WO2025096918A1

WO2025096918A1 - Low temperature, low emission iron production

Info

Publication number: WO2025096918A1
Application number: PCT/US2024/054086
Authority: WO
Inventors: Yan Wang; Panya Thanwisai; Zeyi Yao
Original assignee: Worcester Polytechnic Institute
Current assignee: Worcester Polytechnic Institute
Priority date: 2023-11-01
Filing date: 2024-11-01
Publication date: 2025-05-08
Anticipated expiration: 2026-05-01
Also published as: US20250137154A1

Abstract

Production of high purity iron powder employs high efficiency low temperature electrolysis resulting in a process requiring substantially less energy with no CO₂ gas and has high energy reduction. Configurations provide a renewable electricity supply that is environmental benign with low energy consumption. A hematite (Fe₂O₃), carbon and highly concentrated NaOH combine to form an electronically and ionically conductive suspension for iron production. The suspension is flowable which can also be applied to a flow electrolysis system. High purity iron powder is produced at the cathode side while the anode side can produce O₂ gas as a byproduct.

Description

LOW TEMPERATURE, LOW EMISSION IRON PRODUCTION

Inventors: Yan Wang, Panya Thanwisai and

Zeyi Y ao

Attorney Docket No.: WPI22-29(W23-013)PCT

STATEMENT OF FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT:

This patent application was developed, either in whole or in part, with U.S. Government support under Contract No. W911NF1920108, awarded by the US Army Research Laboratory. The Government has certain rights in the Invention.

BACKGROUND

Steel production is a paramount need of any industrialized civilization. The thermal demands of steelmaking, however, inherently require enormous amounts of heat and generate substantial gaseous byproducts. The iron and steel industry has a history of environmental consciousness and efforts are continually made to reduce energy consumption and CO emissions, however the conventional carbothermic process (~2000°C) limits reduction of green house gas (GHG) emissions and energy usage, and only marginal improvements can be expected with current technology.

SUMMARY

Production of high purity iron powder employs high efficiency low temperature electrolysis for a process requiring substantially less energy with no CO2 gas and has high energy reduction. Configurations provide a renewable electricity supply that is environmental benign with low energy consumption. Hematite (FeOq. carbon and highly concentrated NaOH combine to form an electronically and ionically conductive suspension for iron production. The suspension is flowable which can also be applied to a flow electrolysis system. High purity iron powder is produced at the cathode side while the anode side can produce O2 gas as a byproduct. Configurations herein are based, in part, on the observation that iron is a requisite ingredient in steel, which is constantly in demand as a structural building material, automotive, aeronautical, and various other industrial endeavors.. Unfortunately, conventional steelmaking processes suffer from the shortcoming of substantial energy and emission burdens, due to the high temperatures required to melt the metal ingredients of steel, particularly iron. Accordingly, configurations herein substantially overcome the shortcomings of conventional steelmaking and iron production by providing a low temperature electrolysis process to form an electronically and ionically conductive suspension. The suspension is flowable which can also be applied to a flow electrolysis system. High purity iron powder is produced at the cathode side while the anode side generates O2 gas as a byproduct.

In further detail, a method of iron production includes combining hematite ( Fe^Ch). carbon and highly concentrated NaOH for forming an electronically and ionically conductive suspension for iron production, and circulating the suspension in an electrolysis environment for cycling in the presence of a Ni foam current collector and anode. Iron powder with high purity can be extracted at the cathode side while the anode side produces 02 gas as a byproduct.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the invention will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

Fig. 1 is a context diagram of the iron production process as disclosed herein; Fig. 2 is a schematic diagram of the colloidal electrode in the process of Fig. 1;

Fig. 3 depicts electrochemical reduction in the electrode of Fig. 2;

Fig. 4 shows electrolysis current vs. reaction time in the process of Fig. 1 ;

Fig. 5 shows X-Ray Diffraction (XRD) patterns of the electrolyzed product for Fe20s colloidal electrodes as in Figs. 1 and 2; and Fig. 6 shows the electrolysis cell of Fig. 1 in an overall system for scalable iron powder production and material reuse.

DETAILED DESCRIPTION

In configurations depicted below, a low-temperature electrolysis (LTE) approach proceeds at a significantly lower temperature (~100 °C) compared to conventional processes such as carbothermic reduction (>2000 °C), molten oxide electrolysis (MOE, at >500 °C), and hydrogen flash smelting (HFS) processes (>1000 °C). Unlike the MOE process, the disclosed approach does not require a stable anode for such a high-temperature operation and avoids the use of H2 as a reducing agent, which can be cost-prohibitive for commercialization.

Configurations below generate high purity iron powder by high efficiency LTE. Fig. 1 is a context diagram of the iron production process as disclosed herein. Compared to conventional steel making, this invention consumes substantially less energy, produces no CO2 gas and has high energy reduction in an environmental benign approach. Referring to Fig. 1, hematite (Fe2Ch), carbon and highly concentrated NaOH are combined to form an electronically and ionically conductive suspension to produce iron. Note that the suspension is flowable which can also be applied to a flow electrolysis system. High purity iron powder will be produced at the cathode side while the anode side can produce O2 gas as a byproduct, according to the following electrochemical reactions.

Fe2Os (s)+3H2O+6e ==2Fe(s)-i-6OH^_ Cathode side

4OH ==O2 (g)+4e'+2H2O Anode side

Iron powder produced at the cathode will be collected and separated from carbon powder by using a magnet while O2 gas will be collected at the anode. High surface area Ni foam was employed as both cathode and anode current collectors. Other metals could be employed for reduction, depending on the native form and ionic properties. Using Ni foam at the cathode side provides evenly distribution of charge and increases an available conductive area of the suspension, facilitating an accelerated reaction rate. In addition, the Ni foam anode is reactive to oxygen evolution reaction which facilitates oxygen production. More importantly, Ni foam is much cheaper than a conventional Ti cathode current collector and Nobel-metal anode, for example Pt and Ir, thus imparting feasibility for a commercial and/or industrial scale. Particular organic and inorganic additives are added to promote the reaction and limit the reaction of hydrogen evolution.

In Fig. 1, a flowable suspension 102’ includes a metal compound. The flowable suspension 102 occupies a cathode containment 112 in electrical communication with a conductive foam cathode 114 submerged in an electrolyte 116. A separator 118 and conductive foam anode 122 are communication with the conductive foam cathode 114 in an anode containment 124, all submerged in an electrolyte containment 120 to form an electrolysis cell 150. A voltage source 130 applies a voltage between the conductive form anode 122 and conductive foam cathode 114, which are all in electrical communication within the containments 112, 124. Following application of the voltage source 130, iron 152 is harvested from the conductive foam cathode 114, while oxygen gas 154 may be harvested from the anode. In the particular configuration herein, a flowable Fe2C>3/C colloid is electrolyzed at a low temperature of 100 °C with a constant cell voltage of around -1.7 V in a 50 wt% NaOH electrolyte 116 solution. The final product is high-purity Fe powder while only O2 gas is generated as a by-product, which may also be collected.

Fig. 2 is a schematic diagram of the colloidal electrode in the process of Fig. 1. The colloidal electrode suspension 102 formed from the metal powder, carbon and sodium hydroxide contains Fe2O3/C composite powders suspended in a highly concentrated NaOH solution, which is different from the reported Fe2O3 suspension systems. Here, carbon acts as an electrically conductive network improving the electrical conductivity of Fe2O3, while the NaOH solution serves as an ionic conductive network facilitating ion diffusion during the electrochemical reaction. Thus, a 3D conductive percolation network is formed, as shown in Fig. 2.

Referring to Fig. 2, the flowable suspension from hematite (Fe Os) and carbon particles 164 form aggregations 160 submerged in a sodium hydroxide electrolyte 116 bath to form a network of electrically conductive pathways 162 and ionic conductive pathways 166. Other electrolytes, as well as different voltage ranges, such as 1.4-2.0 volts or other suitable range.

Fig. 3 depicts electrochemical reduction in the electrode of Fig. 2. In Fig. 3, conventional hematite (FezCE) has no carbon network, and the hematite 170 tends to form FezCL (magnetite, another type of iron oxide) particles 172. Reduction with carbon particles 164 reduces the hematite 170 to pure iron 174 and carbon particles 164. A magnetic stirrer may facilitate production, and the conductive foam cathode 114 (cathode) accumulates pure iron 174 and carbon particles 164 at the cathode 114, followed by magnetic separation of the pure iron from the carbon particles. Thus, Fig. 3 depicts the reduction mechanism of suspensions of FezCb particles in an NaOH solution with and without the carbon conductive network. In the conventional FezCE suspension (with no C), FezCL particles need to diffuse to the surface of the Ni foam current collector to be reduced. Due to their sluggish diffusivity in NaOH and intrinsically poor electrical conductivity, most FezCh particles are reduced to FezCL with some Fe depositing on Ni foam surfaces. In contrast, in the designed FezOi suspension with carbon, FejCF particles can be directly reduced to Fe without diffusion owing to the formation of the carbon conductive network. Furthermore, C on FezOz particles also serve as a conductive medium, so FezCh particles do not directly come into contact with the Ni foam surface, alleviating the deposition of Fe powder on the electrode surface. This unique function in turn improves production yield and facilitates product collection. More importantly, as the colloidal electrode is flowable, it can potentially be used in a flow electrolysis design that allows continuous production and facilitates product collection and separation steps. Altogether, utilizing the LTE of FezCh colloidal electrodes can resolve the aforementioned limitations of conventional LTE processes. In addition, it should be noted that the electrolysis design can also be applied to produce other metal and alloy powders such as Cu, Ag, and an FeNi alloy and shows potential for use as an alternative method of metal/alloy powder production.

In the example electrochemical reduction of the FejCL colloidal electrode, a negative voltage of 1.7 V was applied to the two-electrode electrolysis cell, and the reaction was prolonged until reaching the theoretical capacity calculated based on Faraday’s law. The use of used porous Ni foam sheets as a cathode substrate and an anode electrode shows that the utilization of 3D (3 dimensional) porous Ni foam as a substrate improves the electrolysis efficiency and Fe purity over using 2D (planar) Ti foil sheets as a cathode substrate and Pt foil as an anode. This advantage is due to the 3D porous structure of Ni foam that can sufficiently distribute charge for reducing FeiOs to Fe effectively, resulting in a higher current and a shorter reaction time than those of 2D conductive areas of Ti foil. Also, Ni foam is less expensive than either Ti foil and noble-metallic Pt foil and is therefore more feasible for large- scale and industrial production.

Fig. 4 shows electrolysis current vs. reaction time in the process of Fig. 1. Referring to Fig. 4, the reduction current and reaction time of FezOs colloidal electrodes with carbon 401 and without carbon 403 is shown. Of note, the current produced from bare Ni foam is relatively small or negligible compared to that from Ni foam with the colloid. At a glance, there are main reduction kinetics observed during the electrolysis reaction that can be used to predict the FezOs reduction mechanisms. In the first 5 min of the reaction, there is a rapid electrochemical reaction at the Fe^O electrolyte interface resulting in the production of a high current, similarly observed in both colloidal electrodes. During 20 min of the reaction, in the colloid without C, Fe^Ch particles 403 are gradually reduced to FesC and Fe. Then, after about 20 min, the current plateau can be observed implying the sluggish reduction of FesO4 accompanied by H2 evolution until the end of the reaction. In contrast, after 5 min of the reaction in the colloidal electrode with C 401, there is a continuous increase in the current until 36 min of the reaction implying that FezCh is continuously reduced to Fe throughout the reaction period. In the final 4 min of the reaction, the current decreases, indicative of the end of the reaction. It is noticeable that the current produced by the electrolysis of the Fe^Ch/C colloid is higher than that of the colloid without C for the entire reaction period. In addition, the reaction time is shorter, which takes around 40 min to complete the reaction corresponding to lx the theoretical capacity applied, while the colloid with no C takes 55 min. This enhancement benefits from the designed colloidal electrode that provides electrically conductive pathways for rapid charge transfer between Fe^CT, particles and Ni foam 114 substrate surfaces during the electrochemical reduction.

Fig. 5 shows X-Ray Diffraction (XRD) patterns of the electrolyzed product for Fe20s colloidal electrodes as in Figs. 1 and 2. The X-ray powder diffraction (XRD) patterns shown in Fig. 5 reveal the resulting products obtained from electrolyzing the colloidal electrodes with carbon 501 and without carbon 503. For the conventional Fe^Ch electrode, the majority of the electrolyzed product is FesCb with a small amount of Fe. According to peak intensity analysis, the purity of Fe is only 6% while that of FesC is 94%. Calculated based on the capacity applied and the purity of produced Fe, the electrolysis efficiency of the electrode without C is around 16%. It is expected that Fe C is the intermediate phase of Fe^Cb reduction, per the equations below. This intermediate phase demonstrates a sluggish response of electrochemical reaction for further reduction to Fe. Hence, it is difficult to reduce all FeaCh to Fe in the conventional colloid that has poor electrical conductivity, bringing about low purity of Fe and low current efficiency in this process.

In sharp contrast to the conventional suspension, the electrolyzed product of Fe Ch/C colloidal electrodes shows almost no Fe^CL phases according to the XRD pattern shown in Fig. 5. Over 95% of Fe can be obtained with an insignificant amount of Fe3O4. This small amount of impurity may come from unreacted FesO4 remaining on the wall of the sample holder made of polypropylene (a non- conductive material), which lacks the coverage of the conductive properties.

Fig. 1 and the above discussion demonstrate successful production of Fe via LTE on a laboratory scale. The disclosed process also demonstrates a scalable process, as well as a closed-loop production of the LTE process. Accordingly, Fig. 6 shows the electrolysis cell of Fig. 1 in an overall system of iron powder production and reuse. Referring to Fig. 6, the overall flow process of proposed Fe production includes four major parts: (I) colloidal mixing 601 , (II) electrolysis system 602, (III) magnetic separation of electrolyzed iron 603, and (IV) waste recycling and reuse 604. In the first part 601 iron ore powders, C powders, NaOH, water and additives are fed into the colloid mixing tank followed by feeding the colloidal mixture to the electrochemical cell 150. The electrochemical reduction of the colloidal mixture 102’ takes place in the second part 602 The O2 by-product 154 in the scaled process is fed out of the process, which can be stored for further utilization. After the electrolysis reaction, the products comprising electrolyzed Fe powders, C powders, NaOH electrolyte solution 116 and unreacted oxides are fed out from the electrochemical cell 150 for magnetic separation in the third part, where Fe powders will be separated from other components through a magnetic separator. Thereafter, in the final part 604, bowl centrifuges 610 are used to separate NaOH solution and unreacted powders. NaOH electrolyte solution 116 and C powders will be recycled and unreacted remnants will be fed out. The physical apparatus for iron producing apparatus includes a cathode containment 112, and a flowable suspension 102 including a metal compound disposed in the cathode containment 112. The conductive foam cathode 114 is disposed in electrical communication with the flowable suspension 102 to form the cathode as the cathode containment 112 is submerged in an electrolyte 116 in the containment 120. A separator 118 on top of the conductive foam cathode 114 is disposed between the conductive foam anode 122 on top of the separator 118 and in communication with the conductive foam cathode, as shown by the carbon network of Figs. 2 and 3. The voltage source 130 connects between the conductive form anode 122 and conductive foam cathode 114. In the example configuration, the flowable suspension 102 is a combination of hematite (Fe2Oa) and carbon particles and submerged in a sodium hydroxide electrolyte bath 116.

While the system and methods defined herein have been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Claims

CLAIMS What is claimed is:

1. A method of generating iron powder, comprising: forming a flowable suspension including a metal compound; disposing the flowable suspension in electrical communication with a conductive foam cathode submerged in an electrolyte; forming a separator and conductive foam anode in communication with the conductive foam cathode; applying a voltage between the conductive form anode and conductive foam cathode; and harvesting iron from the conductive foam cathode.

2. The method of claim 1 further comprising forming the flowable suspension from hematite (Fe^CL) and carbon particles and submerging in a sodium hydroxide electrolyte bath.

3. The method of claim 1 wherein the suspension is conductive and the electrolyte is sodium hydroxide.

4. The method of claim 1 further comprising submerging the suspension in a sodium hydroxide bath and agitating the suspension with a magnetic stirrer.

5. The method of claim 1 further comprising: accumulating pure iron and carbon particles at the cathode, and separating the pure iron from the carbon particles via magnetic separation.

6. The method of claim 1 further comprising forming a colloid of the metal powder, carbon and sodium hydroxide.

7. The method of claim 1 further comprising applying a voltage between 1.4 and 2.0 volts between the conductive form cathode and the conductive foam anode.

8. The method of claim 1 further comprising delivering a charge via a conductive network formed by the suspended carbon particles for reducing Fe2O3 to Fe.

9 An iron producing apparatus, comprising: a cathode containment; a flowable suspension including a metal compound disposed in the cathode containment; a conductive foam cathode disposed in electrical communication with the flowable suspension, the cathode containment submerged in an electrolyte; a separator on top of the conductive foam cathode; a conductive foam anode on top of the separator and in communication with the conductive foam cathode; and a voltage source connected between the conductive form anode and conductive foam cathode.

10. The apparatus of claim 9 wherein the flowable suspension is a combination of hematite ( Fc2Ch) and carbon particles and is submerged in a sodium hydroxide electrolyte bath.

11. A method of iron production, comprising: combining hematite (Fe20 ), carbon and highly concentrated NaOH for forming an electronically and ionically conductive suspension for iron production; circulating the suspension in an electrolysis environment for cycling in the presence of a Ni foam current collector and anode; and extracting iron powder at the cathode side while the anode side produces O2 gas as a byproduct.