WO2025123053A1

WO2025123053A1 - Systems and methods for extraction of resources from iron-rich feedstocks

Info

Publication number: WO2025123053A1
Application number: PCT/US2024/059245
Authority: WO
Inventors: Yet-Ming Chiang; Pinwen GUAN; Michael Wang; Duhan ZHANG; Venkatasubramanian Viswanathan; Camden HUNT
Original assignee: Carnegie Mellon University; Massachusetts Institute of Technology
Current assignee: Carnegie Mellon University; Massachusetts Institute of Technology
Priority date: 2023-12-09
Filing date: 2024-12-09
Publication date: 2025-06-12
Anticipated expiration: 2026-06-09

Abstract

Described herein are methods, devices, materials, and systems for extracting target materials from iron-rich feedstocks. The iron-rich feedstock may be red mud, a natural occurring mineral, and/or a waste stream. The target materials may include a main constituent of the feedstock, a rare earth element, a precious metal, and/or a platinum group element. The invention may use a combination of electrochemical reactions and physical separation methods.

Description

SYSTEMS AND METHODS FOR EXTRACTION OF RESOURCES FROM IRON- RICH FEEDSTOCKS CROSS REFERENCE TO RELATED APPLICATION(S) [0001] The present application claims a priority benefit to U.S. provisional application serial Nos.63/608,229 filed on December 9, 2023, which is incorporated herein by reference in its entirety. GOVERNMENT SUPPORT [0002] This invention was made with government support under Grant No. DE-AR0001395 awarded by the U.S. Department of Energy. The government has certain rights in this invention. BACKGROUND [0003] Next-generation technologies, ranging from advanced alloys to electronics, are increasingly reliant on a list of materials deemed critical by the US government. Several of these materials, for example the rare earth elements (REE) and the precious metals (PM), have been deemed critical due to their low concentrations in common minerals. This leads to high difficulty for their extraction, which relies on selective separation of a trace amount of desired material from an excess amount of undesired material. For many of these critical material feedstocks, the undesired material is rich in iron, the fourth most abundant element in the Earth’s crust. Thus, there remains a need for methods for separating trace elements (e.g., REEs and PMs) from iron-rich matrices to expand the scope of viable feedstocks for mining of these critical materials. SUMMARY [0004] In some aspects, the techniques described herein relate to a method for extracting at least three target materials from a feedstock, the method including leaching the feedstock in an acid leachate, wherein the feedstock includes at least 30% by weight iron oxide (Fe2O3), filtering the acid leachate to remove an insoluble material, wherein the insoluble material includes a first target material, adding a base to the acid leachate to form a precipitate and a leachate, wherein the leachate has a pH of about 9, filtering the leachate to remove the precipitate, mixing the precipitate with an electrolyte solution to produce an electrolyte mixture, reducing the electrolyte mixture, using an electrochemical reactor, to produce a solution, a solid deposit including a second target material, and a residue including a third target material, and collecting the solid deposit, the residue, and the solution. [0005] In some aspects, the techniques described herein relate to a method wherein the first target material, the second target material, and the third target material are each different from one another and each is selected from iron (Fe), aluminum (Al), sodium (Na), calcium (Ca), chromium (Cr), magnesium (Mg), boron (B), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), manganese (Mn), gallium (Ga), lead (Pb), barium (Ba), strontium (Sr), copper (Cu), bismuth (Bi), lithium (Li), zinc (Zn), nickel (Ni), indium (In), thallium (Tl), cobalt (Co), cadmium (Cd), scandium (Sc), nickel (Ni), cobalt (Co), silicon (Si), titanium (Ti), vanadium (V), gallium (Ga), hafnium (Hf), indium (In), niobium (Nb), tantalum (Ta), zirconium (Zr), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), yttrium (Y), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), thorium (Th), uranium (U), gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), rhenium (Re), palladium (Pd), osmium (Os), iridium (Ir), or platinum (Pt). [0006] In some aspects, the techniques described herein relate to a method wherein filtering the leachate to remove the precipitate further includes collecting a fourth target material from the leachate. [0007] In some aspects, the techniques described herein relate to a method wherein the fourth target material includes at least one of magnesium or calcium. [0008] In some aspects, the techniques described herein relate to a method further including collecting a fifth target material from the solution, wherein the fifth target material includes aluminum. [0009] In some aspects, the techniques described herein relate to a method further including separating, using a magnet, a magnetic material from the residue. [0010] In some aspects, the techniques described herein relate to a method wherein the magnetic material includes iron. [0011] In some aspects, the techniques described herein relate to a method further including leaching the feedstock in an alkaline leachate prior to leaching the feedstock in an acid leachate. [0012] In some aspects, the techniques described herein relate to a method wherein the first target material includes at least one of platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os) iridium (Ir), silicon (Si), or titanium (Ti). [0013] In some aspects, the techniques described herein relate to a method wherein the electrochemical reactor includes an anode electrode and a cathode electrode. [0014] In some aspects, the techniques described herein relate to a method wherein reducing the electrolyte mixture includes reducing an iron oxide of the electrolyte mixture to an iron metal, wherein the iron metal is bound to the cathode electrode and the iron metal includes the second target material. [0015] In some aspects, the techniques described herein relate to a method further including applying an electric potential between the electrodes, wherein the electric potential is in the range of 0.1V to 5V. [0016] In some aspects, the techniques described herein relate to a method wherein the third target material includes at least one of scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), yttrium (Y), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), osmium (Os), ruthenium (Ru), chromium (Cr), manganese (Mn), copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), cadmium (Cd), scandium (Sc), nickel (Ni), cobalt (Co), silicon (Si), titanium (Ti), vanadium (V), hafnium (Hf), niobium (Nb), tantalum (Ta), zirconium (Zr), lanthanum (La), yttrium (Y), gold (Au), silver (Ag), ruthenium (Ru), rhenium (Re), palladium (Pd), osmium (Os), iridium (Ir), or platinum (Pt). [0017] In some aspects, the techniques described herein relate to a method wherein the feedstock includes red mud. [0018] In some aspects, the techniques described herein relate to a method wherein the feedstock includes a natural occurring mineral selected from bauxite, hematite, aeschynite, allanite, gadolinite, magnetite, magmatic magnetite-hematite bodies, iron oxide-copper-gold deposits, and carbonatites. [0019] In some aspects, the techniques described herein relate to a method wherein the feedstock includes a waste stream selected from municipal solid waste incinerator ashes, bauxite residue, magnet waste, coal fly ash, ferrochrome slag, sewage sludges, or mine tailings. [0020] In some aspects, the techniques described herein relate to a method wherein the electrolyte mixture has a solid material concentration from 0.1g/5mL to 0.1g/100mL. [0021] In some aspects, the techniques described herein relate to a system for extracting at least three target materials from a feedstock, the system including a first tank including an acid leachate, a second tank including a supply of the feedstock a third tank, operably connected to the first tank and the second tank via at least one conduit, configured to hold a supply of the acid leachate and the feedstock a first filter, operably connect to the third tank, configured to filter an insoluble material from the acid leachate, wherein the insoluble material includes a first target material a fourth tank, operably connected to the first filter and the third tank, configured to receive the filtered acid leachate a fifth tank, operably connected to the fourth tank, configured to supply a supply of a base to the filtered acid leachate to form a precipitate and a leachate, wherein the leachate has a pH of about 9 a second filter, operably connected to the fifth tank, configured to filter the precipitate from the leachate a sixth tank, operably connected to the fifth tank and the second filter, configured to receive the precipitate and a supply of an electrolyte, wherein the sixth tank is further configured to mix the precipitate and the electrolyte to produce an electrolyte mixture an electrochemical reactor, operably connected to the sixth tank, configured to receive the electrolyte mixture, wherein the electrochemical reactor includes at least an anode electrode and a cathode electrode, and the electrochemical reactor is further configured to reduce the electrolyte mixture to produce a solution, a solid deposit including a second target material, and a residue including a third target material, and a third filter, operably connected to the electrochemical reactor, configured to filter the residue from the solution. [0022] In some aspects, the techniques described herein relate to a system further including a potentiostat, operably coupled to the electrochemical reactor, configured to apply an electric potential between the electrodes, wherein the electric potential is in the range of 0.1V to 5V. [0023] In some aspects, the techniques described herein relate to a system wherein the first target material, the second target material, and the third target material are each different from one another and each is selected from iron (Fe), aluminum (Al), sodium (Na), calcium (Ca), chromium (Cr), magnesium (Mg), boron (B), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), manganese (Mn), gallium (Ga), lead (Pb), barium (Ba), strontium (Sr), copper (Cu), bismuth (Bi), lithium (Li), zinc (Zn), nickel (Ni), indium (In), thallium (Tl), cobalt (Co), cadmium (Cd), scandium (Sc), nickel (Ni), cobalt (Co), silicon (Si), titanium (Ti), vanadium (V), gallium (Ga), hafnium (Hf), indium (In), niobium (Nb), tantalum (Ta), zirconium (Zr), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), yttrium (Y), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), thorium (Th), uranium (U), gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), rhenium (Re), palladium (Pd), osmium (Os), iridium (Ir), or platinum (Pt). [0024] All combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are part of the inventive subject matter disclosed herein. The terminology used herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS [0025] The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally similar and/or structurally similar elements). [0026] FIG.1 shows a schematic of an example method for feedstock (e.g., red mud) processing for total removal of Fe2O3, Al2O3, and SiO2 from the feedstock. Simple processing steps (e.g., grinding and washing) are omitted. [0027] FIG.2 shows a chemical loop of the removal of SiO2, Al(OH)3, and TiF4 from red mud feedstocks. [0028] FIG.3 shows a chemical loop of the removal of SiO2, Al(OH)3, TiF4, and rare earth elements from red mud feedstocks. The removal of Ti for Ti-rich samples is depicted in dotted lines. [0029] FIG.4A shows a schematic of an experimental electrochemical cell for alkaline electrolysis of iron (III) oxide (Fe2O3) and iron (II, III) oxide (Fe3O4) to iron (Fe⁰). [0030] FIG.4B shows an image of the cathode before and after electrolysis showing the deposition of Fe⁰ on the cathode. [0031] FIG.4C shows an image of the current rare earth elements (REE)-rich residue. [0032] FIG.5A shows an energy dispersive spectroscopy (EDS) spectra for the remaining electrochemically inactive residue from FIG.4C after Fe2O3 electrolysis of the starting Fe- Al-Y-La feedstock for 24 hours. [0033] FIG.5B shows a chart illustrating that the primary constituents of the residue shown in FIG.4C are Y and La with low concentrations of Na, Fe, Ca, and Al impurities. [0034] FIG.6 is an image of a red mud sample provided by Rio Tinto (scale bar: 5 cm). [0035] FIG.7A is a pie chart of the main constituents in red mud. [0036] FIG.7B is a pie chart of the rare earth elements (REE) in red mud. [0037] FIG.7C is a pie chart of the platinum group elements in red mud. [0038] FIG.8 is a chart illustrating the operation flow of separating Fe and Al from REE concentrates including three major steps: i) acid leaching; ii) precipitation, and; iii) Fe electrowinning. [0039] FIG.9A shows an image of pH 9 filtered precipitates. [0040] FIG.9B shows an image of dried precipitates. [0041] FIG.9C shows an image of crushed dry precipitates. [0042] FIG.9D shows an image of milled dry precipitates. [0043] FIG.10 is a multi-component Pourbaix diagram for the Fe/Nd/Sc/Pr system. [0044] FIG.11A is an image of an Fe electrowinning cell. [0045] FIG.11B is a schematic of the cell shown in FIG.11A and the Fe electrowinning concept. [0046] FIG.12A is an image showing the deposition on the cathode surface after Fe electrolysis. [0047] FIG.12B is an image showing the electrolyte with remaining residue after Fe electrolysis. [0048] FIG.12C is an image of the filtered residue on filter paper after Fe electrolysis. [0049] FIG.12D is an image of the pH 9 precipitates before Fe electrolysis (left) and the dried remaining residues (right). [0050] FIG.13A is a scanning electron microscopy (SEM) image of the deposit materials on the cathode surface. [0051] FIG.13B is an EDS spectrum of the deposit materials on the cathode surface. The first EDX peak from the left is C Kα from the carbon tape as the background. [0052] FIG.14 shows images of the magnetic residue particles (left) and non-magnetic residue particles in deionized (DI) water after magnetic separation. [0053] FIG.15A is a graph showing the Gibbs free energy of formation for each of the constituent metal oxides in red mud feedstock, as calculated by Equation 4 for the reaction in Equation 3. [0054] FIG.15B is a graph showing the minimum thermodynamic reduction potential, as calculated by Equation 5, using the result of the calculation by Equation 4. The dashed line represents the cathodic potential being applied during electrolytic reduction in alkaline aqueous solution. The potential was adjusted for the Hg/HgO reference such that the applied potential is -1.3 V with respect to the Hg/HgO reference electrode. [0055] FIG.16A shows the SEM characterization of feedstock sample composition after drying, milling, and sieving. [0056] FIG.16B shows the EDX map overlay characterization of the feedstock sample composition after drying, milling, and sieving. [0057] FIG.16C shows the EDX spectrum characterization of the feedstock sample composition after drying, milling, and sieving. [0058] FIG.17A shows the electrochemical cell design. [0059] FIG.17B shows the large bench scale reactor in the lab. [0060] FIG.18 shows a cyclic voltammetry graph of the feedstock in 12.5 M NaOH at 100°C, at a scan rate of 40 mV/s. [0061] FIG.19A shows a photo of the gas generation and bubble foams during the reactions. [0062] FIG.19B shows another photo of the gas generation and bubble foams during the reactions. [0063] FIG.20 shows an EDX point analysis for electrodeposited iron on the working electrode. [0064] FIG.21 shows a schematic of the Bayer process, depicting desilication as well as NaOH recovery and bauxite residue generation. [0065] FIG.22A shows a graph of dissolved aluminate species concentrations as a function of temperature and NaOH concentration. Top curve (T = 25℃), middle curve (T = 50℃), and bottom curve (T = 100℃). [0066] FIG.22B shows a graph of dissolved silicate species concentrations as a function of temperature and NaOH concentration. Top curve (T = 25℃), middle curve (T = 50℃), and bottom curve (T = 100℃). [0067] FIG.23A shows photos of feedstock samples following various alkaline leach conditions. [0068] FIG.23B is a zoomed-in graph showing the concentration of Fe (far left bar), Ti (second to the left bar), Ca (middle bar), Al (second to the right bar), and Si (far right bar) under various alkaline leach conditions. [0069] FIG.23C is the full graph of the graph shown in FIG.23B showing the concentration of Fe (far left bar), Ti (second to the left bar), Ca (middle bar), Al (second to the right bar), and Si (far right bar) under various alkaline leach conditions. [0070] FIG.24 shows a system for the separation of target material(s) a feedstock. DETAILED DESCRIPTION [0071] This invention concerns methods, devices, materials, and systems for extracting valuable components from feedstocks. The invention uses a combination of electrochemical reactions and physical separation methods. [0072] Electrochemical and Thermochemical Methods for Extraction of Iron, Aluminum, Silicon, and/or Rare-earth Elements (REEs) from Bauxite Residue [0073] Aluminum metal (Al⁰) is produced at a scale of approximately 70 million tonnes per year through the Hall-Héroult process, in which alumina (Al2O3) is dissolved at 950 ^oC in a molten Al|Na|F electrolyte (cryolite) and subsequently electrolyzed to produce Al⁰ at the cathode and CO2 gas at the anode. The Al2O3 feedstock used in this process is obtained primarily through the Bayer process, in which aluminum ore—typically bauxite—is digested with caustic soda, filtered, precipitated, and calcined to produce high purity Al2O3. The Bayer process also produces large volumes of alkaline (e.g., a pH of approximately 10–12.5) bauxite residue as a waste slurry, with an estimated four billion tonnes currently stored in slurry impoundments. This bauxite residue or slurry—also referred to herein as red mud— contains approximately 15–40% solids and consists predominantly of Fe, Al, and Si. Table 1 provides the major components of red mud. The composition of red mud may vary between Bayer process sites. The values in Table 1 can be varied by ^0.01%, or ^0.05%, or ^0.1%, or ^0.5%, or ^1.0%, or ^1.5%, or ^2%, or ^2.5%, or ^3.0%, or ^3.5%, or ^4.0%, or ^4.5%, or ^5.0%. [0074] Table 1. The typical major elements (>1%) within red mud.

[0075] Red mud may also contain a variety of trace elements that are listed as critical minerals by the U.S. Department of the Interior, including, but not limited to, titanium (Ti), gallium (Ga), vanadium (V), zirconium (Zr), chromium (Cr), nickel (Ni), and/or zinc (Zn), and several rare-earth elements, including, but not limited to, cerium (Ce), thorium (Th), lanthanum (La), neodymium (Nd), scandium (Sc), yttrium (Y), praseodymium (Pr), samarium (Sm), gadolinium (Gd), uranium (U), dysprosium (Dy), erbium (Er), europium (Eu), ytterbium (Yb), terbium (Tb), holmium (Ho), lutetium (Lu), and/or thulium (Tm). The concentration of the minor elements, including REEs, in red mud are provided in Table 2. The values in Table 2 can be varied by ^0.01%, or ^0.05%, or ^0.1%, or ^0.5%, or ^1.0%, or ^1.5%, or ^2%, or ^2.5%, or ^3.0%, or ^3.5%, or ^4.0%, or ^4.5%, or ^5.0%. [0076] Table 2. The typical minor elements (≤1%) within red mud. The composition of red mud may vary between Bayer process sites.

[0077] The scale of red mud production (approximately 150 Mt per year), concentration of critical minerals, and cost associated with storage and disposal provides an incentive to develop methods to fractionate bauxite residue into pure, valorized component streams. Of particular interest is the development of processes that enable total (e.g., approximately > 90%) removal of Fe, Al, and Si to produce three valorized products (Fe⁰, Al2O3, and SiO2), a concentrated residue of other critical minerals, and/or concomitantly reducing the total volume of red mud requiring storage and disposal. Of particular importance to the bauxite industry would be if the waste from such a process was non-leachable and did not require slurry impoundment, as the cost of red mud storage and disposal can reach approximately $10–40 per tonne due to the leachable nature of the waste. [0078] Disposal and storage of red mud in slurry impoundments is problematic due to several factors, including the high alkalinity (e.g., a pH of approximately 10–12.5), dilute nature (e.g., approximately 15–40 wt% solids), and production volume (e.g., approximately 150 Mt/y). These present major challenges for cost-effective and environmentally responsible disposal and storage methods. [0079] Red mud is historically impounded into large clay-lined dams, and the caustic slurry is pumped into the dam and dried through ambient evaporation. However, this practice has been revised due to the adverse impact on surrounding groundwater supplies, and modern red mud disposal dams may use a polymeric membrane liner and a drainage network in addition to a clay-lined base. Even with modern storage techniques, airborne alkali dust and trace radionuclide seepage may result in problematic environmental concerns. Dry disposal of red mud is also practiced and reduces environmental risk, but dry disposal is of limited application due to the increased cost relative to damming stemming from the need for a filtration plant. Direct disposal into the deep ocean is also practiced, but with a poor understanding of the environmental impacts. Several methods have been proposed to reduce the hazardous nature of red mud and lower the cost of disposal, such as the Bauxsol^TM process in which seawater containing solubilized alkaline earth metals is mixed with bauxite residue to precipitate insoluble carbonates and lower the pH of the material (e.g., to a pH < 9), resulting in a marketable residue that is safe and applicable for niche markets. However, the volume of red mud production outlined above suggests that effective remediation and/or valorization of red mud dams will require the conversion of red mud into a product with a market comparable in scale to the total mass of red mud (e.g., approximately 4.0 Gt globally). [0080] Three markets with production scales comparable or exceeding red mud generation are the aluminum, iron, and cement metal industries, which have annual production scales of approximately 70 Mt, approximately 1.5 Gt, and approximately 4.0 Gt, respectively. All of these markets require oxide feedstocks—Fe2O3, Al2O3, and pozzolanic SiO2, respectively— which also comprise the bulk composition of red mud (see Table 1). [0081] Accordingly, disclosed herein is a method for red mud valorization and remediation that involves total removal (approximately >90%) and fractionation of Fe, Al, and Si as a marketable metal or oxide of sufficient form and purity for their respective industries, while simultaneously reducing the volume of waste that requires disposal. Such an approach may also produce a minable waste stream of concentrated high value elements for further refinement (e.g., Ga, Ti, and/or rare-earth elements). Utilization of red mud slurries directly with minimal purification or processing may be beneficial for the cost-effective removal of Fe, Al, and/or Si from red mud. The value of the generated products may also provide economic justification for remediation steps, including neutralization and de-watering. [0082] It has been shown that Fe⁰ may be recovered from both industrial waste streams and iron ore (e.g., Fe2O3 and/or Fe3O4) through the electrowinning Fe⁰ from an alkaline suspension of ground iron oxide feedstock (e.g., Fe2O3 or an iron-rich waste) to produce Fe⁰ on the cathode surface while simultaneously producing oxygen gas (O2) at the anode. The electrowinning process in an acid electrolyte has been applied to combustion ash as part of the ARPA-E Mining Incinerated Disposal Ash Streams (MIDAS) program and has been previously demonstrated for ground hematite ore in an alkaline electrolyte. The alkalinity and particle diameter previously employed for electrowinning experiments for industrial waste streams and iron ore (Fe²O³) (e.g., a pH of approximately 14–15, D^particle of approximately10 µm) are similar to those typical of red mud (e.g., a pH approximately 10–12.5, Dparticle of approximately 10–100 µm). This suggests that red mud may be used directly as a feedstock for alkaline Fe⁰ electrowinning with minimal pretreatment of the slurry and are disclosed herein. [0083] Additionally, processing aluminosilicate minerals and Al/Si-rich waste streams using low temperature thermochemical loops for producing acid and base were developed. These loops operate by heating an aqueous ammonium salt to release ammonia as a volatile gas that can be collected and used as a base, with concomitant acidification of the non-volatile fraction. This process produces an acid that can be used to selectively leach target elements from minerals and/or waste and a base that can be used to precipitate the solubilized target elements and regenerate the original ammonium salt. These loops can be applied to extract target elements from minerals and waste without stoichiometric consumption of leachant or precipitant. Conversion of leaching/precipitation processes into non-stoichiometric processes may enable the use of effective leachants that are typically precluded from consideration due to high cost. For example, many organic acids—such as citric and oxalic acid—can completely (e.g., >90%) solubilize Al from red mud when used as leachants in conjunction with sulfuric acid (H2SO4) but may be less economical owing to the high price of organic acids. Thus, disclosed herein are the development of ammonium salt chemical loops that produce both an Al/Si leachant and NH3(g) as a precipitant that may provide a low-cost means of selectively removing both Al and Si from red mud mixtures with heat as the primary input. [0084] Red mud is a source of critical minerals of strategic and economic importance, and typical red mud slurry impoundments contain non-trivial quantities of Ti, Ga, V, Zr, Sc, Cr, Y, Ni, Zn, and/or lanthanides (see Tables 1 and 2). Many of these critical minerals have limited or absent (e.g., Ga and Sc) domestic production chains. For example, Ga is required by the semiconductor industry and a lack of a domestic supply of Ga combined with import restrictions may result in supply chain challenges. For example, China is responsible for approximately 94% of global Ga production. Sc is widely used for the production of high- strength alloys, and similarly there is a lack of domestic supply of Sc. Thus, the isolation of these critical minerals from red mud may be beneficial. Thus, there remains a need for methods for removing the major constituents of red mud (Fe2O3, Al2O3, and SiO2) to produce a concentrated residue of critical minerals (e.g., Ga and Sc) with a target element concentration sufficient for further refinement by established methods. [0085] The methods disclosed herein may be capable of removing Fe, Al, Si from red mud at low temperature (e.g., approximately <150 ^oC) and isolating valuable products (e.g., TiF4 and REE-concentrated residues). The total removal (e.g., approximately >90%) of these elements as pure products may be difficult due to the overlapping physical and chemical properties of the major elements. Furthermore, additional complexity may arise from the presence of trace elements. For example, a major challenge specifically for the removal of Al and Si from red mud is that leaching strategies frequently only partially leach out Al and Si from the less stable phases (e.g., sodalite, kaolinite) while more stable phases (e.g., boehmite, gibbsite, quartz) remain recalcitrant to leaching. Moreover, the generated products—Fe⁰, Al2O3, and SiO2—must be of purity and grade marketable for their respective industries. Finally, the methods must also operate at scales relevant to the Bayer process to result in meaningful remediation of slurry impoundments. [0086] Several aspects of the methods described herein may be advantageous towards addressing these challenges listed above. First, alkaline Fe⁰ electrowinning may selectively extract Fe⁰ from red mud directly without pretreatment (e.g., de-watering and/or neutralization) of the feedstock, and make use of the high pH of untreated red mud slurries. The removal of the primary constituent of red mud (Fe2O3) without pretreatment may simplify all downstream steps as well, as Fe can solubilize under a variety of conditions— conditions which also frequently solubilize other components of red mud. [0087] Alkaline Fe electrowinning may be used for the production of Fe⁰ from Fe-rich sources, including hematite ore, industrial waste products, and red mud specifically. However, the removal of Fe⁰ from red mud through electrowinning may present several challenges. As described here, the process involves suspending the Fe-rich oxides in alkaline electrolyte (e.g., 1.0–20.0 M KOH and/or NaOH) and subsequently electrowinning Fe⁰ at a cathode (e.g., a steel cathode) while concomitantly producing H2(g) as a parasitic cathodic reaction and O2(g) at the anode (e.g., a nickel anode). This process may deposit high purity Fe⁰ on the cathode as a rough, scaled layer that may be prone to flaking at high deposition volumes. Direct electrowinning of Fe⁰ in this manner may be unusual due to the need to supply solid, iron oxide-containing particles as a reactant to the electrode. Prior efforts to electrowin Fe⁰ from iron oxide waste streams have revealed that the process may be slow and energy inefficient with conventional electrolyzer designs, possibly due to parasitic H2(g) evolution that may arise from insufficient electrode|particle contact. Accordingly, disclosed herein are improved designs for solid-state Fe electrowinning that focus on maximizing the contact between the iron oxide-containing particles and the electrode to mitigate H^2(g) evolution. Without being bound to a particular theory, it is believed that this may provide a homogeneous current distribution through both space and time, mitigating entropic losses as previously described. Even if H2(g) evolution is successfully mitigated, another challenged presented by current electrowinning methods is that O2(g) evolution at the anode may cause hyperpolarization overpotentials associated with electrode|gas surface blockage. Thus, disclosed herein are cell designs that address these challenges and may also be amenable to high current density, continuous operation, and facile removal of the formed Fe⁰ product. Previous attempts at developing optimized alkaline Fe electrowinning cells have failed to result in commercially viable electrolyzers due to these listed challenges. [0088] Disclosed herein are slurry electrodes for Fe electrowinning described that may address each of the challenges listed above. The slurry electrodes disclosed herein may operate in a continuous manner with magnetic separation of reduced Fe⁰ from remaining red mud residue. The slurry electrodes may include electrically conductive particles that form a 3-dimensional electrode in suspension, where charge transfer may occur through a percolation network of conductive particles rather than through a 2-dimensional conductive electrode surface. The slurry electrodes may increase the electrochemically-active surface area of electrodes, improve charge/discharge rates, and/or increase the total system capacity. Without being bound to a particular theory, it is believed that the transition from a solid electrode to a slurry electrode may solve many of the challenges listed above to provide a mechanism for viable alkaline Fe electrowinning from red mud. The use of a slurry electrode may allow for intimate contact of the iron-oxide containing particles with the electrode in a homogeneous manner, as the entire 3D volume of the slurry is electrically conductive. Gas evolution within the 3D volume of the slurry may exit unhindered, mitigating hyperpolarization effects. The cells may operate as flow cells. Reduced Fe⁰ may be separated using a rotary magnetic separation. [0089] Second, the use of ammonium salt acid-base loops for Al and Si extraction may enable extraction of both elements by leaching in a non-stoichiometric fashion, with recovery of both the leachant and the precipitant. The acid-base loops described herein may be compatible with several different types of aluminosilicate ore and wastes. Third, both of the proposed processes may operate as a continuous, rather than batch process, which may be beneficial for red mud processing due to the large production rates and the total volume of red mud waste. Ultimately, the possibility of producing three major feedstocks for modern trade and general trade markets (e.g., steel, aluminum, and cement) while simultaneously creating a concentrated residue of critical minerals may provide strategic, economic, and environmental value. [0090] Ammonium salt acid-base loops for the extraction of Al and Si have also been developed for use on aluminosilicate minerals (e.g., silica, kaolinite, and several critical mineral-containing aluminosilicates) and industrial waste products. The process involves heating an ammonium salt to evolve ammonia gas and acidifying the non-volatile fraction. The acidified fraction is then used to digest the feedstock, solubilizing the Si fraction and converting the Al fraction into an insoluble solid. Both fractions are subsequently separated by filtration. Reintroduction of the previously evolved ammonia gas to the soluble Si fraction may generate an amorphous SiO2 product suitable for use in a variety of cement-related applications, and treatment of Al fraction with strong acid and then the previously evolved ammonia gas may generate a hydrated alumina fraction (Al2O3·6H2O). The original ammonium salt may be subsequently recovered by filtration for the next cycle. The overall process operates below approximately 100 ℃ and may avoid the stoichiometric consumption of leachant and precipitant, making it well-suited for processes that generate commodity chemicals (e.g., SiO2 and Al2O3) of low price. [0091] In some embodiments, the ammonium salt is ammonium fluoride, NH4F, and said ammonium salt acid-base loop may be used to valorize red mud or any component of the red mud, including but not limited to red mud, red mud from which at least iron has been removed, red mud from which at least iron and aluminum have been removed, according to the processes disclosed herein. [0092] The total removal of silica and alumina may be difficult with conventional acid-base loops. However, both components may also complicate red mud processing if not fully removed, particularly during neutralization steps due to the generation of gel phases. Thus, disclosed herein are proposed loops that may fully remove the Si, Al, and/or Ti fractions from the starting material (e.g., red mud). The methods disclosed herein may result in total removal (approximately >90%) and fractionation of both Si and Al from various aluminosilicate minerals and wastes. Furthermore, Ti may also be readily removed as a pure TiF4 using the chemical loops disclosed herein. [0093] A general method of the invention uses two sequential processes in which, the first process involves electrochemistry to selectively react iron in the feedstock, and a second process involving physical separation of the electrochemically inactive target materials from the remaining feedstock. In many common feedstocks, which include minerals and waste streams, iron exists as iron oxide or iron hydroxide. Iron oxides can be electrolyzed in alkaline environments to produce metallic iron. [0094] FIG.1 shows an overview of a method 100 for the extraction of a target material(s) 113 from a feedstock 111 using an alkaline solution. The method 100 may allow for the extraction of a target material(s) 113 from the feedstock 111 at a low cost and on a large scale. The method 100 may allow for the total (e.g., approximately >90%) extraction of the target material(s) 113 from the feedstock 111. In one embodiment, the target material(s) 113 may include, but are not limited to, Fe, Al, Si, and/or Ti. [0095] As shown in FIG.1, the method 100 may include two parts or processes: process 110 (FIG.1, left) and process 120 (FIG.1, right). Process 110 includes electrowinning Fe⁰ from an alkaline suspension of the feedstock 111. Process 120 includes the extraction of target material(s) 113 (e.g., Al, Si, and/or Ti) using an acid-base loop. It should be appreciated that while FIG.1 illustrates process 110 followed by process 120, the method 100 may also be performed by first using process 120 followed by process 110. Process 110 and 120 are described in greater detail below. [0096] In process 110, for the extraction of Fe (target material 113a), low temperature (e.g., approximately <150 ^oC) electrowinning processes with moderate energy inputs may be used as shown in FIG.1, left. In the first process 110, electrochemistry is conducted in an electrochemical reactor 150 containing an electrolyte 151, an anode electrode 152, a cathode electrode 153, and the feedstock 111. A potentiostat (not shown) or another suitable power source may provide power to the electrochemical reactor 150. In one embodiment, the anode electrode 152 may be a nickel anode. In one embodiment, the cathode electrode 153 may be a steel cathode. In some embodiments, the electrolyte 151 is an alkaline aqueous solution with pH above 7. For example, the pH of the alkaline aqueous solution may be about 7.0, about 8.0, about 9.0, about 10.0, about 11.0, or about 12.0, including all values in between. In one embodiment, the electrolyte 151 may be 1.0–20.0 M KOH. For example, the electrolyte 151 may be 1.0 M KOH, 2.0 M KOH, 3.0 M KOH, 4.0 M KOH, 5.0 M KOH, 6.0 M KOH, 7.0 M KOH, 8.0 M KOH, 9.0 M KOH, 10.0 M KOH, 11.0 M KOH, 12.0 M KOH, 13.0 M KOH, 14.0 M KOH, 15.0 M KOH, 16.0 M KOH, 17.0 M KOH, 18.0 M KOH, 19.0 M, KOH, or 20.0 M KOH, including all values in between. In another embodiment, the electrolyte 151 may be 1.0–20.0 M NaOH. For example, the electrolyte 151 may be 1.0 M NaOH, 2.0 M NaOH, 3.0 M NaOH, 4.0 M NaOH, 5.0 M NaOH, 6.0 M NaOH, 7.0 M NaOH, 8.0 M NaOH, 9.0 M NaOH, 10.0 M NaOH, 11.0 M NaOH, 12.0 M NaOH, 13.0 M NaOH, 14.0 M NaOH, 15.0 M NaOH, 16.0 M NaOH, 17.0 M NaOH, 18.0 M NaOH, 19.0 M NaOH, or 20.0 M NaOH, including all values in between. In certain embodiments, the electrolyte 151 may contain a supporting cation 154, which may include but are not limited to Na, K, Li, Mg, Ca, or Al. The term “about,” when used to describe the pH of the alkaline aqueous solution, is intended to cover variations that may arise when the pH of the alkaline aqueous solution is prepared. For example, “about 1.0 M” may correspond to a molar range of 0.95 M to 1.05 M (+/- 5% variation), including all values and sub-ranges in between. [0097] In some embodiments, the electrochemical reaction is facilitated by an applied cathodic current in the range of about 1 uA/cm² to 1A/cm². For example, the cathodic current may be in the range of about 1 uA/cm², about 10 uA/cm², about 20 uA/cm², about 30 uA/cm², about 40 uA/cm², about 50 uA/cm², about 60 uA/cm², about 70 uA/cm², about 80 uA/cm², about 90 uA/cm², about 100 uA/cm², about 200 uA/cm², about 300 uA/cm², about 400 uA/cm², about 500 uA/cm², about 600 uA/cm², about 700 uA/cm², about 800 uA/cm², about 900 uA/cm², about 150 uA/cm², about 1 mA/cm², about 10 mA/cm², about 20 mA/cm², about 30 mA/cm², about 40 mA/cm², about 50 mA/cm², about 60 mA/cm², about 70 mA/cm², about 80 mA/cm², about 90 mA/cm², about 100 mA/cm², about 200 mA/cm², about 300 mA/cm², about 400 mA/cm², about 500 mA/cm², about 600 mA/cm², about 700 mA/cm², about 800 mA/cm², about 900 mA/cm², to about 11A/cm², including all values in between. The term “about,” when used to describe the cathodic current, is intended to cover variations that may arise when the cathodic current is applied. For example, “about 1 uA/cm²” may correspond to a current range of 0.95 uA/cm² to 1.05 uA/cm² (+/- 5% variation), including all values and sub-ranges in between. [0098] In other embodiments, the electrochemical reaction may be facilitated by an applied potential in the range of about 0.1V to about 5V. For example, the applied potential may be about 0.1V, about 0.5V, about 1.0V, about 1.5V, about 2.0V, about 2.5V, about 3.0V, about 3.5V, about 4.0V, about 4.5V, or about 5.0V, including all values in between. The term “about,” when used to describe the applied potential, is intended to cover variations that may arise when the applied potential is applied. For example, “about 1.0V” may correspond to a potential range of 0.95 V to 1.05 V (+/- 5% variation), including all values and sub-ranges in between. [0099] Preferably, the applied potential or applied currents may be sufficiently low or high to achieve selective reduction of the iron, leaving a solution or suspension enriched in non-iron target material(s) 113. [00100] The electrochemical reactor 150 may also include a porous separator 155 and one or more current collectors 156. The porous separator 155 may separate solid particles. The porous separator 155 may also limit contact with the anode 152. The porous separator 155 include, but is not limited to, a porous polymer and/or porous inorganic material. For example, the porous separator 155 may include an inorganic material (e.g., a glass and/or a ceramic), an organic material (e.g., a fiber of an organic material and/or a fiber of a polymeric material), and/or a hybrid fibers including an inorganic and organic material. [00101] The electrochemical reactor 150 may utilize slurry electrodes as described above. The slurry electrodes may include electrically conductive particles that form a 3- dimensional electrode in suspension, where charge transfer may occur through a percolation network of conductive particles rather than through a 2-dimensional conductive electrode surface. The slurry electrodes may increase the electrochemically-active surface area of electrodes, improve charge/discharge rates, and/or increase the total system capacity of the electrochemical reactor 150. [00102] Following electrolysis, the Fe⁰ (e.g., target material 113a) may be separated using a magnetic separator 160. The magnetic separator 160 may be a rotary magnetic separator or another suitable magnetic separator. [00103] In process 120, one or more target material(s) 113b, 113c, 113d may be extracted using a low temperature thermochemical loop that leach and precipitate the target material(s). In one embodiment, the target material(s) may include Al, and/or Si. In this embodiment, the process 120 may precipitate Al2O3 and/pr SiO2. The process 120 may recover and reuse both the leachant and precipitant as shown in FIG.1, right. In some embodiments, Ti may also be isolated as a pure compound from Ti-rich red mud using the process 120. The generated alkaline waste liquor may be carbonated using atmospheric carbon dioxide. [00104] As shown in FIG.1, the process 120 may form a loop including three main steps. In the first step 120-1, the digest reagent (e.g., Ammonium bifluoride (NH4H2F)) may be generated and/or regenerated at a temperature of approximately 100 ℃. In the second step 120-2, the feedstock 111 may then be digested at a temperature of 25 ℃ to 100 ℃. The feedstock 111 may be unprocessed red mud. Alternatively, the feedstock 111 may be Fe- depleted red mud (e.g., red mud following electrolysis with process 110). In the third step 120-3, the target material(s) may be precipitated at a temperature of 25 ℃ to 100 ℃. [00105] FIGS.2 and 3 show low temperature thermochemical loops 120a and 120b, respectively, that may be used for process 120 in the method 100. Thermochemical loops 120a and 120b may be used to leach and precipitate target element(s) including Al2O3, SiO2, and/or TiF4. [00106] FIG.2 shows thermochemical loop 120a. Thermochemical loop 120a may be used in the method 100. Thermochemical loop 120a may include six steps. In the first step, 120a-1, the digest reagent (e.g., NH4H2F) may be generated and/or regenerated. In the second step, 120a-2, the feedstock 111 may then be digested using the digest reagent. In the third step, 120a-3, a target material 113 (e.g., SiO2) may be precipitated. In the fourth step, 120a- 4), an ammonia gas (e.g., ammonium hydroxide (NH4OH)) may be generated. In the fifth step, 120a-5, ammonium (e.g., ammonium fluoride (NH4F)) may be recovered. In the sixth step, 120a-6, the residue from the feedstock digestion from step 120a-2 may be further decomposed to produce ammonium hexafluorotitanate ((NH4)3TiF6), which may further remove any Ti from the feedstock 111. [00107] FIG.3 shows thermochemical loop 120b. Thermochemical loop 120b may be used in the method 100. Thermochemical loop 120b may include ten steps. In the first step, 120b-1, the digest reagent (e.g., NH4H2F) may be generated and/or regenerated. In the second step, 120b-2, the feedstock 111 may then be digested using the digest reagent. In the third step, 120b-3, a target material 113 (e.g., SiO2) may be precipitated. In the fourth step, 120b- 4), an ammonia gas (e.g., ammonium hydroxide (NH4OH)) may be generated. In the fifth step, 120b-5, ammonium (e.g., ammonium fluoride (NH4F)) may be recovered. In the sixth step, 120b-6, the residue from the feedstock digestion from step 120b-2 may be further decomposed to produce ammonium hexafluorotitanate ((NH4)3TiF6), which may further remove any Ti from the feedstock 111. In the seventh step, 120b-7, ammonium hexafluoroaluminate ((NH4)3AlF6) may be defluorinated, in the eighth step, aluminum sulfate (Al2(SO4)3) may undergo hydrolysis. In the ninth step, the generated Alumina is dehydrated. In the tenth step, REEs are leached and aluminium oxide (Al2O3) is generated. [00108] The method 100 may also include one or more additional steps to collect the target material(s) 113 from the feedstock 111. The target material(s) may be collected from the remaining feedstock after electrolysis and/or acid leaching. Said target material(s) 113 may be dissolved in solution and/or in solid form. In some embodiments, collection of the target material(s) 113 may be conducted by filtration of the electrolyte. In some embodiments, collection of the target material(s) 113 may be conducted by magnetic or eddy current separation. In other embodiments, collection of the target material(s) 113 may be conducted by one or more of the following of filtration and magnetic and eddy current separation. In some embodiments, the target material(s) 113 may be separated from the iron as a solution, and said solution may be subsequently processed to concentrate one or more target material(s) 113 by processes including, but not limited to, drying, crystallization, precipitation, electrodeposition, electrowinning, electrorefining, electrocoagulation, precipitation in an electrolytically produced pH gradient, absorption using ion exchange resins, chelation, bioabsorption, and/or biomining. [00109] Preferably, the feedstock 111 is an iron-containing material. In some embodiments, the feedstock 111 is a natural occurring mineral including, but not limited to, bauxite, hematite, aeschynite, allanite, gadolinite, magnetite, magmatic magnetite-hematite bodies, iron oxide-copper-gold deposits, and/or carbonatites. In other embodiments, the feedstock 111 is a waste stream including, but not limited to, municipal solid waste incinerator ashes, bauxite residue, magnet waste, coal fly ash, ferrochrome slag, sewage sludges, and/or mine tailings. In certain embodiments, the feedstock 111 may have undergone a chemical pretreatment, for example, the removal of metals by acidic leaching (e.g., process 120, 120a, and/or 120b as described above). The feedstock 111 may be suspended in the electrolyte 151 with a ratio of solid material to liquid electrolyte of about 0.1g/5mL to about 0.1g/100mL, including all ratios in between. The term “about,” when used to describe the ratio of solid material to liquid electrolyte, is intended to cover variations that may arise when the feedstock 111 is suspended in the electrolyte 151. For example, “about 0.1g/5mL” may correspond to a range of 0.095g/4.75mL to 0.105g/5.25mL (+/- 5% variation), including all values and sub-ranges in between. [00110] The amount of feedstock 111 used per surface area of cathode electrode 153 may range from about 0.1g/cm² to about 0.1g/50cm², including all ratios in between. The term “about,” when used to describe the amount of feedstock 111 used per surface area of cathode electrode 153, is intended to cover variations that may arise with the amount of feedstock 111 used. For example, “about 0.1g/cm²” may correspond to a range of 0.095 g/cm² to 0.105 g/cm² (+/- 5% variation), including all values and sub-ranges in between. [00111] The target materials 113 may include a main constituent of the feedstock 111, a rare earth element, a precious metal (PM) element, a transition metal element, a metalloid, and/or a platinum group element. For example, the target materials 113 may include, but are not limited to, iron (Fe), aluminum (Al), sodium (Na), calcium (Ca), chromium (Cr), magnesium (Mg), boron (B), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), manganese (Mn), gallium (Ga), lead (Pb), barium (Ba), strontium (Sr), copper (Cu), bismuth (Bi), lithium (Li), zinc (Zn), nickel (Ni), indium (In), thallium (Tl), cobalt (Co), cadmium (Cd), scandium (Sc), nickel (Ni), cobalt (Co), silicon (Si), titanium (Ti), vanadium (V), gallium (Ga), hafnium (Hf), indium (In), niobium (Nb), tantalum (Ta), zirconium (Zr), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), yttrium (Y), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), thorium (Th), uranium (U), gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), rhenium (Re), palladium (Pd), osmium (Os), iridium (Ir), and/or platinum (Pt). [00112] In one embodiment of the invention, the feedstock 111 is in contact with the cathode material under an applied potential. Under the applied potential, the iron compounds in the feedstock 111 may be electrolytically reduced to iron metal (Fe⁰) and bound upon the electrode. The remaining feedstock may contain the target material(s) 113 and may be collected after conducting the electrolysis (e.g., process 110 described above). [00113] In another embodiment of the invention, the feedstock 111 is contacted with the cathode material under an applied potential and surrounded by an aqueous alkaline electrolyte (e.g., electrolyte 151). Under the alkaline conditions, some components of the feedstock including, but not limited to Al, Mg, Ca, and/or Si, may dissolve into the electrolyte 151. Under the applied potential, the iron compounds in the remaining feedstock may be electrolytically reduced to iron metal and bound upon the electrode (e.g., using process 110 described above). The remaining feedstock, which may be soluble or insoluble in alkaline conditions, may contain the target material(s) 113 and may be collected after conducting the electrolysis (e.g., process 110). In another embodiment of the invention, the feedstock 111 is bauxite residue, which is electrolyzed under an applied potential and surrounded by an aqueous alkaline electrolyte (e.g., electrolyte 151). Under the alkaline conditions, the base-soluble components are solubilized into the electrolyte (e.g., electrolyte 151). Under the applied potential, the iron compounds in the bauxite residue are reduced to iron metal and bound to the electrode. The remaining feedstock, which may be soluble or insoluble in alkaline conditions, may contain the target material(s) 113 and may be collected after the electrolysis (e.g., process 110). [00114] Example 1: A Method for Collecting Target Elements of Yttrium (Y) and Lanthanum (La) [00115] In one specific example of the invention, the target elements may include Y and La in the form of Y2O3 and La2O3. The starting feedstock 411 may be a powder containing 2.5wt% La2O3 and 2.5wt% Y2O3, with the remaining material may be composed of 40% Fe(OH)3 and 55% Al(OH)3. The feedstock may be synthesized by dissolving FeCl3, Al(OH)3, Y2O3, and La2O3 in 1M HCl with concentrations of 5000, 5000, 500, and 500 for Fe, Al, Y, and La, respectively. The Fe, Al, Y, and La may then be precipitated out as a mixed hydroxide at pH 9 by the addition of 10M NaOH. [00116] FIG.4A illustrates an example electrochemical cell 450 for collecting target elements from the feedstock 411. The feedstock 411 was placed onto the cathode of the electrochemical cell 450. The electrochemical cell 450 may include an anode 452, a cathode 453, and an electrolyte 451. The electrolyte 451 may be a 10M NaOH electrolyte. The anode 452 and the cathode 453 may both be made of steel, or another suitable material. The electrochemical cell 450 may also include a reference electrode 457. The reference electrode 457 may be a Hg/HgO electrode. A potentiostat (not shown) or another suitable power source may provide power to the electrochemical cell 450. The cell 450 may be designed such that the feedstock powder 411, under no agitation, may sediment onto the cathode electrode 453. About 0.1g of feedstock 411 may be used per 6mL of electrolyte 451. The electrochemical cell 450 may be operated at a temperature of 90℃ and at a constant potential of about 1.8V. At this cell voltage, the corresponding anodic and cathodic reactions are provided in Equations 1 and 2 as follows:

[00117] In an alkaline solution such as 10M NaOH, Al is separated from the feedstock 411 as it may be solubilized as the hydrated AlO2- ion. At 1.8V, which corresponds to a cathodic potential of -1.2V versus a reference Hg/HgO electrode 457, the Y2O3 and La2O3 undergo no phase change, while the Fe may transition from Fe2O3 or Fe(OH)3 to Fe⁰. At these potentials, the iron oxide and hydroxide particles in contact with the electrode surface (e.g., the cathode 453) may undergo a phase change where Fe⁰ nucleation and crystallization may occur on the electrode surface (e.g., the cathode 453). After complete conversion of the iron oxides and hydroxides, all of the Fe is adhered to the electrode surface (e.g., the cathode 453) as recrystallized Fe⁰ (e.g., target material 413a), while any remaining residue 413 may be comprised of electrochemically inactive material. FIG.4B shows the cathode 453 before and after electrolysis and FIG.4C shows the REE rich residue after electrolysis. In this specific case, the remaining electrochemically inactive material (e.g., residue 413) may include the target list of elements, Y2O3 and La2O3. After 24 hours of electrolysis at 1.8V, the electrolyte liquid 451 and the remaining feedstock powder (e.g., the residue 413) may be poured through a polypropylene membrane filter. The remaining powder may be collected as the filter cake, rinsed with deionized water, and analyzed using energy dispersive spectroscopy (EDS). [00118] The EDS spectra and elemental composition are shown in FIGS.5A and 5B, respectively. The EDS spectra shows that the recovered residue 413 consists of 28 wt% and 40 wt% of Y and La respectively. Additional elements include Na, Fe, Ca, and Al, which all constitute less than 3 wt% of the total material weight. [00119] Example 2: A Method for the Separation of Critical Materials (CM) from Fe/Al-Rich Matrices [00120] Red Mud Sourcing [00121] A 5 kg sample of red mud from Rio Tinto - Arvida Research and Development Centre (ARDC), Quebec, Canada was received. A compositional analysis of the feedstock 611 (e.g., the red mud sample) was conducted and is described in more detail below. The sample was received as a wet alkaline solid shown in FIG.6. [00122] Red Mud Composition [00123] Water content [00124] Approximately 0.7 kg of the wet feedstock 611 was dried at 100°C in oven for 24 hours. The water content of the feedstock 611 was measured at about 34% by mass. About 100 g of dried sample was milled using a roller jar mill with 5 mm yttria-stabilized zirconia grinding spherical media and 100 g of ethanol for 24 hours. After the sample was dried, it was sieved using a 1 mm mesh sieve. [00125] Main constituents, rare earth elements (REEs), Platinum Group materials (PGMs), transition metal elements, and/or precious metal (PM) [00126] Approximately 0.1 g of the dried and sieved sample powder was dissolved by stirring in 10 mL of aqua regia using solid-to-liquid ratio of 1:100 at 60°C for 24 hours. The leachate was subsequently filtered with 0.2 µm syringe filter and diluted for Inductively Coupled Plasma Mass Spectrometry (ICP-MS) characterization. Because Ti and Si may not fully dissolve in Aqua regia, they were excluded from the present analysis. The composition of the feedstock 611 is shown in FIGS.7A–7C and in Tables 3–5. The values in Tables 3–5 can be varied by ^0.01%, or ^0.05%, or ^0.1%, or ^0.5%, or ^1.0%, or ^1.5%, or ^2%, or ^2.5%, or ^3.0%, or ^3.5%, or ^4.0%, or ^4.5%, or ^5.0%. [00127] Table 3. Main constituents in feedstock 611 (wt%).

* Other includes Cr, Mg, B, Mn, Ga, Ag, Pb, Ba, Sr, Cu, Bi, Li, Zn, Ni, In, Tl, Co, and/or Cd. [00128] Table 4. Concentrations of REEs in feedstock 611 (mg/kg)

[00129] Table 5. Concentration of Platinum Group materials (PGMs), transition metal elements, and/or precious metal (PM) elements in feedstock 611 (mg/kg).

[00130] The total REE content in the feedstock 611 is about 341 ppm on a metal basis. The top five most concentrated REEs are Ce, Th, La, Nd, and Sc. The most valuable element amongst the REEs present, at current market prices, is Sc at a concentration of about 22 ppm. Sc is rarely concentrated in nature due to its lack of affinity to combine with common ore-forming anions. Materials containing Sc 20-50 ppm can be considered as a Sc ore. Thus, Rio Tinto red mud (e.g., feedstock 611) can be regarded as a “synthetic” Sc ore. Note also that the Au in feedstock 611, about 9 ppm, is similar to that found in high-grade gold ore (about >1.5 ppm open pit and about >8 ppm underground mines); the lowest ore grade of gold that is considered to be economical to mine is about 0.5 ppm. The term “about,” when used to describe the total REE content in the feedstock 611, is intended to cover variations that may arise within the feedstock 611. For example, “about 341 ppm” may correspond to a range of 324 ppm to 358.1 (+/- 5% variation), including all values and sub- ranges in between. [00131] Red Mud Valorization [00132] Disclosed herein are methods for the recovery of Fe and/or Al with a purity upwards of approximately 100% and the recovery of REEs of approximately 11 wt% of red mud on a metal basis and of approximately 13 wt% on an oxide basis. [00133] Because electrowinning potentials are well-separated, electrowinning Cu, Pb, and Zn may be carried out with high selectivity. Since the precipitation pH values are also well-separated, precipitation of Mg and Ca may also be carried out with high selectivity. However, metals with similar precipitation pH ranges—including Fe, Al, and REEs—may be more difficult to separate. Accordingly, these metals are co-precipitated as a mixture of the corresponding hydroxides at intermediate pH values (e.g., a pH of about 3 to about 9). It was noticed that there was a similarity between the pH of about 3 to about 9 precipitation from municipal solid waste acid leachate and red mud (e.g., feedstock 111, 411, and/or 611). Both materials are composed primarily of Fe and Al hydroxides, with smaller quantities of other metals such as REEs. The main qualitative difference is that red mud contains significant amounts of Ca and Ti. The approach to mining the red mud (e.g., feedstock 111, 411, and/or 611) disclosed herein is to separate the major elements (e.g., Fe and Al) from the REEs, aiming to achieve a rare-earth concentrate of similar composition to that obtained in current mining practices involving REE ore (approximately 10% on a metal basis and approximately 30% on an oxide basis). [00134] Herein, FIG.8 discloses a method 800 for processing a feedstock 811 to separate one or more target material(s) 813. The feedstock 811 may be any of the feedstocks described above (e.g., feedstock 111, 411, and/or 611). Preferably, the feedstock 811 may be an iron-containing material. In one embodiment, the feedstock 811 is red mud. The target material(s) 813 may be any of the target materials disclosed above. In one embodiment, the target material(s) 813 is at least one of a main constituent of the feedstock 811, a rare earth element, a precious metal (PM) element, a transition metal element, a metalloid, and/or a platinum group material (PGM). For example, the target materials 113 may include, but are not limited to, iron (Fe), aluminum (Al), sodium (Na), calcium (Ca), chromium (Cr), magnesium (Mg), boron (B), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), manganese (Mn), gallium (Ga), lead (Pb), barium (Ba), strontium (Sr), copper (Cu), bismuth (Bi), lithium (Li), zinc (Zn), nickel (Ni), indium (In), thallium (Tl), cobalt (Co), cadmium (Cd), scandium (Sc), nickel (Ni), cobalt (Co), silicon (Si), titanium (Ti), vanadium (V), gallium (Ga), hafnium (Hf), indium (In), niobium (Nb), tantalum (Ta), zirconium (Zr), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), yttrium (Y), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), thorium (Th), uranium (U), gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), rhenium (Re), palladium (Pd), osmium (Os), iridium (Ir), and/or platinum (Pt). In one embodiment, the target material(s) 813 is a main constituent of the feedstock 811 (e.g., Fe, Si, and/or Ti) and a REE. In another embodiment, the target material(s) 813 is a main constituent of the feedstock 811 (e.g., Fe, Si, and/or Ti), a PGM (e.g., Pt, Pd, Rh, Ru, Os, and/or Ir), and a REE. [00135] The method 800 may include several steps including acid leaching 802, pH 3– 9 precipitation 806, and Fe electrowinning 810. Each of these steps is described in more detail below. [00136] Acid leaching [00137] The as-received feedstock 811 (e.g., a Rio Tinto red mud samples) may be dried, milled, and sieved (1 mm) before use (not shown in FIG.8). In the first step, 802, an acid leachate 870 may be used to leach the feedstock 811, thereby dissolving soluble metals and allowing the separation of one or more insoluble target material(s) 813. The leachate 870 may be a 1.0 M HCl and 2.0 M NaCl solution, or another suitable acid leachate. The acid leachate 870 may be used to acid leach pre-processed feedstock 811 at a solid-to-liquid ratio of about 1:10 under stirring at room temperature for 24 hours. Instead of, or in addition to, the acid leaching disclosed in step 802, the feedstock 811 may also be processed using process 120 described above to precipitate one or more target material(s) 813. [00138] In step 804, the insoluble solids 871 may be subsequently filtered and rinsed under vacuum filtration. The insoluble solids 871 may contain one or more target material(s) 813a. For example, the insoluble solids 871 may include, but are not limited to, Si, Ti, and/or other PGMs. The acid leachate 870 may be collected, separated, and characterized by ICP- MS (not shown in FIG.8). The ICP-MS results are provided in Table 6 below. The values in Table 6 can be varied by ^0.01%, or ^0.05%, or ^0.1%, or ^0.5%, or ^1.0%, or ^1.5%, or ^2%, or ^2.5%, or ^3.0%, or ^3.5%, or ^4.0%, or ^4.5%, or ^5.0%. [00139] Table 6. Fe, Al, and REEs concentrations feedstock 811 and acid leachate 870 as measured by ICP-MS.

[00140] The element concentration may decrease in the leachate 870 compared to the feedstock 811 due to the dilution and the dissolution capacity of the solvent (e.g., the acid leachate 870). The leaching yield of REEs may range from 12% to 55%, including all values in between. The leaching yield of Al may range from approximately 36% to 50%. The leaching yield of Fe may range from approximately 2% to 20%, including all values in between. However, even with a lower leaching yield, Fe and Al may still be the dominant metal elements in the leachate 870. The leaching yield may be increased by decreasing the pH, milling the feedstock 811 into smaller sizes, decreasing the solid-to-liquid ratio during leaching, and/or increasing the temperature during leaching. [00141] Since Si cannot be measured by ICP-MS and Ti has low dissolution under the leaching protocol conditions (e.g., step 802), X-ray fluorescence (XRF) may be used to detect Si and Ti content in addition to ICP. The insoluble solids 871 obtained from step 804 were rinsed with DI water and dried for composition analysis by XRF. The XFR results are provided in Table 7. The values in Table 7 can be varied by ^0.01%, or ^0.05%, or ^0.1%, or ^0.5%, or ^1.0%, or ^1.5%, or ^2%, or ^2.5%, or ^3.0%, or ^3.5%, or ^4.0%, or ^4.5%, or ^5.0%. [00142] Table 7. Feedstock 811 and insoluble solids 871 composition as analyzed by XRF.

[00143] The weight percent of the majority of elements may decrease after leaching. For example, the weight percent of Fe may decrease from approximately 41.8% to approximately 36.2%, the weight percent Al may decrease from approximately 7.4% to approximately 4.6%, the weight percent Si may decrease from approximately 4% to approximately 1.7%, the weight percent Ti may decrease from approximately 2.9% to approximately 2.6%, and the weight percent Ca may decrease from approximately 1.48% to approximately 0.26%. This may indicate the partial dissolution of the majority of elements. The insoluble solids 871 do not include Mg, Sr, Ba, which indicates the full dissolution of these three elements in acid leachate 870. The increase of Na and Cl may be from the solvent (e.g., the acid leachate 870). [00144] Precipitation at pH 9 [00145] In step 806, a base 875 (e.g., NaOH) may be slowly added into the filtered leachate 870a with continuous stirring to induce precipitation until a leachate 870b with a pH of about 9 is reached. Stirring ceased at a pH of about 9 and the leachate 870b was settled over several hours. In step 808, the leachate 870b may be filtered to obtain precipitates 872. The leachate 870b may contain one or more target elements 813b. The precipitates 872 may subsequently vacuum filtered and rinsed with DI water. The precipitates 872 are shown in FIGS.9A–9D. FIG.9A shows an image of the precipitates 872, FIG.9B shows an image of dried precipitates 872, FIG.9C shows an image of crushed dry precipitates 872, and FIG.9B shows an image of milled dry precipitates 872. The term “about,” when used to describe the pH, is intended to cover variations that may arise with the amount of base used. For example, “about 9” may correspond to a pH range of 8.91 to 9.09 (+/- 1% variation) including all values and sub-ranges in between. [00146] The precipitates 872 may be dried and redissolved in acid and diluted and filtered for ICP-MS (not shown in FIG.8). The ICP-MS results of the precipitates 872 are provided in Table 8. The values in Table 8 can be varied by ^0.01%, or ^0.05%, or ^0.1%, or ^0.5%, or ^1.0%, or ^1.5%, or ^2%, or ^2.5%, or ^3.0%, or ^3.5%, or ^4.0%, or ^4.5%, or ^5.0%. [00147] Table 8. Fe, Al, and REEs concentrations in Feedstock 811, precipitates 872, and remaining residues 873 after Fe electrolysis measured by ICP-MS.

[00148] Fe electrowinning [00149] The multi-component Pourbaix diagrams for Fe, Sc, Nd, and Pr are provided in FIG.10. Sc, Nd, and Pr were used as representative REEs within the model and it was assumed that the chemistry of all other REEs was similar. Region 23 was identified of interest for the selective separation of Fe, Al, and REEs, as the Fe can be electrowon from Fe2O3 while Al remains soluble and the REEs remain insoluble in the solution. The Fe electrowinning methods disclosed herein may be performed using an alkaline or an acidic solution and/or suspension. During alkaline electrowinning, the iron may be present as iron hydroxide and/or iron oxide and the electrowinning may convert the iron hydroxide and/or iron oxide to iron metal. During acidic electrowinning, the metals, including any iron, may be dissolved and the electrowinning may generate metal deposits from the ions in the acidic solution. [00150] Alkaline Fe electrolysis [00151] In step 810, the precipitates 872 may be combined with an electrolyte 851 in an electrochemical cell 450. The alkaline Fe electrolysis in step 810 may be performed using the process 110 described above. As described above, the electrochemical cell 850 may include an anode 852, a cathode 853, and an electrolyte 851. A potentiostat (not shown) or another suitable power source may provide power to the electrochemical cell 850. The electrolyte 151 may be 1.0–20.0 M KOH and/or NaOH as described above. The feedstock 811 may be suspended in the electrolyte 851 with a ratio of solid material to liquid electrolyte of about 0.1g/5mL to about 0.1g/100mL, including all ratios in between. The amount of feedstock used per surface area of cathode 853 may range from about 0.1g/cm² to about 0.1g/50cm², including all ratios in between. The anode 852 and the cathode 853 may both be made of steel, or another suitable material as described above. The electrochemical cell 850 may also include a reference electrode (not shown). The reference electrode may be a Hg/HgO electrode as described above. [00152] The alkaline Fe electrolysis in step 810 may be performed using an electrochemical cell 850 as described above. For example, the electrochemical reaction may be facilitated by an applied cathodic current in the range of about 1 uA/cm² to 1A/cm² as described above. In another embodiment, the electrochemical reaction may be facilitated by an applied potential in the range of about 0.1V to about 5V as described above. [00153] In Region 23, Fe and REEs coexist as metal and oxides, respectively, while Al can be separated as it is soluble as the hydrated AlO2^– ion. In the transition from Region 11 to Region 23, REEs undergo no transition, while Fe transitions from Fe2O3 to Fe⁰. For this phase change to occur, the Fe2O3 particles (e.g., precipitate 872) may need to have contact with the electrode surface (e.g., cathode 853) at the correct potential range to enable Fe nucleation and crystallization to occur at the electrode surface (e.g., cathode 853). After the Fe electrowinning, the Fe⁰ (e.g., target material 813c) may be deposited on the electrode surface (e.g., cathode 853) as described above while the electrochemically-inactive materials may remain as insoluble residue (e.g., residue 873) in the solution (e.g., electrolyte 451). The remaining electrolyte 451 may also include one or more target material(s) 413 (e.g., Al). This electrochemically-inactive residue 873 may include the REE concentrates (e.g., target material(s) 813d), as predicted by the Pourbaix diagram depicted in FIG.10. [00154] This was explored using the electrochemical cell 850 shown in FIGS.11A and 11B for the alkaline Fe electrowinning of step 810. The cell 850 may include a steel anode 852 and a steel cathode 853 for the anodic and cathodic reactions, which are provided in the Equations 1 and 2, reproduced again below:

[00155] Approximately 0.5 g of pH 9 milled dry precipitates 872 and an electrolyte 851 (e.g., 200 mL of 10 M NaOH) were used in the cell 850, with applied voltage 1.2 V at 60 °C for 24 hours. The cell 850 and a schematic of the cell 850 and Fe electrowinning concept are depicted in FIGS.11A and 11B. [00156] In step 812, after the electrolysis of the precipitates 872 (see FIG.12D), the remaining electrolyte 851 and residue 873 (see FIG.12B) may be filtered and rinsed with DI water under vacuum filtration to obtain the filtered residue 873 and electrolyte 851a. Electrolyte 851a may include one or more target materials 813e (e.g., Al). The filtered residue 873 on filter paper is shown in FIG.12C. The remaining residue 873 (see FIG.12D, right) may be collected, dried, redissolved in acid, and analyzed by ICP-MS after drying (not shown in FIG.8). Table 8 provides the REE, Al, and Fe concentrations of the pH 9 precipitates 872 and the remaining residue 873 after the Fe electrolysis of step 810. The values in Table 8 can be varied by ^0.01%, or ^0.05%, or ^0.1%, or ^0.5%, or ^1.0%, or ^1.5%, or ^2%, or ^2.5%, or ^3.0%, or ^3.5%, or ^4.0%, or ^4.5%, or ^5.0%. The REE concentrations are approximately 5–4000 times higher than the feedstock 811. The residue 873 may include one or more REE target material(s) 813d. Due to the increased Th concentration, the radiation of residues 873 was measured by a Geiger counter as approximately < 0.01 mR/hr, which is approximately equivalent to the background level. Based on the REEs content of the Fe electrolysis residues 873, approximately 11 wt% of feedstock REEs on a metal basis and approximately13 wt% on an oxide basis were recovered. [00157] The deposition of target material 813c (e.g., Fe⁰) on the cathode 853 surface (see FIG.12A) was rinsed, dried and then analyzed by EDX (see FIG.13B). The EDX results in FIG.13B indicate that the deposition of target material 813c is approximately 100% Fe⁰. EDX was performed on multiple samples and several locations per sample, and the results indicate the full reduction of Fe on the cathode 853 surface. A tree-shaped Fe dendrite formation was observed by SEM (see FIG.13A). This observation may be informative for understanding the mechanism of the alkaline Fe electrolysis within the process disclosed herein. [00158] Additional magnetic separation [00159] After Fe electrolysis in step 810, the electrochemically inactive residue 873 may further be separated from any reduced iron particles that may not deposit on the electrode surface (e.g., cathode 853) by magnetic separation. It was observed that the residue mixture in the electrolyte 851 may be magnetically separated (not shown in FIG.8). After the residues 873 were collected and rinsed after filtration, they may be re-dispersed in DI water, and a strong neodymium-iron-boron (NIB) magnet may be placed outside the container to hold the magnetic materials. The solution and residues were stirred to disperse further and separate the non-magnetic material particles (e.g., residue 873) from the magnetic particles (e.g., reduced iron particles or 813c). The solution with non-magnetic particles (e.g., residue 873) may be subsequently collected, leaving the magnetic particles (e.g., 813c) in the container (see FIG.14). This method may be used in combination with the operation flow disclosed in FIG.8 following step 812 to remove any reduced iron (e.g., 813c) from the residue 873). Magnetic separation may allow for approximately 30 wt% REEs (e.g., 813d) recovery on an oxide basis. [00160] Thermodynamics of reduction of iron and non-iron oxide species [00161] FIGS.15A and 15B show Gibbs free energy of formation of non-iron oxide species and the minimum thermodynamic reduction potential for the non-iron oxide species, respectively. Using published thermodynamic data for the Gibbs free energy of formation for oxides (see FIG.15A) and the minimum reduction potential (see FIG.15B), it was verified that Fe2O3, Mn-oxides, and/or V-oxides, which are only present in low concentrations in red mud (see Table 9), may be the only species able to be reduced at the applied cathodic potentials of approximately 1.3V with respect to a Hg/HgO reference electrode. In FIGS. 15A–15B only the non-iron oxide species that do not contain rare earth elements are plotted, as oxide species containing rare earth elements may require a higher cathodic potential to be reduced. Non-iron oxide species containing rare earth elements may be inert oxides under the applied cathodic potentials (e.g., approximately 1.3V). The concentration of rare earth oxides in red mud may be less than 1 wt%. Using Equation 4 below, the Gibbs free energy of formation for the reaction in Equation 3 was calculated based on 1 mole of O2 (g), using standard states of the metal oxide, metal, and oxygen. In Equation 5, E is the thermodynamic reduction potential, ΔGf is the Gibbs free energy of formation, and n is the number of electrons transferred in the redox reaction, while F is Faraday’s constant.

[00162] Table 9 provides the composition of Fe2O3, Mn-oxides, and/or V-oxides, in red mud. [00163] Table 9. Composition of hematite and red mud, in terms of oxide constituents, wt%. Red mud composition.

[00164] In order to more realistically model the reaction conditions for reduction in this highly alkaline aqueous solution, it may be necessary to further determine how the activities of the soluble species and intermediates in the reaction are affected by temperature and/or concentration of NaOH ranging from 10 M to 20 M. The activities of these soluble species will then in turn influence the minimum thermodynamic potential for reduction of the iron oxide species. [00165] Design of bench-scale reactors for iron electrowinning [00166] Benchtop reactors handling approximately1 kg of starting material (e.g., feedstock 111, 411, 611, and/or 811) were developed for use with the methods disclosed herein. It was shown that iron (e.g., target material 813c) could be electrowon from red mud suspensions (e.g., feedstock 111, 411, 611, and/or 811) at a purity suitable for use as a feedstock in electric arc furnaces (EAFs). The microstructure of the electrowon iron may be dendritic and the iron may have no major impurities, consistent with the expectation that other metal oxides may not be reduced at the cathodic potentials applied. Since the electrowon iron may not be embedded in a matrix of other oxides, further separation of the iron from residue by mechanical and magnetic methods may be possible. The closest comparable product to the output of the alkaline electrowinning reactor may be direct reduced iron (DRI). It was demonstrated that it is feasible to attain the purity of DRI with iron from alkaline electrowinning of red mud when paired using the separation methods described herein. To accommodate the drop-in replacement of this alkaline electrowinning product into existing EAF processes, other post processing (carbon additions, sintering) may also be used to meet the physicochemical requirements for steel production. [00167] The feasibility of producing electrolytic iron from red mud in an alkaline medium at 100°C is demonstrated herein. A feedstock 1611 obtained from Rio Tinto was dried, milled, sieved (e.g., approximately <1 mm), and characterized by various techniques to determine the chemical and mineralogical compositions. FIGS.16A–16C show SEM and EDX mapping scans, which indicate the chemical and possible mineralogical composition of feedstock 1611. Table 10 provides an example of the element content of the sample feedstock 1611. The components of the feedstock 1611 may include, but are not limited to, C, O, Na, Al, Si, Ca, Ti, Fe, Co, and Cu (Table 10). The major phase of iron in the feedstock 1611 was hematite (α-Fe2O3), and the Fe concentration may be approximately 33 wt% based on ICP-MS characterization. [00168] In FIG.16A, the SEM shows the average size is approximately < 3 ^^m for feedstock 1611. The specific surface area (BET) of the processed feedstock 1611 is approximately 26.94 m²/g. In the methods disclosed herein, the feedstock 1611 was observed to readily absorb water and become a flowable slurry when the liquid content was higher than approximately 50%. [00169] The processed feedstock 1611 was mixed with 12.5 M NaOH at room temperature at a solid-to-liquid ratio of 1:3, which was selected based on the lower end of the actual red mud water content range. [00170] Table 10. EDX spectrum table of composition elements of feedstock 1611.

[00171] A reactor or electrochemical cell 1750 shown in FIG.17A was designed in order to have a process capacity of approximately 1 kg feedstock 1711 per day. The electrochemical cell 1750 may be made of polymethylpentene (Kartell®), which was chosen for its resistance to alkaline solutions and its ability to operate at temperatures up to 170°C. Alternatively, the electrochemical cell 1750 may be made of another suitable material that exhibits a resistance to alkaline solutions and may operate at temperatures up to 170°C. The overall volume of the electrochemical cell 1750 is approximately 3.5 L. The electrochemical cell 1750may accommodate approximately 1 kg of feedstock 1711. The suspension was stirred at 300 rpm using a Teflon-coated magnetic bar. The cell 1750 may be submerged in a silicone oil 1758 bath to maintain a temperature of 100°C during the reactions. [00172] The reactor 1750 may be equipped with a three-electrode system. The electrodes may include a working electrode 1753, a counter electrode 1752, and a reference electrode 1757. The working electrode 1753 may be a cylindrical graphite rod (McMaster- Carr) with a wetted area of approximately 37.5 cm². The graphite surface may be polished with a fine sandpaper (e.g., about 100 µm), washed with 1 M HCl (Sigma-Alrich), then rinsed with deionized water, and dried in air. A platinum-coated titanium mesh (Yosoo Health Gear) may be used as the counter electrode 1752 and may roughly form a cylinder around the graphite working electrode 1753, as shown in FIG.17B. A Hg/HgO (1M NaOH) electrode (BASi®) may be used as the reference electrode 1757. A potentiostat 1754 (BIOLOGIC SAS) may provide the power supply and facilitate data measurement and recording. [00173] Iron electrowinning of feedstock 1711 may be performed as described above. For example, cyclic voltammetry (CV) was conducted, sweeping voltage from about -0.2 V to about -1.4 V and then back to about -0.2 V versus Hg/HgO, at a scan rate of about 40 mV/s. The primary phase of iron in the feedstock 1711 investigated was hematite α-Fe2O3, and the solubility of trivalent iron Fe(OH)4- in NaOH was reported at about 2.6 × 10^-3 M. Without being bound to a particular theory, the electrochemical reduction of iron oxide in red mud may involve two parallel reduction processes: (1) reduction of ferric Fe(OH)4- ions, and (2) reduction of hematite particles in contact with the working electrode 1753 surface to magnetite Fe3O4, followed by further reduction to iron Fe. [00174] In FIG.18, the CV curves present peaks labeled as C1, C2, and A1. Peak C1 corresponds to the reduction of Fe(OH)4- to Fe(OH)3-. Peak C2 corresponds to the reduction of intermediate magnetite to iron metal, with a sharp rise of current from -1.22 V vs. Hg/HgO, indicating both iron deposition and hydrogen evolution. Peak A1 represents the anodic dissolution of the iron deposited or the oxidation of intermediate divalent iron to Fe(OH)4-. [00175] During the iron electrowinning, a constant current of about 150 mA was applied, with a current density of 4 mA/cm². The cell voltage and working electrode 1753 potential were monitored throughout the experiment. The cell voltage varied from about -1.2 V to about -2.3 V due to bubbles trapped in the suspension (see FIGS.19A–19B). The electrowinning lasted for about two hours. At the end of the electrowinning, the working electrode 1753 was removed from the reactor, rinsed thoroughly with deionized water, and dried. The deposit was then detached using polypropylene spatulas from the graphite electrode for subsequent characterization. The masses of the working electrode 1753 before (Mbefore) and after (Mafter) the electrowinning test were weighed, and the mass of deposited materials was calculated as Mdeposit = Mafter - Mbefore. Then, the mass of deposited materials ^^ ^^ ^^ was compared with the theoretical value Mtheor = ^^ for Faradaic efficiency estimation _{^^(%) =} ^^^^^^^^^^^^^^^^ ^^^^ℎ^^^^^^ _{× 100 , where m is the molar weight of the metal, I is the current, t is the} duration of the electrowinning, n is the number of the electrons involved, and F is the Faraday constant. [00176] The observed Faradaic efficiencies were relatively low, approximately 23%. This low efficiency may be attributed mainly to two factors, one being hydrogen evolution (HER) at the working electrode 1753, and the other being sluggish transport of particles to the electrode surface due to the high viscosity of the suspension. Over time, it was observed that the generated gas, assumed to be hydrogen, formed a three-phase foam (solid particles, aqueous solution, gas) (see FIGS.19A–19B) which may lower the suspension conductivity and impede particle migration to the electrodes 1751 and/or 1753. [00177] To reduce the generate of gas during the electrowinning, several modifications may be used, including, but not limited to, reducing the NaOH concentration, decreasing the solid-to-liquid ratio, and/or modifying the properties of the feedstock 1711 (e.g., particle size, particle surface area, and particle surface chemistry) using a pretreatment. [00178] The results disclosed herein show that the iron metal electrowon from feedstocks 111, 411, 611, 811, 1611, and/or 1711 has a high metallic content and high purity comparable to or better than direct reduced iron (DRI), and as such, the electrowon iron disclosed herein may be a suitable feedstock for electric arc furnace (EAF) technology. [00179] Steel production by electric arc furnaces (EAFs) has grown in North America. For example, as of 2014 approximately 63% of crude steel was produced by EAFs while only approximately 37% was produced by basic oxygen furnaces (BOFs). Some of the key considerations in using DRI as an input for the electric arc furnace are that in addition to arc melting of the metallic Fe, there is also the endothermic reaction of FeO + C → Fe + CO and in general a higher slag volume when DRI is the feedstock compared to scrap steel. Moreover, DRI is easier to handle and more homogeneous than scrap steel, and there is better control of slag foaming when using DRI. [00180] Several DRI specifications affect the EAF operation and the resulting crude steel product. In order to minimize the slag volume at a given basicity, the gangue mineral content (slag formers) may need to be relatively low. In terms of metallization or the degree to which Fe is present as iron oxides versus metallic iron, a low degree of metallization means more power is consumed for the endothermic reduction of iron oxides, while a high degree of metallization means less gaseous CO is generated in the reduction reaction and thus less bath agitation reduces the heat transfer and increases energy requirements. In both respects, the iron electrowon from red mud may have promising characteristics. First, iron electrowon from red mud (e.g., feedstock 111, 411, 611, 811, 1611, and/or 1711) should have minimal residual metallic elements such as Cr, Ni, Mo, and especially Cu and Sn. These tramp elements may cause embrittlement and have other detrimental effects on properties. Second, the electrowinning method disclosed herein may not thermodynamically reduce such species in feedstocks 111, 411, 611, 811, 1611, and/or 1711 to their metallic form at the potentials used for iron oxide reduction. [00181] Table 11 compares the characteristics of a typical DRI to electrowon iron (e.g., target material 813c) using the methods disclosed herein. In order to make the electrowon iron more closely replicate DRI, carbon may also be added to the iron. Production of DRI may occur in the solid state with macroscopic sintered iron oxide pellets and may result in porous iron pellets of about 4 mm to about 20 mm in diameter. The electrowon iron disclosed herein (e.g., target material 813c) may consist of powdered metallic iron with a much finer primary particle size of about 10 ^^m to about100 m. For example, the electrowon iron (e.g., target material 813c) may have a particle size of about 10 ^^m, about 20 ^^m, about 30 ^^m, about 40 ^^m, about 50 ^^m, about 60 ^^m, about 70 ^^m, about 80 ^^m, about 90 ^^m, or about 100 ^^m, including all values in between. Pelletizing and sintering of the electrowon iron (e.g., target material 813c) may be used to produce pellets of similar size and density to DRI (e.g., about 4 mm to about 20 mm in diameter). [00182] Table 11. Requirements for chemistry and physical properties of DRI as input to EAF. These chemistry specifications may be met for the electrowon iron disclosed herein. The particle size and packing of the electrowon iron may be modified by additional operations to meet the requirements.

[00183] The EDX point scan shown in FIG.20 and the results shown in Table 12, demonstrate that the primary particles of the dendritic Fe are high in purity. The Fe content of approximately 93 wt% is in the appropriate range for the metallization required for DRI charge in the EAF, while the other element compositions (e.g., C, O, and Na) are also within the specifications for DRI. [00184] Table 12. EDX spectrum table of composition elements.

[00185] In conclusion, the chemical composition and primary particle size of the iron electrowon from feedstocks 111, 411, 611, 811, 1611, and/or 1711using methods 100 and/or 800 disclosed herein is comparable to DRI feedstocks currently used in the steel industry. Isolating this electrodeposited iron from the rest of the red mud suspension, may allow the electrowon iron to be used as a product in the steel industry. [00186] Methods for improving the efficiency of electrowinning iron from red mud [00187] Electrowinning Fe from red mud (e.g., feedstock 111, 411, 611, 811, 1611, and/or 1711) may be less efficient and may have more sluggish kinetics compared to electrowinning Fe from synthetic or commercial Fe2O3. Thus, disclosed herein are methods to improve the efficiency of iron separation from red mud (e.g., feedstock 111, 411, 611, 811, 1611, and/or 1711). Without being bound to a particular theory, there may be several reasons for a lower Faradaic efficiency and current density when using red mud (e.g., feedstock 111, 411, 611, 811, 1611, and/or 1711). First, parasitic hydrogen evolution reaction (HER) at the working electrode (e.g., 453, 853, and/or 1753), which may also interfere with Fe deposition. Second, there may be a sluggish transport of reacting species to the working electrode (e.g., 453, 853, and/or 1753) surface. For the solid-state reduction mechanism, this may be due to high viscosity of the suspension and the three-phase foam of solid suspended particles, aqueous solution, and gas. For the solution-redeposition mechanism, this may be due to low diffusivity of Fe(OH)4-, which hinders transport to the working electrode (e.g., 453, 853, and/or 1753) surface. Third, there may also be a sluggish electron transfer due to insulating properties of reacting Fe₂O3 as well as inactive oxide phases, which may hinder a solid-state reduction mechanism. Fourth, the low solubility and dissolution kinetics of Fe(OH)4- dissolved species may hinder a solution-redeposition reduction mechanism. Fifth, the presence of dissolved and solid inactive impurity aluminosilicate species may also affect the efficiency, which is a challenge unique to electrowinning from red mud (e.g., feedstock 111, 411, 611, 811, 1611, and/or 1711). [00188] Herein, methods are disclosed that may improve the Faradaic efficiency and current density of Electrowinning Fe from red mud (e.g., feedstock 111, 411, 611, 811, 1611, and/or 1711) include, but are not limited to, enhancing transport of reacting species, enhancing electron transfer kinetics, and minimizing the aluminosilicate phase fraction in red mud. [00189] Methods for minimizing aluminosilicate phase fraction and liberating bound iron oxide phases in red mud [00190] In one embodiment, the feedstock (e.g., feedstock 111, 411, 611, 811, 1611, and/or 1711) may be pre-leached with an alkaline leach. The alkaline leach may remove aluminosilicate in the feedstock (e.g., feedstock 111, 411, 611, 811, 1611, and/or 1711) and may increase the accessibility and concentration of the target materials (e.g., Fe, Al and/or REEs). To address the problem of aluminosilicate impurities interfering with electroreduction of Fe2O3, the solubility of aluminate and/or silicate species may be increased by raising the pH of the solution phase, such that the dissolved aluminosilicate species may be separated from solid iron oxide or hydroxide by methods including, but not limited to, filtering, sedimentation, and/or centrifugation. As an example, herein an alkaline leach with varying base concentrations (including water leaching, i.e. a zero base concentration) to remove as much of the aluminosilicate phase fraction as possible may be performed. The concentration of the base may range from about 0 M to about 20 M. In one embodiment, the base may be NaOH. For example, the NaOH concentration may range from about 0 M NaOH to about 20 M NaOH, including all values in between. Alternatively, KOH or another suitable base including an OH- ion may be used. [00191] FIG.21 illustrates method 2100 for the removal of aluminosilicate impurities from a feedstock 2111. The Bayer process (see FIG.21) is typically optimized for high aluminate Al(OH)4- solubility, while minimizing SiO3^2- solubility. Traditionally, since it is desired for a pregnant Bayer liquor to contain only aluminate species, a NaOH concentration higher than about 10M is preferably not used in the Bayer process and desilication steps may be taken prior to Al(OH)3 precipitation from the pregnant Bayer liquor. Herein, because it is desirable to increase the solubility of both aluminate and silicate species, we pushed beyond the 10M NaOH concentrations typically employed in the Bayer process (e.g., up to 20 M NaOH) and subsequently washed the leachate away to dissolve some of the aluminosilicate by-products in the feedstock 2111, especially those surrounding bound Fe2O3. For example, water and/or a NaOH solution (e.g., 0 M NaOH to 20 M NaOH) may be used to leach the feedstock 2111 based on the steps provided in the Bayer process shown in FIG.21. In one embodiment, the temperature of the Bayer process may be increased during the leaching of the feedstock 2111. [00192] Method 2100 may be used to process a feedstock 2111 to remove alumina from the feedstock 2111. The resulting alumina free feedstock 2111a may then be used for acid leaching and electrowinning as described herein (e.g., in method 800). [00193] Thermodynamic modeling was performed using a Pitzer model for the Na⁺- Al(OH)4^–-SiO3^2--OH- system for relevant 2-body and 3-body cation-anion as well as anion- anion interactions, to understand the solubility of Al(OH)4- in the presence of SiO3^2- as a function of NaOH concentration. The presence of SiO3^2- may significantly limit the solubility of Al(OH)4- as shown in FIGS.22A–22B. However, increasing the NaOH concentration and remaining at room temperature may maximize the solubility of both the Al(OH)4- and SiO3^2- species, which may be beneficial for the methods disclosed herein. For example, FIG.22A shows that at a NaOH concentration of 4 mol/kg H2O (e.g., 3.72 M NaOH), the solubility of SiO3^2- may decrease as the concentration of dissolved Al(OH)4- increases. This may make it difficult to separate both aluminate and silicate simultaneously from insoluble solids in a feedstock (e.g., feedstock 2111). However, if the NaOH concentration is increased to 7 mol/kg H2O (e.g., 6.2 M NaOH), the solubility of SiO3^2- may go through a minimum with an increasing concentration of Al(OH)4- in the temperature range 25 to 100°C. Thus, it may be possible to achieve a high solubility of both species in the solution phase at a high Al(OH)4- concentration. Maximizing the solubility of these species may allow a significant portion of the solid aluminosilicates in red mud to dissolve from the red mud into the leachate and wash away. Accordingly, in one embodiment, the molar concentration of NaOH, or the molar concentration of OH- if another base is used (e.g., KOH), may be at least 4 M, preferably at least 5 M, and more preferably less than about the value of the solubility limit of the base (e.g., NaOH or KOH) at the temperature of the solution. [00194] In Table 13, the different NaOH concentrations at which feedstock 2111 was leached are provided. After leaching, the leachates were removed and stored, and the solids (e.g., feedstock 2111a) were rinsed by DI water until the supernatant reached a pH of about 7 to about 8. Then, the solids (e.g., feedstock 2111a) were dried for further analysis. [00195] Table 13. Alkaline leach of feedstock 2111 to minimize aluminosilicate content.

[00196] ICP-OES was conducted on all the leached and washed samples described in Table 13, which were subsequently digested in aqua regia (1 HNO3 : 3 HCl) for 36 hours at room temperature to verify that the phase fraction of aluminum-containing mineral phases in the feedstock 2111a content was decreased (see FIG.23A) and that the phase fraction of iron-containing mineral phases in the feedstock 2111a content was increased (see FIGS.23B and 23C). The resulting feedstock 2111a may be used as the feedstock for electrowinning in accordance with the methods (e.g., method 100 and/or 800) as disclosed herein. [00197] As shown in FIG.23A, there may be a smaller volume of an undigested silicate phase fraction (or at least finer undigested particles) in samples with higher NaOH leach concentration (see FIG.23A far right image). Without being bound to a particular theory, it is believed that there is minimal solubility of SiO2 in aqua regia and thus the visible particles 2376 in FIG.23A correspond to SiO2. In some embodiments, the visible particles 2376 may also include some bound Fe2O3 phases that may also not be digested in aqua regia. [00198] FIGS.23B and 23C show graphs of the concentration of Fe (far left bar), Ti (second to the left bar), Ca (middle bar), Al (second to the right bar), and Si (far right bar) under various alkaline leach conditions. About 0.1 g solids were digested in 10 mL aqua regia following different alkaline leach conditions (no leach, H20 leach, 10 M NaOH leach, 14 M NaOH leach, and 18 m NaOH leach) as described above. FIGS.23B and 23C demonstrates a reduced phase fraction of minerals containing Al, Ca and an increased phase fraction of minerals containing Fe, suggesting a liberation of the bound Fe2O3 phase, with increasing NaOH concentrations. [00199] Enhancing electron transfer between working electrode and electroactive iron oxide species [00200] To enhance the electron transfer, a conductive additive and/or coating may be coated on the Fe2O3 in red mud (e.g., feedstock 111, 411, 611, 811, 1611, 1711, and/or 2111a). For example, a high surface area, conductive carbon additive may be coated on the electronically-insulating Fe2O3 particles in feedstock 111, 411, 611, 811, 1611, 1711, and/or 2111a. Preferably the conductive additive is a conductive additive that is compatible with the DRI specifications. Preferably the conductive additive may not significantly alter the kinetics of a dissolution-redeposition mediated process. For example, the conductive additives may include a particle or a material with a similar size to a feedstock particle. The conductive additives may include, but is not limited to, a conductive carbon particle, a graphite particle, and/or a high purity iron particle. With respect to the method disclosed in FIG.8, the conductive additive may be added with the electrolyte 851 prior to step 810 of method 800. [00201] In another embodiment, the electron transfer may be enhanced by increasing the temperature during the electrowinning. For example, the temperature may be increased to about 110 °C, about 120 °C, about 130 °C, about 140 °C, about 150 °C, about 160 °C, about 160 °C, about 180 °C, about 190 °C, or about 200 °C, including all values in between. In another embodiment, the electron transfer may be enhanced by stirring during the electrowinning. For example, with reference to step 810 of method 800, the dry precipitates 872 and the electrolyte 851 in the cell 850 may be stirred continuously during the electrowinning (e.g., step 810). Alternatively, the dry precipitates 872 and the electrolyte 851 in the cell 850 may be stirred periodically during the electrowinning (e.g., step 810). For example, the electrolyte 851 may be stirred every five minutes, every 10 minutes, every 20 minutes, every 30 minutes, every 40 minutes, every 50 minutes, every hour, every few hours (e.g., 2–5 hours), once during the 24 hours, twice during the 24 hours, three times during the 24 hours, four times during the 24 hours, five times during the 24 hours, six times during the 24 hours, seven times during the 24 hours, eight times during the 24 hours, nine times during the 24 hours, and/or 10 times during the 24 hours. [00202] A System for the Separation of Critical Materials (CM) from Fe/Al-Rich Matrices [00203] FIG.24 discloses a system 2400 for processing a feedstock 2411 to separate one or more target material(s) 2413. The system 2400 may be used to perform the method 100 and/or 800 as described herein. The feedstock 2411 may be any of the feedstocks described above (e.g., 111, 411, 611, 811, 1611, 1711, and/or 2111a). Preferably, the feedstock 2411 may be an iron-containing material. In one embodiment, the feedstock 2411 is red mud. The target material(s) 2413 may be any of the target materials disclosed above. In one embodiment, the target material(s) 2413 is at least one of a main constituent of the feedstock 2411, a rare earth element, a precious metal (PM) element, a transition metal element, a metalloid, and/or a platinum group material (PGM). For example, the target materials 2413 may include, but are not limited to, iron (Fe), aluminum (Al), sodium (Na), calcium (Ca), chromium (Cr), magnesium (Mg), boron (B), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), manganese (Mn), gallium (Ga), lead (Pb), barium (Ba), strontium (Sr), copper (Cu), bismuth (Bi), lithium (Li), zinc (Zn), nickel (Ni), indium (In), thallium (Tl), cobalt (Co), cadmium (Cd), scandium (Sc), nickel (Ni), cobalt (Co), silicon (Si), titanium (Ti), vanadium (V), gallium (Ga), hafnium (Hf), indium (In), niobium (Nb), tantalum (Ta), zirconium (Zr), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), yttrium (Y), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), thorium (Th), uranium (U), gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), rhenium (Re), palladium (Pd), osmium (Os), iridium (Ir), and/or platinum (Pt). [00204] The system may include a first tank 2481 to hold a stock of the feedstock 2411 and a second tank 2482 to hold a stock of acid leachate 2470. The first tank 2481 may be connected via a pipe or conduit 2491a to a third tank 2483. The second tank 2481 may also be connected to the third tank 2483 by another conduit 2491b. The first tank 2481 may provide a supply of feedstock 2411 to the third tank 2483 via conduit 2491a. The second tank 2481 may provide a supply of acid leachate 2470 to the third tank 2483 via conduit 2491b. One or more valves 2492 may control the flow of the feedstock 2411 and/or acid leachate 2470 into the third tank 2483. The system may combine a portion of the feedstock 2411 and the acid leachate 2470 in the third tank 2483 to allow leaching of the feedstock 2411 as described above. The third tank 2483 may be connected via a conduit 2491c to a filter and/or filtration system 2460a. The filtration system 2460a may remove the insoluble solids 2471 from the acid leachate 2470 after the acid leaching of the feedstock 2411. The insoluble solids 2471 may be captured in a fourth tank 2484 for storage and/or additional processing to obtain one or more target material(s) 2413a. [00205] The system 2400 may further include a fifth tank 2485 to hold a base 2475. The fifth tank 2485 may be connected to a sixth tank 2486 via a conduit 2491e and a valve 2492. The sixth tank 2486 may be connected to the third tank 2483 via conduit 2491d and one or more valves 2492. The conduit 2491d may supply the filtered acid leachate 2470a to the sixth tank 2486 following the removal of the insoluble solids 2471 from the filtered acid leachate 2470a after the acid leaching of the feedstock 2411. The sixth tank 2486 may be connected via conduit 2491f to a filter and/or filtration system 2460b. The filtration system 2460b may remove the precipitate 2472 formed from the addition of the base 2475 to the filtered acid leachate 2470a. The precipitate 2472 may be removed for further processing in the system 2400. The resulting leachate 2470b may be captured in a seventh tank 2487 for storage and/or additional processing to obtain one or more target material(s) 2413b. One or more valves 2492 may control the flow of the leachate 2470b into the seventh tank 2487. [00206] The system may also include an electrochemical cell 2450 for alkaline electrolysis as described above. The electrochemical cell 2450 may include an anode 2452, a cathode 2453 as described above. The electrochemical cell 2450 may also include a reference electrode 2457 as described above. A potentiostat 2454 or another suitable power source may provide power to the electrochemical cell 2450. The electrochemical cell 2450 may be submerged in a silicone oil 2458 bath to maintain a temperature of 100°C during the operation of the system 2400. [00207] An eighth tank 2488 may provide a supply of an electrolyte 2451 for use in the electrochemical cell 2450. The electrolyte 2451 may be 1.0–20.0 M KOH and/or NaOH as described above. The electrolyte 2451 may be combined with the precipitate 2472 in a ninth tank 2489 as described above. The ninth tank 2489 may contain a stirrer (not shown) to mix the electrolyte 2451 and the precipitate 2472. Conduit 2491g may provide a supply of the electrolyte 2451 to the ninth tank 2489. In one embodiment, a conduit 2491h may provide the precipitate 2472 to the ninth tank 2489. In this embodiment, one or more valves 2492 may control the flow of the electrolyte 2451 into the ninth tank 2489. Alternatively, in this embodiment, a pump (not shown) may also be combined with conduit 2491h to pump the precipitate 2472 from the sixth tank 2486 to the ninth tank 2489. In another embodiment, the precipitate 2472 may be directly added to the ninth tank 2489. In yet another embodiment, the electrolyte 2451 and precipitate 2472 may be combined in the electrochemical cell 2450. [00208] The combined electrolyte 2451 and precipitate 2472 may then be provided to the electrochemical cell 2450 via conduit 2491i. One or more valves 2492 may control the flow of the combined electrolyte 2451 and precipitate 2472 to the electrochemical cell 2450. The electrochemical cell 2450 may operate as described above for alkaline Fe electrolysis of the combined electrolyte 2451 and precipitate 2472. Following operation, a target material 2413c (e.g., Fe⁰) may be deposited on the cathode 2453 as described above. Following operation, the electrochemical cell 2450 may also produce a residue 2473. [00209] The electrochemical cell 2450 may also be connected to a filter and/or filtration system 2460b via conduit 2491j. One or more valves 2492 may control the flow of the electrolyte 2451 into the filtration system 2460b. The filtration system 2460c may filter the residue 2473 and the electrolyte 2451 following operation (e.g., electrolysis) of the electrochemical cell 2450. The residue 2473 may be captured in an eleventh tank 2462 for storage and/or additional processing to obtain one or more target material(s) 2413d. The electrolyte 2451 may be captured in the tenth tank 2461 for storage and/or additional processing to obtain one or more target material(s) 2413e. [00210] In one embodiment, all of the tanks 2481–2499, the electrochemical cell 2450, and tanks 2461–2462 may be operably connected through one or more pipes or conduits. For example, the first tank 2481 may be connected to the second tank 2482, second tank 2482 may be connected to the third tank 2483, the third tank 2483 may be connected to the fourth tank 2484, the fourth tank 2484 may be connected to the fifth tank 2485, the fifth tank 2485 may be connected to the sixth tank 2486, the sixth tank 2486 may be connected to the seventh tank 2487, the eighth tank 2487 may be connected to ninth tank 2488, the ninth tank 2488 may be connected to the electrochemical cell 2450, the electrochemical cell 2450 may be connected to the tenth tank 2461, and the tenth tank 2461 may be connected to the twelfth tank 2462. [00211] In another embodiment, only a portion of the tanks 2481–2499, the electrochemical cell 2450, and the tanks 2461–2462 may be operably connected through one or more pipes or conduits. For example, as shown in FIG.24, the first tank 2481 and the second tank 2481 may be operably connected to the third tank 2483. However, the first tank 2481 and the second tank 2481 may not be operably connected to one another. The third tank 2483 may be operably connected to the fourth tank 2483. The third tank 2483 may also be operably connected to a sixth tank 2486. The sixth tank 2486 may be operably connected to a fifth tank 2485. The sixth tank 2486 may be operably connected to a seventh tank 2487. The sixth tank 2486 may also be operably connected to a ninth tank 2489. The ninth tank 2489 may be operably connected to an eight tank 2488. The ninth tank 2489 may be operably connected to the electrochemical cell 2450. The electrochemical cell 2450 may be operably connected to a tenth tank 2461 and an eleventh tank 2462. However, the tenth tank 2461 and the eleventh tank 2462 may not be operably connected to one another. [00212] In yet another embodiment, the electrochemical cell 2450 may be separate from the system 2400. In yet another embodiment, none of the tanks 2481–2499, the electrochemical cell 2450, and tanks 2461–2462 are operably connected using one or more pipes or conduits. [00213] Conclusion [00214] While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize or be able to ascertain, using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure. [00215] Also, various inventive concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments. [00216] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. [00217] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” [00218] The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc. [00219] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e., “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law. [00220] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc. [00221] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

Claims

CLAIMS 1. A method for extracting at least three target materials from a feedstock, the method comprising: leaching the feedstock in an acid leachate, wherein the feedstock comprises at least 30% by weight iron oxide (Fe2O3); filtering the acid leachate to remove an insoluble material, wherein the insoluble material comprises a first target material; adding a base to the acid leachate to form a precipitate and a leachate, wherein the leachate has a pH of about 9; filtering the leachate to remove the precipitate; mixing the precipitate with an electrolyte solution to produce an electrolyte mixture; reducing the electrolyte mixture, using an electrochemical reactor, to produce: a solution; a solid deposit comprising a second target material; and a residue comprising a third target material; and collecting the solid deposit, the residue, and the solution.

2. The method of claim 1, wherein the first target material, the second target material, and the third target material are each different from one another and each is selected from: iron (Fe), aluminum (Al), sodium (Na), calcium (Ca), chromium (Cr), magnesium (Mg), boron (B), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), manganese (Mn), gallium (Ga), lead (Pb), barium (Ba), strontium (Sr), copper (Cu), bismuth (Bi), lithium (Li), zinc (Zn), nickel (Ni), indium (In), thallium (Tl), cobalt (Co), cadmium (Cd), scandium (Sc), nickel (Ni), cobalt (Co), silicon (Si), titanium (Ti), vanadium (V), gallium (Ga), hafnium (Hf), indium (In), niobium (Nb), tantalum (Ta), zirconium (Zr), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), yttrium (Y), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), thorium (Th), uranium (U), gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), rhenium (Re), palladium (Pd), osmium (Os), iridium (Ir), or platinum (Pt).

3. The method of claim 1, wherein filtering the leachate to remove the precipitate further comprises collecting a fourth target material from the leachate.

4. The method of claim 3, wherein the fourth target material comprises at least one of magnesium or calcium.

5. The method of claim 1, further comprising collecting a fifth target material from the solution, wherein the fifth target material comprises aluminum.

6. The method of claim 1, further comprising separating, using a magnet, a magnetic material from the residue.

7. The method of claim 6, wherein the magnetic material comprises iron.

8. The method of claim 1, further comprising leaching the feedstock in an alkaline leachate prior to leaching the feedstock in an acid leachate.

9. The method of claim 1, wherein the first target material comprises at least one of: platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os) iridium (Ir), silicon (Si), or titanium (Ti).

10. The method of claim 1, wherein the electrochemical reactor comprises an anode electrode and a cathode electrode.

11. The method of claim 10, wherein reducing the electrolyte mixture comprises reducing an iron oxide of the electrolyte mixture to an iron metal, wherein the iron metal is bound to the cathode electrode and the iron metal comprises the second target material.

12. The method of claim 10, further comprising applying an electric potential between the electrodes, wherein the electric potential is in the range of 0.1V to 5V.

13. The method of claim 1, wherein the third target material comprises at least one of: scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), yttrium (Y), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), osmium (Os), ruthenium (Ru), chromium (Cr), manganese (Mn), copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), cadmium (Cd), scandium (Sc), nickel (Ni), cobalt (Co), silicon (Si), titanium (Ti), vanadium (V), hafnium (Hf), niobium (Nb), tantalum (Ta), zirconium (Zr), lanthanum (La), yttrium (Y), gold (Au), silver (Ag), ruthenium (Ru), rhenium (Re), palladium (Pd), osmium (Os), iridium (Ir), or platinum (Pt).

14. The method of claim 1, wherein the feedstock comprises red mud.

15. The method of claim 1, wherein the feedstock comprises a natural occurring mineral selected from bauxite, hematite, aeschynite, allanite, gadolinite, magnetite, magmatic magnetite-hematite bodies, iron oxide-copper-gold deposits, and carbonatites.

16. The method of claim 1, wherein the feedstock comprises a waste stream selected from municipal solid waste incinerator ashes, bauxite residue, magnet waste, coal fly ash, ferrochrome slag, sewage sludges, or mine tailings.

17. The method of claim 1, wherein the electrolyte mixture has a solid material concentration from 0.1g/5mL to 0.1g/100mL.

18. A system for extracting at least three target materials from a feedstock, the system comprising: a first tank comprising an acid leachate; a second tank comprising a supply of the feedstock; a third tank, operably connected to the first tank and the second tank via at least one conduit, configured to hold a supply of the acid leachate and the feedstock; a first filter, operably connect to the third tank, configured to filter an insoluble material from the acid leachate, wherein the insoluble material comprises a first target material; a fourth tank, operably connected to the first filter and the third tank, configured to receive the filtered acid leachate; a fifth tank, operably connected to the fourth tank, configured to supply a supply of a base to the filtered acid leachate to form a precipitate and a leachate, wherein the leachate has a pH of about 9; a second filter, operably connected to the fifth tank, configured to filter the precipitate from the leachate; a sixth tank, operably connected to the fifth tank and the second filter, configured to receive the precipitate and a supply of an electrolyte, wherein the sixth tank is further configured to mix the precipitate and the electrolyte to produce an electrolyte mixture; an electrochemical reactor, operably connected to the sixth tank, configured to receive the electrolyte mixture, wherein: the electrochemical reactor comprises at least: an anode electrode and a cathode electrode; and the electrochemical reactor is further configured to reduce the electrolyte mixture to produce: a solution; a solid deposit comprising a second target material; and a residue comprising a third target material; and a third filter, operably connected to the electrochemical reactor, configured to filter the residue from the solution.

19. The system of claim 18, further comprising a potentiostat, operably coupled to the electrochemical reactor, configured to apply an electric potential between the electrodes, wherein the electric potential is in the range of 0.1V to 5V.

20. The system of claim 18, wherein the first target material, the second target material, and the third target material are each different from one another and each is selected from: iron (Fe), aluminum (Al), sodium (Na), calcium (Ca), chromium (Cr), magnesium (Mg), boron (B), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), manganese (Mn), gallium (Ga), lead (Pb), barium (Ba), strontium (Sr), copper (Cu), bismuth (Bi), lithium (Li), zinc (Zn), nickel (Ni), indium (In), thallium (Tl), cobalt (Co), cadmium (Cd), scandium (Sc), nickel (Ni), cobalt (Co), silicon (Si), titanium (Ti), vanadium (V), gallium (Ga), hafnium (Hf), indium (In), niobium (Nb), tantalum (Ta), zirconium (Zr), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), yttrium (Y), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), thorium (Th), uranium (U), gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), rhenium (Re), palladium (Pd), osmium (Os), iridium (Ir), or platinum (Pt).