WO2023193749A1 - 一种磷酸铁络合物解络合制磷酸铁二水合物的方法 - Google Patents

一种磷酸铁络合物解络合制磷酸铁二水合物的方法 Download PDF

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WO2023193749A1
WO2023193749A1 PCT/CN2023/086517 CN2023086517W WO2023193749A1 WO 2023193749 A1 WO2023193749 A1 WO 2023193749A1 CN 2023086517 W CN2023086517 W CN 2023086517W WO 2023193749 A1 WO2023193749 A1 WO 2023193749A1
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iron phosphate
iron
phosphorus
pressure
phosphoric acid
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PCT/CN2023/086517
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French (fr)
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马晓玲
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黄冈林立新能源科技有限公司
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/37—Phosphates of heavy metals
    • C01B25/375—Phosphates of heavy metals of iron
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/37—Phosphates of heavy metals
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the invention belongs to the technical field of inorganic new materials and relates to a preparation method of iron phosphate used as cathode material for lithium ion batteries.
  • lithium iron phosphate As a cathode material for lithium-ion batteries, lithium iron phosphate has high specific capacity, good safety, long cycle life, and good thermal stability. At the same time, it has wide sources of raw materials and is cheap. It is a cathode material that can coexist with ternary materials for a long time.
  • most industrial production of lithium iron phosphate uses the precursor synthesis method, that is, iron phosphate (FePO 4 ) is first prepared, and then the iron phosphate is used as an iron source and a phosphorus source, mixed with a lithium source and a carbon source, and sintered at high temperature under an inert atmosphere. Lithium iron phosphate with a carbon layer coating on the surface is obtained.
  • Iron phosphate is the precursor for preparing lithium iron phosphate. The quality of the iron phosphate precursor has a great impact on the performance of lithium iron phosphate products.
  • the synthesis methods of iron phosphate mainly fall into the following categories: (1) Synthesis methods using iron salts and phosphates as iron sources and phosphorus sources respectively.
  • the iron source and the phosphorus source introduce impurity anions and impurity cations respectively, which results in the need to use a large amount of deionized water to clean the precipitation after obtaining the iron phosphate precipitation.
  • the wastewater generated by the washing precipitation needs to be treated later to avoid polluting the environment.
  • iron phosphate synthesized by this type of method is high, and companies using this type of preparation method are difficult to survive in the current environment where the price of lithium iron phosphate has dropped significantly;
  • elemental iron powder and phosphoric acid as iron source and phosphorus source respectively
  • the synthesis method is to produce ferrous phosphate and then oxidize it to prepare iron phosphate, such as CN111377426A or CN201510209131.5.
  • the iron source and phosphorus source do not introduce impurity ions, and the washing of the precipitation and later wastewater treatment are relatively simple.
  • Patent application CN112225190A reduces the phosphoric acid content by adding urea to destroy the iron phosphate-phosphoric acid complex to increase the yield of iron phosphate, but impurities will be introduced and by-products (ammonium phosphate) will be produced, resulting in waste water and waste gas.
  • Patent CN103663401B uses low concentration phosphoric acid and a large excess of phosphoric acid (the concentration is 10% phosphoric acid, and the ratio of phosphoric acid to iron substances is greater than 10:1 or even 20:1) to react with iron oxide or iron hydroxide, resulting in low reaction efficiency The problem is that industrial production is economically poor.
  • Patent CN101821197B uses 8-23% concentration of phosphoric acid (approximately 21% concentration of phosphoric acid in Example 1) to react with iron oxide or iron hydroxide to obtain iron phosphate.
  • Paragraph 14 of the patent specification mentions that using high concentration of phosphoric acid will make The iron orthophosphate remains in solution and cannot crystallize in an acceptable time, quality and/or form.
  • this reaction also has the disadvantage of low reaction efficiency due to the use of medium and low concentrations of phosphoric acid.
  • a more serious flaw is that during the reaction, "part of the raw materials and products always exist side by side in the form of solid materials during the reaction. As a result, it is impossible to separate the impurities either as solutions or as solid materials. Therefore, in order to make To achieve a high level of chemical purity of the product, the quality and purity of the raw materials must be relied upon and determined” (see the description in paragraph 10 of the patent CN102333725B, which is directed to the method in the German patent family of CN101821197B). This shows that the applicant of the patent, Chemical Manufacturing Budenheim KG, has no confidence in the industrial application of the patented method, especially large-scale production.
  • Patent application CN106829906A discloses a method for decomplexing iron phosphate.
  • the iron phosphate complex solution is placed in an autoclave, the pressure is controlled at 0.1-0.5Mpa, and the temperature is controlled at 100-180°C to obtain corresponding iron phosphate crystals.
  • the patent application examples do not provide the specific amounts required by those skilled in the art to repeat the experimental operations. The inventor repeated the experiment and did not obtain ideal experimental results (see the comparative examples of this application).
  • the industry still needs a method that can achieve higher yield, lower energy consumption and cost, and higher production efficiency, especially a method that reduces the hindrance of decomplexation of iron phosphate complex.
  • the invention provides a method for decomplexing iron phosphate complex to prepare iron phosphate dihydrate.
  • the industrial method is simple, has low energy consumption, is environmentally friendly and efficient.
  • the present invention discloses a method for preparing iron phosphate, especially a method for preparing high-purity iron phosphate. Preparation.
  • the invention discloses a method for decomplexing an iron phosphate complex solution to prepare iron phosphate dihydrate.
  • the method is: adding 0.3-30 times the volume of the complex solution to the iron phosphate complex solution, preferably 0.3-8 times of water, react for 1min-20h, preferably 10min-6h, solid-liquid separation to obtain solid ferric phosphate dihydrate or ferric phosphate dihydrate.
  • reaction time can be as short as 1 minute, or even a few seconds, or the reaction time can be extended, even beyond 20 hours, to obtain a product with a better crystal form.
  • the method is carried out between room temperature and 180°C, preferably between 60°C and 160°C.
  • the inventor found that increasing the temperature is helpful for the decomplexation reaction, and theoretically this method can be realized at a reaction temperature below the boiling point of the complex solution. However, if the temperature is too high, it will lead to high energy consumption and operation safety risks.
  • the phosphorus-iron ratio in the iron phosphate complex solution is (2.5-10):1, for example (2.5-8):1, adding a small amount of water will cause a decomplexation reaction to occur.
  • the method is carried out under normal pressure or under pressure. Pressurization helps to accelerate the decomplexation reaction.
  • the pressure range of the pressure is between 0.1Mpa and 1Mpa (absolute pressure). Preferably, it is between 0.1Mpa and 0.5Mpa.
  • the pressurization described in the present invention includes only 1 Pa higher than the atmospheric pressure, that is, slight pressurization.
  • adding water to the complex solution can decompose the complex, resulting in the precipitation of ferric phosphate dihydrate, which will occur even at room temperature.
  • adding a large amount of water will result in a large amount of subsequent wastewater (phosphoric acid-containing wastewater), which will also greatly increase the material processing volume, resulting in a reduction in production efficiency. Therefore, the preferred amount of water added is between 0.3 and 8 times that of the complex solution.
  • the water is commonly used in industry and is selected according to the purity requirements of the final product. To avoid bringing in impurities, it is preferred to use purified water or deionized water.
  • the present invention found that after adding water to the complex solution, the precipitation speed of ferric phosphate dihydrate can be accelerated by heating, pressurizing, etc. There is a linkage between the amount of water added, heating temperature and pressure. In the case of heating and/or pressure treatment, reducing the amount of water added can also achieve the decomplexation effect while reducing energy consumption (simple heating and/or pressure).
  • the amount of water added does not need to ensure that all ferric phosphate dihydrate precipitates, because although the mother liquor after solid-liquid separation to obtain ferric phosphate dihydrate still contains ferric phosphate complex, it can be returned to the previous process step and recycled as raw material. On the contrary It can reduce energy consumption and produce no waste water.
  • the insulation reaction of the present invention can be between 1 minute and 20 hours, which also shows that the precipitation speed of ferric phosphate dihydrate can be fast or slow. If the reaction time is short, it means that the precipitation rate is fast, and amorphous ferric phosphate dihydrate will be precipitated; if the reaction time is long, by controlling the temperature and adding water to reduce the precipitation rate, crystalline ferric phosphate dihydrate can be obtained.
  • the precipitate of ferric phosphate dihydrate is white, possibly tinged with pink.
  • the iron phosphate complex solution can be obtained by methods commonly used in the art, such as by reacting Fe with phosphoric acid, or by reacting ferrous iron with phosphoric acid and then oxidizing it, such as ferrous oxide, ferrous hydroxide, or ferric hydroxide. It is obtained by the reaction of ferric iron and phosphoric acid, such as ferric oxide, ferric hydroxide, etc., or obtained by the reaction of ferric tetroxide and phosphoric acid (the conversion of ferric ions into ferric ions requires an oxidation step), or by containing The salt or double salt of iron is converted into a stock solution of iron phosphate.
  • the invention also discloses a method for decomplexing iron phosphate complex to prepare iron phosphate dihydrate, which method includes:
  • Step S1 can be completed by controlling the molar ratio of iron oxide and phosphoric acid in the raw material reaction. For example, increasing the number of moles of iron oxide reduces the phosphorus-to-iron ratio, or in the iron phosphate complex solution, adding phosphoric acid increases the phosphorus-to-iron ratio.
  • the content of Fe ions is preferably between 0.2-2mol/L, the heating temperature is preferably between 60°C and 160°C, and the reaction time is preferably 10min-6h; as needed, iron phosphate dihydrate is obtained through solid-liquid separation. Solid product; it is preferred that step S2 is carried out under pressure, and the pressure is controlled between 0.1-1 MPa (absolute pressure), preferably between 0.1-0.5 MPa (absolute pressure).
  • the above method may also include:
  • step S3 If necessary, return the second mother liquor obtained by solid-liquid separation to step S1 for controlling the phosphorus-iron ratio.
  • the invention further discloses a preparation method of iron phosphate, which includes:
  • S0 Use phosphoric acid with a concentration of 35-85% to react with iron oxide.
  • the reaction temperature is between room temperature and 180°C.
  • the ratio of phosphoric acid to iron oxide is set according to the phosphorus-iron ratio of (2-10):1. Filter and remove after the reaction. For insoluble matter, collect the first mother liquor;
  • the S0 step is preferably carried out between 60°C and 140°C, and the phosphoric acid concentration is between 50-85%;
  • the S2 step is preferably carried out between 60°C and 160°C; optionally, the S2 step can be carried out under pressure, and the pressure is controlled at 0.1-1Mpa (absolute pressure), preferably 0.1-0.5MPa (absolute pressure).
  • the method may also include:
  • S3 The second mother liquor obtained by solid-liquid separation is returned to the S0 step and mixed with concentrated phosphoric acid to adjust the phosphoric acid concentration, or returned to the S1 step to adjust the phosphorus-iron ratio.
  • S4 roast iron phosphate dihydrate to obtain iron phosphate.
  • Iron phosphate complex An iron phosphate-phosphate complex formed by iron phosphate and phosphoric acid, which exists in the form of a solution.
  • Iron phosphate dihydrate It can also be called iron phosphate dihydrate or iron phosphate dihydrate. It is iron phosphate containing two crystal waters. When iron phosphate precipitates from the solution, it often contains two crystal waters.
  • the phosphorus-iron ratio refers to the molar ratio (amount ratio of substances) of phosphorus element to iron element in the iron phosphate complex solution.
  • Phosphorus refers to all phosphorus elements in the solution, including total phosphorus in the iron phosphate complex and excess phosphoric acid in the solution
  • iron refers to all iron elements in the solution.
  • the phosphorus-iron ratio is 3:1, while the phosphorus-iron ratio of 6 mol phosphoric acid and 1 mol ferric oxide is 2:1.
  • Room temperature It refers to the indoor temperature. In the present invention, the room temperature is between 15-25°C and does not require heating.
  • Gauge pressure refers to the amount by which the total absolute pressure exceeds the surrounding atmospheric pressure or the pressure at a certain point in a liquid that is higher than the atmospheric pressure.
  • gauge pressure refers to the pressure value higher than atmospheric pressure.
  • the atmospheric pressure value should be added.
  • the pressure is absolute pressure.
  • Fe ion ferric ion, also written as Fe 3+ .
  • the method of the present invention has low energy consumption, simple operation and safety.
  • Figure 1 is the X-ray diffraction XRD pattern of ferric phosphate dihydrate prepared in Example 8.
  • Figure 2 is a scanning electron microscope image of anhydrous ferric phosphate prepared in Example 8.
  • iron phosphate complex solutions with different phosphorus-to-iron ratios are prepared through the reaction of iron oxide and phosphoric acid. By adjusting the input amount of raw materials and the molar ratio of raw materials, iron phosphate complex solutions with different phosphorus-to-iron ratios can be obtained. Finally, the following complex solutions with different phosphorus-to-iron ratios were obtained.
  • CX1 A complex solution with a phosphorus-iron ratio of 3.75:1, and a Fe concentration of 2mol/L;
  • CX2 A complex solution with a phosphorus-to-iron ratio of 4.5:1 and a Fe concentration of 2mol/L;
  • CX3 A complex solution with a phosphorus-iron ratio of 6:1 and a Fe concentration of 2mol/L;
  • CX4 A complex solution with a phosphorus-to-iron ratio of 8:1 and a Fe concentration of 1.788mol/L.
  • CX2 solution Take 310ml of phosphoric acid solution with a mass fraction of 85% in a 1L flask, and add 190ml of deionized water to it to form a phosphoric acid solution with a concentration of 9mol/L.
  • Accurately weigh 79.84g of iron oxide powder (0.5 mol) add it to the phosphoric acid solution, heat the entire system to 90°C, and stir at 90°C for 3 hours. After the reaction is completed, the system is filtered to obtain a purple-red iron phosphate complex solution.
  • the phosphorus-to-iron ratio is 4.5:1, and the iron concentration is 2 mol/L.
  • test results show that 1. Adding water at room temperature will also cause the precipitation of iron phosphate dihydrate, that is, the decomplexation phenomenon of the iron phosphate complex, regardless of whether it is heated or not. 2. After adding water, heating can help destroy the complex and reduce the amount of water added. 3. An iron phosphate complex solution with a low phosphorus-to-iron ratio requires less water.
  • Example 1 The test results of Example 1 show that after adding water, the complex will be effectively destroyed, resulting in the rapid formation of iron phosphate dihydrate precipitation.
  • the complex is decomposed at room temperature, a larger amount of water needs to be added to precipitate iron phosphate dihydrate. The amount of water added can be reduced by raising the temperature. By adding a large amount of water, the complex will be quickly decomposed, causing iron phosphate dihydrate to rapidly precipitate. At this time, the iron phosphate dihydrate obtained is often amorphous or crystals with extremely small particle sizes.
  • the reaction yield calculation method is: taking the volume of deionized water added and the volume of the complex solution as 1:1 as an example, the volume of the iron phosphate complex solution is 50 ml, the volume of deionized water added is 50 ml, and the iron phosphate complex solution is added.
  • the mixed solution formed by the complex and deionized water is heated to 90°C, and the holding time is 6 hours.
  • the obtained ferric phosphate dihydrate is weighed. The mass is 14.8358g.
  • the amount of iron ions in 50 ml of the ferric phosphate complex solution is 0.1 mol
  • Example 2 Refer to the operation of Example 2, except that the raw material solution CX2 (phosphorus-iron ratio is 4.5:1) is used.
  • Example 2 Refer to the operation of Example 2, except that the raw material solution CX3 (phosphorus-iron ratio is 6:1) is used.
  • Example 2 Referring to the operation of Example 2, different phosphorus-iron ratios, reaction temperatures, and water addition ratios were used to test the reaction yields at different temperatures and water addition amounts.
  • Table 6 shows that increasing the decomplexation temperature will help the decomplexation reaction to occur, and the reaction yields of EX61 and EX63 are significantly higher than those of EX62 and EX64 with lower reaction temperatures, even though EX64 has a lower phosphorus-to-iron ratio than EX63.
  • EX69 shows that when the water added reaches 7 volume multiples, resulting in a Fe 3+ concentration as low as 0.217 mol/L, a yield of more than 93% can still be obtained.
  • Comparative test DB1 When the ratio of phosphorus to iron is 5.23:1, 50ml of the complex solution is added to the pressure bottle without adding water, and the temperature is raised to 110 degrees. As the temperature increases, the reading of the pressure gauge gradually increases. About 20 minutes after the temperature was raised to 110 degrees, the pressure stabilized at 0.1Mpa. At this temperature and pressure, after 6 hours of reaction, the system did not precipitate. The yield is 0%.
  • Comparative test DB2 When the ratio of phosphorus to iron is 6:1, add 50ml of the complex solution into the pressure-resistant bottle, without adding water, and raise the temperature to 110 degrees. As the temperature increases, the reading of the pressure gauge gradually increases. , the temperature was raised to 110 degrees. At this time, the pressure gauge read 0.04Mpa. As time increased, the pressure stabilized at 0.08Mpa. At this temperature and pressure, after 6 hours of reaction, the system did not precipitate. The yield is 0%.
  • step 1 Take 50 ml of the purple iron phosphate complex solution obtained in step 1 (phosphorus to iron ratio is 4.5:1), add 2 volumes of deionized water to the complex solution, and then complex the deionized water with the iron phosphate
  • the mixed system formed by the material solution was heated to 90°C. After reacting for 6 hours, the precipitate was filtered and washed to obtain the product ferric phosphate dihydrate.
  • the product mass was 17.01g and the yield was 90.9%.
  • SEM scanning electron microscopy

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Abstract

本发明公开了一种磷酸铁络合物解络合制磷酸铁二水合物的方法，该方法在磷酸铁络合物溶液中，加入基于络合物溶液体积0.3-30倍，优选0.3-8倍的水，反应1min-20h，优选10min-6h，固液分离，得到固体磷酸铁二水合物。本发明提供的该方法能简单、高效且环境友好地制备得到用于锂电池正极材料的高纯度磷酸铁。

Description

一种磷酸铁络合物解络合制磷酸铁二水合物的方法
本申请要求2022年4月8日向中国国家知识产权局提交的专利申请号为202210366746.9，发明名称为“一种磷酸铁络合物解络合制磷酸铁二水合物的方法”的在先申请的优先权。该在先申请的全文通过引用的方式结合于本申请中。
技术领域
本发明属于无机新材料技术领域，涉及锂离子电池正极材料用磷酸铁的制备方法。
背景技术
作为锂离子电池正极材料，磷酸铁锂比容量高、安全性好、循环寿命长、热稳定性好，同时原材料来源广泛、价格便宜，是一种与三元材料长期共存的正极材料。目前工业上生产磷酸铁锂大多数使用前驱体合成法，即先制备磷酸铁(FePO4)，然后以磷酸铁作为铁源和磷源，与锂源和碳源混合，在惰性气氛下高温烧结得到表面有碳层包覆的磷酸铁锂。磷酸铁是制备磷酸铁锂的前驱体，磷酸铁前驱体的好坏对磷酸铁锂产品的性能有很大的影响。
目前磷酸铁的合成方法主要为以下几类：(1)以铁盐和磷酸盐分别作为铁源和磷源的合成方法。这类合成方法中铁源和磷源分别引入了杂质阴离子和杂质阳离子，导致得到磷酸铁沉淀后需要使用大量去离子水对沉淀进行清洗，洗涤沉淀产生的废水需要后期进行处理以免污染环境。因此这类方法合成出来的磷酸铁成本高，使用这类制备方法的企业在目前磷酸铁锂价格大幅下降的环境下难以生存；(2)以单质铁粉和磷酸分别作为铁源和磷源的合成方法，生产磷酸亚铁，再氧化制备得到磷酸铁，如CN111377426A或CN201510209131.5，这类合成方法中铁源和磷源不引入杂质离子，沉淀的洗涤和后期的废水处理比较简单。但是，铁粉与磷酸反应的同时放出大量的热和易燃易爆的氢气，且因为增加了氧化步骤，工艺复杂，难以控制，在工业生产上，使用这类方法大量合成磷酸铁时安全成本较高。(3)利用氧化铁与磷酸反应得到磷酸铁，可以克服前面2个工艺存在的明显的缺陷，现有技术中有大量相关专利申请。但现有技术记录的第3个路线工艺，往往需 要大量过量磷酸以保证氧化铁与磷酸反应进行，在磷酸过量的情况下，磷酸铁会与磷酸形成络合物从而稳定存在于溶液中而难以析出(可参见专利CN101821197B中第0007段提及可溶性铁络合物的存在，认为该方法不经济，不实用)。专利申请CN112225190A通过加入尿素减少磷酸含量，从而破坏磷酸铁-磷酸络合物，以提高磷酸铁的收率，但会引入杂质且会产生副产物(磷酸氨)，产生废水和废气。专利CN103663401B使用低浓度的磷酸且磷酸大大过量(浓度为10％的磷酸，且磷酸与铁物质的量比大于10:1甚至20:1)与氧化铁或氢氧化铁反应，存在反应效率较低的问题，工业生产经济性差。专利CN101821197B使用8-23％浓度的磷酸(实施例1约为21％浓度的磷酸)与氧化铁或氢氧化铁反应，得到磷酸铁，该专利说明书第14段提及使用高浓度的磷酸将使正磷酸铁留在溶液中，无法以可接受的时间、品质和/或形态结晶。同样，该反应也存在因使用中、低浓度磷酸导致反应效率低的缺陷。更严重的缺陷是反应过程中，“部分原材料和产物在反应过程中总是以固体材料形式并行存在。结果是，杂质无论作为溶液或者作为固体材料进行分离都是不可能的。因此，为了使产物达到高水平化学纯度，必须依赖并确定原材料的质量和纯度”(参见专利CN102333725B第10段描述，该描述针对的是CN101821197B的德国同族专利中的方法)。这表明该专利申请人化学制造布敦海姆两合公司对该专利方法的工业化应用，尤其是大规模生产完全没有信心。
事实上业内的确存在这种需求，一种将磷酸铁磷酸络合物(磷酸铁-磷酸络合物)进行解络合，以更高效且低成本的制备磷酸铁的方法。
专利申请CN106829906A公开了一种磷酸铁解络合方法，该方法将磷酸铁络合溶液放置在高压釜中，控制压力0.1-0.5Mpa，控制温度在100-180℃，得到相应的磷酸铁结晶。但该专利申请实施例并未给出本领域技术人员重复实验操作所需的具体量，本发明人重复该实验并未得到理想的实验结果(参见本申请对比实施例)。即使认为该专利申请公开的方法可行，从工业角度看，该反应使用高压釜，在0.1-0.5Mpa压力(实施例1-4为0.15-0.25Mpa)下进行，解络合温度超过100℃(实施例在120-140℃)，该工艺也存在操作条件苛刻，能耗较高的问题。
业内仍然需要一种能获得更高产率，较低能耗和成本，生产效率更高的方法，尤其是减少磷酸铁络合物解络合阻碍的方法。
发明内容
本发明提供一种磷酸铁络合物解络合制磷酸铁二水合物的方法，该工业方法简单，能耗低，环保且高效。进一步，本发明公开一种制备磷酸铁的方法，尤其是高纯度磷酸铁的 制备方法。
本发明公开了一种磷酸铁络合物溶液解络合制磷酸铁二水合物的方法，该方法为：在磷酸铁络合物溶液中，加入基于络合物溶液体积0.3-30倍，优选0.3-8倍的水，反应1min-20h，优选10min-6h，固液分离，得到固体磷酸铁二水合物或称二水磷酸铁。
事实上，水加到一定量时，会立即出现浑浊，因此，反应时间可以短至1min，甚至几秒，也可以延长反应时间，甚至超出20h以得到更好晶型的产品。
所述方法在室温～180℃，优选60℃～160℃之间进行。发明人发现，温度提高有助于解络合反应，理论上反应温度在络合物溶液的沸点之下都可以实现该方法。但温度过高，将导致能耗高且操作存在安全风险。此外，磷酸铁络合物溶液中磷铁比为(2.5-10):1，例如(2.5-8):1时，少量加水将导致解络合反应发生。
进一步，所述方法在常压下进行，也可以在加压的情况下进行，加压有助加速解络合反应，所述加压的压力范围为0.1Mpa～1Mpa(绝对压力)之间，优选在0.1Mpa～0.5Mpa之间。本发明所述加压，包括仅仅比大气压高1Pa，即略微加压。
使用本发明的方法，在络合物溶液中加水即可解络合，导致二水磷酸铁的沉淀，即使在室温情况下也会出现，具体可以参见本发明实施例的结果。但大量加水将导致后续大量废水(含磷酸废水)，也将大大增加物料处理量，导致生产效率的降低。因此，优选加水量为络合物溶液的0.3-8倍之间。
所述水为工业常用水，根据最终产品纯度需求来选择。为避免带入杂质，优选用纯净水或去离子水。
本发明发现，在络合物溶液中加入水之后，可通过加热、加压等方式加快二水磷酸铁的沉淀速度。水的加入量、加热温度和压力大小三者之间存在联动。在加热和/或加压处理的情况下，减少水的加入量，同样能达到解络合的效果，同时降低能耗(单纯加热和/或加压)。
此外，加水量的衡量需要考虑多种因素，工业生产中，需要严格考虑成本和后续的处理步骤，尤其是废水的处理。因此，加水量无需确保二水磷酸铁全部沉淀，因为固液分离得到二水磷酸铁后的母液中尽管还含有磷酸铁络合物，但可返回前序工艺步骤中，作为原料循环使用，反而可以降低能耗，且不产生废水。
本发明的保温反应可以在1min-20h之间，也表明二水磷酸铁沉淀的速度可快可慢。如果反应时间短，意味着沉淀速度快，将得到无定型的二水磷酸铁的沉淀；反应时间长，通过控制温度、加水量，降低沉淀速度，可以得到具有晶型的二水磷酸铁。二水磷酸铁沉淀为白色，可能带粉色。
所述磷酸铁络合物溶液可以采用本领域常用的方法获得，如使用Fe与磷酸反应得到，或者通过二价铁与磷酸反应再通过氧化得到，如氧化亚铁、氢氧化亚铁，或三价铁与磷酸反应得到，如三氧化二铁，氢氧化铁等，或通过四氧化三铁与磷酸反应得到(二价铁离子转化成三价铁离子还需经过氧化步骤)，还可以通过含铁的盐或复盐转化得到磷酸铁的原液。
本发明还公开了一种磷酸铁络合物解络合制磷酸铁二水合物的方法，该方法包括：
S1：控制磷酸铁络合物溶液中磷铁比为(2.5-10)：1；优选(3-6):1；
S2：在磷酸铁络合物中通过加水稀释，控制Fe离子的含量在0.1mol/L-2mol/L范围之内，控制络合物溶液温度在常温～180℃之间，反应1min-20h，得到二水磷酸铁沉淀。
其中，
S1步骤可通过原料反应中控制氧化铁和磷酸的摩尔比来完成。如增加氧化铁的摩尔数，降低磷铁比，或者在磷酸铁络合物溶液中，增加磷酸来增加磷铁比。
所述S2步骤，Fe离子的含量优选在0.2-2mol/L之间，加热温度优选在60℃～160℃之间，反应时间优选10min-6h；根据需要，通过固液分离得到二水磷酸铁固体产物；优选S2步骤在加压下进行，压力控制在0.1-1Mpa(绝对压力)，优选为0.1-0.5MPa(绝对压力)之间。
进一步，上述方法还可以包括：
S3:非必要地，将固液分离得到的第二母液返回S1步骤中用于控制磷铁比。
本发明进一步公开了一种磷酸铁的制备方法，包括：
S0：使用浓度为35-85％的磷酸与氧化铁反应，反应温度在室温～180℃之间，磷酸与氧化铁的比例按照磷铁比为(2-10):1设置，反应后过滤去除不溶物，收集第一母液；
S1：检测并调节第一母液磷酸铁络合物溶液中磷铁比为(2.5-10)：1；
S2:控制第一母液温度为室温～180℃之间，向第一母液中加水，将Fe离子的浓度控制在0.1mol/L-2mol/L之间，反应10min-8h，固液分离，得到固体二水磷酸铁和第二母液。
其中，S0步骤中优选在60℃～140℃之间进行，磷酸浓度为50-85％之间；
优选S2步骤在60℃～160℃之间进行；非必要地，S2步骤可在加压下进行，压力控制在0.1-1Mpa(绝对压力)，优先0.1-0.5MPa(绝对压力)。
进一步，所述方法还可以包括：
S3:固液分离得到的第二母液返回S0步骤，与浓磷酸混合调节磷酸浓度，或返回S1步骤用于调节磷铁比。
根据需要，和/或，S4:将二水磷酸铁焙烧，得到磷酸铁。
术语解释：
磷酸铁络合物：磷酸铁与磷酸形成的磷酸铁-磷酸络合物，以溶液形式存在。
磷酸铁二水合物：也可称为二水磷酸铁或二水合磷酸铁，为含两个结晶水的磷酸铁，磷酸铁从溶液中沉淀时，往往含有2个结晶水。
磷铁比：在本发明中，磷铁比(P：Fe)是指在磷酸铁络合物溶液中，磷元素与铁元素的摩尔比(物质的量的比)。磷是指溶液中所有磷元素，包括磷酸铁络合物和溶液中过量的磷酸中的总磷，铁为溶液中所有铁元素。比如3mol磷酸与1mol氢氧化铁反应得到的溶液或产物中，磷铁比为3:1，而6mol磷酸与1mol四氧化三铁的磷铁比就是2：1。在本发明中，磷铁比描述成3:1或3，其含义相同，都表示磷：铁＝3:1。
室温：其指的是室内温度，本发明中室温为15-25℃之间，无需加热的温度。
表压：指总绝对压力超过周围大气压力之数或液体中某一点高出大气压力的那部分压力。本发明中表压是指高于大气压后的压力值，转化为绝对压力时，应加上大气压值。本发明中如果没有特别标明，所述压力为绝对压力。
Fe离子：三价铁离子，也写成Fe3+。
min：表示分钟。
H(或h)：表示小时。
有益效果
本发明的方法具有如下效果：
1、提供了一种简单高效的磷酸铁络合物解络合的方法，大大提高磷酸铁制备的效率，降低磷酸铁制备的成本。
2、相对于现有技术中的加压反应，本发明的方法能耗低，操作简单，安全。
附图说明
图1为实施例8制备二水合磷酸铁的X射线衍射XRD图
图2为实施例8制备的无水磷酸铁的扫描电镜图
具体实施方式
下文将结合具体实施例对本发明的技术方案做更进一步的详细说明。应当理解，下列实施例仅为示例性地说明和解释本发明，而不应被解释为对本发明保护范围的限制。凡基于本发明上述内容所实现的技术均涵盖在本发明旨在保护的范围内。
除非另有说明，以下实施例中使用的原料和试剂均为市售商品，或者可以通过已知方法制备。
制备实施例1 制备磷酸铁络合物溶液
本实施例通过氧化铁与磷酸反应，制备得到不同磷铁比的磷酸铁络合物溶液。通过调节原料投入量和原料摩尔比的不同，可以得到不同磷铁比的磷酸铁络合液。最终得到如下不同磷铁比的络合物溶液。
CX1：磷铁比为3.75：1的络合物溶液，Fe的浓度为2mol/L；
CX2：磷铁比为4.5:1的络合物溶液，Fe的浓度为2mol/L；
CX3：磷铁比为6:1的络合物溶液，Fe的浓度为2mol/L；
CX4：磷铁比为8:1的络合物溶液，Fe浓度为1.788mol/L。
具体操作步骤以CX2溶液为例：取质量分数为85％的磷酸溶液310ml于1L的烧瓶中，向其中加入190ml去离子水，形成浓度为9mol/L的磷酸溶液。准确称量79.84g氧化铁粉末(0.5mol)，加入磷酸溶液中，将整个体系加热至90℃，在90℃温度下搅拌3h。反应结束后，将体系过滤，得到紫红色磷酸铁络合物溶液，该磷酸铁络合物溶液中，磷铁比为4.5：1，铁的浓度为2mol/L。
实施例1 加水解络合试验
取50ml不同磷铁比的磷酸铁络合物溶液(CX1-CX3)，缓慢加入去离子水，观察何时出现沉淀，记录出现沉淀时，V水：V溶液的数值，测试结果见EX11-17。
测试结果显示，1、室温状况下，加水也将导致二水磷酸铁沉淀出现，即磷酸铁络合物的解络合现象的出现，无论是否加温。2、加水以后，通过加温能有利于络合物的破坏，减少加水量。3、磷铁比低的磷酸铁络合物溶液，需要的加水量更少。
表1实验1测试结果
实施例1测试结果显示，加入水以后，会有效破坏络合物，导致二水磷酸铁沉淀迅速生成。但如在室温下解络合则需加入更大量的水，才能使得二水磷酸铁沉淀。通过升温可以减少水的加入量。通过大量加水，将迅速解络合，使得二水磷酸铁快速沉淀，此时所得的二水磷酸铁往往为非晶形或颗粒度极小的晶体。
实施例2 使用溶液CX1的解络合试验
取一定体积(一般为50ml)的磷铁比为3.75:1的CX1磷酸铁络合物溶液，通过加入不同量(X倍络合物溶液体积)的水，控制体系温度为Y℃，反应6h，直到沉淀不再增加。通过本实验，寻找和发现磷铁比为3.75:1时，最优的加水量和解络合温度。
反应产率计算方法是：以加入去离子水的体积与络合溶液的体积为1：1为例，磷酸铁络合物溶液的体积为50ml，加入去离子水的体积为50ml，将磷酸铁络合物与去离子水形成的混合溶液升温至90℃，保温时间为6h，将得到的二水合磷酸铁称重，质量为14.8358g，50ml磷酸铁络合物溶液中铁离子的物质的量为0.1mol，理论上合成二水合磷酸铁的质量为0.1mol*187g/mol＝18.7g，则此反应产率为14.8358g/18.7g×100％＝79.3％。需要指出的是，此处的收率是一次反应收率，以区别于经过多次物料循环后的最终收率。使用本发明的方法，经过物料循环使用，磷酸铁的收率通常是100％。
实验反应结果如下：
表2：实施例2测试结果
表2结果显示：在磷铁比大约为3.75:1时，如果不加水，仅仅加热络合物溶液，经过6h以后，没有二水磷酸铁沉淀。意外的是，加水之后，仅加入0.5倍体积的去离子水，使得Fe3+的浓度为1.33mol/L时，就发生解络合反应，导致二水磷酸铁的沉淀。当加入的去离子水的量为1-4倍(相对于络合物溶液体积)时，溶液中的二水磷酸铁大多发生沉淀。
从工业应用来说，一次性将二水磷酸铁100％沉淀可能需要加入更多的水并升到更高的 温度，并没有实际的工业价值。因为过滤二水磷酸铁后的母液将返回到氧化铁与磷酸反应步骤中，用于调节磷酸的浓度，保证磷酸铁和磷酸最终100％被利用。
实验例3 使用溶液CX2的解络合试验
参照实施例2的操作，区别在于使用原料溶液CX2(磷铁比为4.5:1)。
表3：实施例3测试结果
表3结果显示：在磷铁比为4.5:1时，不加水，即使加热络合物溶液到120℃，6h以后，仍然没有得到二水磷酸铁沉淀。加水(体积倍数1-5)之后，导致二水磷酸铁的沉淀。尤其是Fe3+浓度达到0.33mol/L时，超过99％的磷酸铁沉淀分离。
实验例4 使用溶液CX3的解络合试验
参照实施例2的操作，区别在于使用原料溶液CX3(磷铁比为6:1)。
表4：实施例4测试结果
表4结果显示：在磷铁比为6:1时，不加水则无法得到二水磷酸铁沉淀。加水(体积倍数1-5)之后，导致二水磷酸铁的沉淀。但与实施例2、3的数据比较，明显，磷铁比升高将导致解络合产率降低。
实验例5 使用溶液CX4的解络合试验
参照实施例2的操作，区别在于使用原料溶液CX4(磷铁比为8:1)
表5：实施例5测试结果
表5结果显示：在磷铁比为8:1时，不加水同样无法得到二水磷酸铁沉淀。加水(体积倍数3-8)之后，才导致二水磷酸铁的沉淀。同样，磷铁比升高将导致解络合产率降低。
实施例6 其它组测试试验
参照实施例2的操作，采用不同的磷铁比、反应温度、加水比，测试不同温度，加水量情况下的反应产率。
表6：实施例6测试结果

表6显示，提高解络合温度将帮助解络合反应发生，EX61和EX63的反应产率明显高于反应温度较低的EX62和EX64，即使EX64比EX63的磷铁比更低。EX69显示加水量达到7体积倍数，导致Fe3+的浓度低至0.217mol/L时，仍然能得到超过93％的收率。
实施例7 加压解络合试验
加压解络合的实验操作：以110℃反应温度为例，向络合物溶液中按1：1的体积比加入水，转入耐压瓶中，加压力表，反应半小时后体系升温至110℃，此时压力表为0.06Mpa(表压)，稳定20分钟后，压力升至0.09Mpa(表压)，此后压力维持恒定，保温保压4h。测试了不同磷铁比、温度的实验，测试结果见表7。
作为加压对比例的实验操作(DB1，DB2)：测试试验操作如下，测试结果参见表7。
对比试验DB1：磷铁比的比例为5.23：1时，50ml的络合物溶液加入到耐压瓶中，不加水，升温至110度，随着温度的升高，压力表的读数逐渐增加，升温至110度后约20分钟，压力稳定在0.1Mpa，在此温度和压力下，反应6h后，体系无任何析出。产率为0％。
对比试验DB2：磷铁比的比例为6：1时，取50ml的络合物溶液加入到耐压瓶中，不加水，升温至110度，随着温度的升高，压力表的读数逐渐增加，升温至110度，此时压力表读数为0.04Mpa，随着时间增加，压力稳定在0.08Mpa，在此温度和压力下，反应6h后，体系无任何析出。产率为0％。
表7加压实验及对比实验结果
表7结果显示，加压能显著提升解络合反应，与表6数据比较，反应速度和产率明显提升。对比例DB1和DB2的结果显示，如果不加水，加压和加热并不能在合理的时间内实现解络合的目的。如果需要得到显著的结果，需要进一步提高压力和反应温度。
实施例8 磷酸铁的制备
1、制备络合物溶液
取质量分数为85％的磷酸溶液310ml于1L的烧瓶中，向其中加入190ml去离子水，形成浓度为9mol/L的磷酸溶液。准确称量79.84g氧化铁粉末，加入磷酸溶液中，将整个体系加热至90度，在90度温度下搅拌3h。反应结束后，将体系过滤，得到紫红色磷酸铁络合物溶液，该磷酸铁络合物溶液中，磷铁比为4.5：1，铁的浓度为2mol/L。
2、制备磷酸铁产品：
取50ml的步骤1获得的紫红色磷酸铁络合物溶液(磷铁比为4.5：1)，向络合物溶液中加入2体积倍数的去离子水，然后将去离子水与磷酸铁络合物溶液形成的混合体系加热至90℃。反应6h后，将沉淀过滤，洗涤，得产物二水合磷酸铁，产物质量为17.01g，产率为90.9％。将粉末做X射线衍射图，得XRD谱图，如图1。将白色二水磷酸铁粉末置于马弗炉，于600℃，保温6h，冷却后得淡黄色粉末。将该粉末做扫描电镜SEM，得图2。
以上，对本发明的实施方式进行了说明。但是，本发明不限定于上述实施方式。凡在本发明的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (10)

  1. 一种磷酸铁络合物解络合制磷酸铁二水合物的方法，该方法为，在磷酸铁络合物溶液中，加入基于络合物溶液体积0.3-30倍，优选0.3-8倍的水，在室温～180℃之间，反应1min-20h，优选10min-6h，经固液分离，得到固体磷酸铁二水合物。
  2. 如权利要求1所述的方法，其中，所述方法在60℃～160℃之间进行，磷酸铁络合物溶液中磷铁比为(2.5-10):1。
  3. 如权利要求1或2所述的方法，其中，所述方法在常压或压力范围0.1MPa-1Mpa之间的加压情况下进行。
  4. 一种磷酸铁络合物解络合制磷酸铁二水合物的方法，该方法包括：
    S1：控制磷酸铁络合物溶液中磷铁比为(2.5-10)：1；优选(3-6):1；
    S2：在磷酸铁络合物中通过加水稀释，控制Fe离子的含量在0.1-2mol/L范围之内，控制络合物溶液温度在常温～180℃之间，反应1min-20h，固液分离，得到二水磷酸铁沉淀。
  5. 如权利要求4所述的方法，所述S2步骤，控制Fe离子的含量在0.2-2mol/L之间，加热温度在60℃～160℃之间。
  6. 如权利要求4或5所述的方法，S2步骤加压进行，压力在0.1-1MPa之间。
  7. 如权利要求4-6任一项所述的方法，所述方法还包括：S3:非必要地，将固液分离得到的第二母液返回S1步骤中用于控制磷铁比。
  8. 一种磷酸铁的制备方法，包括：
    S0：使用浓度为35-85％的磷酸与氧化铁反应，反应温度在室温～180℃之间，反应后过滤去除不溶物，收集第一母液；
    S1：检测并调节第一母液磷酸铁络合物溶液中磷铁比为(2.5-10)：1；
    S2:控制第一母液温度为室温～180℃之间，向第一母液中加水，将Fe离子的浓度控制在0.1mol/L-2mol/L之间，反应1min-20h，固液分离，得到固体磷酸铁二水合物和第二母液。
  9. 如权利要求8所述的方法，其中，S0步骤在60℃～140℃之间进行，磷酸浓度为50-85％之间；优选S2步骤在60℃～160℃之间进行，反应时间在10min-6h；非必要地，S2步骤可在加压下进行，压力控制在绝对压力0.1-1MPa，优选为0.1-0.5Mpa之间。
  10. 如权利要求8或9所述的方法，所述方法还可以包括：
    S3：固液分离得到的第二母液返回S0步骤，与浓磷酸混合调节磷酸浓度，或返回S1步骤用于调节磷铁比；
    和/或，S4：将磷酸铁二水合物焙烧得到磷酸铁。
PCT/CN2023/086517 2022-04-08 2023-04-06 一种磷酸铁络合物解络合制磷酸铁二水合物的方法 WO2023193749A1 (zh)

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