Description:FIELD OF INVENTION
[0001] The present disclosure relates to a process for recovery of alumina from aluminium dross, and more specifically related to a process of producing at least one of alumina with purity in the range of 90% to 99.99%, speciality, and high purity grade alumina from aluminium dross. 5
BACKGROUND
[0002] In general, aluminium dross generated from aluminium melting majorly includes Aluminium (Al), Aluminium oxide (Al2O3), Aluminium nitride (AlN), Magnesium oxide (MgO), Silicon dioxide (SiO2), Sodium 10 chloride (NaCl), Potassium chloride (KCl), and other oxides in minor quantities. Currently, the aluminium dross is treated to recover Aluminium (Al) metal. The aluminium dross, left over after the recovery of the Al, known as black dross, is disposed to landfills, which puts a toll on surrounding environment. The disposal of the black dross to the landfills 15 possesses harmful heavy metals and releases hazardous gases like ammonia, phosphene, and fluorine when it comes in contact with water bodies. To avoid the above mentioned problems the dross can be utilized in other industrial applications. The black dross can also be used to produce valuable speciality grade or high purity alumina. 20
[0003] The alumina can be recovered from aluminium dross by direct acid leaching. However, it also dissolves several impurities, which makes the subsequent process expensive and time-consuming.
[0004] Thus, it is desired to address the above-mentioned disadvantages or other shortcomings or at least provide a useful alternative. 25
OBJECT OF INVENTION
[0005] The principal object of the embodiments herein is to provide a process to produce alumina from black dross. The proposed process is used
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to recover the aluminum from the aluminum dross and produce specialty-grade or high-purity alumina.
[0006] Another object of the embodiments herein is to provide a process for alumina recovery from black dross containing more than 10% alumina. 5
[0007] Yet another object of the embodiments, herein is to grind the aluminium dross to reduce the particle size of the aluminium dross below 500 microns. The grinded aluminium dross is subjected to leaching, washing, and roasting along with sodium hydroxide (NaOH) to produce precipitate aluminium hydroxide. Washing the precipitated aluminium hydroxide with 10 water and/or mild acid, can produce alumina with purity in the range of 90% to 99.99%.
[0008] Yet another object of the embodiments, herein is to produce sodium carbonate as by product after alumina precipitation is crystallised by evaporation crystallisation. 15
SUMMARY
[0009] Accordingly, embodiments herein disclose a process for obtaining alumina from aluminium dross. The process comprises grinding the aluminium dross for reducing a particle size of the aluminium dross, leaching the grinded aluminium dross with water for removing salts from the 20 grinded aluminium dross, roasting a mixture of the salt removed aluminium dross and sodium hydroxide (NaOH) to obtain sodium aluminate, treating the sodium aluminate with hot water to obtain a sodium aluminate solution, removing silica from the sodium aluminate solution by lime treatment, precipitating the Al(OH)3 from the sodium aluminate solution after removing 25 the silica by carbon dioxide (CO2) gas purging through the sodium aluminate solution, and calcinating the precipitated Al(OH)3 to obtain alumina.
[0010] In an embodiment, removing iron from the produced aluminium salt solution by oxidation followed by filtration, precipitating the
4
Al(OH)3 from iron removed aluminium salt solution before calcinating the precipitated Al(OH)3. In an embodiment, the iron is removed from the produced aluminium salt solution at pH range 3 – 11.
[0011] In an embodiment, the aluminium dross includes at least 10% of alumina. 5
[0012] In an embodiment, the reduced particle size of the aluminium dross after grinding is below 500 microns.
[0013] In an embodiment, leaching of the grinded aluminium dross is performed in a range of room temperature to 1000C.
[0014] In an embodiment, the mixture of the salt removed aluminium 10 dross and the NaOH are roasted by heating a temperature range of 200-10000C.
[0015] In an embodiment, roasting of the mixture of the salt removed aluminium dross and the NaOH converts aluminium and aluminium compounds in the mixture to the sodium aluminate. 15
[0016] In an embodiment, the CO2 gas purging through the sodium aluminate solution is carried out until a pH of the sodium aluminate solution decreases to a range of 2-11.
[0017] In an embodiment, the precipitation of Al(OH)3 from the sodium aluminate solution further includes removing sodium (bi) carbonate 20 solution from the Al(OH)3 precipitate by filtering and washing the Al(OH)3 precipitate. The process includes obtaining one of a sodium bicarbonate solution and a sodium carbonate solution from the Al(OH)3 precipitate. Also, the process includes performing evaporation crystallization of one of the sodium bicarbonate solution and the sodium carbonate solution to recover 25 Na2CO3.H2O as by-product.
[0018] In an embodiment, calcinating the precipitated Al(OH)3 to obtain the alumina includes leaching the precipitated Al(OH)3 with an acid to dissolve aluminium in form of aluminium chloride and separate insoluble
5
residues. The process includes filtering the leached solution of aluminium salts and the insoluble residues. The process further includes treating the filtered leached solution of aluminium salts with one of ammonia gas and ammonia solution to produce an aluminium salt solution. The process further includes removing iron from the produced aluminium salt solution at pH 5 range 3 - 11 by oxidation followed by filtration. The process further includes precipitating the Al(OH)3 from iron removed aluminium salt solution. Also, the process includes calcinating the precipitated Al(OH)3 to obtain the alumina with high purity.
[0019] In an embodiment, the acid leaching the Al(OH)3 precipitate 10 is done with or without silica removal.
[0020] In an embodiment, the Al(OH)3 precipitate is leached with the acid below 2000C.
[0021] In an embodiment, the Al(OH)3 is precipitated from purified aluminium salt solution at the pH of 3 – 11. 15
[0022] In an embodiment, the precipitated Al(OH)3 is calcinated at above 10000C to obtain the alumina.
[0023] In an embodiment, the ammonia gas used to treat the filtered leached solution of aluminium salts is recovered during water leaching process of grinded aluminium dross with water. 20
[0024] In an embodiment, the silica is removed by one of: adding lime during roasting the mixture of the salt removed aluminium dross and the NaOH and before precipitation of the Al(OH)3 from the sodium aluminate solution.
[0025] In another embodiment, the process for calcinating the 25 precipitated Al(OH)3 to obtain the alumina includes washing the precipitated Al(OH)3 with an acid. Wherein the solution comprises a low amount of impurities. The process further includes, removing iron by at least one of increasing pH range from 3 to 11 and increasing oxidation potential. Also,
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the process includes, calcinating the washed precipitated high-purity Al(OH)3 to obtain the alumina with speciality grade.
[0026] In another embodiment, the acid used in calcination process is hydrochloric acid (HCl) acid or any other mineral acid.
[0027] In another embodiment, the acid washing is performed at 5 below 1000C temperature.
[0028] In another embodiment, the purity of the alumina is enhanced by acid washing below 1000C temperature to remove impurities.
[0029] In another embodiment, the mixture of the salts removed aluminium dross and the NaOH comprises the aluminium dross and the 10 NaOH in a ratio range of 1:0.2 - 1:10.
[0030] In another embodiment, the process for precipitating the Al(OH)3 from the sodium aluminate solution by the CO2 gas purging through the sodium aluminate solution includes conversion of the sodium aluminate in the sodium aluminate solution to sodium(bi)carbonate solution followed 15 by the Al(OH)3.
[0031] These and other aspects of the embodiments herein will be 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 20 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 invention thereof, and the embodiments herein include all such modifications. 25
BRIEF DESCRIPTION OF FIGURES
[0032] These and other features and advantages of the present invention are illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The
7
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 alumina from aluminium dross, according to an embodiment as disclosed herein; 5
[0034] Fig. 2 is a flow diagram illustrating a process for recovering alumina from aluminium dross, according to an embodiment as disclosed herein;
[0035] FIG. 3 is an X-Ray illustrating diffraction analysis (XRD) plot of raw aluminium dross, according to an embodiment as disclosed 10 herein;
[0036] FIG. 4A illustrates the XRD plots for the residue obtained after water treatment, according to an embodiment as disclosed herein;
[0037] FIG. 4B illustrates the XRD plots for salt obtained from the leach solution, according to an embodiment as disclosed herein; 15
[0038] FIG. 5 illustrates the XRD plots for precipitate high-purity aluminium hydroxide (Al(OH)3), according to an embodiment as disclosed herein; and
[0039] FIG. 6 illustrates a scenario in which a photograph of aluminium dross (a) as-received dross, (b) ball-milled and water-washed 20 dross, and (c) synthesized Al(OH)3 from dross.
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 25 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
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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 5 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 that carry out a described function or functions. These blocks, which may be referred to herein as units or modules 10 or the like, are physically implemented by analog or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits and the like, and may optionally be driven by firmware. The circuits may, for example, be embodied in one or 15 more semiconductor chips, or on substrate supports such as printed circuit boards and the like. The circuits constituting a block may be implemented by dedicated hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuitry), or by a combination of dedicated hardware to perform some functions of the block and a processor to perform 20 other functions of the block. Each block of the embodiments may be physically separated into two or more interacting and discrete blocks without departing from the scope of the disclosure. Likewise, the blocks of the embodiments may be physically combined into more complex blocks without departing from the scope of the disclosure. 25
[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
9
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 5 various chemical terms used in the description:
Terms
Abbreviations
NaOH
Sodium Hydroxide
Al(OH)3
Aluminium Hydroxide
CO2
Carbon Dioxide
Al2O3
Aluminium Oxide
AlN
Aluminium Nitride
MgO
Magnesium Oxide
SiO2
Silicon Dioxide
NaCl
Sodium Chloride
KCl
Potassium Chloride
Al
Aluminium
HCl
Hydrochloric Acid
pH
Potential of Hydrogen
Na2CO3.H2O
Sodium Bicarbonate
0C
Temperature in Degree Celsius
AlCl3
Aluminium Chloride
TiO2
Titanium Dioxide
NH4Cl
Ammonium Chloride
XRD
X-Ray diffraction analysis
XRF
X-ray fluorescence
Table 1
[0043] Accordingly, embodiments herein disclose a process for obtaining alumina from aluminium dross. The process includes grinding the
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aluminium dross for reducing a particle size of the aluminium dross, leaching the grinded aluminium dross with water for removing salts from the grinded aluminium dross, roasting a mixture of the salt removed aluminium dross and sodium hydroxide (NaOH) to obtain sodium aluminate, treating the sodium aluminate with hot water to obtain a sodium aluminate solution, 5 removing silica from the sodium aluminate solution by lime treatment, precipitating Al(OH)3 from the sodium aluminate solution after removing the silica by carbon dioxide (CO2) gas purging through the sodium aluminate solution, calcinating the precipitated Al(OH)3 to obtain alumina.
[0044] In an embodiment, the solution after alumina precipitation is 10 crystallised by evaporation crystallisation to produce sodium carbonate as by-product.
[0045] In an embodiment, the leaching of grinded aluminium dross with water dissolves the salts and generate first leach solution and first leach residue. 15
[0046] In an embodiment, the alumina generated from the alkali treatment followed by CO2 precipitation is treated with and not limited to hydrochloric acid (HCl) solution to dissolve aluminium hydroxide into the aluminium hydroxide solution. This aluminium hydroxide solution including a low amount of impurities is then treated with ammonia/ammonia gas to 20 precipitate high-purity Al(OH)3. Filtered and washed Al(OH)3 is further calcined to produce alumina with purity range of 90% to 99.99%.
[0047] In an embodiment, washing the precipitated Al(OH)3 removes impurities in the high-purity Al(OH)3.
[0048] Conventional process recover alumina from aluminium dross 25 by direct acid leaching. However, recovered alumina in this process possess several impurities, which makes the subsequent processes expensive and time-consuming. Unlike to the conventional methods and process, the
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proposed process produces alumina not only utilizes the dross but also generates a high value.
[0049] Unlike the conventional process, the proposed process is used for recovering aluminum from the aluminum dross and producing specialty-grade or high-purity alumina. The aluminum dross used in the proposed 5 process includes at least 10% of the alumina. The aluminum dross is milled to reduce the particle size below 500 microns, preferably below 100 microns. After grinding, the aluminum dross is water leached above room temperature to dissolve salt in the dross. The gases generated, such as ammonia, hydrogen etc., during water leaching needs to be scrubbed. 10
[0050] The residue generated after water leaching is mixed with NaOH and roasted above 200 0C, preferably 500 0C, to convert aluminum and aluminum compounds to sodium aluminate. After roasting, the roasted mass is leached with hot water to dissolve sodium aluminate. After filtration, the residue can be used for refractories, refractory castables, or other 15 applications with or without proper treatment.
[0051] Referring now to the drawings and more particularly to FIGS. 1 through 6, where similar reference characters denote corresponding features consistently throughout the figure, these are shown preferred embodiments. 20
[0052] FIG. 1 is a flow diagram (100) illustrating a process for producing alumina from aluminium dross, according to an embodiment as disclosed herein. At S110 aluminium dross with at least but not limited to alumina in the range of 10% to 80% is grinded to reduce the particle size below 500 microns, preferably below 100 microns. After grinding, at S120 25 the grained aluminium dross is water leached in a range of room temperature to 1000C. The salt is removed from the water-leached mixture by crystallization. At S120 during the water leaching the gases such as ammonia, hydrogen, etc generated, and these gases are reused during the
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ammonium chloride precipitation. At S130, the water leached residue is mixed with NaOH and roasted above 2000C, preferably 5000C, to convert aluminium and aluminium compounds to sodium aluminate. At S140, the roasted sodium aluminate is treated with hot water to dissolve a sodium aluminate solution. At S150, the lime treatment removes silica impurities 5 from the sodium aluminate solution. At S160, the impurity removed sodium aluminate solution is purged with carbon dioxide (CO2) gas to the precipitate high purity Al(OH)3. At S170, the precipitated high-purity Al(OH)3 calcinated to obtain alumina with purity in the range of 90% to 99.99%.
[0053] FIG. 2 is a flow diagram (200) illustrating a process for 10 recovering alumina from aluminium dross, according to an embodiment as disclosed herein. At S210 the raw aluminium dross is milled to less than 500 microns. At S220, this grinded aluminium dross is then leached with hot water. The gases generated, such as ammonia, hydrogen etc., during water leaching recused after precipitation of Al(OH)3. At S230, the crystallization 15 process is done to remove salt from the leached solution. At S240, the salt removed aluminium dross is roasted with sodium hydroxide (NaOH) to obtain sodium aluminate.
[0054] In an embodiment, salt removed aluminium dross is roasted at a temperature of above 2000C, preferably 5000C. 20
[0055] At S250, the roasted sodium aluminate is treated with hot water to dissolve a sodium aluminate solution.
[0056] The alumina can be recovered from sodium aluminate solution by hydrothermal precipitation. However, the recovery of alumina is not complete, and hydrothermal precipitation generates highly crystalline 25 product, which is difficult to treat for impurity removal. Hence, in this proposed process, alumina is precipitated with CO2 gas purging into the solution in order to generate fine aluminium hydroxides, which can be further treated to increase the purity. At S261 the CO2 purging is carried out until
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the pH of the solution reaches below 9. The aluminium hydroxide precipitate is filtered and washed to remove sodium as much as possible. The sodium bicarbonate/ sodium carbonate solution generated after aluminium precipitation is subjected to evaporation crystallization to recover Na2CO3.H2O. 5
[0057] At S260 the silica can be removed from the solution either by adding lime during roasting or before the precipitation of alumina from the solution. This helps in producing alumina with less amount of silicon impurity. At S262 the purity of alumina is enhanced by acid washing below 1000C temperature. This removes the impurities and produces specialty 10 grade aluminium hydroxide. At S263 the impurity removed aluminium hydroxide subjected to calcination process to extract alumina.
[0058] In an embodiment the acid washing of silica removed precipitated aluminium hydroxide solution removes impurities and improves the purity of the specialty grade aluminium hydroxide.The purity of the 15 aluminium hydroxide can be improved by acid washing to remove the impurities. Acid washing is carried out with a minimum amount of acid so that a very small amount of aluminium hydroxide dissolves in the solution.
[0059] In another embodiment, the aluminium hydroxide generated after CO2 precipitation in S270 is leached below 2000C to dissolve 20 aluminium in the form aluminium chloride in S271. If the leaching temperature is above 1500C, silica present in the Al(OH)3 will be precipitated out. Hence, for this at S271, acid leaching above 1500C, there will be no lime treatment required either during roasting or subsequent water leaching. After filtration, at S272, the solution is treated with ammonia gas or solution which 25 is generated at initial water leaching (S220) to precipitate out Al(OH)3 at pH 4.5. The Precipitated Al(OH)3 is further heated and subjected to calcination at S273 to convert it into high-purity alumina. The above process can be better understood by the following examples.
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[0060] In an another embodiment, the acid leaching of Al(OH)3 dissolves the aluminium hydroxide and produce Al(OH)3 leach solution
[0061] Example 1: 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 950C for 4 hours to 5 dissolve the salt and convert most of the AlN to Al(OH)3 and ammonia gas. The slurry is filtered, and the solution is evaporated to produce the salt, which is about 6 g. After drying, the solid is mixed with NaOH with a 1:1 ratio in a mortar pestle. Then it is roasted at 5000C for 4 h followed by water leaching at 600C for 1 h. The slurry is subsequently filtered to remove/recover the 10 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. After the removal of silica rich precipitate, the solution is treated with CO2 bubbling until the pH reached below 9. Then the slurry is filtered and washed to separate sodium bicarbonate and Al(OH)3. This Al(OH)3 is 15 further reacted with 5g of HCl containing 100 ml aqueous solution at 900C for 4h to remove the impurities such as iron, calcium, sodium etc. The purified Al(OH)3 is calcine to about 12000C to produce speciality grade alumina.
[0062] The solution generated after CO2 bubbling, is crystallised by 20 evaporation at 1200C for 6 h to recover sodium carbonate.
[0063] Example 2: 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 950C for 4 hours to dissolve the salt and convert most of the AlN to Al(OH)3 and ammonia gas. 25 The slurry is filtered, and the solution is evaporated to produce the salt, which is about 6 g. After drying, the solid is mixed with NaOH with a 1:1 ratio in a mortar pestle. Then it is roasted at 5000C for 4 h followed by water leaching at 600C for 1 h. The slurry is subsequently filtered to remove/recover the
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residue rich with alpha alumina and magnesium aluminate. The pregnant solution is treated with CO2 bubbling until the pH reached below 9. Then the slurry is filtered and washed to separate sodium bicarbonate and Al(OH)3. This Al(OH)3 is further reacted with 200g of 37% HCl at 1600C for 4h to remove the impurities such as silica and titanium dioxide (TiO2). After 5 filtration, aluminium chloride (AlCl3) solution is reacted with ammonia until the pH reached to 4.5. The precipitated Al(OH)3 is subjected to calcination at 12000C to produce high purity alumina.
[0064] The solution generated after CO2 bubbling, is crystallised by evaporation at 1200C for 6 h to recover sodium carbonate. The solution 10 generated after HCl leaching, is crystallised by evaporation at 1200C for 6 h to recover ammonium chloride.
[0065] FIG. 3 is an X-Ray illustrating diffraction analysis (XRD) plot of raw aluminium dross, according to an embodiment as disclosed herein. Table 2 shows exemplary aluminium dross compound and their 15 weights absorbed in XRF analysis.
Compound
Weight (%)
Fe2O3
0.94
MnO
0.19
TiO2
0.29
CaO
0.49
K2O
3.71
Cl
8.52
SO3
0.05
P2O5
0.02
SiO2
3.93
Al2O3
73.19
MgO
6.46
Na2O
1.52
16
F
0.68
Table 2
[0066] Referring to the Table 2, the XRF analysis on raw aluminium dross. In this initial stage the aluminium dross having recoverable Al metal compound i.e., aluminium oxide (Al2O3) 73.19% along with other impurities such as magnesium oxide (MgO) 6.46%, silicon dioxide (SiO2) 3.93%, etc. 5 this dross is treated to produce valuable alumina with purity range of 90% to 99.99%.
[0067] FIG. 4A illustrates the XRD plots for the residue obtained after water treatment, according to an embodiment as disclosed herein. The FIG. 4B illustrates the XRD plots for salt obtained from the leach solution, 10 according to an embodiment as disclosed herein. The Table 3 shows exemplary components absorbed in XRF analysis of ball milled and water washed dross.
Compound
Weight (%)
Fe2O3
0.86
MnO
0.20
TiO2
0.30
CaO
0.46
K2O
0.21
Cl
0.29
SiO2
5.34
Al2O3
84.37
MgO
6.36
Na2O
0.32
F
1.21
P2O5
0.021
SO3
0.024
Table 3
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[0068] Referring to the Table 3, the XRF analysis on ball milled about less than 500 micron size and water washed dross aluminium dross. This dross Al metal compound i.e., aluminium oxide (Al2O3) 84.37% along with other impurities such as magnesium oxide (MgO) 6.36%, silicon dioxide (SiO2) 5.34%, and other oxides in minor quantities. This dross is 5 roasted with NaOH at above 2000C, leached to dissolve sodium aluminate, then treated with CO2 bubbling to produce aluminium hydroxide (Al(OH)3).
[0069] FIG. 5 illustrates the XRD plots for precipitate high-purity Al(OH)3, according to an embodiment as disclosed herein. The salt removed aluminium dross and sodium hydroxide mixture is treated with lime to 10 remove silica to obtain the sodium aluminate solution. FIG. 5 illustrates the X-Ray diffraction pattern analysis plots of speciality grade Al(OH)3 precipitated from Sodium aluminate solution and followed by acid washing to provide information on the particle size and defects on the precipitated speciality grade Al(OH)3. 15
[0070] FIG. 6 illustrates a scenario in which a photograph of aluminium dross (a) as-received dross, (b) ball-milled and water-washed dross, and (c) synthesized Al(OH)3 from dross. The examples of raw aluminium dross with at least but not limited to alumina in the range of 30% to 80% are illustrated in FIG. 6. (a) This aluminium dross grinded to reduce 20 the particle size below 500 microns, this illustrated in FIG. 6. (b). After the proposed process (i.e., leaching the grinded aluminium dross, roasting with NaOH, acid washing, silica removal, precipitating Al(OH)3) the final high purity and speciality grade Al(OH)3 is illustrated in FIG. 6. (c).
[0071] Therefore, the proposed process is cost-effective technique to 25 produce alumina utilizing the dross and also generates a high value.
[0072] The embodiments disclosed herein can be implemented using at least one hardware device to perform recovery of aluminium from aluminium dross and produce specialty-grade or high-purity alumina.
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[0073] 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 and or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are 5 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 10 the embodiments herein can be practiced with modification within the scope of the embodiments as described herein. , C , Claims:CLAIMS
1. A process for obtaining alumina from aluminium dross, wherein the process comprises:
grinding the aluminium dross for reducing a particle size of the aluminium dross; 5
leaching the grinded aluminium dross with water for removing salts from the grinded aluminium dross;
roasting a mixture of the salt removed aluminium dross and sodium hydroxide (NaOH) to obtain sodium aluminate;
treating the sodium aluminate with hot water to obtain a 10 sodium aluminate solution;
removing silica from the sodium aluminate solution by lime treatment;
precipitating Al(OH)3 from the sodium aluminate solution after removing the silica by carbon dioxide (CO2) gas purging through 15 the sodium aluminate solution; and
calcinating the precipitated Al(OH)3 to obtain the alumina.
2. The process as claimed in claim 1, wherein the aluminium dross comprises at least 10% of alumina.
3. The process as claimed in claim 1, wherein the reduced particle size 20 of the aluminium dross after grinding is below 500 microns.
4. The process as claimed in claim 1, wherein leaching of the grinded aluminium dross is performed in a range of room temperature to 1000C.
5. The process as claimed in claim 1, wherein the mixture of the salt 25 removed aluminium dross and the NaOH are roasted by heating a temperature range of 200-10000C, and wherein roasting of the mixture of the salt removed aluminium dross and the NaOH converts
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aluminium and aluminium compounds in the mixture to the sodium aluminate.
6. The process as claimed in claim 1, wherein the CO2 gas purging through the sodium aluminate solution is carried out until a pH of the sodium aluminate solution decreases to a range of 2-11. 5
7. The process as claimed in claim 1, precipitation of Al(OH)3 from the sodium aluminate solution further comprises:
removing sodium (bi) carbonate solution from the Al(OH)3 precipitate by filtering and washing the Al(OH)3 precipitate;
obtaining one of a sodium bicarbonate solution and a sodium 10 carbonate solution from the Al(OH)3 precipitate; and
performing evaporation crystallization of one of the sodium bicarbonate solution and the sodium carbonate solution to recover Na2CO3.H2O as by-product.
8. The process as claimed in claim 1, wherein calcinating the 15 precipitated Al(OH)3 to obtain the alumina comprises:
leaching the precipitated Al(OH)3 with an acid to dissolve aluminium in form of aluminium chloride and separate insoluble residues;
filtering the leached solution of aluminium salts and the 20 insoluble residues;
treating the filtered leached solution of the aluminium salts with one of ammonia gas and ammonia solution to produce an aluminium salt solution;
removing iron from the produced aluminium salt solution by 25 oxidation followed by filtration;
precipitating the Al(OH)3 from iron removed aluminium salt solution; and
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calcinating the precipitated Al(OH)3 to obtain the alumina with high purity.
9. The process as claimed in claim 7, wherein the acid leaching the Al(OH)3 precipitate is done with or without silica removal.
10. The process as claimed in claim 7, wherein the the Al(OH)3 5 precipitate is leached with the acid below 200 0C.
11. The process as claimed in claim 7, wherein the Al(OH)3 is precipitated from purified aluminium salt solution at the pH of 3 – 11, and wherein the iron is removed from the produced aluminium salt solution at pH range 3 - 11. 10
12. The process as claimed in claim 7, wherein the precipitated Al(OH)3 is calcinated at above 10000C to obtain the alumina.
13. The process as claimed in claim 7, wherein the ammonia gas treats the filtered leached solution of aluminium salts is recovered during a water leaching process of grinded aluminium dross with water. 15
14. The process as claimed in claim 1, calcinating the precipitated Al(OH)3 to obtain the alumina comprises:
washing the precipitated Al(OH)3 with an acid; wherein the washed solution comprises a low amount of impurities;
removing iron by at least one of increasing pH range from 3 20 to 11 and increasing oxidation potential; and
calcinating the iron removed Al(OH)3 to obtain the alumina with speciality grade.
15. The process as claimed in claim 14, wherein the acid is hydrochloric acid (HCl) acid. 25
16. The process as claimed in claim 14, wherein the acid washing is performed at below 1000C temperature.
17. The process as claimed in claim 1, wherein the silica is removed by one of: adding lime during roasting the mixture of the salt removed
22
aluminium dross and the NaOH and before precipitation of the Al(OH)3 from the sodium aluminate solution.
18. The process as claimed in claim 1, wherein a purity of the alumina is enhanced by acid washing below 1000C temperature to remove impurities. 5
19. The process as claimed in claim 1, wherein the mixture of the salts removed aluminium dross and the NaOH comprises the aluminium dross and the NaOH in a ratio range of 1:0.2 - 1:10.
20. The process as claimed in claim 1, wherein precipitating the Al(OH)3 from the sodium aluminate solution by the CO2 gas purging through 10 the sodium aluminate solution comprises: conversion of the sodium aluminate in the sodium aluminate solution to sodium(bi)carbonate solution followed by the Al(OH)3.
Dated this 4th Day of April, 2023