CN110562947A - Cationic metal impurity removing agent and application thereof - Google Patents

Abstract

the invention relates to a metal cation impurity removing agent, which comprises the following components: complexing dispersant, buffering agent and precipitating agent. The impurity removing agent can be suitable for removing metal cation impurities contained in a washing liquid obtained by filtering and collecting a mother liquid remaining after iron phosphate crystallization and washing the iron phosphate crystallization in the process of preparing the iron phosphate by taking iron and phosphoric acid as raw materials. The impurity removing agent provided by the invention adopts the principle of dispersion complexation-agglomeration-sedimentation, can effectively remove metal cation impurities in the solution, and enables the filtrate obtained in the process of preparing the iron phosphate by the phosphoric acid method to be recycled, thereby reducing the production cost, ensuring the product purity, reducing the discharge of waste liquid and improving the environment.

Description

Cationic metal impurity removing agent and application thereof

Technical Field

the invention belongs to the technical field of inorganic new materials, and particularly relates to a cationic metal impurity removing agent and application thereof in a preparation process of battery-grade anhydrous ferric phosphate with a sheet structure.

background

The ferric phosphate is mainly used for preparing a precursor of lithium iron phosphate serving as a cathode material of a lithium ion battery, and the preparation process method comprises a sulfuric acid method, an oxalic acid method, a hydrochloric acid method, a nitric acid method and a phosphoric acid method. At present, iron and sulfuric acid react to generate ferrous sulfate solution, hydrogen peroxide is used for oxidation, and then the ferrous sulfate solution reacts with diammonium phosphate or monoammonium phosphate to generate spherical iron phosphate. In the production process, iron powder and phosphoric acid react in a reactor, then oxidation is carried out, crystallization is carried out, water-containing iron phosphate is obtained by filtration, and filtrate and washing liquor are evaporated, concentrated and then added with new phosphoric acid to be prepared to a certain concentration, and then the mixture can be recycled for iron melting.

The iron powder adopted by the process can be iron ore powder selected for many times, high-purity iron ore powder subjected to reduction sintering, electrolytic iron powder, nodular cast iron powder or mixed iron powder of any two or three, but any iron powder contains a plurality of trace impurity metal cations, and metal impurities such as Mn, Ti, K, Na, Cr, Zn, Pb, Ca, Mg, Cu and the like are common. Regardless of the purity and impurity content of the iron powder, after the iron powder is recycled, the metal impurities can enter a ferrous solution, and finally the impurities of the iron phosphate product exceed the standard, so that the performance of the battery product is influenced.

How to remove the harm to the product quality caused by the accumulation of impurity elements in the recycling process of raw materials with low cost and high efficiency is an urgent problem to be solved in the process of producing the iron phosphate.

Disclosure of Invention

the invention aims to overcome the defects of the prior art and provide a metal cation impurity removing agent. The impurity removing agent is preferably suitable for filtering and collecting mother liquor remaining after iron phosphate crystallization and washing liquor after washing the iron phosphate crystallization in the process of preparing iron phosphate by taking iron and phosphoric acid as raw materials. The impurity removing agent provided by the invention adopts the principle of dispersion complexation-agglomeration-sedimentation, can effectively remove impurity elements in the solution, enables the filtrate and wash liquor to be recycled, reduces the production cost, ensures the product purity, reduces the waste liquid discharge and improves the environment.

Specifically, the invention provides a metal cation impurity removing agent, which comprises: complexing dispersant, buffering agent and precipitating agent.

Wherein the molecular formula of the complexing dispersant is C_aH_bN_EO_FWherein a is 3-6, b is 6-8, E is 3-6, and F is 0-3. Specifically, the complex dispersant may be an amine compound or polyamine polyol, such as: triethanolamine, ethylenediamine tetraacetic acid, 1,3, 5-triazine-2, 4, 6-triamine, and the like.

The buffer is an amide organic compound, for example: acetamide, carbamide, ammonium formate, and the like.

the precipitant is an inorganic or organic polymer. In order to realize the optimal precipitation effect, the precipitant is an inorganic polymer with the molecular weight of 1500-2500, such as iron xanthohumate, polymeric ferric sulfate and the like, or an organic polymer with the molecular weight of 1500-2500, such as polyacrylamide and the like.

In order to realize the best dispersion complexation-agglomeration-sedimentation effect, the invention optimizes the contents of the three components. Specifically, the impurity removing agent comprises the following components in percentage by weight: 20-30% of complexing dispersant, 20-30% of buffering regulator and 40-60% of precipitator.

The invention also protects the application of the impurity removing agent in removing metal cation impurities contained in the solution. Wherein the metal cation impurities comprise: one or more of Mn, Ti, K, Na, Cr, Cd, Co, Zn, Ni, Pb, Ca, Mg and Al ions. The impurity removing agent provided by the invention has a better removing effect on Al, Ca, Cr, Mg, Mn, Ni, Po, Zn and Ti ions, and the removing effect on the ions can reach more than 50%. In practical applications, the metal cation impurities may be cations of the metal impurities contained in the iron powder.

Generally, the removal difficulty is greater at lower ion concentrations in the solution. When the content of metal cations in the solution is 0.001 ppm-100 ppm, the impurity removing agent provided by the invention can still realize excellent impurity removing effect.

As a preferred embodiment of the present invention, the solution is: in the process of preparing the iron phosphate by taking iron and phosphoric acid as raw materials, filtering and collecting a mother solution left after the iron phosphate crystals and/or a washing solution obtained after washing the iron phosphate crystals. Preferably, the concentration of the phosphoric acid in the solution is 1-10%, and the conductivity is less than 2000 mu s/m. In the process of preparing the iron phosphate by taking iron and phosphoric acid as raw materials, the filtered solution and the washing solution are subjected to impurity removal and then returned to be used as ingredients, so that the purity requirement of the iron powder can be reduced, and the unit consumption of the phosphoric acid is reduced.

The specific application method of the impurity removing agent provided by the invention is simple to operate and can be as follows: heating the solution to be treated to 50-90 ℃, adding the impurity removing agent, stirring, fully settling, filtering to remove metal precipitates, and collecting a purified solution. Preferably, the addition amount of the impurity removing agent is 0.5-5 g per liter of solution.

The invention further provides a preparation method of the flaky anhydrous iron phosphate, which comprises the following specific steps:

(1) reacting iron powder with phosphoric acid solution to generate Fe (H)₂PO₄)₂A solution;

(2) adding an oxidant into the solution for oxidation reaction, and then crystallizing to generate an iron phosphate precipitate;

(3) solid-liquid separation, collecting solid precipitate and washing, adding the impurity removing agent provided by the invention into the waste liquid obtained by separation and washing to precipitate metal cations in the waste liquid, filtering and collecting filtrate, and returning the filtrate as phosphoric acid solution to the step (1) for reuse;

(4) drying the washed solid precipitate;

(5) And roasting the dried product to obtain the flaky anhydrous iron phosphate.

In the step (1), the iron content of the reduced iron powder is preferably not less than 98%. When the particle size of the reduced iron powder is 60 to 300 meshes, preferably 80 to 200 meshes, more sufficient reaction between the iron powder and the phosphoric acid solution can be ensured. The phosphoric acid solution adopted in the step (1) is a phosphoric acid aqueous solution, and the concentration of the phosphoric acid aqueous solution can be in a wide range of 10-80%, and is preferably 20-45%. The reaction in the step (1) does not need heating, and can be carried out by stirring at 0-40 ℃, preferably at normal temperature. Under the conditions, the dissolution rate of the iron powder in the reaction in the step (1) can reach more than 95%.

The oxidant adopted in the step (2) can be one or a mixture of two or more of hydrogen peroxide solution, ozone and oxygen-enriched air. When oxygen-enriched air is adopted, the oxygen content is preferably 25-99.9%. In order to ensure that a large amount of iron sulfate precipitate with good morphology is formed, the step (2) of the invention is further subjected to a crystallization step after the oxidation reaction, and the crystallization is preferably carried out at 85-95 ℃. The crystallization time is based on obtaining a large amount of ferric sulfate precipitate with good form, and the crystallization can be formed by generally performing the crystallization for 1-3 hours.

The drying mode of the ferric sulfate precipitate in the step (4) is preferably airflow flash drying, and the temperature of the airflow is preferably 180-200 ℃. Under the above-mentioned drying conditions, a good morphological structure of the product is ensured.

The roasting in the step (5) is preferably carried out at 500-700 ℃. Under the above roasting conditions, the product can be ensured to have a good morphological structure.

compared with the prior art, the impurity removing agent provided by the invention adopts the principle of dispersion complexation-agglomeration-sedimentation, can effectively remove metal cation impurities in a solution, and enables a filter washing liquid obtained in the process of preparing iron phosphate by a phosphoric acid method to be recycled, so that the production cost is reduced, the product purity is ensured, the waste liquid discharge is reduced, and the environment is improved.

Drawings

FIG. 1 is a schematic flow chart of a method for using an impurity removing agent in example 4.

Detailed Description

Preferred embodiments of the present invention will be described in detail with reference to the following examples.

Example 1

This example provides a metal cation dedoping agent consisting of 20% 1,3, 5-triazine-2, 4, 6-triamine, 20% carbamide, and 60% polyacrylamide.

Example 2

This example provides a metal cation impurity removing agent, which is composed of 30% of ethylenediamine tetraacetic acid, 30% of amine formate, and 40% of fulvic acid iron.

Example 3

This example provides a metal cation dedoping agent, which is composed of 25% of triethanolamine, 25% of acetamide, and 50% of polyferric sulfate.

Example 4

This example provides a method for removing metal cation impurities from a solution using the scavenger provided in example 3.

the solution to be treated is prepared by the following method:

(1) Adding reduced iron powder into a reactor, adding 45% phosphoric acid solution, starting stirring, carrying out iron-melting reaction, and directly discharging discharged hydrogen into the atmosphere through an upper fan; after reacting for 3-4 hours, filtering to remove undissolved residue, and obtaining green Fe (H)₂PO₄)₂Solution, and determining the molarity of the solution;

(2) Slowly adding H to the solution₂O₂Adding the solution while stirring, wherein the adding amount of hydrogen peroxide is 10% more than the calculated theoretical amount (counted by taking the molar concentration of the solution obtained in the step (1)) and then continuously stirring, after the adding is finished, heating to 90 ℃ while stirring, keeping the temperature for 2 hours to crystallize, and generating iron phosphate precipitate;

(3) Separating solid and liquid, collecting filtrate (phosphoric acid content is 6%), collecting solid precipitate, and washing until the washing liquid conductivity reaches below 200 us/m.

Taking the filtrate and lotion obtained by the method as a solution to be treated, heating to 80 ℃, adding 2 per mill of an impurity removing agent (volume weight ratio, 1L of solution is added with 2g of the impurity removing agent) according to volume, stirring for 5 minutes, stopping stirring, settling for 15 minutes, and filtering out precipitates to obtain a purified solution. The flow of the above-described processing procedure can be referred to as shown in fig. 1.

The results of removing impurities from the solution are shown in Table 1.

Table 1: conditions of impurity removal

As is clear from Table 1, the removal rate of the impurity removing agent provided by the present invention for cationic metal elements such as Al, Ca, Cr, Mg, Mn, Ni, Po, Zn, Ti and the like in the solution was 60% or more.

Although the invention has been described in detail hereinabove by way of general description, specific embodiments and experiments, it will be apparent to those skilled in the art that many modifications and improvements can be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.

Claims (10)

1. A metal cation impurity removing agent is characterized by comprising the following components: complexing dispersant, buffering agent and precipitating agent;

The molecular formula of the complexing dispersant is C_aH_bN_EO_FWherein a is 3-6, b is 6-8, E is 3-6, and F is 0-3;

The buffer is an amide organic compound;

The precipitant is an inorganic or organic polymer.

2. the metal cation impurity removing agent according to claim 1, wherein the complexing dispersant is an amine compound or polyamine polyol, preferably one or more of triethanolamine, ethylenediamine tetraacetic acid, 1,3, 5-triazine-2, 4, 6-triamine.

3. the metal cation impurity removing agent according to any one of claims 1 to 2, wherein the precipitant is an inorganic or organic polymer with a molecular weight of 1500 to 2500, preferably one or more of iron xanthohumate, polymeric ferric sulfate and polyacrylamide.

4. A metal cation impurity removing agent according to any one of claims 1 to 3, characterized by comprising the following components in percentage by weight: 20-30% of complexing dispersant, 20-30% of buffering regulator and 40-60% of precipitator.

5. Use of the agent according to any one of claims 1 to 4 for removing metal cation impurities contained in a solution.

6. the use according to claim 5, wherein the metal cation impurities comprise: one or more of Mn, Ti, K, Na, Cr, Cd, Co, Zn, Ni, Pb, Ca, Mg and Al ions, preferably one or more of Al, Ca, Cr, Mg, Mn, Ni, Po, Zn and Ti ions;

more preferably, the metal cation impurities are cations of the metal impurities contained in the iron powder.

7. use according to claim 5 or 6, wherein the metal cation is present in the solution in an amount of 0.001ppm to 100 ppm.

8. the use according to any one of claims 5 to 7, wherein the solution is: in the process of preparing the iron phosphate by taking iron and phosphoric acid as raw materials, filtering and collecting a mother solution left after iron phosphate crystallization, and/or a washing solution obtained after washing the iron phosphate crystallization;

Preferably, the concentration of the phosphoric acid in the solution is 1-10%, and the conductivity is less than 2000 mu s/m.

9. The application according to any one of claims 5 to 8, wherein the specific application method is as follows: heating the solution to be treated to 50-90 ℃, adding the impurity removing agent, stirring, fully settling, filtering to remove metal precipitates, and collecting a purified solution;

Preferably, the addition amount of the impurity removing agent is 0.5-5 g per liter of solution.

10. a preparation method of sheet anhydrous iron phosphate is characterized by comprising the following steps:

(1) Reacting iron powder with phosphoric acid solution to generate Fe (H)₂PO₄)₂A solution;

(2) Adding an oxidant into the solution for oxidation reaction, and then crystallizing to generate an iron phosphate precipitate;

(3) Solid-liquid separation, collecting solid precipitate and washing, adding the impurity removing agent of any one of claims 1 to 4 into the waste liquid obtained by the separation and washing to precipitate metal cations in the waste liquid, filtering and collecting filtrate, and returning the filtrate as a phosphoric acid solution to the step (1) for reuse;

(4) drying the washed solid precipitate;

(5) And roasting the dried product to obtain the flaky anhydrous iron phosphate.