Feo(oh) solid, ultra-pure iron powder and method of preparation

Abstract

The application discloses a FeO(OH) solid, super-pure iron powder and a preparation method, and belongs to the field of powder metallurgy. The preparation method of the FeO(OH) solid is as follows: pure iron salt solution is obtained by acidolysis of iron concentrate raw materials with a total iron content of not less than 69wt%; then, an amide substance is added into the pure iron salt solution; and then, carbonates are slowly added to make the pH value of the solution increase at a speed of 0.1-0.3 / h to 4.0-6.0 for a precipitation reaction, and the FeO(OH) solid is obtained, wherein the carbonates include at least one of ammonium carbonate and ammonium bicarbonate. The super-pure iron powder is prepared by reducing the FeO(OH) solid to obtain iron powder and then purifying the iron powder through magnetic separation. The FeO(OH) solid prepared by the application has high purity, uniform particle size distribution and good dispersibility, and the super-pure iron powder prepared by the application has the characteristics of extremely low impurity content, good chemical stability and high magnetic permeability.

Description

Technical Field

[0001] This invention relates to a FeO(OH) solid and its preparation method, and also to a method for preparing ultrapure iron powder, belonging to the field of powder metallurgy. Background Technology

[0002] Iron hydroxyl oxide (FeO) is an important iron-based functional material. Due to its unique crystal structure, high specific surface area, good surface activity, and environmentally friendly properties, it shows broad application prospects in water treatment, energy storage and conversion, heterogeneous catalysis, and functional coatings. As an important iron-based intermediate, it has key application value in the preparation of high-performance magnetic materials, catalysts, and electrode materials. In existing technologies, FeO(OH) prepared by direct precipitation of ferrous salts suffers from difficulty in guaranteeing purity. Residual impurity ions can affect the magnetic properties of subsequent products, and there are also problems such as uneven particle size distribution and severe agglomeration.

[0003] High-purity iron powder, as an important basic functional metal powder material, plays an irreplaceable role in many high-end material preparation fields due to its high purity, good chemical stability, excellent magnetic properties, and excellent processing adaptability. In powder metallurgy, high-purity iron powder is a crucial raw material for preparing iron-based alloys and hard alloys, significantly improving material utilization and reducing processing costs. In magnetic material processing, high-purity iron powder, due to its low impurity content, effectively reduces hysteresis loss, making it a vital basic raw material for preparing high-permeability soft magnetic materials, high-frequency inductors, and motor cores. Furthermore, with the development of 3D printing technology, high-purity iron powder is also widely used in the electronics industry, aerospace, and medical devices, enabling high-precision manufacturing and lightweight design of complex and precise structural components.

[0004] The preparation of high-purity iron powder is essentially a process of converting impurity iron sources into high-purity, fine-grained metallic iron, thus possessing characteristics of both purification and powdering. Currently, the main preparation processes for high-purity iron powder include electrolysis, chemical reduction, and atomization, but each process has certain limitations. While electrolysis can yield high-purity iron powder, its high energy consumption, low production efficiency, and complex process flow make it unsuitable for large-scale production. Chemical reduction methods commonly use reducing agents such as NH3 and CO, which produce numerous byproducts and involve cumbersome subsequent processing steps, making clean and continuous preparation difficult. Although atomization offers high production capacity and powder morphology control, it easily introduces impurities during smelting and atomization, and the smelting process is complex. Furthermore, the molten metal in atomization process has a strong tendency to oxidize, resulting in high oxygen content in the powder, making it difficult to meet the stringent purity requirements of magnetic materials and electronic packaging.

[0005] Chinese patent CN108148938B discloses a method for preparing high-purity iron powder by direct reduction of iron scale under a microwave external field using a multi-gradient vacuum method. This process utilizes microwaves to rapidly carbothermally reduce iron scale under vacuum to produce high-purity iron powder. While the process is relatively short and simple, the resulting high-purity iron powder has a TFe content of only 97%, indicating a high impurity content, which fails to meet the purity requirements of high-end materials. Chinese patent CN118204500B discloses a low-cost method for preparing high-purity iron powder. This method uses direct reduced iron as raw material, combining medium-frequency furnace smelting technology and water atomization to prepare high-purity iron powder. Although this process can achieve low-cost preparation of high-purity iron powder, it still requires a steelmaking process, making it more complex, and the obtained high-purity iron powder is only 98.5%, similarly failing to meet the purity requirements of high-end materials. Chinese patent CN104907570B discloses a method for preparing reduced iron powder for powder metallurgy. This method uses raw materials containing metallic iron, which undergo mineral processing, decarburization roasting, and acid washing to obtain raw iron powder. Although the sources of this material are widely available, the decarburization roasting process inevitably produces the greenhouse gas CO2, and the acid washing process easily generates harmful and toxic gases such as H2S, making it not very environmentally friendly.

[0006] Therefore, providing a high-purity, uniformly distributed, and well-dispersed iron hydroxyl oxide, along with a flexible, easily scaled-up, high-purity, and environmentally friendly method for preparing ultrapure iron powder, can provide core foundational support for the innovation and preparation of high-end materials such as high-performance special alloys and high-performance magnetic materials, and has significant implications and market application prospects. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the first objective of this invention is to provide a FeO(OH) solid. This ferric hydroxide has FeO(OH) as the main phase, with a total iron content ≥61.5wt%, an oxygen content ≥35.5wt%, a hydrogen content ≥1.0wt%, uniform particle size distribution, and high dispersibility.

[0008] The second objective of this invention is to provide a method for preparing FeO(OH) solid. This method is simple, controllable, low-cost, and suitable for industrial production.

[0009] The third objective of this invention is to provide a method for preparing ultrapure iron powder. The ultrapure iron powder obtained by this method has a purity of ≥99.5%, which can meet the requirements of high-end materials in terms of raw material purity. Moreover, the process is flexible, low-cost, easy to scale up, and has good scalability.

[0010] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing FeO(OH) solid. The method comprises: acid hydrolyzing an iron concentrate raw material with a total iron content of not less than 69 wt% to obtain a pure iron salt solution; then adding an amide substance to the pure iron salt solution; and then slowly adding a carbonate to raise the pH value of the solution to a range of 4.0 to 6.0 at a rate of 0.1 to 0.3 / h to carry out a precipitation reaction, thereby obtaining the FeO(OH) solid. The carbonate includes at least one of ammonium carbonate and ammonium bicarbonate.

[0011] This invention precisely controls the OH group by creating a dual-controlled, slow-release alkaline environment using amides and ammonium carbonates. - Release rate, directional regulation of FeO(OH) crystallinity and structure, first through the thermal hydrolysis of amide substances (such as urea) to form basic OH groups. - The release system is then supplemented with ammonium carbonate to precisely control the OH- ions in the solution. - The content is adjusted to regulate crystal nucleus growth during the precipitation process. Amide compounds (such as urea) have a relatively slow hydrolysis rate, while ammonium carbonates decompose and release OH- under heating conditions. - The timing was earlier, and the two formed OH groups on different timescales in the same reaction system. - During the release process, this differential dynamic behavior co-constructs NH4 + / NH3 and CO3 2- / HCO3 - The buffer system, which is mainly composed of OH groups, allows the OH groups in the system to... - The generation of urea and ammonium carbonate exhibits a phased and controllable release, thereby achieving a steady increase in the pH gradient of the reaction system. Taking the dual-slow-release alkali system composed of urea and ammonium carbonate as an example, the working process of the dual-slow-release alkali system of this invention is as follows:

[0012] Urea slowly hydrolyzes under heating conditions to produce NH3 and CO2. The NH3 produced further reacts with water to form NH4. + and OH - :

[0013] ;

[0014] ;

[0015] That is, the NH3 produced by the hydrolysis of urea is the OH group in the system. - One of the main sources, and forms NH4 + The NH3 buffer system allows the pH of the system to rise slowly.

[0016] Ammonium carbonate dissociates to form NH4 under heating conditions. + With CO3 2- CO3 2- It further reacts with water to form HCO3- and OH - :

[0017] ;

[0018] ;

[0019] Under conditions where the system pH is 4-6, some HCO3- - The following equilibrium reaction can further occur:

[0020] .

[0021] Therefore, NH4 is formed in this system. + / NH3 and CO3 2- / HCO3 - The system is primarily a buffer system. Among them, NH3 and CO3 produced by urea hydrolysis... 2- Together they regulate the pH of the system, making OH- - It is released gradually at a relatively slow rate.

[0022] As the pH of the system gradually increases, Fe 3+ Stepwise hydrolysis:

[0023] ;

[0024] Fe(OH)3↓ undergoes continuous constant-temperature stirring, dehydration, and rearrangement to form an orange-yellow precipitate of FeO(OH).

[0025] .

[0026] In the dual-release alkali system, ammonium carbonates take effect preferentially in the initial stage of the reaction, releasing carbonate ions earlier. The carbonate ions further hydrolyze to generate bicarbonate ions and OH-. - This allows the pH of the system to stabilize and enter the Fe... 3+ The critical range of hydrolysis, thereby triggering Fe 3+ +3OH - → The nucleation process of Fe(OH)3↓ forms a relatively concentrated nucleation window. Subsequently, urea continues to slowly hydrolyze in the later stages of the reaction, stably supplying OH-. - This causes the system's pH to rise slowly and maintains a low-saturation environment. This is achieved by controlling the OH... -The regulation of the formation rate allows the supersaturation of the system to evolve gradually over time. When the critical conditions for formation are reached, crystal nuclei are concentrated and formed. At the subsequent lower and more stable supersaturation level, the precipitation process gradually transitions to a stage dominated by the uniform growth of existing crystal nuclei and the dehydration and rearrangement of Fe(OH)3 to generate FeO(OH). This achieves relative separation of nucleation and crystal growth in the time dimension and effectively inhibits secondary nucleation and particle agglomeration. Ultimately, this ensures that the obtained FeO(OH) precursor has advantages such as concentrated particle size distribution, low impurity entrainment, and high purity.

[0027] As a preferred embodiment, the total iron content of the iron concentrate raw material is not less than 70 wt%, and more preferably not less than 72 wt%. Controlling the purity of the acid-hydrolyzed iron concentrate raw material can ensure high purity of the obtained ferric chloride solution, reduce impurity interference, and thus facilitate the acquisition of ferric hydroxide product with high purity, uniform particle size distribution, and high dispersibility.

[0028] As a preferred embodiment, the OH group generated by the complete hydrolysis of the amide substance... - Fe in pure iron salt solution 3+ The molar ratio is 2~6:1. Controlling the amount of amide added within a suitable range is beneficial for establishing a relatively stable alkaline environment. When the amount of carbonate added is within the controlled range, excessively low amounts of amide can lead to the release of OH- from the system. - Insufficient concentration leads to incomplete precipitation, making it impossible to control pH changes, resulting in a low FeO(OH) yield and a poor particle size distribution; excessive use of amides can lead to the release of OH- in the later stages of the system. - Excessive pH levels can lead to uncontrollable pH changes, causing localized over-alkalization and particle agglomeration, which is detrimental to obtaining FeO(OH) with higher purity and uniform particle size distribution.

[0029] As a preferred embodiment, the molar ratio of the carbonate to the iron ions in the pure iron salt solution is 0.5~2.0:1. Controlling the amount of carbonate added within a suitable range is beneficial for triggering Fe... 3+ The initial hydrolysis and nucleation stage proceeds steadily, causing the pH to rise steadily and controlling crystal growth. When the amount of amide added is within the controlled range, too low a carbonate dosage will result in insufficient initial alkalinity of the system, a too slow pH rise rate, and difficulty in triggering Fe... 3+ Effective nucleation results in a small number of nuclei, affecting the yield of FeO(OH) and preventing the relative separation of nucleation and crystal growth over time, thus failing to effectively suppress secondary nucleation and particle agglomeration. Excessive carbonate content leads to a rapid increase in the initial pH of the system, which can cause local precipitation to occur too quickly, resulting in uneven particle size, agglomeration, and the potential inclusion of impurities, making it difficult to obtain high-purity FeO(OH).

[0030] As a preferred embodiment, the amide substance includes at least one of urea, formamide, and acetamide. This type of substance can meet the requirements of the present invention for a sustained-release alkaline system.

[0031] As a preferred embodiment, the precipitation reaction conditions are: temperature 70~95℃ and time 2~4h. At this reaction temperature, the dual-release alkali gradually increases the pH of the system from the initial acidic state to the range of 4.0~6.0, forming a relatively concentrated nucleation stage within this range. As the pH of the system continues to rise at a slow rate, the precipitation process gradually enters a reaction stage dominated by the uniform growth of existing crystal nuclei, reducing the probability of new crystal nuclei formation. This achieves a relative separation between the nucleation stage and the crystal growth stage in time, reduces secondary nucleation and particle agglomeration, and is beneficial for controlling the crystallinity of FeO(OH).

[0032] As a preferred method, after the precipitation reaction is complete, the mixture is kept at a constant temperature and aged for 0.5–1 hour. This further promotes crystal structure rearrangement and improves the crystallinity and structural integrity of FeO(OH). After aging, solid-liquid separation is performed to obtain the precipitate, which is then washed until Cl-free. - After drying the residue, high-purity FeO(OH) powder with uniform particle size can be obtained.

[0033] As a preferred embodiment, the content of silicon and aluminum oxides in the iron concentrate raw material does not exceed 0.5 wt%.

[0034] As a preferred embodiment, the iron concentrate raw material contains at least 98% particles with a particle size of -400 mesh.

[0035] As a preferred embodiment, the iron concentrate raw material is prepared by fine grinding, magnetic separation, and reverse flotation purification of magnetite concentrate with a total iron content of not less than 62 wt%. A further preferred embodiment is that the iron concentrate raw material is prepared by fine grinding, magnetic separation, and reverse flotation purification of magnetite concentrate with a total iron content of not less than 65 wt%.

[0036] As a preferred embodiment, the acid solution used in the acidolysis process is a mixture of hydrochloric acid and hydrogen peroxide solution; the volume ratio of hydrochloric acid to hydrogen peroxide solution is 6~10:1, the molar concentration of hydrochloric acid is 1~4 mol / L, and the mass concentration of hydrogen peroxide solution is 3~10%; the solid-liquid ratio in the acidolysis process is 120~150 g / L, the temperature is 30~60℃, and the time is 0.5~1 h. In the acidolysis process, the use of a mixed solution of hydrochloric acid and hydrogen peroxide to treat the iron raw material can promote iron leaching because in a single hydrochloric acid system, an insoluble oxide film is easily formed on the iron surface or Fe is adsorbed. 2+ Salts passivate the iron, reducing the dissolution rate of the iron raw material. Adding hydrogen peroxide can oxidize the Fe... 2+Oxidized to Fe 3+ This further forms soluble chlorine complexes such as [FeCl4]. - This promotes the breakdown of the film and the transfer of iron ions, thereby improving the dissolution efficiency. In addition, oxides such as SiO2, TiO2, and Al2O3 in the raw materials, or those that are difficult or insoluble in acidic environments, can be separated and removed as sediment during dissolution, thus achieving ultimate purification at the raw material end.

[0037] This invention also provides a FeO(OH) solid, which is prepared by the above method. This high-purity FeO(OH) can be used as a standalone product in the fields of catalysis, electrochemical materials, and magnetic materials.

[0038] As a preferred embodiment, the average particle size of the FeO(OH) solid is D50 of 10~25μm, D10 of 4~8μm, and D90 of 30~45μm.

[0039] The present invention also provides a method for preparing ultrapure iron powder, wherein the FeO(OH) solid is subjected to a reduction reaction to obtain iron powder, and the iron powder is then purified by magnetic separation.

[0040] As a preferred embodiment, the conditions for the reduction reaction are: a reducing atmosphere, a temperature of 750~1050℃, and a time of 20min~120min. The preferred reducing atmosphere is hydrogen.

[0041] As a preferred embodiment, the magnetic separation purification method is dry weak magnetic separation. The conditions for dry weak magnetic separation are: a protective atmosphere and a magnetic field strength of 0.1~0.5T. The protective atmosphere includes nitrogen or an inert gas. The inert gas is preferably argon.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] (1) The present invention uses a dual slow-release alkali composite system formed by amides and ammonium carbonates to precisely control the precipitation pH value, so that the nucleation stage and crystal growth stage in the precipitation process are relatively separated in time, reducing secondary nucleation and particle agglomeration. The final FeO(OH) solid has high purity, good dispersibility and uniform particle size distribution.

[0044] (2) The present invention uses FeO(OH) solid with high dispersion, high purity and uniform particle size distribution to further prepare ultrapure iron powder (purity ≥99.5%), which is a qualitative leap compared with conventional hydrogen-reduced iron powder. This ultrapure iron powder has the characteristics of extremely low impurity content, good chemical stability and high magnetic permeability, and has important application value in high-end fields.

[0045] (3) The preparation method is simple and the cost is low, making it suitable for industrial production. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0047] Figure 1 This is a particle size distribution diagram of FeO(OH) prepared in Example 1.

[0048] Figure 2 This is a particle size distribution diagram of FeO(OH) prepared in Example 2.

[0049] Figure 3 This is a particle size distribution diagram of FeO(OH) prepared in Example 3. Detailed Implementation

[0050] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0051] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0052] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0053] Example 1

[0054] A method for preparing ultrapure iron powder includes the following steps:

[0055] In this embodiment, the magnetite concentrate used has the following composition: TFe 65.10%, SiO2 3.52%, Al2O3 0.97%, TiO2 0.086%.

[0056] (1) First, the magnetite concentrate was wet-milled using a conical ball mill with water as the ball milling solvent. The slurry mass concentration was fixed at 65%, the ball-to-material mass ratio was 4:1, the ball milling time was 30 min, and the ball mill speed was 96 r / min. The fineness of the material was ground to -400 mesh, accounting for 98%. The material was then dewatered and dried for reverse flotation purification.

[0057] (2) Magnetic drums were used to remove impurities from the finely ground magnetite concentrate. The magnetic separation process consisted of a three-stage process with magnetic field strengths of 800 Gs, 600 Gs, and 500 Gs for each stage. The concentrate after magnetic separation was transferred to a flotation cell for further purification. Reverse flotation adopted a "one roughing and three cleaning" process, using caustic starch as a depressant and hexadecyltrimethylammonium bromide as a collector to further remove impurities from the magnetite. During the flotation process, the initial dosages of the depressant and collector were 1000 g / t and 200 g / t, respectively, and the dosage was halved with each cleaning cycle. The pulp concentration was controlled at 30%, and the rotor speed of the flotation machine was fixed at 1800 rad / min. After reverse flotation, the chemical composition of the obtained ultrapure iron concentrate was: TFe 72.06%, SiO2 0.13%, Al2O3 0.15%, TiO2 0.086%.

[0058] (3) Add 1.6 L of 3.0 M HCl to a 2 L glass three-necked flask and simultaneously heat to approximately 40 °C. Under stirring, slowly add 200 g of dried ultrapure iron concentrate to the three-necked beaker to disperse it evenly into a slurry. Then, slowly add 200 mL of 8 wt% H2O2 solution dropwise to the slurry, controlling the addition to only produce slight bubbling and avoiding vigorous boiling. After the addition is complete, continue stirring for 30 min until there is no obvious magnetic black slag in the slurry. After stirring, filter the solution. The resulting filtrate is a FeCl3 solution, while SiO2, Al2O3, TiO2, etc., remain essentially insoluble and are treated as tailings.

[0059] (4) Take 1.2 L of the ferric chloride solution obtained in step (3) into a three-necked flask as the mother liquor for the reaction. 3+The concentration was approximately 1.0 mol / L, and the initial pH of the solution was 2.0. 120 g of urea was added to the ferric chloride solution, and the mixture was stirred and heated to 85°C to ensure complete dissolution. Then, ammonium carbonate was added in two equal portions, totaling 80 g, with 30 min intervals between each addition of 40 g. The temperature was maintained at 85°C with constant stirring. During the reaction, the pH of the system slowly increased from 2 to the range of 4.0–6.0, with an average pH change rate of approximately 0.2 / h. When the pH reached the range of 4.0–4.5, a concentrated nucleation stage was formed, followed by a gradual transition to crystal growth as the precipitation process. When the pH reached the range of 4.0–4.5, constant stirring was continued for 3 h, followed by aging for 2 h after stirring. After cooling, the solution was filtered and washed until no Cl- was found. - The residue was dried again to obtain FeO(OH) powder, the chemical composition of which is shown in Table 1.

[0060] (5) The above FeO(OH) powder was placed in a tube furnace and calcined at 950°C in H2 atmosphere for 2 hours. After calcination, N2 protection was introduced and the powder was cooled to room temperature to obtain reduced iron powder.

[0061] (6) The reduced iron powder obtained above was subjected to dry weak magnetic separation under N2 atmosphere to remove impurities. The magnetic field strength was 0.3T. The incompletely reduced FeO(OH) was removed to obtain the final ultrapure iron powder. Its chemical composition and performance indicators are shown in Table 2.

[0062] Table 1. Chemical elemental composition (wt%) and process performance indicators of FeO(OH) obtained in Example 1

[0063] ;

[0064] Combining Table 1 and Figure 1 It can be seen that the FeO(OH) prepared in this embodiment has extremely low impurity element content and uniform particle size distribution, with an average particle size D50 of 16.5 μm.

[0065] Table 2 Chemical elemental composition (wt%) and process performance indicators of the ultrapure iron powder obtained in Example 1

[0066] ;

[0067] As can be seen from the data in Table 2, the iron powder prepared in this embodiment has extremely high purity, reaching 99.91%, and uniform particle size distribution.

[0068] Example 2

[0069] A method for preparing ultrapure iron powder includes the following steps:

[0070] In this embodiment, the magnetite concentrate used has the following composition: TFe 68.20%, SiO2 2.41%, Al2O3 0.47%, TiO2 0.086%. The magnetite concentrate was further purified according to the method of Example 1 to obtain ultrapure iron concentrate with the following chemical composition: TFe 72.06%, SiO2 0.13%, Al2O3 0.15%, TiO2 0.086%. FeO(OH) powder and ultrapure iron powder were then prepared according to the method of Example 1. The difference is that the amount of urea added in step (4) is controlled to be 150g, the amount of ammonium carbonate added is 100g, the precipitation reaction temperature is 95℃, and the reduction temperature in step (5) is controlled to be 1000℃ and the calcination time is 1h.

[0071] Under the conditions of this embodiment, the chemical composition of the FeO(OH) powder obtained is shown in Table 3, and the chemical composition and performance indicators of the ultrapure iron powder are shown in Table 4.

[0072] Table 3 Chemical elemental composition (wt%) and process performance indicators of FeO(OH) obtained in Example 2

[0073] ;

[0074] Combined with Table 3 and Figure 2 It can be seen that the FeO(OH) powder prepared in this embodiment has extremely low impurity element content and uniform particle size distribution, with an average particle size D50 of 18.2 μm.

[0075] Table 4. Chemical elemental composition (wt%) and process performance indicators of the ultrapure iron powder obtained in Example 2

[0076] ;

[0077] As can be seen from Table 4, the iron powder prepared in this embodiment has high purity, reaching 99.88%, and uniform particle size distribution.

[0078] Example 3

[0079] A method for preparing ultrapure iron powder includes the following steps:

[0080] In this embodiment, the iron concentrate used has the following composition: TFe 68.36%, SiO2 2.35%, Al2O3 0.42%, TiO2 0.21%.

[0081] (1) First, the magnetite concentrate was wet-milled using a conical ball mill with water as the ball milling solvent. The slurry mass concentration was fixed at 65%, the ball-to-material mass ratio was 4:1, the ball milling time was 30 min, and the ball mill speed was 96 r / min. The fineness of the material was ground to -400 mesh, accounting for 98%. The material was then dewatered and dried for reverse flotation purification.

[0082] (2) The finely ground magnetite concentrate was treated with a magnetic drum for impurity removal. The magnetic separation process consisted of a three-stage magnetic separation flow, with magnetic field strengths of 800 Gs, 600 Gs, and 500 Gs for each stage. The concentrate after magnetic separation was transferred to a flotation cell for further purification. The reverse flotation adopted a "one roughing and three cleaning" process flow, using caustic starch as a depressant and hexadecyltrimethylammonium bromide as a collector to further remove impurities from the magnetite. During the flotation process, the initial dosage of the depressant and collector was 1000 g / t and 200 g / t, respectively, and the dosage was halved with the number of cleaning cycles. The pulp concentration was controlled at 30%, and the rotor speed of the flotation machine was fixed at 1800 rad / min. After the reverse flotation, the chemical composition of the obtained ultrapure iron concentrate was: TFe 72.08%, SiO2 0.11%, Al2O3 0.13%, TiO2 0.084%.

[0083] (3) Add 1.6 L of 3.0 M HCl to a 2 L glass three-necked flask and simultaneously heat to approximately 40 °C. Under stirring, slowly add 200 g of dried ultrapure iron concentrate to the three-necked beaker to disperse it evenly into a slurry. Then, slowly add 200 mL of 8 wt% H2O2 solution dropwise to the slurry, controlling the addition to only produce slight bubbling and avoiding vigorous boiling. After the addition is complete, continue stirring for 30 min until there is no obvious magnetic black slag in the slurry. After stirring, filter the solution. The resulting filtrate is a FeCl3 solution, while SiO2, Al2O3, TiO2, etc., remain essentially insoluble and are treated as tailings.

[0084] (4) Take 1.2 L of the ferric chloride solution obtained in step (3) into a three-necked flask as the mother liquor for the reaction. 3+ A concentration of approximately 1.0 mol / L was used to add 130 g of formamide to a ferric chloride solution, followed by stirring and heating to 85°C to ensure complete dissolution. Ammonium bicarbonate was then added in two equal portions, totaling 90 g, with 45 g added each time at 30-minute intervals. The temperature was maintained at 85°C with constant stirring. During the reaction, the pH of the system slowly increased from 2 to the range of 4.0–6.0, with an average pH change rate of approximately 0.2 / h. When the pH reached the range of 4.0–4.5, a concentrated nucleation stage was formed, followed by a precipitation process primarily characterized by crystal growth. When the pH reached the range of 4.0–4.5, constant-temperature stirring continued for 3 hours, followed by aging for 4 hours after stirring. After cooling, the solution was filtered and washed until no Cl- was found. - The residue was dried again to obtain FeO(OH) powder, the chemical composition of which is shown in Table 5.

[0085] (5) The above FeO(OH) powder was placed in a tube furnace and calcined at 950°C in H2 atmosphere for 2 hours. After calcination, N2 protection was introduced and the powder was cooled to room temperature to obtain reduced iron powder.

[0086] (6) The reduced iron powder obtained above was subjected to dry weak magnetic separation under N2 atmosphere to remove impurities. The magnetic field strength was 0.3T. The incompletely reduced FeO(OH) was removed to obtain the final ultrapure iron powder. Its chemical composition and performance indicators are shown in Table 6.

[0087] Table 5. Chemical elemental composition (wt%) and process performance indicators of FeO(OH) obtained in Example 3

[0088] ;

[0089] Combined with Table 5 and Figure 3 It can be seen that the FeO(OH) powder prepared in this embodiment has extremely low impurity element content and uniform particle size distribution, with an average particle size D50 of 19.8 μm.

[0090] Table 6 Chemical elemental composition (wt%) and process performance indicators of the ultrapure iron powder obtained in Example 3

[0091] ;

[0092] As can be seen from Table 6, the iron powder prepared in this embodiment has high purity, reaching 99.82%, and uniform particle size distribution.

[0093] Comparative Example 1

[0094] FeO(OH) powder and ultrapure iron powder were prepared using the method in Example 1, with the difference that only urea was added for precipitation reaction. The specific process of step (4) is as follows:

[0095] (4) Take 1.2 L of the ferric chloride solution obtained in step (3) into a three-necked flask as the mother liquor for the reaction. 3+ With a concentration of approximately 1.0 mol / L, 240 g of urea was added to a ferric chloride solution, and the mixture was stirred and heated to 85°C to ensure complete dissolution. The pH of the solution increased to 3.6 at a rate of 0.05 / h until precipitation was complete, and aging continued for 4 hours. After cooling, the solution was filtered and washed until no Cl- was found. - The residue was further dried to obtain FeO(OH) powder, the chemical composition of which is shown in Table 7. Iron powder was prepared using this FeO(OH) powder, and the chemical composition and process performance indicators of the resulting iron powder product are shown in Table 7.

[0096] Table 7 Chemical elemental composition (wt%) and process performance indicators of FeO(OH) and iron powder obtained in Comparative Example 1

[0097] ;

[0098] As shown in Table 7, the (FeO)OH prepared by adding only urea as a slow-release agent has low purity and coarse particle size, and the purity of the prepared iron powder product is also low, only 99.35%. This is because when only urea is used as the alkali release agent, the pH of the system rises slowly, and the Fe... 3+ Insufficient initial nucleation prevents the relative separation of nucleation and crystal growth over time, thus hindering the suppression of secondary nucleation and particle aggregation.

[0099] Comparative Example 2

[0100] FeO(OH) powder and ultrapure iron powder were prepared using the method in Example 1, with the difference that only ammonium carbonate was added for precipitation reaction. The specific process of step (4) is as follows:

[0101] (4) Take 1.2 L of the ferric chloride solution obtained in step (3) into a three-necked flask as the mother liquor for the reaction. 3+ With a concentration of approximately 1.0 mol / L, 288 g of ammonium carbonate was added in two equal portions to a ferric chloride solution, and the mixture was stirred and heated to 85°C to ensure complete dissolution. The pH of the solution increased to 6.4 at a rate of 0.45 / h until precipitation was complete. The mixture was then allowed to age for another 1 hour, cooled, filtered, and washed until no Cl- was found. - The residue was further dried to obtain FeO(OH) powder, the chemical composition of which is shown in Table 8. Iron powder was prepared using this FeO(OH) powder, and the chemical composition and processing performance indicators of the resulting iron powder product are shown in Table 8.

[0102] Table 8 Chemical elemental composition (wt%) and process performance indicators of FeO(OH) and iron powder obtained in Comparative Example 2

[0103] ;

[0104] As shown in Table 8, the (FeO)OH prepared by adding only ammonium carbonate as a slow-release agent had low purity and coarse particle size, and the purity of the prepared ultrapure iron powder was also low, only 99.2%. This is because using only ammonium carbonate as the alkali causes the pH of the system to rise rapidly in the early stage, which can quickly induce Fe... 3+ Hydrolysis and nucleation occur, but there is a lack of sustained OH- release from urea. - Controlling the subsequent particle growth stage can easily lead to excessively rapid local precipitation.

[0105] Comparative Example 3

[0106] FeO(OH) powder and ultrapure iron powder were prepared using the method in Example 1, with the difference being that the ammonium carbonate content was lower than the control range, and more urea was added to ensure that the total alkali release met the requirement of complete precipitation of iron ions. The specific steps (4) are as follows:

[0107] (4) Take 1.2 L of the ferric chloride solution obtained in step (3) into a three-necked flask as the mother liquor for the reaction. 3+ With a concentration of approximately 1.0 mol / L, 225 g of urea was added to a ferric chloride solution, and the mixture was stirred and heated to 85°C to ensure complete dissolution. Ammonium carbonate was then added in two equal portions, totaling 48 g, with a 30-minute interval between each addition. The temperature was maintained at 85°C with constant stirring. During the reaction, the pH of the system slowly increased from 2 to 4.0–6.0 at a rate of 0.08 / h, precipitating iron ions. The mixture was stirred at a constant temperature for 3 hours, and then aged for 2 hours after stirring. After cooling, the mixture was filtered and washed until no Cl- was found. - The residue was further dried to obtain FeO(OH) powder, the chemical composition and performance indicators of which are shown in Table 9. Iron powder was prepared using this FeO(OH) powder, and the chemical composition and processing performance indicators of the resulting iron powder product are shown in Table 9.

[0108] Table 9 Chemical elemental composition (wt%) and process performance indicators of FeO(OH) and iron powder obtained in Comparative Example 3

[0109] ;

[0110] As can be seen from the data in Table 9, the (FeO)OH powder prepared under these comparative conditions has low purity and coarse particle size, and the purity of the prepared iron powder product is also low, only 99.42%. This is because the addition of too little ammonium carbonate results in a slow pH rise rate, which fails to achieve relative separation of nucleation and crystal growth in the time dimension, thus failing to effectively inhibit secondary nucleation and particle agglomeration, affecting the uniformity of the FeO(OH) structure.

[0111] Comparative Example 4

[0112] FeO(OH) powder and ultrapure iron powder were prepared using the method in Example 1, with the difference that the amount of urea added was lower than the control range, and more ammonium carbonate was added to ensure that the total alkali release reached the requirement of complete precipitation of iron ions. The specific steps (4) are as follows:

[0113] (4) Take 1.2 L of the ferric chloride solution obtained in step (3) into a three-necked flask as the mother liquor for the reaction. 3+ With a concentration of approximately 1.0 mol / L, 15 g of urea was added to a ferric chloride solution, and the mixture was stirred and heated to 85°C to ensure complete dissolution. Then, ammonium carbonate was added in two equal portions, totaling 240 g, with a 30-minute interval between each addition. The temperature was maintained at 85°C with constant stirring. During the reaction, the pH of the system increased from 2 to 4.0–6.0 at a rate of 0.35 / h, precipitating iron ions. The mixture was stirred at a constant temperature for 3 hours, and then aged for 1 hour after stirring. After cooling, the mixture was filtered and washed until no Cl- was found. -The residue was further dried to obtain FeO(OH) powder, the chemical composition of which is shown in Table 10. Iron powder was prepared using this FeO(OH) powder, and the chemical composition and process performance indicators of the resulting iron powder product are shown in Table 10.

[0114] Table 10 Chemical elemental composition (wt%) and process performance indicators of FeO(OH) and iron powder prepared in Comparative Example 4

[0115] ;

[0116] As can be seen from the data in Table 10, the (FeO)OH powder prepared under these comparative conditions has low purity and coarse particle size, and the purity of the prepared iron powder product is also low, only 99.28%. This is because the amount of urea added is too low, which causes the pH to rise too quickly, resulting in excessively rapid local precipitation, uneven particle size, and agglomeration, while also carrying impurities.

[0117] As can be seen, this invention precisely controls the OH-release alkali system by constructing a dual-slow-release alkali system through a specific ratio of amides and carbonates. - The release rate, i.e. the pH increase rate, makes the nucleation stage and crystal growth stage in the precipitation process relatively separated in time, reducing secondary nucleation and particle agglomeration. The final FeO(OH) solid has a uniform structure, high purity, good dispersibility and uniform particle size distribution. This FeO(OH) solid can be further used to prepare ultrapure iron powder.

Claims

1. A method for preparing FeO(OH) solid, characterized in that: Iron concentrate with a total iron content of not less than 69 wt% is acid-hydrolyzed to obtain a pure iron salt solution. Then, an amide is added to the pure iron salt solution, followed by the slow addition of carbonates to raise the pH of the solution to 4.0-6.0 at a rate of 0.1-0.3 / h, thereby carrying out a precipitation reaction. The carbonates include at least one of ammonium carbonate and ammonium bicarbonate; the amides include at least one of urea, formamide, and acetamide; the precipitation reaction conditions are: temperature 70-95℃, time 2-4h.

2. The method for preparing FeO(OH) solid according to claim 1, characterized in that: The OH group generated by the complete hydrolysis of the amide substances - Fe in pure iron salt solution 3+ The molar ratio is 2~6:1; The molar ratio of iron ions in the carbonate to pure iron salt solution is 0.5~2.0:

1.

3. The method for preparing FeO(OH) solid according to claim 1, characterized in that: The content of silicon and aluminum oxides in the iron concentrate raw material does not exceed 0.5 wt%.

4. A method for preparing FeO(OH) solid according to claim 1 or 3, characterized in that: The acid solution used in the acidolysis process is a mixture of hydrochloric acid and hydrogen peroxide solution; the volume ratio of hydrochloric acid to hydrogen peroxide solution is 6~10:1, the molar concentration of hydrochloric acid is 1~4 mol / L, and the mass concentration of hydrogen peroxide solution is 3~10%; the solid-liquid ratio in the acidolysis process is 120~150 g / L, the temperature is 30~60℃, and the time is 0.5~1 h.

5. A FeO(OH) solid, characterized in that: Prepared by the method described in any one of claims 1 to 4.

6. A method for preparing ultrapure iron powder, characterized in that: The FeO(OH) solid described in claim 5 is subjected to a reduction reaction to obtain iron powder, which is then purified by magnetic separation.

7. The method for preparing ultrapure iron powder according to claim 6, characterized in that: The conditions for the reduction reaction are: a reducing atmosphere, a temperature of 750~1050℃, and a time of 20min~120min.

8. A method for preparing ultrapure iron powder according to claim 6 or 7, characterized in that: The magnetic separation purification method is dry weak magnetic separation. The conditions for dry weak magnetic separation are: the gas atmosphere is a protective atmosphere and the magnetic field strength is 0.1~0.5T.

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