Method for recycling aluminum and iron from iron-aluminum slag resources

Abstract

The present disclosure provides a method for recycling aluminum and iron from iron-aluminum slag, which comprises: (1) mixing the iron-aluminum slag with a first alkali solution for alkali conversion reaction, and after solid-liquid separation, obtaining a sulfate solution and an iron-aluminum slag after alkali conversion; (2) mixing the iron-aluminum slag after alkali conversion with a second alkali solution for alkali leaching reaction, and after solid-liquid separation, obtaining an aluminate solution and an iron residue; (3) acid dissolving the iron residue, then adding sulfuric acid to precipitate iron sulfate, and after solid-liquid separation, obtaining iron sulfate crystals and an acid solution. The method of the present disclosure can effectively separate and recycle iron and aluminum elements in the iron-aluminum slag.

Description

Technical Field

[0001] This disclosure belongs to the field of waste battery recycling technology and relates to a method for the resource-based recycling of aluminum and iron from iron-aluminum slag. Background Technology

[0002] In recent years, batteries have developed rapidly and are widely used in various fields such as digital electronics, smart grids, electric vehicles, and large-scale energy storage materials. However, the cycle life of batteries is always limited, which means that the amount of waste batteries generated is also increasing year by year, making the recycling of waste batteries an essential industrial chain.

[0003] The current wet recycling process for ternary lithium batteries mainly produces graphite slag, iron-aluminum slag, and sponge copper. Among these, sponge copper can be sold at a low price as a product; the main component of graphite slag is graphite, the negative electrode powder in battery powder; iron-aluminum slag has the largest volume, mainly composed of iron and aluminum, while also containing a certain amount of valuable heavy metals such as nickel, cobalt, and manganese. It is very difficult to recycle or render harmless, and the industry currently treats iron-aluminum slag as solid waste or hazardous waste.

[0004] Iron and aluminum are abundant metallic elements in nature and have high utilization value. The iron and aluminum slag produced by the wet process of waste battery recycling contains a large amount of iron and aluminum, and it is very meaningful to separate and recycle this part of iron and aluminum. Summary of the Invention

[0005] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0006] To address the shortcomings of existing technologies, the purpose of this disclosure is to provide a method for the resource-based recovery of aluminum and iron from iron-aluminum slag. This disclosure first separates sulfate ions from the iron-aluminum slag through an alkaline conversion reaction; then, aluminum is separated from the alkaline-converted iron-aluminum slag through an alkaline leaching reaction to obtain an aluminate solution, which yields aluminum hydroxide. Iron remains in the iron slag, thus achieving the separation of iron and aluminum. Subsequently, ferric sulfate is obtained using the solubility principle of ferric sulfate. Therefore, the method of this disclosure can effectively separate and recover iron and aluminum elements from iron-aluminum slag.

[0007] To achieve this objective, the present disclosure adopts the following technical solution:

[0008] In a first aspect, this disclosure provides a method for the resource recovery of aluminum and iron from iron-aluminum slag, the method comprising:

[0009] (1) Mix the iron-aluminum slag with the first alkaline solution to carry out the alkaline conversion reaction. After solid-liquid separation, the sulfate solution and the alkaline-converted iron-aluminum slag are obtained.

[0010] (2) The iron-aluminum slag after alkali conversion and the second alkali solution are mixed and subjected to alkali leaching reaction. After solid-liquid separation, an aluminate solution and iron slag are obtained.

[0011] (3) The iron slag is acid-dissolved, and then sulfuric acid is added to precipitate ferric sulfate. After solid-liquid separation, ferric sulfate crystals and acid solution are obtained.

[0012] This disclosure provides a method for the resource-based recovery of aluminum and iron from iron-aluminum slag. First, sulfate ions are separated from the iron-aluminum slag through an alkaline conversion reaction to obtain a sulfate solution, thereby obtaining a sulfate product. Then, aluminum is separated from the alkaline-converted iron-aluminum slag through an alkaline leaching reaction to obtain an aluminate solution, thereby obtaining an aluminum hydroxide product. Iron remains in the iron slag, thus achieving the separation of iron and aluminum. Subsequently, utilizing the solubility principle of ferric sulfate, the iron slag is first acid-dissolved and then sulfuric acid is added to obtain a ferric sulfate product. At the same time, the acid solution can be recycled.

[0013] In summary, the method disclosed herein can effectively separate and recover iron and aluminum elements from iron-aluminum slag, yielding sulfate products, aluminum hydroxide products, and ferric sulfate products. These products can be sold to generate revenue, maximizing the utilization of iron-aluminum slag and facilitating industrial applications.

[0014] In one embodiment, the iron-aluminum slag includes iron-aluminum slag generated from the wet recycling of ternary lithium batteries. The iron-aluminum slag contains aluminum ions, iron ions, nickel ions, cobalt ions, manganese ions, sulfate ions, organic matter (COD), and impurities (e.g., phosphorus and / or fluorine). Nickel ions, cobalt ions, and manganese ions precipitate after an alkaline conversion reaction and enter the iron-aluminum slag after alkaline conversion. They then enter the iron slag through an alkaline leaching reaction, are dissolved in acid, and finally remain in an acid solution. This acid solution can be reused in the acid dissolution step or returned to the battery recycling line for nickel, cobalt, and manganese recovery.

[0015] As an optional technical solution of this disclosure, the alkaline substance in the first alkaline solution in step (1) includes at least one of sodium hydroxide, calcium hydroxide and sodium carbonate.

[0016] In this disclosure, when at least one of sodium hydroxide, calcium hydroxide, and sodium carbonate is used as the alkaline substance of the first alkaline solution, it can undergo an alkaline conversion reaction with iron-aluminum slag, and the resulting sulfate solution is a sodium sulfate solution.

[0017] The main chemical components of iron-aluminum slag are iron alum (NaFe3(SO4)2(OH)6) and aluminum alum (NaAl3(SO4)2(OH)6). For example, the reaction equation of iron-aluminum slag with sodium hydroxide is as follows:

[0018] NaAl3(SO4)2(OH)6(s)+6NaOH(aq)=2Na2SO4(aq)+3NaAl(OH)4(aq);

[0019] NaFe3(SO4)2(OH)6(s)+3NaOH(aq)=2Na2SO4(aq)+3Fe(OH)3(s);

[0020] The amount of alkali used will destroy and transform the structure of iron alum, and a small amount of sodium sulfate in aluminum alum will also be transformed out, thus obtaining sodium sulfate; the transformed aluminum sulfate or aluminum hydroxide will be carried in the iron-aluminum slag after alkali transformation.

[0021] In one embodiment, the concentration of the first alkaline solution in step (1) is 20–40 g / L, for example, it can be 20 g / L, 25 g / L, 30 g / L, 35 g / L, or 40 g / L. However, it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0022] In this disclosure, if the concentration of the first alkaline solution is too low, the conversion rate of sodium sulfate will be too low; if the concentration of the first alkaline solution is too high, some aluminum elements will enter the sulfate solution, resulting in aluminum loss.

[0023] In one embodiment, the liquid-solid mass ratio of the first alkaline solution to the iron-aluminum slag in step (1) is 8:1.

[0024] In one embodiment, the temperature of the alkali conversion reaction in step (1) is 60–80°C, for example, 60°C, 65°C, 70°C, 75°C, or 80°C, and the time of the alkali conversion reaction is 2–4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours. However, it is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0025] In this disclosure, carrying out an alkaline conversion reaction at a temperature of 60–80°C for 2–4 hours can improve the conversion rate of sodium sulfate.

[0026] In this disclosure, under the combined effect of the above conditions, the leaching rate of sulfate (such as sodium sulfate) in the sulfate solution obtained after the alkali conversion reaction is between 50% and 90%, for example, it can be 50%, 60%, 70%, 80% or 90%.

[0027] In one embodiment, the aluminum content in the alkali-converted iron-aluminum slag in step (1) is 15-25% (e.g., 15%, 18%, 20%, or 22%), the iron content is 20-30% (e.g., 20%, 22%, 25%, or 28%), and the nickel content is 0.5-1.0% (e.g., 0.5%, 0.7%, 0.8%, or 0.9%).

[0028] As an optional technical solution of this disclosure, the sulfate solution in step (1) is subjected to freeze crystallization to precipitate sulfate. This sulfate can be sold externally.

[0029] In this disclosure, sulfate is precipitated by freeze crystallization, ensuring that the sulfate is free of other impurities. The sulfate recovery rate is 50-90%. The solution after sulfate precipitation is alkaline, and this solution can be returned to the main water treatment system to adjust the wastewater concentration.

[0030] In one embodiment, the temperature for freeze crystallization is 2–5°C, for example, 2°C, 2.5°C, 3°C, 3.5°C, 4°C, 4.5°C, or 5°C. However, it is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0031] As an optional technical solution of this disclosure, the alkaline substance in the second alkaline solution in step (2) includes at least one of sodium hydroxide, calcium hydroxide and sodium carbonate.

[0032] In this disclosure, at least one of sodium hydroxide, calcium hydroxide, and sodium carbonate is used as the alkaline substance in the second alkaline solution, which can react with the iron-aluminum slag after alkaline conversion to undergo an alkaline leaching reaction, and the resulting aluminate solution is a sodium aluminate solution.

[0033] In one embodiment, the amount of alkaline substance in the second alkaline solution in step (2) is 1.5 to 2.5 times the theoretical amount required for all aluminum to be converted into aluminate. For example, it can be 1.5 times, 1.7 times, 2 times, 2.2 times, 2.3 times, 2.4 times, or 2.5 times, etc. However, it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0034] It should be noted that the aluminum element in "all aluminum elements are converted into aluminates" refers to the aluminum element in the iron-aluminum slag after alkali conversion.

[0035] In this disclosure, if the amount of alkaline substance in the second alkaline solution is too small, the leaching rate of aluminum will be low; if the amount of alkaline substance in the second alkaline solution is too large, the leaching effect will not be improved, resulting in waste of reagents.

[0036] As an optional technical solution of this disclosure, in step (2), the liquid-solid mass ratio of the second alkaline solution and the iron-aluminum slag after alkaline conversion is 5:1.

[0037] In one embodiment, the temperature of the alkaline leaching reaction in step (2) is 60–80°C, for example, 60°C, 65°C, 70°C, 75°C, or 80°C, and the time of the alkaline leaching reaction is 2–4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours. However, it is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0038] In this disclosure, an alkaline leaching reaction at a temperature of 60–80°C for 2–4 hours can effectively leach aluminum.

[0039] As an optional technical solution of this disclosure, the caustic ratio α of the aluminate solution in step (2) is... k The range is 1.55 to 1.6, for example, it could be 1.55, 1.56, 1.57, 1.58, 1.59, or 1.6, etc. However, it is not limited to the listed values; other unlisted values ​​within this range also apply.

[0040] In this disclosure, the caustic ratio α of the aluminate solution is... k A caustic ratio of 1.55 to 1.6 is beneficial for subsequent Bayer process treatment of aluminate solutions, and aluminate solutions with this caustic ratio range are suitable for seeding.

[0041] In one embodiment, the mass concentration of aluminum in the aluminate solution is 10–25 g / L, for example, it can be 10 g / L, 12 g / L, 15 g / L, 18 g / L, 20 g / L or 22 g / L.

[0042] In one embodiment, the iron slag contains 0.5-7.0% aluminum by mass (e.g., 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, or 6.5%), 25-45% iron by mass (e.g., 25%, 30%, 35%, or 40%), and 1.0-1.5% nickel by mass (e.g., 1.0%, 1.1%, 1.2%, 1.3%, or 1.4%).

[0043] As an optional technical solution of this disclosure, the aluminate solution in step (2) is treated by the Bayer process to obtain aluminum hydroxide.

[0044] The Bayer process is a chemical process for producing alumina from bauxite. This disclosure describes the preparation of aluminum hydroxide using the Bayer process, which features low energy consumption, low cost, high product purity, and the ability to recycle the separated solution, thus avoiding waste of alkali and significantly reducing costs.

[0045] As an optional technical solution of this disclosure, the Bayer process includes the following steps:

[0046] The aluminate solution and seed crystals described in step (2) are mixed and then separated to obtain aluminum hydroxide and aluminate mother liquor.

[0047] The aluminum hydroxide product obtained in this disclosure conforms to the GB / T4294-2010 product standard and is available for sale.

[0048] In one embodiment, the seed crystal comprises aluminum hydroxide.

[0049] In one embodiment, the amount of seed crystals added is 0.5 to 1.5 times the theoretical amount required for all aluminum in the aluminate solution to be converted into aluminum hydroxide, for example, it can be 0.5 times, 0.7 times, 1 time, 1.2 times, 1.3 times, 1.4 times, or 1.5 times, etc. However, it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0050] In this disclosure, if the amount of seed crystals added is too small, the decomposition rate of aluminum hydroxide will be low; if the amount of seed crystals added is too large, the increase in decomposition rate will be limited, resulting in waste.

[0051] In one embodiment, the temperature of the seeding is 50–60°C, for example, 50°C, 52°C, 54°C, 56°C, 58°C, or 60°C, and the seeding time is 1–10 hours, for example, 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, or 10 hours. However, it is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0052] In this disclosure, aluminum hydroxide can be effectively separated by seeding at a temperature of 50–60°C for 1–10 hours.

[0053] In one embodiment, the seeding process is accompanied by stirring at a speed of 150–300 r / min, such as 150 r / min, 200 r / min, 250 r / min, or 300 r / min. However, it is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0054] In this disclosure, the seed crystals are continuously stirred at a rate of 150–300 r / min during the seeding process, which can fully disperse the seed crystals in the solution and ensure sufficient contact with the solution.

[0055] In one embodiment, the mass concentration of aluminum in the aluminate mother liquor is 9–12 g / L. For example, it can be 9 g / L, 10 g / L, 11 g / L, or 12 g / L.

[0056] In one embodiment, the aluminate mother liquor is mixed with iron-aluminum slag after alkali conversion and subjected to alkali leaching reaction. After solid-liquid separation, an aluminate solution and iron slag are obtained. The aluminate solution is then further seeded using the Bayer process to obtain aluminum hydroxide and a new aluminate mother liquor.

[0057] In this disclosure, aluminate mother liquor is mixed with iron-aluminum slag after alkali conversion, eliminating the need for alkali addition and allowing for the recycling of alkali in the solution, thus reducing alkali costs. The aluminate mother liquor can be recycled multiple times. When the aluminate mother liquor is recycled to a high level of sulfate (such as sodium sulfate) and impurities (such as COD and small amounts of phosphorus and fluorine), it undergoes impurity removal treatment, followed by evaporation and crystallization to obtain sulfate.

[0058] In one embodiment, after the aluminate mother liquor is mixed with the alkali-converted iron-aluminum slag and subjected to an alkali leaching reaction, the resulting aluminate solution has a caustic ratio α. k It ranges from 1.55 to 1.65. For example, it could be 1.55, 1.57, 1.58, 1.6, or 1.65, etc.

[0059] As an optional technical solution of this disclosure, the acid used in the acid dissolution process in step (3) includes sulfuric acid, and the concentration of the acid is 2 to 4 mol / L, for example, it can be 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L, etc. However, it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0060] In this disclosure, when sulfuric acid with a concentration of 2–4 mol / L is used for acid dissolution, the acid solubility rate of iron is 80–98.6% (e.g., 80%, 85%, 90%, or 95%). If the acid concentration used during acid dissolution is too low, the ferric sulfate will remain in solution and will not precipitate after the addition of sulfuric acid; if the acid concentration used during acid dissolution is too high, too much sulfuric acid will remain after the ferric sulfate precipitates.

[0061] In one embodiment, the mass concentration of sulfuric acid in step (3) is 60% to 98%, for example, it can be 60%, 70%, 80%, 98%, or 90%. However, it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0062] In this disclosure, the solute in the solution obtained by acid dissolution is mainly ferric sulfate. Utilizing the principle of ferric sulfate solubility, high-concentration sulfuric acid is added to obtain a saturated solution, which is then cooled to crystallize and precipitate ferric sulfate crystals, thus realizing the resource utilization of iron. When the mass concentration of sulfuric acid in step (3) is 60-98%, the ferric sulfate recovery rate is 90-99.5% (for example, it can be 90%, 92%, 95%, or 98%, etc.). If the mass concentration of sulfuric acid is too low, the ferric sulfate reaches its solubility and does not precipitate.

[0063] The acid solution after solid-liquid separation in step (3) mainly contains nickel sulfate / cobalt / manganese and acid, which can be returned to acid dissolution or to the leaching and impurity removal process of the battery recycling production line to achieve comprehensive recycling and utilization of valuable metals.

[0064] As an optional technical solution of this disclosure, the method specifically includes the following steps:

[0065] (I) Mix the iron-aluminum slag with a first alkaline solution with a concentration of 20-40 g / L, and carry out the alkaline conversion reaction at 60-80℃ for 2-4 h. After solid-liquid separation, a sulfate solution and the alkaline-converted iron-aluminum slag are obtained. The sulfate solution is then subjected to freeze crystallization at 2-5℃ to precipitate sulfate.

[0066] (II) The iron-aluminum slag after alkali conversion and the second alkali solution are mixed and subjected to alkali leaching reaction. After solid-liquid separation, a caustic ratio α is obtained. k The mixture consists of an aluminate solution of 1.55–1.6 and iron slag. The aluminate solution is mixed with seed crystals, and after seed separation, aluminum hydroxide and aluminate mother liquor are obtained.

[0067] The amount of alkaline substance in the second alkaline solution is 1.5 to 2.5 times the theoretical amount required for all aluminum to be converted into aluminate. The alkaline leaching reaction temperature is 60 to 80°C and the time is 2 to 4 hours. The amount of seed crystals added is 0.5 to 1.5 times the theoretical amount required for all aluminum in the aluminate solution to be converted into aluminum hydroxide. The seeding temperature is 50 to 60°C and the time is 1 to 10 hours.

[0068] (III) The iron slag is acid-dissolved with sulfuric acid at a concentration of 2-4 mol / L, and then sulfuric acid at a mass concentration of 60-98% is added to precipitate ferric sulfate. After solid-liquid separation, ferric sulfate crystals and acid solution are obtained.

[0069] The numerical range described in this disclosure includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this disclosure will not exhaustively list the specific point values ​​included in the range.

[0070] Compared with the prior art, the beneficial effects of this disclosure are as follows:

[0071] This disclosure provides a method for the resource-based recovery of aluminum and iron from iron-aluminum slag. First, sulfate ions are separated from the iron-aluminum slag through an alkaline conversion reaction to obtain a sulfate solution, thereby obtaining a sulfate product. Then, aluminum is separated from the alkaline-converted iron-aluminum slag through an alkaline leaching reaction to obtain an aluminate solution, thereby obtaining an aluminum hydroxide product. Iron remains in the iron slag, thus achieving the separation of iron and aluminum. Subsequently, utilizing the solubility principle of ferric sulfate, the iron slag is first acid-dissolved and then sulfuric acid is added to obtain a ferric sulfate product. At the same time, the acid solution can be recycled.

[0072] In summary, the method disclosed herein can effectively separate and recover iron and aluminum elements from iron-aluminum slag, yielding sulfate, aluminum hydroxide, and ferric sulfate products. These products can be sold to generate revenue, maximizing the utilization of iron-aluminum slag and facilitating industrial applications. Furthermore, the method is simple, low-cost, produces no waste, and generates very little wastewater.

[0073] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0074] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0075] Figure 1 This is a schematic diagram of a process for the resource recovery of aluminum and iron from iron-aluminum slag, provided as one embodiment of the present disclosure. Detailed Implementation

[0076] The technical solution of this disclosure will be further illustrated below through specific implementation methods.

[0077] In one embodiment, this disclosure provides a method for the resource recovery of aluminum and iron from iron-aluminum slag, the process of which is as follows: Figure 1 As shown, the method includes the following steps:

[0078] (1) Add NaOH solution to iron-aluminum slag to carry out alkaline conversion, and obtain sodium sulfate solution and iron-aluminum slag after alkaline conversion. Freeze crystallize the sodium sulfate solution to obtain sodium sulfate.

[0079] (2) The iron-aluminum slag after alkali conversion described in step (1) is subjected to alkali leaching to obtain nickel-iron slag and sodium aluminate solution;

[0080] (3) The sodium aluminate solution described in step (2) is treated using the Bayer process to obtain Al(OH)3 and sodium aluminate mother liquor; after adding alkali-converted iron-aluminum slag to the sodium aluminate mother liquor for alkali leaching reaction, sodium aluminate solution is obtained again. The sodium aluminate solution is then treated using the Bayer process, and the process is repeated in this manner; when the sodium aluminate mother liquor becomes a solution containing more sodium sulfate impurities, the solution is purified, and then evaporated and crystallized to obtain sodium sulfate.

[0081] (4) The nickel-iron slag described in step (2) is acid-dissolved and sulfuric acid is added to obtain ferric sulfate crystals. After solid-liquid separation, ferric sulfate and mother liquor are obtained. The mother liquor can be reused to prepare ferric sulfate crystals and can also be used to recover nickel, cobalt and manganese in battery lines.

[0082] Example 1

[0083] This embodiment provides a method for the resource-based recovery of aluminum and iron from iron-aluminum slag. The iron-aluminum slag contains the following components by mass: 0.5% nickel, 56% sulfate, 10.5% aluminum, and 14.5% iron, with the remainder being trace impurities (F and P) and COD. The method includes the following specific steps:

[0084] (1) Alkali conversion process: Take 100g of the above iron-aluminum slag into a beaker, prepare a 20g / L sodium hydroxide solution, stir the iron-aluminum slag into a slurry with a fixed liquid-solid (mass) ratio of 8:1, and react at 60℃ for 4h. After the reaction is completed, filter while hot to obtain about 70g of alkali-converted iron-aluminum slag and sodium sulfate solution. The alkali-converted iron-aluminum slag contains 0.71% nickel, 20.71% iron, and 15% aluminum. The sodium sulfate solution is freeze-crystallized in a 5℃ freeze reactor. After the crystallization is completed, it is quickly centrifuged and dried to obtain alkali solution and sodium sulfate crystals. The sodium sulfate recovery rate is 53.57%.

[0085] (2) Alkali leaching process: The iron-aluminum slag after alkali conversion in step (1) is subjected to alkali leaching. A sodium hydroxide solution is prepared, and the amount of sodium hydroxide used is 1.5 times the theoretical amount required for all aluminum elements to be converted into sodium aluminate. The liquid-solid (mass) ratio is 5:1, and the leaching temperature is 60℃ with stirring for 2 hours. After the reaction is completed, the mixture is filtered while hot to obtain 50g of nickel-iron slag and sodium aluminate solution. The nickel-iron slag contains 1.0% nickel, 29% iron, and 6.3% aluminum. The sodium aluminate solution contains 14.7g / L aluminum. k The value is 1.55, and the aluminum leaching rate is 70%.

[0086] (3) Seeding process: Add seed aluminum hydroxide to the sodium aluminate solution obtained from the alkali leaching process. The amount added is 0.5 times the theoretical amount of aluminum. Stir at 150 r / min and react at 60℃ for 6 h. After the reaction is completed, filter to obtain sodium aluminate mother liquor and aluminum hydroxide with an aluminum content of 9.85 g / L. The aluminum decomposition rate is 33%. The aluminum hydroxide meets the product standard of GB / T4294-2010. The specific data are shown in Table 1.

[0087] (4) Add the iron-aluminum slag from the alkali conversion process to the sodium aluminate mother liquor obtained in step (3) to reduce α k When the concentration reaches 1.55-1.65, there is no need to add sodium hydroxide again. Repeat the alkaline leaching and seed separation process. Alkaline leaching until seed separation is completed in one cycle. When the sodium aluminate mother liquor is rich in impurities such as sodium sulfate, COD and a small amount of phosphorus and fluorine, it is discharged to the water treatment system for impurity removal and extraction of sodium sulfate crystals.

[0088] (5) Add 2 mol / L sulfuric acid to the nickel-iron slag obtained in step (2), at a temperature of 60℃, for a reaction time of 4 h, with a liquid-to-solid (mass) ratio of 5:1; after the reaction is completed, filter the solution, the iron acid solubility is 80%, and 8 g of waste residue and acid-dissolved solution are obtained; the acid-dissolved solution contains 46.4 g / L iron and 1.4 g / L nickel; continue to add an equal volume of 60% sulfuric acid to the acid-dissolved solution, cool it and precipitate ferric sulfate crystals, centrifuge it to separate the solid and liquid, the iron recovery rate is 90%, the solid is the product ferric sulfate, which meets the product standard of HG / T4816-2015, and the data are shown in Table 2; the sulfuric acid solution is reused at the front end for acid dissolution or precipitation of ferric sulfate crystals.

[0089] Example 2

[0090] This embodiment provides a method for the resource-based recovery of aluminum and iron from iron-aluminum slag. The iron-aluminum slag contains the following components by mass: 0.5% nickel, 56% sulfate, 10.5% aluminum, and 14.5% iron, with the remainder being trace impurities (F and P) and COD. The method includes the following specific steps:

[0091] (1) Alkali conversion process: Take 100g of the above iron-aluminum slag into a beaker, prepare a 30g / L sodium hydroxide solution, stir the iron-aluminum slag into a slurry at a liquid-to-solid ratio of 8:1, react at 70℃ for 3h, filter while hot after the reaction to obtain about 60g of alkali-converted iron-aluminum slag and sodium sulfate solution, wherein the alkali-converted iron-aluminum slag has a nickel content of 0.83%, an iron content of 24.17%, and an aluminum content of 17.5%; the sodium sulfate solution is freeze-crystallized in a 5℃ freeze-drying reactor, and after the crystallization is completed, it is quickly centrifuged and dried to obtain alkali solution and sodium sulfate crystals, with a sodium sulfate recovery rate of 71.43%;

[0092] (2) Alkali leaching process: The iron-aluminum slag after alkali conversion in step (1) is subjected to alkali leaching. A sodium hydroxide solution is prepared, and the amount of sodium hydroxide used is twice the theoretical amount required for all aluminum elements to be converted into sodium aluminate. The liquid-to-solid ratio is 5:1, and the leaching temperature is 70℃ with stirring for 2 hours. After the reaction is completed, the mixture is filtered while hot to obtain 40g of nickel-iron slag and sodium aluminate solution. The nickel-iron slag contains 1.25% nickel, 36.25% iron, and 1.8% aluminum. The sodium aluminate solution contains 19.55g / L aluminum. k The value was 1.60, and the aluminum leaching rate was 93.1%.

[0093] (3) Seeding process: Add seed aluminum hydroxide to the sodium aluminate solution obtained from the alkali leaching process. The amount added is 1 times the theoretical amount of aluminum. Stir at 200 r / min and react at 55℃ for 7 h. After the reaction is completed, filter to obtain sodium aluminate mother liquor and aluminum hydroxide with an aluminum content of 11.53 g / L. The aluminum decomposition rate is 41%. The aluminum hydroxide meets the product standard of GB / T4294-2010. The specific data are shown in Table 1.

[0094] (4) Add the iron-aluminum slag from the alkali conversion process to the sodium aluminate mother liquor obtained in step (3) to reduce α k When the pH reaches 1.55–1.65, there is no need to add sodium hydroxide again; repeat the alkaline leaching and seed separation processes.

[0095] (5) Add 3 mol / L sulfuric acid to the nickel-iron slag obtained in step (2), at a temperature of 60℃, for a reaction time of 4 h, with a liquid-to-solid ratio of 5:1; after the reaction is completed, filter the solution, the iron acid solubility is 90%, and 3 g of waste residue and acid solution are obtained; the acid solution contains 65.25 g / L iron and 2.81 g / L nickel; continue to add an equal volume of 80% sulfuric acid to the acid solution, cool it and precipitate iron sulfate crystals, centrifuge it to separate the solid and liquid, the iron recovery rate is 92%, the solid is the product iron sulfate, which meets the product standard of HG / T4816-2015, and the data are shown in Table 2; the sulfuric acid solution is reused for acid dissolution or precipitation of iron sulfate crystals at the front end.

[0096] Example 3

[0097] This embodiment provides a method for the resource-based recovery of aluminum and iron from iron-aluminum slag. The iron-aluminum slag contains the following components by mass: 0.5% nickel, 56% sulfate, 10.5% aluminum, and 14.5% iron, with the remainder being trace impurities (F and P) and COD. The method includes the following specific steps:

[0098] (1) Alkali conversion process: Take 100g of the above iron-aluminum slag into a beaker, prepare a 40g / L sodium hydroxide solution, stir the iron-aluminum slag into a slurry at a liquid-to-solid ratio of 8:1, react at 80℃ for 2h, filter while hot after the reaction to obtain about 50g of alkali-converted iron-aluminum slag and sodium sulfate solution, wherein the alkali-converted iron-aluminum slag has a nickel content of 1.0%, an iron content of 29%, and an aluminum content of 21%; the sodium sulfate solution is freeze-crystallized in a 5℃ freeze-drying reactor, and after the crystallization is completed, it is quickly centrifuged and dried to obtain alkali solution and sodium sulfate crystals, with a sodium sulfate recovery rate of 89.29%;

[0099] (2) Alkali leaching process: The alkali-to-aluminum slag from step (1) above is subjected to alkali leaching. A sodium hydroxide solution is prepared, with the amount of sodium hydroxide being 2.5 times the theoretical amount required for all aluminum to be converted into sodium aluminate. The liquid-to-solid ratio is 5:1, and the leaching temperature is 80℃ with stirring for 2 hours. After the reaction is completed, the mixture is filtered while hot to obtain 35g of nickel-iron slag and sodium aluminate solution. The nickel-iron slag contains 1.43% nickel, 41.43% iron, and 0.7% aluminum. The sodium aluminate solution contains 20.52g / L aluminum. k The value is 1.65, and the aluminum leaching rate is 97.7%.

[0100] (3) Seeding process: Add seed aluminum hydroxide to the sodium aluminate solution obtained from the alkali leaching process. The amount added is 1.5 times the theoretical amount of aluminum. Stir at 250 r / min and react at 50℃ for 8 hours. After the reaction is completed, filter to obtain sodium aluminate mother liquor and aluminum hydroxide with an aluminum content of 11.13 g / L. The aluminum decomposition rate is 47%. The aluminum hydroxide meets the product standard of GB / T4294-2010. The specific data are shown in Table 1.

[0101] (4) Add the iron-aluminum slag from the alkali conversion process to the sodium aluminate mother liquor obtained in step (3) to reduce α k When the pH reaches 1.55–1.65, there is no need to add sodium hydroxide again; repeat the alkaline leaching and seed separation processes.

[0102] (5) Add 4 mol / L sulfuric acid to the nickel-iron slag obtained in step (2), at a temperature of 60℃, for a reaction time of 4 h, with a liquid-to-solid ratio of 5:1; after the reaction is completed, filter the solution, the iron acid solubility is 98.6%, and 1 g of waste residue and acid solution are obtained; the acid solution contains 81.65 g / L iron and 2.82 g / L nickel; continue to add an equal volume of 98% sulfuric acid to the acid solution, cool it and precipitate ferric sulfate crystals, centrifuge it to separate the solid and liquid, the iron recovery rate is 99.5%, the solid is the product ferric sulfate, which meets the product standard of HG / T4816-2015, and the data is shown in Table 2; the sulfuric acid solution is reused for acid dissolution or precipitation of ferric sulfate crystals at the front end.

[0103] Table 1

[0104]

[0105] Table 2

[0106]

[0107] As shown in Tables 1 and 2, the aluminum hydroxide and ferric sulfate products obtained in Examples 1-3 all meet the standards and can be sold externally. Using the method disclosed herein, the iron and aluminum elements in iron-aluminum slag are effectively separated and recovered.

[0108] Example 4

[0109] The difference between this embodiment and Example 1 is that the concentration of sodium hydroxide solution in the alkali conversion process is adjusted to 18 g / L, while the rest of the preparation methods and parameters are exactly the same as in Example 1; this results in only 30% recovery of sodium sulfate, and fluorine and phosphorus impurities remain in the iron-aluminum slag after alkali conversion.

[0110] Example 5

[0111] The difference between this embodiment and Embodiment 3 is that the concentration of sodium hydroxide solution in the alkali conversion process is adjusted to 42 g / L, while the rest of the preparation methods and parameters are exactly the same as in Embodiment 3; this results in the sodium sulfate solution containing 0.1 g / L of aluminum, causing a loss of aluminum in the iron-aluminum slag.

[0112] Example 6

[0113] The difference between this embodiment and Example 1 is that in the alkaline leaching process, the amount of sodium hydroxide used is 1.2 times the theoretical amount required for all aluminum to be converted into sodium aluminate, while the rest of the preparation methods and parameters are exactly the same as in Example 1; resulting in an aluminum leaching rate of only 35%.

[0114] Example 7

[0115] The difference between this embodiment and Example 3 is that in the alkaline leaching process, the amount of sodium hydroxide used is 2.7 times the theoretical amount required for all aluminum elements to be converted into sodium aluminate. The rest of the preparation methods and parameters are exactly the same as in Example 3; the aluminum leaching rate is not much different from that in Example 3.

[0116] Comparative Example 1

[0117] This comparative example provides a method for the resource-based recovery of aluminum and iron from iron-aluminum slag. The iron-aluminum slag is the same as that in Example 1. The method includes the following specific steps:

[0118] (1) Use 80℃ hot water to wash the iron-aluminum slag. Only 8% of sodium sulfate is washed out, resulting in washed iron-aluminum slag.

[0119] (2) Alkali leaching process: Add the theoretical amount of sodium hydroxide solution to the aluminum slag after water washing. At this time, both aluminum alum and iron alum react with sodium hydroxide to obtain sodium aluminate solution and nickel-iron slag. The leaching rate of aluminum is only 25%.

[0120] (3) Seeding: Add the theoretical amount of aluminum hydroxide seed crystals to the sodium aluminate solution, but the aluminum content of the sodium aluminate solution obtained in step (2) is too low, resulting in a low aluminum hydroxide yield;

[0121] (4) Adding 1 mol / L sulfuric acid to the nickel-iron slag resulted in an iron acid solubility of only 50%, yielding 1 g of waste slag and an acid-dissolved solution. Adding an equal volume of 50% sulfuric acid to the acid-dissolved solution resulted in a precipitation rate of only 67% for iron recovery.

[0122] analyze:

[0123] As can be seen from the results of Examples 1-3, the method disclosed herein can effectively separate and recover iron and aluminum elements from iron-aluminum slag, with high aluminum leaching rate and iron recovery rate. Both aluminum hydroxide and ferric sulfate products meet the standards, and sodium sulfate products can also be recovered.

[0124] As can be seen from the results of Examples 1, 3 and Examples 4-5, if the concentration of sodium hydroxide solution in the alkali conversion process is too low, the sodium sulfate conversion rate will be too low; if the concentration of sodium hydroxide solution in the alkali conversion process is too high, aluminum elements will remain in the sodium sulfate solution, resulting in a loss of aluminum recovery.

[0125] The results from Examples 1, 3 and Examples 6-7 show that if the amount of sodium hydroxide used in the alkaline leaching process is too small, the aluminum leaching rate will be low; if the amount of sodium hydroxide used in the alkaline leaching process is too large, the aluminum leaching rate will not be improved significantly, and there will be too much alkali in the solution.

[0126] As can be seen from the results of Example 1 and Comparative Example 1, compared with the aluminum leaching rate and iron recovery rate of Example 1, the method of Comparative Example 1 cannot effectively separate and recover aluminum and iron, the recovery rates of the two are low, and sodium sulfate product is not recovered.

Claims

1. A method for resource recovery of aluminum and iron from iron-aluminum slag, the method comprising: (1) Mix the iron-aluminum slag with the first alkaline solution to carry out the alkaline conversion reaction. After solid-liquid separation, a sulfate solution and the alkaline-converted iron-aluminum slag are obtained. The alkaline substance in the first alkaline solution includes at least one of sodium hydroxide, calcium hydroxide, and sodium carbonate; The concentration of the first alkaline solution is 20~40 g / L; The alkali-converted iron-aluminum slag contains 15-25% aluminum, 20-30% iron, and 0.5-1.0% nickel by mass. (2) The iron-aluminum slag after alkali conversion and the second alkali solution are mixed and subjected to alkali leaching reaction. After solid-liquid separation, an aluminate solution and iron slag are obtained. (3) The iron slag is acid-dissolved, and then sulfuric acid is added to precipitate ferric sulfate. After solid-liquid separation, ferric sulfate crystals and acid solution are obtained. The sulfuric acid has a mass concentration of 60-98%.

2. The method according to claim 1, wherein, The temperature of the alkali conversion reaction in step (1) is 60~80℃, and the time of the alkali conversion reaction is 2~4h.

3. The method according to claim 1, wherein, The sulfate solution described in step (1) is subjected to freeze crystallization to precipitate sulfate.

4. The method according to claim 1, wherein, Step (2) The alkaline substance in the second alkaline solution includes at least one of sodium hydroxide, calcium hydroxide and sodium carbonate.

5. The method according to claim 1, wherein, In step (2), the amount of alkaline substance in the second alkaline solution is 1.5 to 2.5 times the theoretical amount required for all aluminum elements to be converted into aluminates.

6. The method according to claim 1, wherein, The alkaline leaching reaction in step (2) is carried out at a temperature of 60-80°C for 2-4 hours.

7. The method according to claim 1, wherein, The caustic ratio α of the aluminate solution in step (2) k It is 1.55~1.

6.

8. The method according to claim 1, wherein, The aluminate solution described in step (2) was treated using the Bayer process to obtain aluminum hydroxide.

9. The method according to claim 8, wherein, The Bayer process includes the following steps: The aluminate solution and seed crystals described in step (2) are mixed and then separated to obtain aluminum hydroxide and aluminate mother liquor.

10. The method according to claim 9, wherein, The seed crystals include aluminum hydroxide.

11. The method according to claim 9, wherein, The amount of seed crystals added is 0.5 to 1.5 times the theoretical amount required for all aluminum in the aluminate solution to be converted into aluminum hydroxide.

12. The method according to claim 9, wherein, The temperature of the seeding is 50~60℃, and the seeding time is 1~10h.

13. The method according to claim 9, wherein, The seeding process is accompanied by stirring, and the stirring speed is 150~300 r / min.

14. The method according to any one of claims 1-13, wherein, The acid used in step (3) during the acid dissolution process includes sulfuric acid, and the concentration of the acid is 2~4 mol / L.

15. The method according to claim 1, wherein, The method specifically includes the following steps: (I) Mix the iron-aluminum slag with a first alkaline solution with a concentration of 20~40g / L, and carry out the alkaline conversion reaction at 60~80℃ for 2~4h. After solid-liquid separation, a sulfate solution and the alkaline-converted iron-aluminum slag are obtained. The sulfate solution is then subjected to freeze crystallization at 2~5℃ to precipitate sulfate. The alkali-converted iron-aluminum slag contains 15-25% aluminum, 20-30% iron, and 0.5-1.0% nickel by mass. (II) The iron-aluminum slag after alkali conversion and the second alkali solution are mixed and subjected to alkali leaching reaction. After solid-liquid separation, a caustic ratio α is obtained. k The mixture consists of an aluminate solution of 1.55~1.6 and iron slag. The aluminate solution is mixed with seed crystals, and after seed separation, aluminum hydroxide and aluminate mother liquor are obtained. The amount of alkaline substance in the second alkaline solution is 1.5 to 2.5 times the theoretical amount required for all aluminum to be converted into aluminate. The alkaline leaching reaction temperature is 60 to 80°C and the time is 2 to 4 hours. The amount of seed crystals added is 0.5 to 1.5 times the theoretical amount required for all aluminum in the aluminate solution to be converted into aluminum hydroxide. The seeding temperature is 50 to 60°C and the time is 1 to 10 hours. (III) The iron slag is acid-dissolved with sulfuric acid at a concentration of 2-4 mol / L, and then sulfuric acid at a mass concentration of 60-98% is added to precipitate ferric sulfate. After solid-liquid separation, ferric sulfate crystals and acid solution are obtained.

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