AU2021107589A4

AU2021107589A4 - A method for the preparation of smelter grade alumina

Info

Publication number: AU2021107589A4
Application number: AU2021107589A
Authority: AU
Inventors: Jingyuan Liu; Ignatius Kim Seng Tan
Original assignee: Altech Chemicals Australia Pty Ltd
Current assignee: Altech Chemicals Australia Pty Ltd
Priority date: 2017-09-22
Filing date: 2021-10-21
Publication date: 2022-01-06
Anticipated expiration: 2026-09-20
Also published as: AU2023200737A1; AU2018233001A1; AU2018101228A4; AU2019100630A4; AU2021201653A1; AU2019202993A1

Abstract

A method for the preparation of alumina, the method comprising the steps of treating aluminous material to reduce particle size and increase the alumina content calcining the aluminous material leaching the aluminous material with hydrochloric acid solid liquid separation to provide a pregnant liquor crystallising aluminium chloride hexahydrate by adding hydrogen chloride gas, precipitating aluminium chloride hexahydrate and separating the aluminium chloride hexahydrate calcining aluminium chloride hexahydrate to provide alumina, and recycling hydrogen chloride as liquor for leaching and as vapour for aluminium chloride hexahydrate crystalisation.

Description

A METHOD FOR THE PREPARATION OF SMELTER GRADE 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] The dominant method to produce smelter grade alumina is the Bayer process from Bauxite. In the Bayer process, bauxite containing alumina and impurities of typically Fe203, SiO2 , and TiO2 is dried, ground, digested in sodium hydroxide under pressure. Impurities are separated by filtration, before an alumina hydroxide is precipitated and calcined to produce alumina, which is then transferred to the Hall Heroult electrochemical cell for electrolysis to produce aluminium metal. In 1930, the typical alumina grade for bauxite was published at around 60% A1203, today however bauxite's typical alumina grade is -38 to 43% A1203, which shows a declining quality for the remaining unexploited bauxite deposits. In those alumina-producing countries where there is a limited or lack of local supply of easily accessible high-grade bauxite ore (e.g. China, Canada, Russia and the Middle East), industry is looking to alternative methods for producing alumina (A1203) from non-bauxitic, alumina-rich raw materials, such as aluminous clay.

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 reduce particle size and increase the alumina content;

calcining the aluminous material;

leaching the aluminous material with hydrochloric acid;

solid liquid separation to provide a pregnant liquor; crystallising aluminium chloride hexahydrate by adding recycled hydrogen chloride gas, precipitating aluminium chloride hexahydrate and separating the aluminium chloride hexahydrate; calcining aluminium chloride hexahydrate to provide alumina; and recycling hydrogen chloride as liquor for leaching and as vapour for aluminium chloride hexahydrate crystalisation

[0005] Advantageously, the method of the present invention can be used to provide low sodium sandy alumina. Preferably, the alumina is greather than 99.95 %.

[0006] Preferably, the crystallisation process is conducted one time only. That is, adding hydrogen chloride gas and precipitating aluminium chloride hexahydrate from leach pregnant liquor.;

[0007] Preferably, the aluminous material is an aluminous clay. More preferably, the aluminous material is kaolin. More preferably still, the kaolin is sourced from the Meckering area of Western Australia.

[0008] Where the aluminous material is kaolin, the step of:

calcining the aluminous material;

advantageously forms metakaolin.

[0009] Preferably, the aluminous material contains less than 1.5 % iron.

[00010] Preferably, the step of:

comprises drum scrubbing the aluminous material in water.

[00011] Preferably, the step of:

further comprises screening the aluminous material to less than 0.3 mm particle size.

[00012] Advantageously, screening of the aluminous material removes significant portions of quartz material, thereby increasing the wt% of aluminium in the material.

[00013] Preferably, the step of:

increases the alumina content to over about 27 % */w.

[00014] Preferably, the step of:

screening the aluminous material to less than 0.3 mm particle size;

further comprises solid liquid separation of the screened aluminous material.

[00015] Preferably, the step of:

calcining the aluminous material;

is conducted at a temperature of about 400 - 700 °C.

[00016] Preferably, the step of:

calcining the aluminous material;

is conducted for a period of 15 to 60 minutes.

[00017] Preferably, the step of:

calcining the aluminous material;

is conducted for a period of about 15 minutes.

[00018] Preferably, the step of:

calcining the aluminous material;

is conducted in a rotary kiln.

[00019] Preferably, the step of calcining the aluminous material,

is preceded by the step of flash drying the aluminous material to remove at least a portion of the moisture in the aluminous material.

[00020] Preferably, the method of the present invention comprises the further step of: cooling the aluminous material to a temperature of less than about 80 C after the step of: calcining the aluminous material;

[00021] Advantageously, the hydrochloric acid dissolves the aluminium present and facilitates its separation from any remaining silica. The leachate may contain other impurities such as iron, titanium, sodium and potassium.

[00022] It will be appreciated that the concentration of the hydrochloric 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 hydrochloric acid has a concentration of between 1 M and 9 M. More preferably, the hydrochloric acid has a concentration of between 3 M and 9 M. More preferably, the hydrochloric acid has a concentration of between 6 M and 9 M. More preferably, the hydrochloric acid has a concentration of about 9 M. It will be appreciated that the volume of hydrochloric acid will depend on the nature of the aluminous material including particle size distribution and level of impurities. Preferably the addition of the hydrochloric acid forms a mixture with a solid:liquid ratio of between 20 and 35 %.

[00023] The step of:

leaching the aluminous material with hydrochloric acid;

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

[00024] Preferably, the aluminous material is leached for between 15 minutes and 1 hour. More preferably, the aluminous material is leached for about 1 hour.

[00025] Without being limited by theory, it is believed that the process of extraction of aluminium from kaolin into an HCI solution is best described by the equation;

A120.2SiO2.2H20 (s) + 6HCI (aq) - 2AIC13(aq) + 2SiO 2 (S) + 5H20

[00026] 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.

[00027] Preferably, the method of the present invention comprises the further step of:

solid/liquid separation of the leached aluminous material.

[00028] Preferably the step of:

solid/liquid separation of the leached aluminous material;

comprises pressure filtration of the leached material to provide the pregnant leach solution and residue solids.

[00029] 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.

[00030] Preferably, the method of the present invention comprises the further step of:

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

[00031] 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.

[00032] Preferably, the step of precipitation of aluminium chloride hexahydrate further comprises addition of 35 % hydrochloric acid solution to provide further aluminium chloride hexahydrate crystals.

[00033] In one form of the invention, the step of precipitating aluminium chloride hexahydrate comprises hydrochloric gas sparging of the pregnant leach solution to provide aluminium chloride hexahydrate crystals.

[00034] Preferably the aluminium chloride hexahydrate crystals are filtered and washed with hydrochloric acid or demineralised water. The filtrate may be concentrated and recycled to the leaching stage for further use.

[00035] 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.

[00036] Advantageously, the step of hydro-pyrolysing the aluminium chloride hexahydrate crystals removes physically bound hydrogen chloride and water as gases.

[00037] Preferably, the step of calcining the aluminium chloride hexahydrate crystals comprises calcining at about 1100 °C to 1300 OC in a natural gas fired rotary kiln.

[00038] The method of the present invention may comprise the additional step of washing the alumina with a dilute weak clean acid and/or demineralized water.

[00039] BRIEF DESCRIPTION OF THE DRAWINGS

[00040] 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;

Figure 2 is a detailed schematic flow sheet depicting the kaolin activation portion of the process for the production of alumina in accordance with an embodiment of the invention;

Figure 3 is a detailed schematic flow sheet depicting the acid leaching portion of the process for the production of alumina in accordance with an embodiment of the invention;

Figure 4 is a detailed schematic flow sheet depicting the crystallisation portion of the process for the production of alumina in accordance with an embodiment of the invention; and

Figure 5 is a detailed schematic flow sheet depicting the calcination portion of the process for the production of alumina in accordance with an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

[00041] 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.

[00042] 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.

[00043] 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.

[00044] 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.

[00045] In Figure 1 there is shown a process for the production of alumina. All of the unit operations in the process are designed to operate continuously with full process instrumentation and control being provided for.

[00046] Run-of-mine (ROM) un-beneficiated ore 12 is concentrated to a minimum 27 % aluminium as alumina by means of physical methods such as drum scrubbing 14 the ore to separate aluminous and gangue material and screening 16 to obtain particle sizes less than about 0.3 mm. The beneficiated ore having at least 27 % alumina is pressure filtered/tube filtered 18 to form a filter cake.

[00047] The aluminous ore filter cake is dried in a flash drying column 20 from where it is transferred for calcination in a gas fired kiln 22 operating at 700 °C for a residence time of 15 minutes to 60 minutes, more preferably 60 minutes.

[00048] The calcined aluminous ore is cooled to less than about 80 C by means of indirect water assisted cooling system 24.

[00049] The cooled calcined aluminous ore is crushed/milled 26 to less than 300 m and screened 28 again to remove any oversize particles or agglomerates. The ore is stored in a calcined storage area 30 before subsequent leaching.

[00050] The ground calcined ore is leached with hydrochloric acid 31 of at least 20 %

strength at 105 OC in a series of acid leach vessels 32 for 30 minutes to 2 hours, preferably 1 hour to provide a leach slurry. Preferably, there are provided four leach vessels and the residence time in each vessel is about 15 minutes.

[00051] Vent gas from heating or cooling leached slurry is scrubbed in the gas scrubbing system 75.

[00052] The leached slurry is cooled to 80 C and transferred to a series of pressure filters 34 where the pregnant leach solution is separated from the solid residue. The residue solids are neutralised in neutralisation tanks 36 using sodium hydroxide, quicklime, hydrated lime or limestone or such similar alkaline media. The neutralised solid residues are filtered 38 and disposed of accordingly.

[00053] The pregnant leach solution from the pressure filters 34 is sent to a polishing filter 40 to remove any suspended solid particles and provide a clean pregnant leach solution. Preferably, there are provided two polishing filters. The pregnant leach solution from the polishing filter 40 not only contains the desired aluminium chloride but may also contain other leached impurities such as traces of iron, magnesium, manganese, calcium, sodium and potassium.

[00054] The pregnant leach solution is subjected to hydrochloric acid gas sparging 42 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 % of the aluminium being crystallised as aluminium chloride hexahydrate salt. The majority of the impurities remain in solution.

[00055] The crystallised aluminium chloride hexahydrate from the crystallisation process is filtered 46 and washed with demineralised water.

[00056] The spent liquor 50 is recycled to the leach solution and with a portion of it bled to the hydrogen chloride recovery plant 52.

[00057] The hydrogen chloride is recovered as gas in the hydrogen chloride recovery plant 52 and combined with the hydrogen chloride gas from the indirect rotary kiln roaster 64 for aluminium chloride hexahydrate crystallization. A small stream of bleed 53 from the recovery plant removes the impurities from the plant. The bleed stream is nertrolised for disposal after recovering the aluminium.

[00058] The aluminium chloride hexahydrate crystals thus obtained are aluminium chloride hexahydrate crystals having purity of 99.95%.

[00059] The aluminium chloride hexahydrate crystals are subjected to roasting at a temperature up to 700 °C in a gas fired indirect rotary kiln 64. Aluminium chloride hexahydrate decomposes at the temperature to yield a mixture of aluminium hydroxide and aluminium oxide releasing hydrogen chloride vapour and steam. The hydrogen chloride vapour is recycled to a hydrogen chloride recovery plant 52.

[00060] The mixture of aluminium hydroxide and aluminium oxide obtained through the roasting process is subjected to high temperature calcining at 1100 °C to 1300 °C 68 to remove remaining water and chloride, hence and transform to alpha alumina.

[00061] Alpha alumina is cooled to near room temperature 70

.

[00062] Alumina thus obtained having purity 99.95 % is packaged in air tight paper bags with polyethylene lining of required content or bulk bags.

The present application is divided from Australian Patent Application 2021201653, the content of which is incorporated herein in its entirety by reference.

Claims

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

calcining the aluminous material;

leaching the aluminous material with hydrochloric acid;

solid liquid separation to provide a pregnant liquor;

crystallising aluminium chloride hexahydrate by adding hydrogen chloride gas, precipitating aluminium chloride hexahydrate and separating the aluminium chloride hexahydrate;

calcining aluminium chloride hexahydrate to provide alumina, and

recycling hydrogen chloride as liquor for leaching and as vapour for aluminium chloride hexahydrate crystalisation.

2. A method for the preparation of alumina according to claim 1, wherein 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:

comprises drum scrubbing the aluminous material in water.

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

comprises screening the aluminous material to less than 0.3 mm particle size.

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

calcining the aluminous material; is conducted at a temperature of about 400 - 700 °C.

7. A method for the preparation of alumina according to any one of the preceding claims, wherein the hydrochloric acid has a concentration of about 9 M.

8. A method for the preparation of alumina according to any one of the preceding claims, wherein the addition of the hydrochloric acid forms a mixture with a solid:liquid ratio of between and 35 %.

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

leaching the aluminous material with hydrochloric acid;

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

10. A method for the preparation of alumina according to any one of the preceding claims, wherein the aluminous material is leached for about 1 hour.

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

solid/liquid separation of the leached aluminous material.

12. A method for the preparation of alumina according to claim 11, wherein the step of:

solid/liquid separation of the leached aluminous material;

13. A method for the preparation of alumina according to any one of the preceding claims, wherein the step of precipitating aluminium chloride hexahydrate comprises hydrochloric gas sparging of the pregnant leach solution to provide aluminium chloride hexahydrate crystals.

14. A method for the preparation of alumina according to claim 13, wherein the aluminium chloride hexahydrate crystals are filtered and washed with hydrochloric acid.

15. A method for the preparation of alumina according to claim 13, wherein the aluminium chloride hexahydrate crystals are filtered and washed with demineralized water.

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

calcining aluminium chloride hexahydrate to provide alpha alumina.