A low-cost preparation process for nanoscale high-purity iron phosphate

Abstract

The present invention relates to the technical field of battery positive electrode materials, and specifically to a low-cost preparation process for nano-scale high-purity iron phosphate, comprising the following preparation steps: S1, raw material processing; S2, primary precipitation of iron phosphate; S3, secondary precipitation of iron phosphate; S4, washing; S5, drying and calcining. The present invention pre-treats two raw materials, fertilizer-grade ammonium phosphate and titanium dioxide by-product ferrous sulfate, to reduce their impurity element content to a relatively low level, and then controls the co-precipitation pH, controls the co-precipitation material morphology, and performs directional adsorption to control the impurity element content in the product within 20 ppm, achieves a crystallinity of 90%, and has primary particles of about 100 nm. The lithium iron phosphate prepared using the iron phosphate as the raw material has a compacted density of up to 2.55 g / cm 3 The discharge specific capacity can reach 160mAh / g. The original particles of the prepared iron phosphate material are extremely fine, with excellent price performance and good electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of battery positive electrode materials, and in particular to a process for preparing low-cost nano-scale high-purity iron phosphate. Background Art

[0002] Iron phosphate (FePO) is a midstream component of the phosphorus chemical industry chain and a key precursor for lithium iron phosphate (LiFePO), a new energy cathode material. Driven by high demand for LiFePO in new energy vehicles and energy storage, demand for FePO is rapidly increasing. The industry's booming market has attracted numerous companies to establish presence. Among them, Phosphorus chemical companies with access to phosphorus sources and titanium dioxide companies with access to iron sources have leveraged their resource advantages to enter the FePO industry. In the FePO production process, phosphorus sources are essential raw materials and contribute the largest portion of the production cost.

[0003] Currently, the most commonly used phosphorus source for ferric phosphate production is industrial ammonium phosphate, which has a lower impurity content than fertilizer-grade ammonium phosphate and, consequently, a higher price. Processes using industrial ammonium phosphate as a raw material are primarily divided into one-step and two-step methods. Compared to the two-step method, the one-step method produces a product with a lower yield of less than 90%, a relatively high content of impurities, and greater product quality variability, resulting in poor electrochemical performance. The two-step method, while requiring a longer process, produces a more stable product with superior impurity levels, iron-to-phosphorus ratio, and other indicators. It also exhibits superior electrochemical performance and is commonly used in the production of power-grade lithium iron phosphate. From a process source perspective, fertilizer-grade ammonium phosphate is produced from the mother liquor of industrial ammonium phosphate production. Therefore, its use in ferric phosphate production can increase its added value. By selecting a cost-effective phosphorus source as the raw material for ferric phosphate production, process optimization can significantly reduce ferric phosphate production costs and improve product competitiveness. Summary of the Invention

[0004] In order to further control the preparation cost of ferric phosphate, reduce the impurity content, and improve the product yield of ferric phosphate, the present invention discloses a low-cost preparation process of nano-scale high-purity ferric phosphate. The process uses inexpensive fertilizer-grade ammonium phosphate and ferrous sulfate, a by-product of titanium dioxide, as raw materials. After impurity removal, multi-stage precipitation, directional adsorption, and two washings, nano-scale high-purity ferric phosphate is prepared.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A low-cost process for preparing nano-scale high-purity ferric phosphate comprises the following steps:

[0007] S1. Raw material processing: Fertilizer-grade ammonium phosphate and ferrous sulfate, a by-product of titanium dioxide, are pretreated to obtain an ammonium phosphate aqueous solution and a ferrous sulfate solution; desalted water is added to the ammonium phosphate aqueous solution and the ferrous sulfate solution as raw materials to prepare an ammonium phosphate solution and an iron salt solution for later use;

[0008] S2, primary precipitation of ferric phosphate: hydrogen peroxide is slowly added dropwise to the iron salt under stirring until the color of the solution changes to reddish brown, and after the iron salt is completely oxidized, it is transferred to a reactor, W-type zeolite molecular sieve is added thereto, and the ammonium phosphate solution is slowly added dropwise to the iron salt solution under stirring to obtain amorphous ferric phosphate by primary precipitation, and the upper liquid is the mother liquor; the present invention controls the pH of the iron salt and the pH of the phosphate salt itself, thereby controlling the pH of the primary co-precipitation at a lower value. Specifically, when the pH is 1.0-1.5, the crystal nucleus is formed faster, which is beneficial to inhibiting the growth of primary particles and controlling the primary particles of the particles at a smaller level. The higher the pH value, the higher the impurity content;

[0009] S3, secondary precipitation of ferric phosphate: After the ammonium phosphate solution in S2 is added dropwise, a pH regulator is added to adjust the pH, and the residual ferric phosphate in the mother liquor is subjected to secondary precipitation. After the precipitation is completed, the reaction is kept warm; the combined effect of the two precipitations and the directional adsorption of the W-type zeolite molecular sieve further reduces the impurity content of the ferric phosphate product and improves the yield;

[0010] S4, washing: using a sieve to separate the W-type zeolite molecular sieve from the slurry after the reaction in step S3, and then separating the solid and liquid of the slurry and washing the filter cake; the W-type zeolite molecular sieve directional adsorption mainly adsorbs impurity ions such as K in the system to prevent them from being wrapped in iron phosphate during the co-precipitation process, and then washing the W-type zeolite molecular sieve so that it can be reused;

[0011] S5, drying and calcining: drying the filter cake after washing in step S4, and calcining it after drying to obtain nano-scale high-purity anhydrous ferric phosphate.

[0012] Preferably, the fertilizer-grade ammonium phosphate includes one or both of fertilizer ammonium phosphate and 55% powdered ammonium.

[0013] Preferably, the specific method for pretreatment of the fertilizer-grade ammonium phosphate is:

[0014] Add fertilizer-grade ammonium phosphate and desalted water in a ratio of 1:2.0-3.0, mix and stir, then heat to 40-50°C. Add 85% phosphoric acid (1-3% by weight of the ammonium phosphate solids), stir for 3-4 hours to dissolve, and then perform solid-liquid separation to obtain an ammonium phosphate aqueous solution. By adding an appropriate amount of 85% phosphoric acid and under appropriate temperature conditions, the dissolution of fertilizer-grade ammonium phosphate is promoted to obtain an aqueous solution.

[0015] Preferably, the pretreatment method of the titanium dioxide byproduct ferrous sulfate is as follows: adding the titanium dioxide byproduct ferrous sulfate and desalted water in a ratio of 1:1.0-2.0, adding an impurity remover and a pH adjuster after dissolution to adjust the pH of the solution to 4.0-5.0, and after adjustment, performing solid-liquid separation to obtain a purified ferrous sulfate solution. The ferrous sulfate is impurity-removed to remove the Ti element and reduce the impurity content.

[0016] Preferably, the impurity remover and pH regulator are one or both of ammonia water and sodium hydroxide.

[0017] More preferably, the impurity remover and pH adjuster are aqueous ammonia.

[0018] Preferably, the filter cake washing operation specifically includes: first washing the filter cake after solid-liquid separation of S3 with desalted water, crushing the filter cake after washing, then adding desalted water and phosphoric acid, performing solid-liquid separation after the insulation reaction is completed, and then washing with desalted water.

[0019] Preferably, in S1, the concentrations of the ammonium phosphate solution and the iron salt solution are 1.0-1.5 mol / L and 2.0-2.5 mol / L, respectively.

[0020] Preferably, in S2, the amount of hydrogen peroxide added is to reduce the Fe 2+ 1.1-1.3 times the theoretical molar amount for complete oxidation.

[0021] Preferably, in S2, the W-type zeolite molecular sieve is added in an amount of 3-5% by mass of the iron salt.

[0022] Preferably, in S3, a pH regulator is added to adjust the pH to 3.0-4.0.

[0023] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0024] (1) The present invention provides a low-cost preparation process for nano-scale high-purity ferric phosphate, which uses fertilizer-grade ammonium phosphate and ferrous sulfate, a by-product of titanium dioxide, as main raw materials. Its price has a significant price advantage over the commonly used phosphorus and iron sources on the market. The 50,000 tons / year anhydrous ferric phosphate production line uses fertilizer-grade ammonium phosphate and ferrous sulfate, a by-product of titanium dioxide, as raw materials. Compared with the common industrial ammonium phosphate process on the market, it can save about 25 million yuan per year.

[0025] (2) The present invention provides a low-cost preparation process for nano-scale high-purity ferric phosphate, which further reduces the impurity content of the ferric phosphate product and improves the yield through two precipitations and the directional adsorption of W-type zeolite molecular sieves; the first precipitation is mainly when the solution is at a low pH, and a large number of amorphous ferric phosphate particles are generated relatively intact, with less adsorption and encapsulation of impurity elements such as N, S, K, Mn, and Mg; the second precipitation appropriately adjusts the pH value to 3-4 to recover Fe and P in the solution, while ensuring low pH co-precipitation, the product yield is significantly improved. Under the low pH conditions of the present invention, particle growth is inhibited and particle nucleation is promoted, resulting in smaller primary particles. The amorphous ferric phosphate precipitated once acts as a seed crystal. After the second precipitation, the primary particles are also smaller and have better crystallinity.

[0026] (3) The present invention provides a low-cost preparation process for nano-scale high-purity iron phosphate. By pre-treating two raw materials, fertilizer-grade ammonium phosphate and titanium dioxide by-product ferrous sulfate, the impurity element content is reduced to a low level. Then, by controlling the co-precipitation pH, controlling the morphology of the co-precipitated material, and directional adsorption, the impurity element content in the product is controlled within 20 ppm. The crystallinity can reach 90%, and the primary particles are about 100 nm. The lithium iron phosphate prepared using the iron phosphate as the raw material has a compacted density of up to 2.55 g / cm 3 The discharge specific capacity can reach 160mAh / g. The original particles of the prepared iron phosphate material are extremely fine, with excellent price performance and good electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a SEM image of the nanoscale high-purity iron phosphate prepared by the present invention. DETAILED DESCRIPTION

[0028] To better understand the present invention, embodiments of the technical solutions of the present invention are described in detail below. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are therefore only illustrative and are not intended to limit the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the above invention are also considered to fall within the scope of protection of the present invention.

[0029] The present invention provides a low-cost preparation process for nano-scale high-purity ferric phosphate, which specifically includes the following preparation steps:

[0030] S1. Raw material processing:

[0031] Fertilizer-grade ammonium phosphate and titanium dioxide by-product ferrous sulfate are pretreated to obtain an ammonium phosphate aqueous solution and a ferrous sulfate solution; the fertilizer-grade ammonium phosphate is selected from one or more of fertilizer ammonium phosphate and 55% ammonium powder;

[0032] Pre-treat the fertilizer-grade ammonium phosphate: add fertilizer-grade ammonium phosphate and desalted water in a ratio of 1:2.0-3.0, mix and stir, and heat to 40-50°C, add 85% phosphoric acid which is 1-3% of the solid mass of the ammonium phosphate, stir for 3-4 hours to dissolve, and then perform solid-liquid separation to obtain an ammonium phosphate aqueous solution.

[0033] The titanium dioxide by-product ferrous sulfate is pretreated: the titanium dioxide by-product ferrous sulfate and desalted water are added in a ratio of 1:1.0-2.0, and after dissolution, an impurity remover and a pH regulator are added to adjust the pH of the solution to 4.0-5.0, and after stirring, the solid-liquid separation is performed to obtain a purified ferrous sulfate solution; the impurity remover and the pH regulator are selected from one or more of ammonia water and sodium hydroxide.

[0034] The ammonium phosphate aqueous solution and ferrous sulfate solution obtained after pretreatment are used as raw materials, desalted water is added, and the ammonium phosphate solution and ferric salt solution with concentrations of 1.0-1.5 mol / L and 2.0-2.5 mol / L are prepared for use;

[0035] S2. Primary precipitation of iron phosphate:

[0036] Slowly add hydrogen peroxide to the iron salt solution while stirring until the solution turns reddish brown. After the iron salt is completely oxidized, transfer it to the reactor. The amount of hydrogen peroxide added is to reduce the Fe 2+ The method comprises the following steps: adding W-type zeolite molecular sieve to the reactor, wherein the addition ratio of W-type zeolite molecular sieve is 3-5% of the mass ratio of the iron salt, slowly adding the ammonium phosphate solution dropwise to the iron salt solution under stirring, and adjusting the pH of the iron salt and the pH of the phosphate salt itself so that the pH of the primary precipitation system is 1-1.5, and obtaining amorphous iron phosphate by primary precipitation;

[0037] S3. Secondary precipitation of iron phosphate:

[0038] After the ammonium phosphate solution is added dropwise in step S2, a pH regulator is added to adjust the pH to 3.0-4.0, and the residual iron phosphate in the mother liquor is subjected to secondary precipitation. After the precipitation is completed, the reaction is kept warm for 70 minutes; the pH regulator is one or more of ammonia water and sodium hydroxide.

[0039] S4, washing:

[0040] The slurry after the reaction in step S3 is separated from the W-type zeolite molecular sieve using a 200-mesh sieve, and then the slurry is separated into solid and liquid and the filter cake is washed; first, the filter cake after the solid-liquid separation in S3 is washed with desalted water 20 times the mass of the filter cake. After the washing, the filter cake is crushed, and then desalted water 2 times the mass of the desalted water and 0.2 times the mass of phosphoric acid are added, and the reaction is kept warm at 80° C. After the reaction is completed, the solid and liquid are separated, and the filter cake is washed with desalted water 30 times the mass of the filter cake.

[0041] S5, drying and calcining: drying the filter cake after washing in step S4 at 80° C., and then calcining it at 650° C. to obtain nano-scale high-purity anhydrous ferric phosphate.

[0042] Examples and Comparative Examples

[0043] According to the above preparation steps, wherein the fertilizer-grade ammonium phosphate is fertilizer ammonium phosphate, the impurity remover and pH regulator in S1 are ammonia water, and during the secondary precipitation, the pH regulator is ammonia water, Examples 1-4 and Comparative Examples 1-5 respectively treat the fertilizer-grade ammonium phosphate and the titanium dioxide by-product ferrous sulfate under different conditions to obtain fixed concentration ammonium phosphate solutions and iron salt solutions for standby use. The specific treatment process parameters are shown in Table 1 below.

[0044] Table 1. Raw material processing parameters of Examples 1-4 and Comparative Examples 1-5

[0045]

[0046] Note: “-” in the above table means that the step is not performed.

[0047] The ammonium phosphate solution and the iron salt solution prepared from the raw materials of Examples 1-4 and Comparative Examples 1-5 were subjected to precipitation and heat preservation reaction to obtain ferric phosphate. The specific precipitation reaction treatment process parameters are shown in Table 2 below.

[0048] Table 2. Precipitation process parameters for Examples 1-4 and Comparative Examples 1-5

[0049]

[0050] Note: “-” in the above table means that the step is not performed.

[0051] After the precipitation and heat preservation reaction of the above Examples 1-4 and Comparative Examples 2-5 is completed, the W-type zeolite molecular sieve is first separated using a 200-mesh sieve. The molecular sieve can be recycled after washing and drying. After the separation is completed, the slurry is separated into solid and liquid. In Comparative Example 1, no W-type zeolite molecular sieve is added and solid-liquid separation can be performed directly.

[0052] After solid-liquid separation, the filter cake is washed with desalted water 20 times the mass of the filter cake. After washing, the filter cake is crushed and desalted water 2 times the mass of the filter cake and phosphoric acid 0.2 times the mass of the filter cake are added. The mixture is kept warm at 80°C for reaction. After the reaction is completed, solid-liquid separation is performed again, and the filter cake is then washed with desalted water 30 times the mass of the filter cake. After washing, the filter cake is dried at 80°C and calcined at 650°C to obtain nano-scale high-purity anhydrous ferric phosphate.

[0053] The iron phosphate samples prepared in Examples 1-4 and Comparative Examples 1-5 were tested respectively, and the test and analysis results are shown in Table 3 below.

[0054] Table 3. Yield, iron-phosphorus ratio, primary particle size, particle size, and crystallinity of each group of samples

[0055] serial number Yield Iron-phosphorus ratio Primary particle size D50 crystallinity Industry average 98.15％ 0.975 102.3nm 3.14um 87.5％ Example 1 99.45％ 0.982 67.5nm 1.45um 91.4％ Example 2 98.98％ 0.984 64.7nm 1.52um 91.6％ Example 3 99.42％ 0.981 58.9nm 1.80um 90.9％ Example 4 98.69％ 0.980 60.3nm 1.63um 91.6％ Comparative Example 1 62.56％ 0.977 147.7nm 2.89um 85.6％ Comparative Example 2 69.56％ 0.974 198.4nm 2.67um 88.5％ Comparative Example 3 58.79％ 0.969 54.6nm 1.74um 84.7％ Comparative Example 4 99.46％ 0.968 88.56nm 3.56um 88.4％ Comparative Example 5 98.69％ 0.968 198.4nm 2.56 88.3％

[0056] The iron phosphate samples prepared in Examples 1-4 and Comparative Examples 1-5 were used to prepare lithium iron phosphate according to the existing process and their compaction and electrical properties were tested. The test results are shown in Table 4 below.

[0057] The existing preparation method is as follows: after dissolving industrial-grade ammonium phosphate, adding ammonia water to adjust its pH to 7.0, controlling the pH of ferrous sulfate solution to 4.0 after removing impurities, mixing hydrogen peroxide and phosphate salt and adding dropwise to iron salt to obtain amorphous iron phosphate through one precipitation, and then washing, aging and sintering to obtain anhydrous iron phosphate.

[0058] Table 4. Impurity element content of each group of samples, compaction and electrical properties of lithium iron phosphate prepared under the same process conditions

[0059]

[0060]

[0061] Industry average: iron phosphate produced using existing technology.

[0062] From the above sample test data:

[0063] (1) Comparative Example 1 Compared with Example 1, the ferrous sulfate raw material, a by-product of titanium dioxide, was not impurity-removed, W-type zeolite molecular sieve was not added during the first precipitation, and no secondary precipitation was performed subsequently. The product had a high impurity content and a low yield. At the same time, the particle size of the primary particles and D50 was larger, and the crystallinity was lower.

[0064] (2) Compared with Example 1, in Comparative Example 2, no secondary precipitation was performed subsequently. The impurity content of the product was still higher than that of Example 1, and the yield was relatively low.

[0065] (3) In Comparative Example 3, compared with Example 1, the pH value during the ferrous sulfate treatment was lowered, so that the pH value obtained after the primary precipitation was lower than 1.0, and the pH was lowered during the secondary precipitation. The impurity content of the product was low, but the product yield was significantly reduced compared with Example 1.

[0066] (4) In Comparative Example 4, compared with Example 1, the pH was adjusted higher during the secondary precipitation. The product yield was equivalent to that of Example 1, but the impurity content was greatly increased.

[0067] (5) Compared with Example 1, Comparative Example 5 increases the pH value of the primary precipitation, showing an increase in impurity content, but the product yield is relatively high, the particle size of the primary particles and D50 is larger, and the crystallinity is lower.

[0068] When the titanium dioxide by-product ferrous sulfate is not purified, the content of impurity elements in the prepared product is generally high, which does not meet the requirements of battery-grade iron phosphate, and the primary particles of the prepared product are large, which is not conducive to subsequent processing; by using ammonia water, sodium hydroxide and other impurity removers and pH regulators to purify the raw materials, the impurity content is significantly reduced, the adsorption and encapsulation of elements such as N, S, K, Mn, Mg are less, and the subsequent washing pressure is relatively small. Through subsequent aging operations, the above impurities encapsulated in a small amount in the primary particles of this morphology will be further dissolved into the aging mother liquor, thereby further reducing the impurity elements in the solid phase after aging. When the pH is low, the nucleus forms faster, which is beneficial to inhibit the growth of primary particles and make the primary particles smaller. The directional adsorption of W-type zeolite molecular sieve is mainly for K ions in the adsorption system, which will prevent the K ions from being wrapped in iron phosphate during co-precipitation. Then, by washing the W-type zeolite molecular sieve, it can be reused. By controlling the co-precipitation and directional adsorption of W-type zeolite molecular sieve under low pH conditions, the amorphous iron phosphate precipitated has extremely fine primary particles and relatively complete particles. However, after the co-precipitation is completed under low pH conditions, the mother liquor contains more Fe and P, which makes the product yield less than 70%. By further adding ammonia water to the slurry to adjust the pH to 3-4, while ensuring low pH co-precipitation, the product yield is significantly improved, reaching more than 95%. Through subsequent optimization and verification experiments, the iron phosphate product prepared has an impurity element content of less than 20ppm, a crystallinity of up to 90%, and primary particles of about 100nm. The lithium iron phosphate prepared using this iron phosphate as raw material has a compaction density of up to 2.55g / cm 3 , the discharge capacity can reach 160mAh / g.

[0069] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A low-cost preparation process for nano-scale high-purity ferric phosphate, characterized in that: The method comprises the following preparation steps: S1. Raw material processing: Fertilizer-grade ammonium phosphate and ferrous sulfate, a by-product of titanium dioxide, are pretreated to obtain an ammonium phosphate aqueous solution and a ferrous sulfate solution; desalted water is added to the ammonium phosphate aqueous solution and the ferrous sulfate solution as raw materials to prepare an ammonium phosphate solution and an iron salt solution for later use; The specific method for pretreatment of the fertilizer-grade ammonium phosphate is: Add fertilizer-grade ammonium phosphate and desalted water, mix and stir, and heat, add phosphoric acid, stir and dissolve, and then perform solid-liquid separation to obtain ammonium phosphate aqueous solution; The specific method for pretreating the titanium dioxide byproduct ferrous sulfate is as follows: Add ferrous sulfate, a byproduct of titanium dioxide, and desalted water, dissolve, add an impurity remover and a pH adjuster to adjust the pH of the solution to 4.0-5.0, and after adjustment, separate the solid and liquid to obtain a purified ferrous sulfate solution; S2. Primary precipitation of ferric phosphate: hydrogen peroxide is slowly added dropwise to the ferric salt solution under stirring until the solution changes color to reddish brown. After the ferric salt is completely oxidized, the solution is transferred to a reactor, W-type zeolite molecular sieve is added thereto, and the ammonium phosphate solution is slowly added dropwise to the ferric salt solution under stirring. By controlling the pH of the ferric salt and the pH of the phosphate salt itself, the pH of the primary coprecipitation is controlled at 1.0-1.5, and amorphous ferric phosphate is obtained by primary precipitation. The upper liquid is the mother liquor; S3, secondary precipitation of ferric phosphate: After the ammonium phosphate solution in S2 is added dropwise, a pH regulator is added to adjust the pH to 3.0-4.0, and the residual ferric phosphate in the mother liquor is subjected to secondary precipitation. After the precipitation is completed, the reaction is kept warm; S4, washing: using a sieve to separate the W-type zeolite molecular sieve from the slurry after the S3 reaction, and then separating the solid and liquid of the slurry and washing the filter cake; S5, drying and calcining: drying the filter cake after washing in S4, and calcining it after drying to obtain nano-scale high-purity anhydrous ferric phosphate.

2. The process for preparing low-cost nano-scale high-purity ferric phosphate according to claim 1, characterized in that: In S1, the fertilizer-grade ammonium phosphate includes one or both of fertilizer ammonium phosphate and 55% powdered ammonium.

3. The process for preparing low-cost nano-scale high-purity ferric phosphate according to claim 2, characterized in that: In S1, the specific method for pretreatment of the fertilizer-grade ammonium phosphate is: Add fertilizer-grade ammonium phosphate and desalted water in a mass ratio of 1:2.0-3.0, mix and stir, and heat to 40-50°C. Add 85% phosphoric acid which is 1-3% of the solid mass of ammonium phosphate, stir for 3-4 hours to dissolve, and then perform solid-liquid separation to obtain ammonium phosphate aqueous solution.

4. The process for preparing low-cost nano-scale high-purity ferric phosphate according to claim 1, characterized in that: In S1, the specific method for pretreating the titanium dioxide by-product ferrous sulfate is as follows: Ferrous sulfate, a byproduct of titanium dioxide, and desalted water are added in a mass ratio of 1:1.0-2.

0. After dissolution, an impurity remover and a pH regulator are added to adjust the pH of the solution to 4.0-5.

0. After adjustment, solid-liquid separation is completed to obtain a purified ferrous sulfate solution.

5. The process for preparing low-cost nano-scale high-purity ferric phosphate according to claim 4, characterized in that: The impurity remover and pH regulator are one or both of ammonia water and sodium hydroxide.

6. The process for preparing low-cost nano-scale high-purity ferric phosphate according to claim 1, characterized in that: In S4, the filter cake is washed as follows: First, the filter cake after solid-liquid separation of S3 is washed with desalted water. After washing, the filter cake is crushed and desalted water and phosphoric acid are added. After the insulation reaction is completed, solid-liquid separation is performed and then washed with desalted water.

7. The process for preparing low-cost nano-scale high-purity ferric phosphate according to claim 1, characterized in that: In S1, the concentrations of the ammonium phosphate solution and the iron salt solution are 1.0-1.5 mol / L and 2.0-2.5 mol / L, respectively.

8. The process for preparing low-cost nano-scale high-purity ferric phosphate according to claim 1, characterized in that: In S2, the amount of hydrogen peroxide added is to reduce the Fe 2+ 1.1-1.3 times the theoretical molar amount for complete oxidation.

9. The process for preparing low-cost nano-scale high-purity ferric phosphate according to claim 1, characterized in that: In S2, the W-type zeolite molecular sieve is added in a ratio of 3-5% by mass of the iron salt solution.

10. The process for preparing low-cost nano-scale high-purity ferric phosphate according to claim 1, characterized in that: In S3, a pH adjuster is added to adjust the pH to 3.0-4.0.

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