starting dross material.
More particularly, in the case of aluminum dross and other
metal-containing dross materials, the metal enriched fraction
has a metal content of greater than about 65% by weight,
more preferably, greater than about 75%, and most
40 preferably, greater than about 80%. In addition, the metal
enriched fraction typically has an 80% retained particle size
of about 1.0 mm, more preferably, about 1.5 mm, and even
more preferably about 1.75 mm. By "80% retained particle
size," it is meant that 80% by weight of the particles in the
45 fraction would be retained by a screen of the referenced size.
Following removal from the mill via the peripheral ports,
the metal enriched fraction is separated into a recovered
metal fraction and a recycle fraction. This secondary separation
is made on the basis of one or more of a variety of
50 properties which are different for the metal and for recycle
material. Appropriate secondary separation methods for
discriminating metal particles from recycle particles include
eddy current separation, magnetic separation, electromagnetic
separation, density separation, electrostatic separation,
55 electrodynamic separation, size separation, shape separation
and color separation. According to a preferred embodiment
of the present invention, eddy current separation is used.
Eddy current separation is effective in segregating the metal
particles from recycle particles because it distinguishes
60 those particles having a relatively high conductivity from
those particles that are not electrically conductive.
Generally, eddy current separation consists of subjecting the
particles to a time varying magnetic field. This time varying
magnetic field induces electrical currents (eddy currents) in
65 particles that are conductive. These currents then interact
with the magnetic field that produces them, which tends to
accelerate the conductive particles. This acceleration can be
the beneficiation of the larger, metal enriched size fraction.
Specifically, this abrasion promotes the removal of oxides
and salts that were not broken off of the metal enriched
fraction through impact.
The semi-autogenous mill typically consists of a rotating, 5
cylindrical steel shell. The interior of the shell features
protrusions or lifters to carry the material to be ground, such
as dross material, and the mill charge, such as steel balls,
towards the highest point of the mill as the shell rotates
about a center axis. The dross material and the mill charge
then drops across the center portion of the mill and impacts
the bottom. The impact of the dross material against the
bottom of the mill, as well as the impact of the ball charge
and of other dross particles on particles of dross material
resting on the bottom of the mill, causes breakage. As
described above, the portions of dross material having a
relatively high metal content resist being broken into smaller
pieces, while portions having a relatively low metal content
are more easily reduced in size. In addition, the coarse dross
particles abrade each other, promoting the removal of salts
and oxides from particles having a high metal content. This
abrasion thus has the effect of cleaning the larger, metal
enriched particles of oxides, salts, and other waste material.
The metal enriched particles of comminuted dross material
are separated from the waste particles on a size separation
basis. The size separation may be achieved, in part,
using an air sweep to remove smaller particles from a
semi-autogenous mill. Generally, an air sweep consists of a
draft fan that directs a flow of air across the mill to entrain
smaller particles. This flow tends to remove the smaller size
waste material, while leaving the larger size metal enriched
fraction in the mill. Thus, the dross material is categorized
and separated into a metal enriched fraction and a salt
enriched fraction.
Where a rotary mill as described above is used to comminute
the dross material, the air sweep may consist of a fan
that directs a flow of air through the center of the mill. The
air flow then removes the smaller size material from the mill
as the comminuted material falls across the center of the
mill. Accordingly, the air sweep results in a metal enriched
fraction of dross remaining in the mill, and a salt enriched
fraction being removed from the mill. While in a size
separation with a cross flow of air, separation is based
primarily on size differences, differences in density and
particle shape will have some effect. However, the particular
equipment and operation thereof are selected to primarily
achieve a size separation.
The fine, salt enriched particles that are removed from the
mill using an air sweep or other size separation mechanism
may be further processed to increase the metal recovery of
the system. Such further processing may include classification
on the basis of particle density and size, such as by a
vertical vortex classifier. Such classification is beneficial,
because particles having a higher density and larger size will
typically have a higher metal content than those particles
that are less dense and smaller. The portion classified as
larger and having a higher density may be beneficially
returned to the mill for further processing. Further processing
of the higher density and larger fine particles is effective
at liberating a further amount of metal from salt enriched
particles from the mill. More particularly, in the case of
aluminum dross, the portion of the salt enriched fraction to
be returned to the mill for further processing has an aluminum
content of less than about 55% by weight, more
preferably, less than about 50%, and most preferably, less
than about 45%. In addition, the salt enriched fraction
typically has an 80% passing particle size of about 2000,um,
US 6,199,779 B1
7 8
by conventional aluminum processing methods. The nonconductive
or recycle fraction from the eddy current separation
in the eddy current separator 18 includes particles of
waste material and mixed particles which include both waste
material and aluminum values. The entire recycle stream is
conducted back to the feed chute 12 for further processing
through the semi-autogenous mill 14 for recovery of aluminum
values in this stream.
As material is processed in the semi-autogenous mill 14,
an air sweep is conducted through the mill 14 and out
through an air sweep exit port 20. Smaller particles are
entrained in the air sweep and exit through the air sweep exit
port 20. The flow through the air sweep exit port 20 is
conducted to a vertical classifier 22. Relatively large and
dense particles drop from the air flow and exit the vertical
classifier bottom port 24. Such particles may include aluminum
values. This stream is conducted from the vertical
classifier bottom port 24 back to the feed chute 12 and into
the semi-autogenous mill 14 for further processing. The
20 vertical classifier 22 also includes a vertical classifier top
port for smaller and less dense particles to pass from the
vertical classifier 22. The flow of particles exiting the
vertical classifier top port is then conducted to a first air
cyclone 28. A separation is conducted in the first air cyclone
28 with larger and heavier particles exiting through the first
air cyclone bottom port 30. The particles exiting the first air
cyclone bottom port 30 may contain aluminum values, and
therefore, this stream can be concentrated, such as by size
separation 40, to form an aluminum concentrate and a waste
30 product. The first air cyclone 28 also includes a first air
cyclone top port 32 through which light particles are conducted.
These particles are considered to be waste product
and are disposed of. A further stream is conducted from the
first air cyclone 28 to a second air cyclone 34 in which a
35 further separation is conducted. Relatively larger and
heavier particles exit the second air cyclone 34 through a
second air cyclone bottom port 36, and can be concentrated,
such as by size separation 40, to form an aluminum concentrate
and a waste product. Light particles exit the second
40 air cyclone 34 through a second air cyclone top port 38 and
are disposed of.
The foregoing description of the present invention has
been presented for purposes of illustration and description.
Furthermore, the description is not intended to limit the
45 invention to the form disclosed herein. Consequently, variations
and modifications commensurate with the above
teachings, and the skill or knowledge of the relevant art, are
within the scope of the present invention. The embodiments
described hereinabove are further intended to explain the
50 best mode known for practicing the invention and to enable
others skilled in the art to utilize the invention in such or
other, embodiments and with various modifications required
by the particular applications or uses of the present invention.
It is intended that the appended claims be construed to
55 .mclude alternative embodiments to the extent permitted by
the prior art.
What is claimed is:
1. A method to recover metal from a dross material,
comprising:
60
(a) comminuting said dross material in a comminution
device;
(b) removing a salt enriched small size fraction from said
comminuted dross material on a size separation basis;
(c) removing a metal enriched large size fraction from
said comminuted dross material on a size separation
basis;
used to separate the conductive (i.e. high metal content)
particles from the recycle (i.e., salt enriched) particles.
The other separation methods referenced above (i.e.,
magnetic separation, electromagnetic separation, density
separation, electrostatic separation, electrodynamic 5
separation, size separation, shape separation and color
separation) are well-known in the art. Methods for practicing
such methods in the context of the present invention will be
apparent to those skilled in the art.
The particles classified as metal by the secondary sepa- 10
ration preferably have a metal content which is higher than
the metal enriched fraction feeding to the secondary separation
from the size separation step. For instance, the recovered
fraction from the secondary separation has a metal
content of about 70% by weight or higher. More preferably, 15
the metal content of the metal product is about 80% or
higher. Most preferably, the metal has an aluminum or metal
content of about 85% or higher. The particles classified as
metal may then be conducted to a furnace for further
processing.
Because the metal product recovered using the abovedescribed
process is relatively pure, the need to introduce
salt fluxes to the furnace receiving that product is reduced.
Thus, the amount of salt cake produced is lessened, reducing
the amount of material that is waste and that must be 25
landfilled.
The particles classified as recycle by the secondary separation
step are, according to the present invention, conducted
to the feed of the mill for further processing. This stream of
recycle product is characterized as having a significant
amount of recoverable metal, but also as having enough
waste material that the quality or purity of the metal product
stream would be degraded to an unacceptable level if the
recycle product stream were to be included. Accordingly, the
recycle product stream is characterized as having particles
with between about 30% and about 75% by weight metal,
more preferably, between about 40% and about 70% by
weight metal, and most preferably, between about 50% and
about 65% by weight metal. Examples of such particles
include those where metal is joined to a large particle of
waste, or where an oxide shell surrounds a metallic core. By
conducting the recycle product stream back to the mill for
further processing, such particles of mixed quality can be
ground more finely to separate a more pure metal fraction
from a less pure waste fraction. In this manner, as a particle
of mixed quality is conducted for a second or recycle pass
through the mill, the metal portion of the particle can be
separated from waste material, exit through a peripheral
port, and be properly classified as a high purity metal
particle in the secondary separation. The further processing
of the recycle product stream removed from the secondary
separator increases the efficiency of the process and allows
for the recovery of a high quality metal product.
With reference to FIG. 2, a preferred embodiment of the
present invention is illustrated. Aluminum dross feed material
is conducted along a conveyor 10 and into a feed chute
12. The feed chute 12 feeds the aluminum dross material into
a semi-autogenous mill 14. The semi-autogenous mill 14
rotates to cause milling of the dross material, in part, by a
steel charge (not shown). As the dross material is ground in
the mill 14, large particles exit through one or more peripheral
ports 16. The large particle size material exiting the
peripheral port 16 is conducted to an eddy current separator
18.A separation is conducted with the eddy current separator 65
18 to produce an aluminum-enriched conductive fraction as
a product. The aluminum product can be further processed
9
US 6,199,779 B1
10
10
(d) recovering metal from said metal enriched fraction by
a method selected from the group consisting of eddy
current separation, magnetic separation, electromagnetic
separation, density separation, electrostatic
separation, electrodynamic separation, size separation, 5
shape separation and color separation to form a metal
product and a recycle product; and
(e) conducting said recycle product to said comminution
device; and
(f) wherein said method is conducted continuously.
2. The method of claim 1, wherein said comminution
device is a mill.
3. The method of claim 2, wherein said mill is a semiautogenous
mill.
4. The method of claim 1, wherein said step of removing 15
a salt enriched small size fraction comprises removing said
salt enriched small size fraction using an air sweep.
5. The method of claim 1, wherein said dross material is
selected from the group consisting of an aluminum dross, a
copper slag, and a brass dross. 20
6. The method of claim 1, wherein said dross material
comprises between about 5% and about 70% by weight
metal.
7. The method of claim 1, wherein said metal is selected
from the group consisting of aluminum, magnesium, nickel, 25
tin, copper, brass, zinc, gold, silver and platinum.
8. The method of claim 1, wherein said recycle product
comprises between about 30% and about 75% by weight
metal.
9. The method of claim 1, wherein said step of recovering 30
metal from said metal enriched fraction comprises eddy
current separation.
10. The method of claim 1, wherein said recovered metal
is aluminum.
11. The method of claim 1, wherein said dross material 35
comprises between about 50% and about 65% by weight
metal.
12. The method of claim 1, wherein said metal enriched
fraction comprises greater than about 65% by weight metal.
13. The method of claim 1, wherein said recovered metal 40
comprises greater than about 70% by weight metal.
14. The method of claim 1, wherein said salt enriched
small size fraction is further processed by a vertical vortex
classifier.
15. The method of claim 14, wherein a waste product 45
from said vertical vortex classifier is further processed by
cyclone classifiers.
16. The method of claim 1, wherein said dross has a
particle size less than about 150 mm.
17. The method of claim 1, wherein said salt enriched 50
small size fraction has an 80% passing particle size of less
than about 2000 ,urn.
18. The method of claim 1, wherein said metal enriched
large size fraction has an 80% retained particle size of
greater than about 1.0 mm.
19. A method to recover metal from a dross material,
comprising:
(a) comminuting said dross material in a semi-autogenous
mill having a peripheral port;
(b) continuously removing a salt enriched fraction having
an 80% passing particle size of about 2000 ,urn from
said comminuted dross material using an air sweep;
(c) continuously removing a metal enriched fraction comprising
greater than about 65% metal from said comminuted
dross material through said peripheral port of
said semi-autogenous mill;
(d) conducting eddy current separation on said metal
enriched fraction to form an enriched product comprising
greater than about 70% by weight metal and a
recycle product; and
(e) conducting said recycle product to said comminution
mill.
20. The method of claim 19, wherein said dross material
contains aluminum.
21. The method of claim 20, wherein said dross material
contains between about 50% and about 65% by weight
aluminum.
22. A method for recovering aluminum from an
aluminum-containing dross, comprising:
(a) providing a continuous flow of said aluminumcontaining
dross having a particle size of less than
about 150 mm and comprising between about 50% and
about 65% by weight aluminum to a semi-autogenous
mill having at least one peripheral port;
(b) reducing the size of said aluminum-containing dross in
said semi-autogenous mill;
(c) directing a flow of air through said mill to remove a
salt enriched fraction having an 80% passing particle
size of about 2000 ,urn;
(d) removing an aluminum-enriched fraction having an
80% retained particle size of about 1.0 mm and comprising
greater than about 65% by weight aluminum
from said semi-autogenous mill through said at least
one peripheral port;
(e) conducting eddy current separation on said aluminumenriched
fraction to form an enriched product comprising
greater than about 70% by weight aluminum and a
recycle product; and
(f) returning said recycle product of said aluminum
enriched fraction to said semi-autogenous mill.
* * * * *