Short-process purification preparation method of high-purity iron phosphate

Abstract

The invention relates to the field of hydrometallurgy, in particular to a short-process purification preparation method of high-purity iron phosphate, which comprises the following steps: (1) performing solid-phase extraction on ferrous sulfate feed liquid containing impurity metal elements by using a solid-phase extraction agent A, and selectively adsorbing and removing the impurity metal elements in the solution to obtain a purified ferrous sulfate solution; (2) mixing the purified ferrous sulfate solution obtained in the step (1) with a phosphate solution, and carrying out oxidation precipitation reaction to generate an iron phosphate precursor; and (3) the iron phosphate precursor obtained in the step (2) is filtered, washed, dried and roasted, an iron phosphate product is obtained, and the solid-phase extraction agent A comprises resin of a formula (I) and / or resin of a formula (II). The final product is low in impurity content and high in tap density, the industrial problem that multiple impurities are difficult to synchronously and deeply remove under the acidic and high-iron background is solved, and the requirements of the high-end lithium ion battery positive electrode material precursor are completely met. (I) and (II).

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrometallurgy and battery materials, and particularly relates to a short-process purification preparation method of high-purity iron phosphate. BACKGROUND

[0002] With the explosive growth of demand for lithium iron phosphate positive electrode materials in the new energy battery industry, developing low-cost and high-purity iron phosphate precursors has become a key link in the industry. At present, the industry generally seeks cheap iron sources such as titanium dioxide by-product ferrous sulfate (green vitriol) and nickel-iron alloy leaching solution to reduce costs. However, these iron sources have complex compositions and often contain multiple metal impurities such as nickel (Ni), cobalt (Co), chromium (Cr), copper (Cu), manganese (Mn), aluminum (Al), titanium (Ti), magnesium (Mg), zinc (Zn), and calcium (Ca). Traditional chemical precipitation methods cannot achieve selective deep impurity removal and cannot meet the stringent requirements of battery-grade iron phosphate on impurity content (usually requiring each metal element to be less than 10-50 ppm), and there are problems such as long process, high iron loss rate, and easy introduction of new impurities.

[0003] In addition, some chelating resins known in the art for impurity removal have low adsorption capacity, poor selectivity, and high iron loss rate when applied to acidic (pH≤3.5) ferrous sulfate systems, and cannot achieve the simultaneous deep purification of multiple impurities (such as Ni, Mn, Ca, Mg, and Al) targeted by the present technical solution. Therefore, developing a purification technology that can work efficiently in an acidic and high-iron concentration environment is a long-standing technical problem in the field. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art and provide a ferrous sulfate solution purification and high-purity iron phosphate preparation method with good purification effect, short process, and high product quality.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: A short-process purification preparation method of high-purity iron phosphate, comprising the following steps: (1) using a solid-phase extractant A to perform solid-phase extraction on a ferrous sulfate solution containing impurity metal elements, selectively adsorbing and removing the impurity metal elements in the solution to obtain a purified ferrous sulfate solution; (2) mixing the purified ferrous sulfate solution obtained in step (1) with a phosphate solution to perform an oxidation precipitation reaction, generating an iron phosphate precursor; (3) filtering, washing, drying, and calcining the iron phosphate precursor obtained in step (2) to obtain an iron phosphate product; The impurity metal elements include one or a combination of at least two of Ni, Co, Mn, Al, Cu, Ca, Mg, Ti, Cr, Zn and Cd. The solid-phase extraction agent A comprises a resin of formula (I) and / or a resin of formula (II): (I) (II) Wherein: M is a base resin; R1 is -CH2P(O)(R a )2; R2 is hydrogen, -CH2P(O)(R b )2, -CH2P(O)(OH)(Ph), -CH2P(O)(Ph)2, -(CH2) q COR c , wherein R c is OH, ONa, OK, C1-C5 alkoxy, amino (NH2) or C1-C5 alkyl-substituted amino; R a , R3 and R4 are each independently selected from OH, ONa or OK; R b is selected from OH, ONa, OK or C1-C9 alkoxy; t is 0 or 1; q is 0, 1 or 2; Ph is a phenyl group.

[0006] The present application realizes efficient and deep collaborative purification of various impurity metal elements in a complex iron source by combining a specific solid-phase extraction agent with an optimized process. The concentration of each key impurity metal ion in the purified solution can be reduced to below 50 mg / L, thereby stably preparing high-quality battery-grade anhydrous iron phosphate. The process is short and efficient, and can control product quality from the source. DETAILED DESCRIPTION

[0007] In the following, aspects of the present application will be embodied more fully and further objects, features and advantages will be more fully apparent.

[0008] The present application adopts the following technical solutions: A short-process purification preparation method of high-purity iron phosphate, comprising the following steps: (1) using a solid-phase extraction agent A to perform solid-phase extraction on a ferrous sulfate solution containing impurity metal elements, selectively adsorbing and removing the impurity metal elements in the solution to obtain a purified ferrous sulfate solution; (2) mixing the purified ferrous sulfate solution obtained in step (1) with a phosphate solution to perform an oxidation precipitation reaction to generate an iron phosphate precursor; (3) filtering, washing, drying and calcining the iron phosphate precursor obtained in step (2) to obtain an iron phosphate product; The impurity metal elements include one or a combination of at least two of Ni, Co, Mn, Al, Cu, Ca, Mg, Ti, Cr, Zn and Cd. The solid phase extraction agent A comprises a resin of formula (I) and / or a resin of formula (II): (I) (II) Wherein: M is a base resin; R1 is -CH2P(O)(R a )2; R2 is hydrogen, -CH2P(O)(R b )2, -CH2P(O)(OH)(Ph), -CH2P(O)(Ph)2, -(CH2) q COR c , wherein R c is OH, ONa, OK, C1-C5 alkoxy, amino (NH2) or C1-C5 alkyl-substituted amino; R a , R3 and R4 are each independently selected from OH, ONa or OK; R b is selected from OH, ONa, OK or C1-C9 alkoxy; t is 0 or 1; q is 0, 1 or 2; Ph is a phenyl group.

[0009] The resin base M is not particularly limited, and is preferably selected from polystyrene resin, styrene and divinylbenzene copolymer, phenolic resin, polyacrylic acid resin and silicon-based resin. More preferably, the resin base M is selected from polystyrene resin and styrene and divinylbenzene copolymer.

[0010] Preferably, R2 is selected from hydrogen and the following groups: 、 、 、 、 、 、 、 、 、 、 、 and wherein is the group and the N connection site.

[0011] Preferably, the resin of formula (I) or (II) has a structure selected from the group consisting of: , , , , , , , , , , , , , , , , or , wherein M is selected from the group consisting of polystyrene resin, a copolymer of styrene and divinylbenzene.

[0012] More preferably, the resin of formula (I) has a structure selected from the group consisting of: , , , , or , wherein M is selected from the group consisting of polystyrene resin, a copolymer of styrene and divinylbenzene.

[0013] Preferably, in step (1), the pH value of the ferrous sulfate solution is controlled to be 1.0-3.5, more preferably, 1.5-3.

[0014] Preferably, in step (2), the temperature of the precipitation reaction is controlled to be 20-60℃, and the pH value is controlled to be 1.8-3.0, more preferably, the pH value is controlled to be 1.8-2.5.

[0015] Preferably, the time of the precipitation reaction is 1-8 hours, more preferably, 2-6 hours.

[0016] Preferably, the phosphate salt in step (2) is selected from one or more of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate, more preferably, the phosphate salt is ammonium dihydrogen phosphate.

[0017] Further, the oxidant used in step (2) is hydrogen peroxide.

[0018] Further, the amount of the oxidant added is 1.0-2.0 times, preferably, 1.1-1.5 times, of the amount required for oxidizing ferrous ions to ferric ions.

[0019] Further, in step (2), the molar ratio of total iron to total phosphorus (Fe / P) in the purified ferrous sulfate solution and the phosphate solution is controlled at 1:1-1.6, preferably 1:1-1.3.

[0020] Further, the concentration of iron ions in the ferrous sulfate solution is 50-110 g / L.

[0021] When the pH value of the ferrous sulfate solution is controlled to be greater than 2.5, especially higher than 3.0, in order to avoid the divalent iron ions being oxidized to trivalent iron and producing precipitate, affecting the purification effect and the service life of the resin, it is preferred to take anti-oxidation measures. The anti-oxidation measures include but are not limited to: introducing inert gas (such as nitrogen, argon) into the system for protection; and / or, adding a small amount of strong reducing antioxidant (such as ascorbic acid). Preferably, the amount of the antioxidant is less than 5% based on the molar amount of iron.

[0022] When the concentration of nickel in the ferrous sulfate solution is >500 mg / L, before step (1), the solid phase extractant B is used to pre-extract the solution to preferentially remove nickel and / or copper. If copper is contained, optionally, iron powder is used to precipitate and remove copper from the ferrous sulfate solution.

[0023] Preferably, the solid phase extractant B is selected from the following chelating resins: or wherein M is independently selected from polystyrene resins, copolymers of styrene and divinylbenzene, phenol-formaldehyde resin polymers, polyacrylic resins and silicon-based resins.

[0024] Optionally, before mixing the phosphate solution with the purified ferrous sulfate solution, the phosphate solution is subjected to purification treatment, including: using the aluminum-loaded extractant C as a defluorination agent, controlling the equilibrium pH value to be 3.5-5 for defluorination; and then performing deep purification through the solid phase extractant A, controlling the equilibrium pH value of deep purification to be 1.0-3.5, more preferably 1.5-3.0.

[0025] Preferably, the extractant C includes a resin containing an aminophosphonic acid group, P507, P204 or C272.

[0026] Further, the purified ferrous sulfate solution and the phosphate are fully mixed in a reaction kettle or a mixing tank, and are continuously mixed in a pipe mixer before entering the reaction kettle or the mixing tank.

[0027] ​​​​​​​Further, the filtered iron phosphate is washed by multiple-stage countercurrent washing with pure water until the conductivity of the filtrate is ≤200 μS / cm.

[0028] Further, the drying method can be flash drying, spray drying or vacuum drying, and the drying temperature is controlled to be 80-280℃.

[0029] Further, the calcination temperature is controlled to be 350-700℃.

[0030] Further, the ammonium bisulfate mother liquor obtained by filtering in step (2) is neutralized into an ammonium sulfate solution by using a neutralizing agent, and then treated by an MVR evaporation crystallization system to produce ammonium sulfate crystals as a byproduct.

[0031] Preferably, the neutralizing agent can be ammonia water, a sodium hydroxide solution or a potassium hydroxide solution.

[0032] Preferably, the solid-phase extraction agent A is subjected to saponification transformation by using an alkaline solution before extraction.

[0033] Preferably, the alkaline solution is a 0.25-1.25 mol / L sodium hydroxide solution or a potassium hydroxide solution.

[0034] The resins of formula (I) and formula (II) can be prepared by referring to known methods in the art or can be commercially available.

[0035] Further, the solid-phase extraction agent A loaded with impurity metals is subjected to back extraction and regeneration by using a 0.5-6 mol / L sulfuric acid or hydrochloric acid solution.

[0036] Preferably, the resin is a macroporous resin.

[0037] As used herein, the pore size of the macroporous resin is in the range of 10-1000 nm, preferably 20-100 nm.

[0038] By combining the specific solid-phase extraction agent with the optimized process, the present application realizes efficient and deep synergistic purification of various impurity metal elements in a complex iron source. By using the method of the present application, the concentration of each key impurity metal ion in the purified solution can be reduced to below 50 mg / L, so that high-purity iron phosphate can be stably prepared, in which the content of each key impurity (by mass fraction) is less than 50 ppm, Mg is less than 50 ppm, and Ni, Mn, Ca, Cu and Al are all less than 10 ppm. The product also has excellent physical properties, with a tap density of more than 0.8 g / cm³ and uniform particle size distribution, reaching the specification standards of battery-grade materials.

[0039] In this application, the "comprising" and "including" cover the cases where other elements not expressly mentioned are also contained or comprised as well as the cases where only the mentioned elements are contained or comprised.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. If there is a conflict between the definitions of terms in the specification and the meanings that are typically used by those in the art, the former takes precedence.

[0041] Unless otherwise indicated, all numbers expressing quantities of ingredients, temperatures, times, etc. in the specification and claims are to be understood as approximations based on the desired properties sought to be obtained by the employ of the terms "about" and "at or about.” Therefore, unless otherwise indicated, the numerical parameters set forth in the specification and claims are approximations that can vary from the numerical values stated in the specification and claims depending upon the desired properties sought to be obtained by the employ of the terms "about” and “at or about.” At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0042] Embodiments The concept, specific structure and technical effects of the present application will be further described below in conjunction with embodiments, so that those skilled in the art can fully understand the purpose, features and effects of the present application. It is easy for those skilled in the art to understand that the embodiments herein are only for illustrative purposes, and the scope of the present application is not limited thereto.

[0043] The impurity content in the solid product described below is equivalent to μg / g (micrograms / gram) in ppm.

[0044] Example 1 (1) Raw materials and pretreatment Ferrous sulfate solution: nickel-iron alloy sulfuric acid leaching solution, pH value is 1.5, and its main components are shown in Table 1.

[0045] Solid phase extraction agent: solid phase extraction agent A (the resin is composed of , wherein M is polystyrene resin microspheres) and solid phase extraction agent B (the resin is composed of , wherein M is polystyrene resin microspheres).

[0046] Pretreatment: 0.25 mol / L sodium hydroxide solution is used to wash and saponify the solid phase extraction agents A and B until the supernatant pH>10, and then washed with deionized water to neutral (pH ≈ 7.0) for standby.

[0047] Table 1 Initial components of ferrous sulfate solution (mg / L) (2) Purification step The ferrous sulfate feed solution was passed through a fixed bed extraction column (20.0±0.5℃) filled with solid phase extractant B at a flow rate of 3.0 BV / h, and 5 columns were connected in series. The ratio of the ferrous sulfate feed solution to the pretreated solid phase extractant B was 4 mL:1 g, and a ferrous sulfate solution after removal of copper and nickel was obtained.

[0048] The ferrous sulfate solution after removal of copper and nickel was passed through a fixed bed extraction column (20.0±0.5℃) filled with solid phase extractant A at a flow rate of 3.0 BV / h, and 5 columns were connected in series. The ratio of the ferrous sulfate solution after removal of copper and nickel to the pretreated solid phase extractant A was 4 mL:1 g, and other impurities such as Mg, Mn, Ca, Al, etc. were removed in depth.

[0049] An industrial-grade ammonium dihydrogen phosphate solution (P 3500 mg / L, Al 3200 mg / L, F 580 mg / L) was prepared. An aluminum-loaded P507 organic phase was added to the solution as a defluorination agent, and stirring extraction was performed under the condition that the equilibrium pH value was controlled to be 5.0. The extraction was performed in a 3-stage countercurrent manner, and the volume ratio of the organic phase to the aqueous phase was 6:1, so as to effectively remove fluorine ions. The organic phase was prepared by diluting 25% P507, a sulfonated kerosene diluent, to a saponification degree of 50% by saponification with 30% sodium hydroxide solution, and saturating loading with an aluminum sulfate solution. After defluorination, the solution was adjusted to a pH value of 1.8 with a 2 mol / L sulfuric acid solution, and then passed through an extraction column filled with an extractant A (a resin composed of The high-purity ammonium dihydrogen phosphate solution was obtained.

[0050] (3) Synthesis and post-treatment of iron phosphate The purified ferrous sulfate solution was mixed with the ammonium dihydrogen phosphate solution at a molar ratio of Fe:P of 1:1.05, and the amount of hydrogen peroxide added was 1.3 times the theoretical amount required to completely oxidize ferrous ions to trivalent iron ions. The reaction temperature was controlled to be 30℃, ammonia water with a mass fraction of 10% was used to adjust and maintain the pH value of the system to be 2.0, and the reaction was performed for 4 hours. After the reaction, the filter cake was washed with pure water in multiple countercurrent stages until the conductivity of the filtrate was ≤200 μS / cm. Subsequently, the filter cake was dried at 200℃ and then calcined at 350℃ for 2 hours to obtain the iron phosphate product.

[0051] The precipitation mother liquor was neutralized with ammonia water, and then subjected to MVR evaporation crystallization, and the by-product ammonium sulfate crystals were obtained.

[0052] (4) Effect analysis The purified ferrous sulfate solution obtained in step (2) was analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES), wherein the contents of Ni, Mg, Mn, Ca, and Al were 3.2 mg / L, 20.8 mg / L, 0.3 mg / L, 1.9 mg / L, and 0.2 mg / L, respectively, and other impurity elements were less than 5 mg / L. In the purified ammonium dihydrogen phosphate solution, F was 2.5 mg / L, and Al was 2.1 mg / L.

[0053] The ferrous phosphate product obtained in step (3) was subjected to chemical composition analysis (ICP-OES) and physical property testing, wherein the contents of Ni, Mg, Mn, Ca, and Al in the ferrous phosphate product were 2.5 ppm, 16.5 ppm, 0.2 ppm, 1.5 ppm, and 0.15 ppm, respectively, and other impurity elements were less than 5 ppm. The product had a Fe / P molar ratio of 0.992, a tap density of 0.85 g / cm³, and a D50 of 3.2 μm.

[0054] Example 2 (1) Raw materials and pretreatment The ferrous sulfate feed solution was prepared using by-product green vitriol from titanium white, and had a pH of about 2.5. The composition is shown in Table 2.

[0055] Solid-phase extraction agent: solid-phase extraction agent A (with a structure of wherein M is a polystyrene resin) was used, and its preparation method is as follows: 10 g of polystyrene resin microspheres (30 mmol, -NH2) were taken in a three-necked flask, 50 mL of dichloroethane was added for swelling, 12.3 g of phosphorus trichloride (90 mmol) was added, and 13.6 g of aluminum trichloride (90 mmol) was slowly added in batches, and stirring was performed at 40°C for 8 hours. After the reaction was completed, the temperature was cooled to room temperature, and the resin was washed and filtered with methanol and ultrapure water several times. The washed resin was added to a three-necked flask, 35% nitric acid was added, and heating was performed to 60°C. After 8 hours of reaction, the temperature was cooled to room temperature, and the resin was washed with water several times. Finally, the resin was dried under vacuum at 40°C until the weight was constant, to obtain the solid-phase extraction agent A.

[0056] Pretreatment: 0.25 mol / L sodium hydroxide solution was used to wash and saponify the solid-phase extraction agents A and B until the supernatant pH was greater than 10, and then deionized water was used to wash to neutral (pH ≈ 7.0) for standby.

[0057] Table 2 Initial composition of ferrous sulfate feed solution (mg / L) (2) Purification step The ferrous sulfate feed solution was passed through a fixed bed extraction column (20.0±0.5℃) filled with solid phase extractant A at a flow rate of 2.0 BV / h, and 4 columns were connected in series. The ferrous sulfate feed solution was mixed with the pretreated solid phase extractant A at a ratio of 4 mL:1 g, to obtain a purified ferrous sulfate solution.

[0058] An industrial-grade ammonium dihydrogen phosphate solution (P 3500 mg / L, Al 3200 mg / L, F 580 mg / L) was prepared. The impurity removal process was the same as in Example 1, except that the aluminum-loaded P204 organic phase was used as the defluorination agent in the defluorination step, and the stirring extraction was performed under the condition of controlling the equilibrium pH value to be 3.8.

[0059] (3) Synthesis and post-treatment of iron phosphate The purified ferrous sulfate solution was mixed with the ammonium dihydrogen phosphate solution at a molar ratio of Fe:P of 1:1.15, and the amount of hydrogen peroxide added was 1.5 times the theoretical amount required to completely oxidize the ferrous ions to trivalent iron ions. The reaction temperature was controlled at 50℃, and the pH value of the system was adjusted and maintained at 2.2 using ammonia water with a mass fraction of 10%. The reaction was carried out for 3 hours. After the reaction was completed, the filter cake was washed with pure water in multiple stages of countercurrent washing until the conductivity of the filtrate was ≤200 μS / cm. Subsequently, the filter cake was dried at 240℃, and then calcined at 550℃ for 2 hours to obtain the iron phosphate product.

[0060] The precipitation mother liquor was neutralized with ammonia water, and the by-product ammonium sulfate crystals were obtained by MVR evaporation crystallization.

[0061] (4) Effect analysis The contents of Ni, Mg, Mn, Ca, and Al in the purified ferrous sulfate solution were 0.3 mg / L, 15.8 mg / L, 1.9 mg / L, 0.3 mg / L, and 0.5 mg / L, respectively, and the contents of other impurity elements were all less than 5 mg / L. The contents of F and Al in the purified ammonium dihydrogen phosphate solution were 3.2 mg / L and 2.7 mg / L, respectively.

[0062] The contents of Ni, Mg, Mn, Ca, and Al in the obtained iron phosphate product were 0.2 ppm, 12.1 ppm, 1.5 ppm, 0.2 ppm, and 0.4 ppm, respectively, and the contents of other impurity elements were all less than 5 ppm. The molar ratio of Fe to P in the product was 0.997, the tap density was 0.92 g / cm³, and the D50 was 2.9 μm.

[0063] Example 3 The solid phase extractant A was prepared as follows: wherein M is a polystyrene resin. Into a 100 ml flask, 10 g (30 mmol, -NH2) of primary amino polystyrene microspheres were taken, 3 mL (30 mmol) of formaldehyde solution and 2.45 g (30 mmol) of phosphorous acid were added, 70 mL of water was added, and the reaction was carried out at 100°C for 24 hours under mechanical stirring. The obtained intermediate solid phase extraction agent A was obtained.

[0064] Then, 4.3 g (35 mmol) of 2-chloro-N,N-dimethylacetamide and 3.7 g (35 mmol) of sodium carbonate were added to the intermediate solid phase extraction agent A, 50 mL of water was added, and the reaction was carried out at 80°C for 12 hours under mechanical stirring. The solid phase extraction agent A was obtained by reaction.

[0065] Step 1 of Reference Example 1, except that the ferrous sulfate solution containing impurity metal elements was adjusted to pH 3.5 by using 10% ammonia water under nitrogen protection and stirring, and nitrogen protection was maintained during the entire solid phase extraction process.

[0066] After purification, the contents of Ni, Mg, Mn, Ca, and Al in the ferrous sulfate solution were 3.7 mg / L, 23.7 mg / L, 0.4 mg / L, 2.2 mg / L, and 0.2 mg / L, respectively, and other impurity elements were less than 5 mg / L. In the purified ammonium dihydrogen phosphate solution, F was 2.5 mg / L, and Al was 2.1 mg / L.

[0067] The contents of Ni, Mg, Mn, Ca, and Al in the obtained iron phosphate product were 2.9 ppm, 19.0 ppm, 0.3 ppm, 1.7 ppm, and 0.15 ppm, respectively. The product had a Fe / P molar ratio of 0.99, a tap density of 0.83 g / cm3, and a D50 of 3.5 μm.

[0068] Example 4 Step 1 of Reference Example 1, except that the ferrous sulfate solution containing impurity metal elements was adjusted to pH 3.5 by using 10% ammonia water under nitrogen protection and stirring, and nitrogen protection was maintained during the entire solid phase extraction process.

[0069] After purification, the contents of Ni, Mg, Mn, Ca, and Al in the ferrous sulfate solution were 0.1 mg / L, 1.6 mg / L, 0.1 mg / L, 0.8 mg / L, and 0.2 mg / L, respectively, and other impurity elements were less than 5 mg / L. In the purified ammonium dihydrogen phosphate solution, F was 2.5 mg / L, and Al was 2.1 mg / L.

[0070] ​The corresponding impurity contents in the product were 0.08 ppm, 1.3 ppm, 0.08 ppm, 0.6 ppm and 0.12 ppm, respectively. The product had a Fe / P molar ratio of 0.989, a tap density of 0.87 g / cm3 and a D50 of 3.2 μm.

[0071] Example 5 The step was the same as in Example 2, except that the solid-phase extraction agent A (consisting of a resin having a structural formula of , wherein M is polystyrene resin microspheres) was used to purify the ferrous sulfate solution.

[0072] After purification, the contents of Ni, Mg, Mn, Ca and Al in the ferrous sulfate solution were 0.6 mg / L, 39.2 mg / L, 2.1 mg / L, 0.6 mg / L and 0.5 mg / L, respectively, and the contents of other impurity elements were less than 5 mg / L. In the purified ammonium dihydrogen phosphate solution, the content of F was 3.2 mg / L and the content of Al was 2.7 mg / L.

[0073] The contents of Ni, Mg, Mn, Ca and Al in the obtained iron phosphate product were 0.5 ppm, 31.4 ppm, 1.7 ppm, 0.5 ppm and 0.4 ppm, respectively, and the contents of other impurity elements were less than 5 ppm. The product had a Fe / P molar ratio of 0.987, a tap density of 0.81 g / cm3 and a D50 of 3.7 μm.

[0074] Comparative Example 1 The step was the same as in Example 2, except that the solid-phase extraction agent A (consisting of a resin having a structural formula of , wherein M is polystyrene resin microspheres) was used to purify the ferrous sulfate solution.

[0075] After purification, the contents of Ni, Mg, Mn, Ca and Al in the ferrous sulfate solution were 1.9 mg / L, 858 mg / L, 163 mg / L, 26.2 mg / L and 39.1 mg / L, respectively, and the contents of other impurity elements were less than 5 mg / L. In the purified ammonium dihydrogen phosphate solution, the content of F was 3.2 mg / L and the content of Al was 2.7 mg / L.

[0076] The corresponding impurity contents in the product were 1.5 ppm, 686 ppm, 130 ppm, 21.0 ppm and 31.3 ppm, respectively. The product had a Fe / P molar ratio of 0.97, a tap density of 0.67 g / cm3 and a wide particle size distribution. In particular, the contents of magnesium (Mg) and manganese (Mn) impurities were far beyond the standard for battery-grade materials, proving that the product obtained in the comparative example was unqualified and could not meet the requirements of high-end lithium ion battery cathode material precursors.

[0077] Comparative Example 2 Step Reference Example 1, except that the ferrous sulfate solution is purified by using solid phase extraction agent A (a resin composed of polystyrene resin microspheres with the structure of , wherein M is polystyrene resin microspheres), and the remaining steps are the same as Example 1.

[0078] The contents of Ni, Mg, Mn, Ca and Al in the purified ferrous sulfate solution are 5.9 mg / L, 526.9 mg / L, 41.5 mg / L, 262.7 mg / L and 0.8 mg / L, respectively, and the contents of other impurity elements are between 20 mg / L and 50 mg / L. The contents of F and Al in the purified ammonium dihydrogen phosphate solution are 2.5 mg / L and 2.1 mg / L, respectively.

[0079] The contents of Ni, Mg, Mn, Ca and Al in the obtained iron phosphate product are 4.7 ppm, 421 ppm, 33.2 ppm, 210 ppm and 0.67 ppm, respectively, which are much higher than those in the product of the present application. The molar ratio of Fe / P in the product is 0.97, the tap density is only 0.72 g / cm3, and the particle size distribution is wide. Especially, the contents of Mg and Ca impurities are much higher than the standard of battery-grade material, which proves that the product of the comparative example is unqualified and cannot meet the requirements of high-end lithium ion battery cathode material precursor.

[0080] The above only describes the exemplary embodiments or examples of the present application and is not intended to limit the present application. The present application can be variously changed and modified by those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application is included in the scope of the claims of the present application.

Claims

1. A short process purification method for preparing high purity iron phosphate, characterized in that, The method comprises the following steps: (1) using solid phase extraction agent A to extract the ferrous sulfate solution containing impurity metal elements, selectively adsorbing and removing the impurity metal elements in the solution, and obtaining the purified ferrous sulfate solution; (2) mixing the purified ferrous sulfate solution obtained in step (1) with a phosphate solution, and performing an oxidation precipitation reaction to generate an iron phosphate precursor; (3) filtering, washing, drying and calcining the iron phosphate precursor obtained in step (2) to obtain an iron phosphate product; The impurity metal elements include one or a combination of at least two of Ni, Co, Mn, Al, Cu, Ca, Mg, Ti, Cr, Zn and Cd; The solid phase extraction agent A comprises a resin of formula (I) and / or a resin of formula (II): (I) (II) wherein: M is a base resin; R1is -CH2P(O)(R a )2; R2is hydrogen, -CH2P(O)(R b )2, -CH2P(O)(OH)(Ph), -CH2P(O)(Ph)2, -(CH2) q COR c , wherein R c is OH, ONa, OK, C1-C5alkoxy, amino (NH2), or C1-C5alkyl substituted amino; R a , R3and R4are each independently selected from OH, ONa, or OK; R b selected from OH, ONa, OK or C1-C9 alkoxy; t is 0 or 1; q is 0, 1 or 2; Ph is a phenyl group.

2. The method of claim 1, wherein, In step (1), the pH value of the ferrous sulfate solution is controlled to be 1.0-3.5; And / or, in step (2), the temperature of the precipitation reaction is controlled to be 20-60℃, and the pH value is controlled to be 1.8-3.

0.

3. The method of claim 2, wherein, The time of the precipitation reaction is 1-8 hours.

4. The method of claim 1, wherein, M is selected from polystyrene resin, styrene and divinylbenzene copolymer, phenolic resin, polyacrylic acid resin and silicon-based resin, preferably, M is selected from polystyrene resin and styrene and divinylbenzene copolymer.

5. The method of claim 1, wherein, The phosphate is selected from one or more of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate and sodium dihydrogen phosphate.

6. The method of claim 1, wherein, The oxidizing agent used in the oxidation of step (2) is hydrogen peroxide; And / or, the amount of the oxidizing agent added is 1.0-2.0 times the theoretical amount required to completely oxidize ferrous ions to ferric ions.

7. The method of claim 1, wherein, In step (2), the molar ratio of total iron to total phosphorus in the purified ferrous sulfate solution and the phosphate solution is controlled to be 1:1-1.

6.

8. The method of claim 2, wherein, When the nickel concentration in the ferrous sulfate solution is > 500 mg / L, before step (1), the solution is pre-extracted using solid phase extraction agent B to preferentially remove nickel and / or copper, Preferably, the solid phase extraction agent B is selected from a chelating resin comprising: , , , , or , wherein M is independently selected from polystyrene resin, styrene and divinylbenzene copolymer, phenolic resin polymer, polyacrylic acid resin and silicon-based resin.

9. The method of claim 1, wherein, Before mixing the phosphate solution with the purified ferrous sulfate solution, the phosphate solution is subjected to a purification treatment, which comprises: using aluminum-loaded extraction agent C as a defluorination agent, controlling the equilibrium pH value to be 3.5-5 to remove fluorine; and then performing deep purification by the solid phase extraction agent A, The extraction agent C comprises a resin containing an aminophosphoric acid group, P507, P204 or C272.

10. The method of claim 1, wherein, The drying temperature is controlled to be 80-280℃, and the calcination temperature is controlled to be 350-700℃.

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