METHOD FOR PREPARING ALUMINUM FLUORIDE AND ALUMINUM OXIDE BY DECARBURIZATION AND SODIUM REMOVAL OF ALUMINUM ELECTROLYSIS CARBON RESIDUE

Abstract

A method for preparing aluminum fluoride and aluminum oxide by decarburization and sodium removal of an aluminum electrolysis carbon residue is disclosed. The method includes: crushing the aluminum electrolysis carbon residue into fine particles not larger than 3 mm, adding decarburization agent into the carbon residue, mixing to obtain first mixture, adding the first mixture into a high-temperature furnace, conducting I-stage heating treatment in air atmosphere to obtain crude fluoride salt A; adding sodium removal agent into the crude fluoride salt A, mixing to obtain second mixture, adding the second mixture into high-temperature furnace, and conducting

II-stage heating treatment to obtain crude fluoride salt B; adding the crude fluoride salt B into stirring tank, adding industrial pure water, dissolving a sodium salt into water, and conducting solid-liquid separation to obtain precipitate C and sodium salt solution D; drying the precipitate C to obtain aluminum fluoride and aluminum oxide.

Claims

1. A method for preparing aluminum fluoride and aluminum oxide by decarburization and sodium removal of aluminum electrolysis carbon residue, comprising: crushing the aluminum electrolysis carbon residue into fine particles not larger than 3 mm, adding a decarburization agent into the carbon residue, mixing to obtain a first mixture, adding the first mixture into a high-temperature furnace, and conducting a I-stage heating treatment in an air atmosphere, to obtain a crude fluoride salt A; adding a sodium removal agent into the crude fluoride salt A, mixing to obtain a second mixture, adding the second mixture into a high-temperature furnace, and conducting a II-stage heating treatment, to obtain a crude fluoride salt B; adding the crude fluoride salt B into a stirring tank, adding industrial pure water thereto, dissolving a sodium salt into water, and conducting a solid-liquid separation to obtain a precipitate C and a sodium salt solution D; and drying the precipitate C to obtain a mixture of aluminum fluoride and aluminum oxide, concentrating the sodium salt solution D by evaporating to obtain a sodium salt, and returning evaporated condensate water to a stirring tank for recycling.

2. The method of claim 1, wherein the method further comprises the following steps: collecting a flue gas generated in the I-stage heating treatment and the II-stage heating treatment, introducing the flue gas into an aluminum hydroxide reactor, and reacting HF in the flue gas with aluminum hydroxide to obtain aluminum fluoride.

3. The method of claim 1, wherein the decarburization agent is at least one selected from the group consisting of biochar, engine oil, and starch.

4. The method of claim 1, wherein the decarburization agent is added in an amount which is 0.1-0.5 times the mass of carbon in the carbon residue.

5. The method of claim 1, wherein the sodium removal agent is at least one selected from the group consisting of aluminum sulfate, aluminum acetate, aluminum oxalate, aluminum nitrate, and aluminum hydroxide.

6. The method of claim 1, wherein the sodium removal agent is added in an amount which is 1-3 times the mass of sodium in the carbon residue.

7. The method of claim 1, wherein the industrial pure water is added in an amount which is 2-5 times of the crude fluoride salt B.

8. The method of claim 1, wherein the I-stage heating treatment and the II-stage heating treatment are independently conducted at a temperature not lower than 700° C. and lower than the melting points of fluoride salts and sodium salts.

9. The method of claim 1, wherein the I-stage heating treatment is hold for at least 2 h and the II-stage heating treatment is hold for at least 1-3 h.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The following examples are intended to illustrate the present disclosure and are not intended to limit the scope of the present disclosure. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. The test methods in the following examples are conventional, unless otherwise specified.

[0027] The aluminum electrolysis carbon residue used in the examples of the present disclosure is taken from an aluminum electrolysis cell of a smelter in China, and mainly consists of the carbon particles that falls from the surface of prebaked anodes during oxidation combustion process. The decarburization agent is a compound or mixture with a combustion point lower than carbon residue, a composition of C, C—H or C—H—O, which is a solid or a liquid at ambient temperature, and is nontoxic and harmless, and contains less than 2% of silicon, iron, phosphorus and sulfur impurities, and it is preferably biochar, engine oil or starch. The sodium removal agent is an aluminum salt stable at ambient temperature, and is preferably selected from the group consisting of aluminum sulfate, aluminum acetate, aluminum oxalate and aluminum hydroxide.

EXAMPLE 1

[0028] (1) 1000 g of carbon residue was crushed into fine particles not larger than 3 mm, which was analyzed to have a carbon content of 35.4%. 35.4 g of a decarburization agent (7.08 g of engine oil and 28.32 g of biochar) was added thereto, and mixed to obtain a first mixture. The first mixture was added to a high-temperature furnace, and heated at 700° C. for 4 h, during which carbon was oxidized and combusted, obtaining about 645 g of a crude fluoride salt A.

[0029] (2) The crude fluoride salt A was ground and analyzed to have a sodium content of 31.5%. 203 g of aluminum sulfate was added thereto and mixed to obtain a second mixture. The second mixture was added to a high-temperature furnace and heated at 750° C. for 3 h, during which the crude fluoride salt A reacted with a sodium removal agent, obtaining about 848 g of a crude fluoride salt B.

[0030] (3) The crude fluoride salt B was added into a stirring tank, 2544 g of industrial pure water was added thereto, and a sodium salt was dissolved into water. The resulting mixture was subjected to a solid-liquid separation, obtaining about 374 g of a precipitate C and a sodium salt solution D.

[0031] (4) The precipitate C was dried at 120° C. to obtain a mixture of aluminum fluoride and aluminum oxide, wherein the content of impurities in the mixture met the requirements of AF-2 in GBT4292-2017 standard and AO-2 in GBT24487-2009 standard, respectively. The recovery rate of aluminum was 99.90%, and the recovery rate of fluorine was 99.45%. The solution D was concentrated by evaporating, to obtain a sodium salt, and the obtained evaporated condensate water returned to the stirring tank for recycling.

[0032] (5) A flue gas generated in the I-stage heating in step (1) and the II-stage heating in step (2) was collected and introduced into an aluminum hydroxide reactor, and HF in the flue gas reacted with aluminum hydroxide to obtain aluminum fluoride, wherein the quality of aluminum fluoride met the requirement of AF-2 in GBT4292-2017 standard, and the recovery rate of fluorine was higher than 99.50%.

EXAMPLE 2

[0033] (1) 1000 g of carbon residue was crushed into fine particles not larger than 3 mm, which was analyzed to have a carbon content of 30.5%, 91.5 g of a decarburization agent (64.05 g of engine oil, 27.45 g of starch) was added thereto and mixed to obtain a first mixture. The first mixture was added to a high-temperature furnace, and heated at 745° C. for 3 h, during which carbon was oxidized and combusted, obtaining about 695 g of a crude fluoride salt A.

[0034] (2) The crude fluoride salt A was ground and analyzed to have a sodium content of 33.0%. 460 g of aluminum acetate was added thereto and mixed to obtain a second mixture. The second mixture was added to a high-temperature furnace and heated at 790° C. for 1 h, during which the crude fluoride salt A reacted with a sodium removal agent, obtaining about 1150 g of a crude fluoride salt B.

[0035] (3) The crude fluoride salt B was added into a stirring tank, 2300 g of industrial pure water was added thereto, and a sodium salt was dissolved into water. The resulting mixture was subjected to a solid-liquid separation, obtaining about 510 g of a precipitate C and a sodium salt solution D.

[0036] (4) The precipitate C was dried at 260° C. to obtain a mixture of aluminum fluoride and aluminum oxide, wherein the content of impurities in the mixture met the requirements of AF-2 in GBT4292-2017 standard and AO-2 in GBT24487-2009 standard, respectively. The recovery rate of aluminum was 99.92%, and the recovery rate of fluorine was 99.51%. The solution D was concentrated by evaporating to obtain a sodium salt, and the obtained evaporated condensate water returned to the stirring tank for recycling.

[0037] (5) A flue gas generated in the I-stage heating in step (1) and the II-stage heating in step (2) was collected and introduced into an aluminum hydroxide reactor, and HF in the flue gas reacted with aluminum hydroxide to obtain aluminum fluoride, wherein the quality of aluminum fluoride met the requirement of AF-2 in GBT4292 -2017 standard, and the recovery rate of fluorine was higher than 99.53%.

EXAMPLE 3

[0038] (1) 1000 g of carbon residue was crushed into fine particles not larger than 3 mm, which was analyzed to have a carbon content of 38.0%. 190 g of a decarburization agent (76 g of starch, 114 g of biochar) was added thereto and mixed to obtain a first mixture. The first mixture was added to a high-temperature furnace and heated at 790° C. for 2 h, during which carbon was oxidized and combusted, obtaining about 620 g of a crude fluoride salt A.

[0039] (2) The crude fluoride salt A was ground and analyzed to have a sodium content of 32.3%. 600 g of aluminum oxalate was added thereto and mixed to obtain a second mixture. The second mixture was added to a high-temperature furnace and heated at 770° C. for 2 h, during which the crude fluoride salt A reacted with a sodium removal agent, obtaining about 1220 g of a crude fluoride salt B.

[0040] (3) The crude fluoride salt B was added into a stirring tank, 6100 g of industrial pure water was added thereto, and a sodium salt was dissolved into water. The resulting mixture was subjected to a solid-liquid separation, obtaining about 680 g of a precipitate C and a sodium salt solution D.

[0041] (4) The precipitate C was dried at 350° C. to obtain a mixture of aluminum fluoride and aluminum oxide, wherein the content of impurities in the mixture met the requirements of AF-2 in GBT 4292 -2017 standard and AO-2 in GBT24487-2009 standard, respectively. The recovery rate of aluminum was 99.93%, and the recovery rate of fluorine was 99.55%. The solution D was concentrated by evaporating, to obtain a sodium salt, and the obtained evaporated condensate water returned to the stirring tank for recycling.

[0042] (5) A flue gas generated in the I-stage heating in step (1) and the II-stage heating in step (2) was collected and introduced into an aluminum hydroxide reactor, and HF in the flue gas reacted with aluminum hydroxide to obtain aluminum fluoride, wherein, the quality of aluminum fluoride met the requirement of AF-2 in GBT4292-2017 standard, and the recovery rate of fluorine was higher than 99.53%.

EXAMPLE 4

[0043] (1) 1000 g of carbon residue was crushed into fine particles not larger than 3 mm, which was analyzed to have a carbon content of 33%. 132 g of a decarburization agent (39.6 g of engine oil, 13.2 g of starch and 79.2 g of biochar) was added thereto and mixed to obtain a first mixture. The first mixture was added to a high-temperature furnace and heated at 730° C. for 3.5 h, during which carbon was oxidized and combusted, obtaining about 670 g of a crude fluoride salt A.

[0044] (2) The crude fluoride salt A was ground and analyzed to have a sodium content of 34%. 700 g of aluminum sulfate was added thereto and mixed to obtain a second mixture. The second mixture was added to a high-temperature furnace and heated at 760° C. for 2.5 h, during which the crude fluoride salt A reacted with a sodium removal agent, obtaining about 1370 g of a crude fluoride salt B.

[0045] (3) The crude fluoride salt B was added into a stirring tank, 5480 g of industrial pure water was added thereto, and a sodium salt was dissolved into water. The resulting mixture was subjected to a solid-liquid separation, obtaining about 763 g of a precipitate C and a sodium salt solution D.

[0046] (4) The precipitate C was dried at 300° C. to obtain a mixture of aluminum fluoride and aluminum oxide, wherein the content of impurities in the mixture met the requirements of AF-2 in GBT 4292-2017 standard and AO-2 in GBT24487-2009 standard, respectively. The recovery rate of aluminum was 99.92%, and the recovery rate of fluorine was 99.49%. The solution D was concentrated by evaporating to obtain a sodium salt, and the obtained evaporated condensate water returned to the stirring tank for recycling.

[0047] (5) A flue gas generated in the I-stage heating in step (1) and the II-stage heating in step (2) was collected and introduced into an aluminum hydroxide reactor, and HF in the flue gas reacted with aluminum hydroxide to obtain aluminum fluoride, wherein the quality of aluminum fluoride met the requirement of AF-2 in GBT4292-2017 standard, and the recovery rate of fluorine was higher than 99.54%.

[0048] The above examples are only preferred embodiments of the present disclosure, and are merely intended to describe the present disclosure, not to limit the present disclosure. According to the technical content of the present disclosure, those skilled in the art would readily obtain other embodiments by replacement and modification. Accordingly, any modification and improvement made based on the principle of the present disclosure should fall within the scope of the present disclosure.