AU2023200394A1

AU2023200394A1 - A Method for the Preparation of Alumina

Info

Publication number: AU2023200394A1
Application number: AU2023200394A
Authority: AU
Inventors: Annette Margaret Atkins; Ignatius Kim Seng Tan
Original assignee: Altech Chemicals Australia Pty Ltd
Current assignee: Altech Chemicals Australia Pty Ltd
Priority date: 2014-02-26
Filing date: 2023-01-25
Publication date: 2023-02-23
Also published as: AU2014253487A1; AU2020289717A1; AU2019204216A1

Abstract

A method for the preparation of alumina, the method comprising the steps of: treating aluminous material to increase the alumina content to over about 30 %; treating the aluminous material to provide particle size less than about 0.5 mm; calcining the aluminous material at about 400 - 700 °C; treating the aluminous material to provide particle sizes less than about 500 pm; leaching the aluminous material with a mineral acid to provide a pregnant liquor; conducting a plurality of steps of precipitating aluminium chloride hexahydrate; conducting a plurality of ion exchange steps; and calcining aluminium chloride hexahydrate to provide alumina.

Description

A METHOD FOR THE PREPARATION OF ALUMINA TECHNICAL FIELD

[0001] The present invention relates to a method for the preparation of alumina.

BACKGROUND ART

[0002] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0003] There are a number of industrial methods for producing high purity alumina. One the most common methods is hydrolysis of aluminum alkoxide. In this process, high purity aluminum alkoxide is synthesised from aluminum metal and alcohol, and aluminium hydroxide is produced by hydrolysis of alkoxide, and finally high purity alumina is obtained by calcination. Choline hydrolysis of aluminum is another common method which involves the dissolution of aluminum powder to a hydroxide and then subsequent calcination to convert it back to an alumina (A1 2 0 3 ) form. Both of the processes described above utilise pure aluminum metal as a feedstock.

SUMMARY OF INVENTION

[0004] In accordance with the present invention, there is provided a method for the preparation of alumina, the method comprising the steps of:

treating aluminous material to increase the alumina content to over about 30 %;

treating the aluminous material to provide particle size less than about 0.5 mm;

calcining the aluminous material at about 400 - 700 °C;

treating the aluminous material to provide particle sizes less than about 500 pm;

leaching the aluminous material with a mineral acid to provide a pregnant liquor; conducting a plurality of steps precipitating aluminium chloride hexahydrate; conducting a plurality of ion exchange steps; and calcining aluminium chloride hexahydrate to provide alumina.

[0005] Advantageously, the method of the present invention can be used to provide high purity alumina. Preferably, the alumina is 99.99 %.

[0006] Preferably, the aluminous material is an aluminous clay. More preferably, the aluminous material is kaolin.

[0007] Preferably, the aluminous material contains less than 1.5 % iron.

[0008] Preferably, the step of:

treating aluminous material to increase the alumina content to over about 30 %;

comprises crushing the aluminous material to less than 3 mm particle size.

[0009] Preferably, the step of:

treating aluminous material to increase the alumina content to over about 30 %;

comprises drying the crushed aluminous material.

[0010] Preferably, the step of:

treating aluminous material to increase the alumina content to over about 30 %;

further comprises screening the aluminous material .

[0011] Advantageously, screening of the aluminous material removes significant portions of quartz material, thereby increasing the wt% of aluminium in the material.

[0012] In one form of the invention, the method comprises the further step of:

grinding the aluminous material.

[0013] Preferably, the method comprises the further step of:

screening the ground aluminous material to less than 0.5 mm.

[0014] Preferably, the step of:

calcining the aluminous material at about 400 - 700 °C;

is conducted in a natural gas fired rotary kiln.

[0015] Preferably, the method of the present invention comprises the further step of:

cooling the aluminous material to a temperature of about 80 °C after the step of:

calcining the aluminous material at about 400 - 700 °C;

[0016] Preferably, the step of:

treating the aluminous material to provide particle size less than about 500 pm;

comprises ball milling the aluminous material and screening.

[0017] Advantageously, the mineral acid dissolves the aluminum present and facilitates its separation from any remaining silica. The leachate may contain other impurities such as iron, titanium, sodium and potassium.

[0018] The mineral acid may be provided in the form of hydrochloric acid,

[0019] . It will be appreciated that the concentration of the mineral acid will depend on the type of acid itself as well as the nature of the aluminous material including particle size distribution and level of impurities. Preferably, the mineral acid has a concentration of between 1 M and 9 M. More preferably, the mineral acid has a concentration of between 3 M and 9 M. More preferably, the mineral acid has a concentration of about 6 M. It will be appreciated that the volume of mineral acid will depend on the type of acid itself as well as the nature of the aluminous material including particle size distribution and level of impurities. Preferably the addition of the mineral acid forms a mixture with a solid:liquid ratio of between 5 and 20 %.

[0020] The step of:

leaching the aluminous material with a mineral acid;

is preferably conducted at a temperature of between 70 °C and 110 °C.

[0021] Preferably, the aluminous material is leached for between 15 minutes and 1 hour. More preferably, the aluminous material is leached for about 1 hour.

[0022] Without being limited by theory, it is believed that the process of extraction of aluminum from kaolin into an HCI solution is best described by the equation;

A12 03.2SiO2 .2H20 (s) + 6HCI (aq) - 2AIC13 (aq) + 2SiO 2 (s) + 5H 20

[0023] It will be appreciated that the kaolin can be represented in a number of different ways. For the purpose of the present application, the equation detailed above is considered appropriate.

[0024] Preferably, the method of the present invention comprises the further step of:

solid/liquid separation of the leached aluminous material.

[0025] Preferably the step of:

solid/liquid separation of the leached aluminous material;

comprises treatment of the leached material in a thickener with the aid of a flocculant to provide the pregnant leach solution and thickened solids. In one form of the invention, the thickened solids are filtered.

[0026] Preferably, the method of the present invention comprises the further step of:

passing the pregnant leach solution through a polishing filter to remove undesired small particles.

[0027] Preferably, the method of the present invention comprises the further step of:

neutralising the filtered solids with a strong base such as limestone, hydrated lime or caustic soda.

[0028] In one form of the invention, the step of precipitation of aluminium chloride hexahydrate comprises evaporative crystallisation of the pregnant leach solution to provide aluminium chloride hexahydrate crystals.

[0029] Preferably, the step of precipitation of aluminium chloride hexahydrate further comprises addition of 35 % hydrochloric acid solution to provide further aluminium chloride hexahydrate crystals.

[0030] In a second form of the invention, the step of precipitation of aluminium chloride hexahydrate comprises hydrochloric gas sparging of the pregnant leach solution to provide aluminium chloride hexahydrate crystals.

[0031] Preferably the aluminium chloride hexahydrate crystals are filtered and washed with saturated aluminium chloride hexahydrate solution. The filtrate may be recycled to the leaching stage concentrated for further use.

[0032] Preferably, the filtered aluminium chloride hexahydrate crystals are dissolved in water to provide a saturated solution of aluminium chloride hexahydrate.

[0033] Preferably, the step of ion exchange comprises treating the saturated solution of aluminium chloride hexahydrate with an ion exchange resin.

[0034] In one form of the invention, there is provided an ion exchange step after each step of precipitation and subsequent dissolution of aluminium chloride hexahydrate.

[0035] In one form of the invention, there is provided a first precipitation step, followed by a first ion exchange step, followed by a second precipitation step, followed by a second ion exchange step, followed by a third precipitation step.

[0036] Preferably, the method of the present invention comprises the additional step of:

hydro-pyrolysing the aluminium chloride hexahydrate crystals prior to the step of:

calcining aluminium chloride hexahydrate to provide alumina.

[0037] Advantageously, the step of hydro-pyrolysing the aluminium chloride hexahydrate crystals removes physically bound hydrogen chloride.

[0038] Preferably, the step of calcining the aluminium chloride hexahydrate crystals comprises calcining at about 1100 °C in a natural gas fed rotary kiln.

[0039] The method of the present invention may comprise the additional step of micronising the alumina to less than 10 micron.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will now be described, by way of example only, with reference to one embodiment thereof, and the accompanying drawing, in which:-

Figure 1 is a schematic flow sheet depicting a process for the production of alumina in accordance with an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

[0041] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

[0042] The present invention is not to be limited in scope by the specific embodiments described herein, which are intended for the purpose of exemplification only. Functionally equivalent products, compositions and methods are clearly within the scope of the invention as described herein.

[0043] The entire disclosures of all publications (including patents, patent applications, journal articles, laboratory manuals, books, or other documents) cited herein are hereby incorporated by reference.

[0044] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0045] In Figure 1 there is shown a process 1 for the production of high purity alumina. All of the unit operations in the process 1 are designed to operate continuously with full process instrumentation and control being provided for.

[0046] Run-of-mine (ROM) ore 2 is concentrated to a minimum 30 % aluminium as alumina by means of physical methods such as crushing the ore to the required particle size and screening 3. The concentrated ore having at least 30 % alumina is dried 4 and ground using roll crushers 5 and further screening 6 to obtain particle sizes less than 0.5 mm.

[0047] The concentrated aluminous ore with less than 0.5 mm particle size is stored in feed storage area 7, from where it is transferred for calcination in a natural gas fired kiln 8 operating at 500°C for a residence time of 15 minutes to 1 hour, more preferably minutes.

[0048] The calcined aluminous ore is cooled to about 80 °C by means of indirect water assisted cooling system 9.

[0049] The cooled calcined aluminous ore is ball milled 10 to less than 300 Pm. The ore is stored in a calcined storage area 11 before subsequent leaching.

[0050] The ground calcined ore is leached with hydrochloric acid of at least 20

% strength in a series of acid leach vessels 12 for 30 minutes to 2 hours, preferably 30 minutes to provide a leach slurry.

[0051] The leached slurry is transferred to a series thickeners 13 where the pregnant leach solution is separated from the solid residue with the aid of flocculants. The residue solids are filtered and neutralized in neutralization tanks 14 using quicklime or such similar alkaline media. The neutralized solid residues are filtered 15 and disposed accordingly.

[0052] The pregnant leach solution from the thickeners 13 is sent to a polishing filter 16 to remove any suspended solid particles to provide a pregnant solution. The pregnant leach solution from the polishing filter 16 not only contains desired aluminium chloride but can also contain other leached impurities such as iron, magnesium, manganese calcium, sodium and potassium.

[0053] The pregnant leach solution is subjected to hydrochloric acid gas sparging crystallisation to carefully crystallise aluminium chloride hexahydrate crystals by increasing the HCI concentration of the pregnant leach solution. The solubility of aluminium chloride decreases with increased HCI acid concentration. The crystallisation is conducted such that the increased acid concentration results in around -97 % aluminium is crystallized as aluminium hexahydrate salt. The majority of the impurities remain in solution 17.

[0054] The crystallised aluminium chloride hexahydrate from the crystallisation process is filtered and washed with purified saturated solution of aluminium hexahydrate solution 18 . The spent liquor is re-cycled to the leach solution.

[0055] The aluminium chloride hexahydrate crystals are re-dissolved in ultrapure water to prepare a saturated solution of aluminium chloride hexahydrate. The solution is treated with an ion exchange resin to remove impurities which are co-precipitated with aluminium chloride hexahydrate crystals during the crystallisation process.

[0056] The prepared solution of aluminium chloride is treated with an ion exchange resin 19 such as Purolite S940 to provide a purified aluminium chloride solution.

[0057] The purified aluminium chloride solution after ion exchange treatment is passed through a second HCI gas sparging crystallisation stage. It is subjected to controlled crystallisation process to carefully crystallise aluminium chloride hexahydrate crystals by increasing the acid concentration of the aluminium chloride solution in such a way that about 90-97 % aluminium chloride is crystallised as hexahydrate, the majority of those impurities present remaining in solution 20.

[0058] The crystallised aluminium chloride hexahydrate crystals from the above HC gas sparging crystallisation process are filtered and washed with stage 3 crystallisation spent liquor 21. The spent liquor is re-cycled to the leach solution.

[0059] The aluminium chloride hexahydrate crystals thus obtained are re-dissolved in ultrapure water to provide a saturated solution of aluminium chloride hexahydrate. The solution is treated with an ion exchange resin to remove any impurities which co precipitate with aluminium chloride hexahydrate crystals during the crystallisation process 22.

[0060] This solution of aluminium chloride thus obtained after the second crystallisation process is treated with an ion exchange resin such as Purolite S940 to provide a purified aluminium chloride solution 23 .

[0061] The purified aluminium chloride solution after second ion exchange treatment is passed through third stage HCI gas sparging crystallisation process. It is subjected to controlled crystallisation process to carefully crystallise aluminium chloride hexahydrate crystals by increasing the acid concentration of the aluminium chloride solution in such a way that about 90-97 % aluminium chloride is crystallized as hexahydrate whereas most of the other impurities having high solubility in water than aluminium chloride remain in spent liquor 21.

[0062] The crystallised aluminium chloride hexahydrate crystals from the above crystallisation process are filtered and washed with concentrated hydrochloric acid 24 .

The spent liquor is re-cycled to the leach solution.

[0063] The aluminium chloride hexahydrate crystals thus obtained are high purity aluminium chloride hexahydrate crystals having purity of 99.99%.

[0064] The purified aluminium chloride hexahydrate crystals are subjected to calcining at 400 C in a natural gas fired rotary kiln 25 . Aluminium chloride hexahydrate decomposes at this temperature to yield a mixture of aluminium hydroxide and aluminium oxide releasing hydrochloric acid vapour saturated with steam. The hydrochloric acid vapour is condensed and collected 26.

[0065] The mixture of aluminium hydroxide and aluminium oxide obtained through first calcining process 27 is subjected to high temperature calcining at 1100 C 28 to remove remaining water and provide high purity alumina.

[0066] High purity alumina thus obtained having purity 99.99 % is cooled to room temperature 29 and micronised using a microniser 30 to required particle size as per specifications from customer, preferably <10 pm.

[0067] Micronised high purity alumina (HPA) is packaged 31 in air tight paper bags with polyethylene lining of required content.

Claims

1. A method for the preparation of alumina, the method comprising the steps of:

treating aluminous material to increase the alumina content to over about 30 %;

calcining the aluminous material at about 400 - 700 °C;

leaching the aluminous material with a mineral acid to provide a pregnant liquor;

conducting a plurality of steps of precipitating aluminium chloride hexahydrate;

conducting a plurality of ion exchange steps; and

calcining aluminium chloride hexahydrate to provide alumina.

2. A method for the preparation of alumina according to claim 1, wherein the aluminous material is an aluminous clay.

3. A method for the preparation of alumina according to claim 1, wherein the aluminous material is kaolin.

4. A method for the preparation of alumina according to any one of the preceding claims, wherein the step of:

treating aluminous material to increase the alumina content to over about 30 %;

comprises crushing the aluminous material to less than 3 mm particle size.

5. A method for the preparation of alumina according to claim 4, wherein the step of:

treating aluminous material to increase the alumina content to over about 30 %; comprises drying the crushed aluminous material.

6. A method for the preparation of alumina according to claim 5, wherein the step of:

treating aluminous material to increase the alumina content to over about 30 %;

comprises screening the aluminous material.

7. A method for the preparation of alumina according to any one of the preceding claims, comprising the further step of:

grinding the aluminous material.

8. A method for the preparation of alumina according to claim 7, comprising the further step of:

screening the ground aluminous material to less than 0.5 mm.

9. A method for the preparation of alumina according to any one of the preceding claims, wherein the method comprises the further step of:

calcining the aluminous material at about 400 - 700 °C.

10. A method for the preparation of alumina according to any one of the preceding claims, wherein the step of:

comprises ball milling the aluminous material and screening.

11. A method for the preparation of alumina according to any one of the preceding claims, wherein the mineral acid is hydrochloric acid.

12. A method for the preparation of alumina according to claim 11, wherein the concentration of the hydrochloric acid is about 6 M.

13. A method for the preparation of alumina according to any one of the preceding claims, wherein the step of leaching the aluminous material with a mineral acid; is conducted at a temperature of between 70 °C and 110 °C.

14. A method for the preparation of alumina according to any one of the preceding claims, wherein the aluminous material is leached for between 15 minutes and 1 hour.

15. A method for the preparation of alumina according to any one of the preceding claims, wherein the method comprises the further step of:

solid/liquid separation of the leached aluminous material to provide thickened solids and a pregnant leach solution.

16. A method for the preparation of alumina according to claim 15, wherein the method comprises the further step of:

17. A method for the preparation of alumina according to claim 15 or claim 16, wherein the step of precipitation of aluminium chloride hexahydrate comprises evaporative crystallisation of the pregnant leach solution to provide aluminium chloride hexahydrate crystals.

18. A method for the preparation of alumina according to any one of claims 15 to 17, wherein the step of precipitation of aluminium chloride hexahydrate comprises addition of 35 % hydrochloric acid solution to provide aluminium chloride hexahydrate crystals.

19. A method for the preparation of alumina according to claim 15 or claim 16, wherein the step of precipitation of aluminium chloride hexahydrate comprises HCI gas sparging of the pregnant leach solution to provide aluminium chloride hexahydrate crystals.

20. A method for the preparation of alumina according to any one of ht preceding claims, wherein the step of dissolving the filtered and washed aluminium chloride hexahydrate in ultrapure water to form a saturated solution.

21. A method for the preparation of alumina according to any one of the preceding claims, wherein the step of ion exchange comprises treating the saturated solution of aluminium chloride hexahydrate with an ion exchange resin.

22. A method for the preparation of alumina according to any one of the preceding claims, wherein there is provided a first precipitation step, followed by a first ion exchange step, followed by a second precipitation step, followed by a second ion exchange step, followed by a third precipitation step.

23. A method for the preparation of alumina according to any one of the preceding claims, wherein the method comprises the additional step of:

calcining aluminium chloride hexahydrate to provide alumina.