CN118908165A - Doped modified ferric phosphate and preparation method thereof - Google Patents

Abstract

The invention provides a doped modified ferric phosphate and a preparation method thereof, wherein the doped modified ferric phosphate is prepared by doping metal elements in ferric phosphate to improve chemical property and conductivity, the metal elements are one or more of Ni, co, mn, mg, V, ti, al, cu, zn, W, cr, zr, la, mo, nb, ga, Y, and the preparation method is as follows: s1, synthesis reaction: yellow slurry a was obtained; s2, conversion reaction: obtaining white slurry B; s3, dipping reaction: obtaining a filter cake C and filtrate C, and recycling the filtrate C; s4, drying and calcining: obtaining doped modified ferric phosphate; the dipping doping method provided by the invention overcomes the defects of difficult precipitation, difficult doping and low yield of metal ions such as Mn ²⁺、Mg²⁺、Ni²⁺、Co²⁺ and the like in an iron phosphate wet reaction system in the prior art, and can realize the recycling of doped metal liquid.

Description

A kind of doped modified iron phosphate and preparation method thereof

Technical Field

The present invention relates to the technical field of batteries, and in particular to a doped modified iron phosphate and a preparation method thereof.

Background Art

It has been proven that proper doping modification of lithium iron phosphate can improve the conductivity of lithium iron phosphate and enhance its electrochemical performance, but there is a problem of poor doping uniformity when doping during the solid phase reaction of lithium iron phosphate. In theory, advancing the doping to the preparation stage of the precursor (iron phosphate) is conducive to the uniform mixing of iron, phosphorus and doping elements at the molecular level, which can better improve the performance. Currently, there are mainly two technical solutions for doping at the iron phosphate stage: ① doping during the iron phosphate synthesis reaction stage; ② doping during the iron phosphate conversion reaction stage.

The patent "A doped iron phosphate and its preparation method and application, CN113460987 A" provides a doped iron phosphate and preparation method doped in the synthesis stage, and the doping elements involved include Ti, Al, V, Ni, Co, Mn, Mg, Cr, Mo. The specific process route is: ① The iron source and the phosphorus source are mixed in an acidic solution, and a soluble metal salt is added to obtain a raw material solution; ② The divalent iron ions in the raw material solution are oxidized to trivalent, and then the pH is adjusted to 3; ③ The temperature is raised to 90°C for conversion reaction, and doped spherical iron phosphate dihydrate is obtained after solid-liquid separation. The patent "A multi-ion doped battery-grade iron phosphate material and its preparation method, CN 114751390 A" provides a preparation method of Ti-V co-doped iron phosphate doped in the synthesis stage. The specific doping process route is: ① prepare a ferrous solution containing a ferrous source, a titanium source, and a vanadium source, and oxidize it to obtain an iron salt solution; at the same time, prepare a phosphate salt solution; ② mix the iron salt solution and the phosphate salt solution to carry out a synthesis reaction; ③ add phosphoric acid or a mixed acid containing phosphoric acid, heat to 75-105°C for a conversion reaction, and then wash, dry, and calcine to obtain Ti-V co-doped iron phosphate; the above patent is to perform doping during the iron phosphate synthesis reaction stage.

The patent "Metal-doped crystalline iron phosphate, its preparation method and lithium composite metal phosphate prepared therefrom, CN104024154 A" provides a method for preparing doped iron phosphate in the conversion stage, and the doping elements involved include Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Ti, Zn, Al, Ga, and Mg. The specific process route is: ① Mix the iron source and phosphorus source, adjust the pH to 4-7 for reaction, and obtain amorphous iron phosphate after solid-liquid separation, washing, and drying; ② Slurry the amorphous iron phosphate and mix it with a metal salt solution, then add an acid such as phosphoric acid or hydrochloric acid to adjust the slurry pH to 1-3, heat it to 90-100°C for conversion reaction, and obtain dihydrate iron phosphate doped with different elements after solid-liquid separation, washing, and drying. The above patent is to dope in the iron phosphate conversion reaction stage.

However, the iron phosphate doping technology disclosed above is not universal and is not suitable for the doping of certain metal elements (such as Mn ²⁺ and Mg ²⁺ ) because it is difficult for these metal ions to form phosphate or hydroxide precipitates under the lower synthesis/conversion pH window of iron phosphate. According to the report "Study on the Solid-Liquid Distribution Law of Eight Metals in the Iron Phosphate Precipitation Process", when the synthesis pH is 1.5-2.0, only 2-3% of magnesium ions and 10-13% of manganese ions can enter the iron phosphate precipitate. This means that when preparing magnesium-doped iron phosphate and manganese-doped iron phosphate under the process window of pH = 1.5-2.0, a large amount of magnesium ions and manganese ions cannot be effectively utilized.

Summary of the invention

In order to solve the above technical problems, the present invention discloses a doped modified iron phosphate and a preparation method thereof, wherein the doped modified iron phosphate is prepared by doping heterogeneous metal elements into the iron phosphate to improve the electrochemical performance of lithium iron phosphate, wherein the metal elements are one or more of Ni, Co, Mn, Mg, V, Ti, Al, Cu, Zn, W, Cr, Zr, La, Mo, Nb, Ga, and Y. The doping amount of the metal elements is 0-8000 ppm.

On the other hand, the present invention provides a method for preparing the doped modified ferric phosphate, namely, an impregnation doping method, which is specifically as follows:

S1. Synthesis reaction: prepare a hydrogen peroxide solution with a mass concentration of 10-30wt%, a ferrous salt solution with a mass concentration of 0.5-2.0 mol/L, and a phosphate solution with a mass concentration of 0.5-2.0 mol/L respectively; use pure water as the bottom liquid of the reactor, add the hydrogen peroxide solution, the phosphate solution and the ferrous salt solution into the reactor, and obtain a yellow slurry A, i.e., basic ammonium ferric phosphate slurry, through a synthesis reaction; the pH of the synthesis reaction is ≤2.5, the purpose of which is to avoid the formation of precipitations such as ferric hydroxide, ferrous hydroxide, and ferrous phosphate due to an excessively high synthesis pH; other synthesis conditions are the same or similar to the process parameters commonly used in the iron phosphate industry.

S2, conversion reaction: prepare a phosphoric acid solution with a mass concentration of 30-85wt%, and perform solid-liquid separation and washing treatment on the yellow slurry A obtained in S1 to obtain a yellow filter cake A; mix the yellow filter cake A with pure water for slurrying, then add the phosphoric acid solution, and perform heating and heat preservation treatment to obtain a white slurry B, i.e., dihydrate iron phosphate slurry, through a conversion reaction; the method and equipment for solid-liquid separation and washing treatment are the methods and equipment commonly used in the industry.

S3, impregnation reaction: prepare doped metal liquid, perform the first solid-liquid separation and washing treatment on the white slurry B obtained in step S2 to obtain a white filter cake B; mix the white filter cake B with pure water and the doped metal liquid to slurry, stir and react for 1-3 hours to obtain slurry C, perform solid-liquid separation on the slurry C to obtain filter cake C and filtrate C, recover the filtrate C, remove tiny particles through precise filtration, and then recycle it for the preparation of doped metal liquid.

S4, drying and calcining: the filter cake C in S3 is flash dried, calcined and crushed to obtain doped modified iron phosphate. The flash drying, calcination and crushing methods and equipment are also commonly used in the industry.

Moreover, in the step S1: the ferrous salt solution is prepared from any one of ferrous sulfate, ferrous nitrate, ferrous chloride, iron powder, and iron sheet; the phosphate salt solution is prepared from any one of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid; the molar amount ratio of hydrogen _peroxide in the hydrogen peroxide solution to the molar amount ratio of iron element in the ferrous salt solution is controlled to be n(Fe):n( _H2O2 )=1:0.5-1:1; the molar amount ratio of phosphorus element in the phosphate salt solution to the molar amount ratio of iron element in the ferrous salt solution is controlled to be n(Fe):n(P)=1:0.9-1:1.2.

The doped metal liquid contains one or more doping elements such as Ni, Co, Mn, Mg, Cu, Zn, W, Cr, Zr, La, Mo, Nb, Ga, and Y. The common characteristics of these metal ions are that they are difficult to co-precipitate with phosphate and iron ions under conventional synthesis pH values (pH≤2.5), and cannot form phosphate and hydroxide precipitation, or the precipitation ratio is too low.

Moreover, in the step S3, the doped metal liquid does not contain sulfate and phosphate, and the doped metal liquid is prepared by reacting the metal oxide corresponding to the metal element with nitric acid/organic acid, or by the corresponding soluble metal salt. The reason why the doped metal liquid does not contain sulfate and phosphate is that when the dihydrate iron phosphate reacts with the doped metal liquid, it will adsorb the metal liquid. When sulfate ions exist in the doped metal liquid, it is easy to cause fluctuations in the sulfur content in the anhydrous iron phosphate obtained by subsequent calcination; when phosphates exist in the doped metal liquid, it is easy to cause a high phosphorus content in the anhydrous iron phosphate, affecting the main content of the anhydrous iron phosphate.

Moreover, when the doped modified ferric phosphate contains metal elements such as Ti, Al, and V, the ferrous salt solution in step S1 also contains corresponding soluble metal salts, including titanium sulfate, aluminum sulfate, and ammonium metavanadate. The common characteristics of metal ions such as Ti, Al, and V are that they can coprecipitate with phosphate and iron ions under conventional ferric phosphate synthesis conditions, i.e., at a relatively low synthesis pH value (pH ≤ 2.5), to form a precipitate of phosphate or hydroxide.

Moreover, the white filter cake B obtained in step S3 has a high specific surface area after drying, which is convenient for adsorbing metal ions in the doped metal liquid during the impregnation reaction, and its specific surface area is 60-100 ^m2 /g. The specific surface area of the white filter cake B is controlled by controlling the process conditions of the conversion reaction in step S2. When the conversion reaction in step S2 is heated and kept warm, the temperature is raised to 75-95°C and kept warm for 0.5-3.5h.

Moreover, in the step S3, the white filter cake B is mixed with the doped metal liquid for pulping to obtain a mixed slurry, and the solid content of the mixed slurry is 20-40%; the concentration of each metal ion in the doped metal liquid is determined according to the doping amount required for the doping element of the final iron phosphate product, and the concentration of the metal ions is 0.01-2.0 mol/L, and the doped metal liquid can be reused.

Moreover, in step S3, when the slurry C is subjected to solid-liquid separation treatment, the equipment used is a filter press. During the solid-liquid separation process, the pressing pressure of the filter press needs to be controlled to be 0.8-1.2 Mpa, and the blowing time needs to be 5-20 min to ensure that the moisture content in the filter cake C is at a stable value (40-50%), thereby ensuring that the doping amount in the final ferric phosphate product is at a stable value.

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

1. The doping scheme provided by the present invention has a wide application range and is applicable to different metal elements, even if the solubility product K _sp [M ₃ (PO ₄ ) _n ] of the phosphate precipitate corresponding to the doped element is quite different from the solubility product K _sp [FePO ₄ ] of iron phosphate. At the same time, it solves the problem of difficulty in doping metal ions such as Mn ²⁺ , Mg ²⁺ , Ni ²⁺ , and Co ²⁺ in the prior art. The principle is that the present invention uses two doping methods, namely, co-precipitation doping and impregnation doping. On the one hand, for metal ions such as Ti, Al, and V that are easy to form phosphate or hydroxide precipitation at a relatively low pH (pH≤2.5), they are directly mixed with a ferrous salt solution to co-precipitate with ferric ions in the synthesis stage to achieve doping. On the other hand, for metal ions such as Mn, Mg, Ni, and Co that are difficult to form phosphate or hydroxide precipitation at a relatively low pH (pH≤2.5), ferric phosphate dihydrate is immersed in a nitrate or organic salt solution containing metal ions, and the high specific surface area of ferric phosphate dihydrate is used to adsorb the metal ions. During the calcination process of ferric phosphate dihydrate, nitrate and organic acid radicals (such as citrate and acetate) will decompose into components such as _NOx , _COx , and _H2O , while metal ions such as Mn2 ⁺ , Mg2 ⁺ , Ni2 ⁺ , and Co2 ⁺ will diffuse into the grains of ferric phosphate to achieve element doping.

2. The solution provided by the present invention can solve the serious problem of waste of raw materials of doped metal ions in the preparation process of doped iron phosphate such as Mn, Mg, Ni, and Co. The principle is that the present invention immerses dihydrate iron phosphate in a metal doping liquid, and recycles the metal doping liquid. The filtrate containing metal ions produced by solid-liquid separation will be collected and used for the configuration of fresh metal doping liquid after precision filtration treatment; on the one hand, the dihydrate iron phosphate filter cake has been washed twice (synthetic washing and conversion washing) before the immersion treatment, and the free phosphate and sulfate groups remaining in the filter cake have been fully washed away, ensuring that the sulfate and phosphate groups in the metal doping liquid will not be enriched with the increase of the number of cycles; on the other hand, the salt selected for the configuration of the metal doping liquid is a soluble organic salt or nitrate, which avoids the introduction of phosphate and sulfate groups from the raw material selection stage, thereby ensuring the stability of the metal doping liquid system and meeting the conditions for recycling.

3. The method of combining co-precipitation doping and impregnation doping provided by the present invention overcomes the disadvantage that the same iron phosphate process is not compatible with multiple doping elements or multiple gradient doping amounts. The present invention can prepare iron phosphate materials doped with different elements by regulating the type of metal ions in the metal doping solution used for the impregnation reaction, and can prepare iron phosphate materials with different doping amounts by regulating the molar concentration of metal ions in the metal doping solution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a scanning electron microscope image of ferric phosphate dihydrate (before impregnation and doping) prepared by the present invention;

FIG2 is an XRD diagram of ferric phosphate dihydrate (before impregnation and doping) prepared in the present invention;

FIG3 is an XRD diagram of Mn-doped iron phosphate prepared in Example 1-4;

FIG4 is an XRD diagram of Mg-doped, Ni-doped, and Co-doped iron phosphates prepared in Examples 5-7;

DETAILED DESCRIPTION

Example 1

This embodiment provides a method for preparing manganese-doped modified iron phosphate, comprising the following steps:

S1. Synthesis reaction: prepare 180 L of ferrous salt solution with a molar concentration of 0.8 mol/L of iron element and 150 L of phosphate salt solution with a molar concentration of 1 mol/L of phosphorus element. Under stirring conditions, add the ferrous solution, phosphate salt solution and hydrogen peroxide solution into a reactor, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: The yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the yellow filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the slurry pH to 1.8, and the temperature is raised to 85° C. and kept warm for 2 hours, and a white slurry B is obtained through a conversion reaction.

S3, impregnation reaction: the white slurry B is subjected to solid-liquid separation and washing treatment to obtain a white filter cake B; a manganese acetate solution with a molar concentration of manganese element of 0.2 mol/L is prepared, the white filter cake B is mixed with the manganese acetate solution, and stirred for reaction for 2 h to obtain a slurry C; the slurry C is subjected to solid-liquid separation to obtain a filter cake C and a filtrate C; the filtrate C is subjected to precise filtration to remove tiny particles in the filtrate, and manganese acetate and pure water are added again to prepare a 0.2 mol/L manganese acetate solution.

S4, drying and calcining: flash drying, calcining and crushing the filter cake C to obtain a manganese-doped iron phosphate material.

Example 2

This embodiment provides a method for preparing manganese-doped modified iron phosphate, comprising the following steps:

S1. Synthesis reaction: prepare 180 L of ferrous salt solution with a molar concentration of 0.8 mol/L of iron element and 150 L of phosphate salt solution with a molar concentration of 1 mol/L of phosphorus element. Under stirring conditions, add the ferrous solution, phosphate salt solution and hydrogen peroxide solution into a reactor, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: The yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the yellow filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the slurry pH to 1.8, and the temperature is raised to 85° C. and kept warm for 2 hours, and a white slurry B is obtained through a conversion reaction.

S3, impregnation reaction: the white slurry B is subjected to solid-liquid separation and washing treatment to obtain a white filter cake B; a manganese acetate solution with a molar concentration of manganese element of 0.1 mol/L is prepared, the white filter cake B is mixed with the manganese acetate solution, and the mixture is stirred for reaction for 2 h to obtain a slurry C; the slurry C is subjected to solid-liquid separation to obtain a filter cake C and a filtrate C; the filtrate C is subjected to precise filtration to remove tiny particles in the filtrate, and manganese acetate and pure water are added again to prepare a 0.1 mol/L manganese acetate solution.

S4, drying and calcining: flash drying, calcining and crushing the filter cake C to obtain a manganese-doped iron phosphate material.

Example 3

This embodiment provides a method for preparing manganese-doped modified iron phosphate, comprising the following steps:

S1. Synthesis reaction: prepare 180 L of ferrous salt solution with a molar concentration of 0.8 mol/L of iron element and 150 L of phosphate salt solution with a molar concentration of 1 mol/L of phosphorus element. Under stirring conditions, add the ferrous solution, phosphate salt solution and hydrogen peroxide solution into a reactor, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: The yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the yellow filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the slurry pH to 1.8, and the temperature is raised to 85° C. and kept warm for 2 hours, and a white slurry B is obtained through a conversion reaction.

S3, impregnation reaction: the white slurry B is subjected to solid-liquid separation and washing treatment to obtain a white filter cake B; a manganese acetate solution with a molar concentration of manganese element of 0.05 mol/L is prepared, the white filter cake B is mixed with the manganese acetate solution, and stirred for reaction for 2 h to obtain a slurry C; the slurry C is subjected to solid-liquid separation to obtain a filter cake C and a filtrate C; the filtrate C is subjected to precise filtration to remove tiny particles in the filtrate, and manganese acetate and pure water are added again to prepare a 0.05 mol/L manganese acetate solution.

S4, drying and calcining: flash drying, calcining and crushing the filter cake C to obtain a manganese-doped iron phosphate material.

Example 4

This embodiment provides a method for preparing manganese-doped modified iron phosphate, comprising the following steps:

S1. Synthesis reaction: prepare 180 L of ferrous salt solution with a molar concentration of 0.8 mol/L of iron element and 150 L of phosphate salt solution with a molar concentration of 1 mol/L of phosphorus element. Under stirring conditions, add the ferrous solution, phosphate salt solution and hydrogen peroxide solution into a reactor, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: the yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A: the yellow filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the slurry pH to 1.8, and the temperature is raised to 85° C. and kept warm for 2 hours, and a white slurry B is obtained through a conversion reaction.

S3, impregnation reaction: the white slurry B is subjected to solid-liquid separation and washing treatment to obtain a white filter cake B; a manganese acetate solution with a molar concentration of manganese element of 0.03 mol/L is prepared, the white filter cake B is mixed with the manganese acetate solution, and the mixture is stirred for reaction for 2 h to obtain a slurry C; the slurry C is subjected to solid-liquid separation to obtain a filter cake C and a filtrate C; the filtrate C is subjected to precise filtration to remove tiny particles in the filtrate, and manganese acetate and pure water are added again to prepare a 0.03 mol/L manganese acetate solution.

S4, drying and calcining: flash drying, calcining and crushing the filter cake C to obtain a manganese-doped iron phosphate material.

Example 5

This embodiment provides a method for preparing magnesium-doped modified ferric phosphate, comprising the following steps:

S1. Synthesis reaction: prepare 180 L of ferrous salt solution with a molar concentration of 0.8 mol/L of iron element and 150 L of phosphate salt solution with a molar concentration of 1 mol/L of phosphorus element. Under stirring conditions, add the ferrous solution, phosphate salt solution and hydrogen peroxide solution into a reactor, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: The yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the yellow filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the slurry pH to 1.8, and the temperature is raised to 85° C. and kept warm for 2 hours, and a white slurry B is obtained through a conversion reaction.

S3. Impregnation reaction: subject the white slurry B to solid-liquid separation and washing treatment to obtain white filter cake B; prepare a metal doping solution with a magnesium element molar concentration of 0.05 mol/L, mix the white filter cake B with the metal doping solution, and stir and react for 2 h to obtain slurry C; subject slurry C to solid-liquid separation to obtain filter cake C and filtrate C; filtrate C is subjected to precise filtration to remove tiny particles in the filtrate, and is reused for the preparation of the metal doping solution.

S4, drying and calcining: the filter cake C is flash dried, calcined and crushed to obtain a magnesium-doped iron phosphate material.

Example 6

This embodiment provides a method for preparing nickel-doped modified ferric phosphate, comprising the following steps:

S1. Synthesis reaction: prepare 180 L of ferrous salt solution with a molar concentration of 0.8 mol/L of iron element and 150 L of phosphate salt solution with a molar concentration of 1 mol/L of phosphorus element. Under stirring conditions, add the ferrous solution, phosphate salt solution and hydrogen peroxide solution into a reactor, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: The yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the yellow filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the slurry pH to 1.8, and the temperature is raised to 85° C. and kept warm for 2 hours, and a white slurry B is obtained through a conversion reaction.

S3, impregnation reaction: the white slurry B is subjected to solid-liquid separation and washing treatment to obtain a white filter cake B; a metal doping solution with a nickel element molar concentration of 0.05 mol/L is prepared, the white filter cake B is mixed with the metal doping solution, and stirred for reaction for 2 h to obtain a slurry C; the slurry C is subjected to solid-liquid separation to obtain a filter cake C and a filtrate C; the filtrate C is subjected to precise filtration to remove tiny particles in the filtrate, and is reused for the preparation of the metal doping solution;

S4, drying and calcining: flash drying, calcining and crushing the filter cake C to obtain nickel-doped iron phosphate material.

Example 7

The present embodiment provides a method for preparing cobalt-doped modified ferric phosphate, comprising the following steps:

S1. Synthesis reaction: prepare 180 L of ferrous salt solution with a molar concentration of 0.8 mol/L of iron element and 150 L of phosphate salt solution with a molar concentration of 1 mol/L of phosphorus element. Under stirring conditions, add the ferrous solution, phosphate salt solution and hydrogen peroxide solution into a reactor, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: The yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the yellow filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the slurry pH to 1.8, and the temperature is raised to 85° C. and kept warm for 2 hours, and a white slurry B is obtained through a conversion reaction.

S3. Impregnation reaction: subject the white slurry B to solid-liquid separation and washing treatment to obtain white filter cake B; prepare a metal doping solution with a molar concentration of cobalt element of 0.05 mol/L, mix the white filter cake B with the metal doping solution, and stir and react for 2 h to obtain slurry C; subject slurry C to solid-liquid separation to obtain filter cake C and filtrate C; filtrate C is subjected to precise filtration to remove tiny particles in the filtrate, and is reused for the preparation of the metal doping solution.

S4, drying and calcining: flash drying, calcining and crushing the filter cake C to obtain a cobalt-doped iron phosphate material.

Example 8

The present embodiment provides a method for preparing manganese-doped modified ferric phosphate, comprising the following steps:

S1. Synthesis reaction: prepare 180 L of ferrous salt solution with a molar concentration of 0.8 mol/L of iron element and 150 L of phosphate salt solution with a molar concentration of 1 mol/L of phosphorus element. Under stirring conditions, add the ferrous solution, phosphate salt solution and hydrogen peroxide solution into a reactor, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: The yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the yellow filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the slurry pH to 1.8, and the temperature is raised to 85° C. and kept warm for 2 hours, and a white slurry B is obtained through a conversion reaction.

S3, impregnation reaction: the white slurry B is subjected to solid-liquid separation and washing treatment to obtain a white filter cake B; a metal doping solution with a molar concentration of manganese element of 0.1 mol/L is prepared, the white filter cake B and the metal doping solution are mixed, and the mixture is stirred for reaction for 2 h to obtain a slurry C; the slurry C is subjected to solid-liquid separation to obtain a filter cake C and a filtrate C; the filtrate C is subjected to precise filtration to remove tiny particles in the filtrate, and manganese acetate and pure water are added again to prepare a 0.1 mol/L metal doping solution; wherein the metal doping solution used for the impregnation reaction is prepared from the filtrate C produced in Example 2.

S4, drying and calcining: flash drying, calcining and crushing the filter cake C to obtain a manganese-doped iron phosphate material.

Example 9

The present embodiment provides a method for preparing manganese-doped modified ferric phosphate, comprising the following steps:

S1. Synthesis reaction: prepare 180 L of ferrous salt solution with a molar concentration of 0.8 mol/L of iron element and 150 L of phosphate salt solution with a molar concentration of 1 mol/L of phosphorus element. Under stirring conditions, add the ferrous solution, phosphate salt solution and hydrogen peroxide solution into a reactor, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: The yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the yellow filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the slurry pH to 1.8, and the temperature is raised to 85° C. and kept warm for 2 hours, and a white slurry B is obtained through a conversion reaction.

S3, impregnation reaction: the white slurry B is subjected to solid-liquid separation and washing treatment to obtain a white filter cake B; a metal doping solution with a molar concentration of manganese element of 0.1 mol/L is prepared, the white filter cake B and the metal doping solution are mixed, and the mixture is stirred for reaction for 2 h to obtain a slurry C; the slurry C is subjected to solid-liquid separation to obtain a filter cake C and a filtrate C; the filtrate C is subjected to precise filtration to remove tiny particles in the filtrate, and manganese acetate and pure water are added again to prepare a 0.1 mol/L metal doping solution; wherein, the metal doping solution used for the impregnation reaction is prepared from the filtrate C produced in Example 8.

S4, drying and calcining: flash drying, calcining and crushing the filter cake C to obtain a manganese-doped iron phosphate material.

Example 10

The present embodiment provides a method for preparing a nickel-cobalt co-doped modified ferric phosphate, comprising the following steps:

S1. Synthesis reaction: prepare 150 L of ferrous salt solution with a molar concentration of 1.2 mol/L of iron element and 180 L of phosphate salt solution with a molar concentration of 1 mol/L of phosphorus element. Under stirring conditions, add the ferrous solution, phosphate salt solution and hydrogen peroxide solution into a reactor, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: The yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the yellow filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the slurry pH to 1.7, and the temperature is raised to 88° C. and kept warm for 2.0 h, and a white slurry B is obtained through a conversion reaction.

S3. Impregnation reaction: subject the white slurry B to solid-liquid separation and washing treatment to obtain white filter cake B; prepare metal doping solutions with a nickel element molar concentration of 0.03 mol/L and a cobalt element molar concentration of 0.03 mol/L, mix the white filter cake B with the metal doping solution, and stir the mixture for 2 h to obtain slurry C; subject slurry C to solid-liquid separation to obtain filter cake C and filtrate C; precisely filter the filtrate C to remove tiny particles in the filtrate, and re-add cobalt nitrate, nickel nitrate and pure water to prepare the metal doping solution.

S4, drying and calcining: flash drying, calcining and crushing the filter cake C to obtain a cobalt-nickel co-doped iron phosphate material.

Embodiment 11

The present embodiment provides a method for preparing a titanium-magnesium co-doped modified ferric phosphate, comprising the following steps:

S1. Synthesis reaction: prepare 150 L of ferrous salt solution with a molar concentration of iron element of 1 mol/L, and add solid titanium sulfate to the ferrous solution at a ratio of n(Fe):n(Ti)=1:0.006 to dissolve, and simultaneously prepare 150 L of phosphate salt solution with a molar concentration of phosphorus element of 1 mol/L. Under stirring conditions, put the ferrous solution, phosphate salt solution and hydrogen peroxide solution into a reactor, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: the yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the yellow filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the pH of the slurry to 1.9, and the temperature is raised to 90° C. and kept warm for 1.5 hours, and a white slurry B is obtained through a conversion reaction.

S3. Impregnation reaction: subject the white slurry B to solid-liquid separation and washing treatment to obtain a white filter cake B; prepare a magnesium nitrate solution with a magnesium element molar concentration of 0.05 mol/L, mix the white filter cake B with the magnesium nitrate solution, and stir the reaction for 2 h to obtain a slurry C; subject the slurry C to solid-liquid separation to obtain a filter cake C and a filtrate C; precisely filter the filtrate C to remove tiny particles in the filtrate, and re-add magnesium nitrate and pure water to prepare a 0.1 mol/L magnesium nitrate solution.

S4, drying and calcining: flash drying, calcining and crushing the filter cake C to obtain a titanium-magnesium co-doped iron phosphate material.

Example 12

The present embodiment provides a method for preparing titanium-vanadium co-doped modified ferric phosphate, comprising the following steps:

S1. Synthesis reaction: prepare 160 L of ferrous salt solution with a molar concentration of iron element of 1.1 mol/L, and add titanium sulfate and ammonium metavanadate to the ferrous solution at a ratio of n(Fe):n(Ti)=1:0.008 and n(Fe):n(V)=1:0.005 to dissolve, and at the same time prepare 150 L of phosphate salt solution with a molar concentration of phosphorus element of 1.15 mol/L. Under stirring conditions, put the ferrous solution, phosphate salt solution and hydrogen peroxide solution into a reactor, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: The yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the yellow filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the slurry pH to 1.82, and the temperature is raised to 90° C. and kept warm for 2.0 h, and a white slurry B is obtained through a conversion reaction.

S3, drying and calcining: subjecting the white slurry B to solid-liquid separation and washing treatment to obtain a white filter cake B; subjecting the white filter cake B to flash drying, calcination, and crushing treatment to obtain a titanium-vanadium co-doped iron phosphate material.

Embodiment 13

The present embodiment provides a method for preparing titanium-manganese-magnesium co-doped modified ferric phosphate, comprising the following steps:

S1. Synthesis reaction: prepare 150 L of ferrous solution with a molar concentration of iron element of 1.2 mol/L, and add titanium sulfate to the ferrous solution to dissolve it at a ratio of n(Fe):n(Ti)=1:0.008. At the same time, prepare 180 L of phosphate solution with a molar concentration of phosphorus element of 1 mol/L. Under stirring conditions, put the ferrous solution, phosphate solution and hydrogen peroxide solution into a reactor, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: The yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the yellow filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the slurry pH to 1.7, and the temperature is raised to 88° C. and kept warm for 2.0 h, and a white slurry B is obtained through a conversion reaction.

S3. Impregnation reaction: subject the white slurry B to solid-liquid separation and washing treatment to obtain white filter cake B; prepare metal doping solutions with a molar concentration of manganese element of 0.03 mol/L and a molar concentration of magnesium element of 0.03 mol/L, mix the white filter cake B with the metal doping solution, and stir the mixture for 2 h to obtain slurry C; subject slurry C to solid-liquid separation to obtain filter cake C and filtrate C; filtrate C is subjected to precise filtration to remove tiny particles in the filtrate, and is reused for the preparation of metal doping solution.

S4, drying and calcining: the filter cake C is flash dried, calcined and crushed to obtain a titanium-manganese-magnesium co-doped iron phosphate material.

Comparative Example 1

This comparative example provides a method for preparing manganese-doped modified ferric phosphate, and the various process parameters of the ferric phosphate are consistent with those of Example 3. The difference from Example 3 is that manganese is doped in the synthesis reaction stage of the ferric phosphate in this comparative example, and the specific preparation process includes the following steps:

S1. Synthesis reaction: prepare 150 L of ferrous solution with a molar concentration of 1 mol/L of iron element, add 157 g of anhydrous manganese sulfate to the ferrous solution and dissolve it, the molar concentration of manganese element in the solution is 381 ppm, n(Fe):n(Mn)=1:0.0069; at the same time, prepare 150 L of phosphate solution with a molar concentration of 1 mol/L of phosphorus element, put the ferrous solution, phosphate solution and hydrogen peroxide solution into a reactor under stirring conditions, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: The yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the filter cake A is mixed with pure water and slurried, and then a phosphoric acid solution is added to adjust the slurry pH to 1.8, and the temperature is raised to 91° C. and kept warm for 2 hours, and a white slurry B is obtained through a conversion reaction.

S3, drying and calcining: subjecting the white slurry B to solid-liquid separation and washing treatment to obtain a filter cake, then mixing the filter cake with pure water, slurrying, and subjecting the filter cake to a second solid-liquid separation and washing treatment to obtain a white filter cake B; subjecting the filter cake B to flash drying, calcination, and crushing treatment to obtain a manganese-doped iron phosphate material.

Comparative Example 2

This comparative example provides a method for preparing manganese-doped modified ferric phosphate, wherein the process parameters of the ferric phosphate are consistent with those of Example 3, except that manganese is doped in the conversion reaction stage of the ferric phosphate. The specific preparation process includes the following steps:

S1. Synthesis reaction: prepare 150 L of ferrous solution with a molar concentration of 1 mol/L of iron element and 150 L of phosphate solution with a molar concentration of 1 mol/L of phosphorus element. Add the ferrous solution, phosphate solution and hydrogen peroxide solution into a reactor under stirring, control n(Fe):n(H ₂ O ₂ )=1:0.65, and obtain yellow slurry A through synthesis reaction.

S2. Conversion reaction: The yellow slurry A is subjected to solid-liquid separation and washing treatment to obtain a yellow filter cake A; the filter cake A is mixed with pure water and slurried, and 0.3 L of a solution containing 157 g of anhydrous manganese sulfate is added, and n(Fe):n(Mn)=1:0.0069 in the reaction system. Then, a phosphoric acid solution is added, and the pH of the slurry is adjusted to 1.8. The temperature is raised to 91°C and kept warm for 2 hours, and a white slurry B is obtained through a conversion reaction.

S3, drying and calcining: subjecting the white slurry B to solid-liquid separation and washing treatment to obtain a filter cake, then mixing the filter cake with pure water, slurrying, and subjecting the filter cake to a second solid-liquid separation and washing treatment to obtain a white filter cake B; subjecting the filter cake B to flash drying, calcination, and crushing treatment to obtain a manganese-doped iron phosphate material.

Experimental Section

Experiment 1

The contents of doping elements in the iron phosphate materials prepared in Examples 1 to 13 and Comparative Examples 1 and 2 were statistically analyzed. The results are shown in Table 1.

Table 1 Content of doping elements in the finished ferric phosphate products prepared in various embodiments and comparative examples

It can be seen from Table 1 that according to the results of Example 1, Example 2, Example 3, and Example 4, it is shown that by adjusting the concentration of metal ions in the metal doping solution in the impregnation reaction stage (0.20 mol/L, 0.10 mol/L, 0.05 mol/L, 0.03 mol/L), the doping amount of metal elements in the final ferric phosphate product can be controlled (6192 ppm, 3031 ppm, 1535 ppm, 913 ppm).

The results of Examples 3, 5, 6 and 7 indicate that different types of doped iron phosphates can be prepared by adjusting the types of metal ions (Mn ²⁺ , Mg ²⁺ , Ni ²⁺ , Co ^{2+ ,} etc.) in the metal doping solution during the impregnation reaction stage.

According to the results of Example 2, Example 8 and Example 9, it is shown that the continuous recycling of the metal doping solution will not affect the incorporation of the Mn element into the final ferric phosphate product.

According to the results of Example 10, Example 11, Example 12, and Example 13, it is shown that the iron phosphate material co-doped with multiple metal elements can be prepared by combining co-precipitation doping and immersion doping.

According to the results of Comparative Examples 1 and 2, it is shown that when the manganese element is added in the synthesis stage by the co-precipitation doping method, only 2.13% of the manganese element (51 ppm) can enter the finished ferric phosphate product; when the manganese element is added in the conversion stage, only 1054% of the manganese element (253 ppm) can enter the finished ferric phosphate product.

Experiment 2

The contents of Mn, P, Fe and impurities (Fe, ammonia nitrogen) in the manganese-containing solutions (synthesis mother liquor, conversion mother liquor) of Comparative Examples 1 and 2 were measured; the contents of Mn, P, Fe and impurities (Fe, ammonia nitrogen) in the metal-doped solutions (filtrate C) of the manganese-containing solutions obtained in Example 2, Example 8 and Example 9 were measured. The results are shown in Table 2.

Table 2 Impurities and manganese content of manganese-containing solutions in Examples 2, 8, 9 and Comparative Examples 1 and 2

From the results of Example 2, Example 8, and Example 9 in Table 2, it can be seen that the impurity content (S content, ammonia nitrogen content, etc.) of the metal doping liquid after multiple cycles has not changed significantly and the impurity content is relatively low, indicating that the continuous recycling of the metal doping liquid will not cause the enrichment of the impurity content of the metal doping liquid.

According to the data shown in Table 2, the manganese content in the synthetic mother liquor of Comparative Example 1 is 1521 ppm, the sulfur content is 13102 ppm, and the ammonia nitrogen content is 27894 ppm. Since the sulfur content and ammonia nitrogen content of this part of the manganese-containing solution are too high, it is difficult to reuse the manganese-containing solution without impurity removal treatment.

The manganese content in the conversion mother liquor of Comparative Example 2 is 1252 ppm, the sulfur content is 1168 ppm, and the ammonia nitrogen content is 924 ppm. This part of the manganese-containing solution also has excessively high sulfur and ammonia nitrogen contents. It is difficult to reuse it without impurity removal treatment. However, Examples 2, 8, and 9 contain only a small amount of impurities and can still be recycled.

Experiment 3

The different iron phosphates prepared in Examples 1 to 7 were subjected to X-ray analysis. FIG3 shows the XRD spectra of the iron phosphates with different Mn doping amounts prepared in Examples 1 to 4, and FIG4 shows the XRD spectra of the Mg-, Ni-, and Co-doped iron phosphates prepared in Examples 5 to 7.

As shown in Figure 3, the diffraction peak positions of the Mn-doped iron phosphate samples prepared in Examples 1 to 4 are consistent with the standard iron phosphate card, and no impurity peaks exist, indicating that the impregnation doping method provided by the present invention can effectively achieve the incorporation of manganese elements without generating other impurity phases.

As shown in Figure 4, the diffraction peak positions of the Mg-doped, Ni-doped, and Co-doped iron phosphate samples prepared in Examples 5 to 7 are consistent with the standard cards of iron phosphate, and no impurity peaks exist, indicating that the immersion doping method provided by the present invention can effectively achieve the incorporation of magnesium, nickel, and cobalt elements without producing other impurity phases.

Experiment 4

The white slurry B obtained in step S2 of Example 1, i.e., the dihydrate iron phosphate slurry, is dried and then subjected to electron microscopy scanning and X-ray diffraction analysis. FIG1 is a scanning electron microscope image of dihydrate iron phosphate. It can be seen from FIG1 that the primary particles of dihydrate iron phosphate prepared by the present invention are fine and uniformly dispersed, have a high specific surface area, and can better adsorb doped metals.

FIG2 is an XRD diagram of ferric phosphate dihydrate. It can be seen from FIG2 that the ferric phosphate dihydrate prepared by the present invention is a pure phase and does not contain other impurity phases.

Claims (10)

1. A doped modified ferric phosphate, wherein metal elements are doped into the ferric phosphate to improve chemical properties and electrical conductivity, characterized in that the metal elements are one or more of Ni, Co, Mn, Mg, V, Ti, Al, Cu, Zn, W, Cr, Zr, La, Mo, Nb, Ga, and Y. 2. A doped modified ferric phosphate as claimed in claim 1, characterized in that the doping amount of the metal element is 0-8000 ppm. 3. The doped modified ferric phosphate according to claim 1, characterized in that the preparation method of the doped modified ferric phosphate is as follows: S1, synthesis reaction: prepare a hydrogen peroxide solution with a mass concentration of 10-30wt%, a ferrous salt solution with a mass concentration of 0.5-2.0 mol/L, and a phosphate solution with a mass concentration of 0.5-2.0 mol/L respectively; using pure water as the bottom liquid of the reactor, adding the hydrogen peroxide solution, the phosphate solution and the ferrous salt solution into the reactor, and obtaining a yellow slurry A, i.e., basic ammonium ferric phosphate slurry, through a synthesis reaction; the pH of the synthesis reaction is ≤2.5; S2, conversion reaction: prepare a phosphoric acid solution with a mass concentration of 30-85wt%, perform solid-liquid separation and washing treatment on the yellow slurry A obtained in step S1 to obtain a yellow filter cake A; mix the yellow filter cake A with pure water to make a slurry, then add the phosphoric acid solution, perform heating and heat preservation treatment, and obtain a white slurry B through a conversion reaction; S3, impregnation reaction: prepare doped metal liquid, perform the first solid-liquid separation and washing treatment on the white slurry B obtained in step S2 to obtain a white filter cake B; mix the white filter cake B with pure water and doped metal liquid to slurry, stir and react for 1-3 hours to obtain slurry C, and perform solid-liquid separation on the slurry C to obtain filter cake C and filtrate C; S4, drying and calcining: flash drying, calcining and crushing the filter cake C in step S3 to obtain doped modified iron phosphate; S5. Recovery: The filtrate C recovered from S3 is subjected to precise filtration to remove tiny particles and is recycled for the preparation of doped metal liquid. 4. A doped modified ferric phosphate as claimed in claim 3, characterized in that in the step S1: the ferrous salt solution is prepared from any one of ferrous sulfate, ferrous nitrate, ferrous chloride, iron powder, and iron sheet; the phosphate salt solution is prepared from any one of ammonium monohydrogen phosphate, diammonium phosphate, ammonium phosphate, and phosphoric acid; the molar ratio of hydrogen peroxide in the hydrogen peroxide solution to the molar ratio of iron element in the ferrous salt solution is n( _Fe ):n( _H2O2 )=1:0.5-1:1; the molar ratio of phosphorus element in the phosphate salt solution to the molar ratio of iron element in the ferrous salt solution is n(Fe):n(P)=1:0.9-1:1.2. 5. A doped modified iron phosphate as described in claim 3, characterized in that, in the step S3, the doped metal liquid does not contain sulfate and phosphate, and the doped metal liquid is prepared by reacting the metal oxide corresponding to the metal element with nitric acid/organic acid. 6. The doped modified ferric phosphate according to claim 3, characterized in that in the step S3, the doped metal liquid is prepared from a soluble salt corresponding to the metal element and water. 7. A doped modified ferric phosphate as described in claim 3, characterized in that when the doped modified ferric phosphate contains metal elements Ti, Al, and V, the ferrous salt solution in step S1 also contains corresponding soluble metal salts, and the soluble metal salts include titanium sulfate, aluminum sulfate, and ammonium metavanadate. 8. The doped modified ferric phosphate according to claim 3, characterized in that the specific surface area of the white filter cake B obtained in step S3 after drying is 60-100 ^m2 /g; and the temperature of the conversion reaction in step S2 is raised to 75-95°C and kept for 0.5-3.5h during the heating and heat preservation treatment. 9. A doped modified iron phosphate as claimed in claim 3, characterized in that in the step S3, the white filter cake B is mixed with the doped metal liquid for pulping to obtain a mixed slurry, the solid content of the mixed slurry is 20-40%; the concentration of metal ions in the doped metal liquid is 0.01-2.0 mol/L. 10. A doped modified ferric phosphate as described in claim 3, characterized in that, when the slurry C is subjected to solid-liquid separation treatment in step S3, the equipment used is a filter press, and during the solid-liquid separation process, the pressing pressure of the filter press needs to be controlled to be 0.8-1.2 MPa, the blowing time is 5-20 min, and the moisture content in the filter cake C is 40-50%.