A method for preparing alumina by calcining, screening, alkali washing and acid washing secondary aluminum ash

Abstract

The present application relates to the field of solid waste resource utilization, and discloses a method for preparing alumina by calcining, screening, alkali washing and acid washing of secondary aluminum ash. In the present application, aluminum nitride, metallic aluminum and gamma-alumina in the secondary aluminum ash are converted into alpha-alumina which is resistant to acid and alkali, and low-melting-point impurities such as sodium, magnesium, calcium, silicon and iron oxides are gathered into larger particles. The screening process is used to remove large-diameter sodium, magnesium, calcium, silicon and iron impurities. The alkali washing and acid washing process is used to remove residual sodium, magnesium, calcium, silicon and iron impurities. After water washing and drying, alumina is finally obtained. The present application realizes efficient and low-cost preparation of alumina from secondary aluminum ash, significantly reduces the consumption of acid and alkali in the wet resource utilization process, and has the advantages of short process flow, low cost, easy industrialization and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solid waste resource utilization, and particularly relates to a method for preparing alumina by calcining, screening, alkali washing and acid washing of secondary aluminum dross. BACKGROUND

[0002] Secondary aluminum dross is a hazardous waste after aluminum is extracted from aluminum smelting slag, containing alumina (40-60 wt.%), aluminum nitride (15-25 wt.%), salt refining agents (sodium salt, potassium salt and fluoride salt, accounting for 10-20 wt.% in total) and a small amount of metallic aluminum. Secondary aluminum dross has both resource and hazardous properties. The resource comes from alumina, which can be used as an alternative to bauxite as an alumina raw material. The hazard comes from aluminum nitride and salt refining agents. Aluminum nitride is easy to hydrolyze to produce ammonia gas pollution, and salt refining agents are easy to dissolve with rainwater to cause water and soil pollution. With the development of the aluminum industry and the improvement of living standards, the annual production of secondary aluminum dross in China exceeds 2.2 million tons. Therefore, it is urgent to solve the problem of harmless disposal and resource utilization of secondary aluminum dross.

[0003] At present, there are two methods for resource utilization of secondary aluminum dross, namely, the pyrometallurgical method and the hydrometallurgical method. The pyrometallurgical products are mainly building materials and refractory materials, and the resource utilization process is as follows: water washing to remove nitrogen and salt to obtain low-nitrogen and low-salt secondary aluminum dross; mixing the secondary aluminum dross with other raw materials and forming; and sintering or melting to prepare building materials and refractory materials. The hydrometallurgical products are mainly high-purity alumina, and the resource utilization process is as follows: water washing to remove nitrogen and salt to obtain low-nitrogen and low-salt secondary aluminum dross; acid or alkali dissolution of the secondary aluminum dross to leach aluminum elements, and filtration to obtain aluminum leaching solution; and preparation of high-purity alumina through processes such as precipitation and calcination.

[0004] Chinese invention patent (CN110563336A) discloses a method for preparing microcrystalline glass from aluminum dross without removing salt and nitrogen, which oxidizes aluminum nitride in aluminum dross to alumina, and solidifies fluoride salt and chloride salt in the glass phase. However, the application scenarios of microcrystalline glass are few, and the market absorption capacity is low.

[0005] Chinese invention patent (CN106830030B) discloses a method for safely and efficiently producing sand-like alumina from aluminum dross, which uses sodium aluminate solution produced by the Bayer process to dissolve aluminum elements in aluminum dross to produce sand-like alumina, and simultaneously utilizes ammonia gas and hydrogen gas generated in the production process. However, since the aluminum elements in the aluminum dross are prepared into alumina through dissolution-precipitation-calcination, the process is long, the dissolution efficiency is low, and the alkali consumption is large.

[0006] Chinese invention patent (CN108585003A) discloses a method for preparing sheet-like alumina from aluminum dross, which obtains sheet-like alumina by sulfuric acid leaching, impurity removal, synthesis of precursor and calcination of aluminum dross. However, since the aluminum elements in the aluminum dross are prepared into alumina through leaching-precipitation-calcination, the process is long, the dissolution efficiency is low, and the sulfuric acid consumption is large.

[0007] Chinese invention patent (CN114906867A) discloses a method for preparing alumina from aluminum ash. The aluminum ash is treated by hydrolysis-acidolysis to obtain hydrolysis filter washing liquid and acidolysis filter washing liquid. The filter cake is obtained by evaporation, mixing, filtering and washing. The filter cake is dried and calcined to obtain alumina. However, the hydrolysis-acidolysis treatment only dissolves the active aluminum in the aluminum ash, and a large amount of inert aluminum oxide is not realized as a resource.

[0008] Chinese invention patent (CN111960450A) discloses a method for preparing alumina from aluminum ash. The aluminum ash, red mud, fly ash, limestone, iron powder and soda ash are uniformly mixed, calcined, screened and crushed to obtain alumina clinker. The alumina clinker is subjected to alkali dissolution, solid-liquid separation, precipitation, filtration and calcination to obtain alumina. However, the aluminum element in the aluminum ash is prepared into alumina through calcination-dissolution-precipitation-calcination, which has a long process and high alkali consumption.

[0009] Compared with the pyrometallurgical preparation of building materials, the market consumption of secondary aluminum ash wet-process alumina is larger. However, the existing secondary aluminum ash preparation technology for alumina has problems such as long process, low dissolution efficiency, high acid and alkali consumption, etc. Therefore, there is an urgent need for a secondary aluminum ash short-process and low-cost preparation technology for alumina to realize efficient and low-cost resource utilization of secondary aluminum ash. SUMMARY

[0010] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a method for preparing alumina from secondary aluminum ash by calcination, screening, alkali washing and acid washing. The aluminum nitride, metallic aluminum and gamma-alumina in the secondary aluminum ash are converted into alpha-alumina which is resistant to acid and alkali, and the low-melting-point impurities such as sodium, magnesium, calcium, silicon and iron oxides are aggregated into larger particles. The large-particle-size sodium, magnesium, calcium, silicon and iron impurities are removed by screening. The residual sodium, magnesium, calcium, silicon and iron impurities are removed by alkali washing. The alumina is obtained by water washing and drying. The problems of long process, low dissolution efficiency and high acid and alkali consumption in the preparation of alumina from secondary aluminum ash are solved.

[0011] The present application adopts the following technical solutions:

[0012] A method for preparing alumina from secondary aluminum ash by calcination, screening, alkali washing and acid washing, characterized in that the secondary aluminum ash is calcined in an air atmosphere, the aluminum nitride, metallic aluminum and gamma-alumina are converted into alpha-alumina which is resistant to acid and alkali, and the low-melting-point impurities such as sodium, magnesium, calcium, silicon and iron oxides are aggregated into larger particles. The large-particle-size sodium, magnesium, calcium, silicon and iron impurities are removed by screening. The residual sodium, magnesium, calcium, silicon and iron impurities are removed by alkali washing and acid washing. The alumina is obtained by water washing and drying.

[0013] Further, the calcination temperature is 1000-1400℃, and the calcination time is 1.0-4.0 h.

[0014] Further, the screen mesh aperture of the screening treatment is 200 meshes.

[0015] Further, the alkali washing solution is one or more of sodium hydroxide and potassium hydroxide, the hydroxyl ion concentration of the alkali washing solution is 0.5-2.5 mol / L, the liquid-solid ratio is 1.0-5.0 mL / g, and the alkali washing time is 1.0-5.0 h; the acid washing solution is one or more of hydrochloric acid, nitric acid and sulfuric acid, the hydrogen ion concentration of the acid washing solution is 0.2-1.2 mol / L, the liquid-solid ratio is 1.0-5.0 mL / g, and the alkali washing time is 1.0-5.0 h.

[0016] Further, the liquid-solid ratio of the water washing is 2.0-10.0 mL / g, and the water washing time is 1.0-5.0 h; and the drying temperature is 70-110 DEG C.

[0017] Further, the method specifically comprises:

[0018] S1, calcination: calcining the secondary aluminum dross at 1000-1400 DEG C in an air atmosphere for 1.0-4.0 h, converting aluminum nitride, metallic aluminum and gamma-aluminum oxide into acid and alkali resistant alpha-aluminum oxide, and gathering low-melting-point impurities such as sodium, magnesium, calcium, silicon and iron oxides into larger particles;

[0019] S2, screening: screening the calcination product through a 200 mesh screen to obtain fine secondary aluminum dross;

[0020] S3, alkali washing: washing the fine secondary aluminum dross with an alkali solution with a hydroxyl ion concentration of 0.5-2.5 mol / L, a liquid-solid ratio of 1.0-5.0 mL / g, and an alkali washing time of 1.0-5.0 h;

[0021] S4, filtering: filtering the alkali washing solution to obtain primary aluminum oxide residue;

[0022] S5, acid washing: washing the primary aluminum oxide residue with an acid solution with a hydrogen ion concentration of 0.2-1.2 mol / L, a liquid-solid ratio of 1.0-5.0 mL / g, and an alkali washing time of 1.0-5.0 h;

[0023] S6, filtering: filtering the acid washing solution to obtain secondary aluminum oxide residue;

[0024] S7, water washing: water washing the secondary aluminum oxide residue, a liquid-solid ratio of 2.0-10.0 mL / g, and a time of 1.0-5.0 h;

[0025] S8, drying: drying the aluminum oxide residue at 70-110 DEG C to obtain an aluminum oxide product.

[0026] The principle of the application is:

[0027] (1) The present application utilizes the melting point and chemical stability difference of alpha-aluminum oxide and sodium-magnesium-calcium-silicon-iron oxide, the melting point of alpha-aluminum oxide is high (>2000℃), and it has excellent acid and alkali resistance, the melting point of sodium-magnesium-calcium-silicon-iron oxide is low (<1400℃), and it is easy to react with acid and alkali. By calcination, screening, alkali washing, and acid washing, the sodium-magnesium-calcium-silicon-iron oxide impurities in the secondary aluminum ash are removed to obtain an aluminum oxide product.

[0028] (2) The melting point of sodium-magnesium-calcium-silicon-iron oxide is low, and it is easy to partially melt and bond into large particles in a high-temperature environment. The present application uses calcination to treat the secondary aluminum ash, and the sodium-magnesium-calcium-silicon-iron oxide impurities are aggregated into large particles, and then the sodium-magnesium-calcium-silicon-iron oxide impurities are removed by screening.

[0029] (3) The chemical stability of sodium-magnesium-calcium-silicon-iron oxide is poor, and the silicon oxide is easy to react with alkali to generate water-soluble silicate ions, and the sodium-magnesium-calcium-iron oxide is easy to react with acid to generate water-soluble sodium, magnesium, calcium, and iron ions. The present application uses alkali washing and acid washing to treat the secondary aluminum ash, and the residual sodium-magnesium-calcium-silicon-iron oxide impurities are converted into water-soluble ions, realizing the separation of aluminum oxide and sodium-magnesium-calcium-silicon-iron oxide impurities.

[0030] The beneficial effects of the present application are:

[0031] (1) The current secondary aluminum ash preparation technology for aluminum oxide mostly uses acid and alkali to dissolve aluminum oxide, precipitation, and calcination process. The aluminum element needs to undergo a solid state to ion state in solution to solid state transformation process. The Al-O bond in aluminum oxide undergoes a process of breaking and reconnection. The system energy consumption is large, and the waste is serious. The present application uses calcination, screening, alkali washing, and acid washing treatment to remove the sodium-magnesium-calcium-silicon-iron oxide impurities in the secondary aluminum ash. The whole process of aluminum oxide remains in a solid state, and the energy consumption is low and the utilization rate is high.

[0032] (2) In view of the problems of long technical process, low dissolution efficiency, and large acid and alkali consumption in the secondary aluminum ash preparation technology for aluminum oxide, the present application replaces the traditional extraction of aluminum oxide scheme by removing non-aluminum impurities according to the characteristics of high content of aluminum oxide (>60%) in the secondary aluminum ash. The sodium-magnesium-calcium-silicon-iron oxide impurities in the secondary aluminum ash are removed by screening, alkali washing, and acid washing treatment. The technical process is short, the alkali washing and acid washing efficiency is high, and the acid and alkali consumption is low. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The process flow chart of the present application.

[0034] Figure 2 The XRD spectrum of the aluminum oxide product in Comparative Example 2.

[0035] Figure 3 The XRD spectrum of the aluminum oxide product in Example 1. DETAILED DESCRIPTION

[0036] In order to make the objects, technical solutions, and advantages of the present application clearer, further detailed description will be given below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application.

[0037] On the contrary, the present application covers any substitution, modification, equivalent method, and solution defined by the claims within the spirit and scope of the present application. Further, in order to make the public have a better understanding of the present application, some specific details are described in the following detailed description of the present application. The present application can also be completely understood without the description of these details by those skilled in the art.

[0038] Comparative Example 1

[0039] The secondary aluminum dross was washed with a sodium hydroxide solution with a hydroxide ion concentration of 0.5 mol / L, the liquid-solid ratio was 1.0 mL / g, and the alkali washing time was 1.0 h, and the primary aluminum oxide residue was obtained by filtration; the primary aluminum oxide residue was washed with a hydrochloric acid solution with a hydrogen ion concentration of 0.2 mol / L, the liquid-solid ratio was 1.0 mL / g, and the acid washing time was 1.0 h, and the secondary aluminum oxide residue was obtained by filtration; the secondary aluminum oxide residue was washed with water, the liquid-solid ratio was 2.0 mL / g, and the time was 1.0 h; the secondary aluminum oxide residue was dried at 70℃, and the aluminum oxide product was obtained. Table 1 is the composition of the aluminum oxide product, and the aluminum oxide content is 78.8 wt.%.

[0040] Table 1 Composition of the aluminum oxide product in Comparative Example 1

[0041]

[0042] Comparative Example 2

[0043] The secondary aluminum dross was calcined at 1000℃ in an air atmosphere for 1.0 h, and the aluminum nitride, metallic aluminum, and γ-alumina were converted into acid- and alkali-resistant α-alumina; the calcined secondary aluminum dross was washed with a sodium hydroxide solution with a hydroxide ion concentration of 0.5 mol / L, the liquid-solid ratio was 1.0 mL / g, and the alkali washing time was 1.0 h, and the primary aluminum oxide residue was obtained by filtration; the primary aluminum oxide residue was washed with a hydrochloric acid solution with a hydrogen ion concentration of 0.2 mol / L, the liquid-solid ratio was 1.0 mL / g, and the acid washing time was 1.0 h, and the secondary aluminum oxide residue was obtained by filtration; the secondary aluminum oxide residue was washed with water, the liquid-solid ratio was 2.0 mL / g, and the time was 1.0 h; the secondary aluminum oxide residue was dried at 70℃, and the aluminum oxide product was obtained. Table 2 is the composition of the aluminum oxide product, and the aluminum oxide content is 82.4 wt.%; Figure 2 The XRD pattern of the aluminum oxide product is shown in Table 2, and the diffraction peak of the impurity Mg 0.338 Al 2.408 O4 is strong, i.e., the impurity content is high.

[0044] Table 2 Composition of the alumina product in Comparative Example 2

[0045]

[0046] Example 1

[0047] The secondary aluminum dross was calcined at 1000°C for 1.0 h in air atmosphere, and the aluminum nitride, metallic aluminum and γ-alumina were converted into acid- and alkali-resistant α-alumina, and the low-melting-point impurities such as sodium, magnesium, calcium, silicon and iron oxides were aggregated into larger particles. The calcined product was passed through a 200-mesh screen to obtain fine secondary aluminum dross. The fine secondary aluminum dross was washed with a sodium hydroxide solution having a hydroxyl ion concentration of 0.5 mol / L, the liquid-to-solid ratio was 1.0 mL / g, and the alkali washing time was 1.0 h. The primary alumina residue was obtained by filtration. The primary alumina residue was washed with a hydrochloric acid solution having a hydrogen ion concentration of 0.2 mol / L, the liquid-to-solid ratio was 1.0 mL / g, and the acid washing time was 1.0 h. The secondary alumina residue was obtained by filtration. The secondary alumina residue was washed with water, the liquid-to-solid ratio was 2.0 mL / g, and the time was 1.0 h. The secondary alumina residue was dried at 70°C to obtain the alumina product. Table 3 shows the composition of the alumina product, and the alumina content was 91.1 wt.%. Figure 3 The XRD pattern of the alumina product is shown in Figure 1, and the diffraction peaks of the impurity Mg 0.338 Al 2.408 O4 are weak, i.e., the impurity content is low.

[0048] Table 3 Composition of the alumina product in Example 1

[0049]

[0050] Example 2

[0051] The secondary aluminum dross was calcined at 1040°C for 1.3 h in air atmosphere, and the aluminum nitride, metallic aluminum and γ-alumina were converted into acid- and alkali-resistant α-alumina, and the low-melting-point impurities such as sodium, magnesium, calcium, silicon and iron oxides were aggregated into larger particles. The calcined product was passed through a 200-mesh screen to obtain fine secondary aluminum dross. The fine secondary aluminum dross was washed with a potassium hydroxide solution having a hydroxyl ion concentration of 0.7 mol / L, the liquid-to-solid ratio was 1.4 mL / g, and the alkali washing time was 1.4 h. The primary alumina residue was obtained by filtration. The primary alumina residue was washed with a nitric acid solution having a hydrogen ion concentration of 0.3 mol / L, the liquid-to-solid ratio was 1.4 mL / g, and the acid washing time was 1.4 h. The secondary alumina residue was obtained by filtration. The secondary alumina residue was washed with water, the liquid-to-solid ratio was 2.8 mL / g, and the time was 1.4 h. The secondary alumina residue was dried at 74°C to obtain the alumina product.

[0052] Example 3

[0053] The secondary aluminum dross is calcined at 1080°C for 1.6 hours in air atmosphere, the aluminum nitride, metallic aluminum and γ-alumina are converted into acid and alkali resistant α-alumina, and the low melting point impurities such as sodium, magnesium, calcium, silicon and iron oxides are gathered into larger particles; the calcined product is passed through a 200 mesh screen to obtain fine secondary aluminum dross; the fine secondary aluminum dross is washed with sodium hydroxide solution having a hydroxyl ion concentration of 0.9 mol / L, the liquid-solid ratio is 1.8 mL / g, and the alkali washing time is 1.8 hours, and the primary alumina residue is obtained by filtration; the primary alumina residue is washed with sulfuric acid solution having a hydrogen ion concentration of 0.4 mol / L, the liquid-solid ratio is 1.8 mL / g, and the acid washing time is 1.8 hours, and the secondary alumina residue is obtained by filtration; the secondary alumina residue is washed with water, the liquid-solid ratio is 3.6 mL / g, and the time is 1.8 hours; the secondary alumina residue is dried at 78°C to obtain the alumina product.

[0054] Example 4

[0055] The secondary aluminum dross is calcined at 1120°C for 1.9 hours in air atmosphere, the aluminum nitride, metallic aluminum and γ-alumina are converted into acid and alkali resistant α-alumina, and the low melting point impurities such as sodium, magnesium, calcium, silicon and iron oxides are gathered into larger particles; the calcined product is passed through a 200 mesh screen to obtain fine secondary aluminum dross; the fine secondary aluminum dross is washed with potassium hydroxide solution having a hydroxyl ion concentration of 1.1 mol / L, the liquid-solid ratio is 2.2 mL / g, and the alkali washing time is 2.2 hours, and the primary alumina residue is obtained by filtration; the primary alumina residue is washed with hydrochloric acid solution having a hydrogen ion concentration of 0.5 mol / L, the liquid-solid ratio is 2.2 mL / g, and the acid washing time is 2.2 hours, and the secondary alumina residue is obtained by filtration; the secondary alumina residue is washed with water, the liquid-solid ratio is 4.4 mL / g, and the time is 2.2 hours; the secondary alumina residue is dried at 82°C to obtain the alumina product.

[0056] Example 5

[0057] The secondary aluminum dross is calcined at 1160°C for 2.2 hours in air atmosphere, the aluminum nitride, metallic aluminum and γ-alumina are converted into acid and alkali resistant α-alumina, and the low melting point impurities such as sodium, magnesium, calcium, silicon and iron oxides are gathered into larger particles; the calcined product is passed through a 200 mesh screen to obtain fine secondary aluminum dross; the fine secondary aluminum dross is washed with sodium hydroxide solution having a hydroxyl ion concentration of 1.3 mol / L, the liquid-solid ratio is 2.6 mL / g, and the alkali washing time is 2.6 hours, and the primary alumina residue is obtained by filtration; the primary alumina residue is washed with nitric acid solution having a hydrogen ion concentration of 0.6 mol / L, the liquid-solid ratio is 2.6 mL / g, and the acid washing time is 2.6 hours, and the secondary alumina residue is obtained by filtration; the secondary alumina residue is washed with water, the liquid-solid ratio is 5.2 mL / g, and the time is 2.6 hours; the secondary alumina residue is dried at 86°C to obtain the alumina product. Table 4 is the composition of the alumina product, and the alumina content is 92.3 wt.%.

[0058] Table 4 Composition of the alumina product in Example 5

[0059]

[0060] Example 6

[0061] The secondary aluminum dross was calcined at 1200°C for 2.5 h in an air atmosphere, and the aluminum nitride, metallic aluminum and γ-alumina were converted into acid- and alkali-resistant α-alumina, and low-melting-point impurities such as sodium, magnesium, calcium, silicon and iron oxides were aggregated into larger particles. The calcined product was passed through a 200-mesh screen to obtain fine secondary aluminum dross. The fine secondary aluminum dross was washed with a potassium hydroxide solution having a hydroxide ion concentration of 1.5 mol / L, the liquid-to-solid ratio was 3.0 mL / g, and the alkali washing time was 3.0 h. A primary alumina residue was obtained by filtration. The primary alumina residue was washed with a sulfuric acid solution having a hydrogen ion concentration of 0.7 mol / L, the liquid-to-solid ratio was 3.0 mL / g, and the acid washing time was 3.0 h. A secondary alumina residue was obtained by filtration. The secondary alumina residue was washed with water, the liquid-to-solid ratio was 6.0 mL / g, and the time was 3.0 h. The secondary alumina residue was dried at 90°C to obtain an alumina product.

[0062] Example 7

[0063] The secondary aluminum dross was calcined at 1240°C for 2.8 h in an air atmosphere, and the aluminum nitride, metallic aluminum and γ-alumina were converted into acid- and alkali-resistant α-alumina, and low-melting-point impurities such as sodium, magnesium, calcium, silicon and iron oxides were aggregated into larger particles. The calcined product was passed through a 200-mesh screen to obtain fine secondary aluminum dross. The fine secondary aluminum dross was washed with a sodium hydroxide solution having a hydroxide ion concentration of 1.7 mol / L, the liquid-to-solid ratio was 3.4 mL / g, and the alkali washing time was 3.4 h. A primary alumina residue was obtained by filtration. The primary alumina residue was washed with a hydrochloric acid solution having a hydrogen ion concentration of 0.8 mol / L, the liquid-to-solid ratio was 3.4 mL / g, and the acid washing time was 3.4 h. A secondary alumina residue was obtained by filtration. The secondary alumina residue was washed with water, the liquid-to-solid ratio was 6.8 mL / g, and the time was 3.4 h. The secondary alumina residue was dried at 94°C to obtain an alumina product.

[0064] Example 8

[0065] The secondary aluminum dross is calcined in air atmosphere at 1280°C for 3.1 h, the aluminum nitride, metallic aluminum and γ-alumina are converted into acid and alkali resistant α-alumina, and the low melting point impurities such as sodium, magnesium, calcium, silicon and iron oxides are gathered into larger particles; the calcined product is passed through a 200 mesh screen to obtain fine secondary aluminum dross; the fine secondary aluminum dross is washed with a potassium hydroxide solution having a hydroxyl ion concentration of 1.9 mol / L, the liquid-solid ratio is 3.8 mL / g, and the alkali washing time is 3.8 h, and a primary alumina residue is obtained by filtration; the primary alumina residue is washed with a nitric acid solution having a hydrogen ion concentration of 0.9 mol / L, the liquid-solid ratio is 3.8 mL / g, and the acid washing time is 3.8 h, and a secondary alumina residue is obtained by filtration; the secondary alumina residue is washed with water, the liquid-solid ratio is 7.6 mL / g, and the time is 3.8 h; and the secondary alumina residue is dried at 98°C to obtain an alumina product.

[0066] Example 9

[0067] The secondary aluminum dross is calcined in air atmosphere at 1320°C for 3.4 h, the aluminum nitride, metallic aluminum and γ-alumina are converted into acid and alkali resistant α-alumina, and the low melting point impurities such as sodium, magnesium, calcium, silicon and iron oxides are gathered into larger particles; the calcined product is passed through a 200 mesh screen to obtain fine secondary aluminum dross; the fine secondary aluminum dross is washed with a sodium hydroxide solution having a hydroxyl ion concentration of 2.1 mol / L, the liquid-solid ratio is 4.2 mL / g, and the alkali washing time is 4.2 h, and a primary alumina residue is obtained by filtration; the primary alumina residue is washed with a sulfuric acid solution having a hydrogen ion concentration of 1.0 mol / L, the liquid-solid ratio is 4.2 mL / g, and the acid washing time is 4.2 h, and a secondary alumina residue is obtained by filtration; the secondary alumina residue is washed with water, the liquid-solid ratio is 8.4 mL / g, and the time is 4.2 h; and the secondary alumina residue is dried at 102°C to obtain an alumina product.

[0068] Example 10

[0069] The secondary aluminum dross is calcined in air atmosphere at 1360°C for 3.7 h, the aluminum nitride, metallic aluminum and γ-alumina are converted into acid and alkali resistant α-alumina, and the low melting point impurities such as sodium, magnesium, calcium, silicon and iron oxides are gathered into larger particles; the calcined product is passed through a 200 mesh screen to obtain fine secondary aluminum dross; the fine secondary aluminum dross is washed with a potassium hydroxide solution having a hydroxyl ion concentration of 2.3 mol / L, the liquid-solid ratio is 4.6 mL / g, and the alkali washing time is 4.6 h, and a primary alumina residue is obtained by filtration; the primary alumina residue is washed with a hydrochloric acid solution having a hydrogen ion concentration of 1.1 mol / L, the liquid-solid ratio is 4.6 mL / g, and the acid washing time is 4.6 h, and a secondary alumina residue is obtained by filtration; the secondary alumina residue is washed with water, the liquid-solid ratio is 9.2 mL / g, and the time is 4.6 h; and the secondary alumina residue is dried at 106°C to obtain an alumina product. Table 5 is the composition of the alumina product, and the alumina content is 92.8 wt.%.

[0070] Table 5 Composition of alumina product in Example 10

[0071]

[0072] Example 11

[0073] The secondary aluminum dross was calcined in air atmosphere at 1400℃ for 4.0 h, the aluminum nitride, metallic aluminum and γ-alumina were converted into acid and alkali resistant α-alumina, and the low melting point impurities such as sodium, magnesium, calcium, silicon and iron oxides were gathered into larger particles; the calcined product was passed through a 200 mesh screen to obtain fine secondary aluminum dross; the fine secondary aluminum dross was washed with sodium hydroxide solution with a hydroxyl ion concentration of 2.5 mol / L, the liquid-solid ratio was 5.0 mL / g, and the alkali washing time was 5.0 h, and the primary alumina residue was obtained by filtration; the primary alumina residue was washed with nitric acid solution with a hydrogen ion concentration of 1.2 mol / L, the liquid-solid ratio was 5.0 mL / g, and the acid washing time was 5.0 h, and the secondary alumina residue was obtained by filtration; the secondary alumina residue was washed with water, the liquid-solid ratio was 10.0 mL / g, and the time was 5.0 h; the secondary alumina residue was dried at 110℃ to obtain the alumina product.

Claims

1. A method for preparing alumina through secondary aluminum ash calcination, sieving, alkali washing, and acid washing, characterized in that, Secondary aluminum ash is calcined in an air atmosphere to transform aluminum nitride, metallic aluminum, and γ-alumina into acid- and alkali-resistant α-alumina, and to agglomerate low-melting-point impurities of sodium, magnesium, calcium, silicon, and iron oxides into larger particles. Screening is used to remove large-particle sodium, magnesium, calcium, silicon, and iron oxide impurities. Alkali washing and acid washing are used to remove residual sodium, magnesium, calcium, silicon, and iron oxide impurities. After washing and drying, aluminum oxide is finally obtained; Secondary aluminum ash is a hazardous waste produced after aluminum extraction from aluminum slag. It contains 40-60 wt.% alumina, 15-25 wt.% aluminum nitride, 10-20 wt.% sodium salts, potassium salts and fluoride salts as a total of salt refining agents, and a small amount of metallic aluminum.

2. The method for preparing alumina by secondary aluminum ash calcination, sieving, alkali washing, and acid washing as described in claim 1, characterized in that, The calcination temperature is 1000-1400℃, and the calcination time is 1.0-4.0h.

3. The method for preparing alumina by secondary aluminum ash calcination, sieving, alkali washing, and acid washing as described in claim 1, characterized in that, The sieve used for the screening process has a mesh size of 200.

4. The method for preparing alumina by secondary aluminum ash calcination, sieving, alkali washing, and acid washing as described in claim 1, characterized in that, The alkaline washing solution is one or more of sodium hydroxide and potassium hydroxide, with a hydroxide ion concentration of 0.5-2.5 mol / L, a liquid-to-solid ratio of 1.0-5.0 mL / g, and an alkaline washing time of 1.0-5.0 h; the acid washing solution is one or more of hydrochloric acid, nitric acid, and sulfuric acid, with a hydrogen ion concentration of 0.2-1.2 mol / L, a liquid-to-solid ratio of 1.0-5.0 mL / g, and an alkaline washing time of 1.0-5.0 h.

5. The method for preparing alumina by secondary aluminum ash calcination, sieving, alkali washing, and acid washing as described in claim 1, characterized in that, The liquid-to-solid ratio of the water washing is 2.0-10.0 mL / g, the water washing time is 1.0-5.0 h, and the drying temperature is 70-110 ℃.

6. The method for preparing alumina by secondary aluminum ash calcination, sieving, alkali washing, and acid washing as described in claim 1, characterized in that, The specific preparation steps include: S1. Calcination: Calcination of secondary aluminum ash in air at 1000-1400℃ for 1.0-4.0h transforms aluminum nitride, metallic aluminum and γ-alumina into acid and alkali resistant α-alumina, and agglomerates low-melting-point impurities of sodium, magnesium, calcium, silicon and iron oxides into larger particles. S2. Sieving: Pass the calcined product through a 200-mesh sieve to obtain fine secondary aluminum ash; S3. Alkaline washing: Wash the fine secondary aluminum ash with an alkaline solution with a hydroxide ion concentration of 0.5-2.5 mol / L, with a liquid-to-solid ratio of 1.0-5.0 mL / g and an alkaline washing time of 1.0-5.0 h. S4. Filtration: Filter the alkaline washing solution to obtain primary alumina slag; S5. Pickling: Wash the alumina slag once with an acid solution with a hydrogen ion concentration of 0.2-1.2 mol / L, with a liquid-to-solid ratio of 1.0-5.0 mL / g and an alkaline washing time of 1.0-5.0 h. S6. Filtration: Filter the pickling solution to obtain secondary alumina slag; S7. Water washing: Wash the secondary alumina slag with water at a liquid-to-solid ratio of 2.0-10.0 mL / g for 1.0-5.0 h. S8. Drying: Dry the alumina slag at 70-110℃ to obtain the alumina product.

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