METHOD FOR THE PRODUCTION OF FERROUS PHOSPHATE AND ITS USE

Abstract

A process for the production of iron phosphate, comprising the following steps: (1) Mixing an iron phosphide waste, an acidic liquid, an oxidizing agent and an adsorbent with stirring, heating to leaching and subjecting the resulting mixture to solid-liquid separation to obtain a first filtrate and a first filter residue; (2) Adding an alkaline liquid to the first filtrate to adjust the pH of the first filtrate, maintaining a temperature of the resulting mixture, and subjecting the resulting mixture to solid-liquid separation to obtain a second filter residue and a second filtrate; and subjecting the second filter residue to heat treatment to obtain iron oxide; (3) Subjecting the iron oxide to high-energy ball milling and adding a surfactant for activation to obtain a slurry; (4) Adding an extraction agent and an acidic liquid to the second filtrate obtained in step (2), carrying out an extraction and separation on a resulting mixture and subjecting a resulting organic phase to back-extraction to obtain phosphoric acid; and (5) Mixing the slurry obtained in step (3) with the phosphoric acid, heating to enable a reaction, subjecting the resulting mixture to solid-liquid separation to obtain a solid, and washing and sintering the solid to obtain the iron phosphate; where in step (1) the iron phosphide waste comprises a mixture of FeP and Fe2P; in step (1) the acidic liquid contains at least two from the following group: nitric acid, sulfuric acid and hydrochloric acid; In step (1) the oxidizing agent is at least one selected from the group consisting of hydrogen peroxide, oxygen, nitric acid and sodium persulfate; wherein in step (2) the alkaline liquid is at least one selected from the group consisting of a NaOH solution, a KOH solution, ammonia water, a urea solution, NH4Cl, NH4HCO3, Na2CO3 and NaHCO3; In step (2) the pH of the first filtrate is adjusted to 2.5 to 5; and In step (5) the molar ratio of Fe in the slurry to P in the phosphoric acid is 1:1–2; heating to enable a reaction is carried out at a temperature of 50 °C to 80 °C for 20 to 60 min; and the iron phosphate has a D 50 from 2 µm to 6 µm, a tapped density of 0.80 g / cm³ 3 up to 1.30 g / cm³ 3 , and a specific surface area of ​​4 m² 2 / g up to 8 m 2 / g indicates.

Description

TECHNICAL AREA

[0001] The present disclosure belongs to the technical field of lithium-ion batteries (LIBs) and relates in particular to a process for the production of iron phosphate and its use. BACKGROUND

[0002] A cathode material is the most important component of a lithium iron phosphate battery (LIB). Lithium iron phosphate (LFP, LiFePO4) with an olivine structure offers many advantages, such as high theoretical capacity, high safety, environmental friendliness, and low cost. LFP is the preferred cathode material for LIBs among researchers and the energy storage market. FePO4, a precursor to LFP cathode material, can be used for the large-scale production of high-density LiFePO4, and its quality and cost directly impact the performance and cost of an LFP battery. Currently, iron phosphate is primarily produced through co-precipitation processes, using iron(II) sulfate as a byproduct of titanium dioxide production, a phosphorus source, an alkaline liquid, an oxidizing agent, and other components.The raw materials used are alkaline liquid, which is used to adjust the pH, and iron phosphate is precipitated at a suitable pH. The conventional manufacturing process generally involves two stages: reaction and maturation. The reaction stage requires a relatively high temperature and energy consumption. However, adjusting the pH of a system easily introduces impurities into the product (the purity of iron phosphate in the prior art generally barely exceeds 99%), resulting in relatively high costs and a complicated process. Therefore, it is necessary to develop a new process to improve the physical and chemical properties of the product, ensuring that the product's performance characteristics meet the requirements for LFP battery manufacturing.

[0003] CN 1 13 443 640 A discloses a process for producing battery-grade iron phosphate from lithium iron phosphate battery cathode / anode waste powder. The process comprises: mixing lithium iron phosphate cathode / anode waste powder with water to form a slurry, heating, adding an inorganic acid, an oxidizing agent, and a stabilizing agent A for the reaction, then filtering and washing to obtain a lithium-containing solution and a ferrophosphate residue; mixing the ferrophosphate residue with water to form a slurry, heating, adding an inorganic acid, an oxidizing agent, and a stabilizing agent B for the reaction, then filtering and washing to obtain a ferrophosphate solution; performing deep removal of impurities from the ferrophosphate solution and using a obtained high-purity ferrophosphate solution as a raw material for the production of the battery-grade iron phosphate product.

[0004] CN 1 01 659 406 A discloses a process for the production of iron phosphate from ferrophosphorus. In this process, ferrophosphorus is used as a partial or complete phosphorus and iron source, and the phosphorus or iron source is supplemented according to a total phosphorus to total iron molar ratio of 0.8–1.2:1.0. The process comprises roasting ferrophosphorus in a dry, oxygenated atmosphere and the subsequent reaction of the resulting oxidation products by a dry or wet process to obtain the iron phosphate product.

[0005] CN 1 13 292 058 A discloses a manufacturing process for nanodoped lithium iron phosphate. This process includes the use of inexpensive iron phosphide as the main raw material, the addition of nitric acid to the reaction, followed by the addition of a complexing agent to obtain a phosphate-iron solution, and the subsequent performance of a liquid-phase synthesis by adding dopants to obtain the lithium iron phosphate material with improved electrochemical performance.

[0006] WO 2022 / 242 186 A1 discloses a process for producing high-purity iron phosphate using ferrophosphorus waste. The process comprises: first, mixing ferrophosphorus waste with an acid solution for dissolving and leaching; adding iron powder to the leaching solution to remove copper; then adding fluoride to remove aluminum; performing a solid-liquid separation; adding an ion exchange resin to the filtrate to thoroughly remove impurities and obtain a purified ferrophosphorus solution; adding a phosphorus source or an iron source to the purified ferrophosphorus solution to adjust the iron-phosphorus ratio; adding an alkaline solution to adjust the pH; then performing a stirring reaction to obtain iron phosphate dihydrate; and roasting the iron phosphate dihydrate to obtain the iron phosphate. SUMMARY

[0007] The following is a summary of the subject matter described in detail in the present disclosure. This summary is not intended to limit the scope of protection of the claims.

[0008] This disclosure describes a process for the production of iron phosphate and its use. The production process involves inexpensive raw materials, results in less waste, and requires a low temperature, which can effectively reduce energy consumption costs. Furthermore, the iron phosphate produced by this process has a purity of 99.8% or higher.

[0009] To achieve the above-mentioned goal, the following technical solutions are used in the present disclosure: A process for the production of iron phosphate is provided, comprising the following steps: (1) Mixing an iron phosphide waste, an acidic liquid, an oxidizing agent and an adsorbent with stirring, heating to leaching and subjecting the resulting mixture to solid-liquid separation (SLS) to obtain a first filtrate and a first filter residue; (2) Adding an alkaline liquid to the first filtrate to adjust the pH of the first filtrate, maintaining a temperature of the resulting mixture, and subjecting the resulting mixture to SLS to obtain a second filter residue and a second filtrate; and subjecting the second filter residue to heat treatment to obtain iron oxide; (3) Subjecting the iron oxide to high-energy ball milling and adding a surfactant for activation to obtain a slurry; (4) Adding an extraction agent and an acidic liquid to the second filtrate obtained in step (2), carrying out an extraction and separation on a resulting mixture and subjecting a resulting organic phase to back-extraction to obtain phosphoric acid; and (5) Mixing the slurry obtained in step (3) with the phosphoric acid, heating to enable a reaction, subjecting the resulting mixture to SLS to obtain a solid, and washing and sintering the solid to obtain the iron phosphate; where in step (1) the iron phosphide waste comprises a mixture of FeP and Fe2P; in step (1) the acidic liquid contains at least two from the following group: nitric acid, sulfuric acid and hydrochloric acid; In step (1) the oxidizing agent is at least one selected from the group consisting of hydrogen peroxide, oxygen, nitric acid and sodium persulfate; wherein in step (2) the alkaline liquid is at least one selected from the group consisting of a NaOH solution, a KOH solution, ammonia water, a urea solution, NH4Cl, NH4HCO3, Na2CO3 and NaHCO3; In step (2) the pH of the first filtrate is adjusted to 2.5 to 5; and In step (5) the molar ratio of Fe in the slurry to P in the phosphoric acid is 1:1–2; heating to enable a reaction is carried out at a temperature of 50 °C to 80 °C for 20 to 60 min; and the iron phosphate has a D 50 from 2 µm to 6 µm, a tapped density of 0.80 g / cm³ 3 up to 1.30 g / cm³ 3 , and a specific surface area of ​​4 m² 2 / g up to 8 m 2 / g indicates.

[0010] Preferably in step (1) the acidic liquid can be a mixture of nitric acid and sulfuric acid, wherein the molar ratio of nitric acid to sulfuric acid can be 1:0.5 - 5.

[0011] Preferably, the molar ratio of nitric acid to sulfuric acid can be 1:0.5 - 2.

[0012] Preferably in step (1) the oxidizing agent can be one selected from the group consisting of hydrogen peroxide and oxygen.

[0013] Preferably in step (1) the adsorbent can be one selected from the group consisting of activated carbon, graphite, carbon molecular sieve and zeolite molecular sieve.

[0014] Preferably, the adsorbent can be activated carbon or graphite.

[0015] Preferably, in step (1) the stirring speed can be 300 rpm to 500 rpm and even more preferably 350 rpm to 450 rpm.

[0016] Preferably, in step (1) the heating for leaching can be carried out at a temperature of 80 °C to 100 °C for 2 to 6 hours; and further preferably, the heating for leaching can be carried out at a temperature of 90 °C to 100 °C for 2 to 3 hours.

[0017] Preferably in step (2) the alkaline liquid can be selected from the group consisting of a NaOH solution, ammonia water and a urea solution.

[0018] Preferably, in step (2) the pH of the first filtrate can be adjusted to 3.5 to 4.5.

[0019] Preferably, the temperature in step (2) can be maintained at 80 to 100 °C for 2 to 4 hours, and more preferably, the temperature can be maintained at 85 to 95 °C for 2 to 3 hours.

[0020] Preferably, in step (2) the heat treatment can be carried out at a temperature of 400 °C to 650 °C for 2 to 4 hours.

[0021] Preferably, the heat treatment can be carried out at a temperature of 450 °C to 550 °C for 2 to 4 hours.

[0022] In step (2) air can preferably be used as the oxidizing agent for the heat treatment.

[0023] Preferably in step (3) the surfactant may be at least one selected from the group consisting of sodium dodecylbenzenesulfonate (SDBS), polyethylene glycol (PEG), sodium dodecyl sulfate (SDS) and polyvinylpyrrolidone (PVP).

[0024] Preferably, the surfactant may be at least one selected from the group consisting of SDBS and PEG.

[0025] Preferably in step (3) the high-energy ball grinding can be carried out for 0.5 hours to 3 hours, and further preferably the high-energy ball grinding can be carried out for 1 hour to 1.5 hours.

[0026] Preferably in step (3) a device for high-energy ball grinding can be a high-energy ball grinding machine.

[0027] High-energy ball milling is performed to pre-activate the slurry, increase the activity of the iron source (iron oxide), decrease the reaction activation energy, and initiate a chemical reaction at low temperature.

[0028] Preferably in step (4) pure water at a temperature of 85 °C to 100 °C can be filled into an extraction tank which is used for extraction, and further preferably the pure water can have a temperature of 90 °C to 95 °C.

[0029] Preferably in step (4) the extraction agent may be one selected from the group consisting of tributyl phosphate (TBP), isopropyl ether (IPE), isopropyl alcohol (IPA), isoamyl alcohol, n-butanol and dibutyl sulfoxide (DBSO).

[0030] Preferably, the extraction solvent may be selected from the group consisting of TBP, IPA and n-butanol.

[0031] Preferably, in step (4) the mass ratio of the extraction agent to the phosphoric acid can be 1:3 - 6; and further preferably, the mass ratio of the extraction agent to the phosphoric acid can be 1:4.5 - 5.5.

[0032] Preferably in step (4) the extraction can be carried out at a temperature of 50 °C to 80 °C for 10 min to 120 min; and further preferably the extraction can be carried out at a temperature of 60 °C to 70 °C for 40 min to 70 min.

[0033] Preferably, in step (4) the acidic liquid can be sulfuric acid configured to increase the extraction yield; and the amount of sulfuric acid added can be 1% to 3% of the mass of the extracted organic phase.

[0034] Preferably, step (4) may further comprise exposing the phosphoric acid to a concentration to obtain refined concentrated phosphoric acid.

[0035] Preferably, the concentration can be carried out at a temperature of 85 °C to 105 °C for 2 to 10 hours; and preferably, the concentration can be carried out at a temperature of 95 °C to 100 °C for 5 to 8 hours.

[0036] Preferably in step (5) the molar ratio of Fe in the suspension to P in the phosphoric acid can be 1: 1.4 - 1.7.

[0037] Preferably in step (5), the Fe content in a liquid phase obtained by SLS can be less than or equal to 20 mg / liter; and further preferably, the heating can be carried out at a temperature of 60 °C to 70 °C, and the Fe content in the liquid phase can be less than or equal to 10 mg / liter.

[0038] Preferably, the washing in step (5) can be carried out as follows: Digestion of the solid according to a solid-liquid ratio of 1 g : 10 - 15 liters, filtering and rinsing of a resulting filter cake with pure water according to a solid-liquid ratio of 1 g : 10 liters, until the electrical conductivity is ≤ 500 µs / cm.

[0039] Preferably, in step (5) the sintering can be carried out as follows: in an atmosphere generated by one or more substances selected from the group consisting of air and nitrogen, sintering at 200 °C to 350 °C for 1 hour to 3 hours, followed by heating to 500 °C to 650 °C and sintering for 2 hours to 3 hours.

[0040] Preferably, the iron phosphate in step (5) may have an impurity content of less than or equal to 0.10%; and further preferably, the iron phosphate may have an impurity content of less than or equal to 0.05%.

[0041] The present disclosure also provides for the use of iron phosphate from the above-described process for the production of a battery material.

[0042] Compared with the prior art, the present disclosure has the following advantageous effects. (1) In the present disclosure, iron phosphide waste and the like are used as feedstocks to produce iron oxide (an iron source) and phosphoric acid; and then the iron source is activated by high-energy ball milling and a surfactant to increase the activity of the iron source, reduce the reaction activation energy and chemical reaction potential barrier, and initiate a low-temperature chemical reaction to synthesize iron phosphate (without the addition of a precipitating agent and an alkaline liquid). The resulting anhydrous iron phosphate has few impurities, a uniform particle distribution, and a lamellar structure and can be used as a precursor for highly compressed LFP.In contrast to conventional iron phosphate synthesis, the present disclosure uses inexpensive raw materials and conducts reactions that enable a closed-loop production cycle. The manufacturing process generates less waste and requires a relatively low temperature, which can effectively reduce energy consumption costs. The process of the present disclosure involves simple equipment, straightforward operations, and inexpensive raw materials, which can increase the economic benefits for companies. (2) In the present disclosure, a high-energy ball mill and a surfactant are used to activate the iron source in order to increase the activity of the iron source and to reduce the reaction activation energy and the chemical reaction potential barrier, so that the production of iron phosphate, which normally requires a high-temperature reaction, can also be achieved at a low temperature without the addition of a precipitating agent and an alkaline liquid, thus reducing the consumption of reagents. (3) In the present disclosure, an alkaline liquid is used only in the synthesis process of iron oxide, and no alkaline liquid is used to adjust a pH in the synthesis process of iron phosphate, wherein a pH of a reaction system is relatively low and does not increase significantly during the reaction process (does not reach a precipitation pH of impurity elements), which reduces the adsorption of impurity ions into the solid product during the reaction process, so that high-purity iron phosphate can be produced. (4) The phosphorus source used in the present disclosure is phosphoric acid obtained by subjecting a washout liquid of iron phosphide waste to extraction, back-extraction and concentration, and can be used in the subsequent precipitation process to reduce the waste of resources. (5) Conventional iron phosphate synthesis typically requires a temperature above 90 °C, whereas the iron phosphate production described in this disclosure requires a temperature of only 50 °C to 80 °C (high-energy ball milling is performed to pre-activate the slurry, increase the activity of the iron source (iron oxide), reduce the reaction activation energy, and initiate a chemical reaction at a low temperature), which can effectively reduce energy consumption costs. In this disclosure, energy utilization is high, and energy consumption costs are lower than those of the conventional processing method.

[0043] Other aspects can be understood after reading and understanding the drawings and the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The drawings serve to further understand the present technical solution and, together with the examples of the present disclosure, form part of the description to explain the present technical solution and do not represent a limitation of the technical solution of the present disclosure. Fig. Figure 1 is a schematic diagram showing the procedure of an example of the present disclosure; Fig. 2 is an X-ray diffraction (XRD) pattern of iron phosphate dihydrate prepared in Example 1 of the present disclosure; Fig. Figure 3 is a scanning electron micrograph (SEM) of iron phosphate dihydrate prepared in Example 1 of the present disclosure; Fig. 4 is an XRD sample of anhydrous iron phosphate prepared in Example 1 of the present disclosure; Fig.Figure 5 is a SEM image of anhydrous iron phosphate produced in Example 1 of the present disclosure; Fig. Figure 6 is an XRD diagram of LFP synthesized from the anhydrous iron phosphate precursor prepared in Example 1 of the present disclosure; and Fig. Figure 7 shows the charge-discharge curves of the LFP synthesized from the anhydrous iron phosphate precursor prepared in Example 1 of the present disclosure at 0.1 C. DETAILED DESCRIPTION OF THE EXECUTION FORMS Example 1

[0045] This example describes a process for the production of iron phosphate, which includes in particular the following steps: (1) 1 kg of iron phosphide waste, 4 liters of nitric acid with a concentration of 1.5 mol / L, 3 liters of sulfuric acid with a concentration of 1.5 mol / L and 100 g of activated carbon (an adsorbent) were added to a closed high-temperature and high-pressure reactor with the addition of 1 mol of oxygen and thoroughly mixed to obtain a slurry A; (2) The slurry A was heated to 95 °C, stirred at a speed of 350 rpm for combined washing and held at a temperature of 95 °C for 2.5 hours to obtain a first filtrate B and a first filter residue, the reaction equations being as follows: 4 FeP + 8 O2 → 2 Fe2O3 + 2 P2O5, 4 Fe2P + 11 O2 → 4 Fe2O3 + 2 P2O5, and 4 Fe + 3 O2 → 2 Fe2O3; (3) 0.45 liters of a 30% concentration NaOH solution were added to the first filtrate B to adjust the pH to 3.5. The resulting mixture was kept warm for 2 hours and then hot filtered to obtain a precipitate C (a second filter residue), which was rapidly cooled to obtain a filtrate D (a second filtrate). The second filter residue (precipitate C) was then subjected to heat treatment at 500 °C to obtain 1.3 kg of iron oxide. (4) 0.8 kg of the iron oxide obtained in step (3) was weighed and mixed with 10 liters of pure water, then 17.25 g of SDBS was added as a surfactant, and the resulting mixture was stirred for 30 min and then subjected to high-energy ball milling for 1.5 hours in a high-energy ball mill (Tencan Powder, XQM-12, 300 rpm, 100 ml ethanol was used as a dispersant, 10 mm and 20 mm zirconium balls were mixed in a ratio of 3:1, and the mass ratio of milling balls to iron oxide powder was 5:1) to pre-reactivate the iron oxide, and 10.5 kg of a post-ball-milling slurry was collected for later use; (5) 6 liters of the filtrate D obtained in step (3) were added to a 10-liter extraction tank containing 2 liters of pure water, which was heated to 90 °C to obtain impurity-containing phosphoric acid; then 1 liter of n-butanol (as extraction solvent) and 0.5 liters of sulfuric acid with a concentration of 1.5 mol / liter were added, and the resulting mixture was stirred at 95 °C to obtain an organic phase and a raffinate; the organic phase was subjected to back-extraction to obtain dilute phosphoric acid; the dilute phosphoric acid was subjected to high-temperature concentration at 100 °C, and when a concentration of the resulting phosphoric acid was tested as suitable, the high-temperature concentration was completed to obtain refined concentrated phosphoric acid F; (6) 8 kg of the slurry obtained after high-energy ball milling was taken and placed in a 10-liter reactor; 0.824 kg of the refined concentrated phosphoric acid produced in step (5) was added to maintain the overall Fe / P ratio in the system at 1:1.15; and the resulting mixture was stirred thoroughly. The heating temperature was set to 70 °C and the stirring speed to 350 rpm to carry out a reaction for 6 hours. After the slurry had become completely white, SLS was carried out to obtain iron phosphate dihydrate and a mother liquor. The mother liquor was collected, and the Fe and P content in the mother liquor was tested to be 18.5 mg / liter and 3.75 g / liter, respectively. The mother liquor could be recycled to the first filtrate or could be used for the wet production of phosphoric acid. (7) The iron phosphate dihydrate was suspended with 15 liters of pure water to obtain a slurry, and the slurry was rinsed with 10 liters of pure water until the electrical conductivity was 395 µS / cm; and a filter cake obtained after rinsing and filtering was dried at 100 °C for 20 hours, and 1,100 g of a resulting powder were roasted and dehydrated to obtain anhydrous iron phosphate with an impurity content of less than or equal to 0.1%.

[0046] Fig. Figure 1 is a schematic diagram illustrating the procedure of an example of the present disclosure; Fig. 2 and Fig. Figure 3 is an XRD pattern and a SEM image of the iron phosphate dihydrate prepared in Example 1; and Fig. 4 and Fig. Figure 5 is an XRD sample and a SEM image of the anhydrous iron phosphate produced in Example 1. According to Fig. 2 and Fig. 4. Using the 2θ (diffraction angle) as the x-coordinate and the intensity as the y-coordinate, the crystallinity and purity of a product can be provisionally determined, and it can be seen that the iron phosphate produced in Example 1 exhibits high phase purity and pronounced crystallinity before and after dehydration and has no impurity phase. Fig. It is evident from Figure 3 that the primary particles in the prepared iron phosphate dihydrate have a lamellar structure and possess a narrow particle size distribution and good dispersibility. Fig. 5 shows that after high-temperature sintering of the produced iron phosphate, the primary particles still exhibit a flaky overall morphology, and the surface of the primary particles is evidently melting and has a porous structure, which meets the requirements for the formation of a high-density LFP battery precursor. Fig.Figure 6 is an XRD diagram of the LFP synthesized using Example 1 as a precursor, and it can be seen that the LFP produced by the present disclosure has no impurity phase, while exhibiting pronounced crystallinity, a complete crystal structure, and an olivine structure. Fig. Figure 7 shows charge-discharge curves of the LFP, synthesized with Example 1 as a precursor at a constant current of 0.1 C, with specific capacity as the x-coordinate and voltage as the y-coordinate, and it can be seen from the curves that the initial charge and discharge capacities are 159.5 mAh / g and 157.6 mAh / g respectively, the electrical performance results are comparable to those of a commercial product and the compactness is 2.42 g / cm³. 3 can achieve this, which suggests that the iron phosphate produced by the present disclosure is suitable as a precursor material for high-density LFP. Example 2

[0047] This example describes a process for the production of iron phosphate, which includes in particular the following steps: (1) 1 kg of iron phosphide waste, 4.5 liters of nitric acid with a concentration of 1.5 mol / liter, 2 liters of sulfuric acid with a concentration of 1.5 mol / liter and 150 g of activated carbon were added to a closed high-temperature and high-pressure reactor with the addition of 1 mol of oxygen and thoroughly mixed to obtain a slurry A; (2) The slurry A was heated to 93 °C, stirred at a speed of 380 rpm for combined washing and held at a temperature of 93 °C for 3 hours to obtain a first filtrate B and a first filter residue; (3) 0.45 liters of a 30% concentration NaOH solution were added to the first filtrate B to adjust the pH to 4, the resulting mixture was kept warm for 2.5 hours and then hot filtered to obtain a precipitate C (a second filter residue), which was rapidly cooled to obtain a filtrate D (a second filtrate), and the precipitate C was subjected to heat treatment at 550 °C to obtain 1.35 kg of iron oxide; (4) 0.8 kg of the iron oxide obtained in step (3) was weighed and mixed with 10 liters of pure water, then 25.87 g of SDBS was added, and the resulting mixture was stirred for 60 min and then milled in a high-energy ball mill for 2 hours to pre-activate the iron oxide, and 10 kg of a slurry after ball milling was collected for later use; (5) The 6 liters of filtrate D obtained in step (3) were placed in a 10-liter extraction tank containing 2 liters of pure water, which was heated to 90 °C to obtain impurity-containing phosphoric acid; then 1.5 liters of isobutanol (as extraction solvent) and 0.5 liters of sulfuric acid with a concentration of 1.5 mol / liter were added, and the resulting mixture was stirred at 98 °C to obtain an organic phase and a raffinate; the organic phase was subjected to back-extraction to obtain dilute phosphoric acid; the dilute phosphoric acid was subjected to high-temperature concentration at 98 °C; and when a concentration of the resulting phosphoric acid was tested as suitable, the high-temperature concentration was completed to obtain refined concentrated phosphoric acid F; (6) 8.0 kg of the slurry obtained after high-energy ball milling was taken and placed in a 10-liter reactor, 0.739 kg of the concentrated phosphoric acid prepared in step (5) was added to maintain the overall Fe / P ratio in the system at 1:1.1, and the resulting mixture was stirred thoroughly; the heating temperature was set to 60 °C and the stirring speed to 350 rpm to carry out the reaction for 8 hours, and after the slurry had turned completely white, SLS was carried out to obtain iron phosphate dihydrate and a mother liquor (a second filtrate); and the mother liquor was collected, the Fe and P content in the mother liquor was reduced to 19.3 mg / liter and 2.35 g / liter respectively, and the mother liquor (a second filtrate) could be recycled to the first filtrate or used for the wet production of phosphoric acid; and (7) The iron phosphate dihydrate was suspended with 12 liters of pure water to obtain a slurry, and the slurry was rinsed with 10 liters of pure water until the electrical conductivity was 303 µS / cm; and a filter cake obtained after rinsing and filtering was dried at 100 °C for 20 hours, and 900 g of a resulting powder were roasted and dehydrated to obtain anhydrous iron phosphate with an impurity content of less than or equal to 0.1%. Example 3

[0048] This example describes a process for the production of iron phosphate, which includes in particular the following steps: (1) 1 kg of iron phosphide waste, 2.5 liters of nitric acid with a concentration of 1.5 mol / liter, 4.5 liters of sulfuric acid with a concentration of 1.5 mol / liter and 150 g of activated carbon were added to a closed high-temperature and high-pressure reactor with the addition of 2.5 mol of oxygen and thoroughly mixed to obtain a slurry A; (2) The slurry A was heated to 95 °C, stirred at a speed of 400 rpm for combined washing and held at a temperature of 95 °C for 3 hours to obtain a first filtrate B and a first filter residue; (3) 0.6 liters of a 30% concentration NaOH solution were added to the first filtrate B to adjust the pH to 4.5, the resulting mixture was kept warm for 3 hours and then hot filtered to obtain a precipitate C (a second filter residue), which was rapidly cooled to obtain a filtrate D (a second filtrate), and the precipitate C was subjected to heat treatment at 450 °C to obtain 1.4 kg of iron oxide; (4) 0.7 kg of the iron oxide obtained in step (3) was weighed and mixed with 12 liters of pure water, then 31.05 g of SDBS was added as a surfactant, and the resulting mixture was stirred for 45 min and then subjected to high-energy ball milling for 1.5 hours to pre-activate the iron source, and 10 kg of a post-ball milling slurry was collected for later use; (5) 5.5 liters of the filtrate D obtained in step (3) were placed in a 10-liter extraction tank containing 1.5 liters of pure water, which was heated to 95 °C to obtain impurity-containing phosphoric acid; then 2 liters of isoamyl alcohol (as extraction solvent) and 0.7 liters of sulfuric acid with a concentration of 1.5 mol / liter were added, and the resulting mixture was stirred at 95 °C to obtain an organic phase and a raffinate; the organic phase was subjected to back-extraction with hot pure water to obtain dilute phosphoric acid; the dilute phosphoric acid was subjected to high-temperature concentration at 100 °C, and when a concentration of the resulting phosphoric acid was tested as suitable, the high-temperature concentration was completed to obtain refined concentrated phosphoric acid F; (6) 8.0 kg of the slurry obtained after high-energy ball milling was taken and placed in a 10-liter reactor, 0.739 kg of the concentrated phosphoric acid prepared in step (5) was added to maintain the overall Fe / P ratio in the system at 1:1.18, and the resulting mixture was stirred thoroughly; the heating temperature was set to 55 °C and the stirring speed to 330 rpm to carry out a reaction for 7 hours, and after the slurry had become completely white, SLS was carried out; and a resulting mother liquor was collected, the Fe and P content in the mother liquor was tested to be 10.2 mg / liter and 2.13 g / liter respectively, and the mother liquor could be recycled to the first filtrate or used for the wet production of phosphoric acid; and (7) The iron phosphate dihydrate was suspended with 15 liters of pure water to obtain a slurry, and the slurry was rinsed with 10 liters of pure water until the electrical conductivity was 215 µS / cm; and a filter cake obtained after rinsing and filtering was dried at 100 °C for 18 hours, and 890 g of a resulting powder were roasted and dehydrated to obtain anhydrous iron phosphate with an impurity level of not more than 0.1%. Comparative Example 1

[0049] This comparative example describes a process for the production of iron phosphate, which includes in particular the following steps: (1) The by-product iron sulfate from the titanium dioxide production was dissolved in pure water to produce an iron sulfate solution A with an Fe concentration of 45 g / liter; (2) An ammonium dihydrogen phosphate (ADP) solution, phosphoric acid and hydrogen peroxide were mixed to produce a mixed phosphorus source / oxidizing agent solution B; (3) With solution A as a base solution in a reactor, the mixed solution B was pumped into the reactor at a certain rate under a certain temperature and a certain stirring condition, so that an Fe / P ratio in a reaction system was about 1:1.1 and a pH value in a reaction process was maintained at 1.5 to 2; and (4) The reaction system was heated to 88 °C and stirred to obtain an iron phosphate precipitate, and the precipitate was aged for 3 hours after it turned white, then filtered, washed until the electrical conductivity was 400 µS / cm or less, dried and dehydrated to obtain an anhydrous iron phosphate powder.

[0050] Analysis of examples 1 to 3 and comparison example 1: Table 1 shows the levels of impurity elements in the iron phosphate products prepared in Examples 1, 2, and 3, the iron oxide produced, and the commercially available Yarcher iron phosphate, as well as in the iron phosphate products prepared in Comparative Example 1. Specific data were determined using an inductively coupled plasma atomic emission spectroscopy (ICP-AES) instrument.It can be seen from Table 1 that there are many impurities in the prepared iron oxide raw material; and since the process for producing the present disclosure does not change the pH of the system and the impurity elements are not precipitated with the iron phosphate, the impurity content in each of the iron phosphate products produced in the examples is significantly lower than that in the commercially available standard, indicating that the process for producing the present disclosure can greatly purify iron phosphate and improve the physical and chemical properties of the product. Table 1 Contaminant element (%) Example 11 Example 12 Example 3 iron oxide Commercially available Yarcher iron phosphate Index for commercially available iron phosphate Comparative Example 1 Ni 0,0001 0,0009 0,0011 0,0082 0,0005 ≤0,0100 0,0009 C 0,0015 0,0012 0,0014 0,0823 0,0008 ≤0,0100 0,0015 Approx 0,0001 0,0005 0,0011 0,1012 0,0004 ≤0,0100 0,0001 Cr 0,0001 0,0005 0,0003 0,0093 0,0011 ≤0,0100 0,0001 S 0,0030 0,0009 0,0015 0,2786 0,0156 ≤0,0300 0,0286 Si 0,0001 0,0005 0,0009 0,0211 0,0005 ≤0,0100 0,0001 Ti 0,0025 0,0012 0,0014 0,0012 0,0009 ≤0,0100 0,0052 Zn 0,0001 0,0001 0,0002 0,0027 0,0019 ≤0,0100 0,0002 Al 0,0003 0,0001 0,0001 0,0038 0,0058 ≤0,0050 0,0010 Co 0,0003 0,0005 0,0009 0,0012 0,0005 ≤0,0100 0,0009 Mn 0,0005 0,0003 0,0002 0,0138 0,0174 ≤0,0100 0,0001 Mg 0,0001 0,0002 0,0001 0,0093 0,0132 ≤0,0100 0,0001 Insoluble substances 0,0001 0,0004 0,0005 0,0085 0,0021 ≤0,0100 0,0009 Test example

[0051] The anhydrous iron phosphate produced in Examples 1 to 3 and the commercially available Yarcher iron phosphate were each processed to LFP using a conventional method under the same conditions, and the dense density and other electrical properties of the LFP produced were determined. The results are shown in Table 2 below. Table 2 Compacted density (g / cm³) 3 ) Initial charging capacity at 0.1C (mAh / g) Initial discharge capacity at 0.1 C (mAh / g) Initial discharge efficiency at 0.1C (%) Capacity retention after 500 cycles at 25°C and 1°C (%) Example 1 2,42 159,5 157,6 98,81 96,52 Example 2 2,41 160,1 157,3 98,25 96,56 Example 3 2,39 161,2 158,0 98,01 96,11 Commercially available iron phosphate 2,36 159,5 157,2 98,55 95,99 Comparative Example 1 2,38 159,8 157,2 98,37 96,03

[0052] The LFP powders produced from the anhydrous iron phosphate manufactured in Examples 1 to 3 of the present disclosure exhibited a compact density and electrical properties close to those of LFP manufactured from commercially available iron phosphate, indicating that the iron phosphate manufactured in the present disclosure meets the standards of anhydrous iron phosphate of LFP battery quality and exhibits performance that even surpasses that of commercially available iron phosphate.

Claims

[1] Process for the production of iron phosphate comprising the following steps: (1) Mixing an iron phosphide waste, an acidic liquid, an oxidizing agent and an adsorbent with stirring, heating to leaching and subjecting the resulting mixture to solid-liquid separation to obtain a first filtrate and a first filter residue; (2) Adding an alkaline liquid to the first filtrate to adjust the pH of the first filtrate, maintaining a temperature of the resulting mixture, and subjecting the resulting mixture to solid-liquid separation to obtain a second filter residue and a second filtrate; and subjecting the second filter residue to heat treatment to obtain iron oxide; (3) Subjecting the iron oxide to high-energy ball milling and adding a surfactant for activation to obtain a slurry; (4) Adding an extraction agent and an acidic liquid to the second filtrate obtained in step (2), carrying out an extraction and separation on a resulting mixture and subjecting a resulting organic phase to back-extraction to obtain phosphoric acid; and (5) Mixing the slurry obtained in step (3) with the phosphoric acid, heating to enable a reaction, subjecting the resulting mixture to solid-liquid separation to obtain a solid, and washing and sintering the solid to obtain the iron phosphate; where in step (1) the iron phosphide waste comprises a mixture of FeP and Fe2P; in step (1) the acidic liquid contains at least two from the following group: nitric acid, sulfuric acid and hydrochloric acid; In step (1) the oxidizing agent is at least one selected from the group consisting of hydrogen peroxide, oxygen, nitric acid and sodium persulfate; wherein in step (2) the alkaline liquid is at least one selected from the group consisting of a NaOH solution, a KOH solution, ammonia water, a urea solution, NH4Cl, NH4HCO3, Na2CO3 and NaHCO3; In step (2) the pH of the first filtrate is adjusted to 2.5 to 5; and In step (5) the molar ratio of Fe in the slurry to P in the phosphoric acid is 1:1–2; heating to enable a reaction is carried out at a temperature of 50 °C to 80 °C for 20 to 60 min; and the iron phosphate has a D 50 from 2 µm to 6 µm, a tapped density of 0.80 g / cm³ 3 up to 1.30 g / cm³ 3 , and a specific surface area of ​​4 m² 2 / g up to 8 m 2 / g indicates. [2] A process for the production of iron phosphate according to claim 1, wherein in step (1) the adsorbent is one selected from the group consisting of activated carbon, graphite, carbon molecular sieve and zeolite molecular sieve. [3] Process for the production of iron phosphate according to claim 1, wherein in step (3) the surfactant is at least one selected from the group consisting of sodium dodecylbenzenesulfonate, polyethylene glycol, sodium dodecyl sulfate and polyvinylpyrrolidone. [4] Process for the production of iron phosphate according to claim 1, wherein in step (4) the extraction agent is one selected from the group consisting of tributyl phosphate, isopropyl ether, isopropyl alcohol, n-butanol and dibutyl sulfoxide. [5] Use of the process for producing iron phosphate according to any one of claims 1 to 4 in the production of a cathode material.

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