A method for preparing battery-grade nickel sulfate and iron phosphate by using nickel pig iron and phosphorus iron slag as raw materials

Abstract

This invention discloses a method for preparing battery-grade nickel sulfate and iron phosphate using nickel pig iron and ferric phosphate slag as raw materials. The preparation process involves first mixing the ferric phosphate slag with cationic alkyl polyacrylamide to form a uniform mixture. This mixture is then added to dilute acid and stirred to disperse it. Nickel pig iron powder is added, and the mixture is filtered to obtain a leaching solution. The leaching solution is then subjected to nickel-iron separation using resin to obtain an iron-containing solution and a nickel-containing resin. The nickel-containing resin is desorbed to obtain a desorbed solution. A nickel-based pH adjuster is added to this desorbed solution, and the solution is filtered to obtain a nickel sulfate solution. After evaporation and concentration to precipitate crystals, the solution is dried and crushed to obtain battery-grade nickel sulfate. Hydrogen peroxide is added to the iron-containing solution to oxidize ferrous iron to ferric iron. A phosphorus source is added, the pH is adjusted, and the solution is reacted, filtered, and dried to obtain iron phosphate dihydrate. This is then calcined to obtain battery-grade iron phosphate. This invention uses nickel pig iron and ferrophosphate slag as raw materials, and utilizes the ferrophosphate slag to promote the full leaching of iron from nickel pig iron, and nickel pig iron to promote the leaching of phosphate and iron from ferrophosphate. With the addition of cationic alkyl polyacrylamide, it achieves high leaching rates of iron and nickel in a short time, and simultaneously achieves the separation of non-ferrous and nickel metal ions during the acid leaching process, so as to finally obtain high-purity, qualified battery-grade nickel sulfate and ferrophosphate.

Description

Technical Field

[0001] This invention belongs to the field of waste lithium battery recycling technology, and particularly relates to a method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate. Background Technology

[0002] Iron phosphate slag is a waste residue generated during the leaching process of recycled lithium iron phosphate battery powder or cathode powder. It is produced in large quantities and is difficult to handle; direct landfilling would cause significant environmental damage. The main components of iron phosphate slag are iron phosphate and carbon, with impurities such as Ti, Li, and Cu also present. Conventional methods for recycling iron phosphate slag primarily involve acid or alkali dissolution, purification, and reprecipitation to produce battery-grade iron phosphate; however, this method involves the excessive use of acids and alkalis, causing environmental pollution.

[0003] Nickel pig iron, a core product of pyrometallurgical smelting of laterite nickel ore, is rich in elements such as nickel and iron, and is an important carrier of nickel resources. Using it as a raw material to synthesize nickel sulfate can not only expand the supply channels for nickel sulfate raw materials but also achieve efficient cascade utilization of nickel resources. However, because nickel has a very low proportion in nickel pig iron, synthesizing nickel sulfate using conventional extraction and precipitation methods not only results in significant nickel loss but also greatly affects the purity of the product.

[0004] In the process of synthesizing battery-grade nickel sulfate from nickel pig iron, the process involves first heating and acid leaching, then adding an oxidant to generate ferric phosphate, and finally removing impurities from the nickel-containing solution to produce nickel sulfate. However, because the proportion of nickel in nickel pig iron is relatively small, separating nickel and iron is very difficult. Ferric phosphate synthesized by conventional precipitation or extraction methods has excessive nickel content, and nickel sulfate has excessive iron content, resulting in a decrease in the recovery rate and purity of both nickel sulfate and ferric phosphate. Summary of the Invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for preparing battery-grade nickel sulfate and iron phosphate from nickel pig iron and iron phosphate slag, so as to improve the recovery rate and purity of nickel iron.

[0006] Technical solution: This invention provides a method for preparing battery-grade nickel sulfate and iron phosphate using nickel pig iron and iron phosphate slag as raw materials, comprising the following steps:

[0007] (1) Mix the phosphorus iron slag with cationic alkyl polyacrylamide to form a mixture. Add the mixture to dilute acid and stir to disperse. Add nickel pig iron powder, react and filter to obtain a leaching solution.

[0008] (2) The leaching solution is separated into nickel and iron by using resin to obtain an iron-containing solution and a nickel-containing resin;

[0009] (3) Desorb the nickel-containing resin to obtain a desorbed solution. Add a nickel-based pH adjuster to the desorbed solution until the pH of the solution reaches 5.0-7.0. After filtration, obtain a nickel sulfate solution. Then, evaporate and concentrate to precipitate crystals, dry and crush to obtain battery-grade nickel sulfate.

[0010] (4) Add hydrogen peroxide to the iron-containing solution to oxidize ferrous iron to ferric iron; add phosphorus source, adjust pH to 0.5-2, react for 3-6 hours, filter and dry to obtain ferric phosphate dihydrate, and calcine to obtain battery-grade ferric phosphate.

[0011] This invention prepares battery-grade nickel sulfate and iron phosphate using nickel pig iron and ferric phosphate slag as raw materials. The ferric phosphate slag is pretreated with cationic alkyl polyacrylamide to enhance the adsorption capacity of both phosphate slag and nickel pig iron during acid leaching, increasing their reaction contact area and active sites. This allows for the promotion of elemental iron / ferrous iron dissolution in nickel pig iron by the ferric phosphate slag, shortening the leaching time and improving the leaching efficiency of iron and nickel. Simultaneously, it can complex the non-iron and nickel cations leached from the phosphate slag and nickel pig iron onto the slag, achieving the removal of non-target metal ions during leaching, thus shortening the impurity removal process and improving the purity of the prepared nickel sulfate and iron phosphate.

[0012] Furthermore, in step (1) of the preparation method, the mass of the added ferrophosphate slag is 0.8-1.0 times the theoretical mass of ferrophosphate produced, and the molar amount of theoretically produced ferrophosphate is twice the molar amount of iron in nickel pig iron.

[0013] Furthermore, in step (1) of the preparation method, the cationic alkyl polyacrylamide is methacryloyloxyethyltrimethylammonium chloride, and its addition amount is 0.5-3% of the mass of the phosphorus iron slag.

[0014] Furthermore, in step (1) of the preparation method, the dilute acid is one or more of dilute sulfuric acid, dilute hydrochloric acid or dilute phosphoric acid, and the hydrogen ion concentration of the dilute acid is 1-4M.

[0015] Furthermore, in step (3) of the preparation method, the nickel-based pH adjuster is selected from nickel carbonate and / or nickel hydroxide.

[0016] Furthermore, in step (4) of the preparation method, the phosphorus source is selected from one or more of phosphoric acid, ammonium monohydrogen phosphate, and ammonium dihydrogen phosphate, and the amount of phosphorus source added is 1.05-1.2 times the theoretical amount required for the formation of iron phosphate from nickel pig iron.

[0017] Furthermore, in step (4) of the preparation method, the amount of hydrogen peroxide added is 1.2-2 times the theoretical amount required for the oxidation of iron to ferric iron in the iron-containing solution, so as to achieve the oxidation of iron in the iron-containing solution.

[0018] Furthermore, in step (4) of the preparation method, the calcination temperature is 500-600℃ and the calcination time is 2-4h.

[0019] Beneficial effects: Compared with the prior art, the significant advantages of this invention are that the preparation method uses nickel pig iron and ferrophosphate slag as raw materials, and the ferrophosphate slag promotes the full leaching of iron in nickel pig iron, while nickel pig iron promotes the leaching of phosphate and iron in ferrophosphate, with the two promoting each other synergistically; and cationic alkyl polyacrylamide is added to achieve high leaching rates of iron and nickel (nickel leaching rate of up to 99.9% or more and iron leaching rate of up to 96% or more) in a short time (not exceeding 4 hours), and the separation of non-ferrous and nickel metal ions is achieved simultaneously during the acid leaching process, so as to finally obtain high-purity, qualified battery-grade nickel sulfate and ferrophosphate, with iron <5ppm in battery-grade nickel sulfate and nickel <5ppm in battery-grade ferrophosphate. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0021] In the following embodiments and comparative examples of the present invention, the main components of the raw material nickel pig iron are shown in Table 1, and the main components of the ferrophosphate slag are shown in Table 2. When calculating the amount of ferrophosphate slag to be added, the required molar amount of ferrophosphate is calculated as twice the total molar amount of iron in the nickel pig iron. For example, with 10g of nickel pig iron as raw material, according to the content in Table 1, the calculated mass of nickel is rounded to 1g, and the mass of iron is 9g. Based on this, the mass of ferrophosphate slag is calculated to be 45g (0.8 times) - 56.25g (1.0 times).

[0022] Table 1 Main components of nickel pig iron

[0023]

[0024] Table 2 Main components of phosphorus-iron slag

[0025]

[0026] Example 1

[0027] Example 1 describes a method for preparing battery-grade nickel sulfate and iron phosphate using nickel pig iron and iron phosphate slag as raw materials, comprising the following steps:

[0028] (1) Grind 10g of nickel pig iron into powder and pass it through an 80-mesh sieve to obtain nickel iron powder; mix 0.225g of methacryloyloxyethyltrimethylammonium chloride (DMC, CAS No. 5039-78-1) with 45g of phosphorus iron slag evenly and coat the surface of the phosphorus iron slag to form a mixture.

[0029] (2) Add nickel-iron powder and the mixture to 1M sulfuric acid and stir to react until the solution pH>1. The reaction takes about 4 hours. Filter to obtain 395mL of leaching solution. The main components of the leaching solution are shown in Table 3 below.

[0030] (3) The resin used is a macroporous polystyrene molecular skeleton chelating resin (model: Zhengguang resin D851). First, the resin is packed into a column and washed with water. Then, the functional groups of the resin are converted into hydrogen form by 10-15% sulfuric acid for activation. Subsequently, the leachate is passed through a column to obtain nickel-containing resin and iron-containing solution.

[0031] (4) Use sulfuric acid to clean the nickel-containing resin to achieve nickel desorption and obtain nickel sulfate solution; add nickel carbonate powder to the nickel sulfate solution until the solution pH is 6, filter and obtain nickel sulfate solution; evaporate and concentrate the nickel sulfate solution to precipitate nickel sulfate crystals, dry the nickel sulfate crystals at 60°C and then crush them, and pass them through a 100-mesh sieve to obtain battery-grade nickel sulfate.

[0032] (5) Add hydrogen peroxide to the iron-containing solution and react for 0.5 h. The amount of hydrogen peroxide added is 1.5 times the theoretical amount of iron in nickel pig iron that is completely oxidized. Then add ammonium dihydrogen phosphate, the amount of which is 1.1 times the theoretical amount of iron phosphate to be generated. Adjust the pH to 1.0 and continue the reaction for 4 h. After filtration and drying, iron phosphate dihydrate is obtained.

[0033] (6) After crushing the ferric phosphate dihydrate, pass it through a 100-mesh sieve; calcine the crushed and sieved ferric phosphate dihydrate at 550°C for 3 hours, and then naturally cool it to room temperature to obtain battery-grade ferric phosphate.

[0034] Table 3 Main components of the leachate from Example 1

[0035]

[0036] Example 2

[0037] The preparation method of Example 2 is basically the same as that of Example 1, except for the difference in the amount of raw materials added. Specifically, it includes the following steps:

[0038] (1) Grind 10g of nickel pig iron into powder and pass it through an 80-mesh sieve to obtain nickel iron powder; mix 1.68g of methacryloyloxyethyltrimethylammonium chloride with 56g of phosphorus iron slag evenly and coat the phosphorus iron slag to form a mixture.

[0039] (2) Add nickel-iron powder and the mixture to 1M sulfuric acid and stir to react until the solution pH>1. The reaction takes 3 hours. Filter to obtain 630mL of leaching solution. The main components of the leaching solution are shown in Table 4 below.

[0040] (3) The resin used is a macroporous polystyrene molecular skeleton chelating resin (model: Zhengguang resin D851). The resin is first packed into a column, washed with water and activated. Then the leachate is passed through the column to obtain nickel-containing resin and iron-containing solution.

[0041] (4) Use sulfuric acid to clean the nickel-containing resin to achieve nickel desorption and obtain nickel sulfate solution; add nickel carbonate powder to the nickel sulfate solution until the solution pH is 5, filter and obtain nickel sulfate solution; evaporate and concentrate the nickel sulfate solution to precipitate nickel sulfate crystals, dry the nickel sulfate crystals at 60°C and then crush them, and pass them through a 100-mesh sieve to obtain battery-grade nickel sulfate.

[0042] (5) Add hydrogen peroxide to the iron-containing solution and react for 0.5 h. The amount of hydrogen peroxide added is 1.5 times the theoretical amount of iron in nickel pig iron that is completely oxidized. Then add ammonium dihydrogen phosphate, the amount of which is 1.1 times the theoretical amount of iron phosphate to be generated. Adjust the pH to 2.0 and continue the reaction for 4 h. After filtration and drying, iron phosphate dihydrate is obtained.

[0043] (6) After crushing the ferric phosphate dihydrate, pass it through a 100-mesh sieve; calcine the crushed and sieved ferric phosphate dihydrate at 600°C for 2 hours, and then naturally cool it to room temperature to obtain battery-grade ferric phosphate.

[0044] Table 4 Main components of the leachate from Example 2

[0045]

[0046] Comparative Example 1

[0047] Comparative Example 1 uses only nickel pig iron as raw material to prepare battery-grade nickel sulfate and iron phosphate, without adding iron phosphate slag. The specific steps include:

[0048] (1) Grind 10g of nickel pig iron into powder and pass it through an 80-mesh sieve to obtain nickel iron powder.

[0049] (2) Add nickel-iron powder to 1M sulfuric acid and stir to react until the solution pH>1. The reaction takes 10 hours. Filter to obtain 173mL of leaching solution. The main components of the leaching solution are shown in Table 5 below.

[0050] (3) The resin used is a macroporous polystyrene molecular skeleton chelating resin (model: Zhengguang resin D851). The resin is first packed into a column, washed with water and activated. Then the leachate is passed through the column to obtain nickel-containing resin and iron-containing solution.

[0051] (4) Use sulfuric acid to clean the nickel-containing resin to achieve nickel desorption and obtain nickel sulfate solution; add nickel carbonate powder to the nickel sulfate solution until the solution pH is 6, filter and obtain nickel sulfate solution; evaporate and concentrate the nickel sulfate solution to precipitate nickel sulfate crystals, dry the nickel sulfate crystals at 60°C and then crush them, and pass them through a 100-mesh sieve to obtain battery-grade nickel sulfate.

[0052] (5) Add hydrogen peroxide to the iron-containing solution and react for 0.5 h. The amount of hydrogen peroxide added is 1.5 times the theoretical amount of iron in nickel pig iron that is completely oxidized. Then add ammonium dihydrogen phosphate, the amount of which is 1.1 times the theoretical amount of iron phosphate to be generated. Adjust the pH to 1.0 and continue the reaction for 4 h. After filtration and drying, iron phosphate dihydrate is obtained.

[0053] (6) After crushing the ferric phosphate dihydrate, pass it through a 100-mesh sieve; calcine the crushed and sieved ferric phosphate dihydrate at 550°C for 3 hours, and then naturally cool it to room temperature to obtain battery-grade ferric phosphate.

[0054] Table 5 Main components of the leachate from Comparative Example 1

[0055]

[0056] Comparative Example 2

[0057] The preparation method of Comparative Example 2 is basically the same as that of Example 1, except that cationic alkyl polyacrylamide is not introduced. The specific steps are as follows:

[0058] (1) Grind 10g of nickel pig iron into powder and pass it through an 80-mesh sieve to obtain nickel iron powder.

[0059] (2) Add nickel-iron powder and 40.32g of phosphorus-iron slag to 1M sulfuric acid and stir to react until the solution pH>1. The reaction takes 6 hours. Filter to obtain 391mL of leaching solution. The composition of the leaching solution is shown in Table 6 below.

[0060] (3) The resin used is a macroporous polystyrene molecular skeleton chelating resin (model: Zhengguang resin D851). The resin is first packed into a column, washed with water and activated. Then the leachate is passed through the column to obtain nickel-containing resin and iron-containing solution.

[0061] (4) Use sulfuric acid to clean the nickel-containing resin to achieve nickel desorption and obtain nickel sulfate solution; add nickel carbonate powder to the nickel sulfate solution until the solution pH is 6, filter and obtain nickel sulfate solution; evaporate and concentrate the nickel sulfate solution to precipitate nickel sulfate crystals, dry the nickel sulfate crystals at 60°C and then crush them, and pass them through a 100-mesh sieve to obtain battery-grade nickel sulfate.

[0062] (5) Add hydrogen peroxide to the iron-containing solution and react for 0.5 h. The amount of hydrogen peroxide added is 1.5 times the theoretical amount of iron in nickel pig iron that is completely oxidized. Then add ammonium dihydrogen phosphate, the amount of which is 1.1 times the theoretical amount of iron phosphate to be generated. Adjust the pH to 1.0 and continue the reaction for 4 h. After filtration and drying, iron phosphate dihydrate is obtained.

[0063] (6) After crushing the ferric phosphate dihydrate, pass it through a 100-mesh sieve; calcine the crushed and sieved ferric phosphate dihydrate at 550°C for 3 hours, and then naturally cool it to room temperature to obtain battery-grade ferric phosphate.

[0064] Table 6 Main components of the leachate from Comparative Example 2

[0065]

[0066] Performance testing

[0067] The purity of nickel sulfate and ferric phosphate in Examples 1 and 2, and Comparative Examples 1 and 2 was tested, and the specific results are shown in Tables 7 and 8. The leaching rates of nickel and iron are shown in Table 9.

[0068] Table 7. Purity of Nickel Sulfate

[0069]

[0070] Table 8. Purity of Ferric Phosphate

[0071]

[0072] Table 9 Leaching rates of nickel and iron

[0073]

[0074] Combining Tables 3, 4, 7, 8, and 9 of Examples 1 and 2, it can be seen that using nickel pig iron and ferrophosphate slag as raw materials, supplemented by cationic alkyl polyacrylamide, achieves high-efficiency leaching of nickel and iron, with impurities far below the standard requirements. Furthermore, it can be seen that both iron and nickel are significantly leached from the ferrophosphate slag and nickel pig iron, resulting in high recovery rates (high leaching rate, and minimal loss of nickel and iron during subsequent resin separation, thus negligible; leaching rate is used as the evaluation indicator).

[0075] As can be seen from Tables 5, 7, 8 and 9 of Comparative Example 1, in the conventional method, without the aid of ferric phosphate leaching, not only is the leaching time of nickel and iron in nickel pig iron long (up to 10 hours), reducing the leaching efficiency, but also the leaching rate of iron and the purity of the prepared product are reduced.

[0076] As can be seen from Tables 6, 7, 8 and 9 of Comparative Example 2, the absence of cationic alkyl polyacrylamide not only increases the leaching reaction time and reduces the leaching efficiency, but also reduces the leaching rate and purity of both nickel and iron.

[0077] In addition to the above embodiments, it should be noted that the technical effects claimed above can be obtained by using the preparation method of the present invention, and therefore no further experimental verification is required. For example, in step (1), the mass of the ferrophosphate slag added is 0.8-1.0 times the theoretical mass of ferric phosphate produced, and the molar amount of ferric phosphate produced is twice the molar amount of iron in nickel pig iron. The amount of cationic alkyl polyacrylamide added is 0.5-3% of the mass of the ferrophosphate slag. The dilute acid can also be selected from one or more of dilute sulfuric acid, dilute hydrochloric acid, or dilute phosphoric acid, and the hydrogen ion concentration of the dilute acid is 1-4M. In step (3), the nickel-based pH adjuster can also be selected from nickel carbonate and / or nickel hydroxide. In step (4), the phosphorus source can also be selected from one or more of phosphoric acid, ammonium monohydrogen phosphate, and ammonium dihydrogen phosphate, and the amount of phosphorus source added is 1.05-1.2 times the theoretical amount required for the iron in nickel pig iron to produce ferric phosphate. In step (4), the amount of hydrogen peroxide added is 1.2-2 times the theoretical amount required for the iron in the iron-containing solution to oxidize to ferric iron. The roasting temperature can be 500-600℃ and the roasting time can be 2-4 hours.

Claims

1. A method for preparing battery-grade nickel sulfate and iron phosphate from nickel pig iron and ferric phosphate slag, characterized in that, Includes the following steps: (1) Mix the phosphorus iron slag with cationic alkyl polyacrylamide to form a mixture. Add the mixture to dilute acid and stir to disperse. Add nickel pig iron powder, react and filter to obtain a leaching solution. (2) The leaching solution is separated into nickel and iron by using resin to obtain an iron-containing solution and a nickel-containing resin; (3) Desorb the nickel-containing resin to obtain a desorbed solution. Add a nickel-based pH adjuster to the desorbed solution until the pH of the solution reaches 5.0-7.

0. After filtration, obtain a nickel sulfate solution. Then, evaporate and concentrate to precipitate crystals, dry and crush to obtain battery-grade nickel sulfate. (4) Add hydrogen peroxide to the iron-containing solution to oxidize ferrous iron to ferric iron; add phosphorus source, adjust pH to 0.5-2, react for 3-6 hours, filter and dry to obtain ferric phosphate dihydrate, and calcine to obtain battery-grade ferric phosphate.

2. The method for preparing battery-grade nickel sulfate and iron phosphate from nickel pig iron and ferric phosphate slag as raw materials according to claim 1, characterized in that, In step (1), the mass of the added ferrophosphate slag is 0.8-1.0 times the theoretical mass of ferrophosphate produced, and the molar amount of theoretically produced ferrophosphate is twice the molar amount of iron in nickel pig iron.

3. The method for preparing battery-grade nickel sulfate and iron phosphate from nickel pig iron and ferric phosphate slag as raw materials according to claim 1, characterized in that, In step (1), the cationic alkyl polyacrylamide is methacryloyloxyethyltrimethylammonium chloride, and its addition amount is 0.5-3% of the mass of the phosphorus iron slag.

4. The method for preparing battery-grade nickel sulfate and iron phosphate from nickel pig iron and ferric phosphate slag as raw materials according to claim 1, characterized in that, In step (1), the dilute acid is selected from one or more of dilute sulfuric acid, dilute hydrochloric acid or dilute phosphoric acid, and the hydrogen ion concentration of the dilute acid is 1-4M.

5. The method for preparing battery-grade nickel sulfate and iron phosphate from nickel pig iron and ferric phosphate slag as raw materials according to claim 1, characterized in that, In step (3), the nickel-based pH adjuster is selected from nickel carbonate and / or nickel hydroxide.

6. The method for preparing battery-grade nickel sulfate and iron phosphate from nickel pig iron and ferric phosphate slag as raw materials according to claim 1, characterized in that, In step (4), the phosphorus source is selected from one or more of phosphoric acid, ammonium monohydrogen phosphate, and ammonium dihydrogen phosphate, and the amount of phosphorus source added is 1.05-1.2 times the theoretical amount required for the formation of iron phosphate from nickel pig iron.

7. The method for preparing battery-grade nickel sulfate and iron phosphate from nickel pig iron and ferric phosphate slag as claimed in claim 1, characterized in that, In step (4), the amount of hydrogen peroxide added is 1.2-2 times the theoretical amount required for iron in the iron-containing solution to be oxidized into ferric iron.

8. The method for preparing battery-grade nickel sulfate and iron phosphate from nickel pig iron and ferric phosphate slag as raw materials according to claim 1, characterized in that, In step (4), the roasting temperature is 500-600℃ and the roasting time is 2-4h.

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