CN115196609B - A method for recovering iron phosphate from lithium iron phosphate extraction slag and its application - Google Patents

Abstract

This application discloses a method for recovering iron phosphate from lithium iron phosphate extraction slag and its application, which relates to the technical field of lithium batteries, and includes the following steps: (1) adding lithium iron phosphate to the mixed slurry of lithium iron phosphate extraction slag and water Adding a reducing agent for reduction leaching reaction to obtain leaching slag b and leaching solution a containing phosphorus and iron elements; (2) adding an oxidant to the leaching solution a for precipitation reaction to obtain iron phosphate slurry; (3) obtaining the The solid phase material of the iron phosphate slurry, the iron phosphate is obtained after the solid phase material is washed and calcined. The application realizes the comprehensive utilization of lithium iron phosphate extraction residue to prepare battery iron phosphate, which has the advantages of mild leaching conditions, high leaching rate of phosphorus and iron elements, high precipitation rate and high product purity.

Description

A method for recovering iron phosphate from lithium iron phosphate extraction slag and its application

technical field

The present application relates to the technical field of lithium batteries, in particular to a method for recovering iron phosphate from lithium iron phosphate extraction slag and its application.

Background technique

Lithium iron phosphate is widely used in the field of electric vehicles due to its low price and good safety. With the rapid development of my country's new energy industry, the scrapped lithium iron phosphate batteries are increasing year by year. The waste lithium iron phosphate pole powder contains about 4% lithium, 31% iron and 17% phosphorus. It is an important secondary resource and urgently needs resource utilization. The conventional lithium iron phosphate recovery method is to selectively extract lithium by oxidative acid leaching to obtain a lithium-rich leach solution and lithium extraction residue. The lithium extraction residue contains about 90% iron and phosphorus elements as well as some residual carbon and impurity metals. , impurity metals mainly include copper, nickel and cobalt.

The existing lithium iron phosphate extraction lithium slag recovery method is mainly to dissolve iron phosphate with high-concentration sulfuric acid, phosphoric acid and other inorganic acids, and then add alkali to the leaching solution to adjust the pH to make iron phosphate precipitate, but leaching and precipitation will use a lot of acid and Alkali, high reagent cost, low economic benefit, large amount of waste salt, and strong acid is highly corrosive to equipment. At the same time, the leaching rate of iron and phosphorus elements in the strong acid leaching process is low, resulting in a large waste of iron and phosphorus resources.

In the prior art, high-concentration phosphoric acid is used to leach the phosphorus and iron elements in the lithium extraction slag, and then diluted with water to adjust the pH to prepare ferric phosphate dihydrate, and the phosphoric acid is evaporated and reused, but due to the A large amount of water was added, resulting in excessive evaporation. In the prior art, iron powder and phosphoric acid are added to adjust the iron-phosphorus ratio to realize the leaching of iron phosphate in the lithium extraction slag, but this process will make only about 60% of the precipitated product come from the lithium extraction slag, and 40% from the lithium extraction slag. With the addition of Fe and P.

At present, ferric phosphate is mainly prepared by adding phosphate and oxidant to ferrous sulfate solution. Commonly used phosphates include diammonium hydrogen phosphate and phosphoric acid. Since phosphate is expensive, this method is costly. Therefore, it is urgent to provide a method for recovering iron phosphate from lithium iron phosphate extraction slag with mild conditions, low reagent cost, high leaching rate and high precipitation rate. The preparation of iron phosphate from lithium iron phosphate extraction slag can not only eliminate Accommodating solid waste can also create high economic value, and the obtained iron phosphate can also be used in the preparation of lithium iron phosphate batteries to realize green recycling and recycling of waste lithium iron phosphate batteries.

Contents of the invention

This application provides a method for recovering iron phosphate from lithium iron phosphate extraction slag and its application, which can solve the problem of using a large amount of acid and alkali in leaching and precipitation reactions in the prior art, resulting in high reagent costs, large amount of waste salt and Strong acid is highly corrosive to equipment. At the same time, the leaching rate of iron and phosphorus in the strong acid leaching process of the prior art is low, resulting in a large waste of iron and phosphorus resources; this application introduces a suitable reducing agent. On the one hand, it can Optimizing the strong acidic conditions of the leaching reaction, on the other hand, can prevent the leaching of other metal ions, increase the leaching rate of iron and phosphorus elements, and then improve the purity of the product ferric phosphate; moreover, this application can select the appropriate oxidant and control the precipitation reaction The process conditions improve the precipitation rate of hydrated ferric phosphate.

In the first aspect, the application provides a method for reclaiming iron phosphate from lithium iron phosphate lithium extraction slag, comprising the following steps:

(1) Adding a reducing agent to the mixed slurry of lithium iron phosphate extraction slag and water for reduction leaching reaction to obtain leaching slag b and leaching solution a containing phosphorus and iron elements;

(2) adding an oxidizing agent to the leach solution a to carry out a precipitation reaction to obtain an iron phosphate slurry;

(3) Obtain the solid phase material (ferric phosphate dihydrate) of the iron phosphate slurry, wash and calcinate the solid phase material to obtain the iron phosphate (anhydrous iron phosphate).

This application selects the remaining lithium extraction slag after selective extraction of lithium by oxidative acid leaching with waste lithium iron phosphate as the starting material. The lithium extraction slag mainly includes iron phosphate, a small amount of carbon black and other metal impurities; at this time, a On the one hand, solid waste can be absorbed, and on the other hand, high economic value can also be created; the mixed slurry of the lithium extraction slag and water is put into a suitable and appropriate proportion of reducing agent, such as sulfur or sulfide, and the sulfide is in the Under mild acid leaching conditions, the ferric ions in the lithium extraction slag can be reduced to ferrous ions, and the leaching rate of iron and phosphorus elements is higher than that of the prior art strong acid leaching process; and the sulfide The substance can also inhibit the leaching of other metal ions, such as the leaching of copper ions, nickel ions and cobalt ions, so that the purity of the calcined product anhydrous iron phosphate is higher;

In addition, the leachate a is a ferrous solution, and the application can select an appropriate and appropriate ratio of oxidant to convert the ferrous ion solution to the ferric ion solution. At the same time, by controlling the conditions of the precipitation reaction, use In order to obtain a high precipitation rate and a suitable product iron phosphate, the process flow is shown in Figure 1.

In some of these embodiments, the sulfide is at least one selected from sodium sulfide, potassium sulfide, hydrogen sulfide or ammonium sulfide. Preferably, the sulfide is at least one selected from sodium sulfide or ammonium sulfide.

Specifically, in one example, the sulfide is sodium sulfide; in another example, the sulfide is ammonium sulfide; or in other examples, the sulfide includes sodium sulfide and ammonium sulfide.

Sodium sulfide, potassium sulfide, hydrogen sulfide or ammonium sulfide can form new sulfides with other impurity metal ions (such as copper ions, nickel ions and cobalt ions) in the mixed slurry, thereby inhibiting the leaching of other impurity metal ions and improving The purity of the product ferric sulfate is guaranteed.

In some of these embodiments, in step (1), the amount of the reducing agent used is 1 to 1.5 times the molar amount of iron in the lithium iron phosphate extraction slag.

Exemplarily, the amount of the reducing agent is 1 times, 1.1 times, 1.2 times, 1.3 times, 1.4 times, 1.5 times the molar amount of iron in the lithium iron phosphate extraction slag, or a range consisting of any two of the above values. At this time, the leaching effect is good, and low cost can also be achieved while ensuring the leaching effect. If the amount of the reducing agent is too small, the leaching effect of iron and phosphorus elements will not be good. If the amount of the reducing agent If the amount is too much, on the one hand, the effect on improving the leaching rate is not obvious, and on the other hand, it will increase the cost.

In some of these embodiments, in step (1), the conditions of the reductive leaching reaction are: under acidic conditions with a pH value of 1-1.4, the leaching temperature is controlled at 40-60°C, and the leaching time is 1-2h, The solid-liquid ratio is 5~10mL/g. The acidic conditions can be adjusted using conventional acidic reagents in the art, for example, sulfuric acid, nitric acid, hydrochloric acid and the like.

Exemplarily, the pH value of the acidic condition is 1, 1.1, 1.2, 1.3, 1.4 or a range consisting of any two of the above-mentioned values.

Exemplarily, the leaching temperature during the reductive leaching reaction is 40°C, 43°C, 45°C, 48°C, 50°C, 52°C, 54°C, 55°C, 58°C, 60°C or a combination of any two values above range.

Exemplarily, the leaching time during the reductive leaching reaction is 1 h, 1.1 h, 1.2 h, 1.4 h, 1.5 h, 1.6 h, 1.8 h, 2 h or a range consisting of any two values mentioned above.

Exemplarily, the solid-liquid ratio during the reductive leaching reaction is 5mL/g, 6mL/g, 7mL/g, 8mL/g, 9mL/g, 10mL/g or any two of the above-mentioned ranges.

In some of these embodiments, in step (2), the oxidizing agent is at least one selected from manganese dioxide or sodium chlorate; the amount of the oxidizing agent used is 1 to 2 times the molar amount of iron in the leach solution a.

Specifically, in one example, the oxidizing agent is manganese dioxide; in another example, the oxidizing agent is sodium chlorate; or in other examples, the oxidizing agent includes manganese dioxide and sodium chlorate;

Exemplarily, the amount of the oxidizing agent is 1 time, 1.1 times, 1.3 times, 1.5 times, 1.6 times, 1.8 times, 2 times the molar amount of iron in the lithium iron phosphate lithium extraction slag, or any two of the above values. scope.

Preferably, the oxidant is manganese dioxide, and the amount of the oxidant is 1 to 2 times the molar amount of iron in the lithium iron phosphate extraction slag.

In some of these embodiments, in step (2), the precipitation reaction includes a first-stage precipitation reaction and a second-stage precipitation reaction;

The conditions of the first-stage precipitation reaction are: under the condition of 50-70°C, heat preservation for 50-70min;

Therefore, the conditions of the second stage precipitation reaction are: under the condition of 90~105℃, keep warm for 130~150min;

The heating rate of the first-stage precipitation reaction and/or the second-stage precipitation reaction is 6-8° C./min. The low temperature environment of the first-stage precipitation reaction is used to obtain suitable iron phosphate seeds, and the iron phosphate seeds generated at low temperature can be generated in the high-temperature environment (90-105°C) of the second-stage precipitation reaction A large amount of ferric phosphate dihydrate; and, by adding a suitable oxidizing agent and the synergistic cooperation of the first-stage precipitation reaction and the second-stage precipitation reaction, it is beneficial to the generation of a large amount of uniform and dense ferric phosphate dihydrate .

Wherein, the first-stage precipitation reaction is the formation stage of ferric phosphate seed crystals, that is, adding an oxidant to the leaching solution a containing phosphorus and iron elements, stirring fully and slowly raising the temperature of the solution to a suitable temperature (50-70°C), and waiting After the precipitation is formed, keep it warm for a certain period of time (50~70min) to generate suitable ferric phosphate seeds, and then enter the second stage of precipitation reaction, that is, continue to heat up to the preset temperature (90~105°C) and continue to keep warm for a certain period of time ( 130 ~ 150min) to obtain ferric phosphate slurry, and the ferric phosphate in the ferric phosphate slurry is ferric phosphate dihydrate; regulating and controlling the holding temperature and the holding time of the second stage precipitation reaction will help improve the precipitation rate of ferric phosphate dihydrate .

It should be noted that when the oxidizing agent is manganese dioxide, after the first stage of precipitation reaction is completed, filter first to remove the remaining manganese dioxide in the reaction, and then carry out the heating and heat preservation of the second stage of precipitation reaction. The remaining manganese dioxide cannot continue to be dissolved, and the undissolved manganese dioxide will be mixed into the ferric phosphate slurry, resulting in impure solid phase material of the obtained ferric phosphate slurry.

In a second aspect, the present application provides iron phosphate prepared by any one of the methods described above.

In a third aspect, the present application provides the iron phosphate prepared by any one of the methods described above and/or the application of the iron phosphate described in any one of the above in the field of lithium iron phosphate batteries.

The beneficial effects brought by the technical solutions provided by some embodiments of the present application at least include:

This application realizes the comprehensive utilization of lithium iron phosphate extraction lithium slag to prepare battery iron phosphate, which has the advantages of mild leaching conditions, high leaching rate of phosphorus and iron elements, high precipitation rate and high product purity; moreover, the leaching process of this application The introduction of a suitable reducing agent not only improves the leaching rate of phosphorus and iron elements, but also inhibits the leaching of other impurity metals in the lithium iron phosphate extraction slag, so that the precipitated ferric phosphate dihydrate has a high purity, which in turn makes The purity of the product ferric phosphate is high; moreover, the precipitation process of the present application does not require a large amount of alkali neutralization, selection of suitable oxidant and process conditions for controlling the precipitation reaction improves the precipitation rate of ferric phosphate dihydrate, and has low cost and economical efficiency good points.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present application. For those skilled in the art, other drawings can also be obtained based on these drawings without creative work.

Fig. 1 is the schematic process flow diagram of the principle of preparing ferric phosphate from lithium iron phosphate lithium extraction slag of the present application;

Fig. 2 is the XRD figure of the ferric phosphate that the application embodiment 1 prepares;

Fig. 3 is the scanning electron micrograph of the ferric phosphate that the embodiment 1 of the present application prepares;

Fig. 4 is a scanning electron microscope image of ferric phosphate obtained in Comparative Example 6 of the present application without performing the low-temperature heat preservation stage.

detailed description

In order to make the purpose, technical solution and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present application, and are not intended to limit the present application.

The present application is further described by way of examples below.

Example 1

Step 1: Add 1kg of lumpy lithium iron phosphate slag to the water, the liquid-solid ratio is 8mL/g, stir well to disperse, then add sulfuric acid and sodium sulfide, the amount of sodium sulfide is the mole of iron in the lithium iron phosphate slag 1.2 times the amount; react at 50°C for 1 hour, add sulfuric acid during the period to adjust the pH to 1.1; then filter the slurry for solid-liquid separation to obtain leaching residue and leaching solution containing phosphorus and iron elements; the leaching rate of reduction leaching reaction : Fe element 98.7%, P element 98.5%.

Step 2: The leaching solution obtained in step 1 is heated up to 60° C. at a heating rate of 7° C./min, fully stirred after adding manganese dioxide and incubated for 60 minutes, and then filtered to obtain a solution containing iron phosphate, wherein the amount of manganese dioxide is the 1.5 times the molar amount of iron in the leaching solution; then the above ferric phosphate solution was heated to 100°C at a heating rate of 7°C/min and then kept for 140min to obtain ferric phosphate slurry; the precipitation rate of the precipitation reaction: Fe element 95.7%, P Elemental 94.8%.

Step 3: Filter the ferric phosphate slurry obtained in step 2 to obtain a solid ferric phosphate dihydrate product; wash the obtained ferric phosphate dihydrate solid with deionized water, and calcinate at 500°C for 1 hour to obtain anhydrous phosphoric acid Iron products.

The content of Cu in the anhydrous iron phosphate product is 0.003%, the content of Ni is 0.004%, the content of Co is 0.005%, and the content of Zn is 0.0002%. Fig. 2 is the XRD characterization figure of described anhydrous ferric phosphate product, Fig. 3 is the SEM scanning electron micrograph of described anhydrous ferric phosphate product, it can be seen that the described anhydrous ferric phosphate prepared by the present embodiment is smooth and uniform in particle size. dense spherical structure.

Example 2

Step 1: Add 1kg of lumpy lithium iron phosphate slag to the water, the liquid-solid ratio is 8mL/g, stir well to disperse, then add sulfuric acid and ammonium sulfide, the amount of ammonium sulfide is the mole of iron in the lithium iron phosphate slag 1.1 times the amount; react at 50°C for 1 hour, add sulfuric acid during the period to adjust the pH to 1.2; then filter the slurry for solid-liquid separation to obtain leaching residue and leaching solution containing phosphorus and iron elements; the leaching rate of reduction leaching reaction : Fe element 99.5%, P element 98.7%.

Step 2: The leaching solution obtained in step 1 is heated up to 60° C. at a heating rate of 7° C./min, fully stirred after adding manganese dioxide and incubated for 60 minutes, and then filtered to obtain a solution containing iron phosphate, wherein the amount of manganese dioxide is the 1.6 times the molar amount of iron in the leaching solution; then the above ferric phosphate solution was heated to 95°C at a heating rate of 7°C/min and then kept for 140min to obtain ferric phosphate slurry; the precipitation rate of the precipitation reaction: Fe element 96.8%, P Elemental 95.6%.

Step 3: Filter the ferric phosphate slurry obtained in step 2 to obtain a solid ferric phosphate dihydrate product; wash the obtained ferric phosphate dihydrate solid with deionized water, and calcinate at 500°C for 1 hour to obtain anhydrous phosphoric acid Iron products.

The content of Cu in the anhydrous iron phosphate product is 0.004%, the content of Ni is 0.002%, the content of Co is 0.003%, and the content of Zn is 0.0003%.

Example 3

Step 1: Add 1 kg of lumpy lithium iron phosphate slag to the water, the liquid-solid ratio is 8mL/g, stir well to disperse, then add sulfuric acid and potassium sulfide, where the amount of potassium sulfide is the mole of iron in the lithium iron phosphate slag 1.2 times the amount; react at 60°C for 1 hour, add sulfuric acid during the period to adjust the pH to 1.3; then filter the slurry for solid-liquid separation to obtain leaching residue and leaching solution containing phosphorus and iron elements; the leaching rate of reduction leaching reaction : Fe element 97.5%, P element 97.7%.

Step 2: Heat the leachate obtained in step 1 to 60°C at a heating rate of 7°C/min, add sodium chlorate, fully stir and keep it warm for 60 minutes, wherein the amount of sodium chlorate is 1 times the molar amount of iron in the leachate ; Then, the above ferric phosphate solution was heated to 95°C at a heating rate of 7°C/min and then kept for 140min to obtain ferric phosphate slurry; the precipitation rate of the precipitation reaction: Fe element 96.8%, P element 95.6%.

Step 3: Filter the ferric phosphate slurry obtained in step 2 to obtain a solid ferric phosphate dihydrate product; wash the obtained ferric phosphate dihydrate solid with deionized water, and calcinate at 500°C for 1 hour to obtain anhydrous phosphoric acid Iron products.

The Cu content in the anhydrous iron phosphate product is 0.002%, the Ni content is 0.005%, the Co content is 0.002%, and the Zn content is 0.0001%.

Example 4

Step 1: Add 1 kg of lumpy lithium iron phosphate slag to the water, the liquid-solid ratio is 8mL/g, stir well to disperse, then add sulfuric acid and sulfur, wherein the amount of sulfur is 1/2 of the molar amount of iron in the lithium iron phosphate slag 1 times; react at 60°C for 1 hour, add sulfuric acid during the period to adjust the pH to 1.1; then filter the slurry for solid-liquid separation to obtain leaching residue and leaching solution containing phosphorus and iron elements; leaching rate of reduction leaching reaction: Fe Element 98.3%, P element 98.1%.

Step 2: The leaching solution obtained in step 1 is heated up to 60° C. at a heating rate of 7° C./min, fully stirred after adding manganese dioxide and incubated for 60 minutes, and then filtered to obtain a solution containing iron phosphate, wherein the amount of manganese dioxide is the 1 times the molar amount of iron in the leaching solution; then the above ferric phosphate solution was heated to 95°C at a heating rate of 7°C/min and then kept for 140min to obtain ferric phosphate slurry; the precipitation rate of the precipitation reaction: Fe element 96.8%, P Elemental 95.6%.

Step 3: Filter the ferric phosphate slurry obtained in step 2 to obtain a solid ferric phosphate dihydrate product; wash the obtained ferric phosphate dihydrate solid with deionized water, and calcinate at 500°C for 1 hour to obtain anhydrous phosphoric acid Iron products.

The content of Cu in the anhydrous iron phosphate product is 0.003%, the content of Ni is 0.007%, the content of Co is 0.005%, and the content of Zn is 0.002%.

Comparative example 1

Step 1: Add 1 kg of block lithium iron phosphate lithium extraction slag into water, the liquid-solid ratio is 8mL/g, stir well to disperse, react at 60°C for 1 hour, add sulfuric acid during the period to adjust the pH to 1.1; then the slurry Solid-liquid separation was carried out by filtration to obtain leaching slag and leaching solution containing phosphorus and iron elements; the leaching rate of reduction leaching reaction: Fe element 46.5%, P element 45.9%. At this time, the leaching rate of iron and phosphorus elements is greatly reduced due to no reducing agent added.

Step 2: Heat the leachate obtained in step 1 to 60°C at a heating rate of 7°C/min, add sodium chlorate, fully stir and keep it warm for 60 minutes, wherein the amount of sodium chlorate is 1 times the molar amount of iron in the leachate ; Then, the above ferric phosphate solution was heated to 95°C at a heating rate of 7°C/min and then kept for 140min to obtain ferric phosphate slurry; the precipitation rate of the precipitation reaction: Fe element 95.7%, P element 94.8%.

Step 3: Filter the ferric phosphate slurry obtained in step 2 to obtain a solid ferric phosphate dihydrate product; wash the obtained ferric phosphate dihydrate solid with deionized water, and calcinate at 500°C for 1 hour to obtain anhydrous phosphoric acid Iron products.

The content of Cu in the anhydrous iron phosphate product is 0.01%, the content of Ni is 0.015%, the content of Co is 0.012%, and the content of Zn is 0.01%.

Compared with Example 1, Comparative Example 1 does not add reducing agent, and it only carries out reducing leaching reaction under the acidic condition of pH 1.1, on the one hand, because the sulfide reducing agent described in the application can promote ferric ion to The conversion of ferrous ions is beneficial to the occurrence of reduction leaching reaction. On the other hand, the sulfide reducing agent can also inhibit the leaching of other impurity metal ions; Comparative Example 1 does not add the sulfide reduction under acidic environment. agent, resulting in a low leaching rate of only 46.5% of Fe elements and 45.9% of P elements, lower than the 98.7% of Fe elements and 98.5% of P elements in Example 1, which is about 50% lower. Moreover, the impurity content in the anhydrous iron phosphate product of Comparative Example 1 is obviously higher than that of Example 1.

Comparative example 2

Step 1: Add 1kg of lumpy lithium iron phosphate slag to the water, the liquid-solid ratio is 8mL/g, stir well to disperse, then add sulfuric acid and sodium sulfide, the amount of sodium sulfide is the mole of iron in the lithium iron phosphate slag 1.2 times the amount; react at 50°C for 1 hour, add sulfuric acid during the period to adjust the pH to 1.1; then filter the slurry for solid-liquid separation to obtain leaching residue and leaching solution containing phosphorus and iron elements; the leaching rate of reduction leaching reaction : Fe element 98.7%, P element 97.9%.

Step 2: The leaching solution obtained in step 1 is heated up to 60°C at a heating rate of 7°C/min, and incubated for 60 minutes to obtain a solution containing ferric phosphate; then the above-mentioned ferric phosphate-containing solution is heated up to After holding at 95°C for 140 minutes, ferric phosphate slurry was obtained; the precipitation rate of the precipitation reaction: Fe element 43.8%, P element 41.5%. Since manganese dioxide and/or sodium chlorate were not added as oxidants during the precipitation process, the precipitation rate of iron and phosphorus elements was greatly reduced.

Step 3: Filter the ferric phosphate slurry obtained in step 2 to obtain a solid ferric phosphate dihydrate product; wash the obtained ferric phosphate dihydrate solid with deionized water, and calcinate at 500°C for 1 hour to obtain anhydrous phosphoric acid Iron products.

The content of Cu in the anhydrous iron phosphate product is 0.002%, the content of Ni is 0.005%, the content of Co is 0.004%, and the content of Zn is 0.003%.

Comparative example 3

Step 1: Add 1kg of lumpy lithium iron phosphate slag to the water, the liquid-solid ratio is 8mL/g, stir well to disperse, then add sulfuric acid and sodium sulfide, the amount of sodium sulfide is the mole of iron in the lithium iron phosphate slag 0.5 times the amount; react at 50°C for 1 hour, during which time add sulfuric acid to adjust the pH to 1.1; then filter the slurry for solid-liquid separation to obtain leaching residue and leaching solution containing phosphorus and iron elements. The leaching rate of reduction leaching reaction: Fe element 78.3%, P element 79.1%; since the amount of reducing agent sodium sulfide is only 0.5 times the molar amount of iron, the leaching rate of iron element and phosphorus element is significantly reduced. It can be seen that the amount of reducing agent In an appropriate range, it is beneficial to the leaching of iron and phosphorus.

Step 2: The leaching solution obtained in step 1 is heated up to 60°C at a heating rate of 7°C/min, after adding manganese dioxide, fully stir and keep warm for 60min, then filter to obtain a solution containing iron phosphate, wherein the amount of manganese dioxide is 1.5 times the molar weight of medium iron; then the above ferric phosphate solution was heated to 95°C at a heating rate of 7°C/min and then kept for 140min to obtain ferric phosphate slurry; the precipitation rate of the precipitation reaction: Fe element 95.3%, P element 95.8 %.

Step 3: Filter the ferric phosphate slurry obtained in step 2 to obtain a solid ferric phosphate dihydrate product; wash the obtained ferric phosphate dihydrate solid with deionized water, and calcinate at 500°C for 1 hour to obtain anhydrous phosphoric acid Iron products.

The content of Cu in the anhydrous iron phosphate product is 0.006%, the content of Ni is 0.007%, the content of Co is 0.006%, and the content of Zn is 0.004%. Because the addition amount of sodium sulfide is too little, it cannot completely suppress the leaching of other metal ions, resulting in an increase in the content of impurities in the product.

Comparative example 4

Step 1: Add 1kg of lumpy lithium iron phosphate slag to the water, the liquid-solid ratio is 8mL/g, stir well to disperse, then add sulfuric acid and sodium sulfide, the amount of sodium sulfide is the mole of iron in the lithium iron phosphate slag 1.2 times the amount. React at 50°C for 1 hour, add sulfuric acid during the period to adjust the pH to 1.1; then filter the slurry for solid-liquid separation to obtain leaching residue and leaching solution containing phosphorus and iron elements; leaching rate of reduction leaching reaction: Fe element 98.5% , P element 98.3%.

Step 2: The leaching solution obtained in step 1 is heated up to 60°C at a heating rate of 7°C/min, after adding manganese dioxide, fully stir and keep warm for 60min, then filter to obtain a solution containing iron phosphate, wherein the amount of manganese dioxide is 0.5 times the molar weight of the medium iron; then the above-mentioned iron phosphate-containing solution was heated to 95°C at a heating rate of 7°C/min and then kept for 140 minutes to obtain a ferric phosphate slurry; the precipitation rate of the precipitation reaction: Fe element 79.3%, P element 80.2 %. Since the amount of the oxidant manganese dioxide is only 0.5 times the molar amount of iron, the precipitation rate of iron and phosphorus elements in the precipitation process is significantly reduced.

Step 3: Filter the ferric phosphate slurry obtained in step 2 to obtain a solid ferric phosphate dihydrate product; wash the obtained ferric phosphate dihydrate solid with deionized water, and calcinate at 500°C for 1 hour to obtain anhydrous phosphoric acid Iron products.

The Cu content in the anhydrous iron phosphate product is 0.003%, the Ni content is 0.002%, the Co content is 0.002%, and the Zn content is 0.003%.

Comparative example 5

Step 1: Add 1kg of lumpy lithium iron phosphate slag to the water, the liquid-solid ratio is 8mL/g, stir well to disperse, then add sulfuric acid and sodium sulfide, the amount of sodium sulfide is the mole of iron in the lithium iron phosphate slag 1.2 times the amount; react at 50°C for 1 hour, add sulfuric acid during the period to adjust the pH to 1.1; then filter the slurry for solid-liquid separation to obtain leaching residue and leaching solution containing phosphorus and iron elements; the leaching rate of reduction leaching reaction : Fe element 98.6%, P element 98.2%.

Step 2: The leach solution obtained in step 1 is heated to 60° C. at a heating rate of 7° C./min. After adding sodium chlorate, it is fully stirred and incubated for 140 minutes before filtering, wherein the amount of sodium chlorate is 1/2 of the molar amount of iron in the leach solution 1 times to obtain ferric phosphate slurry; precipitation rate of precipitation reaction: Fe element 68.4%, P element 67.5%. Since the temperature did not continue to rise after the heat preservation, the precipitation rate of iron and phosphorus elements was greatly reduced.

Step 3: Filter the ferric phosphate slurry obtained in step 2 to obtain a solid ferric phosphate dihydrate product; wash the obtained ferric phosphate dihydrate solid with deionized water, and calcinate at 500°C for 1 hour to obtain anhydrous phosphoric acid Iron products.

The content of Cu in the anhydrous iron phosphate product is 0.003%, the content of Ni is 0.005%, the content of Co is 0.004%, and the content of Zn is 0.003%.

Comparative example 6

Step 1: Add 1kg of lumpy lithium iron phosphate slag to the water, the liquid-solid ratio is 8mL/g, stir well to disperse, then add sulfuric acid and sodium sulfide, the amount of sodium sulfide is the mole of iron in the lithium iron phosphate slag 1.2 times the amount; react at 50°C for 1 hour, add sulfuric acid during the period to adjust the pH to 1.1; then filter the slurry for solid-liquid separation to obtain leaching residue and leaching solution containing phosphorus and iron elements; the leaching rate of reduction leaching reaction : Fe element 98.3%, P element 97.9%.

Step 2: The leach solution obtained in step 1 is heated up to 95° C. at a heating rate of 7° C./min. After adding sodium chlorate, it is fully stirred and incubated for 140 minutes before filtering, wherein the amount of sodium chlorate is 1% of the molar amount of iron in the leach solution 1 times to obtain ferric phosphate slurry; precipitation rate of precipitation reaction: Fe element 94.6%, P element 94.7%. However, due to the lack of heat preservation (iron phosphate seed formation) stage at low temperature, the morphology of the product changes, and it is an irregular porous structure (as shown in Figure 4). This iron phosphate product will cause the subsequent preparation of lithium iron phosphate batteries. The electrochemical performance is greatly reduced.

Step 3: Filter the ferric phosphate slurry obtained in step 2 to obtain a solid ferric phosphate dihydrate product; wash the obtained ferric phosphate dihydrate solid with deionized water, and calcinate at 500°C for 1 hour to obtain anhydrous phosphoric acid Iron products.

The content of Cu in the anhydrous iron phosphate product is 0.003%, the content of Ni is 0.004%, the content of Co is 0.003%, and the content of Zn is 0.003%.

testing method:

1) Iron molarity test

Use inductively coupled plasma optical emission spectrometer to test the mass of iron in lithium extraction slag or leaching solution, and the molar amount of iron is the mass obtained by dividing by the relative atomic mass of iron.

2) Leaching rate test

The leaching rate of iron and phosphorus elements in the lithium iron phosphate extraction slag leaching process refers to the difference between the content of iron and phosphorus in the lithium extraction slag and the content of iron and phosphorus in the leaching slag as a percentage of the iron and phosphorus in the lithium extraction slag. The ratio percentage of the content of phosphorus element.

3) Sedimentation rate test

The precipitation rate of iron and phosphorus elements in the iron phosphate precipitation process refers to the difference between the content of iron and phosphorus elements in the pre-precipitation liquid and the content of iron and phosphorus elements in the pre-precipitation liquid. Ratio percentage.

4) Impurity content test

The quality of impurities in the anhydrous iron phosphate product is tested with an inductively coupled plasma emission spectrometer, and the impurity content is the quality of the impurities obtained in the test divided by the total mass of the anhydrous iron phosphate product.

The above descriptions are only preferred embodiments of the application, and are not intended to limit the application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the application should be included in the protection of the application. within range.

Claims (8)

1. a method for reclaiming iron phosphate from lithium iron phosphate lithium slag, is characterized in that, comprises the following steps: (1) Adding a reducing agent to the mixed slurry of lithium iron phosphate extraction slag and water for reduction leaching reaction to obtain leaching slag b and leach solution a containing phosphorus and iron elements; the reducing agent includes sulfide or sulfur; (2) adding an oxidizing agent to the leach solution a to carry out a precipitation reaction to obtain an iron phosphate slurry; (3) obtaining the solid phase material of the iron phosphate slurry, washing and calcining the solid phase material to obtain the iron phosphate; The conditions of the reduction leaching reaction include: adjusting the pH value of the mixed slurry to 1~1.4; Wherein, in step (1), the amount of the reducing agent is 1 to 1.5 times the molar amount of iron in the lithium iron phosphate extraction slag; In step (2), the precipitation reaction includes a first-stage precipitation reaction and a second-stage precipitation reaction; The conditions of the first-stage precipitation reaction are: under the condition of 50-70°C, heat preservation for 50-70min; Therefore, the conditions of the second stage precipitation reaction are: under the condition of 90~105℃, keep warm for 130~150min. 2. The method according to claim 1, characterized in that, in step (1), the sulfide is at least one selected from sodium sulfide, potassium sulfide, hydrogen sulfide or ammonium sulfide. 3. The method according to claim 1, wherein the conditions of the reductive leaching reaction further include: controlling the leaching temperature to 40-60°C, the leaching time to 1-2h, and the solid-to-liquid ratio to 5-10mL/g . 4. The method according to claim 1, characterized in that, in step (2), the oxidant is selected from at least one of manganese dioxide or sodium chlorate; The amount of the oxidizing agent is 1-2 times the molar amount of iron in the leaching solution a. 5. The method of claim 1, wherein, The heating rate of the first-stage precipitation reaction and/or the second-stage precipitation reaction is 6-8° C./min. 6 . The method according to claim 4 , wherein when the oxidizing agent comprises manganese dioxide, filtration treatment is also included between the first-stage precipitation reaction and the second-stage precipitation reaction. 7. the iron phosphate that the method described in any one of claim 1～6 makes. 8. the application of the ferric phosphate that the method described in any one of claim 1～6 makes in the lithium iron phosphate battery field.

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