CN115818605A - Iron phosphate dihydrate, preparation method thereof and preparation method of lithium iron phosphate cathode material - Google Patents

Abstract

The invention discloses ferric phosphate dihydrate and a preparation method thereof, and a preparation method of a lithium iron phosphate anode material, and belongs to the technical field of new energy materials of lithium batteries. The method comprises the following steps: removing metal ion impurities in the high-impurity phosphoric acid by using a fluorine-free impurity removal reagent to obtain impurity-removed phosphoric acid; extracting and back extracting the purified phosphoric acid in sequence to obtain purified phosphoric acid; converting an iron source in waste ferrous sulfate in the titanium dioxide industry into ferric hydroxide under the action of an oxidant and a precipitator; mixing purified phosphoric acid and ferric hydroxide, adding alkali liquor to adjust the pH value, performing solid-liquid separation after obtaining a precipitate, and collecting a solid phase substance to obtain ferric phosphate dihydrate. The method adopts two raw materials with high impurity content, and has wide source range and low cost; the synthesized ferric phosphate dihydrate has high purity and good solubility under an acidic condition, can meet the requirement of preparing a lithium iron phosphate battery by a liquid phase method, and achieves the purpose of changing waste into valuable.

Description

Iron phosphate dihydrate and preparation method thereof, preparation method of lithium iron phosphate cathode material

technical field

The invention relates to the technical field of new energy materials for lithium batteries, in particular to iron phosphate dihydrate and a preparation method thereof, and a preparation method of lithium iron phosphate cathode material.

Background technique

There are many metal ion impurities in the high heterophosphoric acid obtained from ore. These impurities are not only high in content but also rich in variety, which seriously reduces the application value of high heterophosphoric acid. Among them, aluminum impurities are particularly difficult to deal with. At present, the common practice is to form aluminum hydroxide to remove impurities by increasing the pH of phosphoric acid. separate. Some people also introduce fluoride to form aluminum fluoride precipitation to remove impurities. Although the removal effect of this method is very good, the fluorine-containing waste residue obtained after the removal of impurities is difficult to handle and does not meet the environmental protection requirements; Fluoride ions are highly corrosive to equipment, which will not only lead to a significant increase in equipment costs, but also increase the danger in the production process.

In the process of producing titanium dioxide, a lot of ferrous sulfate heptahydrate will be produced incidentally, which has high impurities and large output, and there is no high-profit treatment method.

In view of this, the present invention is proposed.

Contents of the invention

One of the objectives of the present invention is to provide a method for preparing ferric phosphate dihydrate, which can meet the requirements of liquid-phase method for preparing lithium iron phosphate batteries, and realize the purpose of turning high-impurity phosphoric acid and waste ferrous sulfate into treasure.

The second object of the present invention is to provide a ferric phosphate dihydrate prepared by the above method.

The third object of the present invention is to provide a method for further preparing lithium iron phosphate cathode material from the above-mentioned iron phosphate dihydrate.

This application can be implemented like this:

First aspect, the application provides a kind of preparation method of ferric phosphate dihydrate, comprises the following steps:

Use a fluorine-free impurity-removing reagent to remove metal ion impurities in high-impurity phosphoric acid to obtain impurity-removing phosphoric acid;

The impurity-removing phosphoric acid is extracted and back-extracted in sequence to obtain purified phosphoric acid;

The iron source in the titanium dioxide industrial waste ferrous sulfate is converted into ferric hydroxide under the action of oxidant and precipitant;

After the purified phosphoric acid and ferric hydroxide are mixed, lye is added to adjust the pH value, after precipitation is obtained, the solid-liquid is separated, and the solid phase is collected to obtain ferric phosphate dihydrate.

In an optional embodiment, the purity of high-impurity phosphoric acid is not lower than 45%, wherein the content of aluminum is not more than 2wt%, and the content of magnesium is not more than 1wt%;

And/or, the mass of iron element in the titanium dioxide industrial waste ferrous sulfate is not less than 18wt%.

In an optional embodiment, the fluorine-free impurity removal reagent includes organic substances with hydrophilic groups and substances that provide sulfate ions and ammonium ions.

In an optional embodiment, the content of organic matter with hydrophilic groups in the fluorine-free impurity removal agent is 10-50 wt%.

In an optional embodiment, the organic substance with a hydrophilic group includes soluble alcohol and/or acetone.

In alternative embodiments, the soluble alcohol includes methanol and/or ethanol.

In an optional embodiment, the substance providing sulfate ions and ammonium ions is a mixture of sulfuric acid and ammonia water, or the substance providing sulfate ions and ammonium ions is a mixture of sulfuric acid and ammonium sulfate or ammonium bisulfate .

In an optional embodiment, in the fluorine-free impurity removal reagent, the content of sulfuric acid is 1-50wt%, the content of ammonia water is 1-50wt%, the content of ammonium sulfate is 1-50wt%, and the content of ammonium bisulfate is 1 -50 wt%.

In an optional embodiment, the removal of metal ion impurities in high-impurity phosphoric acid by the fluorine-free impurity removal reagent is carried out at 20-30° C., and the impurity removal time is 0.5-6 hours.

In an optional embodiment, the dosage of the fluorine-free impurity removal agent is 5-20wt% of the high-impurity phosphoric acid.

In an optional embodiment, the extractant used for extraction includes at least one of P204, tributyl phosphate, N923, isobutanol and sulfonated kerosene.

In an optional embodiment, the extraction is carried out at 5-50° C. for 2-20 minutes.

In an optional embodiment, during extraction, the volume ratio of the organic phase to the aqueous phase is 1:2-4:1.

In an optional embodiment, the stripping agent used for stripping is water or acid.

In an alternative embodiment, the acid includes at least one of sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid.

In an optional embodiment, the mass concentration of the acid is 1-10%.

In an optional embodiment, during stripping, the volume ratio of the organic phase to the aqueous phase is 4:1-2:1.

In an optional embodiment, the addition amount of the oxidizing agent is 1-15wt% of the solution of titanium dioxide industrial waste ferrous sulfate.

In an optional embodiment, the oxidizing agent includes at least one of hydrogen peroxide, ozone and nitric acid.

In an optional embodiment, the precipitant is used to control the pH value of the titanium dioxide industrial waste ferrous sulfate solution at 1-4.

In an optional embodiment, the precipitation agent includes at least one of ammonia water, KOH and NaOH.

In an optional embodiment, the pH adjusted by the lye is 2-4.

In an optional embodiment, the lye includes at least one of ammonia water, KOH and NaOH.

In a second aspect, the present application provides a ferric phosphate dihydrate, which is prepared by the above-mentioned method for preparing ferric phosphate dihydrate.

In a third aspect, the present application provides a method for preparing a lithium iron phosphate cathode material, comprising the steps of:

According to the preparation method of above-mentioned ferric phosphate dihydrate, ferric phosphate dihydrate is obtained;

The obtained iron phosphate dihydrate is mixed with a lithium source to prepare a lithium iron phosphate cathode material.

The beneficial effects of the application include:

The high-impurity phosphoric acid and titanium dioxide industrial waste ferrous sulfate used in this application are both raw materials with high impurity content, a wide range of sources, and low cost; the purified phosphoric acid is obtained by removing impurities in high-impurity phosphoric acid, and the industrial waste of titanium dioxide The iron source in ferrous sulfate is converted into ferric hydroxide under the action of oxidant and precipitant, and then the obtained purified phosphoric acid and ferric hydroxide are co-precipitated to synthesize ferric phosphate dihydrate with high purity. It has good solubility under certain conditions, can meet the needs of preparing lithium iron phosphate batteries by liquid phase method, and realizes the purpose of turning waste into treasure. In addition, the fluorine-free impurity removal reagent used in the impurity removal process of high-impurity phosphoric acid has environmental advantages, is less corrosive to equipment, and greatly reduces production costs and operational risks. The obtained ferric phosphate dihydrate can be further used to prepare phosphoric acid Lithium iron cathode material.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus It should be regarded as a limitation on the scope, and those skilled in the art can also obtain other related drawings based on these drawings without creative work.

Fig. 1 is the schematic flow sheet of the preparation method of a kind of ferric phosphate dihydrate provided by the application;

Fig. 2 is a flowchart of the preparation method of ferric phosphate dihydrate provided in the examples of the present application.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those who do not indicate the specific conditions in the examples are carried out according to the conventional conditions or the conditions suggested by the manufacturer. The reagents or instruments used were not indicated by the manufacturer, and they were all conventional products that could be purchased from the market.

The ferric phosphate dihydrate provided in the present application and the preparation method thereof, and the preparation method of the lithium iron phosphate positive electrode material are described in detail below.

As shown in Figure 1, the application proposes a kind of preparation method of ferric phosphate dihydrate, comprises the following steps:

Use a fluorine-free impurity-removing reagent to remove metal ion impurities in high-impurity phosphoric acid to obtain impurity-removing phosphoric acid;

The impurity-removing phosphoric acid is extracted and back-extracted in sequence to obtain purified phosphoric acid;

The iron source in the titanium dioxide industrial waste ferrous sulfate is converted into ferric hydroxide under the action of oxidant and precipitant;

After the purified phosphoric acid and ferric hydroxide are mixed, lye is added to adjust the pH value, after precipitation is obtained, the solid-liquid is separated, and the solid phase is collected to obtain ferric phosphate dihydrate.

In some optional embodiments, the purity of the above-mentioned high-impurity phosphoric acid is not less than 45%, such as 45%, 50%, 55%, 60%, 65% or 70%, or ≥ 45% other values within. Exemplarily, in the high-impurity phosphoric acid, the aluminum content does not exceed 2wt% (such as 2wt%, 1.8wt%, 1.5wt%, 1.2wt%, 1wt%, 0.8wt%, 0.5wt% or 0.2wt%, etc.), The magnesium content is not more than 1wt% (such as 1wt%, 0.8wt%, 0.5wt%, 0.2wt%, 0.1wt% or 0.05wt%, etc.).

It should be noted that if the purity of high-impurity phosphoric acid is lower than 45%, the impurities in the final product will not meet the standard.

The quality of the iron element in the titanium dioxide industrial waste ferrous sulfate is not less than 18wt%, such as 18wt%, 20wt%, 25wt%, 30wt%, 40wt% or 50wt%, and other values within the range of ≥ 18wt%.

The high-impurity phosphoric acid and titanium dioxide industrial waste ferrous sulfate with the above characteristics have a wide range of sources, low cost, and can be combined to prepare ferric phosphate dihydrate, achieving the effect of turning waste into treasure.

In the present application, the amount of fluorine-free impurity removal reagent can be 5-20wt% of high-impurity phosphoric acid, such as 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt% or 20wt%, etc., can also be 5-20wt%. Any other value within the range of 20wt%.

Controlling the dosage of the fluorine-free impurity-removing agent within the above-mentioned range can ensure the complete precipitation of metal impurities in the high-heterophosphoric acid.

For reference, the above-mentioned fluorine-free impurity removal reagents include organic substances with hydrophilic groups and substances that provide sulfate ions and ammonium ions.

That is to say, the fluorine-free impurity removal agent contains hydrophilic groups, sulfate ions and ammonium ions at the same time.

Among them, the function of sulfate ion is mainly to remove aluminum; the function of ammonium ion is mainly used to form ammonium aluminum sulfate; the hydrophilic group is mainly used to reduce the solubility of ammonium aluminum sulfate precipitation and form an insoluble system.

The above-mentioned fluorine-free impurity removal reagent does not contain fluorine, and the sulfate ions and ammonium ions contained in it can form ammonium sulfate salt precipitation with metal impurities in high-heterophosphoric acid, and then the extraction process is used to further remove other impurities to obtain purification. Phosphoric acid, the whole process is simple and environmentally friendly, less corrosive to equipment, greatly reducing production costs and operational risks.

Exemplarily, the content of organic matter with hydrophilic groups in the fluorine-free impurity removal agent can be 10-50wt%, such as 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt% % or 50wt%, etc., can also be any other value within the range of 10-50wt%. Correspondingly, the content of substances providing sulfate ions and ammonium ions is 100wt% minus the content of organic matter with hydrophilic groups.

It should be noted that the salt formed by the fluorine-free reagent and the impurity ions in the high-heterophosphoric acid has a high solubility in water, and the original single aqueous solution system will be changed after adding organic matter, so the corresponding salt can be precipitated smoothly. Controlling the content of organic compounds with hydrophilic groups in the fluorine-free impurity removal agent to 10-50wt% can reduce the solubility of corresponding compounds and achieve the effect of efficient impurity removal. The above-mentioned organic substance with a hydrophilic group can be exemplarily acetone, and also can be soluble alcohols, such as methanol or ethanol.

For reference, the substance providing sulfate ions and ammonium ions is a mixture of sulfuric acid and ammonia water, or a mixture of sulfuric acid and ammonium sulfate, or a mixture of sulfuric acid and ammonium bisulfate. In other words, both sulfuric acid and ammonia water can be used in combination, ammonium sulfate and sulfuric acid can also be used in combination, and ammonium bisulfate and sulfuric acid can also be used in combination.

When using the combination of sulfuric acid and ammonia water, the content of sulfuric acid can be controlled to 1-50wt% in the mixed solution of sulfuric acid and ammonia water, such as 1wt%, 2wt%, 5wt%, 10wt%, 20wt%, 30wt% , 40wt% or 50wt%, etc., can also be any other value within the range of 1-50wt%. Correspondingly, the content of ammonia water is 100wt% minus the content of sulfuric acid. Certainly, also can be that the content of ammonia water is controlled as 1-50wt%, such as 1wt%, 2wt%, 5wt%, 10wt%, 20wt%, 30wt%, 40wt% or 50wt% etc., also can be in the range of 1-50wt% any other value of . Correspondingly, the content of sulfuric acid is 100wt% minus the content of ammonia water.

Similarly, when sulfuric acid and ammonium sulfate are used together, in the mixed solution of sulfuric acid and ammonium sulfate, the content of sulfuric acid can be controlled to 1-50wt%, such as 1wt%, 2wt%, 5wt%, 10wt% , 20wt%, 30wt%, 40wt% or 50wt%, etc., can also be any other value within the range of 1-50wt%. Correspondingly, the content of ammonium sulfate is 100wt% minus the content of sulfuric acid. Certainly, also can be that the content of ammonium sulfate is controlled as 1-50wt%, such as 1wt%, 2wt%, 5wt%, 10wt%, 20wt%, 30wt%, 40wt% or 50wt% etc., also can be 1-50wt% scope Any other value within . Correspondingly, the content of sulfuric acid is 100wt% minus the content of ammonium sulfate.

Similarly, when sulfuric acid and ammonium bisulfate are used together, in the mixed solution of sulfuric acid and ammonium bisulfate, the content of sulfuric acid can be controlled to 1-50wt%, such as 1wt%, 2wt%, 5wt%, 10wt%, 20wt%, 30wt%, 40wt% or 50wt%, etc., can also be any other value within the range of 1-50wt%. Correspondingly, the content of ammonium bisulfate is 100wt% minus the content of sulfuric acid. Certainly, also can be that the content of ammonium bisulfate is controlled as 1-50wt%, such as 1wt%, 2wt%, 5wt%, 10wt%, 20wt%, 30wt%, 40wt% or 50wt% etc., also can be 1-50wt% Any other value within the range. Correspondingly, the content of sulfuric acid is 100wt% minus the content of ammonium bisulfate.

It is worth noting that the composition of the fluorine-free impurity removal reagent is very important. Improper ratio or lack of ingredients will lead to failure to remove impurities. If the ratio is too high, the cost will increase.

In some embodiments, the fluorine-free impurity removal reagent removes metal ion impurities in high-impurity phosphoric acid at 20-30°C (such as 20°C, 22°C, 25°C, 28°C or 30°C, etc.) 6h (such as 0.5h, 1h, 2h, 3h, 4h, 5h or 6h, etc.).

It should be noted that the above-mentioned use of fluorine-free impurity removal reagents to remove metal impurities is essentially chemical removal of impurities. The sulfate ions and ammonium ions in the fluorine-free impurity removal reagents chemically react with metal impurities to form ammonium sulfate salts. Salt precipitates can be removed by solid-liquid separation (such as filtration).

For reference, the extractant used in the extraction process may include at least one of P204, tributyl phosphate (TBP), N923, isobutanol and sulfonated kerosene.

Extraction can be carried out at 5-50°C (such as 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, etc.) for 2-20min (such as 2min , 5min, 10min, 15min or 20min, etc.).

During extraction, the volume ratio of the organic phase to the aqueous phase can be 1:2-4:1, such as 1:2, 1:1, 2:1, 3:1 or 4:1.

It should be noted that when the volume of the aqueous phase is too small, the extraction efficiency is high, but the corresponding cost is high; when the volume of the aqueous phase is too large, the extraction efficiency is low and the removal of impurities is incomplete.

Through the extraction process, the impurities dissolved in the water phase in the impurity-removing phosphoric acid can be removed.

For reference, the stripping agent used for stripping is water or acid.

Wherein, the acid may include at least one of sulfuric acid, nitric acid, hydrochloric acid and phosphoric acid.

The mass concentration of the acid may be 1-10%, such as 1wt%, 2wt%, 5wt%, 8wt% or 10wt%, or any other value within the range of 1-10%.

It should be noted that if the mass concentration of the acid is too high, the components in the organic phase cannot be recovered; if the mass concentration of the acid is too low, the organic matter will be unstable under strong acid.

During stripping, the volume ratio of the organic phase to the aqueous phase can be 4:1-2:1, such as 4:1, 3.5:1, 3:1, 2.5:1 or 2:1, etc., or 4:1 Any other value in the range of -2:1.

Purified phosphoric acid dissolved in the water phase can be obtained by stripping.

It should be noted that the essence of the above-mentioned extraction and back-extraction process is extraction and impurity removal, so as to obtain purified phosphoric acid by means of physical impurity removal.

In the process of preparing ferric hydroxide from titanium dioxide industrial waste ferrous sulfate, the titanium dioxide industrial waste ferrous sulfate is dissolved in water, and the amount of oxidant is controlled to be 1-15wt% of the solution of titanium dioxide industrial waste ferrous sulfate. Such as 1wt%, 2wt%, 5wt%, 8wt%, 10wt%, 12wt% or 15wt%, etc., can also be any other value within the range of 1-15wt%.

For reference, the oxidizing agent exemplarily includes at least one of hydrogen peroxide, ozone and nitric acid.

The precipitating agent is mainly used to control the pH value of the solution of titanium dioxide industrial waste ferrous sulfate at 1-4 (such as 1, 1.5, 2, 2.5, 3, 3.5 or 4, etc.), so that ferric hydroxide can be precipitated.

For reference, the precipitating agent may be at least one of ammonia water, KOH and NaOH.

Under the joint action of the oxidizing agent and the precipitating agent, the iron source in the industrial waste ferrous sulfate of titanium dioxide can react with the hydroxide ion under the trivalent to form ferric hydroxide precipitation.

Further, the lye can be adjusted at a pH of 2-4 (such as 2, 2.5, 3, 3.5 or 4, etc.).

During the reaction, the lye includes at least one of ammonia water, KOH and NaOH.

Further, the product after the precipitation reaction of purified phosphoric acid and ferric hydroxide is washed and dried to obtain ferric phosphate dihydrate.

Continuing from the above, the ferric phosphate dihydrate synthesized by the above method provided by this application has high purity, low technical difficulty, and good solubility under acidic conditions, which can meet the needs of preparing lithium iron phosphate batteries by liquid phase method, and realize the transformation of waste into treasure. the goal of.

The features and performances of the present invention will be further described in detail below in conjunction with the embodiments and accompanying drawing 2 .

Example 1

This embodiment provides a method for preparing ferric phosphate dihydrate by using high-impurity phosphoric acid and titanium dioxide industrial waste ferrous sulfate. The specific steps are as follows:

(1) Chemical impurity removal of high-heterophosphoric acid: 40% ammonium sulfate, 20% sulfuric acid and 40% acetone are made into a fluorine-free impurity removal reagent, and then 20g of prepared fluorine-free impurity removal is added to 100g of high-heterophosphoric acid Reagent, react at room temperature for 3 hours and then filter, so that the metal impurities in phosphoric acid form ammonium sulfate precipitates to be removed, and impurity-removed phosphoric acid is obtained.

(2) Extraction and impurity removal of high-heterophosphoric acid: first make 40ml tributyl phosphate, 30ml isobutanol and 30ml sulfonated kerosene as extraction agent, then add 100g of impurity-removing phosphoric acid obtained in step (1), and extract at 25°C for 20min Separate layers, remove the raffinate, add 100ml of water to the organic phase (100ml), and back-extract for 10min at 25°C to obtain purified phosphoric acid.

(3) Ferrous sulfate heptahydrate removal of impurities: the waste ferrous sulfate heptahydrate obtained in the production of titanium dioxide process is dissolved in water, then add 10% hydrogen peroxide of the solution quality, and use ammonia to control the pH value of the solution to 1, with Obtain cleaner ferric hydroxide iron precipitation.

(4) Synthesis of ferric phosphate dihydrate: add the purified phosphoric acid in step (2) to the ferric hydroxide obtained in step (3), then use ammonia water at room temperature to adjust the pH value of the solution to 4, filter and wash the precipitate obtained , After drying, high-purity ferric phosphate dihydrate can be obtained.

Example 2

This embodiment provides a method for preparing ferric phosphate dihydrate by using high-impurity phosphoric acid and titanium dioxide industrial waste ferrous sulfate. The specific steps are as follows:

(1) Chemical impurity removal of high-heterophosphoric acid: 40% ammonium sulfate, 20% sulfuric acid and 40% acetone are made into a fluorine-free impurity removal reagent, and then 20g of prepared fluorine-free impurity removal is added to 100g of high-heterophosphoric acid Reagent, react at room temperature for 3 hours and then filter, so that the metal impurities in phosphoric acid form ammonium sulfate precipitates to be removed, and impurity-removed phosphoric acid is obtained.

(2) Extraction and impurity removal of high-heterophosphoric acid: first make 40ml tributyl phosphate, 30ml isobutanol and 30ml sulfonated kerosene as extraction agent, then add 100g of impurity-removing phosphoric acid obtained in step (1), and extract at 25°C for 20min Separate layers, remove the raffinate, add 100ml of water to the organic phase (100ml) and back-extract at 25°C for 10min to obtain purified phosphoric acid.

(3) Ferrous sulfate heptahydrate removal of impurities: the waste ferrous sulfate heptahydrate obtained in the production of titanium dioxide process is dissolved in water, then add 10% hydrogen peroxide of solution quality, and use ammonia to control the pH value of the solution to 4, with Obtain cleaner ferric hydroxide iron precipitation.

(4) Synthesis of ferric phosphate dihydrate: add the purified phosphoric acid in step (2) to the ferric hydroxide obtained in step (3), then use ammonia water at room temperature to adjust the pH value of the solution to 4, filter and wash the precipitate obtained , After drying, high-purity ferric phosphate dihydrate can be obtained.

Example 3

This embodiment provides a method for preparing ferric phosphate dihydrate by using high-impurity phosphoric acid and titanium dioxide industrial waste ferrous sulfate. The specific steps are as follows:

(1) Chemical impurity removal of high-heterophosphoric acid: 40% ammonium sulfate, 20% sulfuric acid and 40% acetone are made into a fluorine-free impurity removal reagent, and then 20g of prepared fluorine-free impurity removal is added to 100g of high-heterophosphoric acid Reagent, react at room temperature for 3 hours and then filter, so that the metal impurities in phosphoric acid form ammonium sulfate precipitates to be removed, and impurity-removed phosphoric acid is obtained.

(2) Extraction and impurity removal of high-heterophosphoric acid: first make 40ml tributyl phosphate, 30ml isobutanol and 30ml sulfonated kerosene as extraction agent, then add 100g of impurity-removing phosphoric acid obtained in step (1), and extract at 25°C for 20min Separate layers, remove the raffinate, add 100ml of water to the organic phase (100ml) and back-extract at 25°C for 10min to obtain purified phosphoric acid.

(3) Ferrous sulfate heptahydrate removal of impurities: the waste ferrous sulfate heptahydrate obtained in the production of titanium dioxide process is dissolved in water, then add 10% hydrogen peroxide of solution quality, and use ammonia water to control the pH value of the solution to 2, to Obtain cleaner ferric hydroxide iron precipitation.

(4) Synthesis of ferric phosphate dihydrate: add the purified phosphoric acid in step (2) to the ferric hydroxide obtained in step (3), then use ammonia water at room temperature to adjust the pH value of the solution to 2, filter and wash the precipitate obtained , After drying, high-purity ferric phosphate dihydrate can be obtained.

Example 4

This embodiment provides a method for preparing ferric phosphate dihydrate by using high-impurity phosphoric acid and titanium dioxide industrial waste ferrous sulfate. The specific steps are as follows:

(1) Chemical impurity removal of hyperheterophosphoric acid: 45% ammonia, 45% sulfuric acid and 10% ethanol are formulated as a fluorine-free impurity removal reagent, and then 5 g of prepared fluorine-free impurity removal reagent is added to 100 g of hyperheterophosphoric acid , react at room temperature for 0.5h and then filter, so that the metal impurities in the phosphoric acid form ammonium sulfate precipitates to be removed, and get impurity-removed phosphoric acid.

(2) High-heterophosphoric acid extraction and impurity removal: first make 50ml tributyl phosphate, 20ml isobutanol and 40ml sulfonated kerosene as an extraction agent, then add 100g of impurity-removing phosphoric acid obtained in step (1), and extract at 5°C for 15min Separate layers, remove the raffinate, add 100ml of sulfuric acid (mass concentration: 5%) to the organic phase (100ml), and back-extract for 10min at 25°C to obtain purified phosphoric acid.

(3) Ferrous sulfate heptahydrate impurity removal: the waste ferrous sulfate heptahydrate obtained in the production of titanium dioxide process is dissolved in water, then add nitric acid of solution quality 1%, and use ammoniacal liquor to control the solution pH value to 1, with Obtain cleaner ferric hydroxide iron precipitation.

(4) Synthesis of ferric phosphate dihydrate: add the purified phosphoric acid in step (2) to the ferric hydroxide obtained in step (3), then use ammonia water at room temperature to adjust the pH value of the solution to 3, filter and wash the precipitate obtained , After drying, high-purity ferric phosphate dihydrate can be obtained.

Example 5

This embodiment provides a method for preparing ferric phosphate dihydrate by using high-impurity phosphoric acid and titanium dioxide industrial waste ferrous sulfate. The specific steps are as follows:

(1) Chemical impurity removal of hyperheterophosphoric acid: 45% ammonium sulfate, 5% sulfuric acid and 50% methanol are made into a fluorine-free impurity removal reagent, and then 10g of prepared fluorine-free impurity removal is added to 100g of hyperheterophosphoric acid Reagent, react at room temperature for 6 hours and then filter, so that the metal impurities in phosphoric acid can form ammonium sulfate precipitates and be removed, and get impurity-removed phosphoric acid.

(2) High impurity phosphoric acid extraction and impurity removal: first make 60ml tributyl phosphate and 40ml sulfonated kerosene as extraction agent, then add 100g of impurity-removing phosphoric acid obtained in step (1), extract at 50°C for 2 minutes, separate layers, remove After the raffinate, 100 ml of hydrochloric acid (mass concentration: 10%) was added to the organic phase (100 ml), and back-extracted at 25° C. for 10 min to obtain purified phosphoric acid.

(3) Ferrous sulfate heptahydrate removal of impurities: the waste ferrous sulfate heptahydrate obtained in the production of titanium dioxide process is dissolved in water, then add 15% ozone of the solution quality, and use ammonia to control the pH value of the solution to 4, to Obtain cleaner ferric hydroxide iron precipitation.

(4) Synthesis of ferric phosphate dihydrate: add the purified phosphoric acid in step (2) to the ferric hydroxide obtained in step (3), then use ammonia water at room temperature to adjust the pH value of the solution to 4, filter and wash the precipitate obtained , After drying, high-purity ferric phosphate dihydrate can be obtained.

The composition content of the high-impurity phosphoric acid used in the above-mentioned each embodiment, titanium dioxide industrial waste ferrous sulfate and the ferric phosphate dihydrate of gained are as shown in table 1, wherein, the high-impurity phosphoric acid used in each embodiment and titanium dioxide industrial waste sulfuric acid Same for ferrous.

Table 1 ingredient content

Comparative example 1

This comparative example provides a kind of method that utilizes industrial iron-containing waste to prepare ferric phosphate dihydrate, and concrete steps are as follows:

Take 500mL of iron-containing waste acid, filter it, add 20g of waste iron slag to the obtained solution, and react at 30°C for 48h until the solution pH=5. Subsequently, the above solution was filtered twice to obtain a green clear solution: under stirring conditions, 80 mL of hydrogen peroxide and 100 mL of phosphoric acid were added to the above clear solution to react for 18 hours. Finally, when the water bath is heated to 92°C, add 110mL of phosphoric acid and 250mL of sodium hydroxide solution, and react for 5 hours to form a yellow suspension: filter, wash until pH = 6, and dry at 100°C for 10 hours to obtain ferric phosphate dihydrate (FePO ₄ · 2H ₂ O) sample.

Among them, the purity of scrap iron slag is 90%, the purity of hydrogen peroxide is 30%, the purity of phosphoric acid is 85%, the purity of ammonium phosphate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate are all greater than 98%, and the mass concentration of ammonia water is 26%. %, the molar concentration of sodium hydroxide is 3mol/L.

By contrast, comparative example 1 selects phosphoric acid purity as 85% to prepare ferric phosphate dihydrate, and the cost of phosphoric acid is 12,000 yuan per ton; and the phosphoric acid purity that the application adopts is 45% high heterophosphoric acid, and the cost only needs 4,000 yuan per ton. It can be seen that the method provided by the present application can significantly reduce the preparation cost.

Comparative example 2

This comparative example provides a kind of preparation method of ferric phosphate dihydrate, and concrete steps are as follows:

Mix and stir the iron powder and urea phosphate solution for reaction, the molar ratio of elemental iron in the iron powder to urea phosphate is 1:1.0008, react at a temperature of 79°C for 1 hour, stop the reaction when the concentration of ferrous ions does not increase, and filter , to obtain the residue and filtrate:

The filtrate is heated to a temperature of 99°C, and air is introduced under stirring at the same time, and the reaction is stopped at this temperature until the concentration of iron ions in the mother liquor is lower than 20mg/L, and then filtered to obtain a precipitate and a mother liquor, and the precipitate is passed through Wash to get the washing material:

The washed material is dried and then calcined at high temperature, and the obtained calcined material is air-pulverized, sieved, iron-removed, and vacuum-packed to obtain ferric phosphate dihydrate.

The purity of the iron powder is greater than 99.0%, Cr≤20ppm, and the concentration of the urea phosphate solution is 1.35mol/L.

The mother liquor is concentrated and crystallized to obtain ammonium carbonate crystals, and the condensed water produced by cold shrinkage crystallization is recovered and returned to wash the precipitate. The washing process uses hot pure water at a temperature of 65°C, and stops washing when the conductivity of the washing water is less than or equal to 100 μS/Cm. The calcination temperature of high-temperature calcination is 545°C, and the calcination time is 6.5°C. After calcination, the high-temperature moisture of the material is lower than 0.3%, and then the material is cooled and discharged.

This comparative example uses iron powder with a purity of 99%, while the iron source used in this application has higher impurities, and the iron content is 18.77%. Compared with Comparative Example 2, the scheme of this application can significantly reduce production costs.

As mentioned above, the raw material purity of the above-mentioned comparative examples 1-2 and examples 1-5 are compared, and the results are shown in Table 2.

Table 2 raw material purity and cost

As can be seen from Table 2, the purity of raw material components such as high-heterophosphoric acid and iron source used in Examples 1-5 of the present application are all lower than the purity of raw material components such as phosphoric acid and iron source adopted in Comparative Example 1-2, by The methods of Examples 1-5 of the present application can fully utilize the active ingredients in the low-purity raw material components, and the methods of the embodiments of the present application have a large tolerance for the purity of raw materials and a high utilization rate.

In summary, the two raw materials with high impurity content used in the method provided by the application have a wide range of sources and low cost; the synthesized ferric phosphate dihydrate has high purity and good solubility under acidic conditions, which can meet the requirements of the liquid phase method. The demand for preparing lithium iron phosphate batteries has realized the purpose of turning waste into treasure.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. The preparation method of the ferric phosphate dihydrate is characterized by comprising the following steps:

removing metal ion impurities in the high-impurity phosphoric acid by using a fluorine-free impurity removal reagent to obtain impurity-removed phosphoric acid;

extracting and back-extracting the impurity-removed phosphoric acid in sequence to obtain purified phosphoric acid;

converting an iron source in waste ferrous sulfate in the titanium dioxide industry into ferric hydroxide under the action of an oxidant and a precipitator;

and mixing the purified phosphoric acid and the ferric hydroxide, adding alkali liquor to adjust the pH value, performing solid-liquid separation after precipitation is obtained, and collecting a solid phase substance to obtain the ferric phosphate dihydrate.

2. The method of claim 1, wherein the high impurity phosphoric acid has a purity of no less than 45%, and wherein the aluminum content is no more than 2wt% and the magnesium content is no more than 1wt%;

and/or the mass of the iron element in the waste ferrous sulfate in the titanium dioxide industry is not less than 18wt%.

3. The method of claim 1, wherein the fluorine-free decontaminating agent comprises an organic substance having a hydrophilic group and a substance providing sulfate ions and ammonium ions;

preferably, the content of the organic matter with hydrophilic groups in the fluorine-free impurity removal reagent is 10-50wt%;

preferably, the organic matter with hydrophilic groups comprises soluble alcohol and/or acetone;

preferably, the soluble alcohol comprises methanol and/or ethanol;

preferably, the substance providing sulfate ions and ammonium ions is a mixed solution of sulfuric acid and ammonia water, or the substance providing sulfate ions and ammonium ions is a mixture of sulfuric acid and ammonium sulfate or ammonium bisulfate;

preferably, in the fluorine-free impurity removing reagent, the content of sulfuric acid is 1-50wt%, the content of ammonia water is 1-50wt%, the content of ammonium sulfate is 1-50wt%, and the content of ammonium bisulfate is 1-50wt%.

4. The method according to any one of claims 1 to 3, wherein the removal of the metal ion impurities in the high-impurity phosphoric acid by the fluorine-free impurity removing agent is carried out at the temperature of 20-30 ℃ and the impurity removing time is 0.5-6h;

preferably, the amount of the fluorine-free impurity removing agent is 5-20wt% of the high-impurity phosphoric acid.

5. The method of claim 1 or 2, wherein the extractant used for the extraction comprises at least one of P204, tributyl phosphate, N923, isobutanol, and sulfonated kerosene;

preferably, the extraction is carried out at 5-50 ℃ for 2-20min;

preferably, the volume ratio of the organic phase to the aqueous phase during extraction is 1:2-4:1.

6. The method according to claim 1 or 2, wherein the stripping agent used for stripping is water or acid;

preferably, the acid comprises at least one of sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid;

preferably, the mass concentration of the acid is 1-10%;

preferably, the volume ratio of the organic phase to the aqueous phase in the stripping is 4:1-2:1.

7. The method according to claim 1 or 2, characterized in that the amount of the oxidant added is 1-15wt% of the solution of the waste ferrous sulfate from titanium dioxide industry;

preferably, the oxidant comprises at least one of hydrogen peroxide, ozone and nitric acid;

preferably, the precipitator is used for controlling the pH value of the solution of the waste ferrous sulfate in the titanium dioxide industry to be 1-4;

preferably, the precipitant comprises at least one of ammonia, KOH, and NaOH.

8. The method according to claim 1 or 2, characterized in that the lye is adjusted to a pH value of 2-4;

preferably, the alkali solution includes at least one of ammonia, KOH, and NaOH.

9. Iron phosphate dihydrate produced by the method according to any one of claims 1 to 8.

10. A preparation method of a lithium iron phosphate positive electrode material is characterized by comprising the following steps:

preparing ferric phosphate dihydrate by the method for preparing ferric phosphate dihydrate according to any one of claims 1-8;

and mixing the ferric phosphate dihydrate with a lithium source to prepare the lithium iron phosphate cathode material.

Images