JPWO2021042176A5 - - Google Patents

Claims (26)

A process for preparing high purity alumina from an aluminum-containing material derived from the Bayer process, comprising:
a) digesting said material with hydrochloric acid to produce an aluminum chloride liquid and an acid-insoluble solid, and separating said solid from said aluminum chloride liquid;
b) depleting said aluminum chloride liquid of one or more impurities;
c) producing aluminum chloride hexahydrate solid from said aluminum chloride liquid produced in step b);
d) pyrolyzing the aluminum chloride hexahydrate solid produced in step c) to produce high purity alumina. 2. The process of claim 1, wherein prior to performing step a), the process comprises removing surface soda from the aluminum-containing material by washing the material with carbon dioxide. Prior to performing step a), the process subjects the aluminum-containing material to one or more of dissolution and recrystallization of the material from an alkaline solution to remove soda and, optionally, other impurities. 2. The process of claim 1, comprising reducing the . 4. The process of claim 3, wherein the recrystallized material is gibbsite. 5. The process of claim 4, wherein if the gibbsite is sourced from a Bayer process, the one or more recrystallizations may be performed within a Bayer process circuit. A process according to any one of claims 1 to 5 , wherein digesting the material in hydrochloric acid can be carried out at a temperature from ambient temperature to the atmospheric boiling point of the resulting aluminum chloride liquid. Process according to any one of the preceding claims , wherein digesting the material in hydrochloric acid can be carried out between 15 minutes and 6 hours. A process according to any preceding claim, wherein the hydrochloric acid has a concentration of 5M- 12M . The process of any one of claims 1-8 , wherein producing aluminum chloride hexahydrate solids from the liquid comprises sparging the liquid with hydrogen chloride gas. 10. The method of any one of claims 1-9 , wherein producing aluminum chloride hexahydrate solids from the liquid comprises seeding the liquid to precipitate aluminum chloride hexahydrate solids. Described process. The process of claim 10, wherein said liquid is seeded with aluminum chloride hexahydrate crystals in an amount of 0.1 g/L to 50 g/L. The process of any one of claims 1-11 , wherein said step of pyrolyzing said purified aluminum chloride hexahydrate solid may be carried out in one or more heating stages. 13. The method of claim 12, wherein pyrolyzing the purified aluminum chloride hexahydrate solid comprises heating the purified aluminum chloride hexahydrate solid to a temperature of about 200°C to 1300°C. process. pyrolyzing the purified aluminum chloride hexahydrate solid,
i) heating the purified aluminum chloride hexahydrate solid at a first temperature to pyrolyze the solid;
13. The process of claim 12, comprising ii) calcining the pyrolyzed solid at a second temperature higher than the first temperature to produce high purity alumina. The process of claim 14, wherein said first temperature is between 200°C and 900°C and said second temperature is between 1000°C and 1300°C. 16. A method according to claim 14 or claim 15, wherein hydrogen chloride gas is produced as a by-product of pyrolyzing said purified aluminum chloride hexahydrate solid at said first temperature and/or said second temperature. process. 17. The process of claim 16, wherein the process further comprises recycling the regenerated hydrogen chloride gas to sparge the aluminum chloride liquid to produce aluminum chloride hexahydrate solids. Depleting the aluminum chloride liquid of said one or more impurities extracts said one or more impurities from said liquid by ion exchange, solvent extraction, or adsorption, optionally in combination with a complexing agent. The process of any one of claims 1-17 , comprising: 18. The process of any one of claims 1-17, wherein depleting the one or more impurity aluminum chloride liquid comprises selectively precipitating the one or more impurity chloride salts. . depleting the one or more impurities of the aluminum chloride liquid comprises reacting the liquid with a complexing agent, the complexing agent selectively forming a complex with the one or more impurities; and said complexing impurities remain in solution when aluminum chloride hexahydrate solids are produced. 21. The process of claim 18 or claim 20, wherein the complexing agent comprises a macrocyclic polyether selective for sodium. 2. The method of claim 1, wherein depleting the aluminum chloride liquid of one or more impurities comprises passing the liquid through a semi-permeable cation-selective membrane, particularly a sodium-selective membrane, to separate sodium impurities from the liquid. 18. The process of any one of claims 1-17. said process,
dissolving the aluminum chloride hexahydrate solid in water to form a second aluminum chloride liquid and depleting the one or more impurity liquids;
and producing aluminum chloride hexahydrate solid from said second aluminum chloride liquid. 23. The process of any one of claims 1-22 , wherein the process further comprises leaching the pyrolytic alumina produced in step d) with water to remove soda. The aluminum-containing material derived from the Bayer process includes acid-soluble aluminum hydroxide compounds, acid-soluble aluminum oxyhydroxide compounds, tricalcium aluminate hexahydrate, dawsonite, Al-substituted iron hydroxide oxides, Bayer sodalite, Process according to any one of the preceding claims, selected from the group comprising calcined dust, DSP and red mud , or mixtures thereof. Use of gibbsite and/or calcined dust and/or DSP as precursors of high purity alumina.