Preparation method of ammonium ferrous sulfate

Abstract

The invention provides a preparation method of ammonium ferrous sulfate, and relates to the technical field of inorganic salt preparation.The preparation method of the ammonium ferrous sulfate comprises the following steps that raw materials of iron and a sulfuric acid solution are taken and mixed for a reaction, and a ferrous sulfate solution is obtained; adding solid ammonium sulfate into the ferrous sulfate solution to obtain an ammonium ferrous sulfate solution; and taking the ammonium ferrous sulfate solution, filtering impurities, taking filtrate, and performing evaporative crystallization to obtain ammonium ferrous sulfate. Ferrous sulfate reacts with ammonium sulfate to form double salt ammonium ferrous sulfate, and since the electron configuration is affected by a ligand field, the electron configuration of ferrous iron in the double salt is not easy to oxidize due to the influence of the ligand field, and the ferrous iron is not easy to oxidize even if the ferrous iron is fully contacted with air in the filtering process; the method has the advantages that oxidation of ferrous ions is reduced, the impurity content is reduced, the product purity and the batch stability are improved, additional secondary purification treatment is not needed, and the technological process is simplified.

Description

Technical Field

[0001] This invention relates to the field of inorganic salt preparation technology, and more specifically, to a method for preparing ferrous ammonium sulfate. Background Technology

[0002] Ferrous ammonium sulfate, as an important chemical intermediate, has wide applications in energy storage batteries, water treatment, and electronic materials. Current industrial preparation generally employs a traditional process: first, iron reacts with sulfuric acid solution to generate ferrous sulfate solution; then, filtration removes solid impurities; ammonium sulfate is added to the filtrate to form ferrous ammonium sulfate solution; and finally, crystallization yields the product. This process has significant drawbacks: during filtration, the ferrous sulfate solution is exposed to air for an extended period, causing ferrous ions to be easily oxidized to ferric ions, resulting in increased impurity content, decreased purity, and insufficient batch stability in the product. Summary of the Invention

[0003] This invention aims to solve the problems of high impurity content, low purity, and insufficient batch stability in ferrous ammonium sulfate products.

[0004] This invention provides a method for preparing ferrous ammonium sulfate, comprising the following steps: S1: Mix raw material iron and sulfuric acid solution and react to obtain ferrous sulfate solution; S2: Add solid ammonium sulfate to ferrous sulfate solution to obtain ferrous ammonium sulfate solution; S3: Take a ferrous ammonium sulfate solution, filter out impurities, collect the filtrate, evaporate and crystallize to obtain ferrous ammonium sulfate.

[0005] Optionally, the steps also include: S4: Wash ferrous ammonium sulfate with anhydrous alcohol, filter and collect the precipitate to obtain purified ferrous ammonium sulfate.

[0006] Optionally, in S4, after washing ferrous ammonium sulfate with anhydrous alcohol, it is filtered at low pressure at -60 to -90 kPa.

[0007] Optionally, the anhydrous alcohol is anhydrous ethanol or isopropanol.

[0008] Optionally, in step S1, when the raw material iron and sulfuric acid solution are mixed and reacted, copper sulfate is added as a catalyst.

[0009] Optionally, in S1, iron, sulfuric acid solution, and copper sulfate catalyst are reacted at 65 to 85°C for 14 to 16 minutes.

[0010] Optionally, in S1, iron, sulfuric acid solution, and copper sulfate catalyst are reacted at 75°C for 15 minutes.

[0011] Optionally, the final concentration of the catalyst copper sulfate in the reaction system is 0.001 to 0.002 mol / L.

[0012] Optionally, the mass ratio of iron to sulfuric acid solution is 1:(5 to 10), wherein the concentration of sulfuric acid solution is 2 to 4 mol / L.

[0013] Optionally, the concentration of the sulfuric acid solution is 3 mol / L.

[0014] The beneficial effects of the preparation method of ferrous ammonium sulfate of the present invention are as follows: ferrous sulfate reacts with ammonium sulfate to form a double salt, ferrous ammonium sulfate. Due to the influence of the ligand field on the electronic configuration, the electronic configuration of ferrous iron in the double salt is not easily oxidized. By placing the filtration step after the formation of the double salt ferrous ammonium sulfate solution, the ferrous ions are encapsulated in the double salt structure, which is equivalent to adding a "protective shield" to the ferrous iron. Even if the ferrous iron is in full contact with air during the filtration process, it is not easily oxidized. This method has the advantages of reducing the oxidation of ferrous ions, reducing impurity content, improving product purity and batch stability, and does not require additional secondary purification treatment, thus simplifying the process. Attached Figure Description

[0015] Figure 1 This is a schematic flowchart of the preparation method of ferrous ammonium sulfate according to an embodiment of the present invention; Figure 2 This is a comparison table of the properties of ferrous sulfate and ferrous ammonium sulfate according to embodiments of the present invention; Figure 3 Colorimetric diagrams of the ferrous ammonium sulfate products prepared in Example 3 and Comparative Example 1 after adding hydrochloric acid and KSCN solution, respectively, for the effect embodiment. Detailed Implementation

[0016] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0017] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this invention's description is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "comprising" and its variations as used herein are open-ended inclusion, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the description below.

[0018] like Figure 1 As shown, an embodiment of the present invention provides a method for preparing ferrous ammonium sulfate, comprising the following steps: S1: Mix raw material iron and sulfuric acid solution and react to obtain ferrous sulfate solution; S2: Add solid ammonium sulfate to ferrous sulfate solution to obtain ferrous ammonium sulfate solution; S3: Take a ferrous ammonium sulfate solution, filter out impurities, collect the filtrate, evaporate and crystallize to obtain ferrous ammonium sulfate.

[0019] Specifically, the reaction principle of S1 is: Fe + H2SO4 = FeSO4 + H2↑; The reaction principle of S2 is: FeSO4 + (NH4)2SO4 + 6H2O = (NH4)2SO4·FeSO4·6H2O.

[0020] In this embodiment, as Figure 2 As shown, ferrous sulfate reacts with ammonium sulfate to form the double salt ferrous ammonium sulfate. Due to the influence of the ligand field on the electronic configuration, the electronic configuration of ferrous iron in the double salt is not easily oxidized. Placing the filtration step after the formation of the double salt ferrous ammonium sulfate solution allows the ferrous ions to be encapsulated in the double salt structure, which is equivalent to adding a "protective shield" to the ferrous iron. Even if the ferrous iron is in full contact with air during the filtration process, it is not easily oxidized. This has the advantages of reducing the oxidation of ferrous ions, reducing impurity content, improving product purity and batch stability, and eliminating the need for additional secondary purification, thus simplifying the process.

[0021] Specifically, ferrous sulfate solution can be understood as a solution containing divalent ferric ions generated by the chemical reaction of iron and sulfuric acid, which can be achieved in various ways. For example, iron powder or iron filings can be reacted with dilute sulfuric acid at room temperature with stirring, or the reaction process can be accelerated under heating conditions to improve reaction efficiency. Further, ferrous ammonium sulfate solution refers to a double salt solution formed by mixing ferrous sulfate solution with solid ammonium sulfate, which can be achieved by directly adding ammonium sulfate powder to the ferrous sulfate solution and stirring thoroughly to dissolve it. In addition, the filtration of impurities and collection of the filtrate can be carried out using conventional solid-liquid separation methods, such as gravity filtration using filter paper, or centrifugation to remove insoluble impurities. The evaporation and crystallization process can be completed by heating and concentrating the solution to saturation, followed by cooling and crystallization; specific operating conditions can be adjusted according to actual needs.

[0022] Optionally, the steps also include: S4: Wash ferrous ammonium sulfate with anhydrous alcohol, filter and collect the precipitate to obtain purified ferrous ammonium sulfate.

[0023] Specifically, anhydrous alcohol refers to an alcohol solvent that does not contain water, which can be achieved using anhydrous ethanol or isopropanol. The purpose of choosing anhydrous alcohol as the detergent in this step is to utilize its high solubility selectivity for soluble impurities (such as chloride ions), while avoiding the oxidation reaction of ferrous ammonium sulfate due to contact with water during the washing process, thereby ensuring the chemical stability of the product.

[0024] In this optional embodiment, the combination of anhydrous alcohol washing and filtration effectively solves the problems of insufficient product purity and impurity residue. First, the selective solubility of anhydrous alcohol can specifically remove soluble impurities from the surface of ferrous ammonium sulfate, while ferrous ammonium sulfate itself has low solubility in anhydrous alcohol, thus maximizing the retention of the target product while removing impurities. Second, filtration immediately after washing rapidly separates impurities from the product, preventing the risk of impurity re-adsorption or product decomposition due to prolonged soaking. Furthermore, the introduction of an anhydrous environment avoids the possibility of ferrous iron being oxidized to ferric iron upon contact with air, thereby further improving the chemical stability and batch consistency of the product.

[0025] Optionally, in S4, after washing ferrous ammonium sulfate with anhydrous alcohol, it is filtered at low pressure at -60 to -90 kPa.

[0026] Specifically, low-pressure filtration refers to solid-liquid separation operations performed under negative pressure, which can be achieved using a vacuum pump system or a negative pressure filtration device. The purpose of introducing this technical feature is to effectively suppress the oxidation process of ferrous ions by reducing the partial pressure of oxygen within the system, thereby improving product purity and batch stability.

[0027] In this optional embodiment, during the filtration process after washing ferrous ammonium sulfate with anhydrous alcohol, the residual alcohol on the product surface is easily volatile under normal pressure and introduces air, causing ferrous ions to be oxidized to ferric ions. However, using a negative pressure environment of -60 to -90 kPa significantly reduces the oxygen content in the system, decreasing the possibility of oxidation. Simultaneously, this pressure range ensures sufficient vacuum to suppress oxidation while avoiding the problem of excessively low pressure potentially leading to violent boiling of the alcohol or damage to the crystal structure. Furthermore, the low-pressure condition accelerates the removal of residual liquid from the filter medium, shortening the time window for product contact with air, fundamentally solving the oxidation risk in the filtration process. This achieves the creation of a low-oxygen environment during the purification stage, effectively inhibiting the conversion of ferrous ions to ferric ions, and ensuring the purity and stability of the ferrous ammonium sulfate product.

[0028] Optionally, the anhydrous alcohol is anhydrous ethanol or isopropanol.

[0029] Specifically, anhydrous alcohols refer to alcohols that do not contain water during the washing process, and can be achieved using anhydrous ethanol or isopropanol. The choice of anhydrous ethanol and isopropanol is based on their molecular structure characteristics, which effectively dissolve impurities such as chloride ions, while preventing the oxidation of ferrous iron to ferric iron due to the introduction of water, thus ensuring stable product purity. Furthermore, the appropriate volatility of these alcohols facilitates subsequent drying operations, reducing process time and improving batch consistency.

[0030] In this optional embodiment, the washing and purification process is specifically optimized by limiting the anhydrous alcohol to anhydrous ethanol or isopropanol. During the washing step, anhydrous ethanol or isopropanol can efficiently remove water-soluble impurities such as chloride ions, avoiding purity fluctuations caused by improper alcohol selection in traditional processes. Simultaneously, because anhydrous ethanol and isopropanol have low water content, the risk of oxidation of ferrous iron is significantly reduced, thereby ensuring the stability of product purity.

[0031] Optionally, in step S1, when the raw material iron and sulfuric acid solution are mixed and reacted, copper sulfate is added as a catalyst.

[0032] Specifically, the activity sequence of metallic elements is: Fe, Sn, Pb, Cu, Hg, Ag. Inspired by the copper-zinc galvanic cell, copper sulfate in the iron-sulfuric acid reaction system is used to construct a galvanic cell-like model system to accelerate the reaction. Copper sulfate, as a catalyst, is a substance that can accelerate the chemical reaction rate but is not consumed before or after the reaction. It can be achieved using appropriate amounts of copper sulfate solution or anhydrous copper sulfate powder. The aim is to significantly improve the efficiency of the reaction between iron and sulfuric acid to produce ferrous sulfate by introducing copper sulfate as a catalyst, while reducing the possibility of ferrous ions being oxidized during the reaction.

[0033] In this optional embodiment, during the reaction of iron and sulfuric acid solution to produce ferrous sulfate, the addition of copper sulfate creates a galvanic cell system between the iron and copper. This galvanic cell structure accelerates electron transfer using the potential difference, significantly increasing the reaction rate. This galvanic cell structure reduces the exposure of ferrous ions to air, suppresses oxidation side reactions, and ensures the stability of ferrous iron in the reaction system. Furthermore, this technical solution, combined with the aforementioned method for preparing ferrous ammonium sulfate, optimizes reaction conditions, not only solving the problem of slow reaction rate but also effectively ensuring the high purity of the ferrous sulfate solution in the subsequent crystallization step, ultimately improving the quality and batch consistency of the ferrous ammonium sulfate product.

[0034] Optionally, in S1, iron, sulfuric acid solution, and copper sulfate catalyst are reacted at 65 to 85°C for 14 to 16 minutes.

[0035] Specifically, reaction temperature refers to the suitable temperature range for the chemical reaction between iron and sulfuric acid solution during the preparation process. In practical applications, this temperature range can be precisely controlled using a constant temperature water bath or heating mantle. The purpose is to avoid excessively slow reaction rates due to low temperatures, which would prolong exposure time and increase the risk of oxidation, while simultaneously suppressing the tendency of high temperatures to accelerate the conversion of ferrous iron to ferric iron through contact with oxygen. Reaction time refers to the time interval required for iron and sulfuric acid solution to be fully converted into ferrous sulfate under the action of a catalyst. This time can be precisely controlled using a timer or automated control system to ensure complete reaction while avoiding excessive oxidation due to prolonged reaction time.

[0036] In this optional embodiment, iron, sulfuric acid solution, and copper sulfate catalyst are first placed in a reaction vessel, and the reaction system is heated to 65-85°C using a heating device. This temperature range is chosen based on in-depth research into reaction kinetics, which significantly increases the reaction rate while effectively reducing the risk of oxidation of ferrous ions. Subsequently, the reaction is controlled to last 14-16 minutes. This time period has been experimentally verified to ensure that iron and sulfuric acid react fully to form ferrous sulfate, while minimizing the occurrence of side reactions. The appropriate matching of temperature and time parameters directly addresses the oxidation sensitivity issue in the reaction stage, providing a high-quality intermediate product basis for subsequent steps. Furthermore, the addition of copper sulfate catalyst further improves reaction efficiency, making the entire reaction process more controllable and efficient.

[0037] Optionally, in S1, iron, sulfuric acid solution, and copper sulfate catalyst are reacted at 75°C for 15 minutes.

[0038] Specifically, a reaction temperature of 75℃ refers to a temperature condition that effectively avoids the risk of accelerated oxidation of ferrous iron in a high-temperature environment, while ensuring that the activity of the copper sulfate catalyst is at its optimal level. In practical applications, precise temperature control can be achieved through equipment such as constant-temperature water baths or temperature-controlled reaction vessels. The purpose is to ensure that the reaction rate is neither too fast, triggering side reactions, nor too slow, affecting efficiency, thereby guaranteeing the stability and controllability of the reaction process.

[0039] In this optional embodiment, the stability and controllability of the reaction process are significantly improved by precisely controlling the reaction temperature and time parameters. Specifically, in step S1, iron, sulfuric acid solution, and copper sulfate catalyst react at 75°C. This temperature setting not only avoids the risk of accelerated oxidation of ferrous iron in a high-temperature environment but also ensures that the activity of the copper sulfate catalyst is at its optimal state. Simultaneously, fixing the reaction time to 15 minutes ensures that the reaction system can fully complete the conversion while minimizing the time the materials are exposed to air. This precise parameter control method, combined with other steps in the above preparation method, achieves a stable improvement in product purity and effectively guarantees batch consistency, ultimately solving the problems of large fluctuations in product purity, excessive impurity content, and poor batch stability existing in traditional processes.

[0040] Optionally, the final concentration of the catalyst copper sulfate in the reaction system is 0.001 to 0.002 mol / L.

[0041] Specifically, copper sulfate catalyst refers to a chemical substance used to accelerate the reaction process between iron and sulfuric acid solution. It can be added to the reaction system in a precise ratio. In practical applications, the selection of this concentration range is based on a comprehensive consideration of reaction efficiency and product purity. The purpose is to ensure the stability of the reaction rate while avoiding the introduction of impurities due to excessive concentration.

[0042] In this optional embodiment, by limiting the final concentration of the copper sulfate catalyst to a specific range of 0.001 to 0.002 mol / L, the problems caused by improper catalyst concentration during use can be effectively solved. Specifically, when the catalyst concentration is too low, its activity is insufficient to fully accelerate the reaction between iron and sulfuric acid solution, resulting in a prolonged reaction time. In subsequent operations, ferrous ions are more easily oxidized to ferric ions, thus affecting product purity and batch stability. Conversely, when the concentration is too high, excessive copper sulfate introduces copper ion impurities, increasing the risk of exceeding impurity limits in the product and potentially interfering with the crystallization process, causing purity fluctuations and decreased batch consistency. Therefore, by precisely controlling this concentration range, a stable increase in the reaction rate is ensured, the reaction cycle is shortened to reduce oxidation risks, and impurity residues are avoided, thereby improving the purity and production reliability of ferrous ammonium sulfate products at the source.

[0043] Optionally, the mass ratio of iron to sulfuric acid solution is 1:(5 to 10), wherein the concentration of sulfuric acid solution is 2 to 4 mol / L.

[0044] Specifically, the mass ratio of iron to sulfuric acid solution refers to the mass ratio between iron and sulfuric acid solution in the reaction system. This ratio can be precisely controlled using weighing equipment to ensure a reasonable reactant ratio and avoid excess iron causing unreacted solid residue or excess sulfuric acid triggering side reactions. The concentration of sulfuric acid solution refers to the molar concentration of sulfuric acid in an aqueous solution. This concentration can be adjusted by changing the ratio of sulfuric acid to water to ensure a moderate reaction rate, preventing the process from being too slow, and simultaneously suppressing the oxidation tendency of ferrous iron at high concentrations.

[0045] In this optional embodiment, by limiting the mass ratio of iron to sulfuric acid solution and the concentration of sulfuric acid solution, the problem caused by suboptimal reaction conditions is effectively solved. The mass ratio of iron to sulfuric acid solution is set to 1:(5 to 10). This ratio range ensures sufficient contact between reactants and facilitates chemical reaction, thereby reducing the introduction of impurities and maintaining the stability of the reaction system. Simultaneously, the concentration of sulfuric acid solution is controlled between 2 and 4 mol / L. This range ensures a moderate reaction rate while reducing the risk of oxidation of ferrous iron at high concentrations, allowing the reaction to proceed efficiently under mild conditions. Based on the aforementioned limitations on the mass ratio of iron to sulfuric acid solution and the concentration of sulfuric acid solution, combined with the use of copper sulfate catalyst in the aforementioned steps, the purity of the ferrous sulfate solution and the quality stability of the subsequent product can be significantly improved. Furthermore, by precisely controlling the reaction conditions, the possibility of ferrous iron being oxidized to ferric iron can be effectively reduced, thereby further improving the purity and batch consistency of the final ferrous ammonium sulfate.

[0046] Optionally, the concentration of the sulfuric acid solution is 3 mol / L.

[0047] Specifically, sulfuric acid solution refers to an aqueous solution with sulfuric acid as the main solute, which can be diluted to the target concentration using industrial-grade concentrated sulfuric acid. In practice, by precisely controlling the volume ratio of sulfuric acid to deionized water, the final solution concentration can be ensured to remain stable at 3 mol / L. The purpose is to provide an optimal reaction environment that ensures the reaction proceeds fully without triggering excessive side reactions.

[0048] In this optional embodiment, by fixing the concentration of the sulfuric acid solution at 3 mol / L, the product stability problem caused by concentration fluctuations is effectively solved. Based on this, when iron reacts with sulfuric acid at this concentration, a suitable reaction rate can be maintained, avoiding the problem of incomplete reaction at low concentrations and inhibiting the reaction of Fe at high concentrations. 2+ Easily oxidized to Fe 3+Side reactions did not occur. This specific concentration was chosen based on in-depth research into reaction kinetics, bringing the entire reaction system to an optimal equilibrium state, thereby significantly reducing the introduction of impurities and ensuring the homogeneity and stability of the ferrous sulfate solution. Furthermore, by optimizing the reaction conditions, not only was the batch consistency of the ferrous ammonium sulfate product improved, but the overall purity was also significantly enhanced, making it more suitable for electronic-grade applications.

[0049] The present invention will be further described below with reference to specific embodiments.

[0050] Example 1: Selection of reaction temperature.

[0051] The preparation method of ferrous ammonium sulfate includes the following steps: 1 g of iron and 7.8 mL of sulfuric acid solution were mixed and reacted to obtain ferrous sulfate solution with a concentration of 3 mol / L. Solid ammonium sulfate was added to the ferrous sulfate solution to obtain ferrous ammonium sulfate solution. The ferrous ammonium sulfate solution was taken, impurities were filtered out, and the filtrate was evaporated to crystallize and obtain ferrous ammonium sulfate. The ferrous ammonium sulfate was washed with anhydrous alcohol, filtered, and the precipitate was obtained to obtain purified ferrous ammonium sulfate.

[0052] The reactions were carried out at 65℃, 75℃, 85℃, and 95℃ respectively. The reaction ended when the production of bubbles stopped, and the reaction time was recorded.

[0053] The purity of ferrous ammonium sulfate products generated at 65℃, 75℃, 85℃, and 95℃ was determined using the national standard method for Fe(II). First, a 76.80 μg / ml Fe(II) standard solution was prepared. 0.00, 0.50, 1.00, 2.00, 3.00, 4.00, and 5.00 ml of the Fe(II) standard solution were transferred to 100 ml volumetric flasks, 20 ml of buffer solution was added, and water was added to make up to volume. The absorbance was then measured using a spectrophotometer, and a concentration-absorbance standard curve was plotted.

[0054] To test the absorbance of the product, its concentration needs to be controlled within the concentration range of the standard curve. Therefore, the sample solution needs to be diluted. The steps for calculating the dilution factor are as follows: Weigh 1.0000g of sample to prepare 100ml of solution. Calculate the concentration using the formula, which is 1424.00 μg / ml. Divide the sample concentration by the median concentration of the standard curve and check if the value is greater than 100. If it is greater than 100, a second dilution is required. The first dilution factor is 25 times, and the second dilution factor is 33.3 times. After dilution, add buffer solution and measure the absorbance. After measurement, determine the true concentration based on the standard curve, and calculate the purity based on the theoretical concentration.

[0055] The final yield is calculated based on purity. It is derived from the initial yield and purity of the product at different temperatures. The initial yield is calculated based on the mass of iron weighed. For example, if 56 g of iron (1 mol) is weighed and completely reacted to produce ferrous ammonium sulfate, theoretically 392.14 g (1 mol) of ferrous ammonium sulfate can be produced, resulting in an initial yield of 100%. The actual yield is 385.14 g, so the initial yield is 98.21%. The initial yield of 98.21% multiplied by the purity of 99.90% equals the final yield of 98.12%.

[0056] The ferrous ammonium sulfate products generated at 65℃, 75℃, 85℃, and 95℃ were graded. 0.50 g of ferrous ammonium sulfate product was weighed and transferred to a 25.00 ml colorimetric tube. A small amount of water was added to dissolve it, followed by the addition of 1.00 ml of hydrochloric acid and 2.00 ml of KSCN solution. The volume was then adjusted to 25.00 ml, and the mixture was shaken well before visual colorimetric analysis. A darker color indicates a lower grade, and a lighter color indicates a higher grade, with grade one being the highest.

[0057] The results of the reaction time, final yield, and grade determination of ferrous ammonium sulfate products at different temperatures are shown in Table 1.

[0058] Table 1. Reaction time and product properties of ferrous ammonium sulfate at different temperatures.

[0059] As shown in Table 1, the optimal reaction temperature for producing ferrous ammonium sulfate is 75℃.

[0060] Example 2: Selection of copper sulfate concentration as catalyst.

[0061] The preparation method of ferrous ammonium sulfate includes the following steps: 1 g of iron, 7.8 mL of sulfuric acid solution, and 2 mL of copper sulfate solution were mixed and reacted at 75 °C to obtain a ferrous sulfate solution with a sulfuric acid concentration of 3 mol / L. Solid ammonium sulfate was added to the ferrous sulfate solution to obtain a ferrous ammonium sulfate solution. The ferrous ammonium sulfate solution was taken, impurities were filtered out, and the filtrate was evaporated to crystallize, yielding ferrous ammonium sulfate. The ferrous ammonium sulfate was washed with anhydrous alcohol, filtered, and the precipitate was obtained to obtain purified ferrous ammonium sulfate.

[0062] The concentrations of the copper sulfate solution were selected as 0, 0.005 mol / L, 0.010 mol / L, 0.020 mol / L, 0.050 mol / L, and 0.100 mol / L, respectively. The reaction ended when the generation of bubbles stopped, and the reaction time was recorded.

[0063] Following the purity and grade determination methods in Example 1, the purity and grade of ferrous ammonium sulfate products with different copper sulfate solution concentrations were determined, and the final yield was calculated according to the final yield calculation method in Example 1. The results are shown in Table 2.

[0064] Table 2. Reaction time and product properties for the formation of ferrous ammonium sulfate at different copper sulfate solution concentrations.

[0065] As shown in Table 2, the reaction time is fast and the ferrous ammonium sulfate product is optimal when the copper sulfate solution concentration is 0.005 mol / L.

[0066] Example 3 Take 1g of iron, 7.8mL of sulfuric acid solution and 2mL of copper sulfate solution and mix them at 75℃ to react and obtain ferrous sulfate solution. The concentration of sulfuric acid solution is 3 mol / L and the concentration of copper sulfate solution is 0.005 mol / L. Adding solid ammonium sulfate to a ferrous sulfate solution yields a ferrous ammonium sulfate solution. Take a ferrous ammonium sulfate solution, filter out impurities, collect the filtrate, evaporate and crystallize to obtain ferrous ammonium sulfate; Wash ferrous ammonium sulfate with anhydrous alcohol, filter and collect the precipitate to obtain purified ferrous ammonium sulfate.

[0067] Comparative Example 1 Take 1g of iron, 7.8mL of sulfuric acid solution and 2mL of copper sulfate solution and mix them at 75℃ to react and obtain ferrous sulfate solution. The concentration of sulfuric acid solution is 3 mol / L and the concentration of copper sulfate solution is 0.005 mol / L. Take a ferrous sulfate solution, filter out impurities, and collect the filtrate. Add solid ammonium sulfate to the filtrate to obtain ferrous ammonium sulfate solution, then crystallize and evaporate to obtain ferrous ammonium sulfate; Wash ferrous ammonium sulfate with anhydrous alcohol, filter and collect the precipitate to obtain purified ferrous ammonium sulfate.

[0068] Effect Example The final yield and grade of the ferrous ammonium sulfate products prepared in Example 3 and Comparative Example 1 were calculated respectively. Figure 3 As shown, the test tube on the left is the ferrous ammonium sulfate product of Comparative Example 1, and the four test tubes on the right are the ferrous ammonium sulfate products of Example 3. It can be seen that in Example 3, when ferrous ammonium sulfate was obtained first and then filtered, the product color was lighter and the grade was higher.

[0069] Following the purity determination method in Example 1, the concentration of ferrous ammonium sulfate product in Example 3 reached 99.79%, and the concentration of ferrous ammonium sulfate product in Comparative Example 1 reached 98.00%. The final yield was calculated according to the final yield calculation method in Example 1, and the results are shown in Table 3.

[0070] Table 3 Properties of ferrous ammonium sulfate products from Example 3 and Comparative Example 1

[0071] As shown in Table 3, ferrous sulfate reacts with ammonium sulfate to form the double salt ferrous ammonium sulfate. During the subsequent filtration process, ferrous ions are in full contact with air and are not easily oxidized, which reduces the oxidation of ferrous ions, reduces the content of impurities, and improves the purity of the product.

[0072] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for preparing ferrous ammonium sulfate, characterized in that, Includes the following steps: S1: Mix raw material iron and sulfuric acid solution and react to obtain ferrous sulfate solution; S2: Add solid ammonium sulfate to the ferrous sulfate solution to obtain a ferrous ammonium sulfate solution; S3: Take the ferrous ammonium sulfate solution, filter out impurities, collect the filtrate, evaporate and crystallize to obtain ferrous ammonium sulfate.

2. The method for preparing ferrous ammonium sulfate according to claim 1, characterized in that, It also includes the following steps: S4: Wash the ferrous ammonium sulfate with anhydrous alcohol, filter and collect the precipitate to obtain purified ferrous ammonium sulfate.

3. The method for preparing ferrous ammonium sulfate according to claim 2, characterized in that, In S4, after washing the ferrous ammonium sulfate with anhydrous alcohol, it is filtered at low pressure at -60 to -90 kPa.

4. The method for preparing ferrous ammonium sulfate according to claim 2, characterized in that, The anhydrous alcohol is anhydrous ethanol or isopropanol.

5. The method for preparing ferrous ammonium sulfate according to claim 1, characterized in that, In step S1, copper sulfate is added as a catalyst in the step of mixing raw material iron and sulfuric acid solution for reaction.

6. The method for preparing ferrous ammonium sulfate according to claim 5, characterized in that, In S1, the iron, the sulfuric acid solution, and the catalyst copper sulfate are reacted at 65 to 85°C for 14 to 16 minutes.

7. The method for preparing ferrous ammonium sulfate according to claim 6, characterized in that, In S1, the iron, the sulfuric acid solution, and the catalyst copper sulfate are reacted at 75°C for 15 minutes.

8. The method for preparing ferrous ammonium sulfate according to claim 5, characterized in that, In the reaction system, the final concentration of the catalyst, copper sulfate, is 0.001 to 0.002 mol / L.

9. The method for preparing ferrous ammonium sulfate according to claim 1, characterized in that, The mass ratio of the iron to the sulfuric acid solution is 1:(5 to 10), wherein the concentration of the sulfuric acid solution is 2 to 4 mol / L.

10. The method for preparing ferrous ammonium sulfate according to claim 9, characterized in that, The concentration of the sulfuric acid solution is 3 mol / L.

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