A method for preparing ferrous oxalate in one step using iron powder

Abstract

This invention discloses a one-step method for preparing ferrous oxalate using iron powder. The method involves a one-step reaction of iron powder and oxalic acid in water with a catalyst. The catalyst is an acid catalyst, and its mass percentage is 0.5%-10% of the sum of the masses of iron powder, oxalic acid, and water. This one-step process eliminates the need for preparing ferrous sulfate solution and sodium oxalate or ammonium oxalate solution, simplifying the process, reducing costs and energy consumption, and achieving high product yield and purity. The mother liquor can be recycled, resulting in no waste liquid or solid waste generated, making it environmentally friendly and safe.

Description

Technical Field

[0001] This invention relates to a one-step method for preparing ferrous oxalate using iron powder, belonging to the field of lithium-ion battery material technology. Background Technology

[0002] Ferrous oxalate is a key precursor for the preparation of lithium iron phosphate (LiFePO4), a cathode material for lithium-ion batteries. With the rapid development of the new energy vehicle industry, the market demand for high-quality ferrous oxalate has exploded.

[0003] Currently, the mainstream industrial method for preparing ferrous oxalate is a two-step process. First, an iron source is dissolved in sulfuric acid or similar solutions to prepare a soluble ferrous salt solution. Then, this solution reacts with oxalic acid or oxalate to form ferrous oxalate. The resulting solid-liquid mixture of ferrous oxalate is then subjected to mother liquor removal, multi-stage washing (wash water is fed into the mother liquor system), and drying to obtain a qualified ferrous oxalate product. Finally, the mother liquor, a sodium sulfate or ammonium sulfate solution, is concentrated using MVR or multi-effect evaporation to obtain the sodium sulfate or ammonium sulfate product. Part of the distilled water is reused, and part is treated for discharge. The main reaction process is as follows: Step 1: Fe + H₂SO₄ = FeSO₄ + H₂↑ H₂C₂O₄ + 2NaOH / 2NH₃ = Na₂C₂O₄ + H₂O or H₂C₂O₄ + 2NH₃ = (NH₃)₂O 4)2 C2O4 Step 2: FeSO4 + Na2C2O4 = FeC2O4↓ + Na2SO4 Or: FeSO4+(NH4+) 4)2 C2O4=FeC2O4↓+(NH 4)2 SO4.

[0004] For example, Chinese patent CN101386575 B discloses a method for preparing ferrous oxalate. The steps are as follows: first, ferrous sulfate is dissolved in dilute sulfuric acid; iron filings are added to remove Fe³⁺ and heavy metal impurities from the solution; the solution is then filtered to obtain a pure ferrous sulfate solution; oxalic acid or ammonium oxalate is added to the filtrate to react; and the solution is then filtered, washed, and dried to obtain the ferrous oxalate product. This method allows for controllable product particle size within the range of 1~80 μm and product purity greater than 99.0%, but it still requires an intermediate filtration step to remove impurities and ferrous sulfate must be prepared first.

[0005] For example, patent application CN107746376 A discloses a green and environmentally friendly method for manufacturing battery-grade ferrous oxalate. It involves continuously reacting 99.95% pure iron rods with a mother liquor containing 12%–16% sulfuric acid for 8–12 hours to generate a ferrous sulfate solution. This solution is then pumped into a reaction vessel and heated to 38–42°C before adding an aqueous oxalic acid solution to produce a precipitate of ferrous oxalate and dilute sulfuric acid. After cooling and separation, the solid ferrous oxalate is washed and dried, while the liquid sulfuric acid is returned to the ferrous sulfate process. This cycle is repeated. While this method saves on the consumption of sulfuric acid, it still requires strict separation of the iron dissolution and precipitation steps, resulting in a complex process and high equipment investment.

[0006] Besides the mainstream two-step method, there are also some non-mainstream preparation methods in the existing technology, which are only applicable to specific scenarios and cannot meet the requirements for large-scale industrial production of battery-grade ferrous oxalate: Iron powder reduction method: This process uses a Fe³⁺-containing ferric oxalate complex solution as raw material, adding reducing iron powder to reduce Fe³⁺ to Fe²⁺ to generate ferrous oxalate. It is mainly used to recover iron from iron-containing waste slag. For example, patent application CN202111198498.3 discloses a method for extracting Fe, Zn, and Pb from electric furnace dust and utilizing them at high value. First, the electric furnace dust is leached with a 10% oxalic acid solution at 90°C for 4 hours to generate [Fe(C₂O₄)₃]₃. - The solution is then reacted with reduced iron powder for 3 hours to produce ferrous oxalate precipitate. This method uses industrial waste residue as raw material, the product has low purity, and it is essentially still a two-step method of "first leaching Fe³⁺, then reducing and precipitating", and requires an intermediate filtration step to remove impurities.

[0007] Solid-phase reaction method: Ammonium oxalate and ferrous sulfate are mixed and subjected to a high-temperature solid-phase reaction at 200-300℃. This method involves high reaction temperature, high energy consumption, and produces products with uneven particle size and high impurity content. It is only used in laboratory research and has no industrial application value. Summary of the Invention

[0008] This invention provides a one-step method for preparing ferrous oxalate using iron powder. The method is simple, easy to operate, has a high yield and high purity, and produces a uniform and fine product.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for preparing ferrous oxalate using iron powder in a one-step process involves reacting iron powder and oxalic acid in water with a catalyst in a single step. The catalyst is an acid catalyst, and the mass amount of the acid catalyst is 0.5%-10% of the total mass of iron powder, oxalic acid, and water.

[0010] The acid catalyst mentioned above is at least one of sulfuric acid, hydrochloric acid, phosphoric acid, phosphorous acid, nitric acid, or sulfonic acid.

[0011] The acid catalyst and pure water used in this application can be recycled for product preparation.

[0012] To improve the yield, as one preferred embodiment, the acid catalyst is a mixture of sulfuric acid and phosphorous acid. More preferably, the acid catalyst is a mixture of sulfuric acid, phosphorous acid, and phosphoric acid. Even more preferably, the acid catalyst is a mixture of sulfuric acid, phosphorous acid, and phosphoric acid in a molar ratio of (90-94):(4-7):(1-3). The inventors found in experiments that this catalytic system exhibits a significant synergistic effect and optimal catalytic performance. The inventors analyzed that the reason for this is that sulfuric acid provides a strongly acidic catalytic environment, reducing the activation energy of iron powder dissolution and efficiently initiating the reaction; phosphorous acid exerts an in-situ antioxidant catalytic function, continuously inhibiting Fe²⁺ through a reversible redox cycle. + Oxidation stabilizes the ferrous oxidation state in the system; phosphoric acid acts as a crystallization-regulating catalyst, through reaction with Fe²⁺. + The reversible complexation precisely regulates the crystallization nucleation and growth rate; the synergistic effect of the three acids constructs a three-in-one catalytic mechanism of dissolution initiation, valence state stabilization, and morphology regulation, achieving simultaneous optimization of reaction rate, product purity, and particle size distribution.

[0013] To reduce costs while ensuring catalytic performance, the mass percentage of acid catalyst used is 0.5%-1.5% of the combined mass of iron powder, oxalic acid, and water.

[0014] The molar ratio of the iron powder to oxalic acid is 1:(1~1.15).

[0015] The reaction temperature is 60~80℃; the reaction time is 1~3h. Preferably, the temperature is 60~65℃ and the reaction time is 2h.

[0016] As a specific preferred solution, the preparation method is as follows: iron powder, solid oxalic acid and catalyst are added to water and reacted at 60~80℃ for 1~3h; after the reaction, iron is removed by magnetic force, filtered, and solid material and filtrate are obtained. The solid material is washed and dried to obtain ferrous oxalate; after replenishing the lost acid catalyst in the filtrate and washing liquid, iron powder and solid oxalic acid are added for the recycling preparation of ferrous oxalate.

[0017] During solid material washing, a three-stage countercurrent washing process is adopted. The washing water is based on the dry solid material mass, with a liquid-to-solid mass ratio of 0.5:1. In the three-stage countercurrent washing process, the direction of solid material movement is completely opposite to the direction of washing water flow. Fresh clean water comes into contact with the cleanest finished solid material last, while the wastewater containing the most impurities comes into contact with the raw solid material with the highest impurity content first. The third stage (final discharge end): Fresh clean water is introduced; after washing the clean solid material here, the clean water becomes a diluted washing liquid containing a small amount of impurities; the diluted washing liquid is sent to the second stage to wash the solid material with a medium impurity content in the second stage; after washing, the impurities increase; it is then sent to the first stage (feed end) to wash the raw solid material with the highest impurity concentration that just entered; finally, the wastewater with the highest concentration is discharged from the first stage; the washed solid material is discharged from the third stage.

[0018] Through long-term experiments, it was found that after a single reaction, the amount of catalyst lost (mother liquor carried by the solid material after filtration) is generally 0.8-5%.

[0019] The above drying method adopts flash continuous drying, with the tower temperature controlled at 90-100℃ and the flow stop time at 2-3 minutes for rapid drying.

[0020] The inventor used iron powder with a purity greater than or equal to 98% in the experiment (1.5% of the main components are carbon, sulfur, water, phosphorus and oxygen, and the content of other metal impurities is less than 0.5%).

[0021] The specific method for magnetic iron removal described above is as follows: Two identical two-stage iron removal units are set up, configured in parallel with one in operation and one on standby. While one iron removal unit receives material and performs iron removal operations, the other standby iron removal unit simultaneously completes cleaning, impurity removal, and regeneration. The two iron removal units operate alternately to achieve uninterrupted continuous production. The configuration of each iron removal unit is as follows: Primary coarse iron removal stage: 3 sets of series-connected permanent magnet iron separators, with a single magnetic field strength of 10,000~13,000 Gs; Secondary fine iron removal section: 1 set of adjustable magnetic field electromagnetic iron separator, with an adjustable excitation current range of 0~10A, corresponding to a magnetic field strength of 5000~15000Gs; Supporting storage tanks: 1 primary intermediate tank, 1 secondary intermediate tank, and 1 metal magnetic particle collection tank.

[0022] Specific operating steps for magnetic iron removal: 1) Primary permanent magnet coarse iron removal: The ferrous oxalate solid-liquid mixture after the reaction is completed is passed through three sets of series permanent magnet separators in the working unit at a stable flow rate of 5L / h to remove large-particle magnetic metal impurities. The processed material is then fed into the primary intermediate tank. Permanent magnet unit flushing and regeneration: After the material is conveyed, pure water is introduced into the reactor (after the process is stabilized, the filtrate from the subsequent solid-liquid separation process can be used instead) to flush the conveying pipeline and the residual product adsorbed on the surface of the permanent magnet rod. All the flushing liquid is incorporated into the first-stage intermediate tank. Then the permanent magnet rod is removed, and the metal impurities adsorbed on the surface are cleaned into the metal magnetic particle collection tank. The permanent magnet unit is regenerated and put into standby mode. 2) Secondary electromagnetic iron removal: The metal particle content of the material in the primary intermediate tank is sampled and tested. The excitation current of the electromagnetic separator is adjusted to the corresponding magnetic field strength according to the test results. Then, the material in the primary intermediate tank is passed through the electromagnetic separator at a stable flow rate of 3L / h to remove small-diameter weak magnetic metal impurities. The treated material is then fed into the secondary intermediate tank. Electromagnetic unit flushing and regeneration: After the material is conveyed, pure water is introduced into the primary intermediate tank (after the process is stabilized, the filtrate from the subsequent solid-liquid separation process can be used instead) to flush the conveying pipeline and the inside of the electromagnetic separator in a positive direction. All the flushing liquid is incorporated into the secondary intermediate tank. Then the excitation is disconnected, and the metal impurities adsorbed by the electromagnetic separator are discharged into the metal magnetic particle collection tank. The electromagnetic unit completes regeneration and turns to standby. 3) Material diversion and full recycling: The material in the secondary intermediate tank is sampled and tested. The metal particle count is ≤50pcs / 1000g to be qualified. Qualified material is sent to the subsequent mother liquor removal process; unqualified material is returned to the primary permanent magnet coarse iron removal process for reprocessing; the material in the metal magnetic particle collection tank is combined with the filtrate generated from the subsequent solid-liquid separation and returned to the reactor for recycling.

[0023] This application involves a simple reaction process, easy operation, and requires no special equipment. Using a strong acid as a catalyst, the oxidation kinetics of oxygen are extremely slow under acidic conditions, and excess oxalic acid reacts with Fe... 2+ The formation of a stable ferrous oxalate complex significantly reduces the oxidation potential. Combined with the self-reducing properties of iron powder, even trace amounts of Fe are generated. 3+ It will also be immediately restored to 2Fe by the iron powder. 3+ +Fe=3Fe 2+ Multiple mechanisms work together to ensure that there are no obvious oxidation side reactions during the reaction process.

[0024] The reaction mechanism of this application is as follows:

[0025] This application overcomes the common misconception in existing technologies that "high-purity products can only be obtained by first dissolving iron and filtering to remove impurities," and can also obtain battery-grade pure products through a one-step method.

[0026] Unless otherwise specified, all percentages in this application are percentages by mass.

[0027] Unless otherwise specified in this application, all technologies are directly adopted.

[0028] Compared with existing technologies, it has the following beneficial effects: 1) From the perspective of the simplicity of the reaction principle, the one-step process of this application directly eliminates the preparation of ferrous sulfate solution and sodium oxalate or ammonium oxalate solution, making the process simpler. The strong acid plays a catalytic role in the reaction of iron powder with oxalic acid to produce ferrous oxalate.

[0029] 2) From the perspective of investment cost, the one-step process of this application is simpler than the traditional process, and saves the construction of equipment such as ferrous sulfate reaction, sodium oxalate or ammonium oxalate reaction, and sodium sulfate or ammonium sulfate concentration and recovery. For the same production capacity, it greatly reduces fixed asset investment, reduces the input of workshop operators, and reduces energy consumption and consumption costs.

[0030] 3) From the perspective of quality control, the one-step process of this application has fewer quality control points due to the shortened process, which is more conducive to quality control and the resulting product has higher purity.

[0031] 4) From a safety perspective, the one-step process of this application significantly reduces safety management risks compared to traditional processes because it does not require the introduction of large amounts of hazardous chemicals such as sulfuric acid, sodium hydroxide, or liquid ammonia.

[0032] 5) From an environmental perspective, compared with traditional processes, the one-step process of this application uses strong acid only as a catalyst, which is in smaller quantity and can be recycled. It does not require washing water and does not produce sodium sulfate or ammonium sulfate as byproducts, thus reducing environmental pressure.

[0033] 6) Existing two-step methods require at least two reactors (iron melting vessel + reaction vessel); while this application is a one-step reaction, which is completed in one reactor.

[0034] 7) Existing two-step methods require an intermediate filtration and impurity removal step; however, this application is a one-step reaction that does not require an intermediate filtration and impurity removal step.

[0035] 8) In the existing two-step method, the sulfuric acid mother liquor needs to be returned to the iron melting kettle; while in this application, the mother liquor after the reaction can be directly recycled.

[0036] 9) The existing two-step method is time-consuming, about 20 to 100 hours (iron melting takes the longest); while this application only takes about 1 to 3 hours, which significantly improves efficiency.

[0037] 10) In the existing two-step method, Fe² has a high risk of oxidation during filtration and transfer; while this application generates an immediate precipitate in situ, which effectively overcomes the problem of high Fe² oxidation risk and results in a product with high purity. Attached Figure Description

[0038] Figure 1 The image shown is of the product obtained in Embodiment 8 of the present invention; Detailed Implementation

[0039] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0040] Unless otherwise specified, all operations in this application shall be carried out at room temperature (15~25℃); unless otherwise specified, all operations shall be carried out at a stirring speed of 300 rpm.

[0041] In each case, the ultrapure iron powder was purchased from Anhui Maanshan Iron & Steel Powder Metallurgy Co., Ltd., MHF80.255 first grade, with a purity of over 98% and a particle size of 300 mesh sieve. The concentrations are as follows: sulfuric acid 98%, hydrochloric acid 32%, phosphoric acid 38%, nitric acid 65%, and methanesulfonic acid 98%. Yield was calculated by gravimetric method, representing the ratio of actual mass to theoretical mass. Purity was measured using potassium permanganate redox titration. Trace metal impurity content was measured using inductively coupled plasma optical emission spectrometry (ICP-OES). Sulfur content was measured using high-frequency induction combustion-infrared absorption spectrometry (carbon-sulfur analyzer). Particle size D50 was measured using laser particle size diffraction (wet method). The number of metal particles was measured using magnetic separation-microscopic counting combined with energy dispersive spectroscopy verification.

[0042] In each example, magnetic iron removal is implemented using two identical two-stage iron removal units, configured in parallel with one unit in operation and the other on standby. While one unit is handling material and performing iron removal, the other standby unit simultaneously completes cleaning, impurity removal, and regeneration. The two units operate alternately to achieve uninterrupted continuous production. The configuration of each iron removal unit is as follows: Primary coarse iron removal stage: 3 sets of series-connected permanent magnet iron separators, with a single magnetic field strength of 11000Gs; Secondary fine iron removal section: 1 set of adjustable magnetic field electromagnetic iron separator, with an adjustable excitation current range of 0~10A, corresponding to a magnetic field strength of 5000~15000Gs; Supporting storage tanks: 1 primary intermediate tank, 1 secondary intermediate tank, and 1 metal magnetic particle collection tank.

[0043] Specific operating steps for magnetic iron removal: 1) Primary permanent magnet coarse iron removal: The ferrous oxalate solid-liquid mixture after the reaction is completed is passed through three sets of series permanent magnet separators in the working unit at a stable flow rate of 5L / h to remove large-particle magnetic metal impurities. The processed material is then fed into the primary intermediate tank. Permanent magnet unit flushing and regeneration: After the material is conveyed, pure water is introduced into the reactor (after the process is stabilized, the filtrate from the subsequent solid-liquid separation process can be used instead) to flush the conveying pipeline and the residual product adsorbed on the surface of the permanent magnet rod. All the flushing liquid is incorporated into the first-stage intermediate tank. Then the permanent magnet rod is removed, and the metal impurities adsorbed on the surface are cleaned into the metal magnetic particle collection tank. The permanent magnet unit is regenerated and put into standby mode. 2) Secondary electromagnetic iron removal: The metal particle content of the material in the primary intermediate tank is sampled and tested. The excitation current of the electromagnetic separator is adjusted to the corresponding magnetic field strength according to the test results. Then, the material in the primary intermediate tank is passed through the electromagnetic separator at a stable flow rate of 3L / h to remove small-diameter weak magnetic metal impurities. The treated material is then fed into the secondary intermediate tank. Electromagnetic unit flushing and regeneration: After the material is conveyed, pure water is introduced into the primary intermediate tank (after the process is stabilized, the filtrate from the subsequent solid-liquid separation process can be used instead) to flush the conveying pipeline and the inside of the electromagnetic separator in a positive direction. All the flushing liquid is incorporated into the secondary intermediate tank. Then the excitation is disconnected, and the metal impurities adsorbed by the electromagnetic separator are discharged into the metal magnetic particle collection tank. The electromagnetic unit completes regeneration and turns to standby. 3) Material diversion and full recycling: Samples are taken from the material in the secondary intermediate tank for testing. If the number of metal particles is ≤50pcs / 1000g, it is considered qualified. Qualified material is sent to the subsequent mother liquor removal process (solid-liquid separation). Unqualified material is returned to the primary permanent magnet coarse iron removal process for reprocessing (there is no return step in the following examples). The material in the metal magnetic particle collection tank is combined with the filtrate generated from the subsequent solid-liquid separation and returned to the reactor for recycling.

[0044] Example 1

[0045] Ferrous oxalate prepared by one-step method using iron powder: A. Add 3880 mL of ultrapure water to a 5L reactor, then add 320 g of ultrapure iron powder, 800 g of solid oxalic acid, and 50 g of sulfuric acid in sequence. Heat the mixture to 60°C and stir for 2 hours.

[0046] B. The ferrous oxalate solid-liquid mixture from step A is first subjected to magnetic iron removal, then separated into solid and liquid components using a filtration device to obtain solid material and mother liquor. The solid material undergoes three-stage countercurrent washing (solid-liquid mass ratio of 0.5:1 based on dry solid material mass), followed by drying using a flash drying device (continuous flash drying, tower temperature controlled at 90-100℃, and stop-flow time should be within 2 minutes for rapid drying). This yields qualified ferrous oxalate product with a layered structure, a yield of 86.5%, purity >99.9%, Cu <0.0005%, total content of Cu+Zn+NI+Cr metal impurities <0.0050%, S, Mn, Mg, K, Na, and Co all <0.0050%, Ca <0.0001%. D50 particle size: 65 micrometers. SPAN: 1.2. Metal particle count ≤50 pcs / 1000g.

[0047] The mother liquor and washing liquid obtained in step B are recycled in place of ultrapure water for step A. During the next reaction, ultrapure water is replenished to the required amount, and the loss of sulfuric acid due to filtration is compensated by testing the pH. Then, ultrapure iron powder and solid oxalic acid are added for another reaction.

[0048] Example 2

[0049] The difference from Example 1 is that sulfuric acid is replaced with H+. + Equimolar amounts of hydrochloric acid were used; all other parameters were as described in Example 1. Yield: 85.2%, purity >99.8%. D50 particle size: 82 micrometers. Metal particle count ≤50 pcs / 1000g. Defect: Cl - The residual concentration of 38 ppm affects battery cycle life.

[0050] Example 3

[0051] The difference from Example 1 is that sulfuric acid is replaced with H+. + Equimolar amounts of phosphoric acid were used, with all other parameters as described in Example 1. Yield: 75.6%, purity >99.7%. D50 particle size: 71 micrometers. Number of metal particles ≤50 pcs / 1000g. Drawback: Slow reaction rate.

[0052] Example 4

[0053] The difference from Example 1 is that sulfuric acid is replaced with H+. + Equimolar amounts of phosphorous acid were used, with all other parameters as described in Example 1. Yield: 82.3%, purity > 99.9%. D50 particle size: 59 micrometers. Number of metal particles: ≤ 50 pcs / 1000g.

[0054] Example 5

[0055] The difference from Example 1 is that sulfuric acid is replaced with H+. +An equimolar mixture of sulfuric acid and phosphorous acid in a molar ratio of 92:6 was used, with all other parameters as described in Example 1. Yield: 90.8%, purity > 99.9%, D50 particle size: 36 micrometers, metal particle count ≤ 20 pcs / 1000g.

[0056] Example 6

[0057] The difference from Example 1 is that sulfuric acid is replaced with H+. + An equimolar mixture of acids, consisting of phosphorous acid and phosphoric acid in a molar ratio of 6:2, with all other parameters as described in Example 1. Yield 83.5%, purity >99.8%. D50 particle size: 48 micrometers. Number of metal particles ≤40 pcs / 1000g.

[0058] Example 7

[0059] The difference from Example 1 is that sulfuric acid is replaced with H+. + An equimolar mixture of sulfuric acid and phosphoric acid in a molar ratio of 92:2 was used, with all other parameters as described in Example 1. Yield: 82.3%, purity > 99.8%, D50 particle size: 66 micrometers, metal particle count ≤ 50 pcs / 1000g.

[0060] Example 8

[0061] The difference from Example 1 is that sulfuric acid is replaced with H+. + An equimolar mixture of acids, consisting of sulfuric acid, phosphorous acid, and phosphoric acid in a molar ratio of 92:6:2, with all other parameters as described in Example 1. Yield: 99.1%, purity > 99.99%, D50 particle size: 2 micrometers, metal particle count ≤ 10 pcs / 1000g, SPAN: 0.9.

[0062] Example 9

[0063] The difference from Example 8 is that sulfuric acid is replaced with H+. + An equimolar mixture of acids, consisting of sulfuric acid, phosphorous acid, and phosphoric acid in a molar ratio of 75:20:5, with all other parameters as described in Example 8. Yield: 92.6%, purity >99.9%. D50 particle size: 28 micrometers. Number of metal particles ≤30 pcs / 1000g.

[0064] Example 10

[0065] The difference from Example 8 is that sulfuric acid is replaced with H+. + An equimolar mixture of acids, consisting of sulfuric acid, phosphorous acid, and phosphoric acid in a molar ratio of 95:3:2, with all other parameters as described in Example 8. Yield: 91.3%, purity > 99.9%. D50 particle size: 31 micrometers. Number of metal particles ≤ 35 pcs / 1000g.

[0066] Example 11

[0067] The difference from Example 8 is that the reaction time was shortened to 1 hour or extended to 3 hours, while all other aspects remained the same as in Example 8. The yield was 76.4% after 1 hour of reaction. The yield was 98.9% after 3 hours of reaction, but the purity decreased to 97.6%.

[0068] Example 12

[0069] The difference from Example 1 is that the reaction time was extended to 3 hours, while all other aspects were the same as in Example 1. The yield was 92.1%.

[0070] Example 13

[0071] The difference from Example 1 is that the reaction time was extended to 3 hours and the reaction temperature was raised to 80°C, while all other aspects were the same as in Example 1. The yield was 95.8%.

Claims

1. A method for preparing ferrous oxalate in one step using iron powder, characterized in that: It is prepared by a one-step reaction of iron powder and oxalic acid in water under the action of a catalyst; the catalyst is an acid catalyst, and the mass amount of the acid catalyst is 0.5%-10% of the total mass of iron powder, oxalic acid and water.

2. The method according to claim 1, characterized in that: The acid catalyst is at least one of sulfuric acid, hydrochloric acid, phosphoric acid, phosphorous acid, nitric acid, or sulfonic acid.

3. The method according to claim 1 or 2, characterized in that: The acid catalyst is a mixture of sulfuric acid and phosphorous acid.

4. The method according to claim 1 or 2, characterized in that: A mixed acid catalyst consisting of a mixture of sulfuric acid, phosphorous acid, and phosphoric acid.

5. The method according to claim 4, characterized in that: The acid catalyst is a mixture of sulfuric acid, phosphorous acid and phosphoric acid in a molar ratio of (90~94):(4~7):(1~3).

6. The method according to claim 1 or 2, characterized in that: The mass of the acid catalyst is 0.5%-1.5% of the total mass of iron powder, oxalic acid, and water.

7. The method according to claim 1 or 2, characterized in that: The molar ratio of iron powder to oxalic acid is 1:(1~1.15); the reaction temperature is 60~80℃; and the reaction time is 1~3h.

8. The method according to claim 1 or 2, characterized in that: Iron powder, solid oxalic acid, and catalyst are added to water and reacted at 60-80℃ for 1-3 hours. After the reaction, iron is removed by magnetic force and filtered to obtain solid material and filtrate. The solid material is washed and dried to obtain ferrous oxalate. The lost acid catalyst is added to the filtrate and washing liquid, and then iron powder and solid oxalic acid are added for the recycling of ferrous oxalate.

9. The method according to claim 8, characterized in that: The drying process employs a flash continuous drying method, with the tower temperature controlled at 90-100℃ and a stop-flow time of 2-3 minutes; the purity of the iron powder is greater than or equal to 98%.

10. The method according to claim 8, characterized in that: The magnetic iron removal method involves setting up two identical two-stage iron removal units in parallel, with one unit in operation and the other on standby. While one unit is receiving material for iron removal, the other standby unit simultaneously completes cleaning, impurity removal, and regeneration. The two units operate alternately to achieve uninterrupted continuous production. Each iron removal unit is configured as follows: Primary coarse iron removal stage: 3 sets of series-connected permanent magnet iron separators, with a single magnetic field strength of 10,000~13,000 Gs; Secondary fine iron removal section: 1 set of adjustable magnetic field electromagnetic iron separator, with an adjustable excitation current range of 0~10A, corresponding to a magnetic field strength of 5000~15000Gs; Supporting storage tanks: 1 primary intermediate tank, 1 secondary intermediate tank, and 1 metal magnetic particle collection tank; Specific operating steps for magnetic iron removal: 1) Primary permanent magnet coarse iron removal: The ferrous oxalate solid-liquid mixture after reaction is passed through three sets of series permanent magnet separators in the working unit at a stable flow rate of 4.5~5.5L / h to remove large-particle magnetic metal impurities. The processed material is then fed into the primary intermediate tank. Permanent magnet unit flushing and regeneration: After the material is conveyed, pure water is introduced into the reactor to flush the conveying pipeline and the residual product adsorbed on the surface of the permanent magnet rod. All the flushing liquid is incorporated into the first-stage intermediate tank. Then the permanent magnet rod is removed, and the metal impurities adsorbed on the surface are cleaned into the metal magnetic particle collection tank. The permanent magnet unit is regenerated and put into standby mode. 2) Secondary electromagnetic iron removal: The metal particle content of the material in the primary intermediate tank is sampled and tested. The excitation current of the electromagnetic separator is adjusted to the corresponding magnetic field strength according to the test results. Then, the material in the primary intermediate tank is passed through the electromagnetic separator at a stable flow rate of 2.5~3.5L / h to remove small-diameter weak magnetic metal impurities. The treated material is then fed into the secondary intermediate tank. Electromagnetic unit flushing and regeneration: After the material is conveyed, pure water is introduced into the primary intermediate tank to flush the conveying pipeline and the inside of the electromagnetic separator in the forward direction. All the flushing liquid is incorporated into the secondary intermediate tank. Then the excitation is disconnected, and the metal impurities adsorbed by the electromagnetic separator are discharged into the metal magnetic particle collection tank. The electromagnetic unit completes regeneration and turns to standby. 3) Material diversion and full recycling: The material in the secondary intermediate tank is sampled and tested. The metal particle count is ≤50pcs / 1000g, which is considered qualified. Qualified material is sent to the subsequent mother liquor removal process; unqualified material is returned to the primary permanent magnet coarse iron removal process for reprocessing; the material in the metal magnetic particle collection tank is combined with the filtrate generated from the subsequent solid-liquid separation and returned to the reactor for recycling.

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