Process for the preparation of iron phosphate

Abstract

The application relates to the technical field of battery material preparation, and discloses a preparation method of iron phosphate, which comprises the following steps: obtaining iron ore acid leaching solution, the pH value of the iron ore acid leaching solution is 1.5-3.5; taking at least part of the iron ore acid leaching solution as the bottom liquid of a reaction kettle, adding a phosphorus-containing mixed solution into the reaction kettle for a synthesis reaction, the dropping time is controlled to Tmin, T <= 420n, n is the unit volume molar number of iron ions in the iron ore acid leaching solution, after the dropping is completed and sufficient reaction is carried out, solid-liquid separation is carried out to obtain first solid material containing iron phosphate; extracting anhydrous iron phosphate from the first solid material; the phosphorus-containing mixed solution contains phosphoric acid and a first oxidant. The method realizes the regulation of the crystal morphology and the microstructure of the iron phosphate, can obtain iron phosphate with various morphologies, provides a feasible direction for preparing iron phosphate with different morphologies, and meets the application requirements in different fields; the preparation process does not introduce alkali liquor, the cost is reduced, and the prepared finished product has low impurity content.

Description

Technical Field

[0001] This invention relates to the field of battery material preparation technology, and more specifically, to a method for preparing iron phosphate. Background Technology

[0002] Lithium iron phosphate (LFP) is widely used in the fields of power batteries and energy storage, offering advantages such as relatively low cost, good cycle stability, and environmental friendliness. As a crucial precursor in the synthesis of LFP, the shape, structure, and properties of iron phosphate particles significantly influence the performance of cathode materials. Specific shapes and structures of iron phosphate crystals possess more active sites on their surface, enhancing their reactivity. Therefore, targeted regulation of iron phosphate crystal morphology is key to improving battery performance.

[0003] Iron phosphate, as an important inorganic compound, is widely used in batteries, catalysts, magnetic materials, and other fields. In these applications, the performance of iron phosphate is often closely related to its crystal morphology. Traditional synthesis methods face challenges in morphology control, often making it difficult to achieve precise control over the crystal morphology of iron phosphate, resulting in poor morphological stability in the product and thus limiting its performance in certain specific applications.

[0004] Industrially, battery-grade iron phosphate is mainly prepared using ferrous sulfate and iron flakes as iron sources and phosphoric acid or phosphates as phosphorus sources. However, with the increasing depletion of related global mineral resources, the preparation of iron phosphate from pure substances faces problems such as raw material depletion and rising costs. If metal elements can be efficiently and economically recovered from minerals, the raw material shortage problem can be effectively solved, while also achieving resource utilization and environmental protection. Furthermore, if the production process for preparing iron phosphate from minerals includes the co-production of sulfates (nickel, manganese) to separate iron and elements such as nickel and manganese, comprehensive resource recovery and utilization can be achieved.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing ferric phosphate.

[0007] This invention is implemented as follows:

[0008] In a first aspect, the present invention provides a method for preparing ferric phosphate, comprising:

[0009] Obtain an iron ore acid leaching solution with a pH value of 1.5–3.5;

[0010] Using at least a portion of the iron ore acid leaching solution as the bottom liquid of the reactor, a phosphorus-containing mixed solution is added dropwise to the reactor to carry out the synthesis reaction. The dropwise addition time is controlled to be Tmin, T≤420n, where n is the number of moles of iron ions per unit volume in the iron ore acid leaching solution, in mol / L. After the dropwise addition is completed and the reaction is fully completed, solid-liquid separation is carried out to obtain the first solid material containing iron phosphate.

[0011] Extract anhydrous ferric phosphate from the first solid material;

[0012] The phosphorus-containing mixture contains phosphoric acid and a primary oxidizing agent.

[0013] In an optional embodiment, the pH of the iron ore leaching solution is 1.5 to 3.0.

[0014] In an optional embodiment, the synthesis reaction process is as follows: a portion of the iron ore acid leaching solution is used as the bottom liquid of the reactor, and the remaining portion of the iron ore acid leaching solution is added dropwise to the reactor together with the phosphorus-containing mixed solution in a co-current manner;

[0015] The ratio of the iron ore acid leaching solution used as the base liquid to the added iron ore acid leaching solution is a:(1-a), where a is greater than or equal to 0.2 and less than 1.

[0016] In an optional implementation, a is 0.2 to 0.7.

[0017] In an optional embodiment, the first oxidant is hydrogen peroxide, and the molar ratio of phosphoric acid to hydrogen peroxide is 1:(0.3 to 0.7).

[0018] In an optional embodiment, the mass concentration of phosphoric acid in the phosphorus-containing mixture is 15-55%.

[0019] In an optional implementation, the method for obtaining the iron ore acid leaching solution includes:

[0020] Iron-containing minerals are roasted to obtain roasting residue;

[0021] The roasted residue is mixed with acid solution, and after the reaction is complete, solid-liquid separation is performed to obtain primary acid leaching solution.

[0022] Chromium is removed from the primary acid leaching solution to obtain an iron ore acid leaching solution.

[0023] In an optional embodiment, a second oxidant is also mixed with the roasted residue.

[0024] In an optional embodiment, the second oxidant is selected from at least one of oxygen, air, ozone, hydrogen peroxide, sodium persulfate, and ammonium persulfate.

[0025] In an optional embodiment, the ratio of the amount of the second oxidant added to the mass of the calcined residue is (0.1 to 0.3):1.

[0026] In an optional embodiment, the iron-bearing mineral is selected from at least one of manganese iron ore, nickel iron ore, and cobalt iron ore.

[0027] In an optional embodiment, the roasting temperature of the iron-containing mineral is 500–750°C.

[0028] In an optional embodiment, the acid solution is selected from at least one of sulfuric acid solution, nitric acid solution, and hydrochloric acid solution.

[0029] In an optional embodiment, the total amount of acid-soluble metal elements in the roasted residue and the molar ratio of hydrogen ions in the acid solution are 1:(2-4). When the iron-containing mineral is manganese iron ore, the acid-soluble metal elements are iron and manganese. When the iron-containing mineral is nickel iron ore, the acid-soluble metal elements are iron and nickel. When the iron-containing mineral is cobalt iron ore, the acid-soluble metal elements are iron and cobalt.

[0030] In an optional embodiment, the concentration of hydrogen ions in the acid solution is 2–5 mol / L.

[0031] In an optional embodiment, the roasted residue is mixed with acid solution and then subjected to acid leaching reaction at a temperature of 60–90°C for 5–15 hours.

[0032] In an optional embodiment, the method for removing chromium from the primary acid leaching solution includes:

[0033] The pH value of the primary acid leaching solution was tested. When the pH value was 1.5 to 3.5, a flocculant was added to the primary acid leaching solution to precipitate chromium.

[0034] When the pH value is less than 1.5, add a pH adjuster to adjust the pH of the primary acid leaching solution to 1.5-3.5; then add a flocculant to the primary acid leaching solution to precipitate chromium.

[0035] In an optional embodiment, the flocculant is selected from at least one of ferric phosphate dihydrate, ferric hydroxide, basic ammonium ferric phosphate and silica, and the ratio of the amount of flocculant added to the mass of the primary acid leaching solution is (1-10):1000.

[0036] In an optional embodiment, the pH adjuster is selected from at least one of nickel carbonate, nickel hydroxide, manganese carbonate, manganese hydroxide, sodium hydroxide, sodium carbonate, and ammonia water.

[0037] In an optional implementation, the dripping time is controlled to be T = (160~420)n.

[0038] In an optional embodiment, the iron ion concentration in the iron ore leaching solution is 30–80 g / L.

[0039] In an optional embodiment, the reaction temperature inside the reactor is controlled at 85–95°C during the dropwise addition of the phosphorus-containing mixture.

[0040] In an optional implementation, the reaction time after the addition is completed is 0.1 to 0.3 hours.

[0041] In an optional implementation, the method for extracting anhydrous ferric phosphate from the first solid material includes:

[0042] The first solid material is mixed with a phosphoric acid solution to replace impurities in the first solid material, and then solid-liquid separation is performed to obtain the second solid material.

[0043] The second solid material is washed to remove impurities;

[0044] After washing and removing impurities, the mixture is dried and sintered to obtain anhydrous ferric phosphate.

[0045] In an optional embodiment, the first solid material is mixed with the phosphoric acid solution and reacted at 85–95°C for 2–5 hours.

[0046] In an optional embodiment, the concentration of the phosphoric acid solution is 0.1–0.4 mol / L.

[0047] In an optional embodiment, the sintering temperature is 550–700°C and the sintering time is 3–6 hours.

[0048] In an optional embodiment, the product is washed with deionized water until the conductivity of the wash water is ≤500μs / cm, and then dried and sintered.

[0049] In an optional embodiment, the acid solution is a sulfuric acid solution;

[0050] After the addition is complete, solid-liquid separation is performed to obtain the first solid material and the mother liquor at the same time.

[0051] The mother liquor was successively evaporated and concentrated, cooled and crystallized, and then centrifuged and dried to obtain sulfate crystals.

[0052] The present invention has the following beneficial effects:

[0053] The method for preparing ferric phosphate provided by this invention involves synthesizing ferric phosphate by dropwise addition of a mixture of phosphoric acid and an oxidant to an iron ore acid leaching solution. This process allows for the modification of the Fe content during the dropwise addition process by adjusting the ratio of phosphoric acid to the oxidant. 3+The / P ratio allows for simultaneous control of product morphology and iron-phosphorus ratio. Therefore, this process enables the control of the morphology and microstructure of iron phosphate crystals, resulting in iron phosphate with various morphologies. This provides a feasible direction for preparing iron phosphate with different morphologies, meeting the application needs of different fields. The entire synthesis process eliminates the need for the introduction of alkaline solutions, simplifying the iron phosphate synthesis process and reducing production costs. The reaction substrate is an acidic leaching solution with a low pH value (1.5–3.5). The phosphorus-containing mixed solution added during the synthesis process is also acidic. Therefore, the pH value of the entire reaction system remains low, not reaching the precipitation pH of impurity elements, resulting in a low impurity element content in the final product. Attached Figure Description

[0054] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0055] Figure 1 A process flow diagram of the method for preparing ferric phosphate provided by the present invention;

[0056] Figure 2 Here is a SEM image of the iron phosphate prepared in Example 1;

[0057] Figure 3 Here is a SEM image of the iron phosphate prepared in Example 2;

[0058] Figure 4 This is a SEM image of the iron phosphate prepared in Comparative Example 7. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0060] The following is a detailed description of a method for preparing ferric phosphate provided by the present invention.

[0061] An embodiment of the present invention provides a method for preparing ferric phosphate, comprising:

[0062] Obtain an iron ore acid leaching solution with a pH value of 1.5–3.5;

[0063] Using at least a portion of the iron ore acid leaching solution as the bottom liquid of the reactor, a phosphorus-containing mixed solution is added dropwise to the reactor to carry out the synthesis reaction. The dropwise addition time is controlled to be Tmin, T≤420n, where n is the number of moles of iron ions per unit volume in the iron ore acid leaching solution, in mol / L. After the dropwise addition is completed and the reaction is fully completed, solid-liquid separation is carried out to obtain the first solid material containing iron phosphate.

[0064] Ferric phosphate was extracted from the first solid material;

[0065] The phosphorus-containing mixture contains phosphoric acid and a primary oxidizing agent.

[0066] The preparation method provided by this invention synthesizes iron phosphate by adding a mixture of phosphoric acid and an oxidant dropwise to an iron ore acid leaching solution. This process can modify the Fe content during the dropwise addition process by adjusting the ratio of phosphoric acid and the oxidant. 3+ The / P ratio allows for simultaneous control of product morphology and iron-phosphorus ratio. Therefore, this process enables the control of the morphology and microstructure of iron phosphate crystals, resulting in iron phosphate with various morphologies. This provides a feasible direction for preparing iron phosphate with different morphologies, meeting the application needs of different fields. The entire synthesis process eliminates the need for the introduction of alkaline solutions, simplifying the iron phosphate synthesis process and reducing production costs. The reaction substrate is an acidic leaching solution with a low pH value (1.5–3.5). The phosphorus-containing mixed solution added during the synthesis process is also acidic. Therefore, the pH value of the entire reaction system remains low, not reaching the precipitation pH of impurity elements, resulting in a low impurity element content in the final product.

[0067] It should be noted that the pH value of the iron ore leaching solution used in the synthesis reaction should be in the range of 1.5 to 3.5. If the pH value is too low, the ferric ions cannot precipitate or cannot precipitate completely to form amorphous iron phosphate. If the pH value is too high, exceeding the precipitation pH of impurity elements, the resulting product will have a high impurity content. During the dropwise addition, the rate should be controlled within the required range. If the dropwise addition is too fast (too short a time), the local acidity will be too high, causing the newly formed amorphous iron phosphate to be re-dissolved by acid, thus failing to successfully obtain the iron phosphate product.

[0068] Optionally, the pH value of the iron ore leaching solution is in the range of 1.5 to 3.0 (e.g., 1.5, 1.8, 2, 2.5, 2.8 or 3). When the pH is in this range, the particle size of the obtained ferric phosphate is suitable, and the BET value of the calcined product is usually not too high.

[0069] Optionally, in order to oxidize ferrous ions to ferric ions and avoid introducing impurities, hydrogen peroxide can be selected as the first oxidant.

[0070] Optionally, to ensure a full reaction and avoid wasting reaction materials, the iron ore acid leaching solution and the phosphorus-containing mixed solution can generally be fed according to the stoichiometric ratio of the reaction between iron ions and phosphate ions.

[0071] like Figure 1 As shown, the specific preparation method is as follows:

[0072] S1. Obtaining roasted residue

[0073] Iron-containing minerals are crushed and ground to 1-5 mm, then sieved through a 150-mesh sieve. The fine residue is then fed into a kiln for roasting to obtain roasted slag. Crushing and grinding the iron minerals before roasting ensures more efficient and thorough roasting.

[0074] Iron-containing minerals are roasted to alter their structure and properties, making them easier to leach with acid.

[0075] Optionally, the kiln firing temperature is 500–750°C (e.g., 500°C, 600°C, 700°C or 750°C), and the firing time is 3–6 hours (e.g., 3 hours, 4 hours, 5 hours or 6 hours).

[0076] S2, acid leaching

[0077] The roasted residue and acid solution are mixed in a container and stirred evenly to allow them to react fully. Then, solid-liquid separation is performed to obtain the primary acid leaching solution (leaching solution A).

[0078] The iron ions in the obtained primary acid leaching solution are mainly ferrous ions, and the pH value is 0.5-2.

[0079] Optionally, the molar ratio of the total amount of acid-soluble metal elements in the roasted residue to the hydrogen ions in the acid solution is 1:(2-4) (e.g., 1:2, 1:3 or 1:4). When the iron-containing mineral is manganese iron ore, the acid-soluble metal elements are iron and manganese. When the iron-containing mineral is nickel iron ore, the acid-soluble metal elements are iron and nickel. When the iron-containing mineral is cobalt iron ore, the acid-soluble metal elements are iron and cobalt.

[0080] Optionally, the concentration of hydrogen ions in the acid solution is 2 to 5 mol / L (e.g., 2 mol / L, 3 mol / L, 4 mol / L or 5 mol / L).

[0081] Optionally, the acid solution is selected from at least one of sulfuric acid solution, nitric acid solution, and hydrochloric acid solution.

[0082] Optionally, to improve the efficiency of the acid leaching process, the acid leaching temperature is 60–90°C (e.g., 60°C, 70°C, 80°C, or 90°C), and the reaction time is 5–15 h (e.g., 5 h, 10 h, or 15 h).

[0083] Optionally, to improve the efficiency of the leaching process, the acid leaching process may also include the addition of an oxidizing agent.

[0084] Optionally, the ratio of the amount of oxidant added during the acid leaching process to the mass of the calcined residue is (0.1 to 0.3):1 (e.g., 0.1:1, 0.2:1, or 0.3:1).

[0085] Optionally, the oxidant added in this step may be selected from at least one of oxygen, air, ozone, hydrogen peroxide, sodium persulfate, and ammonium persulfate.

[0086] S3, Chromium Removal

[0087] The pH value of the primary acid leaching solution was measured.

[0088] When the measured pH value is 1.5 to 3.5, a flocculant is added to the primary acid leaching solution to precipitate chromium.

[0089] When the pH value is less than 1.5, add a pH adjuster to adjust the pH of the primary acid leaching solution to 1.5-3.5; then add a flocculant to the primary acid leaching solution to precipitate chromium.

[0090] Chromium precipitation yields an iron ore acid leaching solution (liquid B after impurity removal).

[0091] Optionally, the pH adjuster is selected from at least one of nickel carbonate, nickel hydroxide, manganese carbonate, manganese hydroxide, sodium hydroxide, sodium carbonate, and ammonia water.

[0092] Optionally, the flocculant is selected from at least one of ferric phosphate dihydrate, ferric hydroxide, basic ammonium ferric phosphate and silica, and the ratio of the amount of flocculant added to the mass of the primary acid leaching solution is (1-10):1000 (e.g. 1:1000, 2:1000, 5:1000 or 10:1000).

[0093] The concentration of iron ions in the obtained iron ore acid leaching solution is 30-80 g / L (e.g., 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L or 80 g / L). This concentration of iron ore acid leaching solution can effectively control the morphology of the finished product and ensure that the obtained iron phosphate has a better particle size.

[0094] S4, Synthesis

[0095] Using at least a portion of the iron ore acid leaching solution as the bottom liquid of the reactor, a phosphorus-containing mixed solution (phosphorus source C) is added dropwise to the reactor. The dropwise addition time is controlled to be Tmin, where T≤420n, and n is the number of moles of iron ions per unit volume in the iron ore acid leaching solution, in mol / L. After the dropwise addition is completed and the reaction is fully completed, solid-liquid separation is performed to obtain the first solid material (filter cake D) and the mother liquor (mother liquor E).

[0096] There are two specific operational methods for the synthesis process:

[0097] 1. Iron ore acid leaching solution is used as the bottom liquid of the reactor. A phosphorus-containing mixed solution is added dropwise to the reactor. After the addition is complete, the mixture is allowed to react for a period of time to separate the solid and liquid and obtain the first solid material and mother liquor.

[0098] 2. Part of the iron ore acid leaching solution is used as the bottom liquid of the reactor. The remaining iron ore acid leaching solution and phosphorus-containing mixed solution are added to the reactor in parallel flow. After the addition is complete, the mixture is allowed to react for a period of time to separate the solid and liquid components and obtain the first solid material and mother liquor.

[0099] To ensure that the morphology of the generated ferric phosphate is controllable and to better avoid the dissolution of amorphous ferric phosphate generated during the dropwise addition process, the second method mentioned above can generally be chosen to synthesize ferric phosphate.

[0100] Optionally, when the synthesis method is the second method described above, the ratio of the iron ore acid leaching solution as the base liquid to the added iron ore acid leaching solution is a:(1-a), where a is greater than or equal to 0.2 and less than 1;

[0101] Optionally, to make the production process more controllable, a is 0.2 to 0.7 (e.g., 0.2, 0.3, 0.4, 0.5, 0.6 or 0.7).

[0102] Optionally, after the addition is complete, the reaction can be allowed to proceed for 0.1 to 0.3 hours (e.g., 0.1 hours, 0.2 hours, or 0.3 hours) to ensure a complete reaction.

[0103] Optionally, to ensure production efficiency, the phosphorus-containing mixture is added dropwise at a rate of n (mol / L) of molar amount of iron ions per unit volume in the iron ore acid leaching solution, and a total dropping time T = n(160-420) min (e.g., 160n, 200n, 240n, 280n, 320n, 380n, or 420n, where n can be 1, 2, 3, 4, 5, 6, 10, or 20, etc.). This dropping rate ensures the successful formation of amorphous iron phosphate. If the dropping rate is too fast, the local pH may be too low, easily causing the generated amorphous iron phosphate to dissolve and preventing the synthesis of iron phosphate. If the dropping rate is less than the above range, the resulting product will have a smaller particle size and a larger specific surface area, affecting production efficiency and energy consumption.

[0104] Correspondingly, the dropping rate is the amount of phosphorus-containing mixture / t1.

[0105] Optionally, when the synthesis method is the second method mentioned above, the dripping time of the added iron ore acid leaching solution is t2, where t2 = t1.

[0106] Optionally, to ensure better synthesis efficiency, the reaction temperature inside the reactor is 85–95°C (e.g., 85°C, 90°C, or 95°C) during the dropwise addition of the phosphorus-containing mixture.

[0107] Optionally, the phosphorus-containing mixture is a mixture of phosphoric acid and hydrogen peroxide, with a molar ratio of phosphoric acid to hydrogen peroxide of 1:(0.3 to 0.7) (e.g., 1:0.3, 1:0.5, or 1:0.7).

[0108] When the molar ratio of phosphoric acid to hydrogen peroxide is 1:(0.3 to 0.7), the iron-to-phosphorus ratio of the finished product can be between 0.960 and 1.000, and the finished product has a better morphology.

[0109] Optionally, the mass concentration of phosphoric acid in the phosphorus-containing mixture is 15% to 55% (e.g., 15%, 20%, 30%, 40%, 50%, or 55%).

[0110] Optionally, the mixture is obtained by mixing a phosphoric acid solution and a hydrogen peroxide solution, wherein the mass concentration of the phosphoric acid solution is 40-85% (e.g., 40%, 60%, 70% or 85%) and the mass concentration of the hydrogen peroxide solution is 5-30% (e.g., 5%, 10%, 20% or 30%).

[0111] S5, Aging and Impurity Removal

[0112] The first solid material (filter cake D) is mixed with phosphoric acid solution and aged to replace impurities in the first solid material, and then solid-liquid separation is performed to obtain the second solid material.

[0113] Optionally, to ensure high aging efficiency, the aging temperature is 85–95°C (e.g., 85°C, 90°C, or 95°C), and to ensure sufficient reaction, the aging time is 2–5 hours (e.g., 2 hours, 3 hours, 4 hours, or 5 hours).

[0114] Optionally, the concentration of the phosphoric acid solution used in this step is 0.1 to 0.4 mol / L (e.g., 0.1 mol / L, 0.2 mol / L, 0.3 mol / L or 0.4 mol / L), and this solution can be recycled in this aging process.

[0115] S6, Post-processing

[0116] The obtained second solid material is then washed and water is removed to obtain anhydrous ferric phosphate.

[0117] Optionally, the washing process uses deionized water for cleaning until the conductivity of the wash water is ≤500μs / cm;

[0118] Alternatively, water removal methods include drying and sintering.

[0119] Optionally, the sintering conditions are: the sintering atmosphere is one or more of air, argon and nitrogen, the sintering temperature is 550 to 700°C (e.g., 550°C, 600°C, 650°C or 700°C), and the sintering time is 3 to 6 hours (e.g., 3 hours, 4 hours, 5 hours or 6 hours).

[0120] S5, Mother liquor recovery

[0121] When the acid used in acid leaching is a sulfuric acid solution, the main component of the mother liquor obtained after solid-liquid separation following the complete reaction of the addition in the synthesis step is sulfate.

[0122] The mother liquor was successively evaporated and concentrated, cooled and crystallized, and centrifuged and dried to obtain one of the sulfate crystals MSO4·xH2O with an impurity content of less than 0.5%.

[0123] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0124] The physicochemical properties of the products of each embodiment and comparative example were obtained by testing with methods and equipment such as titration, gravimetric method, Malvern particle size analyzer, specific surface area analyzer, and ICP-AES. The physicochemical properties of ferric phosphate prepared in some embodiments and comparative examples are recorded in Tables 1 and 2 below. Table 1 shows the physicochemical properties of ferric phosphate dihydrate, and Table 2 shows the physicochemical properties of ferric phosphate anhydrous.

[0125] Example 1

[0126] A method for preparing ferric phosphate includes the following specific steps:

[0127] (1) 1 kg of nickel-iron alloy mineral (Fe: 65.31%, Ni: 31.79%, Cr: 0.09%) was crushed and ground to 2 mm and then sieved through a 150-mesh sieve. The fine slag was then fed into a box furnace and roasted at 550°C for 3 hours.

[0128] 1.4 kg of sulfuric acid was added to 8.26 kg of pure water to prepare a 1.55 mol / L dilute sulfuric acid solution. 600 g of calcined residue (approximately 10.23 mol of Fe + Ni), 9 L of dilute sulfuric acid solution, and 117 g of 30% hydrogen peroxide were stirred evenly and heated to 75 °C for leaching. The leaching solution A was obtained by filtration, with Fe and Ni concentrations of 43.66 g / L and 22.35 g / L, respectively, and a pH of 0.75.

[0129] (2) Add 100g of nickel carbonate solution with a mass concentration of 30% to 8568g of leachate A, adjust the pH to 2.5, then add 45g of ferric phosphate dihydrate, stir for 2h to remove impurities (Cr) in the leachate to obtain impurity-removed solution B.

[0130] (3) 295g of hydrogen peroxide with a mass concentration of 30% was mixed with 630g of phosphoric acid solution with a mass concentration of 85% to obtain phosphoric acid source C, wherein the molar ratio of phosphoric acid to hydrogen peroxide was 1:0.48.

[0131] (4) 2L of purified liquid B (iron ion concentration of 0.77mol / L) was used as the base liquid. After heating to 90℃, 5L (6120g) of purified liquid B and 925g of phosphorus source C were added to the base liquid in parallel. The dropping rates were 25.50g / min and 3.85g / min, respectively. The total dropping time was 240min. 0.2h after the dropping was completed, the solid and liquid were separated to obtain filter cake D and mother liquor E.

[0132] (5) The filter cake D was put into the aging kettle and aged in 0.2 mol / L phosphoric acid solution for 3 h to replace the impurities in the iron phosphate. After aging, the solid and liquid were separated. The filter cake was washed with deionized water until the conductivity of the wash water was ≤500 μs / cm. After drying and calcining at 650℃ for 5 h, anhydrous iron phosphate powder was obtained.

[0133] (6) The mother liquor E was evaporated, concentrated, cooled and crystallized, and then dried by centrifugation to obtain sulfate crystals NiSO4·6H2O with an impurity content of less than 0.5%.

[0134] The anhydrous ferric phosphate powder obtained had a D50 of 5.88 μm and a BET of 8.5 μm. 2 / g, S content is 154ppm.

[0135] The microscopic morphology of the prepared anhydrous ferric phosphate powder was photographed, such as... Figure 2 As shown, by Figure 2 It can be seen that the synthesized iron phosphate precursor is a loose and porous particle with fine and flaky primary particles and good particle dispersion performance. The synthesized iron phosphate dihydrate has a 33-0666 crystal form, which has a low iron-to-phosphorus ratio, meeting the performance requirements of high-pressure compacted lithium iron phosphate. After sintering, the crystal form is 29-0715, with no impurity peaks and good material processing performance.

[0136] Example 2

[0137] A method for preparing ferric phosphate includes the following specific steps:

[0138] (1) 1 kg of nickel-iron alloy mineral (Fe: 65.31%, Ni: 31.79%, Cr: 0.09%) was crushed and ground to 2 mm and then sieved through a 150-mesh sieve. The fine slag was then fed into a box furnace and roasted at 550°C for 3 hours.

[0139] 1.4 kg of sulfuric acid was added to 8.26 kg of pure water to prepare a 1.55 mol / L dilute sulfuric acid solution. 600 g of calcined residue (approximately 10.23 mol of Fe + Ni), 9 L of dilute sulfuric acid solution, and 117 g of 30% hydrogen peroxide were stirred evenly and heated to 75 °C for leaching. The leaching solution A was obtained by filtration, with Fe and Ni concentrations of 43.91 g / L and 22.15 g / L, respectively, and a pH of 0.84.

[0140] (2) Add 100g of nickel carbonate solution with a mass concentration of 30% to 8567g of leachate A to adjust the pH to 2.53, then add 45g of ferric phosphate dihydrate and stir for 2h to remove impurities (Cr) from the leachate to obtain impurity-removed solution B.

[0141] (3) 295g of hydrogen peroxide with a mass concentration of 30% was mixed with 715g of phosphoric acid solution with a mass concentration of 85% to obtain phosphoric acid source C, wherein the molar ratio of phosphoric acid to hydrogen peroxide was 1:0.42.

[0142] (4) 2L of purified liquid B (iron ion concentration of 0.78mol / L) was used as the base liquid. After heating to 90℃, 5L (6120g) of purified liquid B and 1010g of phosphorus source C were added to the base liquid in parallel. The dropping rates were 25.50g / min and 4.20g / min, respectively. The total dropping time was 240min. 0.2h after the dropping was completed, the solid and liquid were separated to obtain filter cake D and mother liquor E.

[0143] (5) The filter cake D was put into the aging kettle and aged in 0.2 mol / L phosphoric acid solution for 3 h to replace the impurities in the iron phosphate. After aging, the solid and liquid were separated. The filter cake was washed with deionized water until the conductivity of the wash water was ≤500 μs / cm. After drying and calcining at 650℃ for 5 h, anhydrous iron phosphate powder was obtained.

[0144] (6) The mother liquor E was evaporated, concentrated, cooled and crystallized, and then dried by centrifugation to obtain sulfate crystals NiSO4·6H2O with an impurity content of less than 0.5%.

[0145] The anhydrous ferric phosphate powder obtained had a D50 of 10.11 μm and a BET of 6.6 μm. 2 / g, S content is 354ppm.

[0146] The microscopic morphology of the prepared anhydrous ferric phosphate powder was photographed, such as... Figure 3 As shown, by Figure 3 It can be seen that the synthesized iron phosphate precursor has a bulk morphology, and the synthesized iron phosphate dihydrate has a 33-0667 crystal form. This crystal form of iron phosphate has a high iron-to-phosphorus ratio, which meets the performance requirements of high-capacity lithium iron phosphate. After sintering, the crystal form is 29-0715, with no impurity peaks present. Due to the relatively dense particles, the material processing performance is poor.

[0147] Example 3

[0148] A method for preparing ferric phosphate includes the following specific steps:

[0149] (1) 1 kg of ferromanganese alloy mineral (Fe: 55.41%, Mn: 35.22%, Cr: 0.11%) was crushed and ground to 2 mm and then sieved through a 150-mesh sieve. The fine slag was then fed into a box furnace and roasted at 550°C for 3 hours.

[0150] 1.08 kg of sulfuric acid was added to 8.41 kg of pure water to prepare a 1.20 mol / L dilute sulfuric acid solution. 600 g of roasted residue (approximately 9.78 mol of Fe + Mn), 9 L of dilute sulfuric acid solution, and 82 g of 30% hydrogen peroxide were stirred evenly and heated to 75 °C for leaching. The leachate A was obtained by filtration, with Fe and Mn concentrations of 36.81 g / L and 23.51 g / L, respectively, and a pH of 0.99.

[0151] (2) Add 100g of nickel carbonate solution with a mass concentration of 30% to 8567g of leachate A to adjust the pH to 2.75, then add 45g of ferric phosphate dihydrate and stir for 2h to remove impurities (Cr) from the leachate to obtain impurity-removed solution B.

[0152] (3) 276g of hydrogen peroxide with a mass concentration of 30% was mixed with 542g of phosphoric acid solution with a mass concentration of 85% to obtain phosphoric acid source C, wherein the molar ratio of phosphoric acid to hydrogen peroxide was 1:0.52.

[0153] (4) 2L of purified liquid B (iron ion concentration of 0.66mol / L) was used as the base liquid. After heating to 90℃, 5L (6120g) of purified liquid B and 818g of phosphorus source C were added to the base liquid in parallel. The dropping rates were 25.50g / min and 3.41g / min, respectively. The total dropping time was 240min. 0.2h after the dropping was completed, the solid and liquid were separated to obtain filter cake D and mother liquor E.

[0154] (5) The filter cake D was put into the aging kettle and aged in 0.2 mol / L phosphoric acid solution for 3 h to replace the impurities in the iron phosphate. After aging, the solid and liquid were separated. The filter cake was washed with deionized water until the conductivity of the wash water was ≤500 μs / cm. After drying and calcining at 650℃ for 5 h, anhydrous iron phosphate powder was obtained.

[0155] (6) The mother liquor E was evaporated, concentrated, cooled and crystallized, and then dried by centrifugation to obtain sulfate crystals MnSO4·H2O with an impurity content of less than 0.5%.

[0156] The anhydrous ferric phosphate powder had a D50 of 6.24 μm and a BET of 8.1 μm. 2 / g, S content is 158ppm.

[0157] Example 4

[0158] A method for preparing ferric phosphate includes the following specific steps:

[0159] (1) 1 kg of ferromanganese alloy mineral (Fe: 55.41%, Mn: 35.22%, Cr: 0.11%) was crushed and ground to 2 mm and then sieved through a 150-mesh sieve. The fine slag was then fed into a box furnace and roasted at 550°C for 3 hours.

[0160] 1.4 kg of sulfuric acid was added to 8.26 kg of pure water to prepare a 1.55 mol / L dilute sulfuric acid solution. 1000 g of roasted residue (approximately 16.3 mol of Fe + Mn), 9 L of dilute sulfuric acid solution, and 140 g of 30% hydrogen peroxide were stirred evenly and heated to 75 °C for leaching. The leachate A was obtained by filtration, with Fe and Mn concentrations of 61.66 g / L and 39.54 g / L, respectively, and a pH of 0.89.

[0161] (2) Add 150g of nickel carbonate solution with a mass concentration of 30% to 8567g of leachate A to adjust the pH to 2.79, then add 45g of ferric phosphate dihydrate and stir for 2h to remove impurities (Cr) from the leachate to obtain impurity-removed solution B.

[0162] (3) 462g of hydrogen peroxide with a mass concentration of 30% and 907g of phosphoric acid with a mass concentration of 85% were mixed to obtain phosphorus source C, wherein the molar ratio of phosphoric acid and hydrogen peroxide was 1:0.52.

[0163] (4) 2L of purified liquid B (iron ion concentration of 1.10mol / L) was used as the base liquid. After heating to 90℃, 5L (6120g) of purified liquid B and 1370g of phosphorus source C were added to the base liquid in parallel. The dropping rates were 25.50g / L and 5.71g / L, respectively. The total dropping time was 240min. 0.2h after the dropping was completed, the solid and liquid were separated to obtain filter cake D and mother liquor E.

[0164] (5) The filter cake D was put into the aging kettle and aged in 0.2 mol / L phosphoric acid solution for 3 h to replace the impurities in the iron phosphate. After aging, the solid and liquid were separated. The filter cake was washed with deionized water until the conductivity of the wash water was ≤500 μs / cm. After drying and calcining at 650℃ for 5 h, anhydrous iron phosphate powder was obtained.

[0165] (6) The mother liquor E was evaporated, concentrated, cooled and crystallized, and then dried by centrifugation to obtain sulfate crystals MnSO4·H2O with an impurity content of less than 0.5%.

[0166] The anhydrous ferric phosphate powder had a D50 of 6.21 μm and a BET of 7.5 μm. 2 / g, S content is 312ppm.

[0167] Example 5

[0168] A method for preparing ferric phosphate includes the following specific steps:

[0169] (1) 1 kg of ferromanganese alloy mineral (Fe: 55.41%, Mn: 35.22%, Cr: 0.11%) was crushed and ground to 2 mm and then sieved through a 150-mesh sieve. The fine slag was then fed into a box furnace and roasted at 550°C for 3 hours.

[0170] 1.62 kg of sulfuric acid was added to 8.12 kg of pure water to prepare a 1.80 mol / L dilute sulfuric acid solution. 1000 g of roasted residue (approximately 16.3 mol of Fe + Mn), 9 L of dilute sulfuric acid solution, and 140 g of 30% hydrogen peroxide were stirred evenly, heated to 75 °C for leaching, and filtered to obtain leachate A, with Fe and Mn concentrations of 61.94 g / L and 39.24 g / L, respectively, and a pH of 0.75.

[0171] (2) Add 180g of nickel carbonate solution with a mass concentration of 30% to 8567g of leachate A to adjust the pH to 2.75, then add 45g of ferric phosphate dihydrate and stir for 2h to remove impurities (Cr) from the leachate to obtain impurity-removed solution B.

[0172] (3) 462g of hydrogen peroxide with a mass concentration of 30% was mixed with 907g of phosphoric acid solution with a mass concentration of 80% to obtain phosphoric acid source C, wherein the molar ratio of phosphoric acid to hydrogen peroxide was 1:0.52.

[0173] (4) 7L of purified liquid B (iron ion concentration of 1.11mol / L) was used as the base liquid. After heating to 90℃, 1370g of phosphorus source C was added dropwise to the base liquid at a rate of 5.71g / min. The total dropwise addition time was 240min. 0.2h after the dropwise addition was completed, the solid and liquid were separated to obtain filter cake D and mother liquor E.

[0174] (5) The filter cake D was put into the aging kettle and aged in 0.2 mol / L phosphoric acid solution for 3 h to replace the impurities in the iron phosphate. After aging, the solid and liquid were separated. The filter cake was washed with deionized water until the conductivity of the wash water was ≤500 μs / cm. After drying and calcining at 650℃ for 5 h, anhydrous iron phosphate powder was obtained.

[0175] (6) The mother liquor E was evaporated, concentrated, cooled and crystallized, and then dried by centrifugation to obtain sulfate crystals MnSO4·H2O with an impurity content of less than 0.5%.

[0176] The anhydrous ferric phosphate powder had a D50 of 3.98 μm and a BET of 8.4 μm. 2 / g, S content is 201ppm.

[0177] Example 6

[0178] This embodiment is basically the same as Embodiment 1, except that:

[0179] In step (2), adjust the pH to 1.5.

[0180] The anhydrous ferric phosphate powder had a D50 of 5.76 μm and a BET of 7.2 μm. 2 / g, S content is 278ppm.

[0181] Example 7

[0182] This embodiment is basically the same as Embodiment 1, except that:

[0183] In step (2), adjust the pH to 3.0.

[0184] The anhydrous ferric phosphate powder obtained had a D50 of 4.50 μm and a BET of 9.7 μm. 2 / g, S content is 91ppm.

[0185] Example 8

[0186] This embodiment is basically the same as Embodiment 1, except that:

[0187] In step (4), the dropping acceleration rate was changed, and the total dropping time was 123 minutes.

[0188] The anhydrous ferric phosphate powder obtained had a D50 of 7.55 μm and a BET of 6.5 μm. 2 / g, S content is 279ppm.

[0189] Example 9

[0190] This embodiment is basically the same as Embodiment 1, except that:

[0191] In step (4), the dropping acceleration rate was changed, and the total dropping time was 323 minutes.

[0192] The anhydrous ferric phosphate powder had a D50 of 4.74 μm and a BET of 10.1 μm. 2 / g, S content is 121ppm.

[0193] Example 10

[0194] This embodiment is basically the same as Embodiment 1, except that:

[0195] In step (5), the concentration of phosphoric acid solution in the aging reactor is 0.1 mol / L.

[0196] The anhydrous ferric phosphate powder obtained had a D50 of 5.99 μm and a BET of 6.7 μm. 2 / g, S content is 249ppm.

[0197] Example 11

[0198] This embodiment is basically the same as Embodiment 1, except that:

[0199] In step (5), the concentration of phosphoric acid solution in the aging reactor is 0.4 mol / L.

[0200] The anhydrous ferric phosphate powder had a D50 of 4.54 μm and a BET of 8.97 μm. 2 / g, S content is 94ppm.

[0201] Example 12

[0202] This embodiment is basically the same as Embodiment 1, except that:

[0203] The acid solution used in step (1) is sulfuric acid with a molar concentration of 0.5 mol / L, and the Fe and Ni in the leaching solution A are 19.12 g / L and 9.31 g / L, respectively.

[0204] As can be seen from the data in Tables 1 and 2, compared with Example 1, this embodiment uses a lower concentration of sulfuric acid, resulting in a lower acid dissolution efficiency, which leads to a lower concentration of iron ions in leachate A and a larger particle size of the synthesized product.

[0205] Example 13

[0206] This embodiment is basically the same as Embodiment 1, except that:

[0207] In step (1), the leaching temperature is 50℃, and the Fe and Ni in the leaching solution A are 31.11 g / L and 15.78 g / L, respectively.

[0208] In this embodiment, the acid leaching temperature is too low, resulting in a slightly lower acid dissolution efficiency and a slightly lower concentration of the solution after impurity removal.

[0209] Example 14

[0210] This embodiment is basically the same as Embodiment 1, except that:

[0211] No hydrogen peroxide was added in step (1), and the Fe and Ni in the leachate A were 38.15 g / L and 18.87 g / L, respectively.

[0212] In this embodiment, since hydrogen peroxide was not added, the acid dissolution efficiency was slightly lower, resulting in a slightly lower concentration of the solution after impurity removal, which in turn resulted in a slightly lower production capacity.

[0213] Example 15

[0214] This embodiment is basically the same as Embodiment 1, except that:

[0215] In step (2), ferric phosphate dihydrate was not added as a flocculant to remove chromium.

[0216] As can be seen from the data in Tables 1 and 2, compared with Example 1, this embodiment contains more Cr impurities in the product because no flocculant was added.

[0217] Example 16

[0218] This embodiment is basically the same as Embodiment 1, except that:

[0219] In step (5), the molar concentration of P in the aging solution is 0 mol / L.

[0220] As can be seen from the data in Tables 1 and 2, compared with Example 1, this embodiment has no aging effect because the aging solution does not contain P, resulting in a higher S content and a lower BET content in the product.

[0221] Example 17

[0222] This embodiment is basically the same as Embodiment 1, except that:

[0223] In step (4), the molar concentration of P in the aging solution is 1.0 mol / L.

[0224] As can be seen from the data in Tables 1 and 2, compared with Example 1, the higher concentration of P in the aging solution in this example results in a higher BET of the product after aging, making filtration difficult and affecting the continuity of product production.

[0225] Example 18

[0226] This embodiment is basically the same as Embodiment 1, except that:

[0227] In step (2), nickel carbonate is added to adjust the pH to 3.5.

[0228] As can be seen from the data in Tables 1 and 2, compared with Example 1, the BET of the synthesized product is larger after sintering because the pH of nickel carbonate is adjusted to be higher and the particle size is lower in this example.

[0229] Example 19

[0230] This embodiment is basically the same as Embodiment 1, except that:

[0231] In step (4), the acceleration rate of liquid B after impurity removal is 17 g / min, the acceleration rate of phosphorus source C is 2.57 g / min, and the total dropping time is 360 min.

[0232] As can be seen from the data in Tables 1 and 2, compared with Example 1, in this example, due to the slow dropping acceleration rate, the product after crystallization is used as a seed crystal, resulting in a smaller particle size and a larger BET.

[0233] Comparative Example 1

[0234] This comparative example is basically the same as Example 1, except that:

[0235] Nickel carbonate was not added in step (2) to adjust the pH.

[0236] As can be seen from the data in Tables 1 and 2, compared with Example 1, the pH value of the solution after impurity removal was too low in this comparative example because nickel carbonate was not added to adjust the pH. The pH value could not be reached during the dropwise addition process, and iron phosphate could not be synthesized.

[0237] Comparative Example 2

[0238] This comparative example is basically the same as Example 1, except that:

[0239] In step (2), nickel carbonate is added to adjust the pH to 1.4.

[0240] As can be seen from the data in Tables 1 and 2, compared with Example 1, in this comparative example, because the pH adjustment of nickel carbonate did not reach 1.5, approximately 4.55 g / L of Fe was generated during the precipitation process. 3+ The sedimentation process was incomplete, affecting production capacity.

[0241] Comparative Example 3

[0242] This comparative example is basically the same as Example 1, except that:

[0243] In step (4), the dropping acceleration rates of the purified solution B and phosphorus source C were 102 g / min and 15.4 g / min, respectively, and the total dropping time was 60 min. Back dissolution occurred, so step (5) was not performed.

[0244] As can be seen from the data in Tables 1 and 2, compared with Example 1, in this comparative example, due to the excessively rapid addition rate, the pH of the slurry decreased rapidly, the amorphous ferric phosphate crystallization time was too long, and the amorphous ferric phosphate was re-acidified, thus failing to synthesize successfully.

[0245] Comparative Example 4

[0246] This comparative example is basically the same as Example 1, except that:

[0247] In step (4), the dropping acceleration rates of the purified solution B and phosphorus source C are 102 g / min and 15.4 g / min, respectively. The excessively rapid dropping acceleration causes the amorphous iron phosphate to be unstable and unable to crystallize. Continue to age this solution for 5 hours.

[0248] Step (5) is no longer transferred to a phosphoric acid solution for aging.

[0249] In this comparative example, due to the excessively rapid addition rate, the pH of the slurry decreased quickly, and the synthesis of iron phosphate failed. The solution was further aged at high temperature for 5 hours to synthesize iron phosphate dihydrate. This iron phosphate was obtained through spontaneous precipitation driven by high temperature, and the particle size was too large and the impurities were too high, which did not meet the requirements for use as a lithium iron phosphate cathode material. Figure 4 The large spherical iron phosphate particles obtained by spontaneous precipitation in this comparative example are relatively large and dense, which affects the processing performance.

[0250] Table 1 shows the physicochemical properties of ferric phosphate dihydrate obtained from some of the examples and comparative examples.

[0251] Fe P Fe / P D50 BET Ni Mn S Cr Cu ％ ％ / μm <![CDATA[m 2 / g]]> ppm ppm ppm ppm ppm Example 1 28.89 16.50 0.971 6.08 37.6 41 5 2155 9 0 Example 2 29.35 16.41 0.992 10.04 39.8 154 4 845 11 0 Example 3 28.91 16.61 0.965 5.99 39.1 1 35 2245 9 1 Example 4 28.99 16.65 0.965 6.54 37.1 5 58 2147 15 0 Example 5 29.01 16.59 0.970 4.20 39.8 4 61 1988 13 0 Example 12 29.11 16.62 0.971 10.11 32.5 21 2 1214 5 0 Example 13 29.00 16.55 0.972 8.14 35.4 35 4 1541 4 0 Example 14 29.11 16.71 0.966 7.11 36.4 51 4 1847 9 0 Example 15 28.85 16.59 0.964 5.99 38.4 42 4 2041 29 0 Example 16 29.11 16.71 0.966 6.41 29.3 48 1 2699 10 0 Example 17 28.97 16.64 0.965 5.69 42.9 45 4 1415 8 0 Example 18 28.99 16.65 0.965 4.35 42.1 35 4 1854 8 1 Example 19 28.95 16.55 0.970 4.11 40.1 38 0 1869 11 0 Comparative Example 2 29.12 16.60 0.973 5.47 38.4 49 1 2355 18 0 Comparative Example 4 29.25 16.34 0.993 36.61 28.1 221 0 1891 12 1

[0252] Table 2 shows the physicochemical properties of anhydrous ferric phosphate obtained from some of the examples and comparative examples.

[0253]

[0254]

[0255] As can be seen from Table 2, the anhydrous ferric sulfate prepared in each embodiment of the present invention has a low content of impurity elements.

[0256] In summary, the method for preparing iron phosphate provided by this invention has the following characteristics:

[0257] 1. Morphology tunability: Compared with existing processes, under the conditions of low energy consumption and environmental protection, the morphology and microstructure of iron phosphate crystals can be controlled, and iron phosphate with various morphologies can be obtained. This provides a feasible direction for the preparation of iron phosphate with different morphologies and meets the application needs of different fields.

[0258] 2. No alkaline solution is introduced: No alkaline solution is introduced during the synthesis of ferric phosphate, which simplifies the synthesis process and reduces production costs;

[0259] 3. The acid leaching solution separation process in the early stage of the process does not require pH adjustment; and the synthesis is also carried out at a low pH, which does not reach the precipitation pH of impurity elements, so the content of impurity elements introduced into the product is low.

[0260] 4. During the production process, the ratio of hydrogen peroxide to phosphoric acid in the phosphorus source can be controlled to alter the Fe content during the dropping process. 3+ The / P ratio allows for simultaneous control of product morphology and iron-phosphorus ratio.

[0261] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing ferric phosphate, characterized in that, include: An iron ore acid leaching solution is obtained, wherein the pH value of the iron ore acid leaching solution is 1.5~2.5 and the iron ion concentration is 30~80 g / L. The method for obtaining the iron ore acid leaching solution includes: Iron-containing minerals are roasted to obtain roasting residue; The roasted residue is mixed with acid and a second oxidant, and after the reaction is complete, solid-liquid separation is performed to obtain a primary acid leaching solution. The iron ore acid leaching solution is obtained by removing chromium from the primary acid leaching solution. The method for removing chromium from the primary acid leaching solution includes: The pH value of the primary acid leaching solution is detected. When the pH value is 1.5 to 2.5, a flocculant is added to the primary acid leaching solution to precipitate chromium. When the pH value is less than 1.5, a pH adjuster is added to the primary acid leaching solution to adjust the pH of the primary acid leaching solution to 1.5~2.5; then a flocculant is added to the primary acid leaching solution to precipitate chromium. The flocculant is selected from at least one of ferric phosphate dihydrate, ferric hydroxide, basic ferric ammonium phosphate and silicon dioxide, and the ratio of the amount of flocculant added to the mass of the primary acid leaching solution is (1~10):1000. The second oxidant is selected from at least one of oxygen, air, ozone, hydrogen peroxide, sodium persulfate, and ammonium persulfate; The ratio of the amount of the second oxidant added to the mass of the calcined residue is (0.1~0.3):1; The iron-bearing mineral is selected from at least one of manganese iron ore, nickel iron ore, and cobalt iron ore. The molar ratio of the total amount of acid-soluble metal elements in the roasted residue to the hydrogen ions in the acid solution is 1:(2~4). When the iron-bearing mineral is manganese iron ore, the acid-soluble metal elements are iron and manganese. When the iron-bearing mineral is nickel iron ore, the acid-soluble metal elements are iron and nickel. When the iron-bearing mineral is cobalt iron ore, the acid-soluble metal elements are iron and cobalt. The concentration of hydrogen ions in the acid solution is 2~5 mol / L; Using at least a portion of the iron ore acid leaching solution as the bottom liquid in a reactor, a phosphorus-containing mixture is added dropwise to the reactor to carry out a synthesis reaction. The synthesis reaction process is as follows: a portion of the iron ore acid leaching solution is used as the bottom liquid in the reactor, and the remaining portion of the iron ore acid leaching solution is added dropwise to the reactor along with the phosphorus-containing mixture in a parallel flow. The ratio of the iron ore acid leaching solution used as the bottom liquid to the added iron ore acid leaching solution is a:(1-a), where a is greater than or equal to 0.2 and less than 1. The phosphorus-containing mixture contains phosphoric acid and a first oxidant, wherein the first oxidant is hydrogen peroxide, the molar ratio of phosphoric acid to hydrogen peroxide in the phosphorus-containing mixture is 1:(0.3~0.7), and the mass concentration of phosphoric acid in the phosphorus-containing mixture is 15~55%. The dripping time is controlled to be Tmin, where T = (160~420)n, and T and n are dimensionless numbers. n represents the number of moles of iron ions per unit volume in the iron ore acid leaching solution, in mol / L. After the dripping is completed and the reaction is complete, solid-liquid separation is performed to obtain the first solid material containing iron phosphate. The first solid material is mixed with a phosphoric acid solution to replace impurities in the first solid material, and then solid-liquid separation is performed to obtain a second solid material. The second solid material is washed to remove impurities; After washing and removing impurities, the mixture is dried and sintered to obtain anhydrous ferric phosphate. The concentration of the phosphoric acid solution is 0.1~0.4 mol / L.

2. The method for preparing ferric phosphate according to claim 1, characterized in that, a is 0.2~0.

7.

3. The method for preparing ferric phosphate according to claim 1 or 2, characterized in that, The roasting temperature of the iron-containing mineral is 500~750℃.

4. The method for preparing ferric phosphate according to claim 1 or 2, characterized in that, The acid solution is selected from at least one of sulfuric acid solution, nitric acid solution and hydrochloric acid solution.

5. The method for preparing ferric phosphate according to claim 1 or 2, characterized in that, The roasted residue is mixed with the acid solution and then subjected to an acid leaching reaction at a temperature of 60-90°C for 5-15 hours.

6. The method for preparing ferric phosphate according to claim 1, characterized in that, The pH adjuster is selected from at least one of nickel carbonate, nickel hydroxide, manganese carbonate, manganese hydroxide, sodium hydroxide, sodium carbonate, and ammonia water.

7. The method for preparing ferric phosphate according to claim 1, characterized in that, The acid solution is a sulfuric acid solution; After the addition is complete, solid-liquid separation is performed to obtain the first solid material and the mother liquor at the same time. The mother liquor was successively evaporated and concentrated, cooled and crystallized, and centrifuged and dried to obtain sulfate crystals.

8. The method for preparing ferric phosphate according to claim 1, characterized in that, During the process of adding the phosphorus-containing mixture, the reaction temperature inside the reactor is controlled to be 85~95℃.

9. The method for preparing ferric phosphate according to claim 1, characterized in that, The reaction time after the addition is complete is 0.1~0.3h.

10. The method for preparing ferric phosphate according to claim 1, characterized in that, The sintering temperature is 550~700℃, and the sintering time is 3~6h.

11. The method for preparing ferric phosphate according to claim 1, wherein deionized water is used for washing until the conductivity of the wash water is ≤500μs / cm, followed by drying and sintering.

Images