Purification method of alumina

Abstract

The present invention provides a method for purifying alumina. The purification method includes step S1 of mixing activated alumina with a first solution, performing hydrothermal leaching treatment, and overflowing to obtain a first precipitate; step S2 of mixing the first precipitate with a second solution, performing first-stage enhanced leaching treatment, and overflowing to obtain a second precipitate; step S3 of mixing the second precipitate with a third solution, performing second-stage enhanced leaching treatment, and overflowing to obtain a third precipitate; step S4 of mixing the third precipitate with water, performing third-stage enhanced leaching treatment, and overflowing to obtain a fourth precipitate; and step S5 of calcining the fourth precipitate to obtain alumina. By adopting the method combining hydrothermal leaching treatment, three-stage enhanced leaching treatment and overflow, the formation of a large amount of aluminum hydroxide colloid is avoided, the leaching rate of lithium is increased, the lithium content in alumina is reduced, the preparation process is simple, and the requirements of industrial continuous production are met.

Description

Technical Field

[0001] The present invention relates to the field of comprehensive utilization of fly ash, and more particularly to a method for purifying alumina. Background Art

[0002] China is a large energy-consuming country. With the rapid development of the national economy, the demand for energy is increasing day by day. In the structure of primary energy production and consumption in China, the proportion of coal has always remained at about 70%. The discharge of fly ash, a solid waste after coal combustion, has increased sharply, causing certain impacts on the ecological environment.

[0003] The Zhungeer area in Ordos, Inner Mongolia, is rich in coal resources, and there are abundant non-ferrous metals such as aluminum, gallium, and lithium associated with the coal. After the mined coal is burned in the power plant boiler, a large amount of alumina and gallium are enriched in the fly ash obtained. The alumina content is usually above 50%, the gallium content is 82.5 g / t, the lithium content is 390 g / t, and the scandium content is 20 g / t. At present, the utilization of fly ash only considers extracting aluminum from the ash, and other valuable metal elements in the fly ash are not extracted.

[0004] The hydrothermal leaching process is to mix the activated alumina obtained by low-temperature roasting with water in a certain proportion, stir evenly quickly, and then heat to about 120°C to dissolve ions such as calcium chloride, magnesium chloride, and lithium chloride in the alumina in water. After the hydrothermal leaching is completed, solid-liquid separation is carried out to achieve the purpose of leaching lithium and removing impurities in the alumina. The following main problems exist in the prior art: during the hydrothermal leaching process, a large amount of aluminum hydroxide colloid is generated in the slurry. By taking measures such as pH adjustment and salt effect in the conventional way, the formation of the colloid cannot be effectively reduced, and during the solid-liquid separation experiment, it is difficult to separate by using methods such as vacuum filtration, positive pressure filter, settling tank, and centrifuge; and the leaching rate of lithium is relatively low.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The main object of the present application is to provide a method for purifying alumina to solve the problems in the prior art that a large amount of aluminum hydroxide colloid is generated in the hydrothermal leaching process, it is difficult to filter and separate, the leaching rate of lithium is relatively low, and the lithium content in the alumina is relatively high.

[0007] To achieve the above object, according to one aspect of the present invention, a method for purifying alumina is provided. The purification method includes the following steps: Step S1, mixing activated alumina with a first solution, performing hydrothermal leaching treatment, and overflowing to obtain a first precipitate and a first overflow clear liquid; Step S2, mixing the first precipitate with a second solution, performing a first-stage enhanced leaching treatment, and overflowing to obtain a second precipitate and a second overflow clear liquid. The first overflow clear liquid and the second overflow clear liquid are mixed to obtain a lithium-containing solution for preparing lithium carbonate; Step S3, mixing the second precipitate with a third solution, performing a second-stage enhanced leaching treatment, and overflowing to obtain a third precipitate and a third overflow clear liquid; Step S4, mixing the third precipitate with water, performing a third-stage enhanced leaching treatment, and overflowing to obtain a fourth precipitate and a fourth overflow clear liquid; Step S5, roasting the fourth precipitate to obtain alumina.

[0008] Further, in Step S3, the third overflow clear liquid is returned to Step S1 as the first solution; in Step S4, the fourth overflow clear liquid is returned to Step S1 as the first solution; the second solution and the third solution are both water.

[0009] Further, in Step S3, the third overflow clear liquid is returned to Step S2 as the second solution; in Step S4, the fourth overflow clear liquid is returned to Step S3 as the third solution; the first solution is water.

[0010] Further, in Step S1, the solid-liquid ratio of the activated alumina to the first solution is 1:(2 - 5) g / mL; and / or, the temperature of the hydrothermal leaching is 110 - 160 °C; and / or, the time of the hydrothermal leaching is 2 - 6 h.

[0011] Further, the solid-liquid ratio of the activated alumina to the first solution is 1:4 g / mL.

[0012] Further, the temperature of the hydrothermal leaching is 145 - 155 °C.

[0013] Further, the time of the hydrothermal leaching is 3 - 5 h.

[0014] Further, in Step S2, the solid-liquid ratio of the first precipitate to the second solution is 1:(2 - 4) g / mL; and / or, the temperature of the first-stage enhanced leaching is 70 - 140 °C; and / or, the time of the first-stage enhanced leaching is 1 - 5 h.

[0015] Further, the solid-liquid ratio of the first precipitate to the second solution is 1:3 g / mL.

[0016] Further, the temperature of the first-stage enhanced leaching is 90 - 110 °C.

[0017] Further, the time of the first-stage enhanced leaching is 1 - 3 h.

[0018] Further, in step S3, the solid-liquid ratio of the second precipitate to the third solution is 1:(1-3) g / mL; and / or, the temperature of the second-stage enhanced dissolution is 50-100 °C; and / or, the time of the second-stage enhanced dissolution is 1-4 h.

[0019] Further, the solid-liquid ratio of the second precipitate to the third solution is 1:2 g / mL.

[0020] Further, the temperature of the second-stage enhanced dissolution is 70-80 °C.

[0021] Further, the time of the second-stage enhanced dissolution is 1-2 h.

[0022] Further, in step S4, the solid-liquid ratio of the third precipitate to water is 1:(1-3) g / mL; and / or, the temperature of the third-stage enhanced dissolution is 50-100 °C.

[0023] Further, the solid-liquid ratio of the third precipitate to water is 1:2 g / mL.

[0024] Further, the temperature of the third-stage enhanced dissolution is 70-80 °C.

[0025] Further, in step S4, the time of the third-stage enhanced dissolution is 1-4 h.

[0026] Further, the time of the third-stage enhanced dissolution is 1-2 h.

[0027] Further, in step S5, the roasting temperature is 900-1100 °C and the time is 60-150 min.

[0028] Further, in step S1, the activated alumina is granular with an average particle size of 10-20 μm.

[0029] Applying the technical solution of the present application, the alumina purification method provided by the present application adopts a method combining hydrothermal dissolution treatment, three-stage enhanced dissolution treatment and overflow, avoiding the formation of a large amount of aluminum hydroxide colloid. At the same time, through multiple enhanced dissolution treatments, the dissolution rate of lithium is increased, the lithium content in alumina is reduced, the preparation process is simple, and the requirements of industrial continuous production are met. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0031] Figure 1 shows a schematic diagram of the first process flow for alumina purification in Embodiment 1 of the present application; and

[0032] Figure 2 It shows a schematic diagram of the second process flow for alumina purification according to Embodiment 2 of the present application. Specific embodiments

[0033] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0034] As analyzed in the background art of the present application, during the hydrothermal digestion process in the prior art, a large amount of aluminum hydroxide colloid is generated in the slurry. By taking measures such as pH adjustment and salt effect in a conventional manner, the formation of the colloid cannot be effectively reduced, and during the solid-liquid separation experiment, it is difficult to separate by using methods such as vacuum filtration, positive pressure filter, settling tank, centrifuge, etc.; moreover, the dissolution rate of lithium is low and the lithium content in alumina is high. To solve this problem, the present application provides a method for purifying alumina.

[0035] In a typical embodiment of the present application, a method for purifying alumina includes the following steps: Step S1, mixing activated alumina with a first solution, performing hydrothermal digestion treatment, and overflowing to obtain a first precipitate and a first overflow clear liquid; Step S2, mixing the first precipitate with a second solution, performing a first-stage enhanced digestion treatment, and overflowing to obtain a second precipitate and a second overflow clear liquid. The first overflow clear liquid and the second overflow clear liquid are mixed to obtain a lithium-containing solution for preparing lithium carbonate; Step S3, mixing the second precipitate with a third solution, performing a second-stage enhanced digestion treatment, and overflowing to obtain a third precipitate and a third overflow clear liquid; Step S4, mixing the third precipitate with water, performing a third-stage enhanced digestion treatment, and overflowing to obtain a fourth precipitate and a fourth overflow clear liquid; Step S5, performing calcination treatment on the fourth precipitate to obtain the alumina.

[0036] Applying the technical solution of the present application, the method for purifying alumina provided by the present application adopts a method combining hydrothermal digestion treatment, three-stage enhanced digestion treatment and overflow, avoiding the formation of a large amount of aluminum hydroxide colloid. At the same time, through multiple enhanced digestion treatments, the dissolution rate of lithium is increased, the lithium content in alumina is reduced, the preparation process is simple, and the requirements for industrial continuous production are met.

[0037] In some embodiments, when mixing activated alumina with a first solution and performing hydrothermal digestion treatment, stirring and vibration during the hydrothermal digestion treatment will form a large amount of aluminum hydroxide colloid. On the one hand, it is difficult to separate the colloid and the solution by solid-liquid separation, and on the other hand, lithium chloride reacts with the aluminum hydroxide colloid, resulting in a small dissolution amount of lithium, and adjusting the pH value of the aluminum hydroxide colloid and adding a salt solution cannot effectively reduce the aluminum hydroxide colloid.

[0038] In order to further increase the dissolution amount of lithium, it is preferred that the hydrothermal dissolution treatment process is carried out in a static state. Among them, lithium chloride is easily soluble in aqueous solution. Based on the principle of free diffusion, in a static state, the lithium chloride contained in activated alumina gradually diffuses into the first solution, avoiding the formation of a large amount of aluminum hydroxide colloid due to stirring and vibration, thereby increasing the dissolution amount of lithium.

[0039] In this application, the solid-liquid separation is achieved by means of overflow. The above overflow can use the liquid level height difference to flow out the upper overflow clear liquid from the overflow port during the static process, thus avoiding the vibration during the filtration process and causing the appearance of a large amount of aluminum hydroxide colloid, resulting in a reduction in the amount of dissolved lithium.

[0040] In this application, on the one hand, the hydrothermal dissolution treatment process increases the solubility of lithium chloride in water and further improves the dissolution of lithium. On the other hand, a chemical reaction occurs between the first solution and activated alumina, forming a colloid on the surface of the activated alumina. As a result, after lithium chloride dissolves in the first solution, part of the lithium chloride reacts with the aluminum hydroxide colloid to form a precipitate of LiCl·2Al(OH)3·mH2O, resulting in a relatively low dissolution rate of lithium. However, the precipitate of LiCl·2Al(OH)3·mH2O can continue to react with the first solution to further generate lithium chloride dissolved in the first solution. In order to further increase the dissolution amount of lithium, it is preferred to perform a staged enhanced dissolution treatment after the hydrothermal dissolution treatment of activated alumina. During the enhanced dissolution process, under the action of water, the reaction of the precipitate of LiCl·2Al(OH)3·mH2O proceeds in the forward direction, increasing the amount of lithium chloride, thereby increasing the overall dissolution amount of lithium. The enhanced dissolution treatment can be carried out multiple times. Increasing the number of enhanced dissolution treatments can increase the overall dissolution amount of lithium. When the lithium in the activated alumina is basically removed, increasing the number of enhanced dissolution treatments cannot significantly increase the overall dissolution amount of lithium. This application adopts three enhanced dissolution treatments.

[0041] The mechanism of the above process is as follows:

[0042]

[0043]

[0044] In order to further avoid waste, it is preferred to mix the first overflow clear liquid obtained in step S1 and the second overflow clear liquid obtained in step S2 to form a lithium-containing solution for the preparation of lithium carbonate. This not only avoids the resource waste and environmental pollution caused by discharging the first overflow clear liquid and the second overflow clear liquid into the waste liquid, but also can recover the lithium in the first overflow clear liquid and the second overflow clear liquid to prepare lithium carbonate, reducing the production cost and increasing the utilization rate of lithium.

[0045] In this application, the purification of alumina includes two purification methods. In some embodiments, the first alumina purification method is adopted. At the start of alumina purification, the first solution, the second solution, and the third solution are all water. When the entire process is in a balanced state, as Figure 1 shown, returning the third overflow clear liquid obtained in step S3 to step S1 as the first solution to be mixed with activated alumina for hydrothermal leaching treatment, and / or returning the fourth overflow clear liquid obtained in step S4 to step S1 as the first solution to be mixed with activated alumina for hydrothermal leaching treatment can effectively reduce the production of waste liquid during the production process, and can avoid resource waste and environmental pollution.

[0046] In other embodiments, the second alumina purification method is adopted. At the start of alumina purification, the first solution, the second solution, and the third solution are all water. When the entire process is in a balanced state, as Figure 2 shown, in step S3, returning the obtained third overflow clear liquid to step S2 as the second solution to be mixed with the first precipitate for the first-stage enhanced leaching treatment, and in step S4, returning the obtained fourth overflow clear liquid to step S3 as the third solution to be mixed with the second precipitate for the second-stage enhanced leaching treatment can effectively reduce the waste of water resources, improve the utilization rate of waste liquid, and save costs.

[0047] In the above step S1, the method for preparing activated alumina is to mix hydrochloric acid with fly ash and react, and then obtain activated alumina through low-temperature roasting. The specific implementation method is as follows: After mixing hydrochloric acid with fly ash, the mixture is heated to 160 ° C, so that the alumina in the fly ash reacts with hydrochloric acid to generate aluminum chloride. Aluminum chloride is an ionic halide and has a large solubility in water. Aluminum chloride dissolves in the solution, and silicon dioxide in the fly ash and other substances that are not easily soluble in the solution form residues. The insoluble residues in the fly ash are removed by solid-liquid separation, and then an aluminum chloride solution is obtained. Then, a resin is used to remove iron chloride impurities in the aluminum chloride solution to obtain a refined aluminum chloride solution. The refined aluminum chloride solution is subjected to evaporation crystallization to obtain aluminum chloride crystals, and the aluminum chloride crystals are obtained as activated alumina after low-temperature roasting. Among them, during the chemical reaction between hydrochloric acid and fly ash, in addition to the generated aluminum chloride dissolving in the solution, other metal ions in the fly ash such as Ca, Mg, Li, etc. generate corresponding chlorides and dissolve in the solution, and the obtained activated alumina contains the corresponding chlorides after evaporation crystallization and low-temperature roasting.

[0048] In order to further increase the amount of lithium dissolved during the hydrothermal leaching process, it is preferred that the activated alumina is in granular form with an average particle size of 10 - 20 μm. In some embodiments, the activated alumina is placed in a pulverizer, and the rotation speed of the pulverizer is controlled at 300 r / min, and the pulverization time is 60 min to obtain granular activated alumina. Among them, if the particle size of the activated alumina is too large, it will lead to a decrease in the dissolution rate of lithium in the activated alumina during the hydrothermal leaching process in a static state. If the particle size of the activated alumina is too small, it will cause energy waste and increase unnecessary production costs. Within the above range, it is possible to increase the amount of lithium dissolved during the hydrothermal leaching process while avoiding energy waste.

[0049] In some embodiments, in order to avoid waste of water resources, in step S1, the first solution is at least one of the third overflow clear liquid, the fourth overflow clear liquid, and water. In step S2, the second solution is at least one of the third overflow clear liquid and water. In step S3, the third solution is at least one of the fourth overflow clear liquid and water. Among them, the third overflow clear liquid is the overflow clear liquid obtained during the second-stage enhanced leaching process, and the fourth overflow clear liquid is the overflow clear liquid obtained during the third-stage enhanced leaching process. This not only saves water and avoids resource waste, but also reduces the cost during the production process.

[0050] In this application, during the hydrothermal leaching process, the solid-liquid ratio of the activated alumina and the first solution is, for example, 1:2 g / mL, 1:3 g / mL, 1:4 g / mL, 1:5 g / mL, or a range value composed of any two values, preferably 1:4 g / mL. If the amount of the first solution is too small, the dissolution amount of ionic impurities such as calcium chloride, magnesium chloride, and lithium chloride in the first solution is less. If the amount of the first solution is too large, when the ionic impurities have been dissolved in the first solution to the maximum extent, increasing the amount of the first solution cannot increase the dissolution amount of the ionic impurities, and too much of the first solution will also increase the time of the hydrothermal leaching process. Within the above range, it is possible to ensure that the ionic impurities are dissolved in the first solution to the maximum extent while avoiding waste of the first solution.

[0051] In order to further increase the dissolution amount of lithium during the hydrothermal leaching process, in the above step S1, the temperature of the hydrothermal leaching is 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, or a range value composed of any two values, preferably 145 - 155°C. Lithium chloride belongs to inorganic salts with ionic bonds and is a polar bond. According to the principle of similar compatibility, the solubility of lithium chloride in water is relatively large, and the solubility of lithium chloride in water increases with the increase of temperature. When the temperature of the hydrothermal leaching is too low, the solubility of lithium chloride in the first solution is relatively low, resulting in a low dissolution amount of lithium. When the temperature of the hydrothermal leaching is too high, the dissolution of lithium chloride in the first solution reaches the limit, and increasing the temperature cannot improve the dissolution efficiency, but instead causes energy waste. Within the above range, it is possible to effectively increase the dissolution amount of lithium.

[0052] In some embodiments, in order to further increase the dissolution amount of lithium, the hydrothermal dissolution time is preferably 2 h, 3 h, 4 h, 5 h, 6 h or a range value composed of any two values, and more preferably 3 - 5 h. Since the hydrothermal dissolution process is carried out under a static state and the free diffusion rate is slow, if the hydrothermal dissolution time is too short, lithium chloride fails to fully diffuse into the solution, and a large amount of lithium chloride remains in the activated alumina, resulting in a small dissolution amount of lithium. If the hydrothermal dissolution time is too long, it will cause waste of energy and increase the production cost. Within the above range, the dissolution amount of lithium can be effectively increased.

[0053] In the above step S2, in the first-stage enhanced dissolution process, the solid-liquid ratio of the first precipitate and the second solution is, for example, 1:2, 1:3, 1:4 or a range value composed of any two values, and preferably 1:3. In the above hydrothermal dissolution process, a large amount of lithium chloride dissolves in the first overflow clear liquid and flows out from the overflow port. The remaining lithium chloride in the first precipitate and the amount of LiCl·2Al(OH)3·mH2O precipitate are less. Within the above range, the dissolution amount of lithium chloride in the first-stage enhanced dissolution process can be effectively increased, further improving the dissolution of lithium.

[0054] In some embodiments, the first-stage enhanced dissolution temperature is, for example, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C or a range value composed of any two values, and preferably 90 - 110°C. The remaining lithium chloride in the first precipitate and the amount of LiCl·2Al(OH)3·mH2O precipitate are less. Within the above temperature range, while increasing the dissolution amount of lithium, it can avoid waste of energy and increase of production cost caused by too high temperature.

[0055] In the above step S2, the time of the first-stage enhanced dissolution is 1 - 5 h, preferably 1 - 3 h. In the first-stage enhanced dissolution process, the amount of water decreases, the standing time required decreases, and the content of lithium in the first precipitate is less. Therefore, within the above range of the first-stage enhanced dissolution time, the dissolution amount of lithium can be effectively increased.

[0056] In order to further increase the overall dissolution amount of lithium, it is preferred to perform a second-stage enhanced dissolution. The LiCl·2Al(OH)3·mH2O precipitate continues to react with the water in the third solution. During the above reaction process, the reaction proceeds in the forward direction, resulting in the formation of lithium chloride from the LiCl·2Al(OH)3·mH2O precipitate, thereby increasing the dissolution amount of lithium. After hydrothermal dissolution treatment and the first-stage enhanced dissolution treatment, the amount of LiCl·2Al(OH)3·mH2O precipitate is small. Therefore, in step S3, the solid-liquid ratio of the second precipitate to water is 1:(1 - 3) g / mL, preferably 1:2 g / mL; the temperature of the second-stage enhanced dissolution is 50 - 100 °C, preferably 70 - 80 °C; the time of the second-stage enhanced dissolution is 1 - 4 h, preferably 1 - 2 h. Under the above reaction conditions, the overall dissolution amount of lithium can be effectively increased.

[0057] In some embodiments, in order to further increase the overall dissolution amount of lithium, in step S4, the solid-liquid ratio of the third precipitate to water is 1:(1 - 3) g / mL, preferably 1:2 g / mL; the temperature of the third-stage enhanced dissolution is 50 - 100 °C, preferably 70 - 80 °C; the time of the third-stage enhanced dissolution is 1 - 4 h, preferably 1 - 2 h.

[0058] In some embodiments, in step S5, the roasting temperature is 900 - 1100 °C, and the roasting time is 60 - 150 min.

[0059] Next, the beneficial effects of the present application will be further described in combination with examples and comparative examples.

[0060] Example 1

[0061] This example provides a method for purifying alumina, including the following steps:

[0062] (1) Take activated alumina (90 g) and add it to the mixed solution of the third overflow clear liquid and the fourth overflow clear liquid with a lithium content of 15 mg / L (360 ml), and mix and stir evenly (the solid-liquid ratio of activated alumina to the solution is 0.25 g / mL). Let it stand for 4 h at a temperature of 150 °C for hydrothermal dissolution treatment. After the hydrothermal dissolution ends, the upper clear liquid is discharged from the overflow port to obtain 235 mL of the first overflow clear liquid with a lithium content of 92.64 mg / L and the first precipitate.

[0063] (2) Mix the first precipitate with water (200 ml), and let it stand for 1 h at a temperature of 90 °C for the first-stage enhanced dissolution treatment. After the first-stage enhanced dissolution ends, obtain 150 ml of the second overflow clear liquid with a lithium concentration of 49.12 mg / L and the second precipitate.

[0064] (3) Mix the second precipitate with water (200 ml), and let it stand for 1 h at a temperature of 80 °C for the second-stage enhanced dissolution treatment. After the second-stage enhanced dissolution ends, obtain 180 ml of the third overflow clear liquid with a lithium concentration of 20.64 mg / L and the third precipitate.

[0065] (4) Mix the third precipitate with water (200 ml), let it stand for 1 h at a temperature of 80 °C for the third-stage enhanced dissolution treatment. After the third-stage enhanced dissolution ends, 180 ml of the fourth overflow clear liquid with a lithium concentration of 9.45 mg / L and the fourth precipitate are obtained.

[0066] (5) Bake the fourth precipitate at 1000 °C for 2 h to obtain alumina.

[0067] As Figure 1 shown, the first process flow chart of alumina purification in Example 1. Through this schematic diagram, the entire preparation process of Example 1 can be obtained.

[0068] Example 2

[0069] This example provides a method for purifying alumina, including the following steps:

[0070] (1) Take activated alumina (90 g) and mix it evenly with water (360 mL) (the solid-liquid ratio of activated alumina to the solution is 0.25 g / mL), let it stand for 4 h at a temperature of 150 °C for hydrothermal dissolution treatment. After the hydrothermal dissolution ends, the upper clear liquid is discharged from the overflow port to obtain 235 mL of the first overflow clear liquid with a lithium content of 77.64 mg / L and the first precipitate.

[0071] (2) Mix the first precipitate with the third overflow clear liquid (180 ml) with a lithium concentration of 20.64 mg / L, let it stand for 1 h at a temperature of 90 °C for the first-stage enhanced dissolution treatment. After the first-stage enhanced dissolution ends, 150 ml of the second overflow clear liquid with a lithium concentration of 69.12 mg / L and the second precipitate are obtained.

[0072] (3) Mix the second precipitate with the fourth overflow clear liquid (180 ml) with a lithium concentration of 10.64 mg / L, let it stand for 1 h at a temperature of 80 °C for the second-stage enhanced dissolution treatment. After the second-stage enhanced dissolution ends, 180 ml of the third overflow clear liquid with a lithium concentration of 31.28 mg / L and the third precipitate are obtained.

[0073] (4) Mix the third precipitate with water (200 ml), let it stand for 1 h at a temperature of 80 °C for the third-stage enhanced dissolution treatment. After the third-stage enhanced dissolution ends, 180 ml of the fourth overflow clear liquid with a lithium concentration of 10.64 mg / L and the fourth precipitate are obtained.

[0074] (5) Bake the fourth precipitate at 950 °C for 2.5 h to obtain alumina.

[0075] As Figure 2 shown, the second process flow chart of alumina purification in Example 2. Through this schematic diagram, the entire preparation process of Example 2 can be obtained.

[0076] Example 3

[0077] The difference between this example and Example 1 is that in step (1), the temperature of hydrothermal dissolution is 110 °C and it is left standing for 6 h.

[0078] Example 4

[0079] The difference between this example and Example 1 is that in step (1), the temperature of hydrothermal dissolution is 160 °C and it is left standing for 2 h.

[0080] Example 5

[0081] The difference between this example and Example 1 is that in step (1), the temperature of hydrothermal dissolution is 90 °C and it is left standing for 8 h.

[0082] Example 6

[0083] The difference between this example and Example 1 is that in step (1), the temperature of hydrothermal dissolution is 170 °C and it is left standing for 1 h.

[0084] Example 7

[0085] The difference between this example and Example 1 is that in step (2), the temperature of the first-stage enhanced dissolution is 70 °C and it is left standing for 5 h.

[0086] Example 8

[0087] The difference between this example and Example 1 is that in step (2), the temperature of the first-stage enhanced dissolution is 140 °C and it is left standing for 1 h.

[0088] Example 9

[0089] The difference between this example and Example 1 is that in step (2), the temperature of the first-stage enhanced dissolution is 50 °C and it is left standing for 7 h.

[0090] Example 10

[0091] The difference between this example and Example 1 is that in step (2), the temperature of the first-stage enhanced dissolution is 150 °C and it is left standing for 0.5 h.

[0092] Example 11

[0093] The difference between this example and Example 1 is that in step (3), the temperature of the second-stage enhanced dissolution is 50 °C and it is left standing for 4 h.

[0094] Example 12

[0095] The difference between this example and Example 1 is that in step (3), the temperature of the second-stage enhanced dissolution is 100 °C and it is left standing for 1 h.

[0096] Example 13

[0097] The difference between this embodiment and embodiment 1 is that the temperature of the second stage enhanced dissolution in step (3) is 30° C. and the mixture is allowed to stand for 6 hours.

[0098] Example 14

[0099] The difference between this embodiment and embodiment 1 is that the temperature of the second stage enhanced dissolution in step (3) is 120° C. and the temperature is left to stand for 0.5 h.

[0100] Example 15

[0101] The difference between this embodiment and embodiment 1 is that the temperature of the third stage enhanced dissolution in step (4) is 50° C. and allowed to stand for 4 hours.

[0102] Example 16

[0103] The difference between this embodiment and embodiment 1 is that the temperature of the third stage enhanced dissolution in step (4) is 100° C. and the mixture is allowed to stand for 1 hour.

[0104] Example 17

[0105] The difference between this embodiment and embodiment 1 is that the temperature of the third stage enhanced dissolution in step (4) is 30° C. and the mixture is allowed to stand for 6 hours.

[0106] Example 18

[0107] The difference between this embodiment and embodiment 1 is that the temperature of the third stage enhanced dissolution in step (4) is 110° C. and the temperature is left to stand for 0.5 h.

[0108] Comparative Example 1

[0109] (1) Activated alumina (90 g) and water (360 mL) were mixed and stirred uniformly (the solid-to-liquid ratio of activated alumina to solution was 0.25 g / mL), and the mixture was stirred and reacted at 150° C. for 4 h. Hydrothermal dissolution was performed. After the hydrothermal dissolution was completed, the pH value of the water was adjusted to 6-7 with aqueous ammonia, and a first precipitate was obtained by filtration.

[0110] (2) The first precipitate was calcined at 1000°C for 2 hours to obtain alumina.

[0111] Comparative Example 2

[0112] (1) Activated alumina (90 g) and CaCl2 salt solution (CaCl2 mass concentration of 1.10%) (270 mL) were mixed and stirred uniformly (solid-to-liquid ratio of activated alumina to solution was 0.33 g / mL), stirred and reacted at 150°C for 4 h, and subjected to hydrothermal dissolution treatment. After the hydrothermal dissolution was completed, a first precipitate was obtained by filtration;

[0113] (2) The first precipitate is calcined at 950 °C for 2.5 h to obtain alumina.

[0114] Comparative Example 3

[0115] The difference between this comparative example and Example 1 is that the first-stage enhanced dissolution, second-stage enhanced dissolution, and third-stage enhanced dissolution treatments are not carried out.

[0116] Comparative Example 4

[0117] The difference between this comparative example and Example 1 is that the second-stage enhanced dissolution and third-stage enhanced dissolution treatments are not carried out.

[0118] Comparative Example 5

[0119] The difference between this comparative example and Example 1 is that the third-stage enhanced dissolution treatment is not carried out.

[0120] Test Example 1

[0121] The purity of the alumina obtained by purification of the above-mentioned examples and comparative examples and the total amount of dissolved lithium were respectively tested for quality, and the yield of alumina was calculated. The results are shown in Table 1.

[0122] Among them, 1) The calculation formula for the yield of alumina = calcined alumina ÷ active alumina × 100%;

[0123] 2) The test method for the purity of alumina is as follows: The content of impurity elements such as CaO, MgO, K2O, and Na2O is mainly tested in the alumina product. The purity of alumina = 100% - (CaO% + MgO% + K2O% + Na2O%). Mainly refer to the industry standard YS / T 803-2012 of alumina products. (Note: This standard is for the production of alumina by the alkaline method. We are the acid method for alumina production, so impurities such as Ca and Mg need to be considered). The content of various impurities in the alumina product is generally tested by instrumental analysis. Among them: The tests of Ca and Mg mainly use ICP-OES; the tests of Na and K use an atomic absorption spectrometer.

[0124] 3) The test method for the total amount of dissolved lithium is as follows: The volume of the overflow liquid is accurately measured, and analytical instruments such as ICP and MS are used to test the content of Li in the overflow liquid. The total amount of dissolved Li = volume of overflow liquid × Li content.

[0125] Table 1

[0126]

[0127]

[0128] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: The purification method of alumina provided by this application adopts a method combining hydrothermal digestion treatment, three-stage enhanced digestion treatment and overflow, avoiding the formation of a large amount of aluminum hydroxide colloid. At the same time, through multiple enhanced digestion treatments, the dissolution rate of lithium is increased, the lithium content in alumina is reduced, and the preparation process is simple, meeting the requirements of industrial continuous production.

[0129] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for purifying aluminum oxide, characterized in that: The purification method comprises the following steps: Step S1, mixing activated alumina with a first solution, performing a hydrothermal dissolution treatment, and overflowing to obtain a first precipitate and a first overflow clear liquid; the hydrothermal dissolution treatment process is performed in a static state; Step S2, mixing the first precipitate with the second solution, performing a first-stage enhanced dissolution treatment, overflowing to obtain a second precipitate and a second overflow clear liquid, and mixing the first overflow clear liquid and the second overflow clear liquid to obtain a lithium-containing solution for preparing lithium carbonate; Step S3, mixing the second precipitate with the third solution, performing a second-stage enhanced dissolution treatment, and overflowing to obtain a third precipitate and a third overflow clear liquid; Step S4, mixing the third precipitate with water, performing a third-stage enhanced dissolution treatment, and overflowing to obtain a fourth precipitate and a fourth overflow clear liquid; Step S5, calcining the fourth precipitate to obtain the alumina; In step S3, the third overflow clear liquid is returned to step S1 as the first solution; in step S4, the fourth overflow clear liquid is returned to step S1 as the first solution; The second solution and the third solution are both water" or "In step S3, the third overflow clear liquid is returned to step S2 as the second solution; in step S4, the fourth overflow clear liquid is returned to step S3 as the third solution; The first solution is water”; The temperature of the hydrothermal dissolution is 110~160℃, and the time of the hydrothermal dissolution is 2~6h; the temperature of the first-level enhanced dissolution is 70~140℃, and the time of the first-level enhanced dissolution is 1~5h; the temperature of the second-level enhanced dissolution is 50~100℃, and the time of the second-level enhanced dissolution is 1~4h; the temperature of the third-level enhanced dissolution is 50~100℃, and the time of the third-level enhanced dissolution is 1~4h.

2. The method for purifying aluminum oxide according to claim 1, wherein: In the step S1, the solid-to-liquid ratio of the activated alumina to the first solution is 1:(2-5) g / mL; and / or, the temperature of the hydrothermal dissolution is 145-155° C.; And / or, the hydrothermal dissolution time is 3 to 5 hours.

3. The method for purifying aluminum oxide according to claim 2, characterized in that: In step S1, the solid-to-liquid ratio of the activated alumina to the first solution is 1:4 g / mL.

4. The method for purifying aluminum oxide according to claim 1, wherein: In step S2, the solid-to-liquid ratio of the first precipitate to the second solution is 1:(2-4) g / mL; And / or, the temperature of the first stage enhanced dissolution is 90-110°C; And / or, the time of the first stage enhanced dissolution is 1 to 3 hours.

5. The method for purifying aluminum oxide according to claim 4, characterized in that: In step S2, the solid-to-liquid ratio of the first precipitate to the second solution is 1:3 g / mL.

6. The method for purifying aluminum oxide according to claim 1, characterized in that: In step S3, the solid-to-liquid ratio of the second precipitate to the third solution is 1:(1-3) g / mL; and / or, the temperature of the second stage enhanced dissolution is 70-80°C; And / or, the time for the second-stage enhanced dissolution is 1 to 2 hours.

7. The method for purifying aluminum oxide according to claim 1, characterized in that: In step S3, the solid-to-liquid ratio of the second precipitate to the third solution is 1:2 g / mL.

8. The method for purifying aluminum oxide according to claim 1, characterized in that: In the step S4, the solid-to-liquid ratio of the third precipitate to the water is 1:(1-3) g / mL; And / or, the temperature of the third stage enhanced dissolution is 70-80°C.

9. The method for purifying aluminum oxide according to claim 8, characterized in that: In step S4, the solid-to-liquid ratio of the third precipitate to the water is 1:2 g / mL.

10. The method for purifying aluminum oxide according to claim 1, characterized in that: In step S4, the time for the third stage enhanced dissolution is 1 to 2 hours.

11. The method for purifying aluminum oxide according to claim 1, characterized in that: In step S5, the calcination temperature is 900-1100° C. and the calcination time is 60-150 min.

12. The method for purifying aluminum oxide according to any one of claims 1 to 11, characterized in that: In the step S1, the activated alumina is in granular form with an average particle size of 10-20 μm.

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