A method for preparing battery-grade iron phosphate by using pyrite cinder

Abstract

This invention discloses a method for preparing battery-grade iron phosphate from pyrite cinder. The method employs a strong alkaline solution-assisted ball milling process to activate and mechanically revitalize the pyrite cinder. After aging, impurities are converted into soluble components or passivated into acid-insoluble components that are then separated from iron oxide. Impurities are further removed by water leaching. Then, ferric sulfate obtained by direct acid leaching of the impurity-removed pyrite cinder with sulfuric acid is used as the iron source, phosphoric acid as the phosphorus source, and ammonia as a neutralizing agent to directly precipitate and prepare battery-grade iron phosphate. This invention achieves highly efficient removal of harmful impurities in the preparation of battery-grade iron phosphate from pyrite cinder, reducing the complexity of conventional methods that require adjusting the pH of the acid leaching solution to remove impurities or reducing the acid leaching solution to ferrous sulfate. This enables efficient and high-value resource utilization of pyrite cinder. The process is simple, the reaction conditions are mild, the operation and control are convenient, and it is easy to implement for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of high-value resource utilization of chemical solid hazardous waste, specifically to a method for preparing battery-grade iron phosphate using pyrite slag. Background Technology

[0002] Lithium iron phosphate (LFP) is the cathode material for second-generation lithium-ion batteries and plays a crucial role in the current new energy industry. With the rapid development of the new energy industry in recent years, my country's demand for LFP is projected to reach tens of millions of tons by 2030. Faced with such a huge demand, finding abundant and inexpensive iron sources is of significant practical importance. In current LFP production processes, the solid-state process using iron phosphate as the iron-phosphorus source precursor accounts for the largest proportion. The elemental composition, particle morphology, and other physicochemical properties of iron phosphate have a significant impact on the electrochemical performance of the final LFP. The chemical structure of iron phosphate is highly dependent on the preparation method; different methods can yield iron-phosphorus compounds with varying crystal structures, sizes, and morphologies. Based on their crystal structure, they can be classified into isophosphorus-iron-manganese type, amorphous, orthorhombic, monoclinic, and α-quartz crystal systems; their electrochemical activity follows the order: isophosphorus-iron-manganese type > amorphous > orthorhombic > monoclinic > α-quartz crystal system. Amorphous iron phosphate is mainly prepared using co-precipitation methods.

[0003] Pyrite slag (PyC) is a solid waste generated during the roasting of pyrite to produce sulfuric acid. Its main phases are Fe2O3, SiO2, Al2O3, and gangue, with Fe content as high as 30% to 50%. In addition, PyC also contains a significant amount of valuable metals such as Al, Zn, Cu, and Mn. my country's annual PyC production is between 11 and 12 million tons, accounting for approximately 30% of the country's total chemical waste (W.Li, S.Wang, Y.Han, Z.Tang, Y.Zhang. Recovery of iron from pyrite cinder by suspension magnetization roasting-magnetic separation method: Process optimization and mechanism study. Sep. Purif. Technol., 2024, 332:125652; T.Jiang, Y.Tu, Z.Su, M.Lu, S.Liu, J.Liu, F.Gu, Y.Zhang. A novel value-added utilization process for pyrite cinder: Selective recovery of Cu / Co and synthesis of iron phosphate. Hydrometallurgy, 2020, 193:105314). Therefore, PyC is a high-quality iron source with abundant content, and can be used as a low-cost iron source for the preparation of iron phosphate / lithium iron phosphate, which has huge demand. However, since PyC is produced by high-temperature roasting of pyrite, the Fe2O3 within it aggregates and agglomerates with impurities and inert gangue and SiO2, causing the Fe2O3 surface to be coated with gangue and SiO2, reducing its reactivity and making it difficult to extract. Furthermore, impurities such as Al, Zn, Mn, Pb, Cr, Ca, and Mg are easily leached along with Fe, resulting in a high impurity content in the Fe-containing solution. Using this method to prepare iron phosphate from the iron-containing solution often results in severely excessive impurity levels, failing to meet the requirements for lithium iron phosphate preparation. Therefore, the key to preparing iron phosphate / lithium iron phosphate using PyC as the iron source lies in impurity control.The common methods for controlling impurity content are mainly as follows: (1) Converting the ferric iron in PyC to ferrous iron, and after impurity removal in this process, converting it to ferric phosphate with oxidants such as H2O2 and phosphates. For example, extracting the ferric iron in PyC with acid and then reducing it to produce ferrous sulfate of higher purity; or dissolving silicon dioxide in PyC with alkali and then leaching it with acid, then reducing it to ferrous solution with iron powder, and then removing impurities with nonionic flocculants (CN109368610A); or calcining PyC with carbon source in an inert atmosphere to reduce it to ferrous iron, then leaching it with dilute phosphoric acid, and adjusting the pH value and Add flocculant to purify leachate (CN114684801A); (2) Extract iron from PyC first, then convert it into ferric hydroxide, and then react it with phosphoric acid to convert it into ferric phosphate. For example, first extract iron from PyC with acid, then add iron powder to reduce it, then add alkali to adjust the pH value to remove impurities, then add oxidant and adjust the pH value to convert ferrous iron into ferric hydroxide (CN114906830A); or leach PyC with strong acid, adjust the pH value with urea or ammonia to remove impurity elements in the reaction solution, and then convert iron into ferric hydroxide colloid (CN108706561A). Clearly, the first method, which converts ferric iron to ferrous iron and then crystallizes it into ferrous sulfate or removes impurities by adjusting the solution pH and adding a flocculant, is cumbersome. Some processes require the consumption of alkali and flocculants, especially the later stages which require the addition of hazardous and expensive H₂O₂. This not only increases the complexity and cost but also poses significant safety risks. The second method, which removes impurities by adjusting the solution pH with alkali, not only consumes alkali but also requires precise pH control, making it difficult to accurately remove impurities or cause iron loss. Furthermore, the resulting ferric hydroxide precipitate or colloid easily carries away impurities, leading to poor purification (impurity removal) results. Therefore, there is an urgent need to develop efficient impurity removal methods, simplify the preparation process, and reduce costs. Summary of the Invention

[0004] In view of the above-mentioned problems in the preparation of iron phosphate using pyrite cinder (PyC) as iron source, the present invention provides a method for preparing battery-grade iron phosphate using pyrite cinder, including steps such as alkaline activation, mechanical activation, aging and impurity removal, acid leaching and precipitation. Its features are: (1) Pyrite cinder is activated and mechanically activated by ball milling with strong alkaline solution as solvent, and then aging is performed to promote the conversion of impurities into soluble components or passivation into components that are difficult to be acid-soluble and thus peeled off from iron oxide, which can significantly improve the removal rate of impurity components and the activity and leaching rate of iron oxide in the subsequent acid leaching process; (2) The pyrite cinder after impurity removal is leached with sulfuric acid to obtain iron sulfate, which can be directly converted into battery-grade iron phosphate by precipitation with phosphoric acid without impurity removal, which simplifies the preparation process, improves the quality of the product and reduces the preparation cost.

[0005] The method for preparing battery-grade iron phosphate using pyrite slag provided by this invention includes the following steps:

[0006] (1) The pyrite slag that has been ground and sieved is mixed with an alkaline solution at a mass-volume ratio of 1g:1.0-1.2mL and added into a ball mill jar, and ball milled for 1-4 hours;

[0007] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured in air at 100-120°C for 1-2 hours, and then the temperature is raised to 150-300°C for 2-4 hours. After natural cooling, distilled water is added at 2-3 times the mass of the matured material, and the mixture is stirred thoroughly for 1.5-2 hours. Then the mixture is filtered and washed with distilled water until neutral. The filter cake is dried to constant weight to obtain impurity-free slag. The filtrate and wash water are collected and treated centrally.

[0008] (3) According to the ratio of sulfuric acid volume to impurity-removed slag mass of 1.6-2.4 mL:1 g, add sulfuric acid solution with a mass percentage concentration of 45%-55% and impurity-removed slag to the reactor, reflux at 110-125℃ for 4-5.5 h, then add distilled water to continue the reaction for 0.5-1 h, then filter, collect the filtrate to obtain ferric sulfate solution, and collect and utilize the filter residue, such as for building materials, etc.

[0009] (4) Dilute the ferric sulfate solution obtained in step (3) with distilled water to a ferric sulfate solution of 0.1-0.3 mol / L; then, according to the molar ratio of phosphorus to iron of 1-1.2:1, take industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.1-0.3 mol / L; add the diluted ferric sulfate solution and phosphoric acid solution to the reactor at the same rate, react at 70-90℃ for 0.5-1 h, then adjust the pH to 1.5-2.5 with alkali, continue to keep the temperature for 1.5-2 h, then filter, wash the filter cake with distilled water until it is nearly neutral, and collect the filtrate and wash water for centralized treatment;

[0010] (5) After drying the filter cake obtained in step (4), ferric phosphate dihydrate is obtained. After grinding, it is placed in a muffle furnace and heated to 500-600℃ at 1-5℃ / min for 2-4 hours to obtain anhydrous ferric phosphate.

[0011] Further, in step (1), the effective components of the pyrite slag are 57.19-78.64% Fe2O3, 2.00-8.47% Al2O3, 3.35-13.82% SiO2, 1.00-10.25% CaO, and 0.62-3.53% MgO; the pyrite slag is ground and sieved through a 60-80 mesh sieve.

[0012] Further, in step (1), the alkali is sodium hydroxide or potassium hydroxide, prepared as a solution with a mass percentage concentration of 10-30%.

[0013] Further, in step (1), the grinding media is added to the ball mill at a ball-to-material mass ratio of 8 to 12:1. The grinding media are stainless steel balls, corundum balls, or zirconia balls. The diameter of the large ball is 10 mm, the diameter of the small ball is 2 mm, and the mass ratio of the large ball to the small ball in the grinding media is 1:5 to 8. The ball milling is carried out at a speed of 450 to 550 r / min.

[0014] Furthermore, in step (1), the drying is carried out in a forced-air drying oven at a temperature of 80–100°C.

[0015] Furthermore, in step (2), the reflux reaction is carried out under stirring conditions, with a stirring speed of 200-300 r / min.

[0016] Furthermore, in step (4), the industrial phosphoric acid has a mass percentage concentration of 85%; the alkali is ammonia water with a mass percentage concentration of 15-20%.

[0017] Furthermore, in steps (3) and (4), the reactor is equipped with a mechanical stirrer and a reflux condenser.

[0018] Furthermore, in step (5), the drying is carried out in a forced-air drying oven at a temperature of 110–130°C for a time of 6–12 hours.

[0019] Further, the filtrate and wash water collected in step (2) are first adjusted to pH 7.0-8.5 with sulfuric acid so that Al is converted into aluminum hydroxide and removed. Then, a chelating flocculant is added to remove heavy metal ions. The filtrate and wash water collected in step (4) are first adjusted to pH 4.5-5.5 with ammonia water, and then concentrated by evaporation and cooled by crystallization to recover ammonium sulfate.

[0020] Tests have shown that the quality indicators of the anhydrous iron phosphate obtained by this invention meet or exceed the technical standards for iron phosphate used in batteries (HG / T4701-2021).

[0021] This invention first grinds and sieves PyC, then mixes it with a strong alkaline solution and activates it through ball milling and mechanical activation. Following water leaching and filtration washing, it yields purified pyrite slag. Then, it directly acid-leaches the purified pyrite slag with sulfuric acid to obtain relatively pure ferric sulfate, which serves as the iron source for ferric phosphate production. Phosphoric acid is then added as the phosphorus source, and the pH of the reaction system is adjusted using ammonia water, allowing ferric iron to be directly converted into battery-grade ferric phosphate. This invention provides an effective method for the efficient removal of harmful impurities in the preparation of battery-grade ferric phosphate from pyrite slag. It reduces the complexity of conventional methods, which require adjusting the pH of the acid leaching solution to remove impurities or reducing the acid leaching solution to ferrous sulfate. This achieves efficient and high-value resource utilization of pyrite slag and opens up a rich and inexpensive raw material route for the mass production of ferric phosphate. It plays a crucial role in promoting the rapid development and economic benefits of the new energy industry using lithium iron phosphate as a material.

[0022] The advantages of this invention compared to the prior art are as follows:

[0023] (1) Using a strong alkaline solution as the ball milling solvent can act as a wetting agent, dispersant, and activator, improving the activation and stimulation of components in PyC. Combined with aging treatment, impurities originally coated and mixed in PyC particles are transformed into soluble components. This further promotes the transformation of impurities into soluble components or passivation into acid-insoluble components, thus separating them from iron oxide. This improves the reactivity of iron oxide, reduces the difficulty of iron leaching, increases extraction efficiency, and significantly reduces the impurity content in the extract. Compared with conventional methods that first convert iron in PyC into high-purity ferrous sulfate, this process is simpler and more efficient. It is also simpler, easier to control, and has a better impurity removal effect than adjusting the pH of the leachate and using other heavy metal precipitants and flocculants to remove impurities.

[0024] (2) Using ferric sulfate obtained by direct acid leaching of impurities from iron ore slag with sulfuric acid as the iron source, phosphoric acid as the phosphorus source, and ammonia water as the neutralizing agent, battery-grade iron phosphate is prepared by direct precipitation. It does not require a complicated impurity removal process. The preparation process is simple, easy to operate and control, and the product has low impurity content, which can reach or even exceed the technical indicators of battery-grade iron phosphate.

[0025] (3) Ferric phosphate is prepared by using ferric sulfate obtained by direct acid leaching with sulfuric acid as the iron source. There is no need to add H2O2, which not only reduces the preparation cost, but also avoids the use of hazardous chemicals, improves the safety of the preparation process, and reduces management costs.

[0026] (4) The preparation process of this invention is simple, easy to operate, and the reaction conditions are mild; it generates less "three wastes" and the wastewater generated in the impurity removal process and the precipitation process for preparing iron phosphate is effectively treated, and the valuable components are fully recovered. The process is environmentally friendly; the required equipment is conventional equipment and it is easy to realize industrial production.

[0027] (5) This invention opens up a new method and approach for preparing iron phosphate / lithium iron phosphate in large quantities using pyrite slag as an iron source, realizing the high-value resource utilization of pyrite slag, and reducing the production cost of iron phosphate / lithium iron phosphate, and has broad application prospects. Attached Figure Description

[0028] Figure 1 This is a flowchart of the process for preparing battery-grade iron phosphate using pyrite slag according to the present invention.

[0029] Figure 2 These are scanning electron microscope (SEM) images of the original pyrite cinder and the pyrite cinder after impurities have been removed, as described in this invention: (a)-(b) are SEM images of the original pyrite cinder at different magnifications, and (c)-(d) are SEM images of the pyrite cinder after impurities have been removed at different magnifications.

[0030] Figure 3 Here are the X-ray diffraction pattern and scanning electron microscope image of the iron phosphate in this invention: Figure 3 In A, (a), (b), and (c) correspond to the X-ray diffraction patterns of ferric phosphate obtained in Examples 1, 3, and 5, respectively; Figure 3 In B, (a), (b), and (c) correspond to the physical images of the ferric phosphate samples obtained in Examples 1, 3, and 5, respectively; Figure 3 C is a scanning electron microscope image of the ferric phosphate obtained in Example 5.

[0031] Figure 4 The infrared spectra of ferric phosphate in this invention are shown in (a), (b), and (c), which correspond to the ferric phosphate obtained in Examples 1, 3, and 5, respectively. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the scope described in the embodiments.

[0033] Examples 1 to 16 are examples of impurity removal from pyrite slag and preparation of battery-grade iron phosphate. Example 17 is an example of the treatment of the impurity removal filtrate and washing water collected in step (2) and the recovery and utilization of valuable components. Example 18 is an example of the treatment of the filtrate and washing water generated in step (4) for the preparation of iron phosphate.

[0034] The process flow diagram of this invention is as follows: Figure 1 As shown in Table 1, the main components of the pyrite slag used in the examples are as follows.

[0035] Table 1. Main components of pyrite cinder

[0036]

[0037]

[0038] Example 1

[0039] (1) 26.465g of pyrite slag that has been ground and sieved and 31mL of 10% NaOH solution were added to a ball mill jar. 264.65g of zirconia balls (40g of large balls and 224.65g of small balls) were added at a ball-to-material mass ratio of 10:1. The mixture was ball-milled at 450r / min for 2h.

[0040] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 110°C for 2 hours in an air atmosphere, and then heated to 300°C for 2 hours. After natural cooling, distilled water is added at twice the mass of the matured material and stirred thoroughly for 2 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 90°C to constant weight to obtain 20.8231g of impurity-removed slag. The filtrate and wash water are collected and processed centrally.

[0041] (3) Add 48.5 mL of sulfuric acid solution with a mass percentage concentration of 50% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 110 °C for 4.5 h, then add 15 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 59 mL of ferric sulfate solution with a concentration of 2.82 mol / L.

[0042] (4) Dilute 35.46 mL of the ferric sulfate solution obtained in step (3) with distilled water to a concentration of 0.2 mol / L; take 6.83 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and the phosphoric acid solution to the reactor at the same rate, react at 70°C for 1 h, then adjust the pH value to 1.5 with ammonia water with a mass percentage concentration of 15%, continue to keep the temperature for 2 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0043] (5) The filter cake obtained in step (4) was placed in a blower drying oven and dried at 120°C for 6 hours to obtain 18.4506 g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 550°C at 5°C / min for 2 hours to obtain 14.9807 g of anhydrous ferric phosphate.

[0044] Table 2 shows the main element content of ferric sulfate solutions obtained by leaching sulfuric acid under the same process conditions with pyrite slag without and after impurity removal by the above methods, as determined by ICP-OE. Table 3 shows the component detection results of ferric phosphate prepared under the same conditions using the above two ferric sulfate solutions as iron sources.

[0045] Table 2 Main components of pyrite cinder leachate

[0046]

[0047]

[0048] Table 3. Main components of iron phosphate prepared from different iron sources

[0049]

[0050]

[0051] Content of other elements

[0052]

[0053]

[0054] As shown in Table 2, the content of elements other than iron in the ferric sulfate solution obtained by directly leaching pyrite cinder with sulfuric acid using the method of this invention is significantly lower than that obtained by directly leaching pyrite cinder without impurity removal with sulfuric acid. The main reason is that the strong alkali activation, ball milling mechanical activation, and aging treatment promote the conversion of Al, Zn, Si, Pb, and As into soluble salts, such as aluminates, zincates, sodium (potassium) silicates, leadates, and arsenates, which are easily dissolved into the filtrate and wash water during water leaching. Other elements, such as Zr, Mo, Mn, V, Sb, and Sn, are easily passivated during the above treatment and are difficult to leach during subsequent acid leaching, remaining in the residual slag. Furthermore, after the above treatment, not only is the activity of iron oxide in the slag increased, but the iron oxide originally bound by gangue and silica is also stripped away, increasing the activity, leaching rate, and leaching speed.

[0055] As shown in Table 3, the technical specifications of anhydrous ferric phosphate prepared using ferric sulfate solution obtained by acid leaching of impurity-removed pyrite slag as the iron source all meet or exceed the technical specifications of anhydrous ferric phosphate for batteries (HG / T4701-2021). However, the anhydrous ferric phosphate prepared using ferric sulfate solution obtained by direct acid leaching of pyrite slag without impurity removal as the iron source only meets some specifications, such as the iron-to-phosphorus ratio, Na, K, Mn, Ti, magnetic materials, tap density, particle size, and specific surface area. Other specifications, such as phosphorus content, calcium content, magnesium content, copper content, zinc content, manganese content, aluminum content, and moisture content, do not meet the technical requirements of HG / T4701-2021. Furthermore, the content of other impurity elements in ferric phosphate prepared by impurity removal is significantly lower than that in ferric phosphate obtained without impurity removal. Therefore, effective methods must be used to remove impurities when preparing battery-grade ferric phosphate using pyrite slag as the iron source.

[0056] Figure 2SEM images of raw pyrite cinder and purified pyrite cinder. From Figure 2 As can be seen from (a)-(b), the untreated raw sample consists of secondary components ranging from hundreds of nanometers to several micrometers of blocky or flaky particles, tightly connected to each other, with smooth and flat surfaces. These blocky or flaky particles are mainly various minerals such as hematite (iron oxide), gangue, and gypsum, which are tightly stacked and aggregated into irregular shapes larger than 10 μm. The reason for this structure may be that after the pyrite undergoes a high-temperature roasting process, as FeS2 is converted into Fe2O3, a large amount of sulfur-containing gas is released, significantly altering the mineral structure. The generated Fe2O3 melts and is encapsulated with the remaining gangue, silica, and other inert components, resulting in very low reactivity and difficulty in extraction. Figure 2 (c)-(d) are SEM images of the purified samples. It can be seen that after ball milling, alkali activation and aging, some of the minerals such as Al, Zn, As and Si are converted into soluble salts. The structure built up by various minerals and impurities is destroyed, which allows the originally agglomerated slag particles to be effectively separated and dispersed. This exposes the hematite that was covered by impurities such as SiO2 and gangue, increasing the specific surface area of ​​the slag particles and providing more reaction sites for subsequent leaching reactions. Figure 2 (d) is a further magnified image of the impurity-removed slag. It can be seen that compared with the smooth and flat original sample, the surface of the impurity-removed sample is rougher and more discontinuous. This can be attributed to the fact that after NaOH is mixed evenly with the slag, it reacts with impurities such as SiO2, Al, As, and Zn on the surface of the slag particles during the aging reaction, generating soluble silicates, aluminates, arsenates, and zincates, which etch the surface of the slag particles, thereby further exposing the hematite (iron oxide) encased within. This can effectively promote the peeling of hematite from inert components and increase its reactivity.

[0057] Example 2

[0058] (1) 26.465g of pyrite slag that has been ground and sieved and 29mL of NaOH solution with a mass percentage concentration of 20% were added into a ball mill jar. 264.65g of zirconia balls (40g of large balls and 224.65g of small balls) were added at a ball-to-material mass ratio of 10:1. The mixture was ball-milled at 500r / min for 3h.

[0059] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 110°C for 2 hours in an air atmosphere, and then heated to 250°C for 3 hours. After natural cooling, distilled water is added at 2.5 times the mass of the matured material, and the mixture is stirred thoroughly for 1.5 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 80°C to constant weight to obtain 21.5309g of impurity-removed slag. The filtrate and wash water are collected and processed centrally.

[0060] (3) Add 42 mL of sulfuric acid solution with a mass percentage concentration of 50% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 120 °C for 5 h, then add 20 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 55 mL of ferric sulfate solution with a concentration of 2.80 mol / L.

[0061] (4) Dilute 35.70 mL of the ferric sulfate solution obtained in step (3) with distilled water to a concentration of 0.2 mol / L; take 6.83 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and the phosphoric acid solution to the reactor at the same rate, react at 80°C for 1 h, then adjust the pH value to 2.0 with ammonia water with a mass percentage concentration of 15%, continue to keep the temperature for 2 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0062] (5) The filter cake obtained in step (4) was placed in a forced-air drying oven and dried at 120°C for 7 hours to obtain 18.3905 g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 550°C at 3°C / min for 4 hours to obtain 14.6514 g of anhydrous ferric phosphate.

[0063] Example 3

[0064] (1) 26.465g of pyrite slag that has been ground and sieved and 28mL of NaOH solution with a mass percentage concentration of 30% were added into a ball mill jar. 211.72g of zirconia balls (35g of large balls and 176.72g of small balls) were added at a ball-to-material mass ratio of 8:1. The mixture was ball-milled at 550r / min for 4h.

[0065] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 120°C for 1 hour in an air atmosphere, and then the temperature is raised to 300°C and matured for 4 hours. After natural cooling, distilled water is added at 3 times the mass of the matured material, and the mixture is stirred thoroughly for 1.5 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 100°C until constant weight, yielding 21.0346g of impurity-removed slag. The filtrate and wash water are collected and processed centrally.

[0066] (3) Add 42.1 mL of sulfuric acid solution with a mass percentage concentration of 50% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 125 °C for 5 h, then add 20 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 55 mL of ferric sulfate solution with a concentration of 2.79 mol / L.

[0067] (4) Take 35.84 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 6.83 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and the phosphoric acid solution to the reactor at the same rate, react at 70°C for 1 h, then adjust the pH to 2.5 with ammonia water with a mass percentage concentration of 20%, continue to keep the temperature and react for 1.5 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0068] (5) The filter cake obtained in step (4) was placed in a blower drying oven and dried at 120°C for 10 hours to obtain 18.4208 g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 550°C at 1°C / min for 2 hours to obtain 14.7211 g of anhydrous ferric phosphate.

[0069] Example 4

[0070] (1) 26.465g of pyrite slag that has been ground and sieved and 27mL of KOH solution with a mass percentage concentration of 40% were added into a ball mill jar. 317.58g of stainless steel balls (45g of large balls and 272.58g of small balls) were added at a ball-to-material mass ratio of 12:1. The mixture was ball-milled at 500r / min for 4h.

[0071] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 100°C for 2 hours in an air atmosphere, and then heated to 150°C for 4 hours. After natural cooling, distilled water is added at twice the mass of the matured material, and the mixture is stirred thoroughly for 2 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 90°C until constant weight, yielding 21.4864 g of impurity-free slag. The filtrate and wash water are collected and processed centrally.

[0072] (3) Add 35 mL of sulfuric acid solution with a mass percentage concentration of 55% and the slag after removing impurities to the reactor, reflux at a stirring speed of 300 r / min and 125 °C for 4.5 h, then add 25 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 51 mL of ferric sulfate solution with a concentration of 2.75 mol / L.

[0073] (4) Take 36.36 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 7.51 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and the phosphoric acid solution to the reactor at the same rate, react at 80°C for 1 h, then adjust the pH to 2.5 with ammonia water with a mass percentage concentration of 20%, continue to keep the temperature and react for 1.5 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0074] (5) The filter cake obtained in step (4) was placed in a blower drying oven and dried at 120°C for 12 hours to obtain 18.3505 g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 600°C at 5°C / min for 3.5 hours to obtain 14.6203 g of anhydrous ferric phosphate.

[0075] Example 5

[0076] (1) 26.465g of pyrite slag that has been ground and sieved and 29mL of 20% NaOH solution were added to a ball mill jar. 264.65g of corundum balls (40g of large balls and 224.65g of small balls) were added at a ball-to-material mass ratio of 10:1. The mixture was ball-milled at 500r / min for 1h.

[0077] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 110°C for 2 hours in an air atmosphere, and then heated to 250°C for 3 hours. After natural cooling, distilled water is added at 3 times the mass of the matured material, and the mixture is stirred thoroughly for 1.5 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 90°C until constant weight, yielding 21.6704 g of impurity-removed slag. The filtrate and wash water are collected and processed centrally.

[0078] (3) Add 35 mL of sulfuric acid solution with a mass percentage concentration of 45% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 120 °C for 5 h, then add 25 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 50 mL of ferric sulfate solution with a concentration of 2.75 mol / L.

[0079] (4) Take 36.36 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 8.19 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and phosphoric acid solution to the reactor at the same rate, react at 90°C for 0.5 h, then adjust the pH to 2.5 with ammonia water with a mass percentage concentration of 15%, continue to keep the temperature for 2 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0080] (5) The filter cake obtained in step (4) was placed in a forced-air drying oven and dried at 120°C for 7 hours to obtain 18.5601g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 550°C at 4°C / min for 4 hours to obtain 15.0207g of anhydrous ferric phosphate.

[0081] Example 6

[0082] (1) 26.465g of pyrite slag that has been ground and sieved and 29mL of NaOH solution with a mass percentage concentration of 20% were added into a ball mill jar. 264.65g of zirconia balls (40g of large balls and 224.65g of small balls) were added at a ball-to-material mass ratio of 10:1. The mixture was ball-milled at 500r / min for 3h.

[0083] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 100°C for 2 hours in an air atmosphere, and then heated to 300°C for 3 hours. After natural cooling, distilled water is added at 3 times the mass of the matured material, and the mixture is stirred thoroughly for 2 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 100°C to constant weight to obtain 21.2995g of impurity-free slag. The filtrate and wash water are collected and processed centrally.

[0084] (3) Add 35 mL of sulfuric acid solution with a mass percentage concentration of 52.5% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 110 °C for 5 h, then add 25 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 52 mL of ferric sulfate solution with a concentration of 2.74 mol / L.

[0085] (4) Take 36.50 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 7.51 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and phosphoric acid solution to the reactor at the same rate, react at 90°C for 0.5 h, then adjust the pH to 2 with ammonia water with a mass percentage concentration of 15%, continue to keep the temperature and react for 1.5 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0086] (5) The filter cake obtained in step (4) is placed in a forced-air drying oven and dried at 120°C for 10 hours to obtain 18.5811 g of ferric phosphate dihydrate; after grinding, it is placed in a muffle furnace and heated to 550°C at 5°C / min for 3 hours to obtain 15.0604 g of anhydrous ferric phosphate.

[0087] Example 7

[0088] (1) 26.465g of pyrite slag that has been ground and sieved and 29mL of KOH solution with a mass percentage concentration of 20% were added into a ball mill jar. 264.65g of zirconia balls (40g of large balls and 224.65g of small balls) were added at a ball-to-material mass ratio of 10:1. The mixture was ball-milled at 500r / min for 4h.

[0089] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 120°C for 1.5 h in an air atmosphere, and then heated to 300°C for 3 h. After natural cooling, distilled water is added at 3 times the mass of the matured material, and the mixture is stirred thoroughly for 2 h. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 100°C to constant weight to obtain 21.4532 g of impurity-free slag. The filtrate and wash water are collected and processed centrally.

[0090] (3) Add 35 mL of sulfuric acid solution with a mass percentage concentration of 50% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 120 °C for 5 h, then add 25 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 51 mL of ferric sulfate solution with a concentration of 2.75 mol / L.

[0091] (4) Take 36.40 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 7.51 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and the phosphoric acid solution to the reactor at the same rate, react at 90°C for 0.5 h, then adjust the pH to 2 with ammonia water with a mass percentage concentration of 20%, continue to keep the temperature and react for 1.5 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0092] (5) The filter cake obtained in step (4) is placed in a forced-air drying oven and dried at 120°C for 10 hours to obtain 18.5506g of ferric phosphate dihydrate; after grinding, it is placed in a muffle furnace and heated to 600°C at 5°C / min for 2 hours to obtain 15.0121g of anhydrous ferric phosphate.

[0093] Example 8

[0094] (1) 26.465g of pyrite slag that has been ground and sieved and 29mL of NaOH solution with a mass percentage concentration of 20% were added into a ball mill jar. 264.65g of zirconia balls (40g of large balls and 224.65g of small balls) were added at a ball-to-material mass ratio of 10:1. The mixture was ball-milled at 500r / min for 4h.

[0095] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 110°C for 2 hours in an air atmosphere, and then heated to 300°C for 2 hours. After natural cooling, distilled water is added at 3 times the mass of the matured material, and the mixture is stirred thoroughly for 2 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 90°C to constant weight to obtain 20.9005g of impurity-removed slag. The filtrate and wash water are collected and treated centrally.

[0096] (3) Add 35 mL of sulfuric acid solution with a mass percentage concentration of 50% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 125 °C for 5 h, then add 25 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 54 mL of ferric sulfate solution with a concentration of 2.71 mol / L.

[0097] (4) Take 36.90 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 7.51 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and the phosphoric acid solution to the reactor at the same rate, react at 90°C for 0.5 h, then adjust the pH to 2 with ammonia water with a mass percentage concentration of 20%, continue to keep the temperature for 1.5 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0098] (5) The filter cake obtained in step (4) was placed in a forced-air drying oven and dried at 120°C for 6 hours to obtain 18.4504 g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 550°C at 5°C / min for 4 hours to obtain 14.8014 g of anhydrous ferric phosphate.

[0099] Example 9

[0100] (1) 26.465g of pyrite slag that has been ground and sieved and 29mL of NaOH solution with a mass percentage concentration of 20% were added into a ball mill jar. 264.65g of zirconia balls (40g of large balls and 224.65g of small balls) were added at a ball-to-material mass ratio of 10:1. The mixture was ball-milled at 500r / min for 3h.

[0101] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 100°C for 2 hours in an air atmosphere, and then heated to 200°C for 4 hours. After natural cooling, distilled water is added at twice the mass of the matured material, and the mixture is stirred thoroughly for 2 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 90°C until constant weight, yielding 21.4555g of impurity-removed slag. The filtrate and wash water are collected and processed centrally.

[0102] (3) Add 35 mL of sulfuric acid solution with a mass percentage concentration of 50% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 120 °C for 5.5 h, then add 20 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 50 mL of ferric sulfate solution with a concentration of 2.85 mol / L.

[0103] (4) Take 35.00 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 8.17 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and phosphoric acid solution to the reactor at the same rate, react at 90°C for 0.5 h, then adjust the pH to 2.5 with ammonia water with a mass percentage concentration of 20%, continue to keep the temperature and react for 2 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0104] (5) The filter cake obtained in step (4) was placed in a forced-air drying oven and dried at 120°C for 6 hours to obtain 18.4303g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 550°C at 5°C / min for 2 hours to obtain 15.1021g of anhydrous ferric phosphate.

[0105] Example 10

[0106] (1) 26.465g of pyrite slag that has been ground and sieved and 29mL of NaOH solution with a mass percentage concentration of 20% were added into a ball mill jar. 264.65g of zirconia balls (40g of large balls and 224.65g of small balls) were added at a ball-to-material mass ratio of 10:1. The mixture was ball-milled at 500r / min for 4h.

[0107] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 120°C for 1 hour in an air atmosphere, and then heated to 250°C for 3 hours. After natural cooling, distilled water is added at twice the mass of the matured material and stirred thoroughly for 2 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 90°C to constant weight to obtain 21.6957g of impurity-removed slag. The filtrate and wash water are collected and treated centrally.

[0108] (3) Add 35 mL of sulfuric acid solution with a mass percentage concentration of 50% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 115 °C for 5.5 h, then add 20 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 52 mL of ferric sulfate solution with a concentration of 2.82 mol / L.

[0109] (4) Take 35.50 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 8.20 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and phosphoric acid solution to the reactor at the same rate, react at 90°C for 0.5 h, then adjust the pH to 2.5 with ammonia water with a mass percentage concentration of 20%, continue to keep the temperature and react for 2 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0110] (5) The filter cake obtained in step (4) was placed in a forced-air drying oven and dried at 120°C for 6 hours to obtain 18.4808 g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 550°C at 5°C / min for 4 hours to obtain 14.9005 g of anhydrous ferric phosphate.

[0111] Example 11

[0112] (1) 26.465g of pyrite slag that has been ground and sieved and 29mL of KOH solution with a mass percentage concentration of 20% were added into a ball mill jar. 264.65g of zirconia balls (40g of large balls and 224.65g of small balls) were added at a ball-to-material mass ratio of 10:1. The mixture was ball-milled at 500r / min for 3h.

[0113] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 100°C for 2 hours in an air atmosphere, and then heated to 300°C for 2 hours. After natural cooling, distilled water is added at twice the mass of the matured material and stirred thoroughly for 2 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 90°C to constant weight to obtain 22.1204g of impurity-removed slag. The filtrate and wash water are collected and treated centrally.

[0114] (3) Add 35 mL of sulfuric acid solution with a mass percentage concentration of 50% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 120 °C for 5.5 h, then add 25 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 55 mL of ferric sulfate solution with a concentration of 2.72 mol / L.

[0115] (4) Take 36.70 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 8.18 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and phosphoric acid solution to the reactor at the same rate, react at 90°C for 0.5 h, then adjust the pH to 1.5 with ammonia water with a mass percentage concentration of 20%, continue to keep the temperature for 2 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0116] (5) The filter cake obtained in step (4) was placed in a blower drying oven and dried at 120°C for 6 hours to obtain 18.3501g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 550°C at 5°C / min for 4 hours to obtain 14.7103g of anhydrous ferric phosphate.

[0117] Example 12

[0118] (1) 26.465g of pyrite slag that has been ground and sieved and 29mL of NaOH solution with a mass percentage concentration of 20% were added into a ball mill jar. 264.65g of zirconia balls (40g of large balls and 224.65g of small balls) were added at a ball-to-material mass ratio of 10:1. The mixture was ball-milled at 500r / min for 3h.

[0119] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 110°C for 2 hours in an air atmosphere, and then heated to 150°C for 4 hours. After natural cooling, distilled water is added at twice the mass of the matured material, and the mixture is stirred thoroughly for 2 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 90°C to constant weight to obtain 21.8509g of impurity-removed slag. The filtrate and wash water are collected and treated centrally.

[0120] (3) Add 35 mL of sulfuric acid solution with a mass percentage concentration of 50% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 115 °C for 5.5 h, then add 25 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 53 mL of ferric sulfate solution with a concentration of 2.74 mol / L.

[0121] (4) Take 36.50 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 8.19 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and phosphoric acid solution to the reactor at the same rate, react at 90°C for 0.5 h, then adjust the pH to 2.5 with ammonia water with a mass percentage concentration of 20%, continue to keep the temperature for 2 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0122] (5) The filter cake obtained in step (4) was placed in a forced-air drying oven and dried at 120°C for 6 hours to obtain 18.6107g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 550°C at 5°C / min for 4 hours to obtain 15.0501g of anhydrous ferric phosphate.

[0123] Example 13

[0124] (1) 26.465g of pyrite slag that has been ground and sieved and 29mL of NaOH solution with a mass percentage concentration of 20% were added into a ball mill jar. 264.65g of zirconia balls (40g of large balls and 224.65g of small balls) were added at a ball-to-material mass ratio of 10:1. The mixture was ball-milled at 500r / min for 3h.

[0125] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 110°C for 1 hour in an air atmosphere, and then heated to 200°C for 1 hour. After natural cooling, distilled water is added at 3 times the mass of the matured material, and the mixture is stirred thoroughly for 2 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 90°C to constant weight to obtain 21.1463g of impurity-removed slag. The filtrate and wash water are collected and processed centrally.

[0126] (3) Add 42.3 mL of sulfuric acid solution with a mass percentage concentration of 50% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 125 °C for 5.5 h, add 20 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 58 mL of ferric sulfate solution with a concentration of 2.69 mol / L.

[0127] (4) Take 37.20 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 7.51 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and phosphoric acid to the reactor at the same rate, react at 90°C for 0.5 h, then adjust the pH to 2 with ammonia water with a mass percentage concentration of 20%, continue to keep the temperature for 2 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0128] (5) The filter cake obtained in step (4) was placed in a forced-air drying oven and dried at 120°C for 6 hours to obtain 18.4504 g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 550°C at 5°C / min for 2 hours to obtain 14.9101 g of anhydrous ferric phosphate.

[0129] Example 14

[0130] (1) 26.465g of pyrite slag that has been ground and sieved and 29mL of NaOH solution with a mass percentage concentration of 20% were added into a ball mill jar. 264.65g of zirconia balls (40g of large balls and 224.65g of small balls) were added at a ball-to-material mass ratio of 10:1. The mixture was ball-milled at 500r / min for 3h.

[0131] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 110°C for 1 hour in an air atmosphere, and then heated to 200°C for 2 hours. After natural cooling, distilled water is added at 3 times the mass of the matured material and stirred thoroughly for 2 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 90°C to constant weight to obtain 21.5567g of impurity-free slag. The filtrate and wash water are collected and treated centrally.

[0132] (3) Add 42.3 mL of sulfuric acid solution with a mass percentage concentration of 50% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 120 °C for 5.5 h, then add 20 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 57 mL of ferric sulfate solution with a concentration of 2.71 mol / L.

[0133] (4) Take 37.00 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 7.53 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and the phosphoric acid solution to the reactor at the same rate, react at 90°C for 0.5 h, then adjust the pH to 2 with ammonia water with a mass percentage concentration of 20%, continue to keep the temperature for 2 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0134] (5) The filter cake obtained in step (4) was placed in a forced-air drying oven and dried at 120°C for 6 hours to obtain 18.3811 g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 550°C at 5°C / min for 4 hours to obtain 14.7303 g of anhydrous ferric phosphate.

[0135] Example 15

[0136] (1) 26.465g of pyrite slag that has been ground and sieved and 29mL of KOH solution with a mass percentage concentration of 20% were added into a ball mill jar. 264.65g of zirconia balls (40g of large balls and 224.65g of small balls) were added at a ball-to-material mass ratio of 10:1. The mixture was ball-milled at 500r / min for 4h.

[0137] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 110°C for 1 hour in an air atmosphere, and then heated to 200°C for 3 hours. After natural cooling, distilled water is added at 3 times the mass of the matured material, and the mixture is stirred thoroughly for 2 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 90°C to constant weight to obtain 22.2133g of impurity-removed slag. The filtrate and wash water are collected and processed centrally.

[0138] (3) Add 42.3 mL of sulfuric acid solution with a mass percentage concentration of 50% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 125 °C for 5.5 h, then add 20 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 54 mL of ferric sulfate solution with a concentration of 2.80 mol / L.

[0139] (4) Take 35.70 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 7.51 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and phosphoric acid solution to the reactor at the same rate, react at 90°C for 0.5 h, then adjust the pH to 2 with ammonia water with a mass percentage concentration of 20%, continue to keep the temperature for 2 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0140] (5) The filter cake obtained in step (4) was placed in a forced-air drying oven and dried at 120°C for 6 hours to obtain 18.4205 g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 550°C at 5°C / min for 4 hours to obtain 14.7413 g of anhydrous ferric phosphate.

[0141] Example 16

[0142] (1) 26.465g of pyrite slag that has been ground and sieved and 29mL of NaOH solution with a mass percentage concentration of 20% were added into a ball mill jar. 264.65g of zirconia balls (40g of large balls and 224.65g of small balls) were added as grinding media at a mass ratio of 10:1. The mixture was ball milled at a speed of 500r / min for 3h.

[0143] (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 110°C for 2 hours in an air atmosphere, and then heated to 200°C for 4 hours. After natural cooling, distilled water is added at 3 times the mass of the matured material, and the mixture is stirred thoroughly for 2 hours. Then it is filtered and washed with distilled water until neutral. The filter cake is placed in a forced-air drying oven and dried at 90°C to constant weight to obtain 21.1059g of impurity-removed slag. The filtrate and wash water are collected and processed centrally.

[0144] (3) Add 42.3 mL of sulfuric acid solution with a mass percentage concentration of 50% and the slag after removing impurities to the reactor, reflux at a stirring speed of 250 r / min and 120 °C for 5.5 h, then add 20 mL of distilled water and continue the reaction for 0.5 h, then filter and collect the filtrate to obtain 56 mL of ferric sulfate solution with a concentration of 2.74 mol / L.

[0145] (4) Take 36.50 mL of the ferric sulfate solution obtained in step (3) and dilute it with distilled water to a concentration of 0.2 mol / L; take 7.51 mL of industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.2 mol / L; add the diluted ferric sulfate solution and phosphoric acid solution to the reactor at the same rate, react at 90°C for 1 h, then adjust the pH to 2 with ammonia water with a mass percentage concentration of 20%, continue to keep the temperature for 2 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment;

[0146] (5) The filter cake obtained in step (4) was placed in a forced-air drying oven and dried at 120°C for 6 hours to obtain 18.3604 g of ferric phosphate dihydrate; after grinding, it was placed in a muffle furnace and heated to 550°C at 5°C / min for 4 hours to obtain 14.6510 g of anhydrous ferric phosphate.

[0147] Example 17

[0148] Take 500 mL of the filtrate and wash water collected in step (2) of each embodiment, add 6 mol / L sulfuric acid to adjust the pH value of the solution to 7.0-8.5, filter and separate to recover Al(OH)3 and other precipitates; add 5% heavy metal chelating flocculant to the filtrate until the precipitation no longer increases, remove various metal ions, especially heavy metal ions, and then add an appropriate amount of cationic polyacrylamide to promote further growth of flocs and produce brown-black precipitates. Filter and separate, collect the filter residue, dry it, and concentrate it as a smelting raw material to recover various metals through smelting.

[0149] Example 18

[0150] Take 500 mL of the filtrate and wash water collected in step (4) of each embodiment, add 15% to 20% ammonia to adjust the pH value to 4.5 to 5.5, then evaporate and concentrate until a film is easily formed at the interface between the solution and the air. Stop heating, then cool and crystallize, filter, and place the filter cake (crystal) in a vacuum drying oven to dry to constant weight at 60°C to obtain ammonium sulfate byproduct; the filtrate is then combined with the filtrate and wash water collected in the next round to recover ammonium sulfate.

[0151] Figure 3 A is the X-ray diffraction pattern of ferric phosphate obtained in Examples 1(a), 3(b), and 5(c). From... Figure 3 As can be seen from A(a), the uncalcined ferric phosphate has no obvious characteristic diffraction peaks, indicating that the uncalcined ferric phosphate (i.e., ferric phosphate dihydrate) in Example 1 has an amorphous structure. However, in Example 3, after calcination at high temperature for 2 hours, the peak shape changed, and diffraction peaks appeared at the (100) and (102) planes. Figure 3 A(b)). Figure 3 A(c) shows the detection results of ferric phosphate after calcination for 4 hours in Example 5. The diffraction peak at 25.8° is enhanced, indicating that the crystallinity of ferric phosphate is further improved. This result is consistent with the FePO4 standard card (JCPDS No. 50-1635). Figure 3 B provides physical images of samples from Example 1(a) (uncalcined), Example 3(b), and Example 5(c). As the calcination time increases, the color of the ferric phosphate product gradually changes from yellow to light white. Figure 3C is a SEM image of the ferric phosphate prepared in Example 5. The calcined ferric phosphate exhibits a nanosheet structure of 82-361 nm.

[0152] Figure 4 Fourier transform infrared (FT-IR) spectra of samples from Examples 1(a), 3(b), and 5(c). From... Figure 4 It can be seen that at wavenumbers of 3420, 1620, 1030, 636, and 593 cm⁻¹, -1 Absorption peaks were observed at all locations; among them, Example 1(a) showed an absorption peak at 3420 cm⁻¹. -1 and 1620cm -1 Strong absorption peaks are observed at all locations, which are the stretching vibrations (Vc) of the crystal water or free water contained in uncalcined ferric phosphate. OH ) and bending vibration (δ OH The peak; while in Examples 3(b) and 5(c), the peak value increased to 3420 cm⁻¹ with increasing calcination time. -1 and 1620cm -1 The intensity of the absorption peak at 1030 cm⁻¹ decreased significantly, indicating that the content of crystal water and free water in the sample further decreased with increasing calcination time. -1 and 636cm -1 The absorption peaks at these locations can be attributed to the stretching and bending vibrations of the PO bond in the phosphate group, respectively. In terms of absorption peak intensity, the uncalcined iron phosphate sample shows the highest absorption peak at 1030 cm⁻¹. -1 The absorption peak shape was not obvious at 550°C; after calcination for 2 hours, the absorption peak shape changed, but the peak intensity did not change much; however, as the calcination time was extended to 4 hours, the absorption peak shape changed significantly and the intensity increased substantially. The main reason for this is that at 550°C, ferric phosphate dihydrate gradually loses its water of crystallization to become anhydrous FePO4, and the crystal structure changes, which is consistent with the X-ray diffraction results. In addition, the absorption peaks in Examples 1(a), 3(b), and 5(c) showed no significant changes at 593 cm⁻¹. -1 The weak absorption peak at that point is the deformation vibration peak of the Fe-O-Fe group in ferric phosphate, and its peak shape also becomes more apparent with the increase of dehydration. Figure 4 The spectrum shows that the prepared iron phosphate has clear absorption peaks and no impurity peaks, indicating that the method of preparing battery-grade iron phosphate by using pyrite slag as raw material, and then directly using iron sulfate obtained by acid leaching with sulfuric acid after alkaline activation, mechanical activation, aging and impurity removal, is feasible.

[0153] The above are merely preferred embodiments of the present invention. Based on the above concept of the present invention, those skilled in the art can make various modifications and transformations. For example, within the range of proportions and process conditions given by the present invention, the proportions and process conditions can be combined and transformed. Such transformations and modifications are all within the scope of the present invention.

Claims

1. A method for preparing battery-grade iron phosphate using pyrite slag, characterized in that, Using a strong alkaline solution as a solvent, ball milling is used to activate and mechanically activate pyrite slag, followed by aging to convert impurities into soluble components or passivate them into acid-insoluble components, thus separating them from iron oxide. Specifically, this includes: (1) mixing the ground and sieved pyrite slag with a strong alkaline solution at a mass-to-volume ratio of 1 g: 1.0~1.2 mL and adding it to a ball mill jar, and ball milling for 1~4 h; (2) after ball separation, placing the resulting slurry in a muffle furnace and aging it in air at 100~120℃ for 1~2 hours. h, then heat to 150~300℃ and mature for 2~4h; after natural cooling, add distilled water at 2~3 times the mass of the matured material, stir thoroughly for 1.5~2h, then filter, wash with distilled water until neutral; dry the filter cake to constant weight to obtain impurity-removed slag, collect the filtrate and wash water for centralized treatment; the impurity-removed pyrite slag is leached with sulfuric acid to obtain ferric sulfate, which is directly precipitated with phosphoric acid without impurity removal to convert into battery-grade ferric phosphate.

2. The method for preparing battery-grade iron phosphate using pyrite slag according to claim 1, characterized in that, Includes the following steps: (1) The pyrite slag that has been ground and sieved is mixed with a strong alkaline solution at a mass-volume ratio of 1 g: 1.0~1.2 mL and added into a ball mill jar, and ball milled for 1~4 h; (2) After the ball material is separated, the resulting slurry is placed in a muffle furnace and matured at 100-120°C for 1-2 h in an air atmosphere, and then heated to 150-300°C for 2-4 h. After natural cooling, distilled water is added at 2-3 times the mass of the matured material, and the mixture is stirred thoroughly for 1.5-2 h. Then the mixture is filtered and washed with distilled water until neutral. The filter cake is dried to constant weight to obtain impurity-free slag. The filtrate and wash water are collected and treated centrally. (3) According to the ratio of sulfuric acid volume to impurity-removed slag mass of 1.6~2.4 mL∶1 g, add sulfuric acid solution with mass percentage concentration of 45%~55% and impurity-removed slag into the reactor, reflux reaction at 110~125℃ for 4~5.5 h, then add distilled water to continue the reaction for 0.5~1 h, then filter, collect the filtrate to obtain ferric sulfate solution, and collect and utilize the filter residue; (4) Dilute the ferric sulfate solution obtained in step (3) with distilled water to a ferric sulfate solution of 0.1~0.3 mol / L; then take industrial phosphoric acid and dilute it with distilled water to a phosphoric acid solution of 0.1~0.3 mol / L according to the molar ratio of phosphorus to iron of 1~1.2:1; add the diluted ferric sulfate solution and phosphoric acid solution to the reactor at the same rate, react at 70~90℃ for 0.5~1 h, then adjust the pH to 1.5~2.5 with alkali, continue to keep the temperature for 1.5~2 h, then filter, wash the filter cake with distilled water until it is nearly neutral, collect the filtrate and wash water for centralized treatment; (5) The filter cake obtained in step (4) is dried to obtain ferric phosphate dihydrate, then ground and placed in a muffle furnace and heated to 500-600℃ for 2-4 h at 1-5℃ / min to obtain anhydrous ferric phosphate.

3. The method for preparing battery-grade iron phosphate using pyrite slag according to claim 2, characterized in that, In step (1), the effective components of the pyrite slag are Fe2O3 57.19~78.64%, Al2O3 2.00~8.47%, SiO2 3.35~13.82%, CaO 1.00~10.25%, and MgO 0.62~3.53% by mass; the pyrite slag is ground and sieved through a 60~80 mesh sieve.

4. The method for preparing battery-grade iron phosphate using pyrite slag according to claim 2, characterized in that, In step (1), the strong alkali is sodium hydroxide or potassium hydroxide, prepared as a solution with a mass percentage concentration of 10-30%.

5. The method for preparing battery-grade iron phosphate using pyrite slag according to claim 2, characterized in that, In step (1), grinding media are added to the ball mill at a ball-to-material mass ratio of 8 to 12:

1. The grinding media are stainless steel balls, corundum balls, or zirconia balls. The diameter of the large ball is 10 mm, and the diameter of the small ball is 2 mm. The mass ratio of the large ball to the small ball in the grinding media is 1:5 to 8. The ball milling is carried out at a speed of 450 to 550 r / min.

6. The method for preparing battery-grade iron phosphate using pyrite slag according to claim 2, characterized in that, In step (2), the reflux reaction is carried out under stirring conditions, with a stirring speed of 200~300 r / min.

7. The method for preparing battery-grade iron phosphate using pyrite slag according to claim 2, characterized in that, In step (4), the industrial phosphoric acid has a mass percentage concentration of 85%; the alkali is ammonia water with a mass percentage concentration of 15-20%.

8. The method for preparing battery-grade iron phosphate using pyrite slag according to claim 2, characterized in that, In steps (3) and (4), the reactor is equipped with a mechanical stirrer and a reflux condenser.

9. The method for preparing battery-grade iron phosphate using pyrite slag according to claim 2, characterized in that, The drying in steps (2) and (5) is carried out in a blower drying oven. The drying temperature of the filter cake in step (2) is 80~100℃, and the drying temperature of the filter cake in step (5) is 110~130℃. The drying time is 6~12 h.

10. The method for preparing battery-grade iron phosphate using pyrite slag according to claim 2, characterized in that, The filtrate and wash water collected in step (2) are first adjusted to pH 7.0-8.5 with sulfuric acid so that Al is converted into aluminum hydroxide and removed. Then, a chelating flocculant is added to remove heavy metal ions. The filtrate and wash water collected in step (4) are first adjusted to pH 4.5-5.5 with ammonia water, and then concentrated by evaporation and cooled by crystallization to recover ammonium sulfate.

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