WO2025076819A1 - Method for recycling aluminum and iron from iron-aluminum slag - Google Patents

Abstract

A method for recycling aluminum and iron from iron-aluminum slag. The method comprises: (1) mixing iron-aluminum slag with a first alkaline liquor to carry out an alkaline conversion reaction, and performing solid-liquid separation, so as to obtain a sulfate solution and alkaline-converted iron-aluminum slag; (2) mixing the alkaline-converted iron-aluminum slag with a second alkaline liquor to carry out an alkaline leaching reaction, and performing solid-liquid separation, so as to obtain an aluminate solution and iron slag; and (3) subjecting the iron slag to acid dissolution, then adding sulfuric acid to precipitate ferric sulfate, and performing solid-liquid separation, so as to obtain ferric sulfate crystals and an acid solution. By means of the method, iron and aluminum in iron-aluminum slag can be effectively separated and recycled.

Description

A method for recycling aluminum and iron from iron-aluminum slag Technical Field

The present invention belongs to the technical field of waste battery recycling and relates to a method for recycling aluminum and iron from iron-aluminum slag.

Background Art

In recent years, batteries have developed rapidly and are widely used in digital electronics, smart grids, electric vehicles, large-scale energy storage materials and other fields. However, the battery cycle life is always limited, which means that the amount of waste batteries generated is also increasing year by year, and the recycling of waste batteries has become an indispensable industrial chain.

In the current wet recycling process of ternary batteries, the main materials produced are graphite slag, iron-aluminum slag and sponge copper. Among them, sponge copper can be sold as a product at a low price; the main component of graphite slag is the negative electrode powder graphite in the battery powder; the iron-aluminum slag has the largest slag volume, and its main components are iron and aluminum, and it also carries a certain amount of valuable heavy metals such as nickel, cobalt and manganese. It is very difficult to recycle or harmlessly dispose of it. The industry currently treats iron-aluminum slag as solid waste or hazardous waste.

Iron and aluminum are metal elements with high content in nature and have high utilization value. The iron-aluminum slag produced by the wet process of recycling waste batteries contains a large amount of iron and aluminum. It is very meaningful to be able to separate and recycle this part of iron and aluminum.

Summary of the invention

The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

In view of the shortcomings of the prior art, the present invention aims to provide a method for recycling aluminum and iron from iron-aluminum slag. The present invention first separates sulfate from the iron-aluminum slag by alkali conversion reaction; then separates aluminum from the iron-aluminum slag after alkali conversion by alkali leaching reaction to obtain an aluminate solution, and then obtains hydroxide. The aluminum product is obtained by smelting the aluminum slag, while the iron element remains in the iron slag, thereby achieving the separation of the iron and aluminum elements; then, the iron sulfate product is obtained by using the solubility principle of iron sulfate. Therefore, the method disclosed in the present invention can effectively separate and recover the iron and aluminum elements in the iron and aluminum slag.

To achieve this purpose, the present invention adopts the following technical solutions:

In a first aspect, the present disclosure provides a method for recycling aluminum and iron from iron-aluminum slag, the method comprising:

(1) mixing the iron-aluminum slag with the first alkali solution to perform an alkali conversion reaction, and after solid-liquid separation, obtaining a sulfate solution and the iron-aluminum slag after the alkali conversion;

(2) mixing the alkali-converted iron-aluminum slag with a second alkali solution to perform an alkali leaching reaction, and after solid-liquid separation, obtaining an aluminate solution and iron slag;

(3) dissolving the iron slag with acid, then adding sulfuric acid to precipitate ferric sulfate, and obtaining ferric sulfate crystals and an acid solution after solid-liquid separation.

The present invention provides a method for recycling aluminum and iron from iron-aluminum slag. First, sulfate radicals in the iron-aluminum slag are separated by an alkali conversion reaction to obtain a sulfate solution, and then a sulfate product is obtained; then, aluminum elements are separated from the iron-aluminum slag after the alkali conversion by an alkali leaching reaction to obtain an aluminate solution, and then an aluminum hydroxide product is obtained, while the iron element remains in the iron slag, thereby achieving separation of the iron and aluminum elements; then, the iron slag is first acid-dissolved and sulfuric acid is added according to the solubility principle of iron sulfate to obtain an iron sulfate product, and the acid solution can be recycled;

In summary, the method disclosed in the present invention can effectively separate and recover the iron and aluminum elements in the iron-aluminum slag, and can obtain sulfate products, aluminum hydroxide products and ferric sulfate products. The products can be sold to generate profits, and the utilization of the iron-aluminum slag can be maximized, which is beneficial to industrial applications.

In one embodiment, the iron-aluminum slag includes the iron-aluminum slag produced by wet recovery of ternary batteries. The iron-aluminum slag includes aluminum ions, iron ions, nickel ions, cobalt ions, manganese ions, sulfate ions, Organic matter (COD) and impurities (such as phosphorus and/or fluorine). Among them, nickel ions, cobalt ions and manganese ions are precipitated into the iron-aluminum slag after alkali conversion through alkali conversion reaction, and then enter the iron slag through alkali leaching reaction, and then dissolved in acid through acid dissolution, and finally remain in the acid solution. The acid solution can be reused in the acid dissolution step or returned to the battery recycling production line to recover nickel, cobalt and manganese.

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

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

The main chemical components of the iron aluminum slag are iron alum (NaFe ₃ (SO ₄ ) ₂ (OH) ₆ ) and aluminum alum (NaAl ₃ (SO ₄ ) ₂ (OH) ₆ ). For example, the reaction equation of the iron aluminum slag and sodium hydroxide is as follows:

NaAl ₃ (SO ₄ ) ₂ (OH) ₆ (s) + 6NaOH (aq) = 2Na ₂ SO ₄ (aq) + 3NaAl (OH) ₄ (aq);

NaFe ₃ (SO ₄ ) ₂ (OH) ₆ (s) + 3NaOH (aq) = 2Na ₂ SO ₄ (aq) + 3Fe (OH) ₃ (s);

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 transferred out, thereby obtaining sodium sulfate; the converted aluminum sulfate or aluminum hydroxide is entrained in the iron-aluminum slag after alkali conversion.

In one embodiment, the concentration of the first alkali solution in step (1) is 20-40 g/L, for example, 20 g/L, 25 g/L, 30 g/L, 35 g/L or 40 g/L, etc. However, it is not limited to the listed values, and other values not listed within the numerical range are also applicable.

In the present disclosure, if the concentration of the first alkali solution is too low, the sodium sulfate conversion rate is too low; if the concentration of the first alkali solution is too high, part of the aluminum element will enter the sulfate solution, resulting in aluminum element loss.

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

In one embodiment, the temperature of the alkaline conversion reaction in step (1) is 60 to 80° C., for example, 60° C., 65° C., 70° C., 75° C. or 80° C., and the time of the alkaline conversion reaction is 2 to 4 hours, for example, It is 2h, 2.5h, 3h, 3.5h or 4h, etc. However, it is not limited to the listed values, and other values not listed in the numerical range are also applicable.

In the present disclosure, the alkali conversion reaction is carried out at a temperature of 60 to 80° C. for 2 to 4 hours to improve the sodium sulfate conversion rate.

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

In one embodiment, in the alkali-converted iron-aluminum slag of step (1), the mass content of aluminum element is 15-25% (for example, it can be 15%, 18%, 20% or 22%, etc.), the mass content of iron element is 20-30% (for example, it can be 20%, 22%, 25% or 28%, etc.), and the mass content of nickel element is 0.5-1.0% (for example, it can be 0.5%, 0.7%, 0.8% or 0.9%, etc.).

As an optional technical solution of the present disclosure, the sulfate solution in step (1) is subjected to freezing crystallization to precipitate sulfate, which can be sold externally.

In the present disclosure, the sulfate is precipitated by freezing crystallization, so that the sulfate is free of other impurities. The recovery rate of the sulfate is 50-90%. The solution after the sulfate is precipitated is alkaline, and the solution can be returned to the large water treatment system to adjust the wastewater.

In one embodiment, the freezing crystallization temperature is 2-5°C, for example, 2°C, 2.5°C, 3°C, 3.5°C, 4°C, 4.5°C or 5°C, etc. However, it is not limited to the listed values, and other values not listed in the numerical range are also applicable.

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

In the present disclosure, at least one of sodium hydroxide, calcium hydroxide and sodium carbonate is used as the alkaline substance in the second alkali solution, which can be subjected to alkali leaching reaction with the alkali-converted iron-aluminum slag to obtain an aluminate solution, i.e., aluminum Sodium acid solution.

In one embodiment, the amount of the alkaline substance in the second alkaline solution in step (2) is 1.5 to 2.5 times the theoretical amount required for all aluminum elements 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 values not listed within the numerical range are also applicable.

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.

In the present disclosure, if the amount of alkaline substance in the second alkali solution is too little, the leaching rate of aluminum is not high; if the amount of alkaline substance in the second alkali solution is too much, the leaching effect will not be improved, resulting in a waste of reagents.

As an optional technical solution of the present invention, in step (2), the liquid-to-solid mass ratio of the second alkali solution to the alkali-converted iron-aluminum slag is 5:1.

In one embodiment, the temperature of the alkali 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 alkali leaching reaction is 2-4h, for example, 2h, 2.5h, 3h, 3.5h or 4h, etc. However, it is not limited to the listed values, and other values not listed within the numerical range are also applicable.

In the present disclosure, the alkali leaching reaction is carried out at a temperature of 60 to 80° C. for 2 to 4 hours to effectively leach aluminum.

As an optional technical solution of the present disclosure, the caustic ratio _αk of the aluminate solution in step (2) is 1.55 to 1.6, for example, 1.55, 1.56, 1.57, 1.58, 1.59 or 1.6, etc. However, it is not limited to the listed values, and other values not listed within the numerical range are also applicable.

In the present disclosure, the caustic ratio α _k of the aluminate solution is 1.55 to 1.6, which is conducive to the subsequent Bayer process treatment of the aluminate solution. The aluminate solution with this caustic ratio range is suitable for seed separation.

In one embodiment, the mass concentration of aluminum element in the aluminate solution is 10-25 g/L, for example, 10 g/L, 12 g/L, 15 g/L, 18 g/L, 20 g/L or 22 g/L.

In one embodiment, the iron slag has an aluminum content of 0.5 to 7.0% by mass (for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6% or 6.5%, etc.), an iron content of 25 to 45% by mass (for example, 25%, 30%, 35% or 40%, etc.), and a nickel content of 1.0 to 1.5% by mass (for example, 1.0%, 1.1%, 1.2%, 1.3% or 1.4%, etc.).

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

The Bayer process is a chemical process for producing aluminum oxide from bauxite. In the present disclosure, the Bayer process is used to prepare aluminum hydroxide, which has low energy consumption, low cost, high product purity, and the separated solution can be recycled without wasting alkali, which greatly reduces costs.

As an optional technical solution of the present disclosure, the Bayer process includes the following steps:

The aluminate solution in step (2) is mixed with seed crystals, and aluminum hydroxide and aluminate mother liquor are obtained after seed separation.

In the present disclosure, the obtained aluminum hydroxide product complies with the product standard GB/T4294-2010 and can be sold externally.

In one embodiment, the seed crystals include aluminum hydroxide.

In one embodiment, the amount of the seed crystal added is 0.5 to 1.5 times the theoretical amount required for all aluminum elements in the aluminate solution to be converted into aluminum hydroxide, for example, it can be 0.5 times, 0.7 times, 1 times, 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 values not listed within the numerical range are also applicable.

In the present disclosure, if the amount of seed crystals added is too little, the decomposition rate of aluminum hydroxide is low; if the amount of seed crystals added is too much, the decomposition rate increases only slightly, resulting in waste.

In one embodiment, the seeding temperature is 50-60°C, for example, 50°C, 52°C, 54°C, 56°C, 58°C or 60°C, and the seeding time is 1-10h, for example, 1h, 2h, 4h, 6h, 8h or 10h. However, it is not limited to the listed values, and other values not listed within the numerical range may be used. The same applies to values.

In the present disclosure, the aluminum hydroxide can be effectively seeded by performing seeding at a temperature of 50 to 60° C. for 1 to 10 hours.

In one embodiment, the seeding process is accompanied by stirring, and the stirring speed is 150-300 r/min, for example, 150 r/min, 200 r/min, 250 r/min or 300 r/min, etc. However, it is not limited to the listed values, and other values not listed in the numerical range are also applicable.

In the present disclosure, during the seeding process, the stirring is continued at a rate of 150 to 300 r/min, so that the seed crystals can be fully dispersed in the solution and fully contact the solution.

In one embodiment, the mass concentration of aluminum in the aluminate mother solution is 9 to 12 g/L, for example, 9 g/L, 10 g/L, 11 g/L or 12 g/L.

In one embodiment, the aluminate mother liquor is mixed with the ferroaluminum slag after alkali conversion to carry out alkali leaching reaction, and an aluminate solution and iron slag are obtained after solid-liquid separation. The aluminate solution is further subjected to seed separation using the Bayer process to obtain aluminum hydroxide and new aluminate mother liquor.

In the present disclosure, the aluminate mother liquor is mixed with the alkali-converted iron-aluminum slag, and no alkali is added, so that the alkali in the solution is recycled and the alkali cost is reduced. The aluminate mother liquor can be recycled for many times. When the sulfate (such as sodium sulfate) and impurities (such as COD and a small amount of phosphorus and fluorine) in the aluminate mother liquor are highly enriched, the impurities are removed and then evaporated and crystallized to obtain sulfate.

In one embodiment, after the aluminate mother liquor is mixed with the alkali-converted iron-aluminum slag for alkali leaching reaction, the caustic ratio α _k of the obtained aluminate solution is 1.55 to 1.65, for example, 1.55, 1.57, 1.58, 1.6 or 1.65.

As an optional technical solution of the present disclosure, the acid used in the acid dissolution process of step (3) includes sulfuric acid, and the concentration of the acid is 2 to 4 mol/L, for example, 2 mol/L, 2.5 mol/L, 3 mol/L, 3.5 mol/L or 4 mol/L. However, it is not limited to the values listed, and other values not listed within the range of the values may be The same applies to the values of .

In the present disclosure, when sulfuric acid with a concentration of 2 to 4 mol/L is used for acid dissolution, the acid dissolution rate of iron is 80 to 98.6% (for example, it can be 80%, 85%, 90% or 95%, etc.). If the acid concentration used in the acid dissolution process is too low, the iron sulfate will be in a solution state, and the iron sulfate will not precipitate after adding sulfuric acid; if the acid concentration used in the acid dissolution process is too high, there will be too much sulfuric acid remaining after the iron sulfate is precipitated.

In one embodiment, the mass concentration of sulfuric acid in step (3) is 60-98%, for example, 60%, 70%, 80%, 98% or 90%, etc. However, it is not limited to the listed values, and other values not listed within the numerical range are also applicable.

In the present disclosure, the solute in the solution obtained by acid dissolution is mainly ferrous sulfate. Using the principle of ferrous sulfate solubility, high mass concentration sulfuric acid is added to obtain a saturated solution, and then cooled and crystallized to precipitate ferrous sulfate crystals to achieve resource utilization of iron. When the mass concentration of sulfuric acid in step (3) is 60-98%, the recovery rate of ferrous sulfate 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 ferrous sulfate reaches the solubility and the ferrous sulfate does not precipitate.

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

As an optional technical solution of the present disclosure, the method specifically comprises the following steps:

(I) mixing the iron-aluminum slag with a first alkaline solution having a concentration of 20 to 40 g/L, and performing an alkaline conversion reaction at 60 to 80° C. for 2 to 4 hours, and obtaining a sulfate solution and an alkaline-converted iron-aluminum slag after solid-liquid separation, and freezing and crystallizing the sulfate solution at 2 to 5° C. to precipitate sulfate;

(II) mixing the alkali-converted iron-aluminum slag with a second alkali solution for alkali leaching reaction, and obtaining an aluminate solution and iron slag with a caustic ratio _αk of 1.55 to 1.6 after solid-liquid separation, and mixing the aluminate solution with seed crystals to obtain aluminum hydroxide and aluminate mother liquor after seed separation;

The amount of alkaline substance in the second alkali solution is the theoretical amount required for all aluminum elements to be converted into aluminate. The amount of the seed crystal is 1.5 to 2.5 times of the theoretical amount required for all aluminum elements in the aluminate solution to be converted into aluminum hydroxide, the temperature of the seed crystal is 50 to 60°C, and the time is 1 to 10 hours;

(III) using sulfuric acid with a concentration of 2 to 4 mol/L to acid-dissolve the iron slag, then adding sulfuric acid with a mass concentration of 60 to 98% to precipitate ferric sulfate, and after solid-liquid separation, obtaining ferric sulfate crystals and an acid solution.

The numerical range described in the present 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, the present disclosure no longer exhaustively lists the specific point values included in the range.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention provides a method for recycling aluminum and iron from iron-aluminum slag. First, sulfate radicals in the iron-aluminum slag are separated by an alkali conversion reaction to obtain a sulfate solution, and then a sulfate product is obtained; then, aluminum elements are separated from the iron-aluminum slag after the alkali conversion by an alkali leaching reaction to obtain an aluminate solution, and then an aluminum hydroxide product is obtained, while the iron element remains in the iron slag, thereby achieving separation of the iron and aluminum elements; then, the iron slag is first acid-dissolved and sulfuric acid is added according to the solubility principle of iron sulfate to obtain an iron sulfate product, and the acid solution can be recycled;

In summary, the method disclosed in the present invention can effectively separate and recover the iron and aluminum elements in the iron and aluminum slag, and obtain sulfate products, aluminum hydroxide products and iron sulfate products, which can be sold to obtain income, and can maximize the utilization of the iron and aluminum slag, which is beneficial to industrial application. In addition, the method is simple, low in cost, no waste is generated, and the wastewater output is extremely small.

Other aspects will be apparent upon reading and understanding the drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are used to provide a further understanding of the technical solution of this invention and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this invention and do not constitute a limitation of the technical solution of this invention. limit.

FIG1 is a schematic diagram of a process for recycling aluminum and iron from iron-aluminum slag provided in one embodiment of the present disclosure.

DETAILED DESCRIPTION

The technical solution of the present disclosure is further illustrated below through specific implementation methods.

In one embodiment, the present disclosure provides a method for recycling aluminum and iron from iron-aluminum slag, the process of which is shown in FIG1 , and the method comprises the following steps:

(1) adding a NaOH solution to the iron-aluminum slag for alkali conversion to obtain a sodium sulfate solution and the iron-aluminum slag after alkali conversion, and freezing and crystallizing the sodium sulfate solution to obtain sodium sulfate;

(2) alkali leaching the ferroaluminum slag after alkali conversion in step (1) to obtain ferronickel slag and sodium aluminate solution;

(3) treating the sodium aluminate solution in step (2) by the Bayer process to obtain Al(OH) ₃ and sodium aluminate mother liquor; adding alkali-converted iron-aluminum slag to the sodium aluminate mother liquor for alkali leaching reaction to obtain a sodium aluminate solution, and continuing to treat the sodium aluminate solution by the Bayer process, and repeating the cycle in this manner; when the sodium aluminate mother liquor becomes a solution containing a large amount of impurity sodium sulfate, the solution is decontaminated, and then evaporated and crystallized to obtain sodium sulfate;

(4) Acid dissolving the nickel-iron slag in step (2) and adding sulfuric acid to obtain ferric sulfate crystals. After solid-liquid separation, ferric sulfate and mother liquor are obtained. The mother liquor can be recycled to prepare ferric sulfate crystals and can also be used to recover nickel, cobalt and manganese in battery lines.

Example 1

This embodiment provides a method for recycling aluminum and iron from iron-aluminum slag, wherein the mass contents of the components in the iron-aluminum slag are: 0.5% nickel, 56% sulfate, 10.5% aluminum and 14.5% iron, and the rest are trace impurities (F and P) and COD. The method comprises the following specific steps:

(1) Alkali conversion process: 100 g of the above iron-aluminum slag is placed in a beaker, and 20 g/L of sodium hydroxide solution is added. The iron-aluminum slag is stirred into a slurry at a fixed liquid-to-solid (mass) ratio of 8:1. The temperature is 60°C and the reaction is carried out for 4 h. After the reaction is completed, the mixture is filtered while hot to obtain about 70 g of the iron-aluminum slag after alkali conversion and a sodium sulfate solution. The nickel content is 0.71%, the iron content is 20.71%, and the aluminum content is 15%. The sodium sulfate solution is frozen and crystallized in a freezing reactor at 5°C. 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%.

(2) Alkali leaching process: the alkali-converted iron-aluminum slag of the above step (1) is subjected to alkali leaching, and a sodium hydroxide solution is prepared, wherein 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-to-solid (mass) ratio is 5:1, and the leaching temperature is 60° C. and stirred for reaction for 2 hours; after the reaction is completed, it is filtered while hot to obtain 50 g of nickel-iron slag and sodium aluminate solution, wherein the nickel content of the nickel-iron slag is 1.0%, the iron content is 29%, and the aluminum content is 6.3%; the aluminum content of the sodium aluminate solution is 14.7 g/L, the α _k is 1.55, and the aluminum leaching rate is 70%;

(3) Seeding process: adding seed aluminum hydroxide to the sodium aluminate solution obtained in the alkali leaching process in an amount of 0.5 times the theoretical amount of aluminum, stirring at a speed of 150 r/min, reacting at 60° C. for 6 h, filtering after the reaction to obtain a sodium aluminate mother liquor with an aluminum content of 9.85 g/L and aluminum hydroxide; the aluminum decomposition rate is 33%, and the aluminum hydroxide meets the product standard GB/T4294-2010. The specific data are shown in Table 1;

(4) adding the ferroaluminum slag after alkali conversion from the alkali conversion process to the sodium aluminate mother liquor obtained in step (3) to reduce α _k to 1.55-1.65, without adding sodium hydroxide, and repeating the alkali leaching and seed separation process; the alkali leaching to seed separation is one cycle, and when the sodium aluminate mother liquor is enriched with more sodium sulfate, COD and a small amount of phosphorus and fluorine, it is discharged to a large water treatment system for impurity removal and extraction of sodium sulfate crystals;

(5) adding 2 mol/L sulfuric acid to the nickel-iron slag obtained in step (2), at a temperature of 60° C., a reaction time of 4 h, and a liquid-to-solid (mass) ratio of 5:1; filtering after the reaction, the iron acid solubility is 80%, and 8 g of waste residue and an acid-dissolved solution are obtained; the acid-dissolved solution contains 46.4 g/L iron and 1.4 g/L nickel; continuing to add an equal volume of 60% sulfuric acid to the acid-dissolved solution, cooling to precipitate iron sulfate crystals, centrifuging to separate the solid and the liquid, the iron recovery rate is 90%, and the solid is the product iron sulfate, which meets the product standard of HG/T4816-2015, and the data are shown in Table 2; wherein the sulfuric acid solution is recycled to the front end acid dissolve or precipitate iron sulfate crystals.

Example 2

This embodiment provides a method for recycling aluminum and iron from iron-aluminum slag, wherein the mass contents of the components in the iron-aluminum slag are: 0.5% nickel, 56% sulfate, 10.5% aluminum and 14.5% iron, and the rest are trace impurities (F and P) and COD. The method comprises the following specific steps:

(1) Alkali conversion process: 100 g of the above-mentioned iron-aluminum slag is placed in a beaker, and 30 g/L of sodium hydroxide solution is prepared. The iron-aluminum slag is stirred into a slurry at a liquid-to-solid ratio of 8:1, and the temperature is 70° C. for 3 h. After the reaction is completed, it is filtered while hot to obtain about 60 g of iron-aluminum slag after alkali conversion and sodium sulfate solution, wherein the iron-aluminum slag after alkali conversion 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 frozen and crystallized in a frozen reactor at 5° C. After the crystallization is completed, it is quickly centrifuged and dried to obtain an alkali solution and sodium sulfate crystals, and the sodium sulfate recovery rate is 71.43%;

(2) Alkali leaching process: the ferronickel-aluminum slag after alkali conversion in the above step (1) is subjected to alkali leaching, and a sodium hydroxide solution is prepared, wherein 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°C, and the stirring reaction is carried out for 2 hours; after the reaction is completed, it is filtered while hot to obtain 40g of nickel-iron slag and sodium aluminate solution, wherein the nickel content of the nickel-iron slag is 1.25%, the iron content is 36.25%, and the aluminum content is 1.8%; the aluminum content of the sodium aluminate solution is 19.55g/L, the α _k is 1.60, and the aluminum leaching rate is 93.1%;

(3) Seeding process: adding seed aluminum hydroxide to the sodium aluminate solution obtained in the alkali leaching process in an amount equal to 1 times the theoretical amount of aluminum, stirring at a speed of 200 r/min, and reacting at a temperature of 55° C. for 7 h. After the reaction is completed, filtering is performed to obtain a sodium aluminate mother liquor with an aluminum content of 11.53 g/L and aluminum hydroxide; the aluminum decomposition rate is 41%, and the aluminum hydroxide meets the product standard of GB/T4294-2010. The specific data are shown in Table 1;

(4) adding the ferroaluminum slag after alkali conversion from the alkali conversion process to the sodium aluminate mother liquor obtained in step (3) to reduce α _k to 1.55-1.65 without adding sodium hydroxide, and repeating the alkali leaching and seed separation process;

(5) adding 3 mol/L sulfuric acid to the nickel-iron slag obtained in step (2), at a temperature of 60° C., a reaction time of 4 h, and a liquid-to-solid ratio of 5:1; filtering after the reaction is completed, the iron acid solubility is 90%, and 3 g of waste residue and an acid solution are obtained; the acid solution contains 65.25 g/L iron and 2.81 g/L nickel; continuing to add an equal volume of 80% sulfuric acid to the acid solution, precipitating ferric sulfate crystals after cooling, and centrifuging the solid and liquid to obtain an iron recovery rate of 92%, and the solid is the product sulfuric acid Iron, in line with the product standard of HG/T4816-2015, the data are shown in Table 2; the sulfuric acid solution is recycled to dissolve or precipitate iron sulfate crystals at the front end.

Example 3

This embodiment provides a method for recycling aluminum and iron from iron-aluminum slag, wherein the mass contents of the components in the iron-aluminum slag are: 0.5% nickel, 56% sulfate, 10.5% aluminum and 14.5% iron, and the rest are trace impurities (F and P) and COD. The method comprises the following specific steps:

(1) Alkali conversion process: 100 g of the above-mentioned iron-aluminum slag is placed in a beaker, and 40 g/L of sodium hydroxide solution is prepared. The iron-aluminum slag is stirred into a slurry at a liquid-to-solid ratio of 8:1, and the temperature is 80° C. for 2 h. After the reaction is completed, it is filtered while hot to obtain about 50 g of iron-aluminum slag after alkali conversion and sodium sulfate solution, wherein the iron-aluminum slag after alkali conversion has a nickel content of 1.0%, an iron content of 29%, and an aluminum content of 21%. The sodium sulfate solution is frozen and crystallized in a frozen reactor at 5° C. After the crystallization is completed, it is quickly centrifuged and dried to obtain an alkali solution and sodium sulfate crystals, and the sodium sulfate recovery rate is 89.29%;

(2) Alkali leaching process: the alkali-converted ferroaluminum slag of the above step (1) is subjected to alkali leaching, and a sodium hydroxide solution is prepared, wherein the amount of sodium hydroxide used is 2.5 times 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 80°C, and the stirring reaction is carried out for 2 hours; after the reaction is completed, it is filtered while hot to obtain 35g of nickel-iron slag and sodium aluminate solution, wherein the nickel content of the nickel-iron slag is 1.43%, the iron content is 41.43%, and the aluminum content is 0.7%; the aluminum content of the sodium aluminate solution is 20.52g/L, the α _k is 1.65, and the aluminum leaching rate is 97.7%;

(3) Seeding process: adding seed aluminum hydroxide to the sodium aluminate solution obtained in the alkali leaching process in an amount of 1.5 times the theoretical amount of aluminum, stirring at a speed of 250 r/min, and reacting at a temperature of 50° C. for 8 h. After the reaction is completed, filtering is performed to obtain a sodium aluminate mother liquor with an aluminum content of 11.13 g/L and aluminum hydroxide; the aluminum decomposition rate is 47%, and the aluminum hydroxide meets the product standard GB/T4294-2010. The specific data are shown in Table 1;

(4) adding the ferroaluminum slag after alkali conversion from the alkali conversion process to the sodium aluminate mother liquor obtained in step (3) to reduce α _k to 1.55-1.65 without adding sodium hydroxide, and repeating the alkali leaching and seed separation process;

(5) Add 4 mol/L sulfuric acid to the nickel-iron slag obtained in step (2), the temperature is 60° C., and the reaction time is 4h, liquid-solid ratio 5:1; after the reaction was completed, it was filtered, the iron acid solubility was 98.6%, and 1g of waste residue and acid solution were obtained; the acid solution contained 81.65g/L iron and 2.82g/L nickel; an equal volume of 98% sulfuric acid was continued to be added to the acid solution, and iron sulfate crystals were precipitated after cooling. The solid and liquid were separated by centrifugation, and the iron recovery rate was 99.5%. The solid was the product iron sulfate, which met the product standard of HG/T4816-2015, and the data are shown in Table 2; the sulfuric acid solution was recycled to dissolve in the front end acid or precipitate iron sulfate crystals.

Table 1

Table 2

From the data in Table 1 and Table 2, it can be seen that the aluminum hydroxide products and ferric sulfate products obtained in Examples 1-3 meet the standards and can be sold. The method disclosed in the present invention can effectively separate and recover the aluminum hydroxide products and ferric sulfate products in the aluminum slag. of iron and aluminum elements.

Example 4

The difference between this embodiment and embodiment 1 is that in the alkali conversion process, the concentration of the sodium hydroxide solution is adjusted to 18 g/L, and the remaining preparation methods and parameters are exactly the same as those in embodiment 1; so that only 30% of the sodium sulfate is recovered, and the fluorine and phosphorus impurities are left in the iron-aluminum slag after the alkali conversion.

Example 5

The difference between this embodiment and embodiment 3 is that in the alkali conversion process, the concentration of the sodium hydroxide solution is adjusted to 42 g/L, and the remaining preparation methods and parameters are exactly the same as those in embodiment 3; so that the sodium sulfate solution contains 0.1 g/L of aluminum element, causing loss of aluminum element in the iron-aluminum slag.

Example 6

The difference between this embodiment and embodiment 1 is that in the alkali leaching process, the amount of sodium hydroxide used is 1.2 times the theoretical amount required to convert all aluminum elements into sodium aluminate, and the remaining preparation methods and parameters are exactly the same as those in embodiment 1; so that the leaching rate of aluminum is only 35%.

Example 7

The difference between this embodiment and embodiment 3 is that in the alkali 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, and the remaining preparation methods and parameters are exactly the same as those in embodiment 3; its aluminum leaching rate is not much different from that in embodiment 3.

Comparative Example 1

This comparative example provides a method for recycling aluminum and iron from iron-aluminum slag, wherein the iron-aluminum slag is the same as that in Example 1, and the method comprises the following specific steps:

(1) Using 80°C hot water to stir and wash the iron-aluminum slag, only 8% of the sodium sulfate is washed out to obtain the iron-aluminum slag after washing;

(2) Alkali leaching process: Add sodium hydroxide solution with a theoretical amount of aluminum element to the washed aluminum slag. At this time, 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%;

(3) Seeding: adding a theoretical amount of aluminum hydroxide seeds 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;

(4) When 1 mol/L sulfuric acid is added to the nickel-iron slag, the acid solubility rate of iron is only 50%, and 1 g of waste slag and an acid-dissolved solution are obtained; an equal volume of 50% sulfuric acid is added to the acid-dissolved solution for precipitation, and the iron recovery rate is only 67%.

analyze:

It can be seen from the results of Examples 1-3 that the method disclosed in the present invention can effectively separate and recover the iron and aluminum elements in the iron-aluminum slag, the aluminum leaching rate and iron recovery rate are high, and the aluminum hydroxide product and the ferric sulfate product both meet the standards, and the sodium sulfate product can be recovered.

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

It can be seen from the results of Examples 1, 3 and Examples 6-7 that if the amount of sodium hydroxide used in the alkali leaching process is too little, the aluminum leaching rate will be low; if the amount of sodium hydroxide used in the alkali leaching process is too much, the aluminum leaching rate will be limited and there will be too much alkali in the solution.

It can be seen from the results of Example 1 and Comparative Example 1 that, 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 no sodium sulfate product is recovered.

Claims (18)

A method for recycling aluminum and iron from iron-aluminum slag, the method comprising: (1) mixing the iron-aluminum slag with the first alkali solution to perform an alkali conversion reaction, and after solid-liquid separation, obtaining a sulfate solution and the iron-aluminum slag after the alkali conversion; (2) mixing the alkali-converted iron-aluminum slag with a second alkali solution to carry out an alkali leaching reaction, and obtaining an aluminate solution and iron slag after solid-liquid separation; (3) acid dissolving the iron slag, then adding sulfuric acid to precipitate ferric sulfate, and after solid-liquid separation, obtaining ferric sulfate crystals and an acid solution. The method according to claim 1, wherein the alkaline substance in the first alkali solution in step (1) comprises at least one of sodium hydroxide, calcium hydroxide and sodium carbonate. The method according to claim 1 or 2, wherein the concentration of the first alkali solution in step (1) is 20 to 40 g/L. The method according to any one of claims 1 to 3, wherein the temperature of the alkaline conversion reaction in step (1) is 60 to 80° C., and the time of the alkaline conversion reaction is 2 to 4 hours. The method according to any one of claims 1 to 4, wherein the sulfate solution in step (1) is subjected to freeze crystallization to precipitate sulfate. The method according to any one of claims 1 to 5, wherein the alkaline substance in the second alkali solution in step (2) comprises at least one of sodium hydroxide, calcium hydroxide and sodium carbonate. The method according to any one of claims 1 to 6, wherein 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 elements to be converted into aluminate. The method according to any one of claims 1 to 7, wherein the temperature of the alkali leaching reaction in step (2) is 60 to 80° C., and the time of the alkali leaching reaction is 2 to 4 hours. The method according to any one of claims 1 to 8, wherein the caustic ratio _αk of the aluminate solution in step (2) is 1.55 to 1.6. The method according to any one of claims 1 to 9, wherein the aluminate solution in step (2) is treated by the Bayer process to obtain aluminum hydroxide. The method according to claim 10, wherein the Bayer process comprises the following steps: The aluminate solution in step (2) is mixed with seed crystals, and after seed separation, aluminum hydroxide and aluminate mother liquor are obtained. The method according to claim 11, wherein the seed crystals comprise aluminum hydroxide. The method according to claim 11 or 12, wherein the amount of the seed crystal added is 0.5 to 1.5 times the theoretical amount required to convert all the aluminum elements in the aluminate solution into aluminum hydroxide. The method according to any one of claims 11 to 13, wherein the seeding temperature is 50 to 60°C and the seeding time is 1 to 10 hours. The method according to any one of claims 11 to 14, wherein the seeding process is accompanied by stirring, and the stirring speed is 150 to 300 r/min. The method according to any one of claims 1 to 15, wherein the acid used in the acid dissolution process in step (3) comprises sulfuric acid, and the concentration of the acid is 2 to 4 mol/L. The method according to any one of claims 1 to 16, wherein the mass concentration of sulfuric acid in step (3) is 60 to 98%. The method according to any one of claims 1 to 17, wherein the method specifically comprises the following steps: (I) mixing the iron-aluminum slag with a first alkaline solution having a concentration of 20 to 40 g/L, and performing an alkaline conversion reaction at 60 to 80° C. for 2 to 4 hours, and obtaining a sulfate solution and an alkaline-converted iron-aluminum slag after solid-liquid separation, and freezing and crystallizing the sulfate solution at 2 to 5° C. to precipitate sulfate; (II) mixing the alkali-converted iron-aluminum slag with a second alkali solution for alkali leaching reaction, and obtaining an aluminate solution and iron slag with a caustic ratio _αk of 1.55 to 1.6 after solid-liquid separation, and mixing the aluminate solution with seed crystals to obtain seed crystals; After separation, aluminum hydroxide and aluminate mother liquor are obtained; The amount of alkaline substance in the second alkali solution is 1.5 to 2.5 times the theoretical amount required for all aluminum elements to be converted into aluminate, the temperature of the alkali leaching reaction is 60 to 80°C, the time is 2 to 4 hours, the amount of the seed crystal added is 0.5 to 1.5 times the theoretical amount required for all aluminum elements in the aluminate solution to be converted into aluminum hydroxide, the temperature of the seed crystal is 50 to 60°C, and the time is 1 to 10 hours; (III) using sulfuric acid with a concentration of 2 to 4 mol/L to acid-dissolve the iron slag, then adding sulfuric acid with a mass concentration of 60 to 98% to precipitate ferric sulfate, and after solid-liquid separation, obtaining ferric sulfate crystals and an acid solution.