A method of producing an ultra-low sulfur iron product and an ultra-low sulfur iron product

Abstract

The application discloses a method for preparing an ultra-low sulfur iron product and the ultra-low sulfur iron product, and relates to the technical field of high-purity iron products. The method comprises the following steps: obtaining a hydroxyl ferric oxide precursor; placing the hydroxyl ferric oxide precursor in a container, and keeping the temperature in the container at 400-800 DEG C; dehydrating and transforming the hydroxyl ferric oxide into a ferroferric oxide crude product; reducing the ferroferric oxide crude product into magnetite under a reducing atmosphere; oxidizing the magnetite into ferroferric oxide under an oxidizing atmosphere; repeating the reduction-oxidation steps at least once to obtain ultra-low sulfur ferroferric oxide, or repeating the reduction steps at least once to obtain ultra-low sulfur magnetite, or repeating the reduction steps at least once to reduce the ferroferric oxide into iron single substance to obtain ultra-low sulfur iron single substance. The reduction and oxidation steps are cycled to efficiently remove the sulfur wrapped in the crystal lattice and the sulfur in the deep layer of the particles, and meanwhile, the temperature of the fire desulfurization is lowered.

Description

Technical Field

[0001] This invention relates to the field of high-purity iron product technology, and in particular to a method for preparing ultra-low sulfur iron products and ultra-low sulfur iron products. Background Technology

[0002] High-purity iron-based materials (iron ingots, iron powder, ferric oxide, and magnetite) are widely used as raw materials in aerospace, electronics, and nuclear industries. Currently, most of the high-purity iron used by Chinese industries and research institutions is imported. The traditional method for producing high-purity iron is electrolysis. However, electrolysis struggles to remove elements with small potential differences from Fe, such as Co, Ni, Cr, Mn, and Cu. Electrolyzed iron often contains significant amounts of non-metallic impurities, such as C, N, H, O, and S, resulting in low product yield and complex electrolysis equipment. Due to related technological barriers, the preparation of high-purity iron in my country is still largely in the research stage.

[0003] Using high-purity ferrous sulfate as raw material, an iron hydroxide precursor is prepared through oxidation and precipitation. This precursor can then be thermally decomposed and crystallized to produce ferric oxide (Fe2O3). Reduction of Fe2O3 can yield elemental iron or magnetite (Fe3O4). This process provides an alternative route for the preparation of high-purity iron. The iron hydroxide obtained through oxidation and precipitation has a high sulfur content, specifically 600-2000 ppm, requiring further deep desulfurization. Related technologies typically involve the thermal decomposition of iron hydroxide at high temperatures for further deep desulfurization. This deep desulfurization process requires temperatures as high as 1000℃, placing high demands on equipment materials and consuming significant energy.

[0004] Therefore, providing a deep desulfurization process for ferric hydroxide to prepare ultra-low sulfur iron products is extremely important for the industrial production of high-purity iron products. Summary of the Invention

[0005] This invention discloses a method for preparing ultra-low sulfur iron products and the ultra-low sulfur iron products themselves, in order to solve the technical problem in related technologies that the thermal decomposition of ferric hydroxide at high temperatures requires high temperatures.

[0006] To solve the above problems, the present invention adopts the following technical solution: The first aspect of the present invention provides a method for preparing ultra-low sulfur iron products.

[0007] The method for preparing ultra-low sulfur iron products according to the present invention includes the following steps: Step 100: Obtain the ferric hydroxide precursor; Step 200: Place the ferric hydroxide precursor in a container and maintain the temperature inside the container at 400~800℃. The ferric hydroxide dehydrates and crystallizes to produce crude ferric oxide. Step 300: Reduce crude ferric oxide to ferric oxide under a reducing atmosphere; Step 400: Under an oxidizing atmosphere, oxidize the iron(III) oxide obtained in step 300 to iron(II) oxide; Repeat the reduction-oxidation step at least once to obtain ultra-low sulfur ferric oxide, or repeat the reduction step at least once to obtain ultra-low sulfur ferric oxide, or repeat the reduction step at least once to reduce ferric oxide to elemental iron to obtain ultra-low sulfur elemental iron.

[0008] A second aspect of the present invention provides an ultra-low sulfur iron product.

[0009] The ultra-low sulfur iron product obtained by the method for preparing ultra-low sulfur iron products according to any one of the technical solutions of the present invention is at least one of ultra-low sulfur iron powder, ultra-low sulfur iron ingot, ultra-low sulfur iron tetroxide, and ultra-low sulfur ferric oxide, and the sulfur content in the ultra-low sulfur iron powder, the ultra-low sulfur iron ingot, the ultra-low sulfur iron tetroxide, and the ultra-low sulfur ferric oxide is less than 1 ppm.

[0010] The technical solution adopted in this invention can achieve the following beneficial effects: Firstly, iron oxides of different valence states (ferric oxide, magnetite) and elemental Fe have different crystal structures. The method for preparing ultra-low sulfur iron products in this invention involves reducing ferric oxide to magnetite or elemental iron. During this process, the removal of lattice oxygen and the migration of iron ions cause a dramatic reconstruction of the original lattice. Sulfur atoms or sulfide ions previously encased in the interstitial spaces or substitutional sites of the ferric oxide lattice are completely disrupted, forcing them to migrate to newly formed grain boundaries or particle surfaces, becoming free or being reduced by H2 to H2S gas and escaping. Then, magnetite is oxidized back to ferric oxide. This lattice reconstruction occurs again on the iron matrix that has already undergone desulfurization, preventing the re-encapsulation of sulfur. Simultaneously, residual sulfur or incompletely decomposed sulfates are oxidized to SO2 and escape.

[0011] In addition, different valence oxides of iron (Fe2O3, Fe3O3) and elemental Fe have different molar volumes. During the reduction and oxidation processes, the volume expands and contracts. Repeated volume changes can generate significant lattice stress and microcracks inside the particles, exposing sulfur-containing impurities such as sulfate and ferrous sulfide, which were originally encased deep in the lattice or inside the dense particles, to the particle surface or gas-solid interface, providing a mass transfer channel for deep desulfurization.

[0012] The method for preparing ultra-low sulfur iron products of the present invention can overcome the limitations of gas diffusion depth and impurity encapsulation degree in a single reduction or oxidation process by repeating the reduction-oxidation step at least once, or repeating the reduction step at least once. Specifically, each phase transformation generates new cracks and exposed surfaces, and reduction and oxidation are carried out alternately, with desulfurization occurring alternately in the form of H2S and SO2, respectively. With each additional cycle, the desulfurization depth is advanced by one layer, thereby achieving efficient removal of sulfur encapsulated in the crystal lattice and sulfur deep in the particles to obtain ultra-low sulfur iron(III) oxide, ultra-low sulfur iron(II) oxide, or ultra-low sulfur iron element.

[0013] Secondly, the method for preparing ultra-low sulfur iron products of this invention, through repeated reduction-oxidation steps or repeated reduction steps for desulfurization, also helps to reduce the temperature of pyrometallurgical desulfurization, solving the technical problem in related technologies where the thermal decomposition of ferric hydroxide at high temperatures requires high temperatures. Specifically, the method for preparing ultra-low sulfur iron products of this invention can perform deep desulfurization at temperatures below 1000℃, avoiding product sintering, facilitating ultrasonic crushing to obtain nano-sized iron oxide, and ensuring the product has a bright color. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0015] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0016] In related technologies, when high-purity ferrous sulfate is used as raw material to obtain ferric hydroxide precursors through oxidation precipitation, the sulfur content in the resulting ferric hydroxide precursors is 600~2000ppm. Due to the high sulfur content in ferric hydroxide, subsequent pyrometallurgical processes typically involve thermal decomposition of the ferric hydroxide at temperatures up to 1000℃ to further desulfurize it. This process requires high-temperature resistant equipment such as corundum crucibles to accommodate the thermal decomposition temperature of ferric hydroxide, resulting in significant equipment investment, high energy consumption, and a tendency for product sintering, which is detrimental to industrialization.

[0017] Therefore, the method for preparing ultra-low sulfur iron products using ferric hydroxide in this application achieves efficient removal of sulfur encapsulated in the crystal lattice and deep-seated sulfur in the particles by cyclically performing reduction and oxidation steps, or cyclically performing reduction steps. At the same time, it also helps to reduce the temperature of pyrometallurgical desulfurization, solving the technical problem in related technologies that the thermal decomposition of ferric hydroxide at high temperatures requires a high temperature.

[0018] The method for preparing ultra-low sulfur iron products and the ultra-low sulfur iron products provided in this application are described in detail below.

[0019] The method for preparing ultra-low sulfur iron products according to the present invention includes the following steps: Step 100: Obtain the ferric hydroxyoxide precursor.

[0020] Preferably, obtaining the iron hydroxyl oxide precursor includes the following steps: Using high-purity ferrous sulfate as raw material, at least a portion of the first alkaline solution is first added to the reaction vessel to maintain an alkaline environment inside the reaction vessel. The temperature is raised and an oxidizing substance is added to the reaction vessel. Then, the ferrous sulfate aqueous solution and the remaining amount of the first alkaline solution are simultaneously and slowly pumped into the reaction vessel, or the ferrous sulfate aqueous solution is slowly pumped into the reaction vessel. After the ferrous sulfate reacts, the solution inside the reaction vessel is maintained in an alkaline environment. Stirring and aging are continued, and the mixture is filtered to obtain crude ferric hydroxide.

[0021] The crude ferric hydroxide was washed with a second alkaline solution and then dried to obtain the ferric hydroxide precursor.

[0022] In the preparation of ferric hydroxide in related technologies, alkaline solution and hydrogen peroxide solution are usually added directly to ferrous sulfate solution. With this feeding method, sulfate ions are easily and firmly adsorbed onto the FeOOH surface through coordination, and the adsorbed sulfate ions are difficult to remove by washing. In addition, when alkaline solution and hydrogen peroxide solution are added directly to ferrous sulfate solution, the concentration of free ferrous ions and sulfate ions in the system is high. Rapid local precipitation of ferrous ions may cause sulfate ions to be mechanically encapsulated inside the particles, making them difficult to remove by subsequent washing.

[0023] This application presents a method for preparing ultra-low sulfur iron products using a combination of wet and dry methods. The method involves first adding at least a portion of a first alkaline solution to a reaction vessel, followed by simultaneously and slowly pumping an aqueous solution of ferrous sulfate and the remaining first alkaline solution into the reaction vessel, or slowly pumping the aqueous solution of ferrous sulfate into the reaction vessel. Throughout the oxidation and precipitation process of ferrous ions, the pH of the reaction system is maintained in an alkaline environment. In this alkaline environment, the surface of ferric hydroxide carries a negative charge (the isoelectric point (IEP) of FeOOH is approximately pH 6.5-7.0; when the solution pH is higher than the isoelectric point, the FeOOH surface carries a negative charge), resulting in strong electrostatic repulsion with the similarly negatively charged sulfate ions. This makes it difficult for sulfate ions to approach the surface of ferric hydroxide, thereby significantly reducing the amount of sulfate ions adsorbed by ferric hydroxide. Furthermore, this method of preparing ferric hydroxide utilizes high concentrations of OH... - With SO4 2- Competing for the active sites on the surface of iron ions can further hinder the chemical adsorption of sulfate ions, while also allowing ferrous sulfate to precipitate uniformly, reducing the risk of sulfate ions being encapsulated inside the particles.

[0024] This application includes at least two feeding methods for ferrous sulfate and the first alkaline solution, which are described in detail below.

[0025] First method of adding ingredients: Add a predetermined amount of water to the reactor, add a calculated portion of the first alkaline solution to the reactor, adjust the pH of the solution in the reactor to be greater than or equal to 7.5, raise the temperature to 40~80℃, and add an oxidizing substance to the reactor. Then, simultaneously and slowly pump ferrous sulfate aqueous solution and the remaining first alkaline solution into the reactor. While simultaneously and slowly pumping ferrous sulfate aqueous solution and the remaining first alkaline solution into the reactor, maintain the pH of the solution in the reactor at 8~9.5. After the ferrous sulfate has reacted completely, continue stirring and aging, filter, and obtain crude ferric hydroxide.

[0026] This application adds a predetermined amount of water to the reactor, the amount of water being 0.8 to 1.5 times the amount of water used in the ferrous sulfate aqueous solution; or the amount of water is sufficient to adjust the pH of the solution in the reactor to 8 to 9.5. In this embodiment, by adding a predetermined amount of water, the ferrous sulfate subsequently pumped in can be diluted, further preventing the formed ferric hydroxide from becoming too viscous and causing the material to be difficult to filter; secondly, it also facilitates the stirring of the material in the reactor; and thirdly, it can adjust the pH of the reactor to a suitable value.

[0027] With this feeding method, the pH fluctuation is small throughout the oxidation and precipitation process, which keeps the surface of ferric hydroxide negatively charged. This avoids the risk of the pH dropping due to excessive iron salts in the system, which could cause the surface of ferric hydroxide to become positively charged. This can further reduce the amount of sulfate ions adsorbed by ferric hydroxide.

[0028] On the other hand, in this feeding method, ferrous sulfate and the remaining alkaline solution are introduced into the reactor in a controlled ratio. The oxidation and precipitation process of ferrous ions tends to be homogeneous nucleation and orderly growth. The resulting iron hydroxide particles have higher crystallinity, fewer crystal defects, and fewer irregular pores on the surface. This makes it difficult for sulfate ions to be encapsulated inside the particles, and also difficult for them to be fixed in the particles by lattice substitution or interlayer embedding. This can further reduce sulfur impurities in iron hydroxide.

[0029] The second method of adding ingredients: Add the calculated amount of the first alkaline solution to the reaction vessel, heat it to 40-80℃, add an oxidizing substance to the reaction vessel, and then slowly pump an aqueous solution of ferrous sulfate into the reaction vessel. After the ferrous sulfate has reacted completely, maintain the pH of the solution at 8-9.5, continue stirring and aging, filter, and obtain crude ferric hydroxide.

[0030] The statement in this application that the ferrous sulfate aqueous solution and the remaining amount of the first alkaline solution are simultaneously and slowly pumped into the reaction vessel, or that the ferrous sulfate aqueous solution is slowly pumped into the reaction vessel, means that after the ferrous sulfate is pumped into the reaction vessel, the ferrous sulfate is completely oxidized and precipitated within 3 seconds.

[0031] More preferably, the mass concentration of the ferrous sulfate aqueous solution is 2-5%. The mass concentration of the ferrous sulfate aqueous solution in this application is less than 5%, which avoids the problem of excessively viscous ferric oxide forming later, making the material difficult to filter.

[0032] More preferably, the first alkaline solution is one or more of the following: ammonia solution, ammonium carbonate solution, ammonium bicarbonate solution, urea solution, sodium hydroxide solution, sodium carbonate solution, sodium bicarbonate solution, potassium hydroxide solution, potassium carbonate solution, and potassium bicarbonate solution.

[0033] More preferably, the oxidizing agent is at least one of air, oxygen, and hydrogen peroxide solution. When the oxidizing agent includes hydrogen peroxide solution, the amount of hydrogen peroxide solution used is 1 to 1.2 times the theoretical amount, and the concentration of the hydrogen peroxide solution is 5 to 20%. Controlling the concentration of hydrogen peroxide solution to 5 to 20% allows the hydrogen peroxide solution to oxidize ferrous ions to ferric hydroxide as much as possible, avoiding the direct formation of ferrous hydroxide by high-concentration hydrogen peroxide solution with ferrous ions. Ferrous hydroxide is colloidal and difficult to filter and wash in subsequent processes.

[0034] More preferably, the aging time is 30 to 60 minutes.

[0035] In related technologies, deionized water is typically used to wash crude ferric hydroxide, but the washing effect is limited. This application uses a second alkaline solution to wash the crude ferric hydroxide. During this washing process, the ferric hydroxide remains in an alkaline environment, resulting in a strong negative charge on its surface. This strong electrostatic repulsion between the ferric hydroxide and the equally negatively charged sulfate ions facilitates the removal of sulfate ions from the surface of the ferric hydroxide particles, reducing the sulfur content in the ferric hydroxide precursor and thus improving the washing effect. Furthermore, the constant alkaline environment ensures a strong negative charge on the surface of the ferric hydroxide, preventing the adsorption of sulfate ions from the solution onto the ferric hydroxide surface. Additionally, the high concentration of OH-... - With SO4 2- Competition will reduce SO4 already adsorbed on the surface of iron hydroxide 2- Replacement can further improve the washing effect.

[0036] Preferably, the crude ferric hydroxide is washed with a second alkaline solution, comprising the following steps: Add a second alkaline solution with a pH of 8 to 14 to the crude ferric hydroxide at a solid-liquid mass ratio of 1:2 to 1:4. Stir the second alkaline solution with the crude ferric hydroxide and filter. Wash the crude ferric hydroxide with the second alkaline solution 2 to 4 times.

[0037] The crude ferric hydroxide product after alkali washing was washed again with deionized water and then dried to obtain the ferric hydroxide precursor.

[0038] More preferably, the second alkaline solution is one or more of the following: ammonia solution, ammonium carbonate solution, ammonium bicarbonate solution, urea solution, sodium hydroxide solution, sodium carbonate solution, sodium bicarbonate solution, potassium hydroxide solution, potassium carbonate solution, and potassium bicarbonate solution.

[0039] More preferably, when washing the crude ferric hydroxide product again with deionized water after alkaline washing, the solid-liquid mass ratio of the crude ferric hydroxide product to the deionized water is 1:2 to 1:4. Specifically, the washing time with deionized water should be as short as possible to avoid the re-adsorption of sulfate ions caused by a decrease in the solution pH.

[0040] For example, after washing the crude ferric hydroxide with alkaline solutions such as ammonia solution, ammonium carbonate solution, ammonium bicarbonate solution, and urea solution, deionized water rinsing is not required, as the residual ammonium salts can be completely decomposed and volatilized in the subsequent pyrometallurgical stage.

[0041] Preferably, when washing the crude ferric hydroxide product with the second alkaline solution, one or more of the following methods are also used to assist the washing process: heating, hydrogen peroxide solution, complexing agent, crushing, and ultrasonic dispersion. This can further improve the washing effect of the second alkaline solution on the crude ferric hydroxide product.

[0042] Step 200: Place the ferric hydroxide precursor in a container and maintain the temperature inside the container at 400~800℃. The ferric hydroxide dehydrates and crystallizes to produce crude ferric oxide.

[0043] This application describes the dehydration and crystallization of ferric hydroxide to produce crude ferric oxide. This process not only decomposes some sulfate ions into gaseous sulfur dioxide or sulfur trioxide, achieving a preliminary desulfurization effect, but also alters the original crystal structure of ferric hydroxide and generates new ferric oxide during the dehydration and crystallization process. This process is accompanied by severe volume shrinkage, internal stress cracking, and collapse of the original structural pores, creating numerous microcracks and pores. These microscopic defects expose the sulfate ions that were originally encapsulated or trapped inside the particles, providing conditions for subsequent deep desulfurization. This reduces the temperature required for the dehydration and crystallization of ferric hydroxide, thus lowering energy consumption.

[0044] Preferably, the dehydration and crystallization of ferric hydroxide to produce crude ferric oxide includes the following process: The ferric hydroxide precursor is placed in a container, and gas is introduced into the container from the bottom to maintain a slightly positive pressure environment, or the gas in the container is discharged to maintain a slightly negative pressure environment. The temperature inside the container is maintained at 400~800℃ for 30~180 minutes, and the ferric hydroxide is dehydrated and crystallized to produce crude ferric oxide.

[0045] For example, the step heating process is as follows: room temperature rises to 200℃ for 10 minutes; 200℃ rises to 350℃ for 60 minutes; 350℃ rises to the target temperature for 60 minutes; then the temperature is maintained for 1-3 hours.

[0046] Not limited to this, when heating up, the temperature can also be directly set to the target temperature.

[0047] Preferably, a third alkaline solution is added to the obtained crude ferric oxide product to wash the crude ferric oxide product. The pH of the third alkaline solution is 9-14.

[0048] The method of washing crude ferric oxide with a third alkaline solution is similar to the method of washing crude ferric hydroxide with a second alkaline solution, and will not be described in detail here.

[0049] Step 300: Reduce crude ferric oxide to ferric oxide under a reducing atmosphere.

[0050] Preferably, the reduction of crude ferric oxide to ferric oxide includes the following steps: The crude ferric oxide is placed in a container, and a mixture of reducing gas and inert gas is introduced into the container. Water vapor is also introduced into the container, and the temperature in the container is raised to 300~800℃ and maintained for 10~120 min. The ferric oxide is reduced to ferric oxide. The reducing gas is hydrogen or carbon monoxide, and the inert gas is nitrogen or argon, with a volume ratio of 1:99 to 10:90 between the reducing gas and the inert gas.

[0051] For example, stop introducing water vapor 30 minutes before the end of the heat preservation period.

[0052] Step 400: Under an oxidizing atmosphere, oxidize the iron(III) oxide obtained in step 300 to iron(II) oxide.

[0053] Preferably, oxidizing iron(III) oxide to iron(III) oxide includes the following steps: Purge the iron(III) oxide or elemental iron with an inert gas for 10-30 minutes, then introduce oxygen and water vapor into the iron(III) oxide or elemental iron to oxidize the iron(III) oxide or elemental iron again to ferric oxide. The oxidation temperature is 400-800℃ and the oxidation time is 10-60 minutes.

[0054] For example, stop introducing water vapor 10 minutes before the end of the heat preservation period.

[0055] By subjecting the ferric oxide obtained in step 400 to at least one reduction-oxidation step, ultra-low sulfur ferric oxide can be obtained; by subjecting the ferric oxide obtained in step 400 to another reduction step, or to at least one reduction-oxidation-reduction step, ultra-low sulfur ferric oxide can be obtained; by subjecting the ferric oxide obtained in step 400 to another reduction step, or to at least one reduction-oxidation-reduction step, ultra-low sulfur elemental iron can be obtained (in the final reduction step, ferric oxide is reduced to elemental iron).

[0056] Preferably, the number of repetitions is 1 to 3.

[0057] Preferably, the reduction of ferric oxide to elemental iron includes the following steps: Ferric oxide is placed in a container, and a reducing gas, or a mixture of reducing gas and inert gas, is introduced into the container. Water vapor is also introduced into the container, and the temperature in the container is raised to 400~800℃ and maintained for 240~480 minutes. Ferric oxide is reduced to elemental iron. The reducing gas is either hydrogen or carbon monoxide; When a mixture of reducing gas and inert gas is introduced into the container, the inert gas is nitrogen or argon, and the volume ratio of reducing gas to inert gas is greater than 10:90.

[0058] For example, stop introducing water vapor 10 minutes before the end of the heat preservation period.

[0059] This application obtains two different reduction products, ferric oxide or ferric oxide, by controlling the amount of reducing gas, the reduction temperature, and the reduction time.

[0060] Iron oxides of different valence states (ferric oxide, iron(II) oxide) and elemental Fe have different crystal structures and molar volumes. The method for preparing ultra-low sulfur iron products in this application can overcome the limitations of gas diffusion depth and impurity encapsulation in a single reduction or oxidation process by repeating the reduction-oxidation step at least once, or repeating the reduction step at least once. Specifically, each phase transition generates new cracks and exposed surfaces. Reduction and oxidation are carried out alternately, and desulfurization is carried out alternately in the form of H2S and SO2, respectively. With each additional cycle, the desulfurization depth is advanced by one layer, thereby achieving efficient removal of sulfur encapsulated in the crystal lattice and sulfur deep in the particles to obtain ultra-low sulfur iron(II), ultra-low sulfur iron(II), or ultra-low sulfur elemental Fe.

[0061] Furthermore, the method for preparing ultra-low sulfur iron products in this application, through repeated reduction-oxidation steps or repeated reduction steps for desulfurization, helps to reduce the temperature of pyrometallurgical desulfurization, solving the technical problem in related technologies where the thermal decomposition of ferric hydroxide at high temperatures requires high temperatures. Specifically, the method for preparing ultra-low sulfur iron products in this application can perform deep desulfurization at temperatures below 1000℃, avoiding product sintering, facilitating ultrasonic crushing to obtain nano-sized iron oxide, and ensuring the product has a bright color.

[0062] Preferably, a third alkaline solution is added to the obtained ultra-low sulfur ferric oxide, ultra-low sulfur ferric oxide, or ultra-low sulfur iron element, and the ultra-low sulfur ferric oxide, ultra-low sulfur ferric oxide, or ultra-low sulfur iron element is washed with the third alkaline solution. The pH of the third alkaline solution is 9-14.

[0063] The method of washing ultra-low sulfur ferric oxide, ultra-low sulfur ferric oxide, or ultra-low sulfur iron with a third alkaline solution is similar to the method of washing crude ferric hydroxide with a second alkaline solution, and will not be described in detail here.

[0064] The ultra-low sulfur iron product obtained by the method for preparing ultra-low sulfur iron products based on any of the foregoing technical solutions in this application is at least one of ultra-low sulfur iron powder, ultra-low sulfur iron ingot, ultra-low sulfur iron tetroxide, and ultra-low sulfur ferric oxide, and the sulfur content in ultra-low sulfur iron powder, ultra-low sulfur iron ingot, ultra-low sulfur iron tetroxide, and ultra-low sulfur ferric oxide is less than 1 ppm.

[0065] The method for preparing ultra-low sulfur iron products and the ultra-low sulfur iron products of this application will be described in detail below through specific embodiments.

[0066] The ferrous sulfate used in each embodiment was high-purity ferrous sulfate that had been purified and dried, and its composition was as follows: 21% sulfur, 25.8 ppm carbon, 0 ppm phosphorus, 8.4 ppm sodium, 1.6 ppm magnesium, 0.5 ppm aluminum, 1.0 ppm potassium, 2.8 ppm calcium, 1.2 ppm boron, 0.2 ppm titanium, 0.05 ppm chromium, 0.08 ppm manganese, 0.06 ppm nickel, and 0.02 ppm copper.

[0067] Example 1

[0068] The method for preparing ultra-low sulfur iron products in this embodiment includes the following steps: Step 100: Using 100g of anhydrous ferrous sulfate as raw material, dissolve the ferrous sulfate in 636g of 50℃ warm water, stir evenly, and obtain a ferrous sulfate aqueous solution with an iron mass concentration of 5% for later use.

[0069] Prepare 600g of 5% dilute ammonia solution by diluting concentrated ammonia solution for later use.

[0070] All the prepared ferrous sulfate aqueous solution was added to the reaction vessel, and the solution in the reaction vessel was heated to 50°C. Then, dilute ammonia water was pumped into the reaction vessel, and oxygen was blown into the reaction vessel at the same time. After the ferrous sulfate solution had reacted completely, the pH of the solution in the reaction vessel was 8.5. The mixture was stirred and aged for another 30 minutes, then filtered to obtain crude ferric hydroxide.

[0071] Deionized water was added to the crude ferric hydroxide at a solid-liquid mass ratio of 1:4. The crude ferric hydroxide was washed with deionized water. After washing was repeated 4 times, the filtered product was placed in an oven at 105℃ and dried for 60 min to obtain the ferric hydroxide precursor.

[0072] The amount of iron hydroxyl oxide precursor in this embodiment was 57.1 g. The impurity elements and their contents in the iron hydroxyl oxide precursor were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the iron hydroxyl oxide precursor are shown in Table 1 below.

[0073] Table 1. Impurity elements and their contents in the iron hydroxyl oxide precursor in this embodiment. Step 200: Place the ferric hydroxide precursor in a vertical furnace and heat the furnace to 600°C and maintain the temperature for 60 minutes. The ferric hydroxide undergoes dehydration and crystallization at high temperature to generate crude ferric oxide.

[0074] The crude ferric oxide (Fe₂O₃) product in this embodiment was measured to be 49.8 g. The impurity elements and their contents in the crude ferric oxide were determined using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the crude ferric oxide are shown in Table 2 below.

[0075] Table 2. Impurity elements and their contents in the crude ferric oxide product of this embodiment. The iron content in ferric oxide is 70%, and the iron content in ferric hydroxide is 62.9%. The content of some metal elements in Table 2 is higher than that in Table 1. This may be because some metal impurity ions combine with iron, and during the crystal transformation process, the iron content of the iron element increases, resulting in the enrichment of these metal impurities. Specifically, the theoretical enrichment factor is 1.11 times.

[0076] Step 300: Place ferric oxide in a reduction furnace and introduce a mixture of hydrogen and nitrogen into the furnace at a volume ratio of 5:95 and a flow rate of 0.5 L / min. Also introduce steam into the container at a flow rate of 0.5 L / min, and stop introducing steam 10 minutes before the end of the reaction. Raise the temperature in the reduction furnace to 600°C and maintain it for 60 minutes. Ferric oxide is reduced to iron(III) oxide.

[0077] The amount of iron(III) oxide in this embodiment was 47.6 g. The impurity elements and their contents in the iron(III) oxide were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the iron(III) oxide are shown in Table 3 below.

[0078] Table 3. Impurity elements and their contents in the iron(III) oxide in this embodiment. Similarly, the higher values ​​for some metals in Table 3 compared to Table 2 may be due to the reduction of ferric oxide to magnetite, resulting in increased iron content and the enrichment of some metal impurities.

[0079] Step 400: Purge the iron(III) oxide with an inert gas for 10 minutes at a flow rate of 0.5 L / min. Then, purge the iron(III) oxide with oxygen at a flow rate of 0.5 L / min. Also, purge the container with water vapor at a flow rate of 0.5 L / min. Stop purging the water vapor 10 minutes before the end of the reaction. Oxidize the iron(III) oxide again to ferric oxide at a temperature of 600℃ for 30 minutes.

[0080] Repeat steps 300 and 400 once each to obtain ultra-low sulfur ferric oxide.

[0081] The amount of ferric oxide in this embodiment was 48.6g. The impurity elements and their contents in the ferric oxide were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the ferric oxide are shown in Table 4 below.

[0082] Table 4. Impurity elements and their contents in ferric oxide in this embodiment. Example 2

[0083] The method for preparing ultra-low sulfur iron products in this embodiment differs from that in Example 1 in that steps 300 and 400 are repeated twice each to obtain ultra-low sulfur iron oxide. The remaining steps are the same as in Example 1 and will not be repeated here.

[0084] The amount of ferric oxide in this embodiment was 47.6g. The impurity elements and their contents in the ferric oxide were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the ferric oxide are shown in Table 5 below.

[0085] Table 5. Impurity elements and their contents in ferric oxide in this embodiment. Example 3

[0086] The method for preparing ultra-low sulfur iron products in this embodiment differs from that in Example 1 in that: steps 300 and 400 are repeated three times each to obtain ultra-low sulfur iron oxide. The remaining steps are the same as in Example 1 and will not be repeated here.

[0087] The amount of ferric oxide in this embodiment was 47.2g. The impurity elements and their contents in the ferric oxide were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the ferric oxide are shown in Table 6 below.

[0088] Table 6. Impurity elements and their contents in ferric oxide in this embodiment. Example 4

[0089] The method for preparing ultra-low sulfur iron products in this embodiment differs from that in Example 1 in that: ferric oxide is placed in a reduction furnace, and a mixture of hydrogen and nitrogen is introduced into the furnace, with a hydrogen to nitrogen volume ratio of 10:90. The remaining steps are the same as in Example 1 and will not be repeated here.

[0090] The amount of iron(III) oxide in this embodiment was 47.4 g. The impurity elements and their contents in the iron(III) oxide were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the iron(III) oxide are shown in Table 7 below.

[0091] Table 7. Impurity elements and their contents in the iron(III) oxide in this embodiment. Example 5

[0092] The method for preparing ultra-low sulfur iron products in this embodiment differs from that in Example 1 in that: after repeating steps 300 and 400 once each to obtain ultra-low sulfur ferric oxide, the method further includes the following steps: placing ferric oxide in a reduction furnace and introducing hydrogen gas into the furnace at a flow rate of 0.5 L / min; also introducing water vapor into a container at a flow rate of 0.5 L / min, stopping the introduction of water vapor 10 minutes before the end of the reaction; raising the temperature in the reduction furnace to 600°C and maintaining it for 360 minutes, thereby reducing ferric oxide to elemental iron. The remaining steps are the same as in Example 1 and will not be repeated here.

[0093] The amount of elemental iron in this embodiment was 32.9g. The impurity elements and their contents in the elemental iron were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the elemental iron are shown in Table 8 below.

[0094] Table 8. Impurity elements and their contents in the iron content of this embodiment. Similarly, the higher values ​​for some metals in Table 8 compared to Table 4 may be due to the reduction of ferric oxide to elemental iron, resulting in increased iron content and the enrichment of some metallic impurities.

[0095] Example 6

[0096] The method for preparing ultra-low sulfur iron products in this embodiment differs from that in Example 2 in that: after repeating steps 300 and 400 twice to obtain ultra-low sulfur ferric oxide, the method further includes the following steps: placing ferric oxide in a reduction furnace and introducing a mixture of hydrogen and nitrogen gas into the furnace at a volume ratio of 20:80 and a flow rate of 0.5 L / min; also introducing water vapor into the container at a flow rate of 0.5 L / min, stopping the introduction of water vapor 10 minutes before the end of the reaction; raising the temperature in the reduction furnace to 600°C and maintaining it for 360 minutes, thereby reducing ferric oxide to elemental iron. The remaining steps are the same as in Example 2 and will not be repeated here.

[0097] The amount of elemental iron in this embodiment was 31.5g. The impurity elements and their contents in the elemental iron were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the elemental iron are shown in Table 9 below.

[0098] Table 9. Impurity elements and their contents in the iron content of this embodiment. Example 7

[0099] The method for preparing ultra-low sulfur iron products in this embodiment differs from that in Example 1 in that steps 300 and 400 are repeated twice each to obtain ultra-low sulfur ferric oxide, and then the ultra-low sulfur ferric oxide is reduced to iron(III) oxide again. The remaining steps are the same as in Example 1 and will not be repeated here.

[0100] The amount of iron(III) oxide in this embodiment was 46.2 g. The impurity elements and their contents in the iron(III) oxide were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the iron(III) oxide are shown in Table 10 below.

[0101] Table 10. Impurity elements and their contents in the iron(III) oxide in this embodiment. Example 8

[0102] The method for preparing ultra-low sulfur iron products in this embodiment differs from that in Example 1 in that the oxidation temperature in step 400 is 400℃ and the oxidation time is 60 min. The remaining steps are the same as in Example 1 and will not be repeated here.

[0103] The amount of ferric oxide in this embodiment was 48.4 g. The impurity elements and their contents in the ferric oxide were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the ferric oxide are shown in Table 11 below.

[0104] Table 11. Impurity elements and their contents in ferric oxide in this embodiment. Example 9

[0105] The method for preparing ultra-low sulfur iron products in this embodiment differs from that in Example 1 in that the oxidation temperature in step 400 is 800℃ and the oxidation time is 10 min. The remaining steps are the same as in Example 1 and will not be repeated here.

[0106] The amount of ferric oxide in this embodiment was 48.3g. The impurity elements and their contents in the ferric oxide were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the ferric oxide are shown in Table 12 below.

[0107] Table 12. Impurity elements and their contents in ferric oxide in this embodiment. Example 10

[0108] The method for preparing ultra-low sulfur iron products in this embodiment differs from that in Example 1 in that, in step 200, the ferric hydroxide precursor is placed in a vertical furnace, and the furnace is heated to 800°C and maintained for 30 minutes. The remaining steps are the same as in Example 1 and will not be repeated here.

[0109] The crude ferric oxide (Fe₂O₃) product in this embodiment was measured to be 49.6 g. The impurity elements and their contents in the crude ferric oxide were determined using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the crude ferric oxide are shown in Table 13 below.

[0110] Table 13. Impurity elements and their contents in the crude ferric oxide product of this embodiment. Example 11

[0111] The method for preparing ultra-low sulfur iron products in this embodiment differs from that in Example 1 in that, in step 200, the ferric hydroxide precursor is placed in a vertical furnace, and the furnace is heated to 400°C and maintained for 180 minutes. The remaining steps are the same as in Example 1 and will not be repeated here.

[0112] The crude ferric oxide (Fe₂O₃) product in this embodiment was measured to be 49.3 g. The impurity elements and their contents in the crude ferric oxide were determined using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the crude ferric oxide are shown in Table 14 below.

[0113] Table 14. Impurity elements and their contents in the crude ferric oxide product of this embodiment. Example 12

[0114] The method for preparing ultra-low sulfur iron products in this embodiment differs from that in Example 1 in that, after step 400, the following steps are also included: Ammonia solution with pH 9.5 was added to ferric oxide at a solid-liquid mass ratio of 1:4. After stirring the ammonia solution and ferric oxide, the mixture was filtered. The ferric oxide was then washed twice with ammonia solution at room temperature. Deionized water was added to the ferric oxide mixture again at a solid-liquid mass ratio of 1:4, and the ferric oxide was rinsed with deionized water. The filtered product was then dried in an oven at 105°C for 60 minutes to obtain ferric oxide.

[0115] The remaining steps are the same as in Example 1, and will not be repeated here.

[0116] The amount of ferric oxide in this embodiment was 47.8g. The impurity elements and their contents in the ferric oxide were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the ferric oxide are shown in Table 15 below.

[0117] Table 15. Impurity elements and their contents in ferric oxide in this embodiment. In this embodiment, when washing ferric oxide with alkaline solution, the carbon phase is slightly reduced because alkaline washing adsorbs CO2 from the air, increasing the carbon content. This problem can be overcome by adding nitrogen protection during the washing process.

[0118] Example 13

[0119] The method for preparing ultra-low sulfur iron products in this embodiment differs from that in Example 1 in that: in step 100, crude iron hydroxyl oxide is prepared in the following manner: Using 100g of ferrous sulfate as raw material, dissolve ferrous sulfate in 636g of 50℃ warm water, stir evenly, and obtain a ferrous sulfate aqueous solution with an iron mass concentration of 5% for later use.

[0120] Prepare 600g of 5% dilute ammonia solution by diluting concentrated ammonia solution for later use.

[0121] Add 700g of water to the reactor and add dilute ammonia to adjust the pH of the solution in the reactor to 9.5. Then heat the solution in the reactor to 50℃.

[0122] Then, ferrous sulfate aqueous solution and dilute ammonia solution are slowly pumped into the reactor simultaneously, and oxygen is blown into the reactor. During this process, the pH of the solution in the reactor is maintained at 8-9.5 (if the pH is below 8, the pumping rate of dilute ammonia solution is increased; if the pH is above 9.5, the pumping rate of ferrous sulfate aqueous solution is increased).

[0123] After the ferrous sulfate solution was added, continue stirring and aging for 30 minutes, then filter to obtain crude ferric hydroxide.

[0124] Add an ammonia solution with pH 8 to the crude ferric hydroxide at a solid-liquid mass ratio of 1:4. After stirring the ammonia solution with the crude ferric hydroxide, filter the mixture and wash the crude ferric hydroxide with the ammonia solution at room temperature. Repeat the washing with the ammonia solution 4 times.

[0125] Deionized water was added to the iron hydroxyl oxide again at a solid-liquid mass ratio of 1:4. After rinsing the iron hydroxyl oxide with deionized water, the filtered product was dried in an oven at 105°C for 60 minutes to obtain the iron hydroxyl oxide precursor.

[0126] The remaining steps are the same as in Example 1, and will not be repeated here.

[0127] The amount of iron hydroxyl oxide precursor in this embodiment was 56.8 g. The impurity elements and their contents in the iron hydroxyl oxide precursor were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the iron hydroxyl oxide precursor are shown in Table 16 below.

[0128] Table 16. Impurity elements and their contents in the iron hydroxyl oxide precursor in this embodiment. The iron content in anhydrous ferrous sulfate is 36.8%, and the iron content in ferric hydroxide is 62.9%. The content of some metal elements in Table 1 is higher than that in ferrous sulfate. This may be because some metal impurity ions combine with iron. During the preparation of ferric hydroxide, the iron content of the iron element increases, resulting in the enrichment of these metal impurities.

[0129] Specifically, ferrous sulfate contains 8.4 ppm sodium, 1.6 ppm magnesium, 0.5 ppm aluminum, 1.0 ppm potassium, 2.8 ppm calcium, 1.2 ppm boron, 0.2 ppm titanium, 0.05 ppm chromium, 0.08 ppm manganese, 0.06 ppm nickel, and 0.02 ppm copper. If fully enriched, ferric hydroxide contains 14.36 ppm sodium, 2.73 ppm magnesium, 0.85 ppm aluminum, 1.71 ppm potassium, 4.79 ppm calcium, 2.05 ppm boron, 0.34 ppm titanium, 0.085 ppm chromium, 0.14 ppm manganese, 0.10 ppm nickel, and 0.034 ppm copper.

[0130] Example 14

[0131] The method for preparing ultra-low sulfur iron products in this embodiment differs from that in Example 1 in that, after obtaining crude ferric oxide in step 200, the method further includes the following steps: After the crude ferric oxide product cools down, an ammonia solution with a pH of 9.5 is added to the crude ferric oxide product at a solid-liquid mass ratio of 1:4. The ammonia solution and the crude ferric oxide product are stirred and then filtered. The crude ferric oxide product is washed with the ammonia solution at 40°C, and the washing is repeated twice with the ammonia solution.

[0132] Add deionized water to ferric oxide again at a solid-liquid mass ratio of 1:4. Rinse the ferric oxide with deionized water, and then dry the filtered product in an oven at 105°C for 60 minutes to obtain ferric oxide.

[0133] The remaining steps are the same as in Example 1, and will not be repeated here.

[0134] The amount of ferric oxide in this embodiment was 47.8g. The impurity elements and their contents in the ferric oxide were detected using an infrared carbon-sulfur analyzer and ICP-MS. The impurities in the ferric oxide are shown in Table 17 below.

[0135] Table 17. Impurity elements and their contents in ferric oxide in this embodiment. The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing ultra-low sulfur iron products, characterized in that, Includes the following steps: Step 100: Obtain the ferric hydroxide precursor; Step 200: Place the ferric hydroxide precursor in a container and maintain the temperature inside the container at 400~800℃. The ferric hydroxide dehydrates and crystallizes to produce crude ferric oxide. Step 300: Reduce crude ferric oxide to ferric oxide under a reducing atmosphere; Step 400: Under an oxidizing atmosphere, oxidize the iron(III) oxide obtained in step 300 to iron(II) oxide; Repeat the reduction-oxidation step at least once to obtain ultra-low sulfur ferric oxide, or repeat the reduction step at least once to obtain ultra-low sulfur ferric oxide, or repeat the reduction step at least once to reduce ferric oxide to elemental iron to obtain ultra-low sulfur elemental iron.

2. The method for preparing ultra-low sulfur iron products according to claim 1, characterized in that, The reduction of crude ferric oxide to ferric oxide includes the following steps: The crude ferric oxide is placed in a container, and a mixture of reducing gas and inert gas is introduced into the container. Water vapor is also introduced into the container, and the temperature in the container is raised to 300~800℃ and maintained for 10~120 min. The ferric oxide is reduced to ferric oxide. The reducing gas is hydrogen or carbon monoxide, and the inert gas is nitrogen or argon, with a volume ratio of 1:99 to 10:90 between the reducing gas and the inert gas.

3. The method for preparing ultra-low sulfur iron products according to claim 1, characterized in that, The reduction of ferric oxide to elemental iron includes the following steps: Ferric oxide is placed in a container, and a reducing gas, or a mixture of reducing gas and inert gas, is introduced into the container. Water vapor is also introduced into the container, and the temperature in the container is raised to 400~800℃ and maintained for 240~480 min. Ferric oxide is reduced to elemental iron. The reducing gas is either hydrogen or carbon monoxide; When a mixture of reducing gas and inert gas is introduced into the container, the inert gas is nitrogen or argon, and the volume ratio of reducing gas to inert gas is greater than 10:

90.

4. The method for preparing ultra-low sulfur iron products according to claim 1, characterized in that, The oxidation of iron(III) oxide to iron(II) oxide includes the following steps: Purge the iron(III) oxide or elemental iron with an inert gas for 10-30 minutes, then introduce oxygen and water vapor into the iron(III) oxide or elemental iron to oxidize the iron(III) oxide or elemental iron again to ferric oxide. The oxidation temperature is 400-800℃ and the oxidation time is 10-60 minutes.

5. The method for preparing ultra-low sulfur iron products according to claim 1, characterized in that, Step 100, obtaining the iron hydroxyl oxide precursor, includes the following steps: Using high-purity ferrous sulfate as raw material, at least a portion of the first alkaline solution is first added to the reaction vessel to maintain an alkaline environment inside the reaction vessel. The temperature is raised and an oxidizing substance is added to the reaction vessel. Then, the ferrous sulfate aqueous solution and the remaining amount of the first alkaline solution are simultaneously and slowly pumped into the reaction vessel, or the ferrous sulfate aqueous solution is slowly pumped into the reaction vessel. After the ferrous sulfate reacts, the solution inside the reaction vessel is maintained in an alkaline environment. Stirring and aging are continued, and the mixture is filtered to obtain crude ferric hydroxide. The crude ferric hydroxide was washed with a second alkaline solution and then dried to obtain the ferric hydroxide precursor.

6. The method for preparing ultra-low sulfur iron products according to claim 1, characterized in that, In step 200, After placing the ferric hydroxide precursor in a container, gas is introduced into the container from the bottom and a slightly positive pressure environment is maintained in the container; or, the gas in the container is vented and a slightly negative pressure environment is maintained in the container. And / or, in step 200, the time for the dehydration and crystallization of ferric hydroxide is 30~180 min; And / or, use a stepped heating method to raise the temperature inside the container to 400~800℃.

7. The method for preparing ultra-low sulfur iron products according to any one of claims 1 to 6, characterized in that, A third alkaline solution is added to the obtained crude ferric oxide product, and the crude ferric oxide product is washed with the third alkaline solution. And / or, add a third alkaline solution to the obtained ultra-low sulfur ferric oxide, ultra-low sulfur ferric oxide or ultra-low sulfur iron element, and use the third alkaline solution to wash the ultra-low sulfur ferric oxide, ultra-low sulfur ferric oxide or ultra-low sulfur iron element.

8. The method for preparing ultra-low sulfur iron products according to claim 7, characterized in that, The pH of the third alkaline solution is 9-14; And / or, the third alkaline solution is one or more of the following: ammonia solution, ammonium carbonate solution, ammonium bicarbonate solution, urea solution, sodium hydroxide solution, sodium carbonate solution, sodium bicarbonate solution, potassium hydroxide solution, potassium carbonate solution, and potassium bicarbonate solution.

9. The method for preparing ultra-low sulfur iron products according to claim 7, characterized in that, The temperature of the third alkaline solution is 40~80℃; And / or, when washing with a third alkaline solution, hydrogen peroxide solution and / or ultrasonic dispersion are also used to assist washing; And / or, when washing with a third alkaline solution, the solid-liquid mass ratio is 1:2 to 1:4; And / or, after washing 1 to 3 times with a third alkaline solution, the ultra-low sulfur ferric oxide, ultra-low sulfur ferric oxide, or ultra-low sulfur iron element after alkaline washing is washed again with deionized water.

10. An ultra-low sulfur iron product obtained by the method for preparing ultra-low sulfur iron products according to any one of claims 1 to 9, characterized in that, The ultra-low sulfur iron product is at least one of ultra-low sulfur iron powder, ultra-low sulfur iron ingot, ultra-low sulfur iron(III) oxide, and ultra-low sulfur iron(II) oxide. Furthermore, the sulfur content in the ultra-low sulfur iron powder, the ultra-low sulfur iron ingot, the ultra-low sulfur iron tetroxide, and the ultra-low sulfur ferric oxide is less than 1 ppm.

Images