FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
THE PATENTS RULES, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION A METHOD FOR PREPARING HIGH GRADE ALUMINIUM
APPLICANTS HINDALCO INDUSTRIES LIMITED,
of address
AHURA CENTRE, 1ST FLOOR, B-WING, MAHAKALI CAVES ROAD, ANDHERI
(EAST), MUMBAl-400 093
COMPLETE SPECIFICATION
The following specification particularly describes this invention and the manner in which it is
to be performed:

FIELD OF THE INVENTION
[001] The present invention relates to a process of preparing high grade auminium.
DESCRIPTION OF THE BACKGROUND ART
[002] Aluminum is a metallic element in the Earth’s crust (about 8%) and is the third most common element after oxygen and silicon. Bauxite is the most important aluminous ore for the production of aluminium. Bauxite usually occurrs close to the surface as small reddish pebbles containing about 40 to 60 mass % alumina combined with smaller amounts of silica, titania and iron oxide.
[003] In aluminium production process, the first stage is mining of bauxites from the ground. In the second stage, mined bauxites are processed into alumina through Bayer’s process. In the third stage, pure aluminium is produced using electrolytic reduction of alumina, through Hall-Heroult process in which alumina is broken down into its components using electric current.
[004] However, aluminium produced by Hall-Heroult process still contains impurities in the form of iron, silicon, copper and other elements. The presence of impurities, even in negligible amounts of admixtures can have a drastic impact on the properties of aluminium. In certain cases, the impurities in aluminium are removed by remelting the aluminium in a special furnace at 800oC.
[005] The presence of impurities results in energy loss in the upstream production line, low recovery of aluminium and and low quality of aluminium.

[006] In aluminium manufacturing, the purity of aluminium is directly propotional to the purity of input alumina, input carbon anode, input anode cover material & input AlF3. To produce high purity metal, high purity input raw material is required with no contamination by impurities. Since, bauxite ores generally occur in nature combined with other metal traces, the bauxite ores are subjected to specific treatment process to remove impurities as disclosed in following Chinese patents.
[007] CN104368440A recites a process and device for Bayer process-based separation of iron in high-iron red mud. CN105536979A recites a method for extracting micro-fine-particle iron ore concentrate from tailings obtained after primary iron separation. CN101648159B recites a method for recovering iron concentrates from alumina red mud.
[008] However, in cases where high quality alumina is not available for electrolytic reduction, high grade aluminium is obtained by additional purification methods. This increases the cost of obtaining aluminium.
[009] Whilst there are many technologies developed to remove impurities from bauxite ore, there is a need for removing iron inpurities from alumina in cases where the purity of alumina is not high.
OBJECT OF THE INVENTION
[010] An object of the present invention is to provide high purity aluminium of P0303 grade.

[011] Another object of the invention is to provide a process to remove elemental iron impurities from enriched alumina in an aluminium smelting process.
SUMMARY OF THE INVENTION
[012] The technical problem to be solved in the present invention is to provide a process for preparing high grade aluminium thereby reducing the energy loss and increasing the recovery of high grade aluminium.
[013] For solving the problems described above, the invention provides a method for preparing high grade aluminium, comprising the steps of:
a) subjecting fresh alumina to a gas treatment to obtain enriched alumina;
b) transporting said enriched alumina through a conveyor system to an electrolytic pot cell; and
c) electrolytic reduction of enriched alumina to aluminium in said electrolytic pot
cell;
wherein at least one magnetic separator is placed in said conveyor system to remove iron particles from enriched alumina prior to electrolytic reduction.
[014] In a aspect, said gas treatment is carried out in a gas treatment center. In another aspect, said conveyor system is a hyper dense phase system.
[015] In an aspect, said magnetic separator comprises of a base plate and at least two cylindrical iron rods integrally projecting and formed on the base plate.

BRIEF DESCRIPTION OF THE DRAWINGS
[016] The foregoing summary, as well as the following detailed description of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of assisting in the explanation of the invention, there are shown in the drawings embodiments which are presently preferred and considered illustrative. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown therein. In the drawings:
[017] Figure 1 is a schematic of smelting process.
[018] Figure 2 is a flowchart of claimed invention.
[019] Figure 3 is a photographic image of the magnetic separator
DESCRIPTION OF THE INVENTION
[020] In describing and claiming the invention, the following terminology will be used in accordance with the definitions set forth below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. As used herein, each of the following terms has the meaning associated with it in this section. Specific and preferred values listed below for individual process parameters, substituents, and ranges are for illustration only; they do not exclude other defined values or other values falling within the preferred defined ranges.

[021] As used herein, the singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise.
[022] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention
[023] As used herein, the terms “comprising” “including,” “having,” “containing,” “involving,” and the like are to be understood to be open-ended, i.e. to mean including but not limited to.
[024] As used herein, the term “smelting” refers to a form of extractive metallurgy to produce a metal from its ore
[025] As used herein, the term “electrolytic reduction” refers to a form of electrolysis in which electric current passes through an ionic substance in a molten or dissolved state causing the electrodes to react chemically and the materials to decompose.
[026] As used herein, the term “enriched alumina” refers to alumina treated with hydrogen fluoride.
[027] As used herein, the term “electrolyte” refers to a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water.

[028] While the present invention is susceptible of embodiment in various forms, there is hereinafter described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated.
[029] In an embodiment, the invention provides a method for preparing high grade aluminium as shown in Figure 2, comprising the steps of:
a) subjecting fresh alumina to a gas treatment to obtain enriched alumina;
b) transporting said enriched alumina through a conveyor system to an electrolytic pot cell; and
c) electrolytic reduction of enriched alumina to aluminium in said electrolytic pot
cell;
wherein at least one magnetic separator is placed in said conveyor system to remove iron particles from enriched alumina prior to electrolytic reduction.
[030] In an embodiment, said gas treatment is carried out in a gas treatment center. In another aspect, said conveyor system is a hyper dense phase system.
[031] In an embodiment, said magnetic separator comprises of a base plate and at least two cylindrical iron rods integrally projecting and formed on the base plate.
[032] Technical solution of the present invention is the magnetic separator in the conveyor system for removing iron impurities that causes high ferrous contents in enriched alumina. The magnetic separator can remove iron particles greater way as there was system to separate iron particle from close conveying system.

WORKING EXAMPLES PROCESSING OF BAUXITE
[033] Bauxite ores are subjected to caustic digestion at high temperature and high pressure, followed by calcination to produce alumina. During caustic digestion at higher temperature, crystallised aluminium hydrate found in bauxite dissolves in a concentrated caustic soda (usually NaOH). Subsequently when the temperature is lowered and the concentration of the solution increases again, aluminium hydrate crystallises while other elements contained in bauxite settle to the bottom. Alumina produced by caustic digestion of bauxite ore is called fresh alumina and is stored under the right conditions in silos prior to be despatched to smelters for electrolytic reduction.
GAS TREATMENT CENTRE
[034] Fresh alumina from the silos are transported to a gas treatment centre. In the gas treatment centre, fresh alumina are subjected to process gas for treatment. The gas treatment of alumina at the gas treatment centre results in formation of aluminium fluoride.
[035] The gas treatment center captures all the process gases generated during reduction process, treats it with fresh alumina and enrich alumina supplied to electrolytic pot for aluminium production and release of clean gas.
MAGNETIC SEPARATOR

[036] From the gas treatment center, enriched alumina is passed through a conveyor system to an electrolytic pot cell for reduction reaction. The conveyor system is a hyper dense phase system. Hyper dense phase system is a close system bottom layer with compressed air with low pressure and above the fabric layer alumina carried from enrich silo to electrolytic pot.
[037] The magnetic separator is placed in said conveyor system to remove iron particles from enriched alumina prior to electrolytic reduction. In an embodiment, said magnetic separator comprises of a base plate and at least two cylindrical iron rods integrally projecting and formed on the base plate.
[038] The iron rods of the magnetic separator removes iron impurities from enriched alumina, before the alumina reaches the electrolytic pot cell.
ALUMINIUM REDUCTION
[039] Electrolytic reduction of enriched alumina is carried out in a series of connected electrolytic pot cell, commonly called a pot. The pot comprises of a highly corrosive molten fluoride electrolyte (or bath, as it is commonly called). Enriced alumina removed of iron impurities is fed into the pot through feed entry.
[040] During electrolytic reduction, enriched alumina dissolved in a electrolyte (also known as bath) is electrolytically reduced to produce molten aluminum. Carbon anodes are immersed into the electrolyte for carrying electrical current which then flows into the cryolite containing dissolved alumina. When current is passed through anodes, the chemical bond between aluminum and oxygen in the alumina is broken, resulting in

deposition of aluminum at the bottom of the cell, while the oxygen reacts with the carbon of the anodes producing carbon dioxide (CO2). A schematic of aluminium electrolysis is shown in Figure 1. The alumina reduction process is described by the following reaction:

[041] The electrolyte bath from pot is tapped periodically. The tapped bath adjusted in the electlytic cell to maintain optimized liquid level inside the pot. In an embodiment, the tapped bath from the pot after electrolytic reduction is processed and the procecessed tapped bath is introduced in the pot. Recycling tapped bath in the smelting process allows considerable energy savings, as well as the efficient use of bath.
ANODES
[042] Carbon anodes are used in aluminum smelters for electrolysis, since carbon acts as good conductor at higher temperature. Typically carbon anodes comprises a mixture of petroleum coke, coal tar pitch and recycled butt. To provide electrical contact, aplurality of metal rods with an iron yoke are attached to the anode.
CATHODE
[043] Cathode is the inner lined carbon (graphitized) material. In general, in an aluminium smelter, enriched alumina is fed to the electrolytic cell at predetermined interval. The electric current flowing through the cell breaks down the bond between aluminium and oxygen, causing aluminium to settle to the bottom of the cell, while the oxygen binds with the carbon in the anode blocks to form carbon dioxide.

ELECTROLYTE
[044] Cryolite comprises of fluoride, sodium, and aluminum, Na3AlF6, which forms the solvent for alumina in the smelting process. Cryolite also exists in a natural form as a rare mineral.
[045] The electrolyte performs the function as the solvent for alumina to enable its electrolytic decomposition, forming molten aluminum and CO2. The electrolyte also enables passage of electricity to anode and to function as a separation barrier between produced molten aluminum and the CO2 gas.
[046] It was observed ferrous content in the smelted aluminium was reduced by the presence of magnetic separator which removed iron contents from enriched alumina.
ADVANTAGES:
1. The process bypass the use of flocculants that may be used to settle iron impurities from alumina. The claimed process is a simple technique which improves the rate of recovery of pure aluminium while being energy efficient.
2. The process removes iron particle from alumina and increases purity of metal.

We Claim:
1) A method for preparing high grade aluminium, comprising the steps of:
a) subjecting fresh alumina to a gas treatment to obtain enriched alumina;
b) transporting said enriched alumina through a conveyor system to an electrolytic pot cell; and
c) electrolytic reduction of enriched alumina to aluminium in said electrolytic pot cell;
wherein at least one magnetic separator is placed in said conveyor system to remove
iron particles from enriched alumina prior to electrolytic reduction.
2) The method as claimed in claim 1, wherein the gas treatment is carried out in a gas
treatment center.
3) The method as claimed in claim 1, wherein said conveyor system is a hyper dense phase
system.
4) The method as claimed in claim 1, wherein said magnetic separator comprises of a base
plate and at least two cylindrical iron rods perpendicular to said base plate.