Abstract
Production of high purity iron powder employs high efficiency low temperature electrolysis resulting in a process requiring substantially less energy with no CO.sub.2 gas and has high energy reduction. Configurations provide a renewable electricity supply that is environmental benign with low energy consumption. A hematite (Fe.sub.2O.sub.3), 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 O.sub.2 gas as a byproduct.
Claims
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.sub.2O.sub.3) 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 Fe.sub.2O.sub.3 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 (Fe.sub.2O.sub.3) and carbon particles and is submerged in a sodium hydroxide electrolyte bath.
11. A method of iron production, comprising: combining hematite (Fe.sub.2O.sub.3), 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 O.sub.2 gas as a byproduct.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] 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.
[0008] FIG. 1 is a context diagram of the iron production process as disclosed herein;
[0009] FIG. 2 is a schematic diagram of the colloidal electrode in the process of FIG. 1;
[0010] FIG. 3 depicts electrochemical reduction in the electrode of FIG. 2;
[0011] FIG. 4 shows electrolysis current vs. reaction time in the process of FIG. 1;
[0012] FIG. 5 shows X-Ray Diffraction (XRD) patterns of the electrolyzed product for Fe.sub.2O.sub.3 colloidal electrodes as in FIGS. 1 and 2; and
[0013] FIG. 6 shows the electrolysis cell of FIG. 1 in an overall system for scalable iron powder production and material reuse.
DETAILED DESCRIPTION
[0014] 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 H.sub.2 as a reducing agent, which can be cost-prohibitive for commercialization.
[0015] 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 CO.sub.2 gas and has high energy reduction in an environmental benign approach. Referring to FIG. 1, hematite (Fe.sub.2O.sub.3), 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 O.sub.2 gas as a byproduct, according to the following electrochemical reactions.
Fe.sub.2O.sub.3(s)+3H.sub.2O+6e.sup.==2Fe(s)+6OH.sup.Cathode side
4OH.sup.==O.sub.2(g)+4e.sup.+2H.sub.2OAnode side
[0016] Iron powder produced at the cathode will be collected and separated from carbon powder by using a magnet while O.sub.2 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.
[0017] 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 Fe.sub.2O.sub.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 O.sub.2 gas is generated as a by-product, which may also be collected.
[0018] 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 Fe.sub.2O.sub.3/C composite powders suspended in a highly concentrated NaOH solution, which is different from the reported Fe.sub.2O.sub.3 suspension systems. Here, carbon acts as an electrically conductive network improving the electrical conductivity of Fe.sub.2O.sub.3, 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.
[0019] Referring to FIG. 2, the flowable suspension from hematite (Fe.sub.2O.sub.3) 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.
[0020] FIG. 3 depicts electrochemical reduction in the electrode of FIG. 2. In FIG. 3, conventional hematite (Fe.sub.2O.sub.3) has no carbon network, and the hematite 170 tends to form Fe.sub.3O.sub.4 (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 Fe.sub.2O.sub.3 particles in an NaOH solution with and without the carbon conductive network. In the conventional Fe.sub.2O.sub.3 suspension (with no C), Fe.sub.2O.sub.3 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 Fe.sub.2O.sub.3 particles are reduced to Fe.sub.3O.sub.4 with some Fe depositing on Ni foam surfaces. In contrast, in the designed Fe.sub.2O.sub.3 suspension with carbon, Fe.sub.2O.sub.3 particles can be directly reduced to Fe without diffusion owing to the formation of the carbon conductive network. Furthermore, C on Fe.sub.2O.sub.3 particles also serve as a conductive medium, so Fe.sub.2O.sub.3 particles do not directly come into contact with the Ni foam surface, alleviating the deposition of Fe powder on the electrode surface.
[0021] 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 Fe.sub.2O.sub.3 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.
[0022] In the example electrochemical reduction of the Fe.sub.2O.sub.3 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 Fe.sub.2O.sub.3 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.
[0023] 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 Fe.sub.2O.sub.3 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 Fe.sub.2O.sub.3 reduction mechanisms. In the first 5 min of the reaction, there is a rapid electrochemical reaction at the Fe.sub.2O.sub.3/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.sub.2O.sub.3 particles 403 are gradually reduced to Fe.sub.3O.sub.4 and Fe. Then, after about 20 min, the current plateau can be observed implying the sluggish reduction of Fe.sub.3O.sub.4 accompanied by H.sub.2 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 Fe.sub.2O.sub.3 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.sub.2O.sub.3/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 1x 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.sub.2O.sub.3 particles and Ni foam 114 substrate surfaces during the electrochemical reduction. FIG. 5 shows X-Ray Diffraction (XRD) patterns of the electrolyzed product for Fe.sub.2O.sub.3 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.sub.2O.sub.3 electrode, the majority of the electrolyzed product is Fe.sub.3O.sub.4 with a small amount of Fe. According to peak intensity analysis, the purity of Fe is only 6% while that of Fe.sub.3O.sub.4 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.sub.3O.sub.4 is the intermediate phase of Fe.sub.2O.sub.3 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 Fe.sub.2O.sub.3 to Fe in the conventional colloid that has poor electrical conductivity, bringing about low purity of Fe and low current efficiency in this process.
[0024] In sharp contrast to the conventional suspension, the electrolyzed product of Fe.sub.2O.sub.3/C colloidal electrodes shows almost no Fe.sub.3O.sub.4 phases according to the XRD pattern shown in FIG. 5. Over 95% of Fe can be obtained with an insignificant amount of Fe.sub.3O.sub.4. This small amount of impurity may come from unreacted Fe.sub.3O.sub.4 remaining on the wall of the sample holder made of polypropylene (a non-conductive material), which lacks the coverage of the conductive properties.
[0025] 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 O.sub.2 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 (Fe.sub.2O.sub.3) and carbon particles and submerged in a sodium hydroxide electrolyte bath 116.
[0026] 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.
