Method for manufacturing ferrous sulfate using microwaves

Abstract

The present invention is characterized by a method for manufacturing ferrous sulfate, which uses iron waste (collectively referred to as iron waste containing ferrous oxide) or waste sulfuric acid, and has excellent quality and can maximize economic effects, the method comprising the steps of: an iron oxide raw material preparation step of preparing, as a raw material, iron waste or ferrous oxide recycled from iron waste by recycling waste materials selected from any one of conditions 1 to 4 or a combination of two thereof, wherein condition 1 is a combination of ferrous oxide recycled from iron waste and a waste sulfuric acid aqueous solution, condition 2 is a combination of iron waste and a sulfuric acid aqueous solution recycled from waste sulfuric acid, condition 3 is a combination of iron waste and a waste sulfuric acid aqueous solution, and condition 4 is a combination of ferrous oxide recycled from iron waste and a sulfuric acid aqueous solution recycled from waste sulfuric acid; a pretreatment step of making iron oxide fine particles using the prepared iron oxide raw material; a SOL treatment step of mixing the iron oxide fine particles with a solvent to perform SOL treatment; a chemical reaction step of obtaining liquid ferrous sulfate by a first reaction of mixing the SOL-treated mixture with a waste sulfuric acid aqueous solution or a sulfuric acid aqueous solution recycled from waste sulfuric acid; and a molecular vibration reaction step of performing a second reaction by applying microwaves to the liquid ferrous sulfate.

Description

Method for producing ferrous sulfate using microwaves

[0001] The present invention relates to a method for producing ferrous sulfate, and more specifically, to a method for producing ferrous sulfate by using iron waste (collectively referred to as iron waste containing ferrous oxide) or waste sulfuric acid to conserve resources, and using microwaves in combination with any one or two of the following conditions 1 to 4.

[0002] Condition 1: Combination of recycled iron waste ferrous oxide and aqueous waste sulfuric acid solution

[0003] Condition 2: Combination of iron waste and aqueous sulfuric acid solution recycled from waste sulfuric acid

[0004] Condition 3: Combination of iron waste and aqueous waste sulfuric acid solution

[0005] Condition 4: Combination of ferrous oxide recycled from iron waste and aqueous sulfuric acid solution recycled from waste sulfuric acid

[0006] In general, sulfuric acid is widely used in various industrial sectors, including the production of semiconductors, fertilizers, paper, and leather. After use in product manufacturing, this sulfuric acid is discarded as waste sulfuric acid. Since the disposal of this waste sulfuric acid incurs high costs, recycling is necessary. Similarly, recycling is required for the disposal of iron waste generated in the steelmaking industry, as the process is equally costly.

[0007] And iron sulfate (FeSO4) is a substance produced through a reaction when iron and sulfuric acid are reacted in an aqueous solution, and exists in the form of a heptahydrate (7H2O).

[0008] In particular, ferrous sulfate heptahydrate, which has a high moisture content, is used as a reducing agent to remove harmful substances by mixing it with cement to convert the chromium hexavalent (Cr+6) contained in the cement, which is harmful to the human body, into chromium trivalent (Cr+3), which is harmless to the human body. It is also used as a coagulant for sludge produced by mixing it with quicklime during water treatment, and is also used in health supplements for iron replenishment.

[0009] Here, the above salts are classified into 1 to 7 salts depending on the number of water molecules contained in the iron sulfate, and all of them are referred to as 'ferrous sulfate n-salts', and hereinafter they will be abbreviated as 'ferrous sulfate'.

[0010] Currently used manufacturing methods for producing such ferrous sulfate include solid-liquid reaction methods and liquid-liquid reaction methods.

[0011] The above method based on a solid-liquid reaction involves mixing solid ferrous oxide (FeO) with liquid sulfuric acid, while the method based on a liquid-liquid reaction involves adding water to ferrous oxide (FeO) to liquefy it and then mixing it with liquid sulfuric acid.

[0012] Since the two types of reactions mentioned above are carried out internally by the heat of reaction between sulfuric acid and water and the heat of oxidation and reduction reactions without external energy input, the frequency of collisions decreases after a certain period of time before the reaction is completed, resulting in a limit to the yield. In addition, temperature changes due to the season can affect the yield.

[0013] More specifically, since ferrous oxide is a solid, the probability of contact between reactants is low when a liquid is added during the reaction, resulting in a low frequency of reaction collisions. Consequently, there is a problem in that the reaction yield within a given reaction time is low, making it feasible only when producing small quantities of ferrous sulfate.

[0014] In addition, liquid-to-liquid reactions involve adding liquid to liquid, which facilitates the flow of substances during the reaction and increases the probability of contact between reactants, resulting in a relatively high frequency of reaction collisions. Consequently, within a given reaction time, ferrous sulfate can be obtained with a yield that is about 5 to 10 percent higher than that of solid-to-liquid reactions; however, as described above, there are also limitations in carrying out a complete reaction over time.

[0015] As prior art regarding such a method for manufacturing ferrous sulfate, there is the Korean Published Patent Application No. 10-2022-0087915 (published June 27, 2022), 'Method for manufacturing ferrous sulfate' disclosed in Patent Document 1 of the prior art literature below.

[0016] Patent Document 1 describes a method for producing ferrous sulfate that can be used as a cement additive without additional processes, without requiring a separate crystallization or filtration step by lowering the moisture content. However, this method has difficulties in mass-producing ferrous sulfate through the solid-liquid reaction described above, and it is difficult to meet quality requirements for industrial application.

[0017] In addition, there is the ‘method for producing ferrous sulfate by sol-forming treatment of an iron material’ (hereinafter referred to as ‘Patent Document 2’) disclosed in Patent Document 2 of the prior art documents below, which was previously filed and registered by the applicant of the present application.

[0018] Patent Document 2 describes a method for producing ferrous sulfate in liquid and liquid forms by a chemical reaction step in which sulfuric acid or waste sulfuric acid is mixed into a sol-forming treatment of iron waste raw materials containing iron material, which is then mixed with a solvent. However, this method has limitations in increasing the yield, and the final drying step to reduce the moisture content of the liquid ferrous sulfate to 30% or less takes a long time, making it difficult to further increase productivity.

[0019] The reason is that although the manufacturing method using liquid-liquid reaction can achieve superior results compared to the manufacturing method using solid-liquid reaction, some unreacted substances were detected. Upon investigating the cause, it was found that as time passed during the manufacturing process, the temperature decreased and the included moisture evaporated due to the temperature, causing the viscosity to increase and resulting in a decrease in the frequency of collisions. Consequently, the reaction was not complete and unreacted substances remained in a limited area.

[0020] Another reason is that during the manufacturing process, the surface is exposed to air to form a film, creating a temperature difference between the inside and outside and restricting the movement of reactive substances, which makes it difficult to mass-produce high-quality ferrous sulfate.

[0021] To this end, some manufacturers have used mechanical mixing reactions with mixing stirrers, but this only provides partial improvement, and especially when the viscosity is high, there is almost no effect from mixing.

[0022] [Prior Art Literature]

[0023] [Patent Literature]

[0024] (Patent Document 1) Republic of Korea Published Patent Application No. 10-2022-0087915 (Published June 27, 2022) 'Method for manufacturing ferrous sulfate'

[0025] (Patent Document 2) Republic of Korea Registered Patent Publication No. 10-2669586 (Published May 28, 2024) 'Method for producing ferrous sulfate by sol-forming treatment of iron material'

[0026] (Patent Document 3) Republic of Korea Registered Patent Publication No. 10-1966060 (Published April 5, 2019) 'Method for obtaining iron sulfate powder from iron-containing sludge, a byproduct of steelmaking dust recycling'

[0027] (Patent Document 4) Republic of Korea Published Patent Application No. 10-2013-0109968 (Published Oct. 08, 2013) 'Process for manufacturing ferrous sulfate monohydrate'

[0028] The present invention has been developed in consideration of the aforementioned conventional problems and prior art. The objective of the present invention is to provide a method for manufacturing ferrous sulfate using microwaves, which enables the mass production of ferrous sulfate from iron waste and aqueous waste sulfuric acid solutions generated in large quantities during the production of semiconductors, fertilizers, paper, leather, etc., thereby conserving resources, replacing high-cost waste treatment, and maximizing the effect of recycling by manufacturing ferrous sulfate that can be utilized in industry.

[0029] To achieve the above objective, the present invention utilizes iron waste (a general term for iron waste containing ferrous oxide) or waste sulfuric acid, but

[0030] Condition 1: Combination of recycled iron waste ferrous oxide and aqueous waste sulfuric acid solution

[0031] Condition 2: Combination of iron waste and aqueous sulfuric acid solution recycled from waste sulfuric acid

[0032] Condition 3: Combination of iron waste and aqueous waste sulfuric acid solution

[0033] Condition 4: Combination of ferrous oxide recycled from iron waste and aqueous sulfuric acid solution recycled from waste sulfuric acid

[0034] A manufacturing method capable of obtaining high-quality ferrous sulfate from waste is characterized by the following steps: a step of preparing an iron oxide raw material, wherein the waste of any one or a combination of two of the above conditions 1 to 4 is recycled, and ferrous oxide recycled from iron waste or iron waste is prepared as a raw material; a pretreatment step of making iron oxide fine particles from the iron oxide raw material; a sol treatment step of mixing a solvent with the iron oxide fine particles to perform sol treatment; a chemical reaction step of obtaining liquid ferrous sulfate by a primary reaction in which an aqueous solution of waste sulfuric acid or an aqueous solution of sulfuric acid recycled from waste sulfuric acid is mixed with the sol-treated mixture; and a molecular vibration reaction step of causing a secondary reaction by applying microwaves to the liquid ferrous sulfate.

[0035] In the above molecular vibration reaction step, the microwave that generates heat by vibration to cause the unreacted iron oxide fine particles, the unreacted sulfuric acid aqueous solution, and the water molecules in the aqueous solution to react with each other is characterized by having a wavelength of 1 mm to 1 M, a frequency of 300 MHz to 300 GHz, and an output of 500 W to 500 KW per unit module.

[0036] The above sol treatment step is characterized by including a dispersant added when mixing iron oxide fine particles and a solvent, and the iron waste is one or more of steel sludge, iron scrap, an oxide layer such as mill scale, iron ore, and iron powder, and the waste sulfuric acid aqueous solution is characterized by using industrial waste containing a sulfuric acid aqueous solution.

[0037] The present invention has the effect of enabling the production of uniform, high-quality ferrous sulfate by first treating iron oxide fine particles made from iron waste or iron oxide recycled from iron waste into a sol, and then sequentially performing a chemical reaction step and a molecular vibration reaction step of the contained material by microwaves to ensure a uniform reaction under conditions with the highest collision frequency.

[0038] In addition, by increasing the frequency of intermolecular collisions through the above two reaction steps, moisture can be removed and a large amount of low-cost ferrous sulfate can be obtained with high yield through heat generated by the molecular vibration of the contained material by microwaves without external heating conditions to lower the moisture content, thus saving resources and having the effect of recycling iron waste and waste sulfuric acid.

[0039] In particular, the present invention enables a reaction regardless of changes in temperature or viscosity due to the passage of reaction time or seasonal changes; since the reaction occurs internally, drying also begins internally and propagates externally, thus eliminating film formation; it is unaffected by seasonal temperature changes; and because it utilizes heat generated by molecular vibrations, it enables a reaction with a high collision frequency; there is no concern about oxidation, so product quality is not affected; and since it facilitates mass production with a high yield free of unreacted materials, it offers highly economical benefits and is applicable to industry.

[0040] FIG. 1 is a block diagram showing the ferrous sulfate manufacturing process of the present invention as one embodiment.

[0041] FIG. 2 is a block diagram showing the ferrous sulfate manufacturing process of the present invention as another embodiment.

[0042]

[0043] [Explanation of the symbol]

[0044] S100: Iron oxide raw material preparation stage

[0045] S200: Preprocessing step

[0046] S300: Sol formation treatment step

[0047] S400: Chemical reaction step (first-order reaction)

[0048] S500: Molecular vibration reaction step (secondary reaction)

[0049] The following description regarding the present invention is merely an example for structural or functional explanation, and therefore the scope of the present invention shall not be interpreted as being limited by the examples specified in the text.

[0050] That is, since the embodiments can be modified in various ways and can take various forms, the scope of the present invention should be understood to include equivalents capable of realizing the technical concept.

[0051] Furthermore, the purposes or effects presented in this invention do not imply that specific embodiments must include all of them or only such effects; therefore, the scope of the rights of this invention should not be understood as being limited by them.

[0052] The preferred technical configuration and operation for implementing the present invention will be described in more detail below with reference to the attached drawings.

[0053] FIG. 1 is a block diagram showing the ferrous sulfate manufacturing process of the present invention as one embodiment, and FIG. 2 is a block diagram showing the ferrous sulfate manufacturing process of the present invention as another embodiment.

[0054] As described herein, the method for producing ferrous sulfate according to the present invention utilizes iron waste (collectively referred to as iron waste containing ferrous oxide) or waste sulfuric acid,

[0055] Condition 1: Combination of recycled iron waste ferrous oxide and aqueous waste sulfuric acid solution

[0056] Condition 2: Combination of iron waste and aqueous sulfuric acid solution recycled from waste sulfuric acid

[0057] Condition 3: Combination of iron waste and aqueous waste sulfuric acid solution

[0058] Condition 4: Combination of ferrous oxide recycled from iron waste and aqueous sulfuric acid solution recycled from waste sulfuric acid

[0059] It is characterized by obtaining ferrous sulfate by recycling waste according to any one or a combination of two of the above conditions 1 to 4.

[0060] The present invention is characterized by comprising: a step of preparing an iron oxide raw material, wherein one or two of the waste materials of conditions 1 to 4 are recycled, and the iron waste or ferrous oxide recycled from iron waste is prepared as an iron oxide raw material; a pretreatment step of making iron oxide fine particles from the prepared iron oxide raw material; a sol treatment step of mixing a solvent with the iron oxide fine particles to perform sol treatment; a chemical reaction step of obtaining liquid ferrous sulfate by a chemical reaction (first reaction) in which an aqueous solution of waste sulfuric acid or an aqueous solution of sulfuric acid recycled from waste sulfuric acid is mixed with the sol-treated mixture; and a molecular vibration reaction step of applying microwaves to the liquid ferrous sulfate to perform a second reaction.

[0061] However, since using commercially available ferrous oxide and commercially available sulfuric acid is expensive, the present invention provides an alternative to this by using waste materials as they are or recycling them as per conditions 1 to 4 above, and by using a primary chemical reaction with an aqueous sulfuric acid solution and a secondary reaction in which the collision frequency between water molecules, ferrous oxide molecules, and sulfuric acid molecules is maximized by microwaves, thereby enabling the mass production of uniform and high-quality ferrous sulfate.

[0062] The above steps in the manufacturing method of the present invention are specifically explained as follows.

[0063] <Iron Oxide Raw Material Preparation Stage>

[0064] The iron oxide raw material preparation step (S100) is a step of preparing iron waste containing iron oxide material or ferrous oxide recycled from iron waste as a raw material.

[0065] The iron waste, which is the iron oxide raw material mentioned above, may be one or more of steel sludge, which is steel particles contained in the atmosphere at a steel plant settled by water spraying, iron scrap, or mill scale, which is an oxide layer produced during the rolling or heat treatment process of steel products. In addition to the iron waste mentioned above, any material containing iron, such as mined iron ore, may be used.

[0066] In the above iron oxide raw material preparation step (S100), the moisture content of the iron waste can be said to be approximately 20%. If it is necessary to store the iron oxide raw material prepared in the above iron oxide raw material preparation step for a long period, it is preferable to store it by adding an antioxidant in a weight ratio of 100:0.01 to 0.1 relative to the iron oxide raw material.

[0067] Then, the process of ferrous oxide (FeO) being oxidized to ferric oxide (Fe2O3) can be prevented, so the oxidative corrosion of the iron oxide raw material can be effectively prevented even when the prepared iron oxide raw material is stored for a long period.

[0068]

[0069] <Preprocessing Step>

[0070] The pretreatment step (S200) is a step of grinding the iron oxide raw material prepared in the iron oxide raw material preparation step into iron fine particles with a size of '0.1 to 100,000 micrometers (um)'.

[0071] The above pretreatment step may further include a 'pre-pretreatment step' in which the moisture of the iron oxide raw material prepared in the above raw material preparation step is first dried in a dryer.

[0072] That is, in the case where the iron oxide raw material in the above raw material preparation step is steel sludge, it has a moisture content of about 20%, so it is desirable to first perform a pretreatment step in which such iron oxide raw material is placed in a dryer and dried with hot air or a heater to make the moisture content constant at about 10%.

[0073] As described above, the iron oxide raw material dried to a moisture content of about 10% can become recycled waste through a drying process in a pretreatment step of drying steel sludge corresponding to waste, and here, when the iron material of the crushed iron oxide raw material is dried to a moisture content of about 10%, it can be rapidly processed into significantly fine iron particles.

[0074]

[0075] <SOL processing step>

[0076] The sol treatment step (S300) is a step in which a solvent is mixed with the iron oxide microparticles from the pretreatment step to disperse the iron oxide microparticles in a colloid and suspension state within the liquid solvent.

[0077] The above colloidal state refers to a state in which fine particles larger than ordinary molecules or ions, with a diameter of about 0.1 to 100,000 μm (micrometers), are dispersed in a liquid, and the above suspension state refers to a state in which solid particles larger than the particles in the above colloidal state are dispersed.

[0078] In addition, the colloid and suspension state of the sol-forming treatment step (S300) is an emulsion state in which a solution mixed with colloid and suspension is sol-formed. And the solvent in the sol-forming treatment step includes water.

[0079] Here, it is preferable to mix the iron oxide fine particles and the solvent in a weight ratio of 100 iron oxide fine particles to 20 to 200 solvent.

[0080] That is, if the solvent is less than 20, the iron oxide fine particles tend to settle without being effectively dispersed, and if the solvent exceeds 200, there is a problem that it is too dilute and difficult to solidify the product. In addition, when mixed with the solvent, a dispersant may be added to increase the dispersion rate of the iron oxide fine particles and prevent the settling of the iron oxide fine particles.

[0081] At this time, it is preferable to mix the iron oxide fine particles, solvent, and dispersant in a weight ratio of 100 iron oxide fine particles : 20 to 200 solvent : 0.01 to 5 dispersant so that the settling of the iron oxide fine particles can be prevented and they can be dispersed into a jelly-like state without flow.

[0082]

[0083] Chemical reaction steps

[0084] The chemical reaction step (S400) is a step in which an aqueous solution of waste sulfuric acid or an aqueous solution of sulfuric acid recycled from waste sulfuric acid is mixed in a predetermined ratio with a liquid in which the iron oxide fine particles are dispersed after sol treatment, so that ferrous sulfate is produced in a liquid state through a chemical reaction (first reaction).

[0085] Here, the aforementioned aqueous waste sulfuric acid solution is a waste product generated in large quantities during the production of semiconductors, fertilizers, paper, leather, etc.

[0086] In addition, as described above, the liquid in which iron oxide fine particles are well dispersed by the sol treatment improves mobility and simultaneously increases chemical reactivity with sulfuric acid, thereby increasing the yield.

[0087] Here, if the mixing ratio of the above waste sulfuric acid solution or the sulfuric acid solution recycled from waste sulfuric acid is less than 0.1, the chemical reaction rate decreases, and the productivity of ferrous sulfate decreases. If the mixing ratio of waste sulfuric acid or recycled sulfuric acid is greater than 2, drying is slow, so it takes a long time to obtain ferrous sulfate, and residual sulfuric acid is generated, which lowers the performance of the cement.

[0088]

[0089] Therefore, it is preferable to mix the above-mentioned sol-treated liquid with the waste sulfuric acid aqueous solution or the sulfuric acid aqueous solution recycled from waste sulfuric acid in a ratio within the range of 1:0.1 to 2.

[0090]

[0091] <Molecular Vibration Reaction Step>

[0092] The molecular vibration reaction step (S500) is a step in which the iron material is uniformly subjected to a secondary reaction using heat generated by applying energy of vibration of unreacted iron oxide, unreacted sulfuric acid, and water molecules in an aqueous solution to the liquid ferrous sulfate obtained in the chemical reaction step using microwaves, which are one of the electromagnetic waves.

[0093] Electromagnetic waves include X-rays, ultraviolet rays, visible light, infrared rays, microwaves, and radio waves. This invention utilizes the dielectric heating properties of microwaves, which allow for excellent heat generation results when the material molecules are vibrated by irradiating microwaves onto unreacted substances remaining in an aqueous solution of liquid ferrous sulfate obtained from a chemical reaction of adding sulfuric acid solution to iron oxide with added water.

[0094] This molecular vibration reaction step is characterized by causing unreacted iron oxide fine particles, unreacted sulfuric acid aqueous solution, and water molecules in the aqueous solution to react with each other using heat generated by applying vibrations by microwaves, wherein the microwaves have a wavelength of 1 mm to 1 M, a frequency of 300 MHz to 300 GHz, and an output of 500 W to 500 KW per unit module.

[0095] In other words, microwaves, which are electromagnetic waves, transmit vibrational energy to the molecules of unreacted substances remaining in the aqueous solution state from the ferrous sulfate produced in the liquid state at the speed of light, thereby causing a uniform reaction under conditions with the highest collision frequency.

[0096] In addition, when microwave energy is applied to a mixture, the microwave beam penetrates deep into the mixture and initiates a reaction from within, exhibiting excellent reactivity. Furthermore, as it is absorbed by polar molecules in both liquids and solids, it causes unreacted substances and water molecules to vibrate rapidly, thereby generating significant thermal energy and enabling the uniform production of high-quality ferrous sulfate.

[0097] In addition, since the internal water remaining in the liquid ferrous sulfate can be easily discharged to the outside due to the significant thermal energy generated as described above, the final drying process to reduce the moisture content of the ferrous sulfate to 30% or less is unnecessary after the molecular vibration reaction step. In other words, energy efficiency can be maximized with only the molecular vibration reaction step without external heating conditions.

[0098] In addition, although an aging step is required during the process to obtain ferrous sulfate heptahydrate, the above molecular vibration reaction step can easily produce heptahydrate using the energy of water molecule vibrations, so an aging step is not required, and thus it can be said that productivity is excellent.

[0099] The method for producing ferrous sulfate according to the present invention recycles iron waste such as steelmaking sludge, iron scrap, and mill scale, and uses waste sulfuric acid, while obtaining ferrous sulfate with a yield that is about 20 to 30 percent higher than the conventional method of reacting liquids with liquids.

[0100] In addition, if the manufacturing method of the present invention is established as a continuous production system, mass production is possible, thereby enabling the provision of ferrous sulfate, which is widely used across various industries such as wastewater treatment and cement production, at the lowest possible production cost.

[0101] In this invention, the iron oxide raw material preparation step may be a step of preparing iron waste containing ferrous oxide or recycled iron waste as an iron oxide raw material, and the sulfuric acid aqueous solution mixed in the chemical reaction step may be waste sulfuric acid or recycled sulfuric acid, and high-quality ferrous sulfate can be obtained by sequentially performing the steps from the <iron oxide raw material preparation step> to the <molecular vibration reaction step> with such ferrous oxide and sulfuric acid.

[0102] Although the invention made by the inventors has been specifically described according to the above embodiments, it is obvious to those skilled in the art that the invention is not limited to the above embodiments and can be modified in various ways without departing from the gist thereof.

Claims

1. Use iron waste (a general term for iron waste containing ferrous oxide) or waste sulfuric acid, but Condition 1: Combination of recycled iron waste ferrous oxide and aqueous waste sulfuric acid solution Condition 2: Combination of iron waste and aqueous sulfuric acid solution recycled from waste sulfuric acid Condition 3: Combination of iron waste and aqueous waste sulfuric acid solution Condition 4: Combination of ferrous oxide recycled from iron waste and aqueous sulfuric acid solution recycled from waste sulfuric acid By recycling waste according to any one or a combination of two of the above conditions 1 to 4, - Iron oxide raw material preparation stage, which prepares iron waste or ferrous oxide recycled from iron waste as a raw material; - Pretreatment step for producing iron oxide fine particles using prepared iron oxide raw materials; - Sol formation treatment step in which iron oxide fine particles are mixed with a solvent to form a sol; - A chemical reaction step to obtain liquid ferrous sulfate by a primary reaction in which an aqueous solution of waste sulfuric acid or an aqueous solution of recycled waste sulfuric acid is mixed into a sol-formed mixture; - A molecular vibration reaction step in which microwaves are applied to the above liquid ferrous sulfate to induce a secondary reaction; A method for producing ferrous sulfate using microwaves characterized by being made of 2. In Paragraph 1, The preprocessing step is, The step of producing iron oxide fine particles by grinding the prepared iron oxide raw material to a size of '0.1 to 100,000 micrometers (um)', and The sol treatment step is, This is a step in which iron oxide microparticles are dispersed in a liquid solvent in a colloidal and suspension state and mixed into a sol to form an emulsion. The chemical reaction step is, A step in which ferrous sulfate is produced in a liquid state by a chemical reaction in which an aqueous solution of waste sulfuric acid or an aqueous solution of sulfuric acid recycled from waste sulfuric acid is mixed with a liquid mixture treated for solification in a ratio of 1:0.1 to 2. The molecular vibration reaction step is, A step of uniformly carrying out a secondary reaction using heat generated by applying energy from the vibrations of water molecules in unreacted iron oxide, unreacted sulfuric acid, and water in an aqueous solution using microwaves. A method for producing ferrous sulfate using microwaves, characterized by being able to obtain ferrous sulfate without external heating conditions.

3. In Paragraph 1 or 2, The microwaves in the molecular vibration reaction stage are, A method for producing ferrous sulfate using microwaves characterized by a wavelength of 1 mm to 1 M, a frequency of 300 MHz to 300 GHz, and an output of 500 W to 500 KW per unit module.

4. In Paragraph 1 or 2, The sol treatment step includes a dispersant added during the mixing of iron oxide fine particles and a solvent, and A method for producing ferrous sulfate using microwaves, characterized in that the mixing ratio of iron oxide fine particles, solvent, and dispersant is 100 : 20 to 200 : 0.01 to 5 by weight of iron oxide fine particles : solvent : dispersant.

5. In Paragraph 1 or 2, If there is a need to store the iron oxide raw material prepared during the iron oxide raw material preparation stage for a long period A method for producing ferrous sulfate using microwaves, characterized by adding and storing an antioxidant in a weight ratio of 100:0.01 to 0.1 relative to the iron oxide raw material to prevent the oxidation of ferrous oxide (FeO) into ferric oxide (Fe2O3).

6. In Paragraph 1 or 2, The iron oxide raw material is one or more of the following iron wastes: steel sludge, iron scrap (scrap metal), mill scale (oxide layer), iron ore, and iron powder, or mined iron ore raw material, and A method for producing ferrous sulfate using microwaves, characterized in that the waste sulfuric acid aqueous solution contains a sulfuric acid aqueous solution.

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