DENG BING (US)
WHAT IS CLAIMED IS: 1. A method of recovering metal, wherein the method comprises: (a) mixing a material with a conductive additive to form a mixture, wherein the material is prepared from e-waste; (b) applying a voltage across the mixture to recover metal from the material, wherein (i) the voltage is applied in one or more voltage pulses, and (ii) duration of each of the one or more voltage pulses is for a duration period; and (c) collecting the recovered metal. 2. The method of Claim 1, wherein the conductive additive is a carbon source. 3. The method of Claim 1, wherein the e-waste is a printed circuit board. 4. The method of Claim 1, wherein the e-waste comprises a plastic. 5. The method of Claim 1, wherein the e-wast is a waste material from a device selected from a group consisting of computers, smartphones, electronic devices, and displays. 6. The method of Claim 1, wherein the material is prepared by performing a mechanical process to transform the material into a fine powder. 7. The method of Claim 6, wherein the mechanical process is selected from a group consisting of cutting the material into small pieces, crushing the material, grinding the material, milling the material, and combinations thereof. 8. The method of Claim 6, wherein the fine powder is a microscale fine powder. 9. The method of Claim 1, wherein the conductive additive is selected from a group consisting of elemental carbon, carbon black, graphene, flash graphene, coal, anthracite, coke, metallurgical coke, calcined coke, activated charcoal, biochar, natural gas carbon that had been stripped of its hydrogen atoms, activated charcoal, shungite, plastic waste, plastic waste- derived carbon char, food waste, food waste-derived carbon char, biomass, biomass-derived carbon char, hydrocarbon gas, and mixtures therefrom. 10. The method of Claim 1, wherein the conductive additive is carbon black. 11. The method of Claim 1, wherein the conductive additive is predominately elemental carbon. 12. The method of Claim 1, wherein the conductive additive is selected from the group consisting of metals, metal salts, metal oxides, metalloids, metal complexes, conductive posphorus, and non-metal conductive materials. 13. The method of Claim 12, wherein the conductive additive is selected from the group consisting of metals, metal salts, metal oxides, metalloids, and metal complexes. 14. The method of Claim 12, wherein the conductive additive is a metalloid. 15. The method of Claim 14, wherein the metalloid is selected from the group consisting of B, Si, As, Te, and At. 16. The method of Claim 1, wherein the material and the conductive additive are mixed at a weight ratio in a range of 1:2 and 25:1. 17. The method of Claim 1, wherein the voltage applied is in a range of 15 V and 300 V. 18. The method of Claim 1, wherein (a) mass of the mixture to which the voltage is applied is more than 1 kg; and (b) the voltage applied is between 100 V and 100,000 V. 19. The method of Claim 18, wherein the mass of the mixture to which the voltage is applied is more than 100 kg. 20. The method of Claim 1, wherein (a) mass of the mixture to which the voltage is applied is more than 1 kg; and (b) the current applied is between 1,000 amps and 30,000 amps. 21. The method of Claim 20, wherein the mass of the mixture to which the voltage is applied is more than 100 kg. 22. The method of Claim 1, wherein the mixture has a resistance in the range of 0.1 ohms and 25 ohms when the voltage is applied. 23. The method of Claim 1, wherein the duration period for the duration of each of the one or more voltage pulses is between 1 microsecond and 25 seconds. 24. The method of Claim 1, wherein the duration period for the duration of each of the one or more voltage pulses is between 1 microsecond and 10 seconds. 25. The method of Claim 1, wherein the duration period for the duration of each of the one or more voltage pulses is between 1 microsecond and 1 second. 26. The method of Claim 1, wherein the duration of each of the one or voltage pulses is between 100 microseconds and 500 microseconds. 27. The method of Claim 1, wherein the one or more voltage pulses is between 2 voltage pulses and 100 voltage pulses. 28. The method of Claim 1, wherein the voltage pulse is performed using direct current (DC). 29. The method of Claim 1, wherein the method is performed utilizing a pulsed direct current (PDC) Joule heating process. 30. The method of Claim 1, wherein the voltage pulse is performed using alternating current (AC). 31. The method of Claim 1, wherein the voltage pulse is performed by using both direct current (DC) and alternating current. 32. The method of Claim 31, wherein the method switches back and forth between the use of direct current (DC) and alternating current (AC). 33. The method of Claim 31, wherein the method concurrently uses direct current (DC) and alternating current (AC). 34. The method of Claim 1, wherein the one or more voltage pulses increase the temperature of the mixture to at least 3000 K. 35. The method of Claim 1, wherein the metal comprises a rare earth element. 36. The method of Claim 1, wherein the metal comprises precious metal. 37. The method of Claim 1 wherein the metal comprises a toxic heavy metal. 38. The method of Claim 1, wherein (a) the materials comprises a metal oxide; and (b) the step of applying a voltage across the mixture results in a carbothermic reaction of the metal oxide to recover the metal. 39. The method of Claim 1, wherein the applying of the voltage across the mixture to recover the metal from the material is performed at a pressure between 0.001 and 25 atmospheres. 40. The method of Claim 39, wherein the pressure is below 0.5 atmospheres. 41. The method of Claim 39, wherein the pressure is below 0.001 atmospheres. 42. The method of Claim 39, wherein the pressure is around 1 atmosphere. 43. The method of Claim 39, wherein the pressure is at least 2 atmospheres. 44. The method of Claim 39, wherein the pressure is at least 10 atmospheres. 45. The method of Claim 39, wherein the pressure is at least 20 atmospheres. 46. The method of Claim 39,wherein the method is performed using a pressurized cell. 47. The method of Claim 46, wherein the wherein the applying of the voltage across the mixture to recover the metal from the material results in a majority of the metal remaining with graphene created by the method. 48. The method of Claim 47, wherein the collecting of the recovered metal comprises separating the metal from the graphene. 49. The method of Claim 48, wherein the separating of the metal from the graphene comprises oxidizing the graphene away chemically. 50. The method of Claim 49, wherein the graphene is oxidized with an oxidant. 51. The method of Claim 50, wherein the oxidant is HNO3 or H2O2. 52. The method of Claim 51, wherein the oxidant is HNO3 or H2O2 with H2SO4. 53. The method of Claim 48, wherein the separating of the metal from graphene comprises calcinating the graphene away to leave a metal species selected from a group consisting of metal, metal oxide, metal carbide, metal salt, and combinations thereof. 54. The method of Claim 1, wherein the mixture of the material and the conductive additive further comprises a halogen containing compound. 55. The method of Claim 54, wherein the halogen containing compound is selected from a group consisting of NaCl, NaF, KCl, NaI, halogentated polymers, halogentated organics, halogenated inorganics, halogenated salts, and combinations thereof. 56. The method of Claim 54, wherein the halogen containing compound comprising a halogenated polymer selected from a group consisting of PTFE, PVC, and CPVC. 57. The method of Claim 1, wherein the step of collecting comprises collecting a gas stream comprising volatized products produced by the application of the voltage across the mixture. 58. The method of Claim 57, wherein the volatized products comprise a metal halide. 59. The method of Claim 1, wherein the step of collecting further comprises cooling the gas stream. 60. The method of Claim 1, wherein (a) the step of applying a voltage across the mixture heats and evaporates metals from the mixure forming a metal vapor; (b) the step of collecting the recovered materials comprises: (i) transporting the metal vapors under low pressure, and (ii) utilizing a condenser or cold trap to condense the metal vapor for collection. 61. The method of Claim 60, wherein the metal vapor comprises metal halides. 62. The method of Claim 60, wherein the transporting of the metal vapors is under a vacuum. 63. The method of Claim 1, wherein the step of collecting further comprises performing a leaching process after applying the voltage across the mixure. 64. The method of Claim 63, wherein the leachability of metals in the mixture after applying a voltage across the mixture is more than two times the leachability content of the metals in the mixture before applying the voltage across the mixture, when conducted using the same pH and same volume of aqueous treatment. 65. The method of Claim 63, wherein the leaching process is performed using a diluted acid. 66. The method of Claim 65, wherein the diluted acid is at least 1 M of the acid. 67. The method of Claim 63, wherein the applying of the voltage across the mixture to recover the metal from the material is performed at a pressure above 1 atmosphere such that volatile components of the e-waste are trapped in residual solids of the material after the application of the voltage. 68. The method of Claim 1, wherein the method is performed in a continuous process or automated process. 69. A system for performing the method of recovering metal utilizing at least one of the methods of Claims 1-68, wherein the system comprises: (a) a source of the mixture comprising the material and conductive additive; (b) a cell operably connected to the source such that the mixture can be flowed into the cell and held under compression; (c) electrodes operatively connected to the cell; and (d) a flash power supply for applying a voltage across the mixture to recover the metal from the material. 70. The system of Claim 69, wherein the system performs the method of recovering metal utilizing at least one of the methods of Claims 40-53, and wherein the system further comprises: (a) the cell that is a pressure cell; and (b) a gas supply for pressurizing the pressure cell. 71. The system of Claim 70, wherein the system further comprises an adjustable relief value. 72. The system of Claim 70, wherein the system further comprises a particle collector. 73. The system of Claim 70, wherein the system further comprises a gas collector. 74. The system of Claim 69, wherein the system is operable to perform a continuous process or automated process. |
[0166] The typical bright-field TEM (BF-TEM) image of a β-Mo2C nanocrystal showed the regular hexagonal nanoplate (depicted by hexagon 201) with a lateral size of ~20 nm supported on carbon (FIG. 2D). The high-resolution TEM (HRTEM) image shows the lattice fringes (FIG.2E, top), where the 0.26 nm interplanar spacing (d) corresponds to the (300) plane of β- Mo2C. According to the atomic-resolution image and corresponding fast Fourier transform (FFT) pattern (FIG. 2E, bottom), the nanoplate orientation was assigned to be β-Mo2C(001). The high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) image and EDS elemental maps under STEM mode reveal the uniform spatial distribution of Mo, C, and O (FIG. 2F). Note that the O is attributed to the surface contamination, consistent with the XPS results (FIG. 2C). The HRTEM image and corresponding FFT pattern of α-MoC 1-x (FIG.2G) and η-MoC 1-x (FIG.2H) were also obtained with the orientation of α-MoC 1-x (110) and η-MoC 1-x (116) for the specific samples. Nevertheless, no preferred orientation was observed for these carbide nanocrystals according to XRD results (FIG.2A). Phase Transformation Process Of Molybdenum Carbides [0167] To explain the voltage-dependent phase formation, the current passing through the samples and the temperature under different FJH voltages were firstly recorded. A higher voltage leads to higher temperatures and energy inputs. The maximum temperatures at FJH voltages of 30 V, 60 V, and 120 V were measured to be 839 K, 1468 K, and 3242 K, respectively. [0168] The formation energies of β-Mo2C, α-MoC1-x, and η-MoC1-x varied with carbon content were calculated by first principles density functional theory (DFT) (FIG.3A, curves 301-303, respectively). It was found that the β-Mo2C phase is the most stable phase with the lowest formation energy; hence, β-Mo2C forms at a relatively low voltage and temperature (point 301). [0169] In contrast, the α-MoC1-x and η-MoC1-x were metastable phases [Hugosson 1999] and were formed and stabilized at a higher temperature according to the Mo-C phase diagram. The α-MoC1-x (x = 1/2) structure has a slightly higher formation energy and the same stoichiometric composition with β-Mo2C (FIG.3B). Hence, the topotactic transition from β-Mo2C to α-MoC1- x is expected when the carbon content is slightly increased (see line 304, which line denotes the projected phase transformation pathway). As more carbon is incorporated into the Mo-C system, the α-MoC 1-x formation energy continuously increases (curve 302), and the energy curve intersects with that of η-MoC 1-x (curve 303). [0170] The η-MoC 1-x phase becomes the relatively stable phase near x = 3/8 (FIG. 3B), and continues to be the stable phase up to higher carbon contents. This result showed that the carbon vacancy dominated the energy landscape of the Mo-C system, and served as the driving factor for the topotactic transition pathway from β-Mo 2 C to α-MoC 1-x and then to η-MoC 1-x phase. [0171] The FJH process with broadly tunable energy input permits the access of the metastable phases with higher formation energy than the thermodynamically stable phase; then, the ultrafast cooling rate of the FJH process (>10 4 K s -1 ) helps to kinetically retain the metastable phases, including α-MoC 1-x and η-MoC 1-x phases, to room temperature. As a control, at the same temperature when metastable α-MoC1-x phase was produced by FJH, the synthesis using a conventional tube furnace with its slow cooling rate of ~10 K min -1 only produced the thermodynamically stable β-Mo2C phase. This explicitly showed the role of the ultrafast cooling rate of the FJH process in kinetically accessing the metastable phases. Phase Dependent HER Performance Of Molybdenum Carbides [0172] The side-by-side electrochemical comparison of the three phases of molybdenum carbide reveal the effect of the phase control on their individual intrinsic characteristics and catalytic behaviors. To demonstrate their catalytic properties, the HER performances of the three molybdenum carbide phases were measured in 0.5 M H2SO4 using a standard three- electrode configuration. Linear scan voltammogram (LSV) curves of the different electrocatalysts as well as the Pt/C benchmark are shown in FIG.4A (with curves 401-405 for Pt/C, β-Mo2C, α-MoC1-x, η-MoC1-x, and flash graphene (FG). The flash graphene (FG) obtained from FJH of carbon black was used as a control and showed negligible HER activity. [Luong 2020]. [0173] The phase-dependent HER activity of molybdenum carbides was observed. The overpotential (η) vs a reversible hydrogen electrode (RHE) at geometric current densities of 10 mA cm -2 for β-Mo 2 C, α-MoC 1-x , and η-MoC 1-x were –220 mV, –310 mV, and –510 mV, respectively (FIG. 4A). The Tafel slopes (b) for β-Mo 2 C, α-MoC 1-x , and η-MoC 1-x were calculated to be 68 mV dec -1 , 84 mV dec -1 , and 113 mV dec -1 , respectively (curves 411-413 of FIG.4B), showing the phase-dependent HER reaction kinetics. [0174] The fast electrode kinetics of β-Mo 2 C phase is reflected in the small charge transfer resistance of ~60 Ω at the potential of –0.5 V vs RHE according to the electrochemical impedance measurement. (See FIG.4C with curves 421-423 showing alternating current (AC) impedance of β-Mo 2 C, α-MoC 1-x , and η-MoC 1-x , respectively.) [0175] The durability of the three molybdenum carbides phases was evaluated by sweeping the electrocatalysts for 1000 cycles using the cyclic voltammetry method. The LSV curves of the 1 st and 1000 th cycle (curves 431-432, respectively) for the three phases of molybdenum carbides are shown in FIG. 4D. No obvious current degradation was observed for all three phases, and the overpotential at 10 mA cm -2 declined little (graph 433), demonstrating the excellent long-term stability. [0176] DFT calculations were conducted to elucidate the phase dependent HER performance. The Gibbs free energy of hydrogen adsorption (ΔGH) has been a descriptor in the selection of HER electrocatalysts [Mavrikakis 2006], and optimal catalysts have ΔGH near 0 eV according to the Sabatier principle [Greenley 2006]. The ΔGH of β-Mo2C(001), α-MoC1-x(110), and η- MoC1-x(001) were calculated to be 0.48 eV, 0.71 eV, and 1.09 eV, respectively (FIG. 4E). These results show that β-Mo2C and α-MoC1-x have smaller hydrogen adsorption energies than η-MoC1-x, consistent with previous reports. [Fan 2017; Matanovic 2018]. Other than ΔGH, the electronic structures provide valuable insights into the metallic character of carbide phases. [Politi 2013]. [0177] FIG. 4F illustrates the partial density of states (DOS) of Mo and C in molybdenum carbides. The DOS of β-Mo 2 C near the Fermi level is substantially larger than those of α-MoC 1- x and η-MoC 1-x . The higher Mo content in β-Mo 2 C results in a higher carrier density and enhanced metallicity, which is beneficial for the charge transfer during electrochemical reactions (FIG. 4C). The larger surface area of β-Mo 2 C in comparison to the other two phases as measured by the Brunauer–Emmett–Teller (BET) method also contributes to the larger current density. The observed best HER performance of β-Mo 2 C was a collective effect of the relatively small hydrogen adsorption energy, enhanced metallic character, and high surface area. In addition, the flash graphene support provided a conductive pathway and prevented the carbide nanocrystals aggregating, which was beneficial for improving the HER performance [Li 2019]. Generalized Strategy For Carbide Nanocrystals Synthesis [0178] Because of the ultrahigh available temperature by the FJH process, various TMCs are readily synthesized regardless of the availability of metal precursors with high vapor pressure. A series of carbide nanocrystals from transition groups IVB, VB, and VIB were successfully synthesized (FIGS. 5A-5D). The uniform temperature distribution permits the phase-pure synthesis throughout the whole sample. (The peak at ~26° (star) for all the samples is attributed to graphene support). [0179] According to the Ellingham diagram, the reduction temperatures of the metal oxides were calculated, which serve as reference values to evaluate carbide formation since the reaction of metal with carbon is exothermic (FIG.5A). The ultrahigh temperature (~3000 K) of the FJH process makes it possible for the reduction of all the listed oxides to elemental metals, including the most challenging HfO2 at temperature up to ~2510 K. Nearly all the low- cost metal or metal compounds, including oxides, hydroxides, and chlorides, could be used as precursors, making FJH a promising low-cost production method when compared to previous methods that rely on the availability of volatile compounds. [Kolel-Veetil 2005; Wolden 2011; Pol 2009]. [0180] Group IVB carbides only have the stable rock salt crystal structure, including TiC, ZrC, and HfC, which were readily synthesized (FIG. 5B). The particle sizes of the TiC, ZrC, and HfC were measured to be ~30.4 nm, ~38.6 nm, and ~30.6 nm, respectively. These values matched well with the crystalline sizes determined by XRD (see TABLE I, above), demonstrating that the as-synthesized carbide nanoparticles are mostly single-crystal. For group VB carbides, the competing M 2 C (M = V, Nb, and Ta) phase could exist at a lower C content. [Hugosson 1999]. Nevertheless, by using a large molar ratio of C/M, synthesized the pure phases of VC, NbC, and TaC nanocrystals were successfully synthesized with the cubic structure and particle sizes ranging from ~20 to ~ 30 nm (FIG.5C). In contrast, the phases of group VIB carbide (Cr, Mo, and W) are much more complex. [Hugosson 2001]. Here, the orthorhombic Cr3C2 phase and hexagonal W2C phase were synthesized with particle sizes of ~14.2 nm and ~18.7 nm, respectively (FIG.5D). W2C is not thermodynamically favored over the WC phase below 1250 ℃ according to the W-C phase diagram. [Kurlov 2006]. The successful synthesis of the metastable W2C is attributed to the high energy input and ultrafast cooling rate of the ultrafast electrical thermal reaction, once again demonstrating the excellent phase engineering ability of the FJH process. Apart from the TMCs, the covalent carbides of B4C and SiC were synthesized, demonstrating the generality of the FJH process. System and Synthesis Process [0181] Accordingly, for the synthesis of metal carbides, the present invention provides, among other things, (i) an ultrafast synthesis that is thousands of times faster than previous reported methods; (ii) the phase control ability, which is hard to realize by other methods; (iii) the generality, as demonstrated by the synthesis of up to 13 carbides, which is impossible by any other methods. [0182] The metal carbides resulting from the present invention, especially molybdenum carbides and tungsten carbides, can be utilized as electrocatalysts, such as for hydrogen evolution, which is critical for the application of fuel cells in clean energy. Moreover, the nanoscale carbides are important precursors for the fabrication of high-performance carbide ceramics. [0183] An exemplary system and process used included the electrical circuit diagram and setup of the FJH system are shown in FIGS.6A-6B. (Additional details of the electrical components could be found in Luong 2020). A capacitor bank with a total capacitance of 60 mF was used as the power supply. The metal precursors and carbon black with specific weight ratios (TABLE I) were mixed by grinding using a mortar and pestle. The reactants (~50 mg) were loaded into a quartz tube with an inner diameter (ID) of 4 mm and outside diameter (OD) of 8 mm. When scaling up the process, a quartz tube with ID of 8 mm and OD of 12 mm was used for the ~200 mg sample, and a quartz tube with ID of 16 mm and OD of 20 mm was used for the ~1 g sample. Further scaling up the mass to kilogram scale will need containers that need no be quartz. Graphite rods were used as the electrodes in both ends of the quartz tube. The electrodes were loosely fitting in the quart tube to permit outgassing. The resistance was controlled by the compression force of the electrodes across the sample. The tube was then loaded on the reaction stage (FIG. 6C). The reaction stage was loaded into a sealed reaction chamber which was evacuated to a mild vacuum (~10 mm Hg) to accommodate degassing and avoid sample oxidation (FIG.6D). The reaction stage was then connected to the FJH system. [0184] The capacitor bank was charged by a direct current (DC) supply that can reach voltages up to 400 V. A relay with programmable ms-level delay time was used to control the discharge time. The charging, flash Joule heating, and discharging were automatically controlled by using the National Instruments Multifunction I/O (NI USB-6009) combined with a customized LabView program. After the FJH reaction, the apparatus rapidly cooled on its own to room temperature. Before removing the sample, make sure that the capacitor bank is fully discharged. The detailed conditions for the synthesis of various carbides are listed in TABLE I. Features and Applications [0185] In embodiments, the as-synthesized carbide nanocrystals were supported on flash graphene. The necessity of separation of graphene and carbides depends on the further application. For the application of nanocrystalline carbides in electrocatalysts, the graphene support is beneficial for improving the performance by providing conduction and preventing particle aggregation. For another major application of nanocrystalline carbides as precursors for ultra-strong ceramics, the removal of excess carbon is necessary. [0186] It was realized that the efficient purification of the carbides by post-synthesis processes, including the simple calcination in air for SiC; the Ca metal etching [Dyjak 2013] for TiC, ZrC, HfC, VC, NbC, TaC, Cr3C2, β-Mo2C, and W2C; and the density-in-liquid purification procedure for metastable molybdenum carbides, α-MoC1-x and η-MoC1-x. In addition, the greatly improved purity of B4C was shown by using controlled feeding during the synthesis. [0187] Due to the ultrafast heating/cooling rate, the direct sampling heating feature, and the short reaction duration within 1 s, the FJH process for carbide synthesis is highly energy efficient compared to traditional furnace heating where large amounts of energy are used to maintain the temperature of the chamber. The carbide nanocrystals were synthesized at only 2.2 to 8.6 kJ g -1 in electrical energy. The FJH synthesis possesses excellent scalability, that a constant temperature value and uniformity on different mass scales could be obtained by adjusting the discharging voltage and/or the capacitance. [0188] The synthesis of carbide nanocrystals up to gram scale was demonstrated by increasing the FJH voltage. The FJH process can be extended to the synthesis of carbide alloys [Sarker 2018], heteroatom-decorated carbides, [Song 2019], and phase engineering of metastable carbides, [Demetriou 2002], which provides a powerful technique for carbide production. [0189] The controlled synthesis of metastable phases is challenging in the synthesis of inorganic materials [Chen 2020]. The FJH process provides broadly tunable energy input that can exceed 3000 K coupled with kinetically controlled ultrafast cooling rate (> 10 4 K s -1 ). Hence, the FJH process provide access to many non-equilibrium phases and subsequently retain it at room temperature, thus serving as a potential tool for engineering the metastable phases of various materials, such as metal nanomaterials [Chen 2020], layered oxides [Bianchini 2020], metal nitrides [Sun W 2017], and two-dimensional materials. Ultrafast Synthesis of Corundum Nanoparticles [0190] The present invention further includes flashing Joule heating [see Luong 2020; Stanford 2020; Tour PCT ’000 Application] for ultrafast processes to synthesize metal corundum nanoparticles, i.e., ultrafast phase transformation from γ-Al 2 O 3 (as well as γ-AlOOH) to α- Al 2 O 3 by a flash Joule heating method. Briefly, carbon black (or other carbon additive, such as discussed above) was mixed with γ-Al 2 O 3 (or γ-AlOOH) nanoparticles, which then is subjected to flash Joule heating. The phase transformation is ultrafast within 1 s, thousands of times faster than other start-of-art methods. [0191] Embodimets of the present invention thus include a Joule heating process based on pulsed direct current (PDC) to complete the phase transformation from γ- to α-Al 2 O 3 at a significantly reduced average bulk temperature and reaction duration (~573 K, <1 s). The rapid transformation can be enabled by the resistive hotspot-induced local heating in the PDC process when an appropriate volume fraction ratio of γ-Al 2 O 3 precursors and carbon black conductive additives are used. The pulsed and local heating mitigates the agglomeration, leading to the synthesis of α-Al 2 O 3 NPs with average particle size of ~23 nm and surface area ~65 m 2 g -1 . Ab initio calculations reveal that the topotactic phase transformation process (from γ- to δʹ- to α- Al 2 O 3 ) is determined by the surface energy difference of the three phases. A particle size of ~21 nm was achieved that is the thermodynamic limit for the synthesis of dehydrated α-Al 2 O 3 NPs with the δʹ-Al 2 O 3 as the intermediate phase by a thermal process. [0192] Further, based on the Joule heating technique, an alternating current sintering (ACS) process has been developed that shows the ultrafast and pressureless sintering of these α-Al 2 O 3 NPs into alumina ceramics with nanoscale grain size and improved strength and hardness. [0193] A calcination process was also developed to totally remove the carbon black or formed flash graphene, and pure phased α-Al 2 O 3 was obtained. In embodiments, the synthesized α- Al 2 O 3 was shown to have a surface area up to 65 m 2 /g, that means that these materials are usefulin the applications of catalyst support and high-strength ceramics. Phase Transformation Synthesis [0194] Methods for ultrafast synthesizing of corundum nanoparticles (i.e., the transformation from γ-Al 2 O 3 (as well as γ-AlOOH) to α-Al 2 O 3 can include the following. [0195] Since the γ-Al 2 O 3 NPs precursors are electrically insulative, commercial carbon black (CB) was used in embodiments as the conductive additive. For instance, the mixture of γ-Al 2 O 3 NPs and CB were compressed inside a quartz tube between two graphite electrodes. See FIG. 7 (showing the PDC apparatus 701 and the resistive hotspots 702 around and at the gap of the insulative γ-Al 2 O 3 NPs with the arrows depict the electric current lines) and FIG. 13A (with aluminum electrolytic capacitors (450 V, 13 mF) having total capacitance of 0.624 F used for charging), [0196] The CB also works as separators to avoid the agglomeration of Al 2 O 3 NPs during heating. The resistance was controlled by the compressive force on the two electrodes, which is shown in TABLE II. TABLE II Parameters for PDC Joule Heating Initial P recursors Mass R atio Mass Rs (Ω) V0 (V) V1 (V) Duration Final Mass (mg) (ms) (mg) Note: V0: the start voltage, V1: the voltage after Joule heating. [0197] The electrodes were connected to a capacitor bank with capacitance of C = 0.624 F and charging voltage up to V 0 = 500 V. The discharge circuit was a series resistor-inductor- capacitor circuit with the characteristic time of τ = 0.1 ms, which permitted the PDC with frequency of f = 1000 Hz. FIG.13B shows a pulsed voltage generation that can be used in the system to generate the PDC, with the frequency 1000 Hz, and the ON state is set to be 20%, which gives a 0.2 ms voltage pulse. [0198] Joule heating affects the entire electric conductor; for a homogeneous conductor, the current density is uniform so the Ohmic dissipation enables the homogeneous temperature distribution throughout the sample. [Johnson 2011]. However, when an electrical field is applied to an inhomogeneous medium, as in the composite of conductive CB and insulative Al 2 O 3 , the current and powder densities have strong spatial variation. [Soderberg 1987]. The power dissipation is substantially larger than the neighboring regions at some regions, which are termed resistive hotspots 702 (illustrated in FIG. 7A). Even though the average bulk temperature is low, the hotspots permit local heating and trigger the transformation that happens at a much higher temperature. [0199] By using this effect, the phase transformation from γ-Al 2 O 3 to α-Al 2 O 3 accompanied by the intermediate t-phase of δʹ-Al 2 O 3 at an average bulk temperature of ~573 K in <1 s was realized. See pulsed direct current method 814 shown in FIG. 8. As shown in FIG. 8, this pulsed direct current method 814 is compared to the representative phase transformation methods reported in the literature, namely flame spray pyrolysis method 811 [Laine 2006], furnace annealing method 812 [Steiner 1971], and high energy ball milling method 813 [Amrute 2019]. [0200] The liquid-feed flame spray pyrolysis method 811 produced α-Al 2 O 3 at temperatures near 1873 K; however, the kinetically controlled process may render it difficult to access the pure phase (80 – 85% purity of α-phase). [Laine 2006]. Traditional heating methods that supply heat through the sample boundary, such as furnace annealing method 812, require an extended period to permit uniform heating; hence 1473 K and 10 to 20 h was necessary to complete the phase conversion. [Steiner 1971]. Other room-temperature nonequilibrium processes, such as high-energy ball milling method 813, have been reported to form α-Al 2 O 3 . [Amrute 2019]. Nevertheless, the γ-Al 2 O 3 could agglomerate, which leads to loss of surface area during the extended time and high-energy collisions. [Zielinski 1993; Chauruka 2015]. [0201] The detailed phase transformation process of γ-Al 2 O 3 was investigated by the PDC approach. See FIGS.9-11. (In FIG.9, the marks represent γ-Al 2 O 3 (■), δʹ-Al 2 O 3 (▲), α-Al 2 O 3 (●), and γ-AlOOH (○); the precursor was γ-Al 2 O 3 with slight γ-AlOOH phase (crystal system: monoclinic; space group: P21/n; PDF No.07-0324); and the 0.8 s treated sample was calcined). Commercial γ-Al 2 O 3 NPs with particle size of ~10 nm and surface area of ~156 m 2 g -1 were used as the precursors. A small ratio of γ-AlOOH phase appeared in the precursors (FIG.9, 0 s). The mass ratio of γ-Al 2 O 3 NPs and CB was 4 to 1, which gave a sample resistance of ~8 Ω (TABLE II). A discharging voltage of 60 V was applied with different discharging times controlled by a relay. The X-ray diffraction (XRD) patterns of the products with different PDC on-state time are shown in FIG. 9. As the discharging time increased, the γ-AlOOH first disappeared at 0.3 s; then, the γ-Al 2 O 3 was transferred to δʹ- and α- Al 2 O 3 phase at 0.4 to 0.5 s; last, the intermediate δʹ-Al 2 O 3 phase was fully converted to α-Al 2 O 3 phase after 0.8 s of discharge (FIG. 11 with curves 1121-1123 for γ-Al 2 O 3 , δʹ-Al 2 O 3 , and α-Al 2 O 3 , respectively). The orthorhombic δʹ-Al 2 O 3 was observed as the single intermediate phase (FIG.10), which is distinct from other thermal processes where δ- and θ- Al 2 O 3 usually appear before the final α- Al 2 O 3 phase (FIG.8). [Steiner 1998; Levin 1998; Lamouri 2017]. [0202] Unlike previous report [Luong 2020] on the synthesis of graphene by the high-voltage flash Joule heating at a high temperature of ~3000 K, the 60 V PDC did not provide enough energy to graphitize the CB. FIG. 13C (with no observation of the 2D peaks for the product after Joule heating at 60 V). As a result, the CB could be easily removed by heating in air, according to thermal gravimetric analysis (TGA). Here, the as-synthesized mixture of α-Al 2 O 3 NPs and CB was calcined in air at 700 °C for 1 h to purify the product. The X-ray photoemission spectrum (XPS) of the α-Al 2 O 3 product after calcination showed very minor carbon signal, which could be caused by the carbon adsorption in air. [0203] Raman spectra are sensitive to even a monolayer of carbon [Wang 2008]; intriguingly, no characteristic Raman bands of carbon were detected after calcination at 700 °C (FIG. 12 with curves 1224-1226 for 700 °C calcination, 650 °C calcination, and CB/Al 2 O 3 , respectively), demonstrating the efficient removal of carbon. As a control, it was determined that the calcination process itself does not trigger the phase transformation and has negligible effect on the coarsening or aggregation of the γ-Al 2 O 3 phase. Characterization of the Corundum Nanoparticles [0204] The α-Al 2 O 3 NPs derived by PDC followed by mild calcination were further characterized in detail. Bright field transmission electron microscopy (BF-TEM) images showed the well-dispersed particles. See FIG.14A. High resolution TEM (HRTEM) showed the high degree of crystallinity of the α-Al 2 O 3 NPs. See FIG. 14B. The interplanar spacing values of ~2.57 Å and ~2.09 Å correspond to the d(104) and d(113) of α-Al 2 O 3 , respectively. It was observed that some α-Al 2 O 3 NPs with surface roughness features at a few nm, which is similar to the particle size of the γ-Al 2 O 3 precursors. This revealed that the rapid PDC process triggers the phase transformation while no significant agglomeration of the NPs occurs. The TEM images show that the particle size ranged from 14 to 36 nm, with an average particle size of 25.4 nm and standard derivation (σ) of 5.8 nm. See FIG.14C. [0205] Brunauer–Emmett–Teller (BET) measurement showed that the surface area of the α- Al 2 O 3 NPs is ~65 m 2 g -1 . See inset 1401 of FIG. 14D (which inset shows N 2 adsorption- desorption isotherms of α-Al 2 O 3 NPs at 77 K). The average particle size (D) is estimated to be ~23 nm by Eq (1): D = 6/(ρS) Eq. (1) where ρ is the density of α-Al 2 O 3 (3.96 g cm -3 ) and S is the specific surface area [Karagdov 1999]. [0206] The pore size determined from the N2 adsorption-desorption isotherm using the density functional theory (DFT) model indicates the distribution with high probability at 3 to 10 nm. See FIG.14D. The observed surface area was attributed to the nanoscale grain size, as well as to the pores and surface roughness features within the NPs. The crystalline size of the α-Al 2 O 3 NPs was estimated to be ~22 nm based on the Halder-Wagner method. The crystalline size (~22 nm) agrees well with the particle size measured from TEM statistics (~25 nm) and BET estimation (~23 nm), demonstrating the single-crystal feature of the NPs. [0207] Unlike the starting γ-Al 2 O 3 NPs that had hydrated surfaces, the synthesized α-Al 2 O 3 NPs surfaces were highly dehydrated because of the thermal process. FIG. 14E, with curves 1411-1412 showing α-Al 2 O 3 product and γ-Al 2 O 3 precursor, respectively (and the black arrow 1413 pointing to the hydroxyl group absorbance). [0208] The XPS fine spectra showed the dominate O 2- peak at a binding energy of ~531.2 eV and single Al 3+ peak at a binding energy of ~74.0 eV from the α-Al 2 O 3 NPs. See FIG.14F. This demonstrated that the ultrafast PDC process did not result in obvious oxygen deficiencies or the carbothermic reduction of Al 2 O 3 even with the existence of CB, presumably due to the high reduction potential of Al 3+ . No other peaks were detected in the XPS full spectrum, indicating the high-purity synthesis ability of the electric thermal process. This makes it superior to the solvent-based methods including ball milling [Amrute 2019] or co-precipitation [Guo 2016], which suffer from lengthy purification processes and chemical contaminants. Resistive Hotspot Effect [0209] The composition of the inhomogeneous media can be important for local power dissipation during the PDC process. To quantitatively show the effect of the composition on the phase transformation, a series of precursors with different mass ratio of γ-Al 2 O 3 and CB were treated by PDC under the same voltage and time. FIG. 15A (with marks: γ-Al 2 O 3 (■), δʹ-Al 2 O 3 (▲), and α-Al 2 O 3 (●), and numbers being the mass ratio of γ-Al 2 O 3 to CB); TABLE II. According to the densities of γ-Al 2 O 3 and CB, the volume fractions (f) of γ-Al 2 O 3 were obtained (shown in TABLE III), and the phase mass ratios varied with f(γ-Al 2 O 3 ) after the PDC process were calculated. FIG.15B (showing curves 1501-1502 for α-Al 2 O 3 and δʹ-Al 2 O 3 , respectively).. TABLE III [0210] The phase transformation degree was increased as the f(γ-Al 2 O 3 ) increased from 0.41 to 0.73; the phase-pure α-Al 2 O 3 was obtained at f(γ-Al 2 O 3 ) ~0.73. Further increase in the f(γ- Al 2 O 3 ) to >0.78 led to no phase transformation. [0211] To explain the f(γ-Al 2 O 3 )-dependent phase transformation, the electrical conductivity and temperature were measured. The conductivities were determined based on the measured resistance (R) and the feature size of the samples. TABLE II; FIG. 15C (with curves 1503- 1504 for conductivity and temperature, respectively, versus f(γ-Al 2 O 3 ). The conductivity was inversely proportional to f(γ-Al 2 O 3 ) (curve 1504 in FIG. 15C), which was reasonable since γ- Al 2 O 3 is electrically insulative. The real-time temperature was measured using an infrared (IR) thermometer. The average bulk temperature was decreased with the increase of f(γ- Al 2 O 3 )(curve 1503 in FIG. 15C). This could be explained by the power (P) equation of Joule heating by Eq. (2): where V is the voltage, and σ is the conductivity of the sample. [0212] Since the start voltages were fixed to V0 = 60 V, the power was proportional to the conductivity of the sample. Intriguingly, the phase pure α-Al 2 O 3 NPs were obtained at a low average bulk temperature of ~573 K with f(γ-Al 2 O 3 ) ~0.73. FIG.15C. [0213] Such a low temperature was not supposed to trigger the phase transformation from γ- to α-Al 2 O 3 with a high activation energy of ~485 kJ mol -1 . [Steinr 1971]. Moreover, the higher phase transformation degree at a lower temperature is counterintuitive. FIG.15C. [0214] To explain the phenomenon, a numerical simulation was conducted based on the finite element method (FEM) on the current density distribution of the γ-Al 2 O 3 /CB composite during PDC process. As shown in FIGS. 15D-15F, the current density is inhomogeneous in the composite of γ-Al 2 O 3 and CB; the current densities at the regions of vertical gaps between γ- Al 2 O 3 NPs are larger than the bulk regions. (In FIGS.15D-15F, the balls are γ-Al 2 O 3 and the continuous phase is CB, with the vertical side bars showing the current density values). The gaps become narrower as the f(γ-Al 2 O 3 ) increased, leading to significantly large current densities in those regions. Considering that the resistivity (R) of the conductive CB phase is constant, the heat (Q) per volume produced by PDC is proportional to the square of the current density (j) by Eq. (3): Q ∝ j 2 R Eq. (3) [0215] The large thermal dissipation in the regions with high current densities leads to the hotspots near γ-Al 2 O 3 NPs with much higher temperature than the bulk regions, which triggers the phase transformation. A shown in FIG.16, the quantitative analysis of the current densities revealed a decreased bulk temperature (curve 1601) but an increased hotspot temperature (curve 1602) as the f(γ-Al 2 O 3 ) increased, which agreed well with the temperature measurement shown in FIG.15C. Topotactic Transition Pathway [0216] To provide deeper insight into the topotactic transition pathway, thermodynamic analysis of the three Al 2 O 3 phases were conducted based on DFT. The bulk energy and surface energy of the three Al 2 O 3 phases were calculated. FIG.17A. The bulk energy of α-Al 2 O 3 is the lowest, followed by that of δʹ-Al 2 O 3 , and then γ-Al 2 O 3 , indicating that the α-Al 2 O 3 is the most stable phase as a dense bulk crystal. In contrast, the surface energy is opposite: γ-Al 2 O 3 (100) has the lowest surface energy, followed by δʹ-Al 2 O 3 (100), α-Al 2 O 3 (1ī0) and (001). The surface energy difference determines the thermodynamic stability of the three Al 2 O 3 phases as the surface area increases. FIG. 17B, with curves 1701-1703 for α-Al 2 O 3 , δʹ-Al 2 O 3 , and γ-Al 2 O 3 , respectively. When smaller than a surface area of ~79 m 2 /g, or larger than a particle size of ~21 nm, the α-Al 2 O 3 phase becomes more stable than the δʹ-phase. Hence, the particle size of ~21 nm is suggested as the thermodynamic limit for the synthesis of dehydrated α-Al 2 O 3 by a thermal process that involves an intermediate δʹ-phase. The particle size of α-Al 2 O 3 (~23 nm) synthesized by PDC approaches the thermodynamically limited value, and smaller than that obtained by most other thermal processes (TABLE IV). TABLE IV [0217] The ultrafast, pulsed, and low-temperature PDC process to a large extent avoids mass transfer and grain coarsening during the phase transformation process. [0218] To gain insight into the structural origin of the phase-dependent bulk and surface energy, the partial charge density contour at the highest bands (0.3 eV below the Fermi levels) of the surface states of the three Al 2 O 3 phases were plotted. FIGS.17C-17D. All of the surface atoms on α-Al 2 O 3 (001) are active, while the sites with missing Al atoms on the δʹ-Al 2 O 3 (100) and γ-Al 2 O 3 (100) surfaces are relatively active (FIG. 17C). Closer analysis indicated that the active states go deep into the bulk for the δʹ-Al 2 O 3 (100) and γ-Al 2 O 3 (100) but not for α- Al 2 O 3 (001) (FIG.17D). This explains the bulk as well as surface energy sequences of the three Al 2 O 3 phases, and identifies the Al vacancies in γ- and δʹ-phases as the structural origin of their thermodynamic stability/instability vs the α-phase. Applications [0219] Accordingly, for the synthesis of corundum nanoparticles, the present invention provides, among other things, an ultrafast synthesis, which is within 1 second, and is much faster than any reported methods, which requires at least several hours. The corundum (α- Al 2 O 3 ) nanoparticles resulting from the present invention have small particles size and high- surface area, which can utilized in a number of applications, such as for stable catalysis support and in ceramics with high fracture strength and toughness. [0220] For instance, one prominent application of α-Al 2 O 3 NPs is as a precursor for sintering nanometer-grained alumina ceramics (i.e., ultrafast ACS for nano-grained alumina ceramics). The typical alumina ceramics sintering processes occur under high-pressure and high- temperature conditions (HP-HT), such as hot isostatic pressing, [Mizuta 1992], spark plasma sintering [Balima 2019], and pulse electric current sintering [Zhou 2004]. The high pressure, usually several GPa, retains the grain growth and advances densification [Wang 2013], which can be a main factor for dense ceramic sintering using coarse grained precursors. However, the HPHT process is not suitable for complex structures. The nanocrystalline precursors could undergo the pressureless sintering yet it would suffer from an elevated sintering temperature and prolonged time (>10 h). [Guo 2016; Cao 2017; Li 2006]. Very recently, an ultrafast high- temperature sinter method [Wang 2020] based on direct current heating was reported for the rapid screening of ceramics. [0221] Here, based on the Joule heating technique, an alternative current sintering (ACS) process has been created for ultrafast sintering of the alumina ceramics. The ACS system is capable of providing stable and high energy output with voltages up to 63 V and currents up to 100 A (FIG. 18A), making it suitable for the sintering of structural ceramics. For the ACS system, the total capacitance was 1.5 F and the largest available voltage was 63 V. The capacitor was simultaneous charged by the AC supply and provided energy output to the samples by discharging. The energy output was continuous and enabled an extended sinter of seconds with high energy output. [0222] Two separated, highly graphitized carbon papers 1801a-1801b in FIG.18C connected to electrodes were used as the heating elements. See FIG.18B (in which carbon papers 1801a- 1801b were attached to a glass slide and adhered by copper tabs). The α-Al 2 O 3 NPs, mixed with polyethylene glycol (PEG) binder [Taktak 2011], were pressed at 500 MPa into pellets 1802. Commercial α-Al 2 O 3 nanopowder (~300 nm) was used as a control. After removal of the binder (5 °C min -1 to 500 °C for 2 h hold; in air), the pellets 1802 were put between the carbon papers and under the ACS at ~15 V. [0223] FIG.19A shows the rapid heating 1901, stable sintering 1902, and rapid cooling 1903. The temperature was recorded by fitting the blackbody radiation. The temperature rapidly ramped up to ~2250 K with a heating rate of ~10 3 K s -1 . After stable sintering for 5 s, the sample cooled also with a rapid cooling rate of ~10 3 K s -1 . See FIG. 19B. FIG. 19C shows sintered ceramic pellets 1911-1912 supported on carbon papers 1913. [0224] The XRD patterns confirm the pure α-phase of the alumina ceramics. FIG. 19D. The microstructure by scanning electron microscopy (SEM) showed the equal-sized grains and tightly bonded grain boundaries with a polyhedral morphology (FIG.19E), demonstrating the well-developed sintering. The average grain size of the alumina ceramics was ~270 nm (FIG. 19F). In comparison, the alumina ceramics sintered from the commercial α-Al 2 O 3 powders exhibited high residual porosity with grain size of ~1200 nm, demonstrating that the sinter was in its initial stage. This result shows that the fine grain size of the α-Al 2 O 3 NPs helps the ultrafast sintering, presumably assisted by the grain growth at high temperature. [Guo 2016]. The mechanical properties of the ceramics were measured. See FIGS.19G-19H. The ceramics sintered by α-Al 2 O 3 NPs precursors demonstrated a Young’s modulus of ~11.7 GPa, significantly higher than that from the commercial α-Al 2 O 3 powders (~1.5 GPa). By using a traditional high pressure based sintering process [Mizuta 1992; Balima 2019; Zhou 2004] or elongating the sintering time, [Guo 2016; Laine 2006], the mechanical properties of the alumina ceramics derived from the α-Al 2 O 3 NPs would likely improve. [0225] Accordingly, the ACS process can be utilized in the sintering of functional ceramics, porous ceramics, or for materials screening. [Wang 2020]. Effectiveness and Scalability [0226] Being a highly efficient energy supplies technology, Joule heating has a coefficient of performance of 1.0. The localized heating by resistive hotspots in PDC makes the process more effective because most of the electrothermal energy was directly targeted to the phase transformation, making the synthesis possible with a low energy input of ~4.77 kJ g -1 or 0.027 $ kg -1 in electrical energy cost. Moreover, the PDC process can be scaled by adjusting sample cross-sectional area and the PDC voltage. A synthesis of α-Al 2 O 3 NPs up to 1.4 g-scale has been performed. See FIGS.20A-20B and 21A-21B (in FIGS.20A and 21A, the black powders are as-synthesized mixture of CB and α-Al 2 O 3 , and the white powders are α-Al 2 O 3 after calcination). The PDC process combined with the resistive hotspot effect greatly reduces the required temperature for reactions that should be originally triggered at a high energy input, serving as an alternative technique for cost-efficient synthesis. Recovery of Metal From E-Waste [0227] The present invention includes flashing Joule heating [see Luong 2020; Stanford 2020; Tour PCT ’000 Application] for ultrafast processes to recover metals (precious metals) from waste (such as e-waste). Waste can be mixed with carbon black, then subjected to ultrafast Joule heating flashing. According to the Ellingham diagram, multiple precious metals are reduced to elemental metal by the carbothermic reaction. The recycling process is ultrafast, within seconds. Of import, the process is a totally dry process without any solvents, and hence is extremely environmentally friendly. Synthesis Processes [0228] Methods for ultrafast synthesis to recover metal from waste can include the following. [0229] The method can include preparation of the electronic wastes for flashing. For instance, a printed circuit board (PCB) from a used electronic printer was used as the starting materials. The PCB board was first cut into pieces and then crushed into small particles. Ball milling was used to grind it to a microscale fine powder, which was then available for flash Joule heating by adding carbon black (or other carbon materials as discussed above) and treated as described below in a flash Joule heating apparatus. Evaporative Separation [0230] It has been discovered that the different vapor pressure of metals -- compared to that of substrate materials (carbon, ceramics, and glass) -- enables the separation of metals from e- waste. This is termed “evaporative separation.” The high vapor pressure of precious metals is obtained by an ultrafast flash Joule heating (FJH) process under vacuum. A subsecond current pulse is passed through the precursors, which brings the sample to an ultrahigh temperature of ~3400 K, enabling the evaporative separation of precious metals. Halide additives are used to improve the recovery yield greater than 80% for Rh, Pd, and Ag, and greater than 60% for Au that are abundant in the tested e-waste. Alternatively, compared with directly leaching e-waste raw materials, by leaching the residual solids after FJH, the recovery yield is significantly improved with tens of times increase for Ag and few times increase for Rh, Pd and Au. The toxic heavy metals, including Cd, Hg, As, Pd, and Cr, could also be removed and collected, minimizing the health risks and environmental impact of the recycling process. [0231] The FJH process to recover precious metals from e-waste involves three stages. See FIG.22 showing a schematic of the system 2200. In the metal evaporation stage 2201 (which included FJH apparatus having capacitor bank 2205 and porous Cu electrode 2206), the metals in e-waste were heated and evaporated by ultrahigh-temperature FJH. Then, in mass transport stage 2202, the metal vapors were transported under vacuum (using vacuum system having pump 2207), and, in condensation stage 2203, were collected by condensation (using cold trap 2208). A printed circuit board (PCB) from a discarded computer, a representative e-waste, was used as the starting material. See FIG.23. The PCB was ground to small powder and mixed with carbon black (CB), which served as the conductive additive. Inset 2310 of FIG.23. [0232] To establish baseline concentrations, the PCB was digested using dilute aqua regia [Hong 2020], and the concentration of precious metals was determined by inductively coupled plasma mass spectrometry (ICP-MS). Among the precious metals, Rh, Pd, Ag, and Au are abundant with concentration of several to tens of parts per million (ppm), as shown in FIG.24. [0233] In a FJH process, the mixture of PCB powder and ~30 wt% CB was slightly compressed inside a quartz tube between two sealed electrodes. FIG.22. FIG.29A shows a photograph of the system, which included the flash stage 2901, the power source 2902, the pump 2903, and the cold trap 2904 (liquid nitrogen, Dewar). One electrode was a porous Cu electrode to facilitate gas diffusion, and the other was a graphite rod. FIG.30. The resistance of the sample was tunable by adjusting the compressive force on the two electrodes. The two electrodes were connected to a capacitor bank with total capacitance of 60 mF. The detailed separation conditions are shown in TABLE V. TABLE V
[0234] The high-voltage discharge of the capacitor bank brings the reactant to a high temperature. With the fixed sample resistance of ~1 Ω, the current passing through the sample was measured under different FJH voltages. See FIG.25, showing curves 2521-2523 for 150 V, 120 V, and 100 V, respectively. The real-time temperature of the sample was estimated by fitting the blackbody radiation in the 600 – 1100 nm emission. The temperature varied according to the FJH voltage, reaching ~3400 K at 150 V in <50 ms. See FIG. 26, showing curves 2631-2633 for 150 V, 120 V, and 100 V, respectively . [0235] Since the resistance of the sample is much larger than that of the graphite and porous Cu electrode, the voltage drop was mainly imposed on the sample. Hence, the high-temperature region was limited to the sample and the FJH setup has good durability even though it can achieve a high temperature of >3000 K. Such a high temperature (>3000 K) volatilizes most of the non-carbon components. According to the calculated vapor pressure-temperature relationships (FIG.27), the precious metals have a higher vapor pressure than carbon, the latter not subliming until ~3900 K. [Abrahamson 1974]. [0236] As a result, the metals are evaporated, and the major carbon-containing components such as plastics were carbonized. [Luong 2020; Algozeeb 2020] The evaporated metal vapors were captured by condensation in a cold trap (FIGS.22 and 29A). Some of the vapor remained gaseous even at the liquid N2 temperature (77 K); these gases were presumed to be H2 and CO. [Algozeeb 2020]. [0237] The content of the precious metals in the condensed solid was measured and the recovery yield was calculated. FIG. 28. The recovery yield of Ag was ~40%, while Rh, Pd, and Au had a relatively low recovery yield of ~3%. This is because Ag has a high vapor pressure and relatively low boiling point. The concentration of precious metals in the starting commercial CB is 1 – 2% of the concentration in PCB, hence their presence in CB will not introduce significant errors. Moreover, the precious metals tend to not form stable carbide phases even at high temperature due to their extremely low C solubility. [Okamoto 2016]. Hence, the use of CB as conductive additive will not affect the evaporative behavior of precious metals. Halide Assisted Improvement Of Recovery Yield [0238] The high recovery yield of the evaporative separation relies on the generation of more volatile components. To improve the recovery, halides were used as additives because of the much higher vapor pressure of metal halides compared with the elemental metals. [Lide 2005]. Fluorine-containing components were first used as the additive, including the sodium fluoride (NaF) and polytetrafluoroethylene (PTFE, Teflon). With the additives, the recovery yields of Rh and Pd were improved to >80% and 70%, respectively. See FIGS.31A-31B, demonstrating ~20 times improvement compared to the experiments without additives. The concentration of precious metals in the additives were <2% of those in PCB, hence this exclude the additives from introducing significant error in the recovery of precious metals. [0239] Chlorine-containing compounds were tried because of their abundance and low cost. Both sodium chloride (NaCl) and potassium chloride (KCl) were used (FIG. 31C). The recovery yields of Rh, Pd, and Ag increased for both NaCl and KCl additives. In addition, both polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC) plastics were used (FIG. 31D). The recovery yield of all four precious metals were increased, especially for Ag, with the recovery yield improving to >80%. The plastic additives were ground post-consumer samples with very low or negative values, so they will not introduce significant materials cost during the e-waste recycling process. [0240] Even with the F and Cl additives, the recovery yield of Au is <10%. Interestingly, the recovery yields of all four precious metals were improved when sodium iodine (NaI) was used as the additive; the recovery yield of Au was improved to >60% (FIG. 31E). The I additive has the best performance among halides for Au recovery. According to the hard and soft acids and bases (HSAB) theory, Au + is a soft Lewis acid, and I- is a soft Lewis base while F- and Cl- are harder than I- [Pearson 1963], favoring AuI. By using an additive mixture of NaF, NaCl and NaI, the precious metals all had a good recovery yield, >60% for Rh, >60% for Pd, >80% for Ag, and >40% for Au (FIG. 31F). The composition analysis of the raw materials and the remaining solid after FJH by X-ray photoemission spectroscopy (XPS) showed that 10 – 40% of the halide additives were evaporated during the FJH process, which could be recovered and reused by a water washing and precipitation process. [0241] A total composition analysis of the collected metals in the cold trap was conducted. In both cases with or without the chemical additives, in additions to the precious metals, the most abundant metals were Cu with mass ratio >60 wt%, followed by other prominent metals in e- waste including Al, Sn, Fe, and Zn. Further purification and refining could be done by selective precipitation, solvent extraction, and solid-phase extraction, which are commercially well- established practices and are known in the art. [Ueda 2016]. [0242] The morphology and chemical composition of the condensed solids were characterized using scanning transmission electron microscopy (STEM) and energy dispersion spectroscopy (EDS). The elemental maps showed the clustered alloy particles of Rh, Pd, Ag, and Au (FIG. 31G), which were formed by the ultrafast heating and rapid cooling of the FJH process. This is similar to the case of the carbothermic shock synthesis of high-entropy alloy nanoparticles, which could be potentially used in catalysts. [Yao 2018]. In other regions, the precious metals spreading over the entire product was also observed. Moreover, the XPS analysis of the collected volatiles showed that Ag and Au were mainly in the elemental state, while elemental state and higher oxidation state coexisted for Rh and Pd, presumably due to their different chemical reactivity. Improved Leaching Efficiency Of Precious Metals [0243] Apart from the condensation of the volatile composition, the other pathway to recover the precious metals was by leaching the residual solids obtained by FJH. See FIG. 32A. Different from the use of a vacuum to facilitate the metal volatilization in the evaporative separation scheme (FIG. 22), a pressurized setup was built to trap the metals in the reactor (FIG. 33A). An inert gas (N 2 ) cylinder was connected to the FJH reactor, where the pressure was monitored by a pressure gauge. The inner pressure (P 0 ) during FJH was estimated to be ~5 atm according to the amount of collected gas. [0244] Based on the pressure drop and the size of the FJH chamber, the gas diffusion was simulated under different pressures (P out ) (FIG.33B). When vacuum was used (P out = 0 atm), as it is in the evaporative separation (FIG. 22), the gas velocity was up to 800 m s -1 . Such a high gas velocity aided the volatile components to quickly diffuse to the cold trap and prevent the condensation loss at the tube sidewalls. In contrast, the gas velocity was greatly reduced with the increase in pressure (FIG. 33B). As a result, more of the originally volatile components were trapped within the residual solids in the reactor. The detailed reaction conditions for the pressurized FJH are shown in TABLE VI. TABLE VI [0245] The leaching of the residual solids after FJH (denoted as PCB-Flash) was started at 120 V and atmospheric pressure using dilute acids (1 M HCl, 1 M HNO 3 ). The leachable content of Rh, Pd, and Ag in PCB-Flash was substantially higher than that in the PCB raw materials (FIG. 33C). The ratio of the recovery yield by leaching the PCB-Flash (Y) and leaching the PCB raw materials (Y 0 ) was calculated. FJH with leaching was far more effective than leaching alone. The recovery yield of Rh, Pd, and Ag was increased by 4.17 ± 0.48, 2.90 ± 0.31, 56.0 ± 18.1 times, respectively (FIG. 33C). (In FIG. 33C, Y0 and Y mean the recovery yield by leaching printed circuit board (PCB) and PCB-Flash, respectively. The dashed line denotes Y/Y0 = 1. The error bars denote the standard deviation where n = 3). The deviations could be from the inhomogeneous distribution of precious metals in e-waste. Interestingly, the Au recovery yield was reduced after the FJH process. The reason was presumably the formation of covalent bonds between Au and carbon [Olavarria-Contreras 2016], which could significantly increase the difficulty of acid leaching. [0246] The thermogravimetric analysis (TGA) of the PCB-Flash showed that the carbon could be removed in air at ~700 °C (FIG. 32B). (The TGA curve in FIG.32B shows that the PCB- Flash started to lose weight at ~400 °C and remains stable at ~800 °C). Hence, the PCB-Flash solid was calcined at 700 °C for 1 h (denoted as PCB-Flash-Calcination). Inset 3201 shows photographs of PCB-Flash and PCB-Flash-Calcination The PCB raw materials were also calcined as a control (denoted as PCB-Calcination, FIG.32C). [0247] The XPS analysis showed the efficient removal of carbon by calcination (FIG. 32D). (In FIG.32D, the XPS of PCB shows mostly C and some inorganic signals. The XPS of PCB- Flash shows mostly C signals, indicating that O was removed by the FJH process, and the inorganic element peaks are not detected, presumably because the inorganics were covered by carbon during the FJH process. The XPS of PCB-Flash-Calcination show abundant elemental signals, demonstrating the removal and exposure of inorganic materials). With the FJH and calcination process, the recovery yields of Rh, Pd, Ag, and Au were increased by 3.11 ± 0.37, 2.64 ± 0.39, 28.5 ± 9.8, 7.24 ± 2.22 times, respectively (FIG. 33D). (In FIG. 33D, Y 0 and Y mean the recovery yield by leaching PCB and PCB-Flash-Calcination, respectively. The dashed line denotes Y/Y0 = 1. The error bars denote the standard deviation where n = 3). The values are larger than those achieved with the calcination-only process (FIGS.32E-32F). [0248] The mechanism of the improved leaching efficiency by FJH is shown in FIGS. 34A- 34E. Modern electronics are fabricated and packaged by a planar process and have a laminated configuration, where the useful metals are embedded into polymer or ceramic matrices (FIG. 34A). [Sun Z 2017]. Even after the pulverization, the particle size was large ~5 μm (FIG.34B). The laminated structure hinders the extraction of metals in a typical hydrochemistry process, resulting in elongated leaching times and low leaching efficiencies. [Sun Z 2017]. During the FJH process, the matrix was rendered as an ultrafine powder at the ultrahigh temperature (FIGS. 34C-34D), and the metals were exposed (FIG. 34E), which greatly accelerated the leaching rate and extent of metal extraction. [0249] The effect of the FJH voltage and pressure on the recovery yield were evaluated. It was found that the modest FJH voltages between 30 to 50 V led to the best recovery yield (FIG. 33E, showing curves 3301-3304 for Rh, Pd, Ag, and Au, respectively, with the shaded region of FIG. 33E is the approximate optimal voltage for all metal recovery). Too low voltage did not provide enough energy to thermally decompose the matrix, while too high voltage presumably resulted in evaporative loss. It was found that a higher surrounding pressure was beneficial (FIG. 33F, showing curves 3311-3314 for Rh, Pd, Ag, and Au, respectively). This is because the volatile components were trapped in the residual solid, as projected by the gas flow simulations (FIG.33B). The mild acid leaching condition (1 M HCl, 1 M HNO3) used in the processes of the present invention are more cost-effective and environmentally friendly compared to other hydrometallurgical processes, which use the highly concentrated mineral acids such as aqua regia [Sun Z 2017; Park 2009], or toxic cyanides [Sethurajan 2019; Quinet 2005] as extractants for achieving a high recovery yield. Removal And Collection Of Toxic Heavy Metals [0250] Removal of toxic components is another major concern for e-waste processing. [Ogunseitan 2009; Leung 2008; Julander 2014; Sun 2020]. The heavy metal removal capability of the FJH process was evaluated. Compared to precious metals, the heavy metals, including Cr, Pb, Cd, As, and Hg, have much higher vapor pressures and lower boiling points (FIG.35A). Especially for the most toxic Cd, As, and Hg, the separation factors between them and precious metals could achieve ~10 5 based on the theoretical analysis. The levels of heavy metals in PCB waste are in the range of 0.1 – 20 ppm (FIG.35B). These values are above the safe limits of heavy metals in soils for agriculture as recommended by the world health organization (WHO). [Kinuthia 2020]. [0251] After one FJH, the heavy metal contents in the remaining solid (PCB-Flash) were greatly reduced (FIG. 35C). The removal efficiencies of Hg and Cd were calculated to be >80%, followed by Pb and As (>50%), and Cr (>35%) (FIG.35D). These efficiencies were consistent with their vapor pressure values (FIG. 35A). The heavy metals were collected by condensation in the cold trap, as was done for the evaporative separation, and the collection yields were calculated (FIG. 35D). The collection yield matched well with the removal efficiency, demonstrating that most of the evaporated heavy metal was trapped by the cold trap, minimizing the leakage of heavy metals into the environment during the recycling process. [0252] The concentration of heavy metals in the residue solids could be further reduced by multiple FJH reactions. After one FJH reaction, the concentration of Hg was reduced to below the safe limit of Hg in soils for agriculture (0.05 ppm) (FIG.35E) [Kimuthia 2020], the highest standard for waste disposal. As for Cd, three consecutive FJH cycles reduced the concentration to below the safe limit (0.003 ppm) (FIG. 35F). [Kimuthia 2020]. The concentration of As, Pb, and Cr were all reduced with an increase in the number of FJH reactions. Since each FJH only takes 1 s, multiple flashes are easily accomplished. Metal Separation [0253] The above-described processes utilizing the evaporative separation scheme is discussed directed to the recovery of metals from e-waste. Nevertheless, such processes could exhibit the capability for the separation of metals. Calculation shows that large separation factors up to ~10 5 could be realized for most metals with large vapor pressure differences. The chart of FIG.36 provides the theoretical separation factors of the evaporative separation process based on the vapor pressure difference. The factors represent practical values for trace metals separation from abundant metals. For the separation of abundant metals, the values should be corrected according to their activity in the alloy melt. [0254] The different recovery yields of precious metals (FIG. 28) has been shown by the separation of the FJH process based on the vapor pressure difference. As shown in FIG. 28, without chemical additives, the recovery yields for the precious metals were Y(Rh) = 4.0%, Y(Pd) = 3.1%, Y(Ag) = 38.0%, and Y(Au) = 1.3%. These different recovery yield values demonstrate the separation ability of the FJH process. See TABLE VII below. TABLE VII Separation Factors Of Precious Metals [0255] The chemical additives (FIGS.31A-31F) also regulated the precious metals separation presumably due to their different chemical reactivity. See TABLES VIII-X, below. TABLE VIII Separation Factors Of Precious Metals By Using NaCl Additives Table IX Separation Factors Of Precious Metals By Using NaF Additives TABLE X Separation Factors Of Precious Metals By Using NaI Additives [0256] The separation ability of the evaporative separation scheme could be further improved by progressively increasing the FJH temperature. Carbothermic Reduction [0257] The flash Joule heating process can also be used for carbothermic reduction of metal from oxide. Before recovery, various metal oxides were used that showed the availability to recovery metal by the flash Joule heating method. As shown in FIGS. 37A-37F, it was found that Al can be recovered from Al 2 O 3 , Fe can be recovered from Fe2O3, Cu can be recovered from CuSO4, Ni can be recovered from NiSO4, Mn can be recovered from MnO2, Pb can be recovered from PbNO3. During the flash Joule heating process, carbon from carbon black reduces the metal oxides and metal salts to the metal while oxidizing the carbon presumably to carbon dioxide and carbon monoxide. [0258] In certain embodiment of the present invention, the process can include a mechanism used to trap the metals in waste. For example, the mechanism can use reduced pressure and have the volatilized metals, metal carbides, metal oxides, or other metal complexes volatilize out of the reaction chamber enter a cold trap upon flash Joule heating of the source. The cold trap can be, but need not be, liquid N2. Even at room temperature, these can be collected in the trap. [0259] Further, for example, the mechanism can use atmospheric or higher pressure (such, as, for instance, 10 atmospheres or 20 atmospheres), and have the metals remain in with the newly formed graphene. The graphene can be calcined away (such as, for instance, at 700-800°C in air), leaving the metals (or metal oxides, etc.) isolated. Or the graphene can be oxidized away chemically, like with HNO 3 . For this latter mechanism, a pressure release valve can be used at the end of the electrode-hole assembly for the flash Joule heating process. Some of the metals being recovered have very high boiling points and they will stay with the carbon, especially at the higher pressures utilized Designs and Scalability [0260] FIG. 38 shows a flash joule heating pressure and gas collection system 3800 that can be used for embodiments of the present invention. System 3800 includes the following: (a) Timing sprockets and belt 3801; (b) Manual or motor drive 3802; (c) Driver 3803 (such as twin screw drive); (d) Power supply 3804 (such as AC or DC from flash power supply); (e) Sample compression 3805; (f) Nuts 3807a-3807b and soft spacers 3806a-3806b; (g) Electrode 3808a (such as a solid brass electrode with thread) and electrode 3808b (such as a brass electrode with a thread and with a hole drilled); (h) Tube 3809 (such as quartz tube); (i) Cooper wool 3810; (j) Torsional spring compression 3811; (k) Electrode 3812 (such as brass electrode with O-rings seals and axial bore); (l) Sample 3813; (m) Conduit 3814 (such as PTFE tube) inside electrode 3812; (n) Pressure seal 3815 (such as with Swagelok reducing union); (o) Particle collector 3816; (p) Adjustable pressure relief value 3817; (q) Gas collector 3818; (r) Flow to vacuum or gas analysis 3819; (s) Vent 3820; (t) Safety relief valve 3821; (u) Conduit 3822 (such as PFE tubing); (v) Flow to vacuum 3823; (w) Pressurized input from gas supply 3824; and (x) Pressure gauges 3825-3826. [0261] System 3800 is a pressurizable flash Joule heating cell that has a gas collector 3818 should gas overpressure ensue. In some embodiments, system 3800 utilizes electrodes having 5/16 inches or 8 mm diameter. Conduits can have 1/8 inch outer diameter. [0262] In system 3800, the two brass electrodes with O-ring grooves are inserted into the quartz tube that is tightly wrapped with a compression spring to put the quartz under compression and resist the outward force of the pressure. One electrode is hollow, with a PTFE tube inserted to provide a smooth and continuous exit path. A reducing Swagelok fitting provides a pressure and vacuum tight seal to the PTFE tube, which exits the electrode without a joint. System 3800 is capable of withstanding tens of atmospheres of pressure. Generally, with respect to pressure, the limiting factor is the quartz tube, and how well a strong spring can prevent breakage. The twin-screw supporting frame also should be sufficiently robust to resist the thrust when the sample is pressurized or when pressure is created by the flash. The quartz tube can be replaced by any non-conductive tube, and crosslinked polyethylene has also been used since the temperature reach on the tube is generally below 250°C and generally for less than 1 second. While not shown in FIG.38, a motor drive can be added and utilized. Furthermore, because the system is fully sealed, there is no need for an external vacuum chamber surrounding the flash assembly. [0263] Rubber bushings between the nut and the support frame can be useful in absorbing the shock when short-duration flashes are used. [0264] System 3800 can be sealed with O-rings. Silicon O-rings are heat resistant and even with overheating, do not melt but tend to harden, and should maintain a seal. Because no hot gases can typically flow past the O-rings, they do not overheat. While discoloration of the first O-ring has been observed, the double O-ring remained sealed. [0265] System 3800 can be fully evacuated and would hold pressure following the flashing of the sample 3813 as the gases exited into a heavy wall glass pressure tube. In some embodiments, a right angle joint can be used so that the gas exhaust would not interfere with the end connections of the electrodes. However, if particulates or nanoparticles are ejected, a straight exit tube is generally preferred. System 3800 shows a straight and continuous conduit 3814 (PTFE exit tube), and the wires are connected with rings on threaded brass electrodes 3808a-3808b. [0266] System 3800 uses of the twin-screw translation, which provides consistent alignment of the electrodes. It was found that for single-screw translators, when pressure or force is applied, the electrodes angle upward, which in turn had put strain on quartz tube 3809. The twin screws are connected by timing sprockets and a belt 3801 for simultaneous thrust, and can be driven either manually or with a stepper motor. [0267] As for the vacuum and gas supply, the tubing that exits the end of the hollow electrode can be connected through valves to vacuum 3823, a gas supply 3824, and a pressure gauge 2925. The gas supply can be inert, or be used to infuse reagents into the sample like hydrogen, methane, or other reactive species like halocarbons, ammonia, boron compounds, etc. These can be added to the porous carbon/graphene in a subsequent flash. [0268] The pressure relief can be preset for system 3800. Adjustable pressure relief valve 3817 determines the ultimate pressure on the sample 3813. The cell can be fully pressurized before the flash, or allow the flash to generate high pressure. The opening pressure is set by a spring and threaded cap on the valve, and when the pressure exceeds the set force of the spring, the valve opens and the gases enter the gas collector, which was evacuated previously. Subsequently, the gases can be analyzed, or just pumped away. Pressure gauge 3826 and the volume of gas collector 3818 provide information on the total yield of gases. Gas collector 3818 also has a pressure relief valve 3821 connected to a vent 3820 in case of excessive gas production. [0269] As for the effect of wide range of pressures that can utilized by system 3800, with the sealed flash chamber and adjustable relief valve, the effect of a wide range of pressures on the yield of the flash has been evaluted. Because of the pressure, volatile additives can be incorporated in the sample and will not depart until the relief valve opens. [0270] System 3800 can be utilized for a variety of particle/metal collection methods. For instance, when it is desirable to collect particulates, the PTFE tube can go straight (without bends) into particle collector 3816 (i.e., a test-tube impactor). This would be inside a larger evacuated vessel (not shown), and the momentum of the particles can cause them to stick to tube while the non-condensable gases can be pumped away. This can be used to collect volatile metals and metal compounds, which will aggregate as they cool and form nanoparticles that will adhere to particle collector 3816. [0271] This design can be varied and modified as needed with materials changes and design changes depending upon the intended use. [0272] The cost and benefit of the FJH processing were evaluated since economic incentives are the main driver for waste recycling. [Awasthi 2019]. FJH is a highly efficient heating process due to the ultrafast heating/cooling rate, the direct sample heating feature, and the short reaction duration, compared to traditional smelting furnaces where large amounts of energy are used to maintain the temperature of the whole chamber. [Khaliq 2014]. The FJH method has an energy consumption of ~939 kWh ton -1 , which is ~1/500 th of that for a lab-scale tubular furnace, [Balaji 2020], and ~1/80 th of that for a commercially used Kaldo furnace in industrial scale [Theo 1998]. Hence, the FJH process for e-waste processing have advantages over traditional pyrometallurgical processes. [0273] The FJH process is scalable. According to the analysis performed, the FJH voltage and/or the capacitance of the capacitor bank can be increased when scaling up the sample mass. FIGS. 39A-39D show scaling up of the flash Joule heating (FJH) process. FIG. 39A is a photograph of samples treated with the condition of m 0 = 0.2 g, V 0 = 150 V, and C 0 = 0.06 F (sample 3901), m 1 = 2 g, V 1 = 150 V, and C 1 = 0.6 F (sample 3902), m 2 = 4 g, V 2 = 300 V, and C 2 = 0.6 F (sample 3903). FIGS.39B-30D are realtime temperature curves for samples 3901- 3903, respectively. [0274] FIG.40A is a scheme of a continuous flash Joule heating (FJH) reactor 4000 having a continuous feed 4001 (such a e-waste and carbon black), Cu electrodes 4002-4003 (with Cu electrode having a hole), porous electrode 4004, graphite electrode 4005, O-ring 4006, and baffle 4007. The volatile components can go to collection system 3108 for collection using a cooling trap, and the non-volatile compoents can be collected in collector 4009. [0275] FIG.40B is is a scheme of a continuous flash Joule heating (FJH) reactor 4020 having continuous feed of feedstock 4021 (such as e-waste and carbon black) that flows from bin 4022. In step 4031, feedstock 4021 is loaded onto the chamber 4023 of conveyor belt 4024. In step 4032, feedstock 4021 in chamber 4023 is compressed (using compressor 4025) to a predetermined resistance. In step 4033, the feedstock 4021 then undergoes the FJH reaction using the FJH system 4026 having Cu electrode 4027 and graphite electrodes 4028. In step 4034, the product 4034 is then unloaded in collector 4029. [0276] While the schemes of FIGS. 40A-40B are described with relation to feedstock of e- waste and carbon block, these can be utilized for other materials utilized in FJH reaction. [0277] Through the use of an automation system integrated with a FJH setup, a production rate of >10 kg day -1 has already been realized. [0278] Accordingly, for the metal recovery from e-waste, the present invention provides, among other things, (i) the flash Joule heating is a dry process without usage of any solvent, which endows it as environmentally friendly; (ii) the flash Joule heating can recover most of metal elements in waste in one step, which is hard to realize by other methods; (iii) the flash Joule heating process also removes nearly all the harmful materials in waste, so it will not result in secondary pollution; and (iv) the flash Joule heating process uses far less electrical energy than a furnace since the heating durations are short and the is little energy that escapes the sample being flash Joule heated. [0279] The precious metals recovered from e-waste, are very important raw materials for various industry. Indeed, mixtures of metals like this are quite valuable since many mining companies already implement automated systems that do the base metal separations. [0280] Moreover, the recovery process removes the harmful materials such as heavy metal within the waste, which has import for solving the environmental issues raised by those waste. Ores, Fly Ash, and Bauxite Residue (Red Mud) [0281] Similar situations to e-waste likewise pertains to ores, fly ash, and red mud (red mud is more recently referred to as bauxite residue), again because rare earth elements (REE) are strategic resources in modern electronics, clean energy, and automotive industries. Thus, the above-described methods and systems can likewise be implemented for the recovery of metals from ores, fly ash, and bauxite residue (red mud). [0282] Embodiments of the present invention include the ultrafast electrothermal process based on flash Joule heating (FJH) to activate the ores, fly ash, and red mud to improve the acid extractability of REE simply using a mild acid such as 0.1 M HCl. A pulsed voltage in seconds brings the raw materials to a temperature of ~3000 °C, leading to the thermal decomposition of the hard-to-dissolve REE phosphates in CFA into highly soluble REE oxides, and the carbothermic reduction of REE components to highly reactive REE metals. The activation process can enable the increase of REE recovery yields to ~206% for class F-type CFA (CFA-F) and ~187% for class C-type CFA (CFA-C) compared to directly leaching the raw materials with more concentrated acids. The activation strategy is feasible for various secondary wastes, as demonstrated by coal fly ash (CFA) and red mud (bauxite residue (BR)). The rapid FJH process is scalable and highly energy-efficient with a low electrical energy consumption of (such as 600 kWh ton -1 or $12 ton -1 ) enabling a profit percentage of greater than 10 times. FJH System and Process [0283] The FJH system that can be utilized is similar to those described and discussed above. For instance, an electrical diagram of the FJH system that can be utilized for fly ash is shown in FIG. 41A (which is similar to previously described FJH systems, such as shown in FIGS. 6A, 13A, and 30 above). [0284] In a typical experiment, the secondary wastes (CFA, BR) were mixed with carbon black with the mass ratio (such as 2:1) by using the ball miller (MSEsupplies, PWV1-0.4L). The carbon black served as the conductive additive.200-mg mixture (133 mg waste and 67 mg CB) was added into a quartz tube (inner diameter of 8 mm and outer diameter of 12 mm). The resistance was controlled by compressing the two electrodes. The samples were loaded into a jig (FIGS. 41B-41C), and the electrodes were connected to the capacitor bank. In such embodiments, 10 aluminum electrolytic capacitors (450 V, 6 mF, Mouser #80-80- PEH200YX460BQU2) were used for charging, and the capacitor bank with a total capacitance of 60 mF was charged by a direct current (DC) supply. A relay with programmable ms-level relay was used to control the discharging time. TABLE XI reflects from detailed parameters of some secondary wastes that were utilized. After the FJH, the samples were rapidly cooled to room temperature. TABLE XI *The results on the printed circuit boards are shown as a comparison of this method being used on e-waste. Acid-Extractable REE Content In CFA [0285] There are two types of CFA categorized by the chemical composition, CFA-F, with the total content of SiO 2 , Al 2 O 3 , and Fe 2 O 3 >70 wt%, and CFA-C, with a higher abundance of CaO. [Liu 2019]. In examples evaluated herein, CFA-F was collected from the Appalachian Basin (App), and CFA-C from the Powder River Basin (PRB) [Taggart 2016], both in the US. FIG. 42 is a photograph of CFA-C 4201 and CFA-F 4202 (scale bar, 4 cm). [0286] CFA is composed of primary amorphous phases (60 – 90%) [Zhang 2020], and the remaining crystalline materials include mainly quartz and mullite, as shown by the X-ray diffraction patterns (XRD). FIG. 43A. In addition to the enrichment of Ca in CFA-C, the elemental analysis by X-ray photoelectron spectroscopy (XPS) (FIG. 43B) and energy- dispersive X-ray spectroscopy (EDS) show a high C content in CFA-F, which was may have been caused by the incomplete combustion of coal feeds. The high C content in CFA-F was also evident by the large weight loss at ~700 °C by thermal gravimetric analysis (TGA). [0287] The total quantification of REEs in CFA was done by the HF:HNO3 digestion method. [Taggart 2016]. The total REE content, ctotal(CFA Raw), was 516 ± 48 mg kg -1 for CFA-F, and 418 ± 71 mg kg -1 for CFA-C. FIG. 43C. The CFA from App has a higher REE content than that from PRB, consistent with Taggart 2016. Acid-leachable REE contents from CFA raw materials, c 0 (CFA Raw), were measured by using a 1 M HCl or 15 M HNO 3 [Taggart 2016; Middleton 2020]. For CFA-F, the HNO 3 - and HCl-extractable REE contents were 144 ± 32 mg kg -1 and 160 ± 50 mg kg -1 (FIG. 43C), respectively, corresponding to the REE extractability (Y 0 ) of ~28% and ~31%, respectively. For CFA-C, the HNO 3 - and HCl-extractable REE contents were 246 ± 71 mg kg -1 and 231 ± 81 mg kg -1 (FIG.43C), respectively, corresponding to the REE extractability of ~59% and ~55%, respectively. It is concluded that the acid concentration has limited effect on the REE leachability once it is greater 1 M. Hence, 1 M HCl leaching was utilized in the standard protocol for subsequent evaluations. [0288] The acid extractability of REE from CFA-C was higher than that from CFA-F. This is consistent with [Liu 2019], which attributes the higher extractability to the higher content of easy-to-dissolve REE species like REE oxides in CFA-C. The morphology image by scanning electron microscopy (SEM) of CFA-F is shown in FIG.43D, and the high carbon content could retard the accessibility of aqueous acids to REE-bearing species, leading to the low extractability ranging from 21% to 42% for individual REE. FIG.43E. In contrast, CFA-C is composed of fine, uncovered spheric particles (FIG. 43F), which benefits the acid leaching process, leading to a relatively higher extractability ranging from 33% to 67% for individual REE (FIG.43G). Improved Recovery Yield of REE From CFA By Electrothermal Activation [0289] In the electrothermal activation process by FJH, CFA raw materials were first mixed with carbon black (CB), which serves as the conductive additive. The mixture of CFA and CB (~30% CB) was loaded inside a quartz tube between two graphite electrodes. FIGS.41A and 44A. The resistance (R) of the sample was tunable by adjusting the compressive force between the two electrodes, that were connected to a capacitance bank of 60 mF. The sample was brought to a high temperature by high voltage discharging of the capacitors. The detailed experimental parameters are shown in TABLE XI. [0290] In a typical discharging process with FJH voltage of 120 V, R of 1 Ω, and discharging time (t) of 1 s, the current curve passing through the sample was recorded with the peak current at ~120 A followed by a current plateau at ~7 A. FIG. 44B. The corresponding real-time temperature curve exhibits a peak temperature up to ~3000 °C followed by the stable heating at ~1150 °C. FIG.44C. The obtained solid after the FJH is termed as activated CFA. FIG.45 (showing a flow chart of REE recovery from CFA 4501 to CFA + CB 4502 synthesized (via FJH) to activated CFA 4503). The acid leachable REE content from the activated CFA, c(activated CFA), was measured by a 1 M HCl leaching procedure. The recovery yield of REE from the activated CFA (Y) was calculated and compared with that of the CFA raw materials (Y 0 ). [0291] A series of FJH voltage ranging from 50 V to 150 V were applied. FIG. 44D. At the ~120 V, the HCl-leachable content of total REE (1 M HCl, 85 °C) from the activated CFA-F was improved to 329 ± 14 mg kg -1 . FIG. 44D. This corresponds to the recovery yield of Y ~64%, representing an increase to ~206% over that of the CFA-F raw materials (Y0 ~31%). The pH-dependent leaching dynamics of REE from CFA-F raw materials and activated CFA- F were investigated. FIG.44E (with curves 4401-4402 for CFA-F raw materials and activated CFA-F, respectively). Generally, the yield was reduced as the acid pH increased. Remarkably, the recovery yield of REE from the activated CFA-F remained Y ~45% at pH 2 (or 0.01 M HCl), significantly higher than that of the CFA raw materials at the same leaching condition (Y0 ~9% at pH 2), and even under a much higher acid concentration (Y0 ~31% at pH 0). [0292] For CFA-C, under the optimized FJH condition, the acid leachability of REE from the activated CFA-C was measured to be Y ~103% using the HCl leaching procedure (1 M HCl, 85 °C) (FIG. 44F, with curves 4403-4404 for CFA-F raw materials and activated CFA-F, respectively), corresponding to the ratio of ~187% of that from the CFA-C raw materials (Y0 ~55%). [0293] Even using a dilute acid (pH 1, 0.1 M HCl), the recovery yield of REE from the activated CFA-C remains Y ~94%, significantly higher than that of the CFA-C raw materials (Y 0 ~54%). This would render far more manageable wastewater streams. [0294] For individual REE, with the FJH activation process, the acid leachability was improved ranging from 170% to 230% for CFA-F (FIG. 44G), and from 170% to 210% for CFA-C (FIG. 44H) using the same leaching procedure (1 M HCl, 85 °C). Similar improvements were realized using a dilute acid leaching (0.1 M HCl, 85 °C). No significant deviation among the REE was observed, demonstrating that the FJH activation process works indiscriminately for all REE. [0295] As control, the REE content in carbon black was measured using the same digestion method. The total REE content in carbon black was ~5 mg kg -1 , corresponding to ~1% of the REE content in CFA. Hence, the use of carbon black does not induce significant error into these measurements. In practical applications, the carbon black could be substituted with anthracite coal or any other inexpensive sources of mildly conductive carbon, but the REE content in that source should be considered in yield calculations. The Mechanism of the Improved REE Extractability [0296] The mechanism of the improved REE leachability by the electrothermal activation process was investigated. The REE speciation and distribution in CFA determine the REE extractability. REE phosphate, including monazite and xenotime, is one of the primary counterions of REE in coal. [Liu 2019; Stuckman 2018]. REE phosphates are rather stable components, and no melting or thermal dissociation occur up to ~2000 °C in air. [Ushakov 2001; Hikichi 1987]. The coal-fire combustion temperature typically ranges from 1300 °C to 1700 °C. [Stuckman 2018]. As a result, the REE-bearing trace phases, including monazite and xenotime, persist in CFA. [Kolker 2017; Smolka-Danielowska 2010]. The REE could also be partitioned and encapsulated into the glass fraction of CFA by diffusion into the melt (e.g., aluminosilicates) formed at the coal boiler temperature. [Dai 2014]. Those hard-to-dissolve REE phosphates and glass phases are detrimental for REE extraction [Liu 2019], while REE oxides and carbonates in CFA are relatively easier to extract by acid leaching. [0297] The high temperature of ~3000 °C generated by the FJH process, which is significantly higher than the coal boiler temperature, could thermally degrade the REE species. Lanthanum phosphate (LaPO 4 ) and yttrium phosphate (YPO 4 ) were used as representatives for REE phosphates. As shown in Fig. 46A, after FJH of the LaPO 4 precursor, the La 2 O 3 phase was identified. Similarly, YPO 4 was thermally decomposed to Y 2 O 3 after the FJH process. FIG. 46B. The REE oxides have much higher solubility (log 10 K sp of 5 to 33) than REE phosphates (log 10 K sp of -27 to -24). See TABLE XII. TABLE XII [0298] To further provide insight on the solubility of REE phosphates and oxides, the dissolution curves as a function of pH were calculated. FIG.46C (with curves 4601-4604 for La 2 O 3 , Y 2 O 3 , LaPO 4 , and YPO 4 , respectively). It was found that LaPO 4 and YPO 4 showed significant solubility only when pH approaches 0, while the oxide counterparts readily dissolve at a low acidity with pH ~6. This partially explains the pH-dependent REE leaching dynamics, that higher REE leachabilities were achieved for the activated CFA than the raw materials using dilute acid. FIG.46E-46F. (For FIG.46E, the Si signal might be from the quartz tube during FJH). [0299] In addition to the thermal decomposition of REE phosphates, the ultrahigh temperature could also trigger the thermal reduction of REE compounds. According to the Ellingham diagram (FIG.46D), the carbothermic reduction temperatures of REE oxides are estimated to be between ~1900 °C (for Eu2O3) and ~2500 °C (for Dy2O3). The FJH at ~120 V generates a temperature up to ~3000 °C (FIG.44C), which permits the reduction of REE oxides. [0300] Y2O3 and La2O3 were used as representatives to verify the carbothermic reduction of REE oxides by the FJH process. The fitting of the XPS fine spectrum of Y2O3 after FJH shows four peaks. FIG.46E and TABLE XIII. The peaks at 157.5 and 159.6 eV are assigned to 3d5/2 and 3d3/2 of Y in Y2O3 [Barreca 2001], and the peaks at 156.4 and 158.5 eV are assigned to 3d5/2 and 3d3/2 of Y in Y(0) [Cole 2020]. TABLE XIII [0301] The XPS analysis proved the reduction of Y 2 O 3 to Y metal by the FJH process, while the small ratio of Y 2 O 3 might be from the surface oxidation. Similarly, the fitting of XPS fine spectra of La 2 O 3 precursor and La 2 O 3 after FJH (FIG. 46F, TABLE XIII) verifies the reduction of La2O3 to La metal. [Deasha 1995; Li 2019]. The reduced REE species with low oxidation state are highly active materials that readily react with even pure water. [Greenwood 1997]. The calculated Gibbs free energy change (ΔG) values for the REE metals dissolution reaction are much more negative than those of REE oxides (FIG. 46G, TABLE XII), demonstrating a much larger thermodynamic solubility of REE metals than for their oxide counterparts. [0302] This suggests that the required temperature for the thermal activation is >2000 °C for thermal decomposition of REE phosphates, and >2500 °C for carbothermic reduction of REE oxides, which also provides insight on the voltage dependent REE leachability. FIG. 44D. A FJH voltage of ≥120 V can be needed for achieving a temperature >2000 °C, while a voltage of <100 V can have limited effect on the REE leachability. Nevertheless, too high of a FJH voltage, ≥150 V, can lead to a prolonged high temperature of >3000 °C, which could in turn result in the evaporative loss of the REE during the FJH process. [0303] In addition to speciation, the REE distribution also affects the extractability, where the REE encapsulated in or distributed throughout the glass phases are hard to dissolve. [Liu 2019]. The FJH permits an ultrafast heating and rapid cooling (>10 4 K s -1 , FIG. 44C), which would induce thermal stress and cracking of the glass phases in CFA, contributing to the improved leachability. Generality Of The Electrothermal Activation Process [0304] The electrothermal activation process is applicable to other waste products for REE recovery, including BR [Deady 2016; Rivera 2018; Reid 2017] and e-waste (including as discussed above) [Maroufi 2018; Deshmane 2020; Peelman 2018]. [0305] BR (red mud) is the waste product of the Bayer process for alumina production. BR is one of the most abundant industrial wastes with 3 billion tons already stored in waste ponds and an additional 150 million tons produced each year, yet just 3% is currently recycled [Service 2020]. BR contains a significant amount of REE, for example, a total REE content of ~1000 ppm is found in BR from MYTILINEOS “Aluminum of Greece.” [Deady 2016]. The BR is a dried powder with fine particle size, and has major components including Fe2O3, CaCO3, FeO(OH), and SiO2. FIGS. 47A-47B. The REE in BR was extracted by a direct leaching process using 0.5 M HNO3. [Ochsenkuhn-Petropulu 1996]. The acid extractable REE content from BR raw materials is 428 ± 9 mg kg -1 . FIGS.47C and 48A-48B. [0306] Similar to CFA, the REE extractability of the BR after the electrothermal activation process is also dependent on the FJH voltage. FIG.48A. At the optimized FJH voltage of 120 V, the extractable REE content increased to 757 ± 30 mg kg -1 (FIG. 48B), corresponding to Y/Y 0 ~177% of that from the BR raw materials (FIG.47C). The mechanism of the improvement of REE extractability from BR by the FJH process is presumed to be similar to that of CFA (FIGS.46A-46G), since the phosphate is one of the dominant counterions for BR. [Boni 2013]. [0307] This FJH strategy was also applied for for activating e-waste and it is shown here as a complement to the methods described that used no mild acid leaching. More than 40 million tons of e-waste are produced globally each year due to the rapid upgrade of personal electronics, with <20% being recycled. [Zeng 2018]. REE are widely used in electronics in permanent magnets [Deshmane], and capacitors [Alam 2012]. In turn, the recovery of REEs from high-grade e-waste has its economic feasibility compared to REE mining from ores. [0308] The e-waste used in this FJH process was a printed circuit board (PCB) from a discarded computer. FIG. 49A (showing e-waste ground to powder). As shown in the FIG. 49B, the abundant metals in e-waste include Cu and Al, which are mainly used as the interconnects. The REEs in the PCB waste was extracted by 1 M HCl leaching process at 85 °C. The acid leachable REE content is 61 ± 4 mg kg -1 from the e-waste raw materials. FIGS. 50A-50B. After the activation process at an optimized voltage (FIGS.50A-50B), the extractable REE content was increased to 94.6 ± 0.2 mg kg -1 , corresponding to Y/Y0 ~156% of that from the e-waste raw materials. FIGS.49C and 50A-50B. [0309] Different from CFA or BR, the REE species in e-waste are usually in the form of easy- to-dissolve REE metals or oxides. [Alam 2012]. However, the REEs are usually embedded into the matrix materials due to the laminated configuration of the electronics, which could hinder the REE extraction by the hydrometallurgical process. The FJH process could expose the metals by cracking the matrices, accelerating the leaching rate and extent of metal extraction. Scalability and Utility [0310] The FJH process for REE recovery is scalable. To maintain a constant temperature when scaling up the sample mass per batch, the FJH voltage or the total capacitance of the capacitor bankcan be increased. A production rate of >10 kg day -1 by the batch-by-batch process has already been realized. The FJH process can be integrated into the continuous production manner for further automation, such as by using the schemes shown in FIGS.40A- 40B. The ongoing commercial scaling of the FJH process to tons per day paves the way for future REE recovery from large-scale waste products. [0311] The economics since the profit margin is often the sustainer of recycling. Due to the direct sample heating feature, short duration, and rapid heating/cooling rate, embodiments of the FJH process are highly energy-efficient with a low electrical energy consumption of 600 kWh ton -1 or $12 ton -1 , enabling a profit percentage of >10× compared to directly leaching the raw materials. [0312] For further refining, the removal of dissolved impurities, including mainly Al, Si, Fe, Ca, and Mg, in the REE-containing leachate and subsequent separation are needed. It was observed that the content ratio of REE and impurity (c(REE)/c(Impurity)) in the leachate was improved with the FJH process in most cases, indicating that the FJH process would also be beneficial for the subsequent REE separation. Ores [0313] Since monazite, (Ce, La, Y, Th)PO4, and xenotime, YPO4, are the main commercial sources for REE production [Cheisson 2019], embodiments can also be used for REE mining to improve the leachability from REE ores. Commercially, alkaline digestion (70% NaOH, 140 – 150 °C) is the main leaching technology for monazite [Peelman 2016], or acid baking (concentrated H2SO4, 200 °C) for monazite and xenotime [Kim 2016]. This FJH process could be faster and less dependent on the use of concentrated bases and acids. Existing individual elemental separation technologies, such as solvent extraction and ion exchange [Xie 2014] can utilized to work with the REE mixtures obtained by FJH since these are often less contaminated than those generated through traditional mining methods. [0314] While embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described and the examples provided herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. The scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. [0315] The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated herein by reference in their entirety, to the extent that they provide exemplary, procedural, or other details supplementary to those set forth herein. [0316] Amounts and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a numerical range of approximately 1 to approximately 4.5 should be interpreted to include not only the explicitly recited limits of 1 to approximately 4.5, but also to include individual numerals such as 2, 3, 4, and sub-ranges such as 1 to 3, 2 to 4, etc. The same principle applies to ranges reciting only one numerical value, such as “less than approximately 4.5,” which should be interpreted to include all of the above-recited values and ranges. Further, such an interpretation should apply regardless of the breadth of the range or the characteristic being described. [0317] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the presently disclosed subject matter belongs. Although any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the presently disclosed subject matter, representative methods, devices, and materials are now described. [0318] Following long-standing patent law convention, the terms “a” and “an” mean “one or more” when used in this application, including the claims. [0319] Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter. [0320] As used herein, the term “about” and “substantially” when referring to a value or to an amount of mass, weight, time, volume, concentration or percentage is meant to encompass variations of in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed method. 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