DESC:FORM 2
The Patent Act 1970
(39 of 1970)
&
The Patent Rules, 2005

COMPLETE SPECIFICATION
(SEE SECTION 10 AND RULE 13)

TITLE OF THE INVENTION

“Process to Produce Alumina from Aluminium Dross”

APPLICANT:
Name Nationality Address
Runaya Refining LLP INDIA Runaya Refining LLP, Burkhamunda,Jharsuguda, Odisha, India - 768201
Indian Institute of Technology Kharagpur INDIA Kharagpur, West Bengal 721302

The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed: -

FIELD OF INVENTION
[0001] The present disclosure relates to process for recovering high purity alumina from aluminium dross. More particularly, it relates to process for recovery of high purity alumina from aluminium dross by using combined neutral, alkali and acidic processing. The present application is based on and claims priority from an Indian Provisional Application Number 202331052626 filed on 04th August 2023, the disclosure of which is hereby incorporated by reference herein.

BACKGROUND
[0002] Aluminium dross, generally a byproduct of aluminium melting, occurs when oxygen reacts with molten aluminium, forming a "scum" or "oxide phase" on the surface of the metal pool. This scum mainly consists of aluminum oxide (Al2O3), aluminum nitride (AlN), magnesium oxide (MgO), silicon dioxide (SiO2), sodium chloride (NaCl), potassium chloride (KCl), and other minor oxides. The dross is then treated to extract Aluminium metal, leaving behind a residue known as black dross that forms during secondary/recycled aluminium refining. This residue is refined using a relatively large amount of chloride salt flux and is typically disposed of in landfills, posing environmental hazards due to the heavy metal content and the emission of harmful gases such as ammonia (NH3), phosphene (PH3), and fluorine (F2) upon contact with water bodies.
[0003] Presently, the established techniques for extracting alumina from aluminium dross involve direct acid leaching. However, this approach also dissolves impurities, resulting in escalated expenses and longer processing times in subsequent stages. Consequently, it is imperative to tackle the aforementioned drawbacks or any other limitations and offer a valuable substitute.

OBJECT OF INVENTION
[0004] The principal object of the embodiments herein is to provide a process for recovering high-purity alumina from aluminium dross containing at least 40% of alumina by using combined neutral, alkali, and acidic processing.
[0005] Another objective of the embodiments is to achieve the reduction of particle size of raw aluminium dross through grinding, followed by leaching the grinded material with hot water to dissolve salt and obtain aluminium dross that is entirely free of salt.
[0006] Yet another objective of the embodiments herein is to remove the presence of salt, which is comprised of a blend of potassium chlorides (KCl) and sodium chlorides (NaCl), from finely pulverized dross. This is achieved through a process of hot water leaching, conducted within a temperature range spanning from ambient to 100°C. The resulting substance is subsequently combined with sodium hydroxide (NaOH) in a ratio that may vary between 1:0.2 to 1:10, and subjected to roasting at temperatures exceeding 200°C. The ultimate objective of this process is to convert the aluminum/alumina existing within the waste dross into sodium aluminate (NaAlO2).
[0007] Yet another objective of the embodiments herein is to leach the roasted dross with hot water to dissolve NaAlO2 presented in the roasted mixture in hot water, followed by filtration and reaction with CaO/Ca(OH)2 to eliminate soluble silica.
[0008] Yet another objective of the embodiments herein is to precipitate the pure aluminium hydroxide (Al(OH)3) by introducing carbon dioxide (CO2) bubbles into the silica-removed sodium aluminate solution.
[0009] Yet another objective of the embodiments herein is employing an acid wash with a mild acid to remove sodium from the alumina during the precipitation of aluminum hydroxide.
[0010] Yet another objective of the embodiments herein is to refine aluminum hydroxide through a process of leaching at temperatures ranging from 130°C to 300°C, employing a solution of hydrochloric acid (HCl) to dissolve the aluminum hydroxide and incorporate it into the solution.
[0011] Yet another objective of the embodiments herein is to remove iron through oxidative precipitation at a pH above 3.
[0012] Yet another objective of the embodiments herein is to refine the solution with utmost precision by subjecting it to HCl gas treatment, leading to the precipitation of high-quality aluminium chloride hexahydrate (AlCl3.6H2O) while minimizing impurities.
[0013] Yet another objective of the embodiments herein is to enhance the purity of the AlCl3.6H2O through water dissolution followed by precipitation with HCl gas.
[0014] Yet another objective of the embodiments herein is to repeat the purification process until the desired level of purity is achieved.
[0015] Yet another objective of the embodiments herein is to thermally decompose the AlCl3.6H2O, yielding high-quality alumina and gaseous Hydrochloric acid (HCl) that can be utilized again in the process.

SUMMARY
[0016] Accordingly, embodiments herein disclose a process for producing high-purity alumina. The process comprises grinding the aluminium dross to reduce a particle size of the aluminium dross; leaching the grinded aluminium dross with hot water to dissolve salt from the aluminium dross and obtain a salt-free aluminium dross; mixing the salt-free aluminium dross with one of a sodium hydroxide (NaOH) and a sodium carbonate (Na2CO3); roasting the mixture of the salt-free aluminium dross and one of the NaOH or the Na2CO3; leaching the roasted mixture with hot water to dissolve a sodium aluminate (NaAlO2) presented in the roasted mixture and obtain a sodium aluminate solution; removing silica from the sodium aluminate solution by lime treatment; precipitating an aluminium hydroxide (Al(OH)3) from the silica removed sodium aluminate solution by a carbon dioxide (CO2) gas purging; purifying an Al(OH)3 precipitate by acid washing and obtain a purified Al(OH)3; reacting the purified Al(OH)3 with a Hydrochloric Acid (HCl) to remove impurities and obtain an impurity-removed AlCl3 solution; filtering the impurity-removed AlCl3 solution, and reacting filtered AlCl3 solution with HCl gas to precipitate aluminum chloride hexahydrate (AlCl3.6H2O); and calcinating the precipitated AlCl3.6H2O to obtain alumina.
[0017] In an embodiment, grinding aluminium dross to a particle size of less than 500 microns then removing salt (a mixture of potassium chlorides (KCl) and sodium chlorides (NaCl)) through hot water leaching then mixed with sodium hydroxide (NaOH) and roasted at temperatures above 200°C to convert the aluminum/alumina in the waste dross into sodium aluminate (NaAlO2).
[0018] In an embodiment, the particle size of the grinded aluminium dross after grinding is between 100 to 500 microns.
[0019] In an embodiment, the leaching of the grinded aluminium dross to obtain the salt-free aluminium dross is performed above room temperature.
[0020] In an embodiment, the mixture of the salt-free aluminium dross and one of the NaOH and the Na2CO3 are roasted by heating at a temperature range of 200-1000°C, for the mixture of the salt-free aluminium dross and the NaOH, the roasting temperature is in the range of 200°C-500°C, and for the mixture of the salt-free aluminium dross and the Na2CO3, the roasting temperature is in the range of 200°C-900°C or 1000°C.
[0021] In an embodiment, the mixture comprises the salt-free aluminium dross and one of the NaOH and the Na2CO3 in a ratio ranging from 1:0.2 to 1:10.
[0022] In an embodiment, the roasting of the mixture of the salt-free aluminium dross and one of the NaOH and the Na2CO3 converts the aluminium and the aluminium compounds in the mixture of the salt-free aluminium dross and one of the NaOH and the Na2CO3 to the sodium aluminate.
[0023] In an embodiment, the leaching of the roasted mixture is performed at room temperature to 100°C range to dissolve the NaAlO2.
[0024] In an embodiment, the precipitation of the Al(OH)3 from the silica removed solution further comprises: removing a sodium from the Al(OH)3 precipitate by filtering and washing the Al(OH)3 precipitate; obtaining one of a sodium (bi) carbonate solution and a sodium carbonate solution from a sodium removed Al(OH)3 precipitate; and performing an evaporation crystallization of one of the sodium bicarbonate solutions and the sodium carbonate solution to recover sodium carbonate monohydrate (Na2CO3.H2O) as a by-product.
[0025] In an embodiment, the silica is removed by one of adding a lime during the roasting of the mixture of the salt-free aluminium dross; and before precipitation of the Al(OH)3 from the sodium aluminate solution.
[0026] In an embodiment, the acid washing of the Al(OH)3 precipitate removes impurities such as iron and sodium present in the Al(OH)3 precipitate and produces the purified Al(OH)3 along with an acid-washed Al(OH)3 solution.
[0027] In an embodiment, a leftover iron impurity in the acid-washed Al(OH)3 solution is removed at a potential of Hydrogen (pH) of 3 by adding one of additional Al(OH)3 or other basic oxides/hydroxide in the acid-washed Al(OH)3 solution and increasing a oxidation potential (OP) of the acid-washed Al(OH)3 solution.
[0028] In an embodiment, the purified Al(OH)3 reacted with the HCl at the temperature of 160°C to remove impurities such as silica and titanium dioxide (TiO2).
[0029] In an embodiment, the purity of the precipitated AlCl3.6H2O is enhanced by performing the same iteration again and again, the iteration includes dissolving the precipitated AlCl3.6H2O by-product of previous iteration and precipitating with the HCl gas until the precipitated AlCl3.6H2O purity reaches more than 90%.
[0030] In an embodiment, the calcination of precipitated AlCl3.6H2O is performed at a temperature of 1200°C to produce alumina with high purity.
[0031] These and other aspects of the embodiments herein are better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the scope thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF FIGURES
[0032] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
[0033] FIG. 1 is a flow diagram illustrating a process for producing high purity alumina from aluminium dross, according to the embodiment disclosed herein;
[0034] FIG. 2 is a sequence diagram (200) illustrating a process for producing high purity alumina from aluminium dross, according to the embodiment disclosed herein;
[0035] FIG. 3 is an image of grinded aluminium dross, according to the embodiment disclosed herein;
[0036] FIG. 4A-4B are scanning electron microscope (SEM) images of grinded aluminium dross, according to the embodiment disclosed herein;
[0037] FIG.5 shows an X-Ray diffraction analysis (XRD) pattern of high-quality aluminium chloride hexahydrate (AlCl3.6H2O), according to the embodiment disclosed herein; and
[0038] FIG. 6 shows the image of high-purity alumina produced after the calcination, according to the embodiment disclosed herein.
[0039] It may be noted that to the extent possible, like reference numerals have been used to represent like elements in the drawing. Further, those of ordinary skill in the art will appreciate that elements in the drawing are illustrated for simplicity and may not have been necessarily drawn to scale. For example, the dimension of some of the elements in the drawing may be exaggerated relative to other elements to help to improve the understanding of aspects of the invention. Furthermore, the elements may have been represented in the drawing by conventional symbols, and the drawings may show only those specific details that are pertinent to the understanding the embodiments of the invention so as not to obscure the drawing with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

DETAILED DESCRIPTION OF INVENTION
[0040] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The term “or” as used herein, refers to a non-exclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0041] As is traditional in the field, embodiments may be described and illustrated in terms of blocks which carry out a described process. Each block of the embodiments may be physically separated into two or more interacting and discrete blocks without departing from the scope of the invention. Likewise, the blocks of the embodiments may be physically combined into more complex blocks without departing from the scope of the invention.
[0042] The accompanying drawings are used to help easily understand various technical features and it should be understood that the embodiments presented herein are not limited by the accompanying drawings. As such, the present disclosure should be construed to extend to any alterations, equivalents and substitutes in addition to those which are particularly set out in the accompanying drawings. Although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are generally only used to distinguish one element from another. Table 1 shows the definitions of various chemical terms used in the description:
Terms Abbreviations
NaOH Sodium Hydroxide
Na2CO3 Sodium Carbonate
NaAlO2 Sodium Aluminate
Al(OH)3 Aluminium Hydroxide
CO2 Carbon Dioxide
HCl Hydrochloric Acid
AlCl3 Aluminium chloride
KCl Potassium Chloride
NaCl Sodium Chlorides
AlCl3.6H2O Aluminum Chloride Hexahydrate
pH Potential of Hydrogen
0C Temperature in Degree Celsius
TiO2 Titanium Dioxide
AlN Aluminium Nitride
MgO Magnesium Oxide
SiO2 Silicon Dioxide
Al Aluminium
Ca(OH)2 Calcium Hydroxide
CaSiO3 Calcium Silicate
H2O Water
NH3 Ammonia
PH3 Phosphene
F2 Fluorine

Table 1
[0043] Table 2 shows the XRF (X-ray fluorescence) results of aluminium hydroxide synthesized from dross:-
Elements Mass (%)
Al2O3 99.90%
Na2O 0.05%
SiO2 0.02%
CaO 0.01%
Fe2O3 0.02%
Ga2O3 81 ppm (parts per million)
K2O 46 ppm (parts per million)
NiO 23 ppm (parts per million)

Table 2
[0044] Accordingly, embodiments herein disclose a process for obtaining alumina from aluminium dross. The process includes grinding the aluminium dross to reduce a particle size of the aluminium dross; leaching the grinded aluminium dross with hot water to dissolve salt from the aluminium dross and obtain a salt-free aluminium dross; mixing the salt-free aluminium dross with one of a sodium hydroxide and a sodium carbonate ; roasting the mixture of the salt-free aluminium dross and one of the NaOH or the Na2CO3; leaching the roasted mixture with hot water to dissolve a sodium aluminate (NaAlO2) presented in the roasted mixture and obtain a sodium aluminate solution; removing silica from the sodium aluminate solution by lime treatment; precipitating an aluminium hydroxide (Al(OH)3) from the silica removed sodium aluminate solution by a carbon dioxide (CO2) gas purging; purifying an Al(OH)3 precipitate by acid washing and obtain a purified Al(OH)3; reacting the purified Al(OH)3 with a hydrochloric acid (HCl) to remove impurities and obtain an impurity-removed AlCl3 solution; filtering the impurity-removed AlCl3 solution, and reacting filtered AlCl3 solution with HCl gas to precipitate aluminum chloride hexahydrate (AlCl3.6H2O); and calcinating the precipitated AlCl3.6H2O to obtain alumina.
[0045] In an embodiment, grinding aluminium dross to a particle size of less than 500 microns then removing salt (a mixture of potassium chloride (KCl) and sodium chlorides (NaCl)) through hot water leaching then mixed with sodium hydroxide (NaOH)/sodium carbonate (Na2CO3) and roasted at temperatures above 200°C to convert the alumina in the waste dross into sodium aluminate (NaAlO2) as shown in equation 1.
Al2O3 + 2NaOH (or Na2CO3) ? 2NaAlO2 + H2O (1).
[0046] The dross material is subjected to hot water treatment, dissolving the sodium aluminate into a solution then the solution is filtered and reacted with CaO/Ca(OH)2 to remove soluble silica, forming a residue as shown in equation 2 and 3.
SiO2 + 4NaOH ? Na4SiO4 + 2H2O (2).
Na4SiO4 + 2Ca(OH)2 ? Ca2SiO4 + 4NaOH (3).
[0047] In an embodiment, commercial pure Al(OH)3 is then precipitated with CO2 bubbles as shown in equation 3.
NaAlO2 + CO2 + 2H2O ? NaHCO3 + Al(OH)3 (3).
[0048] In an embodiment, precipitated aluminum hydroxide is washed with a mild acid to eliminate sodium compounds from the alumina. The purified aluminum hydroxide is subsequently leached above 150°C using an HCl acid solution as shown in equation 4.
Al(OH)3 + 3HCl ? AlCl3 + 3H2O (4).
[0049] The conventional method for extracting alumina from aluminium dross involves direct acid leaching. However, the alumina obtained through this process is often contaminated with impurities, necessitating costly and time-consuming additional treatments.
[0050] In contrast to conventional methods, the proposed process employs a unique combination of neutral alkali and acidic processing, resulting in the production of high-value alumina.
[0051] In an embodiment, iron can be removed through oxidative precipitation at a pH above 3. The purified solution, containing minimal impurities, undergoes treatment with HCl gas to precipitate high-purity AlCl3.6H2O. Further, purity is enhanced through water dissolution and precipitation with HCl gas. And repeating the purification process until the desired level of purity is achieved.
[0052] In an embodiment, pure AlCl3.6H2O is further calcined to produce high-purity alumina and HCl gas, which can be recycled within the process.
[0053] Referring now to the drawings and more particularly to FIGS. 1–6, where similar reference characters denote corresponding features consistently throughout the figure, these are shown preferred embodiments.
[0054] FIG. 1 is a flow diagram (100) illustrating a process for producing high purity alumina from aluminium dross, according to the embodiment disclosed herein. Referring to FIG. 1, at S101, the aluminium dross with at least but not limited to the 40% of is grinded to reduce the particle size between 100 to 500 microns. After grinding, at S102, the grinded aluminium dross leached with hot water at above room temperature to dissolve salt from the aluminium dross and obtain a salt-free aluminium dross. At S103, the salt-free aluminium dross mixed with one of a sodium hydroxide (NaOH) and a sodium carbonate (Na2CO3) in a ratio ranging from 1:0.2 to 1:10. At S104, the mixture of salt-free aluminium dross and one of the NaOH or the Na2CO3 roasted at a temperature range of 200-1000°C, for the mixture of the salt-free aluminium dross and the NaOH, the roasting temperature is in the range of 200°C-500°C, and for the mixture of the salt-free aluminium dross and the Na2CO3, the roasting temperature is in the range of 200°C-900°C or 1000°C. The roasting of salt-free aluminium dross and one of the NaOH or the Na2CO3 converts the aluminium and the aluminium compounds to the sodium aluminate. At S105, the roasted mixture leached with hot water at room temperature to 100°C range to dissolve a sodium aluminate (NaAlO2) presented in the roasted mixture and obtain a sodium aluminate solution. At S106, the sodium aluminate solution subjected to lime treatment to remove silica. At S107, the silica removed solidum aluminate solution subjected to carbon dioxide (CO2) gas purging to precipitate an aluminium hydroxide (Al(OH)3). At S108, the Al(OH)3 precipitate is acid washed to remove impurities such as iron and sodium present in the Al(OH)3 precipitate and produces the purified Al(OH)3. At S109, the purified Al(OH)3 is reacted with a hydrochloric acid (HCl) to remove impurities and obtain an impurity-removed AlCl3 solution. At S110, the impurity-removed AlCl3 solution is filtered, and reacted with HCl gas to precipitate aluminum chloride hexahydrate (AlCl3.6H2O). At S111, precipitate aluminum chloride hexahydrate (AlCl3.6H2O) is calcinated at a temperature of 1200°C to produce alumina with high purity.
[0055] FIG. 2 is a sequence diagram (200) illustrating a process for producing high purity alumina from aluminium dross, according to the embodiment disclosed herein. Referring to FIG. 2, at step S201 the dross grinded to below 500 microns, preferably below 100 microns. After grinding, at step S202 the dross undergoes a water leaching process conducted above room temperature to dissolve the salt present in the dross.
[0056] Then at step S203 the residue obtained after water leaching is mixed with sodium carbonate (Na2CO3)/sodium hydroxide (NaOH) and roasted at temperatures exceeding 200°C, preferably 500°C for NaOH and 900°C for Na2CO3. This roasting process converts aluminum and aluminum compounds into sodium aluminate.
[0057] Then at step S204 the roasted mass is leached with hot water to dissolve the sodium aluminate. After filtration, the resulting residue can be used for refractories, refractory castables, or other applications with or without further treatment.
[0058] Then at step S205 the solution obtained after leaching with hot water contains a significant amount of dissolved silica. Further, process for filtration of silica by adding lime during roasting after filtration. The filtered solution is then subjected to lime (Ca(OH)2) treatment to remove the silica from the solution.
[0059] Then at step S206 after removal of silica rich precipitate, the solution is treated with CO2 bubbling until the 70-90% of the aluminium hydroxide is precipitated.
[0060] At step S207 then the slurry is filtered and washed with HCl aqueous solution to separate impurities such as sodium bicarbonate, iron with aluminium hydroxide (Al(OH)3).
[0061] At step S208 the purified Al(OH)3 further reacted with HCl to remove the impurities such as silica and TiO2. The leftover iron impurity in the solution is removed at a pH of 3 by adding HCl acid in Al(OH)3 or other basic oxide/hydoxide and increasing the oxidation potential of the solution.
[0062] At step S209 after filtration, the solution is treated with HCl gas to precipitate high-purity AlCl3.6H2O. The precipitated AlCl3.6H2O can be dissolved and further precipitated with HCl gas to enhance its purity.
[0063] Then at step S210 the high-purity AlCl3.6H2O is subjected to calcination at 1200°C to produce high purity alumina.
[0064] The above process can be better understood by the following examples.
[0065] Example 1: 50 gm dross is milled in a planetary ball mill with a ball to powder ration of 1:10 for 1 hour to convert the dross to 90 microns. The milled dross is leached with water with a 1:2 ratio at 95°C for 4 hours to dissolve the salt and convert most of the AlN to Al(OH)3 and ammonia gas.
[0066] The slurry is filtered, and the solution is evaporated to produce the salt (NaCl+KCl), which is about 6g. After drying, the solid is mixed with NaOH with a 1:1 wt ratio in a mortar pestle. Then it is roasted at 500°C for 4 h followed by water leaching at 60°C for 1h. The slurry is subsequently filtered to remove/recover the residue rich with alpha alumina and magnesium aluminate. The filtered solution is then subjected to 2g lime treatment to remove the silica from the solution.
[0067] After the removal of the silica-rich precipitate, the solution is treated with CO2 bubbling until 70-90% of the aluminium hydroxide is precipitated. Then the slurry is filtered and washed to separate sodium bicarbonate and Al(OH)3. This Al(OH)3 is further reacted with 5g of HCl containing 100ml aqueous solution at 90°C for 4h to remove the impurities such as iron, calcium, sodium etc.
[0068] The purified Al(OH)3 further reacted with 200g of 37% HCl at 160°C for 4h to remove the impurities such as silica and titanium dioxide (TiO2). After filtration, AlCl3 solution is reacted with HCl gas to precipitate AlCl3.6H2O.
[0069] The precipitated AlCl3.6H2O is subjected to calcination at 1200°C to produce high-purity alumina.
[0070] Example 2: 50 gm dross is milled in a planetary ball mill with a ball to powder ratio of 1:10 for 1 hour to convert the dross to 90 microns. The milled dross is leached with water with a 1:2 ratio at 95°C for 4 hours to dissolve the salt and convert most of the AlN to Al(OH)3 and ammonia gas.
[0071] The slurry is filtered, and the solution is evaporated to produce the salt (NaCl+KCl), which is about 6g. After drying, the solid is mixed with Na2CO3 with 1:1 wt ratio in a mortar pestle. Then it is roasted at 900°C for 4h followed by water leaching at 60°C for 1h. The slurry is subsequently filtered to remove/recover the residue rich with alpha alumina and magnesium aluminate.
[0072] The filtered solution is then subjected to 2g lime treatment to remove the silica from the solution. After the removal of the silica-rich precipitate, the solution is treated with CO2 bubbling until 70-90% of the aluminium hydroxide is precipitated. Then the slurry is filtered and washed to separate sodium bicarbonate and Al(OH)3.
[0073] This Al(OH)3 is further reacted with 5g of HCl containing 100 ml aqueous solution at 90°C for 4h to remove the impurities such as iron, calcium, sodium etc. The purified Al(OH)3 further reacted with 200 g of 37% HCl at 160°C for 4h to remove the impurities such as silica and TiO2. After filtration, AlCl3 solution is reacted with HCl gas to precipitate AlCl3.6H2O.
[0074] The precipitated AlCl3.6H2O is subjected to calcination at 1200°C to produce high-purity alumina.
[0075] FIG. 3 is an image of grinded aluminium dross, according to the embodiment disclosed herein. The raw aluminium dross grinded to below 500 microns preferably 100 microns.
[0076] FIG. 4A-4B are scanning electron microscope (SEM) images of grinded aluminium dross, according to the embodiment disclosed herein. After grinding the grinded aluminium dross subjected to a series of processes such as but not limited to leaching with hot water to remove salt impurities from the grinded aluminium dross, mixing one of the Sodium Hydroxide and the Sodium Carbonate with salt-free aluminium dross, roasting the mixture, removing silica, precipitating the Aluminium Hydroxide from the silica removed sodium aluminate solution by the Carbon Dioxide gas purging, acid washing the Al(OH)3 precipitate for purification, reacting the purified Al(OH)3 with Hydrochloric Acid to remove impurities, reacting HCl gas to precipitate aluminum chloride hexahydrate and calcinating the precipitated AlCl3.6H2O to obtain alumina.
[0077] FIG.5 shows an X-Ray diffraction analysis (XRD) pattern of high-quality aluminium chloride hexahydrate (AlCl3.6H2O), according to the embodiment disclosed herein, wherein the high-quality AlCl3.6H2O synthesized from the Al(OH)3.
[0078] Fig. 6 shows the image of high-purity alumina produced after the calcination, according to the embodiment disclosed herein. The produced high-purity alumina has a purity above 99.9%.
[0079] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
,CLAIMS:CLAIMS
We Claim:
1. A process for obtaining alumina from aluminium dross, wherein the process comprises:
grinding the aluminium dross to reduce a particle size of the aluminium dross;
characterised in that:
leaching the grinded aluminium dross with hot water to dissolve salt from the aluminium dross and obtain a salt-free aluminium dross;
mixing the salt-free aluminium dross with one of a Sodium Hydroxide (NaOH) and a Sodium Carbonate (Na2CO3);
roasting the mixture of the salt-free aluminium dross and one of the NaOH or the Na2CO3;
leaching the roasted mixture with hot water to dissolve a Sodium Aluminate (NaAlO2) presented in the roasted mixture and obtain a Sodium Aluminate solution;
removing silica from the Sodium Aluminate solution by lime treatment;
precipitating an Aluminium Hydroxide (Al(OH)3) from the silica removed Sodium Aluminate solution by a Carbon dioxide (CO2) gas purging;
purifying an Al(OH)3 precipitate by acid washing and obtain a purified Al(OH)3;
reacting the purified Al(OH)3 with a Hydrochloric Acid (HCl) to remove impurities and obtain an impurity-removed Aluminium Chloride (AlCl3) solution;
filtering the impurity-removed AlCl3 solution, and reacting filtered AlCl3 solution with HCl gas to precipitate aluminum chloride hexahydrate (AlCl3.6H2O); and
calcinating the precipitated AlCl3.6H2O to obtain alumina.
2. The process as claimed in claim 1, wherein the aluminium dross comprises at least 40% of alumina.
3. The process as claimed in claim 1, wherein the particle size of the grinded aluminium dross after grinding is between 100 to 500 microns.
4. The process as claimed in claim 1, wherein the leaching of the grinded aluminium dross to obtain the salt-free aluminium dross is performed at a temperature range of 40-100°C.
5. The process as claimed in claim 1, wherein the mixture of the salt-free aluminium dross and one of the NaOH and the Na2CO3 are roasted by heating at the temperature range of 200-1000°C,
wherein the mixture of the salt-free aluminium dross and the NaOH, is roasted at the temperature range of 200°C-500°C, and
wherein the mixture of the salt-free aluminium dross and the Na2CO3, is roasted at the temperature range of 200°C-900°C or 1000°C.
6. The process as claimed in claim 5, wherein the mixture comprises the salt-free aluminium dross and one of the NaOH and the Na2CO3 in a ratio ranging from 1:0.2 to 1:10.
7. The process as claimed in claim 1, wherein the roasting of the mixture of the salt-free aluminium dross and one of the NaOH and the Na2CO3 converts the aluminium and an aluminium compound in the mixture of the salt-free aluminium dross and one of the NaOH and the Na2CO3 to the sodium aluminate.
8. The process as claimed in claim 1, wherein the leaching of the roasted mixture is performed at room temperature to 100°C range to dissolve the NaAlO2.
9. The process as claimed in claim 1, wherein the precipitation of the Al(OH)3 from the silica removed Sodium Aluminate solution comprises:
removing a sodium from the Al(OH)3 precipitate by filtering and washing the Al(OH)3 precipitate;
obtaining one of a sodium (bi) carbonate solution and a sodium carbonate solution from a sodium removed Al(OH)3 precipitate; and
performing an evaporation crystallization of one of a sodium bicarbonate solution and the sodium carbonate solution to recover sodium carbonate monohydrate (Na2CO3.H2O) as a by-product.
10. The process as claimed in claim 1, wherein the silica is removed by one of:
adding a lime during the roasting of the mixture of the salt-free aluminium dross; and
before precipitation of the Al(OH)3 from the sodium aluminate solution.
11. The process as claimed in claim 1, wherein the acid washing of the Al(OH)3 precipitate removes impurities such as iron and sodium present in the Al(OH)3 precipitate and produces the purified Al(OH)3 along with an acid-washed Al(OH)3 solution.
12. The process as claimed in claim 11, wherein a leftover iron impurity in the acid-washed Al(OH)3 solution is removed at pH range of 2-4 by adding one of additional Al(OH)3 or other basic oxides/hydroxide in the acid-washed Al(OH)3 solution and increasing a oxidation potential (OP) of the acid-washed Al(OH)3 solution.
13. The process as claimed in claim 1, wherein the purified Al(OH)3 reacted with the HCl at the temperature of 160°C to remove impurities such as silica and Titanium dioxide (TiO2).
14. The process as claimed in claim 1, wherein a purity of the precipitated AlCl3.6H2O is enhanced by performing the same iteration again and again,
the iteration includes dissolving the precipitated AlCl3.6H2O by-product of previous iteration and precipitating with the HCl gas until the precipitated AlCl3.6H2O purity reaches more than 99%.
15. The process as claimed in claim 1, wherein the calcination of precipitated AlCl3.6H2O is performed at a temperature of 1200°C to produce high purity alumina with having purity level of 99.9%.