阅读说明：本技术 一种利用酸性废液与磷酸钙废渣制备片状磷酸铁的方法 (Method for preparing flaky iron phosphate by utilizing acid waste liquid and calcium phosphate waste residue ) 是由 林奕 万文治 颜志雄 杨政 李万 罗强 于 2020-06-08 设计创作，主要内容包括：本发明公开了一种利用酸性废液与磷酸钙废渣制备片状磷酸铁的方法,包括以下步骤：将磷酸钙废渣、酸性废液、草酸溶液混合,加热反应后,滤除沉淀渣,得到含磷浸出液；将步骤S1制得的含磷浸出液升温至30～70℃,加入铁原料液升温至80～100℃,反应2～5h,获得磷酸铁浆料,磷酸铁浆料经压滤获得二水片状磷酸铁；将步骤S2制得的二水片状磷酸铁经两段保温焙烧脱水获得无水片状磷酸铁。本发明方案不仅巧妙地解决了酸性废液难处理、处理成本高、磷酸钙废渣难回用、片状无水磷酸铁难制备等问题；同时,浸出过程引入了草酸根,可以与磷酸钙废渣或酸性废液所带入的锰、镁、铜等金属杂质离子形成草酸盐沉淀,保证了磷酸铁成品的纯度。(The invention discloses a method for preparing flaky iron phosphate by utilizing acid waste liquid and calcium phosphate waste residue, which comprises the following steps: mixing the calcium phosphate waste residue, the acidic waste liquid and the oxalic acid solution, heating for reaction, and filtering out precipitation slag to obtain a phosphorus-containing leaching solution; heating the phosphorus-containing leaching solution prepared in the step S1 to 30-70 ℃, adding an iron raw material solution, heating to 80-100 ℃, reacting for 2-5 hours to obtain an iron phosphate slurry, and performing pressure filtration on the iron phosphate slurry to obtain dihydrate flaky iron phosphate; and (4) carrying out two-stage heat preservation, roasting and dehydration on the dihydrate flaky iron phosphate prepared in the step (S2) to obtain anhydrous flaky iron phosphate. The scheme of the invention not only skillfully solves the problems of difficult treatment of acid waste liquid, high treatment cost, difficult recycling of calcium phosphate waste residue, difficult preparation of flaky anhydrous iron phosphate and the like; meanwhile, oxalate is introduced in the leaching process, and can form oxalate precipitation with metal impurity ions such as manganese, magnesium, copper and the like brought by calcium phosphate waste residues or acidic waste liquid, so that the purity of the finished iron phosphate product is ensured.)

1. A method for preparing flaky iron phosphate by utilizing acid waste liquid and calcium phosphate waste residue is characterized by comprising the following steps: the method comprises the following steps:

s1, leaching phosphate: mixing the calcium phosphate waste residue, the acidic waste liquid and the oxalic acid solution, heating for reaction, and filtering out precipitation slag to obtain a phosphorus-containing leaching solution;

s2, preparing dihydrate flaky iron phosphate: heating the phosphorus-containing leaching solution prepared in the step S1 to 30-70 ℃, adding an iron raw material solution, heating to 80-100 ℃, reacting for 2-5 hours to obtain an iron phosphate slurry, and performing pressure filtration on the iron phosphate slurry to obtain dihydrate flaky iron phosphate;

s3, preparation of anhydrous flaky iron phosphate: and (4) carrying out two-stage heat preservation roasting on the dihydrate flaky iron phosphate prepared in the step (S2) to remove crystal water, thus obtaining the anhydrous iron phosphate.

2. The method for preparing flaky iron phosphate by using acidic waste liquid and calcium phosphate waste residue according to claim 1, which is characterized in that: the pH value of the acidic waste liquid is 0.7-5.0.

3. The method for preparing flaky iron phosphate by using acidic waste liquid and calcium phosphate waste residue according to claim 1, which is characterized in that: the solid-to-liquid ratio of the calcium phosphate waste residue to the acidic waste liquid is 100-300 g/L.

4. The method for preparing flaky iron phosphate by using acidic waste liquid and calcium phosphate waste residue according to claim 1, which is characterized in that: the mass fraction of the oxalic acid solution is 15-30%, and the volume ratio of the oxalic acid solution to the acidic waste liquid is 0.1: 1-1: 1.

5. The method for preparing flaky iron phosphate by using acidic waste liquid and calcium phosphate waste residue according to claim 1, which is characterized in that: the reaction temperature of the step S1 is 30-50 ℃, and the reaction time is 2-4 h.

6. The method for preparing flaky iron phosphate by using acidic waste liquid and calcium phosphate waste residue according to claim 1, which is characterized in that: the iron raw material liquid contains at least one of ferric salt solution or ferrous salt solution; preferably, the iron salt is ferric sulfate; preferably, when the iron raw material liquid contains a ferrous salt, the method further comprises a step of oxidizing ferrous ions into ferric ions before adding the iron raw material liquid.

7. The method for preparing flaky iron phosphate by using acidic waste liquid and calcium phosphate waste residue according to claim 1, which is characterized in that: the molar ratio of the phosphorus element in the phosphorus-containing leachate in the step S2 to the iron element in the iron raw material liquid is 1: 1-1.5: 1.

8. The method for preparing flaky iron phosphate by using acidic waste liquid and calcium phosphate waste residue according to any one of claims 1 to 7, which is characterized in that: the temperature during the baking process of the dihydrate flaky iron phosphate in the step S3 is set as follows: firstly, carrying out low-temperature heat preservation treatment and then carrying out high-temperature heat preservation treatment; wherein the low temperature is not more than 300 ℃ and the high temperature is not less than 500 ℃.

9. The method for preparing flaky iron phosphate by using acidic waste liquid and calcium phosphate waste residue according to claim 8, which is characterized in that: the temperature during the baking process of the dihydrate flaky iron phosphate in the step S3 is set as follows: firstly, heat preservation treatment is carried out for 0.5-2 h at 150-300 ℃, and then the temperature is raised to 500-800 ℃ for heat preservation for 2-5 h.

Technical Field

The invention relates to the technical field of lithium batteries, in particular to a method for preparing flaky iron phosphate by utilizing acid waste liquid and calcium phosphate waste residues.

Background

Lithium batteries prepared from olivine-structured lithium iron phosphate have the advantages of large discharge capacity, long cycle life, high safety, environmental friendliness and the like, and are widely applied to traffic equipment such as electric vehicles and hybrid electric vehicles. At present, iron phosphate is generally used as a precursor in industry, and a high-temperature solid-phase method is adopted to prepare lithium iron phosphate. Researches find that lithium iron phosphate with a sheet structure can be more tightly stacked compared with other lithium iron phosphate with irregular morphology, thereby being beneficial to improving the compaction density of the lithium iron phosphate anode material. The ferric phosphate is an important raw material for preparing the lithium iron phosphate, the shape and the purity of the ferric phosphate have extremely important influence on the electrochemical performance of the lithium iron phosphate, and one idea for preparing the flaky lithium iron phosphate lies in preparing the ferric phosphate with a flaky structure. However, the prior art can only prepare the ferric phosphate dihydrate with a sheet structure, and the prepared anhydrous ferric phosphate can not maintain the sheet structure of the ferric phosphate dihydrate due to the melting phenomenon in the high-temperature roasting dehydration process of the ferric phosphate dihydrate.

Meanwhile, phosphorus chemical enterprises can generate a large amount of industrial solid waste phosphogypsum in the process of producing wet-process phosphoric acid, and the phosphogypsum has rich phosphorus content and higher recycling value. However, in the prior art, the phosphorus resource in the calcium phosphate waste residue can not be effectively recycled.

In addition, chemical plants usually generate a large amount of acidic waste liquid in the production process, such as acidic waste liquid generated in the chemical processes of iron phosphate production, electroplating production, circuit board etching, high-purity graphite purification and the like, and chemical enterprises in the prior art usually need to treat the acidic waste liquid by means of evaporative crystallization, reverse osmosis and the like so as to remove pollutants such as heavy metal ions in the waste liquid and avoid environmental and water pollution, thereby greatly increasing the production cost of the enterprises.

Therefore, an effective method is needed to be found for solving the problems that the industrial acidic waste liquid is difficult to treat, the phosphorus-containing waste residue is difficult to utilize, and the flaky anhydrous iron phosphate is difficult to prepare.

Disclosure of Invention

The present invention is directed to solving at least one of the problems of the prior art. Therefore, the invention provides a method for preparing flaky iron phosphate by using acidic waste liquid and calcium phosphate waste residue, which can effectively treat the acidic waste liquid, effectively recycle the calcium phosphate waste residue and simultaneously prepare anhydrous iron phosphate with a flaky structure by using the acidic waste liquid and the calcium phosphate waste residue.

A method according to an embodiment of the invention comprises the steps of:

s1, leaching phosphate: mixing the calcium phosphate waste residue, the acidic waste liquid and the oxalic acid solution, heating for reaction, and filtering out precipitation slag to obtain a phosphorus-containing leaching solution;

s2, preparing dihydrate flaky iron phosphate: heating the phosphorus-containing leaching solution prepared in the step S1 to 30-70 ℃, adding an iron raw material solution, heating to 80-100 ℃, reacting for 2-5 hours to obtain an iron phosphate slurry, and performing pressure filtration on the iron phosphate slurry to obtain dihydrate flaky iron phosphate;

s3, preparation of anhydrous flaky iron phosphate: and (4) carrying out two-stage heat preservation roasting on the dihydrate flaky iron phosphate prepared in the step (S2) to remove crystal water, thus obtaining the anhydrous flaky iron phosphate.

According to the method provided by the embodiment of the invention, the method has at least the following beneficial effects: the scheme of the invention utilizes the acidic waste liquid as the leaching acid for leaching the phosphate radical in the calcium phosphate waste residue, not only skillfully solves the problems of difficult treatment, high cost and the like of the acidic waste liquid, but also does not need to use inorganic acid with strong corrosivity such as hydrochloric acid, sulfuric acid and the like as the leaching acid compared with the technology for preparing the iron phosphate by utilizing the phosphorus-containing waste residue in the prior art, thereby reducing the corrosion of the leaching acid to production equipment and the maintenance cost of the equipment; in the process of leaching calcium phosphate, oxalic acid solution is added, so that on one hand, the acidity of the acidic waste liquid can be increased, and the leaching rate of calcium phosphate waste residue is improved; on the other hand, the introduced oxalate can form oxalate precipitates with metal impurity ions such as manganese, magnesium, copper and the like brought by calcium phosphate waste residues or acidic waste liquid, so that the impurities are prevented from being brought into finished iron phosphate products, the product purity is improved, and the subsequent impurity removal cost is reduced; the iron phosphate is prepared by taking the calcium phosphate waste residues as a phosphorus source, so that a low-price raw material is provided for iron phosphate enterprises, and the production cost of the iron phosphate is effectively reduced. In addition, in the high-temperature roasting dehydration stage of the dihydrate flaky iron phosphate, a low-temperature-high-temperature two-stage heat preservation system is adopted, so that the dihydrate flaky iron phosphate is effectively prevented from being excessively molten, and the anhydrous iron phosphate effectively inherits the flaky structure of the dihydrate flaky iron phosphate.

According to some embodiments of the present invention, the acidic waste liquid in step S1 is an acidic waste liquid in industrial processes such as iron phosphate preparation, circuit board etching, high-purity graphite purification, and the like. The embodiment scheme of the invention can directly utilize the acidic waste liquid so as to solve the problems of difficult treatment, high treatment cost and the like of the acidic waste liquid in the prior art.

According to some embodiments of the invention, the pH of the acidic waste liquid is 0.7 to 5.0; preferably 0.7 to 4.0; more preferably 0.7 to 3.

According to some embodiments of the invention, the solid-to-liquid ratio of the calcium phosphate waste residue to the acidic waste liquid is 100-300 g/L; preferably 100-200 g/L; more preferably 100 to 150 g/L.

According to some embodiments of the invention, the mass fraction of the oxalic acid solution is 15-30%, and the volume ratio of the oxalic acid solution to the acidic waste liquid is 0.1: 1-1: 1; preferably, the volume ratio of the oxalic acid solution to the acidic waste liquid is 0.1: 1-0.2: 1.

According to some embodiments of the present invention, the reaction temperature of step S1 is 30 to 50 ℃, and the reaction time is 2 to 4 hours.

According to some embodiments of the present invention, the stirring speed in the step S1 is 100 to 600 rpm.

According to some embodiments of the invention, the iron feed solution comprises at least one of a solution of an iron salt or a solution of a ferrous salt; preferably, the iron salt is ferric sulfate; preferably, when the iron raw material liquid contains a ferrous salt, the method further comprises a step of oxidizing ferrous ions into ferric ions before adding the iron raw material liquid.

According to some embodiments of the present invention, the molar ratio of the phosphorus element in the phosphorus-containing leachate in step S2 to the iron element in the iron raw material solution is 1:1 to 1.5: 1.

According to some embodiments of the present invention, the temperature during the baking of the dihydrate flaky iron phosphate in step S3 is set as follows: firstly, carrying out low-temperature heat preservation treatment and then carrying out high-temperature heat preservation treatment; wherein the low temperature is not more than 300 ℃, the high temperature is not less than 500 ℃, and the time of the low-temperature heat preservation treatment is not longer than that of the high-temperature heat preservation treatment; preferably, the temperature during the roasting process of the dihydrate flaky iron phosphate in the step S3 is set as follows: firstly, heat preservation treatment is carried out for 0.5-2 h at 150-300 ℃, and then the temperature is raised to 500-800 ℃ for heat preservation for 2-5 h. The method comprises the following steps of dehydrating the dihydrate flaky iron phosphate by adopting a two-section heat-preservation roasting mode, firstly performing low-temperature heat preservation treatment on the dihydrate flaky iron phosphate, and then heating to a high-temperature section for dehydration treatment, so that excessive melting of the dihydrate flaky iron phosphate in the roasting process is effectively avoided, and the prepared anhydrous iron phosphate still keeps the flaky shape of the dihydrate flaky iron phosphate.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

FIG. 1 is an SEM image of dihydrate flaky iron phosphate prepared in example 1 of the present invention;

FIG. 2 is an SEM image of anhydrous iron phosphate prepared in example 1 of the present invention;

FIG. 3 is an SEM image of dihydrate flaky iron phosphate prepared in example 2 of the present invention;

FIG. 4 is an SEM image of anhydrous iron phosphate prepared in example 2 of the present invention;

FIG. 5 is an SEM image of dihydrate flaky iron phosphate prepared in comparative example 1 of the present invention;

fig. 6 is an SEM image of anhydrous iron phosphate prepared in comparative example 2 of the present invention.

Detailed Description

In order to explain technical contents, achieved objects, and effects of the present invention in detail, the following description is made with reference to the accompanying drawings in combination with the embodiments.

The first embodiment of the invention is as follows: a method for preparing flaky iron phosphate by utilizing acid waste liquid and calcium phosphate waste residue comprises the following steps:

(1) leaching phosphate radical: adding calcium phosphate waste residues into acidic waste liquid with the pH value of 0.9 at the stirring speed of 300rpm at 40 ℃, wherein the acidic waste liquid is acidic mother liquid generated in the process of preparing the iron phosphate by a coprecipitation method, the solid-to-liquid ratio of the calcium phosphate to the acidic waste liquid is controlled to be 100g/L, then adding oxalic acid solution with the mass concentration of 15% into the acidic waste liquid according to the volume ratio of the acidic waste liquid to the oxalic acid solution of 1:0.1, stirring and reacting for 3 hours, and performing pressure filtration to obtain precipitation residues and phosphorus-containing leachate, wherein the mass concentration of phosphorus in the phosphorus-containing leachate is 14.14 g/L.

(2) Preparing dihydrate flaky iron phosphate: and (3) heating the phosphorus-containing leaching solution to 50 ℃, gradually adding the ferric sulfate raw material solution into the phosphorus-containing leaching solution according to the molar ratio of the iron element in the ferric sulfate raw material solution to the phosphorus element in the phosphorus-containing leaching solution of 1:1.3, heating to 94 ℃, keeping the temperature for 4 hours at the temperature, and performing pressure filtration to obtain the dihydrate flaky ferric phosphate filter cake.

(3) Preparation of anhydrous flaky iron phosphate: and (3) placing the dihydrate flaky iron phosphate filter cake into a muffle furnace for roasting and dewatering, firstly preserving heat for 1h at the temperature of 200 ℃, then heating to 600 ℃, preserving heat for 3h at the temperature, and cooling to room temperature to obtain the anhydrous iron phosphate.

The microscopic morphologies of the dihydrate flaky iron phosphate and the anhydrous iron phosphate prepared in the above steps S2 and S3 were observed by a Scanning Electron Microscope (SEM), and the results are shown in fig. 1 and fig. 2, respectively. As can be seen from the figure, both the dihydrate flaky iron phosphate and the anhydrous iron phosphate prepared in this example exhibit a flaky morphology.

The prepared iron phosphate is taken to carry out physical and chemical index detection according to a conventional method, and the results are shown in the following table 1:

table 1 physicochemical indices of iron phosphate produced in example 1 of the invention

As shown in the table, the test results of various physical and chemical indexes of the finished product of the prepared iron phosphate all meet the requirements of battery-grade iron phosphate.

The second embodiment of the invention is as follows: a method for preparing flaky iron phosphate by utilizing acid waste liquid and calcium phosphate waste residue comprises the following steps:

(1) leaching phosphate radical: adding calcium phosphate waste residues into acidic waste liquid with the pH value of 1.6 at the stirring speed of 300rpm at 40 ℃, wherein the acidic waste liquid is generated in the etching process of a circuit board, the solid-to-liquid ratio of the calcium phosphate to the acidic waste liquid is controlled to be 150g/L, then adding oxalic acid solution with the mass concentration of 15% into the acidic waste liquid according to the volume ratio of the acidic waste liquid to the oxalic acid solution of 1:0.15, stirring and reacting for 3 hours, and performing pressure filtration to obtain precipitation residues and phosphorus-containing leachate, wherein the mass concentration of phosphorus in the phosphorus-containing leachate is 23.51 g/L.

(2) Preparing dihydrate flaky iron phosphate: and (3) heating the phosphorus-containing leaching solution to 60 ℃, gradually adding the ferric sulfate raw material solution into the phosphorus-containing leaching solution according to the molar ratio of the iron element in the ferric sulfate raw material solution to the phosphorus element in the phosphorus-containing leaching solution of 1:1.2, heating to 90 ℃, keeping the temperature for 4 hours at the temperature, and performing pressure filtration to obtain the dihydrate flaky ferric phosphate filter cake.

(3) Preparation of anhydrous flaky iron phosphate: and (3) placing the dihydrate flaky iron phosphate filter cake into a muffle furnace for roasting and dehydration, firstly preserving heat for 1h at the temperature of 180 ℃, then heating to 650 ℃, preserving heat for 3h at the temperature, and cooling to room temperature to obtain the anhydrous iron phosphate.

The shapes of the dihydrate flaky iron phosphate and the iron phosphate prepared in the above steps S2 and S3 were observed by a Scanning Electron Microscope (SEM), and the results are shown in fig. 3 and 4. As can be seen from the figure, both the dihydrate flaky iron phosphate and the anhydrous iron phosphate prepared in this example exhibit a flaky morphology.

The prepared iron phosphate is taken to carry out physical and chemical index detection according to a conventional method, and the results are shown in the following table 2:

table 2 physicochemical indices of iron phosphate prepared in example 2 of the invention

As shown in Table 2, the results of various physical and chemical index tests of the finished product of the prepared iron phosphate all meet the requirements of battery-grade iron phosphate.

The third embodiment of the invention is as follows: a method for preparing flaky iron phosphate by utilizing acid waste liquid and calcium phosphate waste residue comprises the following steps:

(1) leaching phosphate radical: adding calcium phosphate waste residues into an acidic waste liquid with the pH value of 0.77 at the stirring speed of 200rpm at 50 ℃, wherein the acidic waste liquid is an acidic mother liquid generated in the process of preparing iron phosphate by a coprecipitation method, the solid-to-liquid ratio of calcium phosphate to the acidic mother liquid of iron phosphate is 150g/L, then adding an oxalic acid solution with the mass concentration of 15% into the acidic mother liquid of iron phosphate according to the volume ratio of the acidic mother liquid of iron phosphate to the oxalic acid solution of 1:0.2, stirring and reacting for 3 hours, and performing filter pressing to obtain precipitation residues and a phosphorus-containing leachate, wherein the mass concentration of phosphorus in the phosphorus-containing leachate is 24.04 g/L.

(2) Preparing dihydrate flaky iron phosphate: and (3) heating the phosphorus-containing leaching solution to 60 ℃, gradually adding the ferric sulfate raw material solution into the phosphorus-containing leaching solution according to the molar ratio of the iron element in the ferric sulfate raw material solution to the phosphorus element in the phosphorus-containing leaching solution of 1:1.25, heating to 90 ℃, keeping the temperature for 3 hours at the temperature, and performing pressure filtration to obtain the dihydrate flaky ferric phosphate filter cake.

(3) Preparation of anhydrous flaky iron phosphate: and (3) placing the dihydrate flaky iron phosphate filter cake into a muffle furnace for roasting and dewatering, firstly preserving heat for 1h at the temperature of 220 ℃, then heating to 600 ℃, preserving heat for 3h at the temperature, and cooling to room temperature to obtain the anhydrous iron phosphate.

The fourth embodiment of the invention is as follows: a method for preparing flaky iron phosphate by utilizing acid waste liquid and calcium phosphate waste residue comprises the following steps:

(1) leaching phosphate radical: adding calcium phosphate waste residues into an acidic waste liquid with the pH value of 3.4 at the stirring speed of 350rpm at 50 ℃, wherein the acidic waste liquid is generated by a pressure oxidation plant, the solid-to-liquid ratio of calcium phosphate to the acidic waste liquid is controlled to be 300g/L, then adding an oxalic acid solution with the mass concentration of 30% into the acidic waste liquid according to the volume ratio of the acidic waste liquid to the oxalic acid solution of 1:1, stirring and reacting for 3 hours, and carrying out pressure filtration to obtain precipitated slag and a phosphorus-containing leachate, wherein the mass concentration of phosphorus in the phosphorus-containing leachate is 30.51 g/L.

(2) Preparing dihydrate flaky iron phosphate: and (3) heating the phosphorus-containing leaching solution to 70 ℃, gradually adding the ferric sulfate raw material solution into the phosphorus-containing leaching solution according to the molar ratio of the iron element in the ferric sulfate raw material solution to the phosphorus element in the phosphorus-containing leaching solution of 1:1.5, heating to 98 ℃, keeping the temperature for 5 hours at the temperature, and performing pressure filtration to obtain the dihydrate flaky ferric phosphate filter cake.

(3) Preparation of anhydrous iron phosphate: and (3) placing the dihydrate flaky iron phosphate filter cake into a muffle furnace for roasting and dewatering, firstly, preserving heat for 2h at the temperature of 250 ℃, then, heating to 750 ℃, preserving heat for 2h at the temperature, and cooling to room temperature to obtain the anhydrous iron phosphate.

The anhydrous iron phosphate prepared in the third and fourth embodiments is also flaky as observed by a scanning electron microscope, and the physicochemical indexes of the iron phosphate prepared by using the anhydrous iron phosphate also meet the requirements of battery-grade iron phosphate, so that the redundancy is avoided and no further description is given here.

The first comparative example of the present invention is: a method for preparing flaky iron phosphate by utilizing acid waste liquid and calcium phosphate waste residue comprises the following steps:

this comparative example uses a procedure similar to that of example 1, the only difference from example 1 being: after the dihydrate flaky iron phosphate is prepared according to the comparative example, the dihydrate flaky iron phosphate is roasted and dehydrated by adopting a conventional one-stage heat preservation roasting mode, namely, the dihydrate flaky iron phosphate is directly heated to 600 ℃ and is subjected to heat preservation for 3 hours.

The SEM scanning result of the obtained anhydrous iron phosphate is shown in fig. 5, and it can be seen from fig. 5 that the surface melting of the anhydrous iron phosphate is severe after the calcination and dehydration, and the existence of flaky iron phosphate is hardly observed. With reference to the first embodiment and the first comparative example, in the scheme of the invention, to obtain the flaky anhydrous iron phosphate, a two-stage heat-preservation roasting system is adopted to dehydrate the flaky dihydrate iron phosphate.

The second comparative example of the present invention is: the comparative example adopts the steps similar to the method of the first embodiment, and the only difference from the first embodiment is that: in the preparation of the dihydrate flaky iron phosphate, the comparative example adopts a feeding mode that the iron raw material solution is used as a base solution (i.e. the phosphorus-containing leaching solution is added into the iron sulfate raw material solution).

The SEM scanning result of the prepared anhydrous ferric phosphate is shown in fig. 6, and it can be seen from fig. 6 that the ferric phosphate prepared in the comparative example is clearly different from the ferric phosphate prepared in the first example in morphology, and the ferric phosphate in the comparative example is formed by mutually agglomerating spheroidal particles. With reference to the first example and the second comparative example, the scheme of the invention is beneficial to preparing the flaky iron phosphate by adopting a feeding mode of taking the phosphorus-containing leaching solution as a base solution.

The third comparative example of the present invention is: the comparative example adopts the steps similar to the method of the first embodiment, and the only difference from the first embodiment is that: during the calcium phosphate leaching, no oxalic acid solution was added.

The physical and chemical indexes of the iron phosphate prepared in the first embodiment are detected under the same conditions, and the results are shown in the following table 3:

TABLE 3 physicochemical indices of iron phosphate prepared according to comparative example III of the present invention

As can be seen from table 3, compared with the first example, the content of impurities such as calcium, manganese, and magnesium in the anhydrous iron phosphate prepared by the comparative example is significantly higher than that of the first example, which is mainly because some of the impurity ions such as calcium, manganese, and magnesium in the calcium phosphate waste residue form divalent metal ions during the leaching process, and the divalent metal ions are brought into the phosphorus-containing leachate and finally brought into the anhydrous iron phosphate. Therefore, the scheme of the invention can greatly remove impurity ions in the calcium phosphate waste residue by adding the oxalic acid solution in the phosphate radical leaching process so as to ensure the purity of the prepared iron phosphate.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all equivalent changes made by using the contents of the present specification and the drawings, or applied directly or indirectly to the related technical fields, are included in the scope of the present invention.