FIELD OF INVENTION
This present invention relates to recovery of alumina by processing the dross generated during the
process of manufacturing aluminium metal.
BACKGROUND OF INVENTION
Aluminium is a metal which is abundantly present on earth. Aluminium present in the form of its salts
including aluminium oxides and aluminium silicates comprise about 8% of the earths crust. Aluminium
metal is known to be extracted from alumina which intern is extracted from bauxite. India is considered
to be the fifth largest producer of alumina in the world. India is also known to account for
approximately 7.5 % of the world's bauxite reserves. Aluminium is known to be the third most
abundant element on earth. It is also considered as one of the most used metals after steel. Due to
India's booming economy the demand for aluminum has been increasing considerably. Aluminium is
primarily used in the power, transportation, construction and packaging industries.
Production of pure quality aluminium involves consumption of large amounts of power. Thus,
aluminium manufacturing facilities are usually located within vicinity of areas with low cost of power.
Coal is one major resource which is used for power generation in India. Further, coal being a nonrenewable
resource is available in limited quantity and is bound to run out of stocks in the future. It is
estimated that only one fourth of aluminium used worldover is recycled. Moreover, as already stated,
production of aluminium metal involves consumption of large amount of energy supplied through
power. Hence, it is desirable to have a method of recycling aluminium which allows recovery of
alumina from the byproducts formed during smelting process used for manufacturing aluminium metal.
The recovered alumina can then be used along-with fresh alumina for production of aluminium metal.
Dross comprises of various aluminium salts present in the form of oxides, nitrides, carbides etc.
Aluminium comprising dross can be formed during formation, processing or recycling of aluminium.
Dross is generated due to the oxidation of molten aluminium metal in hot atmospheric conditions in
melting and holding furnaces. Dross generated usually contains 30-90% of molten aluminium in pure
form, depending on technique and type of furnace. The dross formed may vary in size from small sized
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lumps approximating to one inch of diameter to larger sized lumps.
Dross is known to be recycled with either mechanical or chemical processes. Though the mechanical
means have been known to be inefficient, but they also prove to be non-toxic and environmentally
sensitive as opposed to chemical means of dross treatment.
The practice of secondary aluminium production by recycling and utilizing scrap treatment is already
known in the industry. Scrap treatment of aluminium using mechanical means involves physically
separating aluminium metal from other fonn of scrap using hammer mills, ring crushers etc. to
breakdown aluminium containing scrap into smaller pieces and uses magnetic separation for separating
iron from aluminium. However, the said process is a generic process used for treating aluminium scrap
obtained from consumers and industry alike and is totally different from the case of treating dross
generated during the process of aluminium manufacturing.
Furthennore, the process of alloying of metals is also known to be perfonned in the metallurgical
industry. Using alloy agents to combine with aluminium metal, one is able to achieve aluminium alloys
of varying strength and ductility. However, alloying of aluminium is a cumbersome process as it is
required to be performed independently of the aluminium manufacturing process. Thus, in order to save
capital and resources, the present invention overcomes this shortcoming by not only recovering
alumina from dross, but also allowing the recovered alumina containing metals (alloy agents) present in
the fonn of impurities, to be used in the process of manufacturing aluminium metal resulting in the
production of alumium metal in its alloy fonn.
Thus, there exists a need for a process of recovering alumina from dross to minimize the loss of
alumina during the manufacturing process of aluminium metal.
There also exists a need to for a process of recovering alumina from dross which does not adversely
affect the environment.
There exists a need for an alternate process for extraction or recovery of alumina which requires less
consumption of energy as compared to the process of manufacturing primary aluminium.
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There exists a need for a process of recovering alumina from dross which allows the recovered alumina
(containing alloying agents present in the form of impurities) to be used for manufacturing of
aluminium metal in its alloy form.
Accordingly, there exists a need for a mechanical process for recovering alumina from dross wherein
the pure form of alumina containing dross can be collected and segregated following a series of
crushing processes followed by screening and purification thereby allowing the use of recovered
alumina with fresh alumina for manufacturing of aluminium metal.
OBJECT OF THE INVENTION:
It is an object of the present invention to provide a process for recovering alumina from dross generated
during the manufacturing process of aluminium metal, thereby allowing the use of recovered alumina
with fresh alumina in smelter pots for manufacturing aluminium metal.
SUMMARY OF INVENTION.:
According to an aspect of the invention there is provided a process for recovering alumina from dross
generated during aluminium smelting, the process comprising:
(a) crushing aluminum dross into smaller pieces with about 85-90 % in the size range 50 - 120 mm;
(b) further crushing the crushed dross of step (a) into smaller pieces with about 80-85% in the size
range 25 -50 mm;
(c) pulverizing the crushed dross of step (b) into granules with about 45-50 % in the size range 0.1 0.5mm;
(d) screening the pulverized dross of step (c) through a 50 Mesh screen with 0.297 mm sieve size
thereby obtaining an underflow ofpulverized dross through the mesh of about 35-40 % and a
remainder as an overflow remaining over the screen;
(e) removing iron particles from the underflow pulverized dross of step (d) by magnetic separation;
and
(t) charging the pulverized dross of step (e) along-with fresh alumina into a aluminium smelter pot for
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recovering aluminium.
In an embodiment of the invention the dross generated during aluminium smelting is introduced into
jaw crushers for crushing.
In yet another embodiment of the invention the crushed dross of step (a) is introduced into roll crushers
for further crushing.
In still another embodiment of the invention the crushed dross of step (b) is introduced into tumbling
mills for pulverization.
In another embodiment of the invention, the underflow of pulverized dross of step (d) is fed into a
magnetic separator for removing iron particles.
BRIEF DESCRIPTION OF DRAWINGS
The advantages and features of the present invention will become better understood with reference to
the detailed description taken in conjunction with the accompanying drawing, wherein like elements
are identified with like symbols, and in which:
Figure I illustrates a flow diagram of the process for recovering alumina from dross, in accordance
with an embodiment of the present invention.
DETAILED DESCRIPTION OF INVENTION WITH REFERENCE TO DRAWINGS
The exemplary embodiments described herein detail of illustrative purposes are subject to many
variations in structure and design. It should be emphasized, however, that the present invention is not
limited to a particular form as described. It is understood that various omissions and substitutions of
equivalents are contemplated as circumstances may suggest or render expedient, but these are intended
to cover the application or implementation without departing from the spirit or scope of the claims of
the present invention.
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The terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of
at least one of the referenced item. Further, the terms "first", "second", and the like, herein do not
denote any order, quantity, or importance, but rather are used to distinguish one element from another.
According to a non-limiting embodiment of the disclosure there is provided a process for recovering
alumina from dross generated during the manufacturing process of aluminium metal, the process
comprising of feeding 110 the dross particles into jaw crushers 120 for crushing, followed by further
crushing of the obtained dross in roll crushers 130 and pulverizing the further crushed dross particles in
tumbling mills 140, which is followed by a screening process 150, eventually followed by the step of
purification of the screened dross from iron impurities with the aid of magnetic separation 160,
followed by charging the recovered alumina containing dross with fresh alumina in smelter pots 170
for recovering aluminium.
The following explanation is a non limiting embodiment of the disclosure and is not exhaustive or
intended to limit the present invention to the precise forms disclosed. Further, many modifications and
variations are possible in light of the teachings provided in the aforesaid disclosure. Such
modifications and variations shall fall within scope of the invention.
In an embodiment of the invention the dross generated during the manufacturing of aluminium metal
was collected and fed 110 into jaw crushers 120 to bring the dross particles into the size range of 50120
mm. Around 85-90 % of dross particles got crushed to the aforesaid size range. The metal particles
not in form of dross were hand picked and removed. The above-said crushed dross material was then
fed into the roll crushers 130 for further reduction of size of the already crushed dross material to a size
range of 25-50 mm size. Between 80-85% of dross particles got crushed to the size range of 25-50 mm
in roll crushers during the crushing process and were present in the form of unbreakable lumps. The
above obtained dross material in the size range of 25-50 mm was then introduced into tumbling mills
140 for pulverization to bring them to a size range of 0.1-0.5 mm. About 45-50 % dross particles got
pulverized to the size range of 0.1-0.5 mm during the above discussed step. The above-obtained
pulverized dross particles were then screened 150 with a 50 mesh screen with 0.297 mm sieve size
thereby resulting in an underflow of pulverized dross with about 35-40 % particles in the underflow
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while the remaining were left as overflow over the screen.
The underflow (- 50 mesh) obtained after the above described screening 150 process was fed into
Magnetic separator 160 for removing the iron particles present as impurities in dross. The aforesaid
dross which was now in its purified form after removal of iron impurities was charged with fresh
alumina into aluminium smelter pots 170 for extraction/recovery of aluminium metal.
By using the disclosed process, one was able to recover 40-45 % of alumina from dross.
The foregoing descriptions of specific embodiments of the present invention have been presented for
purposes of illustration and description. They are not intended to be exhaustive or to limit the present
invention to the precise forms disclosed, and many modifications and variations are possible in light of
the above teaching. The embodiments were chosen and described in order to best explain the principles
of the present invention and its practical application, and to thereby enable others skilled in the art to
best utilize the present invention and various embodiments with various modifications as are suited to
the particular use contemplated. It is understood that various omissions and substitutions of equivalents
are contemplated as circumstances may suggest or render expedient, but such omissions and
substitutions are intended to cover the application or implementation without departing from the spirit
or scope of the claims of the present invention.

We claim:
1. A process for recovering alumina from dross generated during aluminium smelting, the process
comprising:
(a) crushing aluminum dross into smaller pieces with about 85-90 % in the size range 50l20mm;
(b) further crushing the crushed dross of step (a) into smaller pieces with about 80-85% in the
size range 25 - 50 mm;
(c) pulverizing the crushed dross of step (b) into granules with about 45-50 % in the size
range 0.1 - 0.5 mm;
(d) screening the pulverized dross of step (c) through a 50 Mesh screen with 0.297 mm sieve
size thereby obtaining an underflow ofpulverized dross through the mesh of about 35-40 %
and a remainder as an overflow remaining over the screen;
(e) removing iron particles from the underflow pulverized dross of step (d) by magnetic
separation; and
(1) charging the pulverized dross of step (e) along-with fresh alumina into a aluminium smelter
pot for recovering aluminium.
2. The process as claimed in claim 1, wherein the dross generated during aluminium smelting is
introduced into jaw crushers for crushing.
3. The process as claimed in claim 1, wherein the crushed dross of step (a) is introduced into roll
crushers for further crushing.
4. The process as claimed in claim 1, wherein the crushed dross of step (b) is introduced into
tumbling mills for pulverization.
5. The process as claimed in claim 1, wherein the underflow ofpulverized dross of step (d) is fed
into a magnetic separator for removing iron particles.
Dated this 16th day of November, 2012.
~~
(Anuradha Salhotra)
ofLALL LAHIRI & SALHOTRA
AGENTS FOR THE APPLICANT