CN115806280B - Method for preparing ferric phosphate by taking phosphorus chemical byproduct ferrophosphorus powder as raw material - Google Patents

Abstract

The invention discloses a method for preparing iron phosphate using iron phosphorus powder, a by-product of phosphorus chemical industry, as raw material, which includes the following steps: 1) immersing the iron phosphorus powder in a sodium hydroxide solution to react, filtering, washing and drying to obtain silicon-removed Iron phosphate powder; 2) Mix and grind the iron phosphate powder obtained in step 1) with an alkali metal salt, and then sinter it at high temperature; 3) Leach the sintered solid in deionized water, and separate the solid and liquid to obtain a phosphate leaching solution and iron oxide filter residue; 4) Add dilute sulfuric acid to the iron oxide filter residue for leaching to obtain an iron sulfate filtrate; 5) Add acid to the phosphate leach solution to acidify, then add the iron sulfate filtrate, and then add a supplementary phosphorus source to adjust the iron-phosphorus ratio ; 6) Add ammonia water to adjust the pH, stir and heat to obtain hydrated iron phosphate precipitation; dehydrate the hydrated iron phosphate to obtain anhydrous iron phosphate. This process has the advantages of low cost, simple process, environmental protection, and is easy to scale up.

Description

A method for preparing iron phosphate using phosphorus chemical by-product phosphorus iron powder as raw material

Technical field

The invention belongs to the technical field of phosphorus chemical recycling, and specifically relates to a method for preparing iron phosphate using phosphorus chemical by-product iron phosphorus powder as raw material.

Background technique

In recent years, due to the requirements of environmental protection and energy conservation, the new energy automobile industry has developed rapidly. Benefiting from the rapid development of new energy vehicles and energy storage industries, lithium iron phosphate has gradually gained market recognition for its high safety and long cycle life. Its demand is increasing, and its production capacity has also increased from 181,200 tons/year at the end of 2018 to 2021. At the end of the year, it was 898,000 tons/year, with a compound annual growth rate of 70.5%, and the year-on-year growth rate in 2021 is as high as 167.9%. The current mainstream new energy vehicle battery life is about 8 years. Every time it is retired, it will trigger a wave of research and development of lithium iron phosphate. Therefore, it is necessary to explore new ideas for the preparation process of lithium iron phosphate. Ferrophosphate is a by-product of the yellow phosphorus industry, which is cheap, non-toxic and harmless. The main components of phosphorus iron are FeP and Fe ₂ P. The Fe element content of high-quality phosphorus iron is more than 60% and the P element content is more than 25%. Compared with phosphoric acid and ammonium dihydrogen phosphate, iron phosphate is cheaper. Using iron phosphate as the raw material for preparing battery cathode materials will greatly reduce costs. At present, the mainstream method for treating iron phosphate in the industry is nitric acid leaching, which has the advantages of simple process and low cost. However, leaching with oxidizing acids such as nitric acid is very dangerous and will also produce nitrogen oxides that pollute the environment.

Contents of the invention

The purpose of the present invention is to provide a method for preparing ferric phosphate using ferrophosphorus powder, a by-product of phosphorus chemical industry, as raw material, so as to solve the current problem that the phosphorus element and iron element in ferrophosphorus cannot be extracted and utilized.

The invention provides a process route for preparing phosphate through roasting with alkali metal salts, separating iron and phosphorus elements through water dissolution, and then recycling them respectively to prepare iron phosphate. The process route of the present invention only needs to add carbonate and carry out solid-liquid separation through sintering and water leaching, so that phosphorus and iron can be recovered respectively, and iron phosphate can be prepared by supplementing quantitative phosphorus acid salts. This process has the advantages of low cost, simple process, environmental protection, and is easy to scale up.

The technical solutions provided by the invention are as follows:

The method provided by the invention for preparing iron phosphate from phosphorus chemical by-product phosphorus iron powder as raw material includes the following steps:

1) Dip the iron phosphorus powder into the sodium hydroxide solution for reaction, then filter, wash and dry to obtain the iron phosphorus powder with silicon removed;

2) Mix and grind the silicon-removed ferrophosphorus powder obtained in step 1) with an alkali metal salt, and then sinter them in an air atmosphere to obtain iron oxide and phosphate;

3) Immerse the iron oxide and phosphate obtained in step 2) into deionized water, heat and stir, and separate the solid and liquid after the leaching is completed to obtain the phosphate leachate and iron oxide filter residue;

4) Add dilute sulfuric acid to the iron oxide filter residue obtained in step 3) for leaching, and filter to remove insoluble matter to obtain an iron sulfate filtrate;

5) Add acid solution to the phosphate leachate obtained in step 3) to acidify it, and then add it to the iron sulfate filtrate obtained in step 4) to obtain a mixed solution;

6) Add a supplementary phosphorus source to the mixed solution obtained in step 5) to bring the phosphorus to iron ratio to a suitable range, then add ammonia water to adjust the pH to the set range, heat and stir the reaction to obtain hydrated ferric phosphate, and heat the obtained hydrated ferric phosphate. Dehydrate to obtain anhydrous iron phosphate.

Preferably, in step 1), the iron phosphorus is a by-product of yellow phosphorus industry, the iron content in the iron phosphorus is greater than 50%, and the phosphorus content is greater than 20%.

Preferably, in step 1), the concentration of the sodium hydroxide solution is 0.1 mol/L ~ 1.0 mol/L, and the reaction time is 240 min ~ 360 min.

Preferably, in step 2), the alkali metal salt is one of carbonate, nitrate, and chloride whose cation is an alkali metal, and the iron phosphorus powder and the alkali metal salt are mixed according to the composition ratio of the product alkali metal phosphate. .

Further preferably, in step 2), the alkali metal salt is one of sodium carbonate, sodium bicarbonate, and potassium nitrate.

Preferably, in step 2), the temperature for sintering the mixture of iron phosphorus powder and alkali metal salt is 600°C to 850°C, and the duration of sintering the mixture is 6 to 10 hours.

Preferably, in step 3), the water is immersed and heated to a temperature of 40 to 80°C, and the leaching time is 4 to 6 hours.

Preferably, in step 4), the concentration of dilute sulfuric acid is 1 to 1.5 mol/L, and the leaching time is 120 to 240 minutes.

Preferably, in step 5), the acid liquid is one of phosphoric acid-containing liquids such as phosphoric acid and sodium dihydrogen phosphate.

Preferably, in step 6), the supplementary phosphorus source is phosphoric acid or phosphate, and the phosphorus-to-iron ratio n(Fe):n(P)=0.9:1 to 1:3.

Preferably, in step 6), the pH is adjusted to 1.5 to 3, the reaction time is 4 to 6 hours, the iron phosphate dehydration temperature is 300°C to 600°C, and the dehydration time is 4 to 6 hours.

Among the above technical solutions:

In step 1), the sodium silicate solution prepared by reacting sodium hydroxide and iron phosphorus powder is filtered to remove silicon impurities in the iron phosphorus; after removing silicon, the main impurity components in the iron phosphorus are calcium and manganese;

In step 2), through high-temperature calcination, the iron in the iron phosphorus powder can be oxidized into iron oxide, and the Fe-P bond in the iron phosphorus powder can be broken, and the phosphorus can be extracted in the form of phosphate;

In step 3), solid-liquid separation of phosphate and iron oxide can be carried out through solution leaching;

In step 4), the iron oxide slag is leached by dissolving dilute sulfuric acid, and the insoluble matter is removed to obtain an iron sulfate solution containing lower impurity content;

In step 5), the pH of the system is reduced by acidifying phosphate;

In step 6), by adjusting the iron to phosphorus ratio, the prepared iron phosphate has better performance; by adjusting the pH to perform an iron phosphate precipitation reaction, hydrated iron phosphate can be obtained; and through high-temperature calcination, high-purity anhydrous iron phosphate can be further obtained.

Beneficial effects of the present invention:

1) The present invention can remove silicon impurities, calcium impurities, and manganese impurities that are difficult to remove. The impurity removal agents used can only be commonly used acids and alkali, and there is no waste gas emission;

2) The present invention can extract iron and phosphorus from raw materials by solid phase method from iron phosphorus powder. The process is simple and there are no toxic or harmful reagents;

3) In the iron phosphate prepared by the present invention, the content of each impurity is less than 0.1%.

Description of the drawings

Figure 1 is a process flow diagram of an embodiment of the present invention;

Figure 2 is the XRD pattern of ferric phosphate dihydrate and ferric phosphate anhydrous prepared in Example 1 and the standard PDF card of ferric phosphate anhydrous;

Figure 3 is a test chart of the electrochemical performance of lithium iron phosphate prepared by mixing lithium with the iron phosphate prepared in Example 1.

Detailed ways

The principles and features of the present invention are described below. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

Example 1

Preparing iron phosphate from phosphorus chemical by-product phosphorus iron powder as raw material includes the following steps:

1) Mix ferrophosphorus powder and sodium hydroxide solution at n(Na):n(Si)=15:1 and stir for 4 hours, then filter and wash to obtain ferrophosphorus with silicon removed;

2) Mix the silicon-removed iron phosphorus powder and sodium carbonate evenly according to the composition ratio of the product sodium phosphate, and sinter in an air atmosphere at 600°C for 8 hours to obtain a mixture of sodium phosphate and iron oxide;

3) Immerse the above mixture in water, heat and leach at 50°C for 250 minutes, and filter to obtain sodium phosphate solution and iron oxide slag;

4) Mix iron oxide slag with 1.0 mol/L dilute sulfuric acid, heat and stir at 60°C for 4 hours, filter to remove insoluble matter, and obtain an iron sulfate solution;

5) Add phosphoric acid to the obtained sodium phosphate solution to adjust the pH of the sodium phosphate solution. After stirring evenly, pour the obtained iron sulfate solution and add supplementary phosphoric acid so that n(Fe):n(P)=1:1.25;

6) Drop ammonia water into the solution, adjust the pH of the system to 2.0, heat to 100°C and stir for 6 hours. After the reaction is complete, filter, wash and dry to obtain hydrated iron phosphate; insulate the hydrated iron phosphate at 550°C for 6 hours to obtain Anhydrous iron phosphate. The 0.2C first discharge specific capacity of lithium iron phosphate prepared by mixing lithium carbonate and starch sintering ball milling is 150.1mAh·g ^-1 , and the 1C discharge specific capacity is 139mAh·g ^-1 .

The element content in the iron phosphate product prepared in this example and the impurity content in the raw materials are shown in Table 1.

Table 1 Element content in iron phosphate products and impurity content in raw materials (wt%)

Example 2

Preparing iron phosphate from phosphorus chemical by-product phosphorus iron powder as raw material includes the following steps:

1) Mix ferric phosphorus and sodium hydroxide solution at n (Na): n (Si) = 10:1 and stir for 6 hours, filter and wash to obtain ferric phosphorus with silicon removed;

2) Mix the silicon-removed iron phosphorus and sodium bicarbonate evenly according to the composition ratio of sodium phosphate, and sinter it in an air atmosphere at 700°C for 8 hours to obtain a mixture of sodium phosphate and iron oxide;

3) Immerse the mixture in water, heat and leach at 60°C for 240 minutes, and filter to obtain sodium phosphate solution and iron oxide slag;

4) Mix iron oxide slag with 1.1 mol/L dilute sulfuric acid, heat and stir at 65°C for 4 hours, remove insoluble matter, and obtain an iron sulfate solution;

5) Add sodium dihydrogen phosphate to the sodium phosphate solution to adjust the pH. After stirring evenly, pour the iron sulfate solution and add supplementary phosphoric acid to make n(Fe):n(P)=1:2;

6) Drop ammonia water into the solution to adjust the pH of the system to 1.5, heat to 90°C and stir for 6 hours. After the reaction is complete, filter, wash and dry to obtain hydrated iron phosphate; insulate the hydrated iron phosphate at 600°C for 4 hours to obtain anhydrous Iron phosphate. The 0.2C first discharge specific capacity of lithium iron phosphate prepared by mixing lithium carbonate and starch ball milling and sintering is 149.8mAh·g ^-1 , and the 1C discharge specific capacity is 138mAh·g ^-1 .

Example 3

Preparing iron phosphate from phosphorus chemical by-product phosphorus iron powder as raw material includes the following steps:

1) Mix ferric phosphorus and sodium hydroxide solution at n(Na):n(Si)=8:1 and stir for 5 hours, filter and wash to obtain ferric phosphorus with silicon removed;

2) Mix the silicon-removed iron phosphorus and calcium carbonate evenly according to the composition ratio of calcium phosphate, and sinter it in an air atmosphere at 850°C for 8 hours to obtain a mixture of calcium phosphate and iron oxide;

3) Immerse the mixture in water, heat and leach at 65°C for 300 minutes, and filter to obtain calcium phosphate solution and iron oxide slag;

4) Mix iron oxide slag with 1.2 mol/L dilute sulfuric acid, heat and stir at 70°C for 4 hours, remove insoluble matter, and obtain an iron sulfate solution;

5) Add phosphoric acid to the calcium phosphate solution to adjust the pH, stir evenly, pour the iron sulfate solution, and add supplementary phosphoric acid to make n(Fe):n(P)=1:2;

6) Drop ammonia water into the solution to adjust the pH of the system to 1.8, heat to 98°C and stir for 6 hours. After the reaction is complete, filter, wash and dry to obtain hydrated iron phosphate; insulate the hydrated iron phosphate at 575°C for 4 hours to obtain anhydrous Iron phosphate. The 0.2C first discharge specific capacity of lithium iron phosphate prepared by mixing lithium carbonate and starch ball milling and sintering is 148mAh·g ^-1 , and the 1C discharge specific capacity is 137mAh·g ^-1 .

Example 4

Preparing iron phosphate from phosphorus chemical by-product phosphorus iron powder as raw material includes the following steps:

1) Mix ferric phosphorus and sodium hydroxide solution at n(Na):n(Si)=12:1 and stir for 270 minutes, filter and wash to obtain ferric phosphorus with silicon removed;

2) Mix the silicon-removed iron phosphorus and potassium nitrate evenly according to the composition ratio of potassium phosphate, and sinter in an air atmosphere at 700°C for 8 hours to obtain a mixture of potassium phosphate and iron oxide;

3) Immerse the mixture in water, heat and leach at 65°C for 250 minutes, and filter to obtain potassium phosphate solution and iron oxide slag;

4) Mix iron oxide slag with 1.5 mol/L dilute sulfuric acid, heat and stir at 65°C for 4 hours, remove insoluble matter, and obtain an iron sulfate solution;

5) Add phosphoric acid to the potassium phosphate solution to adjust the pH, stir evenly, pour the iron sulfate solution, and add supplementary phosphoric acid to make n(Fe):n(P)=1:2;

6) Drop ammonia water into the solution to adjust the pH of the system to 2.0, heat to 99°C and stir for 6 hours. After the reaction is complete, filter, wash, and dry to obtain hydrated iron phosphate; insulate the hydrated iron phosphate at 580°C for 6 hours to obtain anhydrous Iron phosphate. The 0.2C first discharge specific capacity of lithium iron phosphate prepared by mixing lithium carbonate and starch ball milling and sintering is 151mAh·g ^-1 , and the 1C discharge specific capacity is 139mAh·g ^-1 .

Example 5

Preparing iron phosphate from phosphorus chemical by-product phosphorus iron powder as raw material includes the following steps:

1) Mix ferric phosphorus and sodium hydroxide solution at n(Na):n(Si)=10:1 and stir for 4 hours, filter and wash to obtain ferric phosphorus with silicon removed;

2) Mix the silicon-removed iron phosphorus and sodium carbonate evenly according to the composition ratio of sodium phosphate, and sinter in an air atmosphere at 800°C for 8 hours to obtain a mixture of sodium phosphate and iron oxide;

3) Immerse the mixture in water, heat and leach at 55°C for 300 minutes, and filter to obtain sodium phosphate solution and iron oxide slag;

4) Mix iron oxide slag with 1.25 mol/L dilute sulfuric acid, heat and stir at 60°C for 4 hours, remove insoluble matter, and obtain an iron sulfate solution;

5) Add sodium dihydrogen phosphate to the sodium phosphate solution to adjust the pH. After stirring evenly, pour in the dissolved iron sulfate solution and add supplementary phosphoric acid to make n(Fe):n(P)=1:1.5;

6) Drop ammonia water into the solution to adjust the pH of the system to 1.5, heat to 100°C and stir for 6 hours. After the reaction is complete, filter, wash and dry to obtain hydrated iron phosphate; insulate the hydrated iron phosphate at 600°C for 6 hours to obtain anhydrous Iron phosphate. The 0.2C first discharge specific capacity of lithium iron phosphate prepared by mixing lithium carbonate and starch ball milling and sintering is 150.3mAh·g ^-1 , and the 1C discharge specific capacity is 140.1mAh·g ^-1 .

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (10)

1. A method for preparing ferric phosphate by taking phosphorus chemical byproduct ferrophosphorus powder as a raw material comprises the following steps:

1) Immersing the ferrophosphorus powder into sodium hydroxide solution for reaction, and then filtering, washing and drying to obtain ferrophosphorus powder with silicon removed;

2) Mixing and grinding the ferrophosphorus powder with silicon removed in the step 1) and alkali metal salt uniformly, and sintering in an air atmosphere to obtain ferric oxide and phosphate;

3) Immersing the ferric oxide and the phosphate obtained in the step 2) into deionized water, heating and stirring, and carrying out solid-liquid separation after the leaching is finished to obtain phosphate leaching solution and ferric oxide filter residues;

4) Adding dilute sulfuric acid into the ferric oxide filter residue obtained in the step 3) for leaching, and filtering to remove insoluble matters to obtain ferric sulfate filtrate;

5) Adding acid liquor into the phosphate leaching solution obtained in the step 3) for acidification, and then adding the acid liquor into the ferric sulfate filtrate obtained in the step 4) to obtain a mixed solution;

6) Adding a supplementary phosphorus source into the mixed solution obtained in the step 5) to enable the phosphorus-iron ratio to be in a proper range, adding ammonia water to adjust the pH value to a set range, heating and stirring for reaction to obtain hydrated ferric phosphate, and heating and dehydrating the obtained hydrated ferric phosphate to obtain anhydrous ferric phosphate.

2. The method for preparing ferric phosphate by using phosphorus chemical byproduct ferrophosphorus powder as raw material according to claim 1, wherein in the step 1), the ferric phosphate is yellow phosphorus industrial byproduct, and the iron content in the ferric phosphate is more than 50% and the phosphorus content is more than 20%.

3. The method for preparing ferric phosphate by using phosphorus chemical byproduct ferrophosphorus powder as raw material according to claim 1, wherein in the step 1), the concentration of sodium hydroxide solution is 0.1-1.0 mol/L, and the reaction time is 240-360 min.

4. The method for preparing iron phosphate by using phosphorus chemical byproduct ferrophosphorus powder as raw material according to claim 1, wherein in the step 2), the alkali metal salt is one of carbonate, nitrate and chloride of which the cation is alkali metal; the ferrophosphorus powder and the alkali metal salt are mixed according to the composition proportion of the product alkali metal phosphate.

5. The method for preparing iron phosphate by using phosphorus chemical byproduct ferrophosphorus as raw material according to claim 1, wherein in the step 2), the sintering temperature of the mixture of ferrophosphorus and alkali metal salt is 600-850 ℃, and the sintering reaction time of the mixture is 6-10 h.

6. The method for preparing ferric phosphate by using phosphorus chemical byproduct ferrophosphorus powder as raw material according to claim 1, wherein in the step 3), water is soaked and heated to 40-80 ℃ for 4-6 hours.

7. The method for preparing ferric phosphate by using phosphorus chemical byproduct ferrophosphorus powder as raw material according to claim 1, wherein in the step 4), the concentration of dilute sulfuric acid is 1-1.5 mol/L, and the leaching time is 120-240 min.

8. The method for preparing iron phosphate from phosphorus chemical byproduct ferrophosphorus powder as raw material according to claim 1, wherein in the step 5), the acid solution is phosphoric acid solution.

9. The method for preparing iron phosphate from phosphorus chemical byproduct ferrophosphorus powder as raw material according to claim 1, wherein in the step 6), the supplemental phosphorus source is phosphoric acid or phosphate, and the ratio of ferrophosphorus to n (Fe): n (P) =0.9:1 to 1:3.

10. The method for preparing iron phosphate by using phosphorus chemical byproduct ferrophosphorus powder as raw material according to claim 1, wherein in the step 6), the pH is adjusted to 1.5-3, the reaction time is 4-6 h, the dehydration temperature of the iron phosphate is 300-600 ℃, and the dehydration time is 4-6 h.