A method for preparing ferric phosphate by recycling by-products

Abstract

The application discloses a method for preparing iron phosphate by recycling by-products, and belongs to the technical field of by-product recycling and utilization in chemical production. The method comprises the following steps: taking by-product disodium phosphate dodecahydrate of glyphosate and by-product ammonium chloride of glycine as raw materials, and adding hydrochloric acid to react; then, through first centrifugation, crystallization, second centrifugation, dissolution and third centrifugation, ammonium dihydrogen phosphate is prepared; then, the by-product ferrous sulfate of titanium white powder and hydrogen peroxide are used to synthesize iron phosphate. In the method, by-products are used as raw materials, and specific conditions are controlled to synthesize ferrous sulfate; meanwhile, waste liquid / waste residue formed in the synthesis process is recycled and utilized, which not only forms a circular economy, changes waste into treasure and saves cost, but also reduces the discharge of waste liquid and waste residue and is friendly to the environment.

Description

Technical Field

[0001] This invention relates to a method for preparing ferric phosphate, specifically a method for preparing ferric phosphate by recycling by-products, in the field of chemical production by-product recycling technology. Background Technology

[0002] There are many types of cathode materials for lithium-ion batteries, mainly including lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, ternary materials, and lithium iron phosphate. Currently, most lithium-ion batteries use lithium cobalt oxide as the cathode material, while other cathode materials are not yet in mass production on the market due to various reasons.

[0003] Lithium iron phosphate (LiFePO4) is an important battery material in lithium-ion batteries. Lithium iron phosphate batteries refer to lithium-ion batteries that use lithium iron phosphate as the positive electrode material. They offer high energy density and long lifespan, and are therefore widely used in mobile devices, electric vehicles, and other fields. Their main advantages include: (1) Long lifespan, with a cycle life of over 2000 cycles. Under the same conditions, lithium iron phosphate batteries can be used for 7 to 8 years; (2) Safe to use. They will not explode even in the most serious traffic accidents; (3) High-current 2C fast charging and discharging. Using a dedicated charger, charging at 1.5℃ for 40 minutes can fully charge the battery to its starting current, reaching up to 2C; (4) High temperature resistance, with peak heat generation of lithium iron phosphate reaching 350–500℃; (5) Large capacity, with lithium iron phosphate capacity being 3–4 times that of lead-acid batteries of the same mass; (6) No memory effect; (7) Green and environmentally friendly, non-toxic, pollution-free, with widely available and inexpensive raw materials.

[0004] From a materials science perspective, lithium iron phosphate (LFP) involves an intercalation / deintercalation process, a principle identical to that of lithium cobalt oxide and lithium manganese oxide. Currently, the synthesis of LFP requires iron phosphate as a raw material, and the existing methods for synthesizing iron phosphate mainly include:

[0005] 1. Ammonium method: Ferrous sulfate solution reacts with ammonium dihydrogen phosphate, and after precipitation and filtration, excess acid is neutralized with ammonia water to obtain ferric phosphate.

[0006] II. Sodium method: Ferrous sulfate is acidified with phosphoric acid, then reacts with hydrogen peroxide to produce ferric dihydrogen phosphate. The pH is then adjusted to around 2 with sodium hydroxide solution to produce ferric phosphate.

[0007] 3. The iron method involves reacting phosphoric acid with iron powder (or iron block) to obtain a ferrous solution, which is then oxidized with hydrogen peroxide to obtain ferric phosphate. Summary of the Invention

[0008] This invention aims to overcome the shortcomings of existing technologies by using disodium hydrogen phosphate dodecahydrate (a byproduct of glyphosate), ammonium chloride (a byproduct of glycine – ammonium chloride, when used as a nitrogen fertilizer, can lead to soil compaction, resulting in significant sales pressure), and ferrous sulfate (a byproduct of titanium dioxide) as raw materials to synthesize ferric phosphate. This not only forms a circular economy, turning waste into treasure and saving costs, but also reduces the discharge of waste liquid and residue, making it environmentally friendly. Therefore, this invention proposes a method for preparing ferric phosphate by recycling byproducts.

[0009] To achieve the above technical objectives, the following technical solution is proposed:

[0010] This technical solution provides a method for preparing ferric phosphate by recycling by-products, comprising the following steps:

[0011] 1) Melting: Disodium hydrogen phosphate dodecahydrate, a byproduct of glyphosate, is melted at 70-80°C to obtain a melt solution;

[0012] 2) Reaction: The obtained melt solution is mixed with ammonium chloride, a byproduct of glycine, and the pH is adjusted to 4.4-4.6 with 30% hydrochloric acid. The temperature is raised to 70-80℃ and kept at that temperature to obtain a slurry containing sodium chloride and ammonium dihydrogen phosphate. The molar ratio of disodium hydrogen phosphate dodecahydrate, a byproduct of glyphosate, ammonium chloride, and hydrochloric acid is 1:(0.9-1.1):(0.9-1.1).

[0013] Hydrochloric acid is used for pH adjustment, which does not introduce other new impurities. At the same time, under the limit of this pH value, disodium hydrogen phosphate dodecahydrate can be effectively converted (sodium hydrogen phosphate is converted into dihydrogen phosphate, and ammonium dihydrogen phosphate is ensured not to precipitate at higher temperatures), thus obtaining ammonium dihydrogen phosphate with a high content.

[0014] 3) First centrifugation: The obtained slurry is centrifuged to obtain the first filtrate and the first filter cake;

[0015] 4) Crystallization: Cool the obtained first filtrate to 0-5℃ to crystallize, and obtain a crystalline solution;

[0016] 5) Second centrifugation: Centrifuge the obtained crystallization liquid to obtain a second filtrate and a second filter cake; the second filtrate can be directly reused in the reaction process of step 2), or it can be removed from the glyphosate mother liquor treatment process;

[0017] 6) Dissolving: Add 2-3 L of deionized water to the obtained second filter cake per kg of second filter cake to dissolve and obtain slurry;

[0018] 7) Third centrifugation: The obtained slurry is centrifuged at 40-50℃ to obtain the third filtrate and the third filter cake; the third filter cake is directly treated as solid waste, and the third filtrate is ammonium dihydrogen phosphate solution (ammonium dihydrogen phosphate has the characteristic of low solubility at low temperatures).

[0019] 8) Synthesis of ferric phosphate: Hydrogen peroxide, ferrous sulfate (a byproduct of titanium dioxide), and the resulting ammonium dihydrogen phosphate solution are mixed at 50-70°C and reacted to obtain a mixture containing amorphous ferric phosphate and ammonium sulfate; the mixture is filtered and washed to obtain a dispersion containing amorphous ferric phosphate; the mixture is aged at 80-100°C to obtain white ferric phosphate dihydrate.

[0020] The molar ratio of ammonium dihydrogen phosphate, ferrous sulfate (a byproduct of titanium dioxide), and hydrogen peroxide is 1.05:1:0.65.

[0021] Further, the processing of the first filter cake includes: adding 1-1.5L of deionized water per kg of the first filter cake, pulping, centrifuging, and obtaining the fourth filtrate and the fourth filter cake, which is sodium chloride. The fourth filter cake is then purified using a deion-exchange membrane caustic soda brine process (i.e., using an ion-exchange membrane caustic soda device). The fourth filtrate is directly reused in the melting process of step 1). Specifically, the first filter cake (mainly sodium chloride) is purified using conventional pulping techniques to remove any trapped phosphate salts. It is then dissolved to saturation in dilute brine from the ion-exchange membrane caustic soda solution and further refined by conventional methods in the raw material brine. The fourth filtrate contains a small amount of phosphate salts and is reused in the melting process. The amount of deionized water added ensures effective recovery of sodium chloride. Adding too much deionized water leads to excessive sodium chloride dissolution; adding too little deionized water prevents pulping, resulting in incomplete phosphorus removal from the sodium chloride.

[0022] Furthermore, the glyphosate byproduct disodium hydrogen phosphate dodecahydrate is obtained by crystallization after high-temperature wet oxidation of glyphosate mother liquor. The disodium hydrogen phosphate dodecahydrate contains no more than 1000 ppm of sodium chloride, indicating a low impurity content, and can be used directly.

[0023] Furthermore, the glycine byproduct ammonium chloride is formed by synthesizing glycine from ammonium chloride-based chloroacetic acid and liquid ammonia. The glycine byproduct ammonium chloride contains no more than 100 ppm of aminoacetic acid, indicating a low impurity content, and can be used directly.

[0024] Furthermore, the ferrous sulfate byproduct of titanium dioxide production is a byproduct generated after the reaction of iron in titanium dioxide ore with sulfuric acid, which is then purified and separated. The purified byproducts include: FeSO4·7H2O: 89–92%, MgSO4·7H2O: 2–5%, MnSO4·5H2O: 0.1–1%, Al2(SO4)3·7H2O: 0.1–1%, CaSO4·2H2O: 0.1–1%, and TiOSO4: 0.1–1%.

[0025] This technical solution provides: a suitable iron phosphate preparation system, including a storage tank for disodium hydrogen phosphate dodecahydrate (a byproduct of glyphosate), a storage tank for ammonium chloride (a byproduct of glycine), a hydrochloric acid storage tank, a reaction vessel, centrifuge device I, a crystallization device, centrifuge device II, a dissolving device, centrifuge device III, a hydrogen peroxide storage tank, a storage tank for ferrous sulfate (a byproduct of titanium dioxide), an iron phosphate synthesis device, a filtration device, a washing device, and an aging vessel;

[0026] The glyphosate by-product disodium hydrogen phosphate dodecahydrate storage tank, the glycine by-product ammonium chloride storage tank, and the hydrochloric acid storage tank are all connected to the reactor via feed pipelines, and metering pumps are installed on the corresponding feed pipelines.

[0027] The reactor is equipped with a pH meter, a temperature control jacket is fitted on the outside of the reactor, and a stirring mechanism is installed inside the reactor.

[0028] Centrifuge device I is located at the rear of the reactor station. The outlet of the reactor is connected to the inlet of centrifuge device I, and the filtrate outlet of centrifuge device I is connected to the inlet of the crystallization device.

[0029] The crystallization device is located behind the station of centrifuge device I, and the outlet of the crystallization device is connected to the inlet of centrifuge device II.

[0030] Centrifuge device II is located at the rear of the crystallization unit, and the filter cake outlet of centrifuge device II is connected to the feed inlet of the dissolving unit.

[0031] The dissolving device is fitted with a temperature regulating jacket on the outside, and a stirring mechanism is installed inside the dissolving device. The dissolving device is connected to a deionized water storage tank. The dissolving device is located behind the station of centrifuge device II, and the outlet of the dissolving device is connected to the inlet of centrifuge device III.

[0032] Centrifuge device III is located behind the work station of the dissolving device, and the filtrate outlet of centrifuge device III is connected to the feed inlet of the ferric phosphate synthesis device.

[0033] The ferric phosphate synthesis unit is located behind the station of centrifuge unit III. The hydrogen peroxide storage tank and the ferrous sulfate storage tank (a byproduct of titanium dioxide) are both connected to the ferric phosphate synthesis unit through feed pipelines. Similarly, a metering pump is installed on the feed pipelines. The outlet of the ferric phosphate synthesis unit is connected to the inlet of the filter unit.

[0034] The filtration device is located behind the station of the ferric phosphate synthesis unit. The filter media outlet of the filtration device is connected to the feed inlet of the washing device, which is located behind the station of the filtration device. The material outlet of the washing device is connected to the feed inlet of the aging kettle, which is located behind the station of the washing device.

[0035] A continuous pathway for the synthesis and purification of ferric phosphate is formed between the reaction vessel, centrifuge device I, crystallization device, centrifuge device II, dissolution device, centrifuge device III, ferric phosphate synthesis device, filtration device, washing device, and aging vessel.

[0036] Furthermore, a melting device is installed at the front of the reactor station. The storage tank of disodium hydrogen phosphate dodecahydrate, a byproduct of glyphosate, is connected to the melting device. This means that the raw material disodium hydrogen phosphate dodecahydrate, a byproduct of glyphosate, is effectively melted before being introduced into the reactor for reaction. This improves the mixing uniformity between disodium hydrogen phosphate and ammonium chloride (a byproduct of glycine) and hydrochloric acid, thereby facilitating the reaction and improving the effectiveness, orderliness, and stability of the reaction process.

[0037] Furthermore, a ferrous sulfate purification device is installed between the titanium dioxide by-product ferrous sulfate storage tank and the ferric phosphate synthesis unit. This device purifies the titanium dioxide by-product ferrous sulfate before using it for ferric phosphate synthesis, thereby improving the efficiency and quality of ferric phosphate synthesis.

[0038] Furthermore, the filter cake outlet of centrifuge device I is connected to a pulping device, which is connected to centrifuge device IV. The filtrate outlet of centrifuge device IV is connected to a melting device, and the filter cake outlet of centrifuge device IV is connected to an ion-exchange membrane caustic soda device. The ion-exchange membrane caustic soda device is connected to a sodium chloride storage tank. The pulping device is connected to a deionized water storage tank.

[0039] Furthermore, the filtrate outlet of the centrifuge device II is connected to the glyphosate mother liquor treatment system.

[0040] Furthermore, the filter cake outlet of the centrifuge device III is connected to the solid waste treatment system, which is also connected to the waste residue outlet of the ferrous sulfate purification device.

[0041] Furthermore, the waste liquid outlet of the filtration device is connected to a crystallization device, and the washing device is also connected to the crystallization device. The outlet of the crystallization device is connected to an ammonium sulfate temporary storage tank.

[0042] In this technical solution, the solubility of the corresponding substance is used as the basis:

[0043] Sodium hydrogen phosphate dodecahydrate has a solubility of 10g at 20℃ and 70g at 80℃; ammonium chloride has a solubility of 29.4g at 20℃ and 71.3g at 80℃; sodium chloride has a solubility of 36g at 20℃ and 39g at 80℃; and ammonium dihydrogen phosphate has a solubility of 9g at 10℃ and 70g at 80℃.

[0044] In this technical solution, the chemical reaction formulas involved include:

[0045]

[0046] .

[0047] The positional relationships involved in this technical solution, such as "between", "above", "front side of the workstation", and "rear side of the workstation", are defined according to the actual usage conditions and are common terms in this technical field, as well as common terms used by those skilled in the art in actual use.

[0048] The beneficial technical effects of adopting this technical solution are as follows:

[0049] I. This invention utilizes disodium hydrogen phosphate dodecahydrate (a byproduct of glyphosate production), ammonium chloride (a byproduct of glycine production), ferrous sulfate (a byproduct of titanium dioxide production), and hydrogen peroxide to synthesize ferric phosphate. This effectively achieves the reuse of multiple byproducts and avoids the formation of sodium sulfate (a byproduct of ferric phosphate production) (directly using disodium hydrogen phosphate dodecahydrate and ferrous sulfate to produce ferric phosphate results in a large amount of difficult-to-treat sodium sulfate, which has low market demand, is difficult to sell, and has high processing costs).

[0050] The ammonium dihydrogen phosphate obtained using this preparation method is used in the synthesis of iron phosphate, following the mainstream "ammonia process" to ensure stable product quality. Meanwhile, the byproduct ammonium sulfate can be sold as fertilizer, generating an economic benefit of approximately 1000 yuan / ton (excluding a processing cost of 300 yuan / ton), resulting in a net profit of 700 yuan / ton. Furthermore, based on an annual iron phosphate production of 100,000 tons, this would generate 75,000 tons of ammonium sulfate annually, yielding an economic benefit of 52.5 million yuan / year.

[0051] Second, in the preparation of ammonium dihydrogen phosphate, the present invention adopts the "sodium method" process. However, in the existing iron phosphate synthesis process, the cost of treating the by-product sodium sulfate (ferrous sulfate is formed by the reaction of iron in titanium dioxide with sulfuric acid, and then purified and separated) is 100-300 yuan / ton. Moreover, this product is difficult to sell. After being made into anhydrous sodium sulfate, it is sold for about 300 yuan / ton, which is basically not economically profitable.

[0052] Third, in this invention, sodium chloride is co-produced and used in an ion-exchange membrane caustic soda unit for the concentration of dilute brine, thereby reducing the cost of brine concentration. Chloride ions from ammonium chloride, a byproduct of glycine production, are transferred to sodium chloride and then to the ion-exchange membrane caustic soda unit, achieving the recycling of chlorine. Therefore, a co-production process of glyphosate-glycine-ion-exchange membrane caustic soda-ferric phosphate can be formed.

[0053] IV. In this invention, the effective preparation of intermediates / targets is ensured through the control of specific conditions. For example, in the reaction process of step 2), the temperature is controlled at 70-80°C to ensure complete reaction; the crystallization temperature is controlled at 0-5°C to ensure effective precipitation of ammonium dihydrogen phosphate, thereby improving its purity and yield; in the dissolution process of step 6), 2-3 L of deionized water is added per kg of the second filter cake for dissolution to ensure effective dissolution of ammonium dihydrogen phosphate. If too much deionized water is added, the sodium chloride content in the ammonium dihydrogen phosphate solution will be too high. By controlling the amount of deionized water added and subsequently increasing the temperature, ammonium dihydrogen phosphate can be dissolved, while sodium chloride dissolution can be inhibited, thereby reducing the sodium chloride content in ammonium dihydrogen phosphate and ensuring the stability and smoothness of the subsequent iron phosphate synthesis process. Attached Figure Description

[0054] Figure 1 This is a process flow diagram related to the present invention;

[0055] Figure 2 The present invention relates to a logic connection block diagram of the fabrication system (I);

[0056] Figure 3 The following is a logic connection block diagram (II) of the fabrication system involved in this invention;

[0057] Figure 4 Here is a SEM image of the iron phosphate product in this invention;

[0058] In the diagram: 1. Storage tank for disodium hydrogen phosphate dodecahydrate, a byproduct of glyphosate; 2. Storage tank for ammonium chloride, a byproduct of glycine; 3. Deionized water storage tank; 4. Hydrochloric acid storage tank; 5. Hydrogen peroxide storage tank; 6. Storage tank for ferrous sulfate, a byproduct of titanium dioxide; 7. Reactor; 8. Centrifuge unit I; 9. Crystallization unit; 10. Centrifuge unit II; 11. Dissolving unit; 12. Centrifuge unit III; 13. Ferric phosphate synthesis unit; 14. Melting unit; 15. Pulping unit; 16. Centrifuge unit IV; 17. Ion-exchange membrane caustic soda unit; 18. Sodium chloride storage tank; 19. Glyphosate mother liquor treatment system; 20. Filtration unit; 21. Washing unit; 22. Ferrous sulfate purification unit; 23. Aging kettle; 24. Concentration and crystallization unit; 25. Ammonium sulfate temporary storage tank. Detailed Implementation

[0059] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0060] Example 1

[0061] This embodiment provides a method for preparing ferric phosphate by recycling by-products, comprising the following steps:

[0062] 1) Dissolution: Disodium hydrogen phosphate dodecahydrate, a byproduct of glyphosate, is melted at 70°C to obtain a melt solution;

[0063] 2) Reaction: The obtained melt solution was mixed with ammonium chloride, a byproduct of glycine, and the pH was adjusted to 4.4 with 30% hydrochloric acid. The temperature was raised to 70°C and kept at that temperature to obtain a slurry containing sodium chloride and ammonium dihydrogen phosphate.

[0064] The molar ratio of glyphosate byproduct disodium hydrogen phosphate dodecahydrate, glycine byproduct ammonium chloride, and hydrochloric acid is 1:0.9:0.9.

[0065] 3) First centrifugation: The obtained slurry is centrifuged to obtain the first filtrate and the first filter cake;

[0066] 4) Crystallization: Cool the obtained first filtrate to 0℃ to crystallize, and obtain a crystalline solution;

[0067] 5) Second centrifugation: Centrifuge the obtained crystallizing solution to obtain a second filtrate and a second filter cake;

[0068] 6) Dissolving: Add 2L of deionized water to the obtained second filter cake per kg of second filter cake to dissolve and obtain slurry;

[0069] 7) Third centrifugation: The obtained slurry is centrifuged at 40°C to obtain the third filtrate and the third filter cake; the third filtrate is an ammonium dihydrogen phosphate solution (ammonium dihydrogen phosphate has the characteristic of low solubility at low temperatures);

[0070] 8) Synthesis of ferric phosphate: Hydrogen peroxide, ferrous sulfate (a byproduct of titanium dioxide), and the resulting ammonium dihydrogen phosphate solution are mixed at 50°C and reacted to obtain a mixture containing amorphous ferric phosphate and ammonium sulfate; the mixture is filtered and washed to obtain a dispersion containing amorphous ferric phosphate; the dispersion is aged at 80°C to obtain white ferric phosphate dihydrate.

[0071] The molar ratio of ammonium dihydrogen phosphate, ferrous sulfate (a byproduct of titanium dioxide), and hydrogen peroxide is 1.05:1:0.65.

[0072] Furthermore, the glyphosate byproduct, disodium hydrogen phosphate dodecahydrate, is obtained by crystallization after high-temperature wet oxidation of glyphosate mother liquor. The disodium hydrogen phosphate dodecahydrate contains no more than 1000 ppm of sodium chloride, indicating a low impurity content, and can be used directly.

[0073] Ammonium chloride, a byproduct of glycine synthesis, is formed from the synthesis of glycine from ammonium chloride, chloroacetic acid, and liquid ammonia. The ammonium chloride byproduct contains no more than 100 ppm of glycine, indicating a low impurity content, and can be used directly.

[0074] Ferrous sulfate, a byproduct of titanium dioxide production, is a byproduct generated from the reaction of iron in titanium dioxide ore with sulfuric acid, and is obtained through conventional purification and separation techniques. The purified byproducts include: FeSO4·7H2O: 89–92%, MgSO4·7H2O: 2–5%, MnSO4·5H2O: 0.1–1%, Al2(SO4)3·7H2O: 0.1–1%, CaSO4·2H2O: 0.1–1%, and TiOSO4: 0.1–1%.

[0075] Example 2

[0076] This embodiment provides a method for preparing ferric phosphate by recycling by-products, comprising the following steps:

[0077] 1) Dissolution: Disodium hydrogen phosphate dodecahydrate, a byproduct of glyphosate, is melted at 80°C to obtain a melt solution;

[0078] 2) Reaction: The obtained melt is mixed with ammonium chloride, a byproduct of glycine, and the pH is adjusted to 4.6 with 30% hydrochloric acid. The temperature is raised to 80°C and kept at that temperature to obtain a slurry containing sodium chloride and ammonium dihydrogen phosphate.

[0079] The molar ratio of glyphosate byproduct disodium hydrogen phosphate dodecahydrate, glycine byproduct ammonium chloride, and hydrochloric acid is 1:1.1:1.1.

[0080] 3) First centrifugation: The obtained slurry is centrifuged to obtain the first filtrate and the first filter cake;

[0081] 4) Crystallization: Cool the obtained first filtrate to 5°C to crystallize, and obtain a crystalline solution;

[0082] 5) Second centrifugation: Centrifuge the obtained crystallizing solution to obtain a second filtrate and a second filter cake;

[0083] 6) Dissolving: Add 3L of deionized water to the obtained second filter cake per kg of second filter cake to dissolve and obtain slurry;

[0084] 7) Third centrifugation: The obtained slurry is centrifuged at 50°C to obtain the third filtrate and the third filter cake; the third filtrate is an ammonium dihydrogen phosphate solution (ammonium dihydrogen phosphate has the characteristic of low solubility at low temperatures);

[0085] 8) Synthesis of ferric phosphate: Hydrogen peroxide, ferrous sulfate (a byproduct of titanium dioxide), and the resulting ammonium dihydrogen phosphate solution are mixed at 70°C and reacted to obtain a mixture containing amorphous ferric phosphate and ammonium sulfate; the mixture is filtered and washed to obtain a dispersion containing amorphous ferric phosphate; the dispersion is aged at 100°C to obtain white ferric phosphate dihydrate.

[0086] The molar ratio of ammonium dihydrogen phosphate, ferrous sulfate (a byproduct of titanium dioxide), and hydrogen peroxide is 1.05:1:0.65.

[0087] Furthermore, the glyphosate byproduct, disodium hydrogen phosphate dodecahydrate, is obtained by crystallization after high-temperature wet oxidation of glyphosate mother liquor. The disodium hydrogen phosphate dodecahydrate contains no more than 1000 ppm of sodium chloride, indicating a low impurity content, and can be used directly.

[0088] Ammonium chloride, a byproduct of glycine synthesis, is formed from the synthesis of glycine from ammonium chloride, chloroacetic acid, and liquid ammonia. The ammonium chloride byproduct contains no more than 100 ppm of glycine, indicating a low impurity content, and can be used directly.

[0089] Ferrous sulfate, a byproduct of titanium dioxide production, is a byproduct generated from the reaction of iron in titanium dioxide ore with sulfuric acid, and is obtained through conventional purification and separation techniques. The purified byproducts include: FeSO4·7H2O: 89–92%, MgSO4·7H2O: 2–5%, MnSO4·5H2O: 0.1–1%, Al2(SO4)3·7H2O: 0.1–1%, CaSO4·2H2O: 0.1–1%, and TiOSO4: 0.1–1%.

[0090] Example 3

[0091] This embodiment provides a method for preparing ferric phosphate by recycling by-products, comprising the following steps:

[0092] 1) Dissolve the glyphosate byproduct disodium hydrogen phosphate dodecahydrate at 75°C to obtain a melt solution;

[0093] 2) Reaction: The obtained melt is mixed with ammonium chloride, a byproduct of glycine, and the pH is adjusted to 4.5 with 30% hydrochloric acid. The temperature is raised to 75°C and kept at that temperature to obtain a slurry containing sodium chloride and ammonium dihydrogen phosphate.

[0094] The molar ratio of glyphosate byproduct disodium hydrogen phosphate dodecahydrate, glycine byproduct ammonium chloride, and hydrochloric acid is 1:1:1.

[0095] 3) First centrifugation: The obtained slurry is centrifuged to obtain the first filtrate and the first filter cake;

[0096] 4) Crystallization: Cool the obtained first filtrate to 2℃ to crystallize, and obtain a crystalline solution;

[0097] 5) Second centrifugation: Centrifuge the obtained crystallizing solution to obtain a second filtrate and a second filter cake;

[0098] 6) Dissolving: Add 2.5L of deionized water to the obtained second filter cake per kg of second filter cake to dissolve and obtain slurry;

[0099] 7) Third centrifugation: The obtained slurry is centrifuged at 45°C to obtain the third filtrate and the third filter cake; the third filtrate is an ammonium dihydrogen phosphate solution (ammonium dihydrogen phosphate has the characteristic of low solubility at low temperatures);

[0100] 8) Synthesis of ferric phosphate: Hydrogen peroxide, ferrous sulfate (a byproduct of titanium dioxide), and the resulting ammonium dihydrogen phosphate solution are mixed at 60°C and reacted to obtain a mixture containing amorphous ferric phosphate and ammonium sulfate; the mixture is filtered and washed to obtain a dispersion containing amorphous ferric phosphate; the dispersion is aged at 90°C to obtain white ferric phosphate dihydrate.

[0101] The molar ratio of ammonium dihydrogen phosphate, ferrous sulfate (a byproduct of titanium dioxide), and hydrogen peroxide is 1.05:1:0.65.

[0102] Furthermore, the glyphosate byproduct, disodium hydrogen phosphate dodecahydrate, is obtained by crystallization after high-temperature wet oxidation of glyphosate mother liquor. The disodium hydrogen phosphate dodecahydrate contains no more than 1000 ppm of sodium chloride, indicating extremely low impurity content, and can be used directly.

[0103] Ammonium chloride, a byproduct of glycine synthesis, is formed from the synthesis of glycine from ammonium chloride, chloroacetic acid, and liquid ammonia. The ammonium chloride byproduct contains no more than 100 ppm of glycine, indicating extremely low impurity levels, and can be used directly.

[0104] Ferrous sulfate, a byproduct of titanium dioxide production, is a byproduct generated from the reaction of iron in titanium dioxide ore with sulfuric acid, and is obtained through conventional purification and separation techniques. The purified byproducts include: FeSO4·7H2O: 89–92%, MgSO4·7H2O: 2–5%, MnSO4·5H2O: 0.1–1%, Al2(SO4)3·7H2O: 0.1–1%, CaSO4·2H2O: 0.1–1%, and TiOSO4: 0.1–1%.

[0105] Example 4

[0106] Based on Examples 1-3, this example recycles and reuses the filter cake and filtrate formed during the preparation process, or performs effective subsequent treatment, thereby improving the recyclability of by-products, increasing utilization rate, and reducing emissions. Specifically, this includes:

[0107] The first filter cake processing procedure includes: adding 1-1.5L of deionized water to each kg of the first filter cake, pulping, centrifuging to obtain the fourth filtrate and the fourth filter cake. The fourth filter cake is sodium chloride, which is refined using a deion membrane caustic soda brine purification process (i.e., using an ion membrane caustic soda device for purification). The fourth filtrate is directly reused in the melting process of step 1).

[0108] 2. The second filtrate is directly returned to the glyphosate mother liquor treatment process;

[0109] Third, the third filter cake is directly treated as solid waste.

[0110] Example 5

[0111] Based on Examples 1-4, this example provides a suitable iron phosphate preparation system, such as... Figure 2 As shown, the system includes: a glyphosate byproduct disodium hydrogen phosphate dodecahydrate storage tank 1, a glycine byproduct ammonium chloride storage tank 2, a hydrochloric acid storage tank 4, a reaction vessel 7, a centrifuge device I 8, a crystallization device 9, a centrifuge device II 10, a dissolving device 11, a centrifuge device III 12, a hydrogen peroxide storage tank 5, a titanium dioxide byproduct ferrous sulfate storage tank 6, an iron phosphate synthesis device 13, a filtration device 20, a washing device 21, and an aging vessel 23;

[0112] Storage tanks 1 (for glyphosate byproduct disodium hydrogen phosphate dodecahydrate), 2 (for glycine byproduct ammonium chloride), and 4 (for hydrochloric acid) are all connected to reactor 7 via feed pipelines, with metering pumps installed on the corresponding feed pipelines. Reactor 7 is equipped with a pH meter, a temperature-regulating jacket, and a stirring mechanism. Centrifuge device I8 is located behind reactor 7, with its outlet connected to the inlet. The filtrate outlet of centrifuge device I8 is connected to the inlet of crystallization device 9. Crystallization device 9 is located behind centrifuge device I8, with its outlet connected to the inlet of centrifuge device II10. Centrifuge device II10 is located behind crystallization device 9, with its filter cake outlet connected to the inlet of dissolving device 11. Dissolving device 11 is equipped with a temperature-regulating jacket, a stirring mechanism, and a deionized water storage tank 3. Unit 11 is located behind the station of centrifuge device II 10. The outlet of dissolving device 11 is connected to the inlet of centrifuge device III 12. Centrifuge device III 12 is located behind the station of dissolving device 11. The filtrate outlet of centrifuge device III 12 is connected to the inlet of ferric phosphate synthesis device 13. Ferric phosphate synthesis device 13 is located behind the station of centrifuge device III 12. Hydrogen peroxide storage tank 5 and titanium dioxide by-product ferrous sulfate storage tank 6 are both connected to ferric phosphate synthesis device 13 through feed pipelines. Similarly, a metering pump is installed on the feed pipeline. The outlet of ferric phosphate synthesis device 13 is connected to the inlet of filter device 20. Filter device 20 is located behind the station of ferric phosphate synthesis device 13. The filter media outlet of filter device 20 is connected to the inlet of washing device 21. Washing device 21 is located behind the station of filter device 20. The material outlet of washing device 21 is connected to the inlet of aging kettle 23. Aging kettle 23 is located behind the station of washing device 21.

[0113] A continuous pathway for the synthesis and purification of ferric phosphate is formed between the reaction vessel 7, centrifuge device I 8, crystallization device 9, centrifuge device II 10, dissolution device 11, centrifuge device III 12, ferric phosphate synthesis device 13, filtration device 20, washing device 21, and aging vessel 23.

[0114] In addition, such as Figure 3 As shown, a melting device 14 is installed on the front side of the work station of the reactor 7. The glyphosate by-product disodium hydrogen phosphate dodecahydrate storage tank 1 is connected to the melting device 14. That is, after the raw material glyphosate by-product disodium hydrogen phosphate dodecahydrate is effectively melted, it is introduced into the reactor 7 for reaction, which improves the mixing uniformity between it and glycine by-product ammonium chloride and hydrochloric acid, so as to facilitate the reaction, that is, improve the effectiveness, order and stability of the reaction process.

[0115] A ferrous sulfate purification device 22 is installed between the ferrous sulfate storage tank 6 (a byproduct of titanium dioxide) and the ferric phosphate synthesis unit 13. This device purifies the ferrous sulfate byproduct of titanium dioxide before using it in the synthesis of ferric phosphate, thereby improving the efficiency and quality of the synthesis.

[0116] Centrifuge device I8 has a filter cake outlet connected to a pulping device 15, which is connected to centrifuge device IV 16. The filtrate outlet of centrifuge device IV 16 is connected to a melting device 14. The filter cake outlet of centrifuge device IV 16 is connected to an ion-exchange membrane caustic soda unit 17, which is connected to a sodium chloride storage tank 18. The pulping device 15 is connected to a deionized water storage tank 3.

[0117] The filtrate outlet of centrifuge device II10 is connected to glyphosate mother liquor treatment system 19.

[0118] The filter cake outlet of centrifuge unit Ⅲ12 is connected to the solid waste treatment system, which is also connected to the waste residue outlet of ferrous sulfate purification unit 22.

[0119] The waste liquid outlet of the filter device 20 is connected to the concentration and crystallization device 24, and the washing device 21 is also connected to the concentration and crystallization device 24. The outlet of the concentration and crystallization device 24 is connected to the ammonium sulfate temporary storage tank 25.

[0120] Example 6

[0121] Based on Examples 1-5, this example provides a method for preparing ferric phosphate by recycling byproducts, such as... Figure 1 As shown, the specific steps include the following:

[0122] (1) Heat 2310g of glyphosate by-product disodium hydrogen phosphate dodecahydrate (disodium hydrogen phosphate dodecahydrate content is 93%) to 70-80℃ to melt, add 321g of glycine by-product ammonium chloride; then add 730g of 30% hydrochloric acid, adjust pH to 4.4, keep warm to 70-80℃, stir at 300r / min, keep warm for 1h, centrifuge while hot to obtain 3045g of first filtrate and 316g of first filter cake. The first filter cake is pulped and purified to obtain pure sodium chloride, which can be reused in the ion-exchange membrane caustic soda unit.

[0123] (2) Crystallize the first filtrate (0℃) and centrifuge to obtain 2345g of the second filtrate and 700g of the second filter cake; dissolve the second filter cake in 1400g of deionized water at 50℃;

[0124] (3) Then, centrifuge at 40-50℃ to obtain 2100g of ammonium dihydrogen phosphate solution and a very small amount of solid. The solid is treated as solid waste, and the ammonium dihydrogen phosphate solution is used to synthesize iron phosphate.

[0125] (4) Mix 380g of 27.5% hydrogen peroxide, 4500g of 1mol / L ferrous sulfate solution and the resulting 2100g of ammonium dihydrogen phosphate solution at 50-70℃ and react to obtain a mixture containing amorphous ferric phosphate and ammonium sulfate.

[0126] After filtration and washing, a dispersion containing amorphous ferric phosphate was obtained; after aging at 90°C, filtration, washing, and drying, 890g of white ferric phosphate dihydrate (as shown in the image) was obtained. Figure 4 (As shown in the image); at the same time, the resulting ammonium sulfate byproduct will be sold as fertilizer.

Claims

1. A method for preparing ferric phosphate by recycling byproducts, characterized in that, Includes the following steps: 1) Melting: Disodium hydrogen phosphate dodecahydrate, a byproduct of glyphosate, is melted at 70-80°C to obtain a melt solution; 2) Reaction: The obtained melt is mixed with ammonium chloride, a byproduct of glycine, and the pH is adjusted to 4.4-4.6 with 30% hydrochloric acid. The temperature is raised to 70-80℃ and kept at that temperature to obtain a slurry containing sodium chloride and ammonium dihydrogen phosphate. The molar ratio of disodium hydrogen phosphate dodecahydrate (a byproduct of glyphosate), ammonium chloride (a byproduct of glycine), and hydrochloric acid is 1: 0.9–1.1: 0.9–1.

1. 3) First centrifugation: The obtained slurry is centrifuged to obtain the first filtrate and the first filter cake; The first filter cake processing includes: adding 1-1.5L of deionized water to the obtained first filter cake per kg of first filter cake, pulping, centrifuging to obtain the fourth filtrate and the fourth filter cake. The fourth filter cake is sodium chloride, which is purified using an ion-exchange membrane caustic soda device. The fourth filtrate is directly reused in the melting process of step 1). 4) Crystallization: Cool the obtained first filtrate to 0-5℃ to crystallize, and obtain a crystalline solution; 5) Second centrifugation: Centrifuge the obtained crystallizing solution to obtain a second filtrate and a second filter cake; The resulting second filtrate is directly returned to the glyphosate mother liquor treatment process. 6) Dissolving: Add 2-3 L of deionized water to the obtained second filter cake per kg of second filter cake to dissolve and obtain slurry; 7) Third centrifugation: The obtained slurry is centrifuged at 40-50℃ to obtain the third filtrate and the third filter cake; the third filtrate is ammonium dihydrogen phosphate solution; 8) Synthesis of ferric phosphate: Hydrogen peroxide, ferrous sulfate (a byproduct of titanium dioxide), and the resulting ammonium dihydrogen phosphate solution are mixed at 50-70°C and reacted to obtain a mixture containing amorphous ferric phosphate and ammonium sulfate; the mixture is filtered and washed to obtain a dispersion containing amorphous ferric phosphate; the mixture is aged at 80-100°C to obtain white ferric phosphate dihydrate. The molar ratio of ammonium dihydrogen phosphate, ferrous sulfate (a byproduct of titanium dioxide), and hydrogen peroxide is 1.05:1:0.

65.

2. The method for preparing ferric phosphate by recycling byproducts according to claim 1, characterized in that, In step 8), the waste liquid formed after filtration and washing is concentrated and crystallized to obtain ammonium sulfate.

3. The method for preparing ferric phosphate by recycling byproducts according to claim 1, characterized in that, The glyphosate byproduct, disodium hydrogen phosphate dodecahydrate, is obtained by crystallization after high-temperature wet oxidation of glyphosate mother liquor.

4. The method for preparing ferric phosphate by recycling byproducts according to claim 1, characterized in that, The ferrous sulfate byproduct of titanium dioxide production is a byproduct generated after the reaction of iron in titanium dioxide ore with sulfuric acid. It is obtained by purifying and separating the byproduct.

5. A system for preparing iron phosphate, characterized in that, The system used in the method of any one of claims 1-4 includes a glyphosate byproduct disodium hydrogen phosphate dodecahydrate storage tank (1), a glycine byproduct ammonium chloride storage tank (2), a hydrochloric acid storage tank (4), a reaction vessel (7), a centrifuge device I (8), a crystallization device (9), a centrifuge device II (10), a dissolving device (11), a centrifuge device III (12), a hydrogen peroxide storage tank (5), a titanium dioxide byproduct ferrous sulfate storage tank (6), an iron phosphate synthesis device (13), a filtration device (20), a washing device (21), and an aging vessel (23). The glyphosate byproduct disodium hydrogen phosphate dodecahydrate storage tank (1), the glycine byproduct ammonium chloride storage tank (2) and the hydrochloric acid storage tank (4) are all connected to the reactor (7) through feed pipelines; Centrifuge device I (8) is set behind the work station of reactor (7). The outlet of reactor (7) is connected to the inlet of centrifuge device I (8). The filtrate outlet of centrifuge device I (8) is connected to the inlet of crystallization device (9). The crystallization device (9) is located behind the station of the centrifuge device I (8), and the outlet of the crystallization device (9) is connected to the inlet of the centrifuge device II (10); Centrifuge device II (10) is located behind the work station of crystallization device (9), and the filter cake outlet of centrifuge device II (10) is connected to the feed inlet of dissolving device (11); The dissolving device (11) is connected to the deionized water storage tank (3). The dissolving device (11) is located behind the station of the centrifuge device II (10). The outlet of the dissolving device (11) is connected to the inlet of the centrifuge device III (12). Centrifuge device Ⅲ (12) is located behind the work station of dissolving device (11), and the filtrate outlet of centrifuge device Ⅲ (12) is connected to the feed inlet of ferric phosphate synthesis device (13); The ferric phosphate synthesis unit (13) is located behind the station of the centrifugal device III (12). The hydrogen peroxide storage tank (5) and the titanium dioxide by-product ferrous sulfate storage tank (6) are connected to the ferric phosphate synthesis unit (13) through the feed pipeline. The outlet of the ferric phosphate synthesis unit (13) is connected to the inlet of the filter device (20). The filter device (20) is located behind the station of the iron phosphate synthesis unit (13). The filter media outlet of the filter device (20) is connected to the feed inlet of the washing device (21). The washing device (21) is located behind the station of the filter device (20). The material outlet of the washing device (21) is connected to the feed inlet of the aging kettle (23). The aging kettle (23) is located behind the station of the washing device (21). A continuous pathway for the synthesis and purification of ferric phosphate is formed between the reaction vessel (7), centrifuge device I (8), crystallization device (9), centrifuge device II (10), dissolution device (11), centrifuge device III (12), ferric phosphate synthesis device (13), filtration device (20), washing device (21) and aging vessel (23).

6. The ferric phosphate preparation system according to claim 5, characterized in that, A melting device (14) is provided on the front side of the work station of the reactor (7), and the glyphosate by-product disodium hydrogen phosphate dodecahydrate storage tank (1) is connected to the melting device (14).

7. The ferric phosphate preparation system according to claim 5 or 6, characterized in that, Metering pumps are distributed on all the feed lines.

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