Method for producing iron (III) oxide using mill scale and iron (III) oxide for lfp

Abstract

A method for producing iron (III) oxide using mill scale comprises: a step of preparing mill scale; a leaching step of leaching an Fe component by introducing the mill scale into a strong acid; an impurity removal step of removing impurities from a leachate obtained in the leaching step; an iron oxide (III) precipitation step of precipitating iron oxide (III) by oxidizing the solution from which impurities are removed; a washing step of washing the precipitated iron oxide (III); and a drying step of drying the washed iron oxide (III). The iron(III) oxide includes 99 wt% or more of Fe2O3 derived from mill scale, less than 0.02 wt% of Al2O3, less than 0.05 wt% of SiO2, and less than 0.2 wt% of Cr2O3, and may be used as a raw material for preparing lithium iron phosphate.

Description

Method for producing iron oxide (III) using mill scale and iron oxide (III) for LFP

[0001] A method for manufacturing iron oxide (III) using mill scale and the manufactured iron oxide (III) for LFP (Lithium Ferro Phosphate) are provided. More specifically, a method for manufacturing high-purity iron oxide (III) using mill scale as a raw material and the manufactured iron oxide (III) for LFP are provided.

[0002] This application claims priority to Korean Patent Application No. 10-2024-0190796, filed on December 19, 2024, the entire contents of which are incorporated herein by reference.

[0003] Mill scale is a thin, black film formed on the surface of iron when it is processed at high temperatures during the steelmaking process. For example, mill scale is a byproduct generated when iron comes into contact with air at high temperatures and can be produced during high-temperature processes such as rolling, heat treatment, and forging in steel mills. Additionally, mill scale has a purity of approximately 91% based on FeO. As such, mill scale, produced as a byproduct of steel mills, is generally recycled as a raw material for iron or steelmaking.

[0004] Meanwhile, among secondary batteries, lithium-ion batteries can be broadly classified based on the cathode material into lithium cobalt batteries (LCO), which use only cobalt; lithium high-nickel batteries, which reduce the proportion of cobalt and primarily use nickel; and lithium iron phosphate (LFP) batteries, which use iron phosphate instead of cobalt. Among these, lithium iron phosphate batteries are currently being developed and utilized as batteries for electric vehicles because, although they have a lower energy density than other types of lithium-ion batteries, they offer superior safety and are economical. To manufacture the lithium iron phosphate used as the cathode material for these batteries, iron components are required as raw materials, and methods to produce lithium iron phosphate using various forms of iron are currently being researched.

[0005] One embodiment of the present invention is to produce high-purity iron oxide (III) using mill scale produced as a byproduct of a steel mill as a raw material, and to use it as a raw material for the production of lithium iron phosphate, which is a cathode material for a lithium iron phosphate battery.

[0006] In addition to the above-mentioned tasks, embodiments according to the present invention may be used to achieve other tasks not specifically mentioned.

[0007] A method for manufacturing iron oxide (III) using mill scale according to one embodiment of the present invention comprises: a step of preparing mill scale; a leaching step of leaching Fe components by introducing the mill scale into a strong acid; an impurity removal step of removing impurities from the leaching solution obtained in the leaching step; an iron oxide (III) precipitation step of precipitating iron oxide (III) by oxidizing the solution from which impurities have been removed; a washing step of washing the precipitated iron oxide (III); and a drying step of drying the washed iron oxide (III).

[0008] In one embodiment, the iron(III) oxide precipitation step can be carried out under conditions of oxygen pressurization.

[0009] In one embodiment, the iron oxide (III) precipitation step can precipitate nano-sized iron oxide (III).

[0010] In one embodiment, the iron oxide (III) precipitation step can precipitate iron oxide (III) with a purity of 99% or more.

[0011] In one embodiment, the amount of strong acid added during the leaching step may be 1 to 1.4 times the equivalent of the Fe content in the mill scale.

[0012] In one embodiment, mill scale can be added to the leachate and reacted during the impurity removal step.

[0013] In one embodiment, the residue after the reaction in the impurity removal step can be transferred to the leaching step.

[0014] In one embodiment, deionized water and a pH adjuster may be added during the washing step.

[0015] In one embodiment, the washing water used in the washing step can be transferred to the iron(III) oxide precipitation step and recycled.

[0016] In one embodiment, a method for producing iron oxide (III) using mill scale may further include a concentration control step for controlling the concentration of the Fe component in the leaching solution obtained in the leaching step.

[0017] In one embodiment, the concentration of the Fe component in the leaching solution can be controlled by controlling the amount of deionized water input during the concentration control step.

[0018] In one embodiment, the solution after precipitation in the iron(III) oxide precipitation step can be transferred to a concentration control step and recycled.

[0019] In one embodiment, the washing water used in the washing step can be transferred to the concentration control step and recycled.

[0020] Iron oxide (III) according to one embodiment of the present invention comprises Fe2O 399 wt% or more derived from mill scale, Al2O 30.02 wt% or less, SiO 20.05 wt% or less, and Cr2O 30.2 wt% or less, and can be used as a raw material for the manufacture of lithium iron phosphate.

[0021] In one embodiment, iron oxide (III) may contain less than 0.08 wt% P2O and less than 0.04 wt% SO3.

[0022] In one embodiment, iron oxide (III) may contain less than 0.3 wt% of CaO and less than 0.04 wt% of MnO and less than 0.08 wt% of P2O.

[0023] According to a method for manufacturing iron oxide (III) according to one embodiment of the present invention, iron oxide (III) having a high purity of 99% or more can be manufactured using mill scale having a low purity of about 91% based on FeO as a raw material. Mill scale was conventionally recycled as a raw material for iron or steelmaking, but according to one embodiment of the present invention, high-purity iron oxide (III) manufactured from mill scale can be used to manufacture lithium iron phosphate, which is a cathode material for a lithium iron phosphate battery.

[0024] According to a method for manufacturing iron oxide (III) according to one embodiment of the present invention, high-purity iron oxide (III) of nano size can be manufactured under high temperature and high pressure conditions.

[0025] According to a method for manufacturing iron oxide (III) according to one embodiment of the present invention, filtration and washing process conditions can be derived by applying pH conditions in which the cohesive force of iron oxide (III) of small particle size is maintained.

[0026] FIG. 1 is a schematic flowchart of a method for manufacturing iron oxide (III) using mill scale according to one embodiment of the present invention.

[0027] FIG. 2 is a detailed flowchart of a method for manufacturing iron oxide (III) using mill scale according to one embodiment of the present invention.

[0028] Figure 3a is a photograph showing mill scale used as a raw material, and Figure 3b is a photograph showing iron oxide (III) produced.

[0029] Figure 4 is a graph showing the amount of Fe component leached according to the amount of hydrochloric acid added in the leaching process.

[0030] Embodiments of the present invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. In the drawings, parts unrelated to the explanation have been omitted to clearly explain the invention, and the same reference numerals are used for identical or similar components throughout the specification. Furthermore, specific descriptions of widely known prior art are omitted.

[0031] Throughout the specification, technical terms used are intended merely to refer to specific embodiments and are not intended to limit the invention. Throughout the specification, singular forms used include plural forms unless phrases clearly indicate otherwise.

[0032] Throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0033] Then, the method for manufacturing iron oxide (III) according to an embodiment of the present invention and the manufactured iron oxide (III) for LFP will be described in detail.

[0034] FIG. 1 is a schematic flowchart of a method for manufacturing iron oxide (III) using mill scale according to one embodiment of the present invention, FIG. 2 is a detailed flowchart of a method for manufacturing iron oxide (III) using mill scale according to one embodiment of the present invention, FIG. 3a is a photograph showing mill scale used as a raw material, and FIG. 3b is a photograph showing manufactured iron oxide (III). The flowcharts of FIG. 1 and FIG. 2 are merely for illustrating the present invention, and the present invention is not limited to these flowcharts.

[0035] First, a process for preparing mill scale is performed (S10).

[0036] Mill scale is a thin, black film formed on the surface of iron when it is processed at high temperatures during the steelmaking process. For example, mill scale is a byproduct generated when iron comes into contact with air at high temperatures and can be produced during high-temperature processes such as rolling, heat treatment, and forging in steel mills. Additionally, mill scale can have a low purity of approximately 91% or less based on FeO.

[0037] A leaching process is performed by introducing mill scale into strong acid to leach out the Fe component (S20).

[0038] For example, strong acids such as hydrochloric acid, sulfuric acid, and nitric acid can be used. However, if sulfuric acid is used, gypsum (CaSO4·2H2O) may be formed by reaction with CaO during the mill scale leaching process; consequently, reaction efficiency may decrease due to impurities in the form of CaSO4 during the subsequent high-temperature, high-pressure iron oxide precipitation step. If nitric acid is used, it acts as an oxidizing agent and can oxidize leached Fe(2+) to Fe(3+); consequently, Fe(OH)3 may be formed during the subsequent impurity removal step, resulting in Fe loss. However, when hydrochloric acid is used as a leaching agent, the highest recovery rate and high-purity iron oxide can be obtained compared to other strong acid leaching agents.

[0039] The hydrochloric acid used may be hydrochloric acid with a concentration of about 30% to about 35% without a separate dilution step. If hydrochloric acid with a concentration of less than 20% is used, the leaching time of mill scale is prolonged, and Fe(2+) may naturally oxidize to Fe(3+) by reacting with air in the atmosphere; therefore, avoiding the use of diluted hydrochloric acid as much as possible can shorten the reaction time and increase reaction efficiency. In addition, oxidation can be delayed as much as possible as the leached Fe ions precipitate in the form of FeCl2 due to differences in solubility.

[0040] The leaching process must be carried out quickly to minimize the oxidation of the leached Fe(2+), but since hydrochloric acid vaporizes into a gaseous state if the leaching temperature is too high, the leaching temperature must not exceed 70°C, which is the boiling point of 34% hydrochloric acid, and can be stably carried out at approximately 50°C to approximately 70°C for approximately 3 to 5 hours. Furthermore, the leaching process can be carried out at approximately 55°C to approximately 65°C for approximately 3.5 to 4.5 hours, influenced by the non-uniform size of the mill scale, and the highest leaching rate can be secured when carried out within this temperature and time range.

[0041] In the leaching process, the amount of strong acid added may be approximately 1 to 1.4 times the equivalent of the Fe content in the mill scale. If the amount of strong acid added is lower than approximately 1 times the equivalent of the Fe content in the mill scale, the leaching rate of the Fe component is low, resulting in a lower ratio of Fe to impurities, which may affect the purity of the iron oxide. If it is greater than approximately 1.4 times the equivalent, the excess hydrochloric acid equivalent remains in the leaching solution, causing the pH of the leaching solution to decrease and potentially increasing the amount of neutralizing agent added. Furthermore, the amount of strong acid added may be approximately 1.25 to 1.35 times the equivalent of the Fe content in the mill scale; when within this range of equivalents, the leaching rate of the Fe component is maximized, the ratio of Fe to impurities is highest, and the pH of the leaching solution can be controlled to a level of approximately 1.3 to 1.5.

[0042] After leaching, the leaching rate of Fe components in the solution is 95% or more, the leaching rate of Al components is less than 30%, the leaching rate of Cr components is less than 15%, and the leaching rate of Si components is 2% or less, and the pH of the leaching solution is about 1.3 to about 1.5.

[0043] Although FeO is also contained in the leaching residue, the amount of leaching residue is very small compared to the amount of mill scale raw material, so a high leaching rate of Fe components can be secured.

[0044] A concentration control process is performed to control the concentration of the Fe component in the leachate obtained from the leachate process (S30).

[0045] FeCl2 crystals are precipitated in the solution after leaching due to the high Fe concentration, and the Fe concentration can be adjusted to suit the downstream process by controlling the amount of deionized water (DI Water) input according to the operating conditions of the downstream process. For example, since it has been shown that the iron oxide precipitation efficiency decreases when the Fe concentration in the leaching solution is 0.5M or higher, an Fe concentration of about 0.5M to about 0.6M in the leaching solution is required to secure the maximum iron oxide precipitation rate. Therefore, by using deionized water at an amount of about 9 to 12 times the amount of hydrochloric acid input and through an additional reaction of about 20 to 40 minutes at room temperature, the Fe concentration can be adjusted to about 20g / L to about 30g / L.

[0046] An impurity removal process is performed to remove impurities from the leachate (S40).

[0047] To remove residual hydrochloric acid in the leachate and eliminate impurities such as Al, Cr, and Si components resulting from the increase in pH, mill scale is added to the leachate and reacted. After the reaction, the residue can be transferred to the initial leachate process.

[0048] In the impurity removal process, the amount of mill scale added may be approximately 6% to 8% by weight based on the total amount of the leaching solution. The amount of mill scale added to the impurity removal process can be calculated by adding the amount of Fe that reacts with the remaining hydrochloric acid in the leaching solution during the impurity removal step to the amount of mill scale added to the next leaching reaction. Since the reaction rate is faster when the amount of mill scale added to the impurity removal reaction is higher, the minimum amount is approximately 6% by weight, which is the amount of mill scale required in the next step, and the maximum amount is approximately 8% by weight, which reflects the amount of Fe dissolved in the impurity removal step. If approximately 8% or more by weight is added, fluctuations occur in the amounts of hydrochloric acid and deionized water added to the next reaction, and if approximately 6% or less by weight is added, the impurity removal reaction rate may slow down.

[0049] The impurity removal process can be performed at approximately 50°C to approximately 70°C for approximately 3 to 5 hours, and when performed within this temperature and time range, residual hydrochloric acid in the leaching solution can be removed and impurities can be stably removed.

[0050] In the impurity removal process, the pH of the solution after the reaction can be adjusted to about 3.5 to about 5, and Al, Cr, etc. can be removed when the pH is in this range. Preferably, the pH of the solution after the reaction can be adjusted to a maximum of about 4 to about 4.5, and when the pH is in this range, the content of Al and Cr in the liquid after impurity removal can be controlled to 1 ppm or less.

[0051] An iron oxide (III) precipitation process is performed to precipitate iron oxide (III) by oxidizing the solution from which impurities have been removed (S50).

[0052] The iron oxide (III) precipitation process is carried out under high temperature and oxygen pressurization conditions to precipitate nano-sized high-purity iron oxide (III). For example, the iron oxide (III) precipitation process can be performed in an autoclave. Accordingly, iron oxide (III) with a purity of 99% or more and a particle size of about 180 nm to about 250 nm can be produced. The precipitated high-purity iron oxide (III) can be used to manufacture lithium iron phosphate, which is used as a cathode material for lithium iron phosphate batteries. The solution after precipitation can be transferred to a concentration control process and recycled. Additionally, the solution after precipitation can be bleed out and fed into a waste acid treatment process.

[0053] In the iron(III) oxide precipitation process, under conditions of approximately 150°C or higher, an O2 pressure of approximately 10 kgf / cm² 2 Up to about 15 kgf / cm² 2 Under these conditions, the solution from which impurities have been removed can undergo an oxidation reaction in an autoclave for approximately 2 to 4 hours. If the temperature is approximately 150°C or lower, FeOCl or β-FeOOH, rather than Fe2O3, may be mixed as the product. Since precipitation occurs exclusively in the form of Fe2O3 under conditions above approximately 150°C, reacting within the range of approximately 150°C to approximately 200°C can reduce energy loss. The O2 pressure is approximately 10 kgf / cm². 2 If the value is lower than this, Fe(2+) in the solution is not oxidized to Fe(3+), which may result in a low Fe2O3 yield. When the Fe(2+) content in the aforementioned solution is about 20 g / L to about 30 g / L, the O2 pressure is about 10 kgf / cm² 2 Up to about 15 kgf / cm² 2 This is appropriate. Approximately 15 kgf / cm² 2Although there are no issues with the product even at pressures above O2, it is desirable to maintain an appropriate O2 pressure range because manufacturing costs increase and equipment usage increases. When the iron oxide precipitation temperature is about 200℃, the precipitation reaction is completed after 2 hours, and when it is about 150℃, the reaction time may take up to 6 hours.

[0054] A washing process is performed to wash the precipitated iron oxide (III) (S60).

[0055] To remove Cl from the precipitated iron oxide (III), deionized water and a pH adjuster may be added. For example, a washing process is performed at a pH of 10 to 12 using about 4 to 6 times the volume of deionized water and a pH adjuster as the volume of the precipitated iron oxide (III). When the precipitated iron oxide (III) is washed at a pH of 10 to 12, the cohesiveness of the precipitated iron oxide (III) can be well maintained. Furthermore, when the precipitated iron oxide (III) is washed at a pH of 10.5 to 11.5, the cohesiveness of the precipitated iron oxide (III) can be best maintained.

[0056] The wash water used in the washing process can be transferred to the concentration control process and the iron(III) oxide precipitation process and recycled.

[0057] A drying process is performed to dry the washed iron oxide (III) (S70).

[0058] Washed iron oxide (III) can be dried under atmospheric conditions at 90°C for 24 hours to obtain high-purity iron oxide (III).

[0059] The manufactured iron oxide (III) contains 99 wt% or more of iron oxide (III), less than 0.02 wt% of Al2O3, less than 0.05 wt% of SiO2, more than 0 wt% of Cr2O3, and less than 0.2 wt% of iron oxide, and can be used as a raw material for the manufacture of lithium iron phosphate.

[0060] In addition, the manufactured iron oxide (III) may contain less than 0.08 wt% and more than 0 wt% of P2O5, and less than 0.04 wt% and more than 0 wt% of SO3.

[0061] In addition, the manufactured iron oxide (III) may contain less than 0.3 wt% and more than 0 wt% of CaO, and less than 0.04 wt% and more than 0 wt% of MnO.

[0062] In addition, the manufactured iron oxide (III) may contain less than 0.4 wt% Cl and more than 0 wt% SO3, less than 0.04 wt% SO3 and more than 0 wt% SO3.

[0063] The elemental content of the prepared iron(III) oxide may be Fe 61% or more, Si less than 0.07% and greater than 0%, Mn less than 0.03% and greater than 0%, Ca less than 0.03% and greater than 0%, Al less than 0.005%, Cr less than 0.08%, and Na less than 0.008%.

[0064] The present invention will be explained in more detail below with reference to examples, but the following examples are merely embodiments of the present invention and the present invention is not limited to the following examples.

[0065] Preparation Example 1: Preparation of Iron(III) Oxide

[0066] After adding mill scale to 35% hydrochloric acid, a leaching process is performed to leach Fe components at approximately 60°C for about 4 hours. During leaching, the amount of hydrochloric acid added is approximately 1 to 1.3 times the equivalent of the Fe content in the mill scale. Here, 1 equivalent is prepared with 20 g of mill scale and 34 mL of 35% hydrochloric acid, 1.1 equivalent is prepared with 10 g of mill scale and 18.5 mL of 35% hydrochloric acid, 1.2 equivalent is prepared with 10 g of mill scale and 20 mL of 35% hydrochloric acid, and 1.3 equivalent is prepared with 10 g of mill scale and 22 mL of 35% hydrochloric acid.

[0067] FeCl2 crystals are precipitated in the solution after leaching due to the high Fe concentration, and the Fe concentration is adjusted to about 20 g / L to about 30 g / L by using deionized water at about 9 to 12 times the amount of hydrochloric acid added and reacting for about 30 minutes at room temperature.

[0068] After leaching, the leaching rate of Fe components in the solution is 95% or more, the leaching rate of Al components is less than 30%, the leaching rate of Cr components is less than 15%, and the leaching rate of Si components is 2% or less, and the pH of the leaching solution is about 1.3 to about 1.5.

[0069] To remove impurities such as Al, Cr, and Si components from the leaching solution, mill scale is added at a specific gravity of about 30% by weight, and the mixture is reacted at about 60°C for about 4 hours. After the reaction, the pH of the solution is about 4 to about 4.5. The residue after the reaction is transferred to the first leaching process.

[0070] The solution from which impurities have been removed is placed in an autoclave at approximately 150°C to approximately 300°C and an O2 pressure of approximately 10 kgf / cm² 2 Up to about 15 kgf / cm² 2 Under these conditions, the reaction takes place for about 2 to 6 hours, and Fe2O3 with a purity of 99% or higher and a particle size of about 180 nm to about 250 nm is produced. The produced Fe2O3 can be used to produce lithium iron phosphate.

[0071] To remove Cl from the manufactured Fe2O3, a washing process is performed under pH conditions of pH 10 to pH 12 using deionized water and a pH adjuster in an amount of about 5 times the volume of the manufactured Fe2O3. Furthermore, when the pH is adjusted to pH 10.5 to pH 11.5, the cohesive strength of the manufactured Fe2O3 can be best maintained.

[0072] Preparation Example 2: Preparation of Iron(III) Oxide

[0073] Iron(III) oxide is prepared in the same manner as in Preparation Example 1 described above, except that 180 g of mill scale and 396 mL of 35% hydrochloric acid are used in 1.3 equivalent amounts. At this time, the leaching residue is approximately 18.93 g. Although the FeO content in the leaching residue is measured to be 46.9%, since the amount of leaching residue is very small compared to the amount of mill scale raw material, a high leaching rate of Fe components can be secured.

[0074] Results of hydrochloric acid leaching of mill scale

[0075] In the leaching process of Preparation Example 1 described above, when the amount of hydrochloric acid added is set to approximately 1, 1.1, 1.2, and 1.3 equivalents of the Fe content in the mill scale, the amount of Fe component leached is measured. The results of measuring the amount of Fe component leached are shown in FIG. 4. Referring to FIG. 4, when hydrochloric acid corresponding to 1.3 equivalents of the Fe content in the mill scale is used, the leaching rate of the Fe component can reach a maximum value. Furthermore, even if the Fe leaching rate increases, the impurity leaching rate remains stagnant.

[0076] XRF (X-ray Fluorescence) and ICP-MS (Inductively Coupled Plasma Mass Spectrometer) measurement results

[0077] When the amount of hydrochloric acid added in the leaching process of Preparation Example 1 described above is approximately 1.3 times the equivalent of the Fe content in the mill scale, the XRF measurement results and ICP-MS measurement results for the iron(III) oxide produced are shown in Table 1 and Table 2 below, respectively. Referring to Table 1, it can be seen that Fe2O3 with a purity of 99% or higher was produced.

[0078] No. Component Measurement Value 1SiO20.0401 mass%2P2O50.0313 mass%3SO30.0145 mass%4Cl0.269 mass%5CaO0.0178 mass%6MnO0.0213 mass%7Fe2O399.3 mass%

[0079] No. Component Measurement Value 1 Fe 6 4.1% 2 Si 0.049% 3 Mn 0.013% 4 Ca 0.016% 5 Al 0.003% 6 Cr 0.001% 7 Na 0.002%

[0080] Particle size measurement results

[0081] In the leaching process of the above-described manufacturing example, when the amount of hydrochloric acid added is approximately 1.3 times the equivalent of the Fe content in the mill scale, the conditions and results for particle size measurement of the iron(III) oxide produced are shown in Table 2 below. Particle size measurement is performed using a laser scattering particle size distribution analyzer. Referring to Table 2, it can be seen that Fe2O3 with a particle size of approximately 180 nm to approximately 250 nm was produced.

[0082] Division valueTransmittance(R)87.8%Transmittance(B)50.5%Circulation Speed10Agitation Speed9Ultrasonic30 secDistribution BaseVolumeRefractive Index1.2 waterMean Size192.68 nmMedian Size183.52 nmStd. Dev.71.6 nmMode Size185.1 nmDiameter on Cumulative10%: 108.5 nm30%: 150.3 nm50%: 184.5 nm70%: 221.7 nm90%: 287.8 nm

[0083] Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

Claims

1. Step of preparing the Mill Scale, A leaching step in which the above mill scale is introduced into a strong acid to leach out the Fe component, An impurity removal step for removing impurities from the leachate obtained in the above leaching step, Iron oxide (III) precipitation step in which the solution from which the above impurities have been removed is oxidized to precipitate iron oxide (III), A washing step for washing precipitated iron oxide (III), and Drying step for drying washed iron oxide (III) A method for producing iron oxide (III) using mill scale, comprising:

2. In Paragraph 1, A method for producing iron oxide (III) using mill scale, wherein the above iron oxide (III) precipitation step is carried out under conditions of oxygen pressurization.

3. In Paragraph 2, A method for manufacturing iron oxide (III) using mill scale, wherein the above iron oxide (III) precipitation step precipitates nano-sized iron oxide (III).

4. In Paragraph 3, A method for manufacturing iron oxide (III) using mill scale, wherein the above iron oxide (III) precipitation step precipitates iron oxide (III) having a purity of 99% or more.

5. In Paragraph 1, A method for producing iron oxide (III) using mill scale, wherein the amount of strong acid added in the above leaching step is 1 to 1.4 times the equivalent of the Fe content in the mill scale.

6. In Paragraph 1, A method for producing iron oxide (III) using mill scale, wherein in the impurity removal step above, mill scale is added to the leaching solution and reacted.

7. In Paragraph 6, A method for producing iron oxide (III) using mill scale, wherein the residue after reaction in the above impurity removal step is transferred to the above leaching step.

8. In Paragraph 1, A method for producing iron(III) oxide using mill scale, wherein washing water containing deionized water and a pH adjuster is introduced in the washing step above.

9. In Paragraph 8, A method for manufacturing iron oxide (III) using mill scale, wherein the washing water used in the washing step above is transferred to the iron oxide (III) precipitation step above and recycled.

10. In Paragraph 1, A method for producing iron oxide (III) using mill scale, further comprising a concentration control step for controlling the concentration of the Fe component in the leaching solution obtained in the above leaching step.

11. In Paragraph 10, A method for producing iron oxide (III) using mill scale, wherein the concentration of Fe component in the leaching solution is controlled by controlling the amount of deionized water input in the concentration control step above.

12. In Paragraph 10, A method for manufacturing iron oxide (III) using mill scale, wherein the solution after precipitation in the above iron oxide (III) precipitation step is transferred to the above concentration control step and recycled.

13. In Paragraph 10, A method for producing iron(III) oxide using mill scale, wherein washing water containing deionized water and a pH adjuster is introduced in the washing step, and the washing water used in the washing step is transferred to the concentration control step and recycled.

14. Fe2O399 wt% or more derived from mill scale, Less than 0.02 wt% of Al2O3 Less than 0.05 wt% SiO2, and Less than 0.2 wt% of Cr2O3 Iron oxide (III), which includes and is used as a raw material for the manufacture of lithium iron phosphate.

15. In Paragraph 14, The above iron(III) oxide is Less than 0.08 wt% of P2O, and Iron oxide (III), containing less than 0.04 wt% SO3.

16. In Paragraph 15, The above iron(III) oxide is Less than 0.3 wt% CaO, and Iron(III) oxide containing less than 0.04 wt% MnO.

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