Ultrafast flash joule heating synthesis method and system for performing the same

Abstract

An ultra-rapid flash joule heating synthesis method and system, more particularly an ultra-rapid synthesis method for recovering metals from ores, fly ash, and bauxite residues (red mud).

Description

Related applications

[0001] Cross-references to related patent applications

[0001] This application claims priority to U.S. Patent Application No. 63 / 082,592, filed on 24 September 2020, entitled "Ultrafast Flash Joule Heating Synthesis Methods And Systems For Performing Same," which is co-owned with the owner of the present invention. This patent application is incorporated herein by reference in its entirety. [Technical Field]

[0002]

[0002] The present invention relates to an ultrafast flash Joule heating synthesis method and system, more particularly to an ultrafast synthesis method for recovering metals from ore, fly ash, and bauxite residue (red clay).

[0003] Government interests

[0003] This invention was made with government support under authorization number DE-FE0031794 granted by the U.S. Department of Energy and authorization number FA9550-19-1-0296 granted by the U.S. Department of Defense / Air Force Agency of Scientific Research. The U.S. Government has certain rights in this invention. [Background technology]

[0004]

[0004] Highly efficient and low-cost synthesis of nanomaterials is essential for their commercial applications.

[0005] carbide

[0005] Nano-sized transition metal carbides (TMCs) have been widely used as precursors for ultrahard and ultrastrong ceramics [Zou 2013; Zhang 2019; Reddy 2012], as high-performance electrochemical catalysts due to their platinum-like electronic structure [Li 2018; Zhong 2016; Gao 2019; Gong 2016; Han 2018], and as catalyst supports due to strong metal-substrate interactions [Lin 2017; Yao 2017]. Conventional methods for bulk carbide synthesis include carburizing metal precursors with gaseous carbon precursors, or sintering metal precursors with graphite-like carbon at high temperatures. [Rosa 1983] These procedures can be problematic due to the excessive supply of carbon sources detrimental to catalytic performance, and the resulting coked carbide surfaces due to large particle size and low surface area. [Chen 2013; Zeng 2015]

[0006]

[0006] To synthesize carbides with fine particle sizes, considerable effort has been made, including temperature-programmed reduction [Oyama 2992], carbonothermal reduction of metal precursors [Wu 2020; Wang K 2019], laser-spray high-temperature decomposition of metal composites [Kolel-Veetil 2005], and solution-based precipitation and carburization [Wan 2014]. The TPR method has many applications for the synthesis of metal carbides with high surface area, but requires a well-optimized reaction window [Claridge 2000]. Carbonothermal reduction of metal precursors in a furnace is common in the synthesis of TMCs [Wu 2020]; however, prolonged high-temperature conditions are essential to compensate for slow solid-state reaction rates, which inevitably leads to sintering or aggregation [Wang K 2019].

[0007]

[0007] To avoid severe aggregation, a microwave combustion method has been developed for the rapid synthesis of Mo2C and WC nanodots within 2 minutes. [Wan 2019]. High-temperature decomposition of metal composites involves the use of expensive and toxic metal-organic compounds such as Cp2Mo2(CO)6 [Kolel-Veetil 2005; Wolden 2011] for the synthesis of Mo2C and W(CO)6 [Pol 2009] for the synthesis of WC.

[0008]

[0008] The type of carbide is also limited by the availability of volatile metal compounds. Solution-based precipitation and carburizing require long annealing times for complete conversion. For example, ammonium heptamolybdate ((NH4)6Mo7O) as a precursor. 24 The synthesis of MoC using 4H2O requires annealing at 850°C for 12–24 hours [Wan 2014].

[0009]

[0009] In recent years, several unconventional electrical thermal processes have been developed for energy-efficient high-temperature synthesis. [Wang 2020; Giorgi 2018; Yan 2018]. Thermal shock (CTS) processes have used short current pulses for the synthesis of high-entropy alloy nanoparticles on carbon supports at approximately 2000 K. [Yan 2018]. Ultra-high temperature sintering (UHS) based on current-induced heating has been proposed for the sintering and sieving of ceramics in less than 10 seconds. [Wang 2020]. Spark flash sintering (SPS) applied current for the reactive carbonthermal synthesis of zirconium carbide (ZrC) in 10 minutes. [Giorgi 2018]. However, these approaches are directed towards the sintering of bulk ceramics and lack the capability to synthesize fine nanocrystals.

[0010]

[0010] Furthermore, the phase and crystal surface structure play a significant role in the behavior of carbides, for example, in their hydrogen adsorption / desorption energy. [Gong 2016; Politi 2013] However, there are few procedures for selectively processing the phase and crystal surface of carbides for maximum performance. [Gong 2016; Wan 2014]

[0011]

[0011] Electrocatalytic hydrogen evolution (HER) reactions depend on the availability of low-cost electrocatalysts. TMCs are extremely promising in HER due to their platinum-like electronic structure. [Gao 2019] However, state-of-the-art methods for synthesizing metal carbide nanoparticles are limited by high cost and low productivity. [Gong 2016] Seriously, most methods are too specialized, lack generality, and are difficult to control phases. [Wan 2014]

[0012] corundum

[0012] High surface area corundum nanoparticles (α-Al2O3NP) have a wide range of applications. For example, corundum is widely used in ceramics for artificial implants [De Aza 2002] and high-speed cutting tools [Kumar 2003]. α-Al2O3NP precursors make available nanometer-sized alumina ceramics with significantly improved fracture toughness [Ighodaro 2008], wear resistance [Krell 1996], and high density at low sintering temperatures [Guo 2016]. Although γ-Al2O3NP is primarily used as a catalyst support due to its high surface area [Peterson 2014], α-Al2O3NP is also used as a catalyst support, exhibiting higher mechanical stability in Pt-Mo-Co catalytic converters for automotive exhaust gases [Frank 1998] and enhancing Ru catalytic activity for ammonia synthesis [Lin 2019].

[0013]

[0013] Considerable effort has been made to improve the synthesis of α-Al2O3, but due to its inherent thermodynamic limitations, there are few processes that yield high surface area NPs. [Guo 2016; McHale 1997; Amrute 2019]. Even though corundum is a thermodynamically stable phase of coarsely crystalline aluminum oxide (Al2O3), the synthesis of nanocrystalline Al2O3 typically yields a surface area of ​​125 m². 2 When the value exceeds / g, it yields γ-Al2O3 due to its lower surface energy. [McHale 1997]

[0014]

[0014] Another reason is the high activation energy barrier of approximately 485 kJ / mol for the phase conversion from the cubic close-packed structure of the γ phase to the hexagonal close-packed structure of the α phase. [Steiner 1971] As a result, the thermal process typically requires temperatures >1470K along with long annealing times of 10-20 hours to facilitate the conversion. [Steiner 1971; Levin 1998] High energy input and long high-temperature annealing allow for substantial mass transfer of <10 m 2 This results in a surface area of ​​ / g. [Amrute 2019]. Furthermore, polymorphism of Al2O3 during phase transitions further increases complexity, potentially leading to mixed transitions of (t)-alumina and undesirable δ- and θ-Al2O3. [Steiner 1971; Chang 2001; Laine 2006]. Rather, typical methods for corundum nanoparticles are time- and energy-consuming, such as annealing of γ-Al2O3 at 1473–1673K for 10–20 hours [Lodziana 2004] and hydrothermal reactions of γ-AlOOH at 723K and 1200 bar for 35 days [McHale 1997; Loffler 2003].

[0015]

[0015] Therefore, the production of α-Al2O3 by phase conversion from cubic close-packed gamma phase (γ-Al2O3) is usually hindered by a high activation energy barrier (approximately 485 kJ / mol) that requires long high-temperature thermal annealing (approximately 1500 K, 10-20 hours) and suffers from severe aggregation. Thus, developing an ultrafast and energy-saving method is important for the wide range of applications of α-Al2O3 nanoparticles.

[0016] Electronic waste

[0016] The recovery of useful metals from waste is important for the circular economy and also important for solving environmental problems. Specifically, electronic waste (electronic junk) contains valuable components.

[0017]

[0017] Electronic waste is generated from discarded electrical or electronic devices. The recovery of precious metals from electronic waste, known as "urban mining," is important for the circular economy. Current methods for urban mining, mainly smelting and leaching, suffer from long refining processes and negative environmental impacts.

[0018]

[0018] More than 40 million tons of electronic waste (electronic waste) are generated worldwide every year [Zhang 2012; Zeng 2018], which is a rapidly growing component of solid waste due to the rapid upgrading of personal electrical and electronic devices [Ogunseitan 2009; Wang 2016]. Most electronic waste ends up in landfills, and only about 20% is recycled [Ghosh 2015], which can cause negative environmental impacts due to the widespread use of heavy metals in electronic devices [Leung 2008; Julander 2014; Awasthi 2019].

[0019]

[0019] Electronic waste can be a sustainable resource because it contains abundant useful metals. [Kaya 2016] The concentration of some precious metals in electronic waste is higher than that in ore. [Zhang 2012] Recovering precious metals from electronic waste, i.e., urban mines, is more cost-effective than untouched mines [Zeng 2018] and is important for the circular economy [Awasthi 2019].

[0020]

[0020] Similarly, due to the widespread use of heavy metals such as Cd, Co, Cu, Ni, Pb, and Zn in electronic devices, electronic waste can pose significant health risks and negative environmental impacts. [Leung 2008; Julander 2014; Awasthi 2019]. Leakage of heavy metals due to improper landfill disposal leads to environmental damage. [Zhang 2012; Awashthi 2019]. The release of hazardous components during the recycling process in the form of dust or smoke [Leung 2008] worsens the health of recyclers and local residents. For example, significantly higher concentrations of Pb have been found in the blood of electronic waste workers.

[0021]

[0021] The lack of high-yield, environmentally friendly recovery processes is a major obstacle to urban mining. [Kaya 2016] Conventional methods for electronic waste recycling are based on dry metallurgy processes [Hall 2007], in which the metal is melted by heating at high temperatures. Dry metallurgy is energy-intensive, unselective, and requires high-grade precursors. [Cui 2008] Dry metallurgy also produces harmful fumes containing heavy metals, especially those with low melting points such as Hg, Cd, and Pb. [Kaya 2016] Wet metallurgy processes are more selective and are carried out by leaching the metal using acids, bases, or cyanides. [Sun Z 2017] Leaching rates are usually slow. The use of highly concentrated leaching agents makes wet metallurgy processes difficult for large-scale applications and produces large amounts of liquid waste and sludge that can cause secondary pollution. [Jafhav 2015] Biometallurgy is highly selective and potentially environmentally sustainable, but it is still in its early stages. [Zhuang 2015]. The separation of useful metals from various material matrices such as plastics, glass, and ceramics is based on their differences in physical or chemical properties. For example, gravity separation techniques rely on different specific gravities. [Sarvar 2015]. Magnetic separation is used to separate magnetic metals from iron-free waste. [Yamane 2011]. Wet metallurgical separation is based on the chemical reactivity of the metal with the leaching agent. [Sethurajan 2019].

[0022]

[0022] Electronic components contain potentially highly toxic materials such as lead (Pd), cadmium (Cd), beryllium (Be), and chromium (Cr). When released into the environment, these toxic materials can cause numerous waterborne or airborne diseases. At the same time, circuit boards contain many precious metals such as gold (Au), silver (Ag), and platinum (Pt), as well as rare earth elements such as neodymium (Nd) and dysprosium (Dy), which are difficult to mine and are considered essential elements for electronic equipment manufacturing and electric motors. The mining or processing of these latter rare earth elements is controlled by foreign governments, raising concerns about the security of essential elements in the United States for the need to manufacture them. However, less than 20% of electronic waste is recycled, and 80% ends up in landfills. One method for recycling electronic waste is to melt down circuit boards and leach out useful metals. [Sthiannopkao 2013] Conventional recycling methods commonly used in developing countries expose workers to hazardous and carcinogenic substances. Therefore, there is a strong need for extremely clean and highly efficient methods for recycling useful metals from electronic waste.

[0023] Ore, fly ash, and bauxite residue (red mud)

[0023] Similar situations are observed with ore, fly ash, and red clay (red clay, more recently referred to as bauxite residue), also because rare earth elements (REEs) are strategic resources in the modern electronics, clean energy, and automotive industries. [Cheisson 2019]. Concentrated aqueous acid leaching of REE inorganics followed by biphasic solvent extraction has been the dominant scheme for the mass production of REEs. [Cheisson 2019]. However, the intensive production of resources and pollution has a large environmental footprint, in this case the cost of the bio-threatening environment reached $14.8 billion in 2015, and sustainable solutions need to be sought. [Lee 2018]. As readily available REE inorganics decrease, REE extraction from industrial waste is attracting considerable interest. [Jyothi 2020]. Applicable secondary wastes include coal fly ash (CFA) [Taggart 2016; Smith 2019; Zhang 2020; Liu 2019; Sahoo 2016; Middleton 2020], bauxite residue (BR, also known as red mud) obtained as a result of bauxite treatment for aluminum production [Deady 2016; Rivera 2018; Reid 2017], and electronic waste (electronic waste) from consumer electronics and electric vehicles [Maroufi 2018; Deshmane 2020; Peelman 2018]. Annual alumina production in 2018 was approximately 160 million tons. Red mud is a highly alkaline waste composed mainly of oxides such as Fe2O3, Al2O3, TiO2, CaO, SiO2, and Na2O. Furthermore, red mud also contains useful rare earth elements such as La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y. [Deady 2016]. Thus, similar situations to those discussed above regarding the need to recover metals from electronic waste also apply to ore, fly ash, and bauxite residue (red mud).

[0024]

[0024] The reuse of these wastes, in turn, reduces the environmental burden of their removal. [Sahoo 2016] However, the REE content in these secondary wastes is usually lower than that in REE inorganic materials, and the recycling yield remains extremely low, which hinders the search for establishing circular economy programs. [Taggart 2016]

[0025]

[0025] Taking CFA as an example, it is a byproduct of coal combustion, with an annual global production rate of approximately 750 million tons. [Sahoo 2016]. CFA has an average total REE content of about 500 ppm, which varies depending on the geological origin of the supply coal. [Taggart 2016; Middleton 2020]. However, the acid-extractable REE content is usually much lower and highly dependent on the CFA feed. For example, Taggart 2016 reported that the HNO3 extractability of REE from major US power plants ranged from 1.6% to 93.2%, with a median of about 30%, or from 7.4 ppm to 372 ppm, with a median of about 127 ppm. The REE extractability in CFA depends on the REE species, e.g., oxides, phosphates (churchite, xenotime, monazite, etc.), apatite, zircon, and glass phases. [Liu 2019]. The low REE extraction rate in most CFA resources is due to the high proportion of REE species that are difficult to dissolve, such as REE phosphates, zircon, and glass phase. [Liu 2019].

[0026]

[0026] The acid leaching process can be optimized, depending on the feed, by using a highly concentrated mineral acid, e.g., 15M HNO3 at 85-90°C for an extraction rate of 70% [Taggart 2016], or by using 12M HCl at 85°C for an extraction rate of 35-100% [King 2018], thereby improving the extraction rate to some extent. However, the use of concentrated acid inevitably increases the extraction cost and waste burden. Chemical or thermal pretreatment of CFA before acid leaching contributes to achieving high REE recovery [Wang Z 2019; Taggart 2018]. For example, a total REE recovery of 88% is achieved by NaOH hot water treatment followed by acid leaching [Wang Z 2019]. Alkali roasting with NaOH results in a recovery yield of >90% [Taggart 2018]. However, such pre-processing processes typically require a lot of time and energy, significantly reducing profit margins and incentives.

[0027]

[0027] Furthermore, there are environmental hazards to the discharge of these materials. The discharge of red mud is extremely harmful to the environment due to its alkalinity. In October 2010, approximately 1 million cubic meters of red mud were accidentally released into a rural area of ​​Hungary, killing 10 people and contaminating the surrounding area. In fact, methods developed to separate and recover rare earth elements, such as leaching and cation exchange chromatography [Ochsenkuhn-Petropulu 1995], can cause secondary contamination, given that large amounts of acid are used. [Overview of the project] [Problems that the invention aims to solve]

[0028]

[0028] Therefore, current methods for REE recovery suffer from lengthy purification processes, low extraction rates, and large wastewater streams. Thus, there is still a need for rapid and energy-efficient pretreatment for REE recovery from ore, fly ash, and bauxite residue (red mud). Furthermore, there is still a need to develop "dry" methods for the direct recovery of rare earth elements from ore, fly ash, and bauxite residue (red mud). [Means for solving the problem]

[0029]

[0029] The present invention relates to an ultrafast flash Joule heating synthesis method, and more specifically, embodiments of the present invention include an ultrafast synthesis method for recovering metals from ore, fly ash, and bauxite residue (red clay).

[0030]

[0030] Such solvent-free processes based on flash Joule heating can provide ultrafast synthesis for activating ore, fly ash, and bauxite residue (red mud) to improve REE extraction rates. The FJH process thermally decomposes or reduces hard-to-dissolve REE species into components with high thermodynamic solubility, resulting in approximately a twofold increase in leaching content and high recovery yield using dilute acid (e.g., 0.1 M HCl). Activation can be used for various wastes such as coal fly ash and bauxite residue (red mud). The rapid FJH process is energy efficient, with low electrical energy consumption of 600 kWh / ton, enabling more than a tenfold increase in profits.

[0031]

[0031] Generally, in another embodiment, the present invention features a method for recovering metal. The method includes the step of mixing a material with a conductive additive to form a mixture. The material is prepared from ore, fly ash, and / or bauxite residue. The method further includes the step of applying a voltage to the mixture to recover metal from the material. The voltage is applied in one or more voltage pulses. The duration of each of the one or more voltage pulses is over the duration of the duration. The method further includes the step of collecting the recovered metal. The recovery and collection of the metal includes performing a leaching process after applying a voltage to the mixture.

[0032]

[0032] An embodiment of the present invention may include one or more of the following features:

[0033] The conductive additive may be a carbon source.

[0033]

[0034] The materials can be prepared from ore.

[0035] The material can be prepared from fly ash.

[0036] The material can be prepared from bauxite residue.

[0034]

[0037] The material can be prepared by performing a mechanical process to convert it into a fine powder.

[0038] Mechanical processes can be selected from a group consisting of cutting the material into small pieces, crushing the material, grinding the material, grinding the material, and combinations thereof.

[0035]

[0039] The fine powder may be a microscale fine powder.

[0040] The conductive additive may be selected from the group consisting of elemental carbon, carbon black, graphene, flash graphene, coal, anthracite, coke, metallurgical coke, calcined coke, activated carbon, biochar, carbon from natural gas stripped of hydrogen atoms, activated carbon, shungite, plastic waste, carbon char derived from plastic waste, food waste, carbon char derived from food waste, biomass, carbon char derived from biomass, hydrocarbon gases, and mixtures thereof.

[0036]

[0041] The conductive additive may be carbon black.

[0042] The conductive additive may be primarily elemental carbon.

[0043] The materials and conductive additives may be mixed in a weight ratio ranging from 1:2 to 25:1.

[0037]

[0044] The applied voltage may be within the range of 15V to 300V.

[0045] The mass of the mixture to which the voltage is applied may be greater than 1 kg. The applied voltage may be between 100V and 100,000V.

[0038]

[0046] The mass of the mixture to which the voltage is applied may be greater than 100 kg.

[0047] The mass of the mixture to which the voltage is applied may be greater than 1 kg. The applied current may be between 1,000 amp and 30,000 amp.

[0039]

[0048] The mass of the mixture to which the voltage is applied may be greater than 100 kg.

[0049] The mixture may have a resistance ranging from 0.1 ohms to 25 ohms when a voltage is applied.

[0040]

[0050] The duration of each of the one or more voltage pulses may be between 1 microsecond and 25 seconds.

[0051] The duration of each of the one or more voltage pulses may be between 1 microsecond and 10 seconds.

[0041]

[0052] The duration of each of the one or more voltage pulses may be between 1 microsecond and 1 second.

[0053] The duration of each voltage pulse, or the duration of each pulse, may be between 100 microseconds and 500 microseconds.

[0042]

[0054] One or more voltage pulses may be between 2 and 100 voltage pulses.

[0055] Voltage pulses can be performed using direct current (DC).

[0043]

[0056] This method can be carried out using a pulsed direct current (PDC) Joule heating process.

[0057] Voltage pulses can be performed using alternating current (AC).

[0044]

[0058] Voltage pulses can be created using both direct current (DC) and alternating current (AC).

[0059] This method allows for the alternating use of direct current (DC) and alternating current (AC).

[0045]

[0060] This method allows for the simultaneous use of direct current (DC) and alternating current (AC).

[0061] One or more voltage pulses can increase the temperature of the mixture to at least 3000K.

[0046]

[0062] The metal may contain rare earth elements.

[0063] The metal may include precious metals.

[0064] The material may contain metal oxides. Applying voltage to the mixture brings about a carbonothermal reaction of the metal oxides, allowing the metal to be recovered.

[0047]

[0065] The application of voltage to a mixture for recovering metal from materials can be carried out at pressures ranging from 0.001 to 25 atmospheres.

[0066] The pressure can be approximately 1 atmosphere.

[0048]

[0067] The pressure may be at least 2 atmospheres.

[0068] The pressure may be at least 10 atmospheres.

[0069] The pressure may be at least 20 atmospheres.

[0049]

[0070] This method can be performed using a pressurized cell.

[0071] Applying voltage to the mixture to recover metal from the material allows a large portion of the metal to remain in the graphene produced by this method.

[0050]

[0072] The collection step may include collecting a gas stream containing volatile products produced by applying voltage to the mixture.

[0073] The collection process may further include cooling the gas stream.

[0051]

[0074] The leaching of metal in the mixture after applying voltage to the mixture may be greater than twice the amount of metal leached in the mixture before applying voltage, provided that the aqueous treatment is carried out using the same pH and volume.

[0052]

[0075] The leaching process can be carried out using dilute acid.

[0076] The dilute acid may be an acid with a maximum concentration of 1M.

[0077] The dilute acid may be an acid with a maximum concentration of 0.1 M.

[0053]

[0078] The dilute acid may be at least a 1M acid.

[0079] This method can be executed as a continuous or automated process.

[0080] In general, in another embodiment, the present invention features a system for performing a method for recovering metals utilizing at least one of the methods described above. The system includes a source of a mixture comprising a material and a conductive additive. The system further includes a cell operably connected to the source so that the mixture can be flowed into the cell and held under compression. The system further includes an electrode operably connected to the pressure cell. The system further includes a flash power supply for the step of applying a voltage to the mixture to recover metals from the material.

[0054]

[0081] An embodiment of the present invention may include one or more of the following features:

[0082] The cell may also be a pressure cell. The system may further include a gas supply for pressurizing the pressure cell.

[0055]

[0083] The system may also include an adjustable relief valve (relief value).

[0084] The system may further include a particle collection device.

[0056]

[0085] The system may further include a gas collection device.

[0086] The system can be operated to execute a continuous process or an automated process. [Brief explanation of the drawing]

[0057] [Figure 1A]

[0087] Figures 1A to 1E illustrate the ultrafast synthesis of carbides by flash Joule heating (FJH). Figure 1A is a schematic diagram of the FJH synthesis of carbides using (i) a route showing the high-temperature FJH process of an embodiment of the present invention and (ii) a route showing the conventional carburizing process. [Figure 1B] Figure 1B shows current measurements during the FJH process. [Figure 1C] Figure 1C shows the real-time spectral radiance at wavelengths of 640–1000 nm. The inset is a photograph of the sample before FJH, during FJH, and during rapid cooling. [Figure 1D] Figure 1D shows real-time temperature measurements obtained by fitting blackbody radiation from a sample during the FJH process. [Figure 1E] Figure 1E shows the relationship between temperature and vapor pressure for various metal precursors and carbon. [Figure 2A]

[0088] Figures 2A–2H show the phase-controlled synthesis of molybdenum carbide. Figure 2A shows the X-ray diffraction (XRD) patterns of β-Mo2C, α-MoC1-x, and η-MoC1-x synthesized at voltages (V) of 30V, 60V, and 120V, respectively. The corresponding PDF reference cards are β-Mo2C, 35–0787; α-MoC1-x, 65–8092; and η-MoC1-x, 08–0384. [Figure 2B] Figure 2B shows the crystal structures of the three phases of molybdenum carbide. β-Mo2C is a hexagonal system with ABAB stacking, α-MoC1-x is a cubic system, and η-MoC1-x is a hexagonal system with ABCABC stacking. [Figure 2C] Figure 2C shows the X-ray photoelectron spectroscopy (XPS) spectra of the three phases of molybdenum carbide. [Figure 2D] Figure 2D is a bright-field transmission electron microscope (BF-TEM) image of graphene-supported β-Mo2C nanocrystals. 0.339 nm corresponds to the interplane distance (d) of the graphene. [Figure 2E]Figure 2E shows a high-resolution transmission electron microscope (HRTEM) image of β-Mo2C and the corresponding fast Fourier transform (FFT) pattern. [Figure 2F] Figure 2F shows the high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image and energy-dispersive X-ray spectroscopy (EDS) elemental map of β-Mo2C. [Figure 2G] Figure 2G shows HRTEM images of α-MoC1-x and the corresponding FFT pattern. [Figure 2H] Figure 2H shows HRTEM images of η-MoC1-x and the corresponding FFT pattern. [Figure 3A]

[0089] Figures 3A and 3B illustrate the phase transformation process of molybdenum carbide (which was elucidated by density functional theory (DFT) calculations). Figure 3A shows the formation energies of β-Mo2C with different carbon content, as well as α-MoC1-x and η-MoC1-x. [Figure 3B] Figure 3B shows the calculated crystal structures of β-Mo2C, α-MoC1-x(x=1 / 2), α-MoC1-x(x=3 / 8), and η-MoC1-x(x=3 / 8) (shaded circles represent carbon vacancies). [Figure 4A]

[0090] Figures 4A–4F show the phase-dependent hydrogen evolution (HER) performance of molybdenum carbide. Figure 4A shows the polarization curves of the three phases of molybdenum carbide. Pt / C and pure flash graphene (FG) were used as controls. Performance was normalized to the same mass loading of molybdenum carbide. [Figure 4B] Figure 4B shows the Tafel curves for the three phases of molybdenum carbide. [Figure 4C] Figure 4C shows the alternating current (AC) impedances of the three phases of molybdenum carbide. [Figure 4D] Figure 4D shows the durability of molybdenum carbide. Polarization curves of α-MoC1-x for the 1st and 1000th cycles. The inset in Figure 4D shows the change in overpotential of the three phases of molybdenum carbide. [Figure 4E]Figure 4E shows diagrams of the free energies of HER for β-Mo2C(001), α-MoC1-x(110), and η-MoC1-x(001) at a single monolayer hydrogen adsorption coverage. [Figure 4F] Figure 4F shows the calculated partial densities of states of Mo and C in β-Mo2C(001), α-MoC1-x(110), and η-MoC1-x(001), where the dotted lines indicate the positions of the Fermi levels. [Figure 5A]

[0091] Figures 5A–5D show a generalized strategy for carbide synthesis. Figure 5A shows the carbonothermal reduction temperatures of oxides derived from Ellingham diagrams. [Figure 5B] Figure 5B shows X-ray diffraction (XRD) patterns and high-resolution transmission electron microscope (HRTEM) images of Group IVB metal carbides. The PDF reference cards are for TiC, 65–7994; ZrC, 65–8834; and HfC, 65–7326. [Figure 5C] Figure 5C shows the XRD patterns and HRTEM images of VB group metal carbides. The respective PDF reference cards are VC, 65-8825; NbC, 65-8780; and TaC, 65-0282. [Figure 5D] Figure 5D shows the XRD patterns and HRTEM images of VIB group metal carbides. The respective PDF reference cards are Cr3C2, 65–0897; Mo2C, 35–0787; and W2C, 20–1315. (The scale bar in Figures 5B–5D is 5 nm). [Figure 6A]

[0092] Figures 6A–6D show the setup for flash Joule heating (FJH). Figure 6A is an electrical schematic of the FJH system. Ten aluminum electrolytic capacitors (450V, 6mF, Mouser No. 80-PEH200YX460BQU2) with a total capacitance of 60mF were used for charging. Additional details of the electrical components can be found in the publication [Luong, 2020]. [Figure 6B] Figure 6B is a photograph of the FJH setup. [Figure 6C] Figure 6C is a photograph of the reaction steps. [Figure 6D] Figure 6D is a photograph of the reaction chamber. [Figure 7]

[0093] Figures 7-12 illustrate the ultrafast phase conversion of alumina by pulsed DC Joule heating. Figure 7 shows the scheme of pulsed DC Joule heating and the resistive hotspot effect. [Figure 8] Figure 8 shows a typical method for phase conversion from γ-Al2O3 to α-Al2O3. [Figure 9] Figure 9 shows the XRD patterns of γ-Al2O3 and the α-Al2O3 product after calcination at different PDC durations. [Figure 10] Figure 10 shows the crystal structures of the alumina phase: γ-Al2O3 (crystal system: cubic; space group: Fd-3m), δ'-Al2O3 (crystal system: orthorhombic; space group: P222), and α-Al2O3 (crystal system: trigonal; space group: R-3c). In the case of γ-Al2O3, all Al moieties are depicted as exhibiting a crystalline structure, but in the actual structure, not all moieties are occupied. [Figure 11] Figure 11 shows the phase mass ratio of alumina polymorphs as it changes with PDC duration. [Figure 12] Figure 12 shows the Raman spectra of the as-synthesized α-Al2O3 / CB mixture and α-Al2O3 NP purified by calcination in air. [Figure 13A]

[0094] Figures 13A and 13B show the PDC Joule heating system. Figure 13A is the electrical circuit diagram of the system. [Figure 13B] Figure 13B shows the generation of pulse voltages that can be used in a system to generate PDC. [Figure 13C]

[0095] Figure 13C shows the Raman spectra of the CB precursor and the product after PDC Joule heating at 60 V for 0.8 seconds. [Figure 14A]

[0096] Figures 14A to 14F show the characterization of α-Al2O3 NPs. Figure 14A is a BF-TEM image of α-Al2O3 NPs. [Figure 14B] Figure 14B is an HRTEM image of α-Al2O3 NP. [Figure 14C] Figure 14C shows the histogram and distribution of α-Al2O3 NP particle sizes determined by TEM. [Figure 14D] Figure 14D shows the pore width distribution determined by applying the DFT model. [Figure 14E] Figure 14E shows the Fourier transform infrared spectra of the γ-Al2O3 NP precursor and the α-Al2O3 NP product. [Figure 14F] Figure 14F shows the XPS fine spectra of Al and O in α-Al2O3 NP. [Figure 15A]

[0097] Figures 15A-15F show the resistive hotspot effect in the PDC process. Figure 15A is the XRD pattern of γ-Al2O3 / CB with different mass ratios after the PDC process. [Figure 15B] Figure 15B shows the phase mass ratios of the products after the PDC process, with varying volume fractions of γ-Al2O3 and f(γ-Al2O3). [Figure 15C] Figure 15C shows the conductivity and temperature as f(γ-Al2O3) is varied. [Figure 15D] Figures 15D–15F show the current density maps of samples in PDC at different γ-Al2O3 volume fractions of f=0.41, f=0.73, and f=0.78, respectively. [Figure 15E] Figures 15D–15F show the current density maps of samples in PDC at different γ-Al2O3 volume fractions of f=0.41, f=0.73, and f=0.78, respectively. [Figure 15F] Figures 15D–15F show the current density maps of samples in PDC at different γ-Al2O3 volume fractions of f=0.41, f=0.73, and f=0.78, respectively. [Figure 16]

[0098] Figure 16 shows the current density in the bulk region and the hotspot region. [Figure 17A]

[0099] Figures 17A to 17D show the topotactic phase transformation process elucidated by DFT calculations. Figure 17A shows the bulk cohesive energy (μ, eV / Al2O3) and surface formation energy (ε, eV / Å2) of the three Al2O3 phases. [Figure 17B] Figure 17B shows the free energies of the three phases of Al2O3 nanocrystals plotted against their specific surface area. [Figure 17C] Figures 17C-17D are contour plots of partial charge density in the highest band (0.3 eV below the Fermi level) of the surface states of γ-Al2O3(100), δ'-Al2O3(100), and α-Al2O3(001) from a top view (Figure 17C) and a side view (Figure 17D). [Figure 17D] Figures 17C-17D are contour plots of partial charge density in the highest band (0.3 eV below the Fermi level) of the surface states of γ-Al2O3(100), δ'-Al2O3(100), and α-Al2O3(001) from a top view (Figure 17C) and a side view (Figure 17D). [Figure 18A]

[0100] Figures 18A–18C show the ultrafast AC sintering (ACS) system and sample holder. Figure 18A is the electrical circuit diagram of the ACS system. [Figure 18B] Figures 18B to 18C are top and side view photographs of the carbon paper holder for sintering, respectively. [Figure 18C] Figures 18B to 18C are top and side view photographs of the carbon paper holder for sintering, respectively. [Figure 19A]

[0101] Figures 19A–19H show ultrafast ACS of alumina ceramics. Figure 19A shows photographs of carbon paper during heating, sintering, and cooling. [Figure 19B] Figure 19B shows real-time temperature measurements during the ACS process. [Figure 19C]Figure 19C shows an image of sintered ceramic pellets supported on carbon paper. [Figure 19D] Figure 19D shows the XRD patterns of alumina ceramics using α-Al2O3 NP or commercially available α-Al2O3 nanopowder as a precursor. [Figure 19E] Figure 19E is an SEM image of a ceramic obtained by using α-Al2O3 NP as a precursor. [Figure 19F]

[0102] Figure 19F shows the grain size distribution of alumina ceramics. [Figure 19G] Figure 19G shows the statistics of the Young's modulus of alumina ceramics using the α-Al2O3 NP precursor. [Figure 19H] Figure 19H shows the Young's modulus statistics for alumina ceramics using a commercially available α-Al2O3 precursor. [Figure 20A]

[0103] Figures 20A-20B and 21A-21B illustrate the scalability of the PDC process. Figure 20A is a photograph of a sample with a mass of 700 mg synthesized using a tube (D=15 mm) and a PDC voltage of 60 V. [Figure 20B] Figure 20B shows the XRD pattern of the product shown in Figure 20A. [Figure 21A] Figure 21A is a photograph of a sample with a mass of 1.4 g, synthesized using a tube (D=15 mm) and a PDC voltage of 120 V. [Figure 21B] Figure 21B shows the XRD pattern of the product shown in Figure 21A. [Figure 22]

[0104] Figures 22-28 illustrate the recovery of precious metals by flash Joule heating (FJH). Figure 22 is a schematic diagram of the FJH and evaporation separation system. [Figure 23] Figure 23 is a photograph of a printed circuit board (PCB) (scale bar, 5cm), and the inset shows a mixture of carbon black (CB) and PCB powder (scale bar, 2cm). [Figure 24]Figure 24 shows the concentrations of noble metals in PCBs as determined by inductively coupled plasma mass spectrometry (ICP-MS). [Figure 25] Figure 25 shows the current versus time recorded under different FJH voltages. [Figure 26] Figure 26 shows real-time temperature measurements at different FJH voltages by fitting the blackbody radiation emitted from the sample. [Figure 27] Figure 27 shows the relationship between vapor pressure and temperature for precious metals and carbon. [Figure 28] Figure 28 shows the recovery yield of precious metals by condensing the evaporated gaseous components. [Figure 29A]

[0105] Figures 29A to 29E are photographs of systems for collecting evaporated metal vapors. Figure 29A is a photograph of the evaporation collection system. [Figure 29B] Figures 29B and 29C are photographs of the vacuum gauge before and after flash Joule heating (FJH), respectively. [Figure 29C] Figures 29B and 29C are photographs of the vacuum gauge before and after flash Joule heating (FJH), respectively. [Figure 29D] Figures 29D to 29E are photographs of the condensation vessel before and after the FJH reaction, respectively. [Figure 29E] Figures 29D to 29E are photographs of the condensation vessel before and after the FJH reaction, respectively. [Figure 30]

[0106] Figure 30 is an electrical circuit diagram of the flash Joule heating (FJH) system used in the system shown in Figure 29. [Figure 31A]

[0107] Figures 31A–31G show the improved recovery yield assisted by halides. Figures 31A–31F show the recovery yield of precious metals by using (Figure 31A) NaF, (Figure 31B) PTFE, (Figure 31C) NaCl, (Figure 31D) CPVC, (Figure 31E) NaI, and (Figure 31F) a mixture of NaF, NaCl, and NaI as additives, respectively. Y0 and Y represent the recovery yield of precious metals with and without additives, respectively. The dotted line indicates Y / Y0=1, and if Y / Y0≦1, it means there is no benefit from the additive. [Figure 31B] Figures 31A–31G show the improved recovery yield assisted by halides. Figures 31A–31F show the recovery yield of precious metals by using (Figure 31A) NaF, (Figure 31B) PTFE, (Figure 31C) NaCl, (Figure 31D) CPVC, (Figure 31E) NaI, and (Figure 31F) a mixture of NaF, NaCl, and NaI as additives, respectively. Y0 and Y represent the recovery yield of precious metals with and without additives, respectively. The dotted line indicates Y / Y0=1, and if Y / Y0≦1, it means there is no benefit from the additive. [Figure 31C] Figures 31A–31G show the improved recovery yield assisted by halides. Figures 31A–31F show the recovery yield of precious metals by using (Figure 31A) NaF, (Figure 31B) PTFE, (Figure 31C) NaCl, (Figure 31D) CPVC, (Figure 31E) NaI, and (Figure 31F) a mixture of NaF, NaCl, and NaI as additives, respectively. Y0 and Y represent the recovery yield of precious metals with and without additives, respectively. The dotted line indicates Y / Y0=1, and if Y / Y0≦1, it means there is no benefit from the additive. [Figure 31D]Figures 31A–31G show the improved recovery yield assisted by halides. Figures 31A–31F show the recovery yield of precious metals by using (Figure 31A) NaF, (Figure 31B) PTFE, (Figure 31C) NaCl, (Figure 31D) CPVC, (Figure 31E) NaI, and (Figure 31F) a mixture of NaF, NaCl, and NaI as additives, respectively. Y0 and Y represent the recovery yield of precious metals with and without additives, respectively. The dotted line indicates Y / Y0=1, and if Y / Y0≦1, it means there is no benefit from the additive. [Figure 31E] Figures 31A–31G show the improved recovery yield assisted by halides. Figures 31A–31F show the recovery yield of precious metals by using (Figure 31A) NaF, (Figure 31B) PTFE, (Figure 31C) NaCl, (Figure 31D) CPVC, (Figure 31E) NaI, and (Figure 31F) a mixture of NaF, NaCl, and NaI as additives, respectively. Y0 and Y represent the recovery yield of precious metals with and without additives, respectively. The dotted line indicates Y / Y0=1, and if Y / Y0≦1, it means there is no benefit from the additive. [Figure 31F] Figures 31A–31G show the improved recovery yield assisted by halides. Figures 31A–31F show the recovery yield of precious metals by using (Figure 31A) NaF, (Figure 31B) PTFE, (Figure 31C) NaCl, (Figure 31D) CPVC, (Figure 31E) NaI, and (Figure 31F) a mixture of NaF, NaCl, and NaI as additives, respectively. Y0 and Y represent the recovery yield of precious metals with and without additives, respectively. The dotted line indicates Y / Y0=1, and if Y / Y0≦1, it means there is no benefit from the additive. [Figure 31G] Figure 31G shows scanning transmission electron microscope (STEM) images of the collected solid in a rectangular region, as well as energy-dispersive X-ray spectroscopy (EDS) maps of Rh, Pd, Ag, and Au. (Scale bar in STEM image: 0.5 μm; scale bar in EDS map: 100 nm). [Figure 32A]

[0108] Figures 32A to 32F show the recovery of precious metals by flash Joule heating (FJH) and sintering. Figure 32A shows different processes for recovering precious metals from printed circuit boards (PCBs). [Figure 32B] Figure 32B shows the thermogravimetric analysis (TGA) curve of the PCB after FJH (PCB-flash) in air. The inset figures are photographs of the PCB after PCB-flash, FJH, and firing (PCB-flash-firing). [Figure 32C] Figure 32C shows the TGA curve of the PCB. [Figure 32D] Figure 32D shows X-ray photoelectron spectroscopy (XPS) of PCB, PCB-flash, and PCB-flash-sintering. [Figure 32E] Figure 32E shows the concentration of noble metals in PCBs after calcination (PCB-calcination). [Figure 32F] Figure 32F shows the improvement in leaching yield due to calcination. Y0 and Y represent the PCB leaching and PCB-calcination recovery yields, respectively. [Figure 33A]

[0109] Figures 33A to 33F show the improved leaching efficiency of precious metals by the flash Joule heating (FJH) process. Figure 33A shows a schematic diagram of the pressurized setup for FJH. [Figure 33B] Figure 33B shows gas flow simulations under different pressures. The internal pressure (P0) in the FJH was calculated to be approximately 5 atm. Pout at 0 atm, 1 atm, and 4 atm corresponds to the FJH under vacuum, atmospheric pressure, and positive pressure of 3 atm. [Figure 33C] Figure 33C shows the improvement in precious metal concentration and recovery yield using FJH. [Figure 33D] Figure 33D shows the improvement in precious metal concentration and recovery yield due to FJH and calcination. [Figure 33E] Figure 33E shows the improvement in recovery yield when the FJH voltage is varied under atmospheric pressure. [Figure 33F]Figure 33F shows the improvement in recovery yield with varying pressure. For Figures 33E to 33F, the recovery yields of Rh, Pd, and Ag are calculated from PCB-flash, and the recovery yield of Au is calculated from PCB-flash-calcination. [Figure 34A]

[0110] Figures 34A-34E illustrate the mechanism of improved leaching efficiency by flash Joule heating (FJH). Figure 34A shows a scheme of stacked arrangements of various types of electronic devices. [Figure 34B] Figure 34B is a scanning electron microscope (SEM) image of printed circuit board (PCB) powder. [Figure 34C] Figure 34C is an SEM image of the PCB flash. [Figure 34D] Figure 34D is an SEM image of the PCB-flash-firing process. [Figure 34E] Figure 34E shows a scheme of morphological and structural changes of the PCB during the FJH and firing processes. [Figure 35A]

[0111] Figures 35A to 35F illustrate the removal of heavy metals from electronic waste using the flash Joule heating (FJH) process. Figure 35A shows the relationship between the vapor pressure and temperature of toxic heavy metals and carbon. [Figure 35B] Figure 35B shows the concentrations of toxic heavy metals in printed circuit boards (PCBs). [Figure 35C] Figure 35C shows the concentrations of toxic heavy metals in PCBs after FJH. [Figure 35D] Figure 35D shows the removal efficiency and collection yield of heavy metals. [Figure 35E] Figure 35E shows the concentration of Hg in the residue after multiple FJH reactions. [Figure 35F] Figure 35F shows the concentration of Cd in the residue after multiple FJH reactions. The dotted lines in Figures 35E–35F represent the initial content and the approved World Health Organization (WHO) levels for safety limits in agricultural soils. [Figure 36]

[0112] Figure 36 is a chart showing the theoretical separation coefficients for the evaporation separation process. [Figure 37A]

[0113] Figures 37A to 37F show the carbonothermal reaction for recovering metal from metal oxides. Figure 37A is the XRD pattern of Al recovered from Al2O3. [Figure 37B] Figure 37B shows the XRD pattern of Fe recovered from Fe2O3. [Figure 37C] Figure 37C shows the XRD of Cu recovered from CuSO4. [Figure 37D] Figure 37D shows the XRD of Ni recovered from NiSO4. [Figure 37E] Figure 37E shows the XRD of Mn recovered from MnO2. [Figure 37F] Figure 37F shows the XRD of Pb recovered from PbNO3. This is similar to what occurs in bauxite residue (red mud). [Figure 38]

[0114] Figure 38 is a schematic diagram of a flash Joule heating pressure and gas collection system that can be used in embodiments of the present invention. [Figure 39A]

[0115] Figures 39A-39D illustrate the scale-up of the flash Joule heating (FJH) process. Figure 39A is a photograph of the treated samples. Samples were treated under the following conditions: m0=0.2g, V0=150V, and C0=0.06F (left), m1=2g, V1=150V, and C1=0.6F (center), and m2=4g, V2=300V, and C2=0.6F (right). [Figure 39B] Figures 39B to 39D show the real-time temperature curves of the sample. [Figure 39C] Figures 39B to 39D show the real-time temperature curves of the sample. [Figure 39D] Figures 39B to 39D show the real-time temperature curves of the sample. [Figure 40A]

[0116] Figures 40A-40B show a scheme for a continuous flash Joule heating (FJH) reactor. [Figure 40B]

[0116] Figures 40A to 40B show a scheme for a continuous flash Joule heating (FJH) reactor. [Figure 41A]

[0117] Figures 41A to 41C show the FJH system used for fly ash. Figure 41A shows the electrical circuit diagram of the FJH system. [Figure 41B] Figures 41B and 41C are photographs of the FJH jig used to connect the sample to the FJH system for the synthesis of 200 mg and 2 g, respectively. [Figure 41C] Figures 41B and 41C are photographs of the FJH jig used to connect the sample to the FJH system for the synthesis of 200 mg and 2 g, respectively. [Figure 42]

[0118] Figure 42 shows photographs of CFA-C and CFA-F. The scale bar is 4 cm. [Figure 43A]

[0119] Figures 43A–43G show the acid-extractable REE content in CFA. Figure 43A shows the XRD patterns of CFA-F and CFA-C. [Figure 43B] Figure 43B shows the full XPS spectra of CFA-F and CFA-C. [Figure 43C] Figure 43C shows the total REE concentrations in CFA-F and CFA-C obtained by HNO3 leaching (15M, 85°C), HCl leaching (1M, 85°C), and total quantification. [Figure 43D] Figure 43D is an SEM image of CFA-F (scale bar, 2 μm). [Figure 43E] Figure 43E shows the HCl-extractable REE content (1M, 85°C) and total REE quantification in CFA-F, as well as the REE recovery yield. [Figure 43F] Figure 43F is an SEM image of CFA-C (scale bar, 5 μm). [Figure 43G] Figure 43G shows the HCl-extractable REE content (1M, 85°C) and total REE quantification in CFA-C, as well as the REE recovery yield. (All error bars represent the standard deviation for N=3). [Figure 44A]

[0120] Figures 44A–44H show the improved REE recovery yield from CFA by electrothermal activation. Figure 44A is the FJH scheme for CFA. [Figure 44B] Figure 44B shows the current curve under the conditions of 120V and 1 second. [Figure 44C] Figure 44C shows real-time temperature measurement. [Figure 44D] Figure 44D shows the relationship between HCl-elutable REE content (1M, 85°C) from CFA-F, increase in recovery yield, and FJH voltage. [Figure 44E] Figure 44E shows pH-dependent REE leaching from CFA-F raw materials and activated CFA-F. [Figure 44F] Figure 44F shows the pH-dependent leaching of REE from CFA-C raw materials and activated CFA-C. [Figure 44G] Figure 44G shows the HCl-elutable REE content (1M, 85°C) and the increased recovery yield from activated CFA-F. [Figure 44H] Figure 44H shows the HCl-elutable REE content (1M, 85°C) and the increase in recovery yield from activated CFA-C. (Y0 represents the REE recovery yield from HCl-leached CFA raw materials, and Y represents the REE recovery yield from HCl-leached activated CFA. All error bars represent the standard deviation for N=3). [Figure 45]

[0121] Figure 45 is a flowchart showing the recovery of REE from secondary waste by electrothermal activation. [Figure 46A]

[0122] Figures 46A-46G illustrate the mechanism of improved REE extraction rate due to electrothermal activation. Figure 46A shows the XRD patterns of YPO4 (bottom) and reference PDF (YPO4, #11-0254), and YPO4 (top) and reference PDF (Y2O3, #43-0661) after FJH. [Figure 46B]Figure 46B shows the XRD patterns of LaPO4 (bottom) and reference PDF (LaPO4, #35-0731), and LaPO4 (top) after FJH and reference PDF (La2O3, #05-0602). [Figure 46C] Figure 46C shows the calculated dissolution curves for Y2O3, YPO4, La2O3, and LaPO4 using 1g mass in 100mL solution. Cl- is used to balance the charge. [Figure 46D] Figure 46D is an Ellingham diagram of carbon monoxide and REE oxide. The vertical dashed line represents the temperature required to reduce Sc2O3. [Figure 46E] Figure 46E shows the XPS fine spectrum of Y2O3 after FJH. [Figure 46F] Figure 46F shows the XPS fine spectrum of La2O3 after FJH. [Figure 46G] Figure 46G shows the Gibbs free energy changes for the dissolution reactions of REE oxides and REE metals. [Figure 47A]

[0123] Figures 47A-47C show the recovery of REE from BR. Figure 47A is a photograph of BR (scale bar is 5cm). [Figure 47B] Figure 47B shows the XRD pattern of BR. [Figure 47C] Figure 47C shows the acid-leached REE content (0.5M HNO3) from BR raw materials and 120V FJH-activated BR, as well as the increase in recovery yield. (Y0 represents the REE recovery yield by acid leaching of the raw materials, and Y represents the REE recovery yield by acid leaching of the activated materials. All error bars represent the standard deviation for N=3). [Figure 48A]

[0124] Figures 48A-48B show the FJH voltage-dependent REE recovery yield from BR. Figure 48A shows the acid-leaching content of total REE (0.5 M HNO3) from BR and the increase in REE yield with varying FJH voltage. [Figure 48B]Figure 48B shows the increase in REE content (0.5M HNO3) for acid leaching and the recovery yield at 120V FJH. (Y0 represents the REE recovery yield by directly leaching BR raw material. Y represents the REE recovery yield by leaching activated BR. Error bars represent the standard deviation for N=3). [Figure 49A]

[0125] Figures 49A-49C show the recovery of REE from electronic waste. Figure 49A is a photograph of electronic waste glided into powder, with a scale bar of 5 cm. [Figure 49B] Figure 49B shows the XRD pattern of electronic waste. [Figure 49C] Figure 49C shows the acid-leached REE content (1M HCl) from the raw material of electronic waste and the activated electronic waste at 50V FJH, as well as the increase in recovery yield. (Y0 represents the REE recovery yield by acid leaching the raw material, and Y represents the REE recovery yield by acid leaching the activated material. All error bars represent the standard deviation for N=3). [Figure 50A]

[0126] Figures 50A and 50B show the improvement in REE recovery yield from electronic waste due to FJH activation. Figure 50A shows the increase in REE recovery yield as the acid-leached content of total REE (1M HCl) from electronic waste and the FJH voltage are varied. [Figure 50B] Figure 50B shows the acid-leached content of total REE (1M HCl) at FJH at 50V, and the increase in REE recovery yield. (Y0 represents the REE recovery yield by directly leaching the electronic waste raw material. Y represents the REE recovery yield by leaching the activated electronic waste. Error bars indicate the standard deviation for N=3). [Modes for carrying out the invention]

[0058]

[0127] The present invention relates to an ultrafast flash Joule heating synthesis method, and more particularly, embodiments of the present invention include an ultrafast synthesis method for forming carbides, an ultrafast synthesis method for forming corundum nanoparticles, an ultrafast synthesis method for recovering precious metals from electronic waste (electronic junk), and an ultrafast synthesis method for recovering metals from ore, fly ash, and bauxite residue (red mud).

[0059] Ultrafast synthesis of carbides Synthesis process

[0128] The present invention includes flash Joule heating for an ultrafast process for synthesizing metal carbide nanoparticles [Luong 2020; Stanford 2020; see Tour PCT application '000]. Metal carbides were synthesized within seconds, which is hundreds of hours faster than previous methods [Gong 2016; Wan 2014; Ma 2015]. Therefore, in some embodiments, the present invention provides phase-controlled synthesis of transition metal carbide nanocrystals by ultrafast flash Joule heating.

[0060]

[0129] Such a solvent-free process based on flash Joule heating can provide ultrafast synthesis of coke-free carbide nanocrystals in less than one second. A millisecond current pulse can pass through the precursor, thereby raising the sample to an ultra-high temperature (>3000K), which is then rapidly cooled to room temperature (>10K). 4 (K / sec). It is possible to synthesize carbides of 13 elements, including interstitial TMCs of TiC, ZrC, HfC, VC, NbC, TaC, Cr2C3, MoC, and W2C, as well as covalent carbides of B4C and SiC, offering excellent versatility. Furthermore, by controlling the FJH pulse voltage, phase-pure molybdenum carbides including β-Mo2C, and metastable α-MoC 1-x and η-MoC 1-xThe ability to selectively synthesize these compounds demonstrates the ability to manipulate phases in synergistic electrothermal processes. Phase-dependent HER performance of molybdenum carbide was also discovered; β-Mo2C exhibited the best HER performance (-220mV overpotential, 68mV / dec Tafel slope, and excellent durability).

[0061]

[0130] Figure 1A is a schematic diagram of FJH synthesis of carbides using various precursors. Route (i) 101 demonstrates the ultra-high temperature FJH process described herein in which carbon black and metal oxides form metal carbides and graphene. Graphene can then be removed by a post-synthesis purification process (not shown). This can be referred to as a reverse gas-solid reaction boundary. Route (ii) 102 demonstrates a conventional carburizing process called a solid-gas reaction interface.

[0062]

[0131] Methods for the ultrafast synthesis of carbides may include the following:

[0132] A reaction precursor (or precursor) is selected and mixed with a conductive carbon additive, such as carbon black. Alternatively, the conductive additive may be another carbon source in addition to or in place of carbon black, because these temperatures are expected to convert almost all of any carbon source to carbon at these temperatures. Carbon black can be replaced with graphene, flash graphene, coal, anthracite, coke, metallurgical coke, calcined coke, activated carbon, biochar, carbon from natural gas stripped of hydrogen atoms, activated carbon, shungite, plastic waste, carbon char derived from plastic waste, food waste, carbon char derived from food waste, biomass, carbon char derived from biomass, hydrocarbon gases, and mixtures thereof. The use of carbon black described herein is representative of the conductive additives available in the present invention. In certain embodiments of the present invention, the ratio of precursor to conductive additive is in the range of 1:2 to 15:1 based on weight, and in further specific embodiments, the ratio of precursor to conductive additive is in the range of 1:2 to 2:1 based on weight.

[0063]

[0133] As shown in FIG. 1A, versatile precursors such as metals as elements and metal components such as metal oxides, metal chlorides, and metal hydroxides can all be used as precursors. Carbon black (or other conductive additives) and metal precursors were well mixed by manual grinding or using a ball mill.

[0064]

[0134] The mixture of carbon black (or other conductive additives) and metal precursors is flash-joule heated. As shown in FIG. 1A, the mixture can be filled into a quartz tube and compressed to have a resistance of 0.5 to 20 ohms. As electrodes, two copper or graphite rods were placed on both sides. A high voltage in the range of 30 V to 150 V was charged by a capacitor bank (this may also be done using AC, which may be advantageous in some cases). However, as the reaction scale becomes larger, as the scale increases, the voltage (and current) must be increased to induce the same reaction temperature, so the voltage is even higher and is expected to reach several thousand volts (it may exceed 10,000 amp). For example, if the reaction scale is for materials in kilograms or hundreds of kilograms, the voltage may be 10,000 volts or may be as high as 100,000 volts (the current may be 10,000 amp or may be as high as 30,000 amp).

[0065]

[0135] In one embodiment, a mixture of metal precursors and commercial carbon black was slightly compressed inside a quartz tube between two graphite electrodes (FIG. 1A). Widely applicable metal precursors are elemental metals (M), metal oxides (MO x ), chlorides (MCl x ), and hydroxides (M(OH) x) or other materials may also be used. Carbon black functions simultaneously as a carbon source for carbonthermal reduction and as a carbon source for conductive additives. Two electrodes were connected to a capacitor bank, which was first charged by a power supply, and then the precursor was heated to a high temperature by high-voltage discharge. In a typical FJH process using a voltage of 100V and a sample resistor of 1Ω, the current flowing through the sample was recorded as approximately 100A with a discharge time of approximately 50ms (Figure 1B).

[0066]

[0136] Rapid light emission was observed during the FJH process (see photographs 110–112 in Figure 1C). The temperature was measured by fitting the sample's blackbody emission spectrum (Figure 1C). The maximum temperatures obtained for 80V and 100V FJH were estimated to be approximately 2700K and 3000K, respectively (shown as curves 121–122 in Figure 1D).

[0067]

[0137] The cooling rate is extremely fast, approximately 10 4 The temperature is measured in K / s. The sample temperature distribution is simulated using the finite element method (FEM), which further provides insight into the effect of FJH parameters on the achievable temperature. It was found that higher temperature values ​​can be obtained by applying a larger FJH voltage and a suitable sample electrical conductivity. In contrast, a higher thermal conductivity of the sample results in lower temperatures due to faster heat dissipation. The temperature map shows that the temperature distribution is uniform throughout the sample, i.e., it exhibits a uniform heating characteristic of the FJH process.

[0068]

[0138] Exposure of samples to such high temperatures (approximately 3000K) in FJH volatilized most of the non-carbon components. According to the relationship between temperature and vapor pressure (Figure 1E), all typical metal precursors, including elemental metals, metal oxides, and chlorides, have a higher vapor pressure than carbon, which sublimes at approximately 3900K [Abrahamson 1974]. As a result, the metal precursors are volatile components, while the carbon source remains solid during the reaction. In this case, the vapor of the metal precursor reacts with carbon to form a metal carbide, which is referred to herein as the reverse gas-solid reaction interface (Figure 1A, route (i) 101). In contrast, in conventional carburizing processes [Rosa 1983], gaseous hydrocarbons, such as methane (CH4), are introduced into the solid metal precursor. Carbon diffusion across solid-gas interfaces is typically rapid, leading to a coked carbide surface due to an oversupply of carbon sources (Figure 1A, pathway (ii)102), which can passivate the catalytic activity of the final product [Gong 2016].

[0069] Phase-controlled synthesis of molybdenum carbide nanocrystals

[0139] Molybdenum carbide [Yao 2017; Wan 2014; Li 2016; Ma 2015], an attractive catalyst, was synthesized using embodiments of the present invention. The phases of molybdenum carbide are complex due to their temperature, composition, and vacancy-dependent stability [Hugosson 1999]. Different phases have distinct geometric and electronic structures [Politi 2103; Baek 2019], with catalytically relevant phases being hexagonal β-Mo2C [Wan 2014; Ma 2015; Fan 2017] and cubic α-MoC 1-x [Yao 2017; Baek 2019; Song 2019], and hexagonal η-MoC 1-x 34 This is [Song 2019].

[0070]

[0140] MoCl3 was selected as a precursor due to its high vapor pressure (Figure 1E). It was found that three pure phases of molybdenum carbide could be selectively synthesized by adjusting the FJH voltage (Figures 2A-2B). The β-Mo2C phase was produced under a voltage of 30V, according to X-ray diffraction (XRD) (Figure 2A, bottom); when the voltage was increased to 60V, pure α-MoC was produced. 1-x A phase was obtained (Figure 2A, center); when the voltage was further increased to 120V, η-MoC 1-x The result was obtained (Figure 2A, top). Note that the diffraction peak at approximately 26° (indicated by the asterisk) was due to the graphene support.

[0071]

[0141] From hexagonal β-Mo2C to cubic α-MoC 1-x Next, the hexagonal η-MoC 1-x The phase transition to is a newly discovered topotactic transition pathway, which, unlike previous reports [Wan 2019], involves annealing at 850°C for approximately 24 hours before α-MoC 1-x When converted to β-Mo2C, by using NiI2 additives at higher temperatures, η-MoC 1-x Only the first one was stabilized.

[0072]

[0142] To investigate the electronic structure, X-ray photoelectron spectroscopy (XPS) spectra were collected at the Mo 3d core level (Figure 2C). The Mo 3d spectra were collected as 3d 3 / 2 and 3D 5 / 2 The peaks were split. Peak fitting was performed using Mo in molybdenum carbide. 0 Mo 2+ Mo 4+ , and Mo 6+ This shows the four chemical states of Mo, including the dominant Mo. 0 Peak and smaller Mo 2+ The peak is attributed to molybdenum carbide, which is due to the coexistence of Mo-Mo and Mo-C bonds in molybdenum carbide [Wan 2014]. 4+ and Mo 6+These were assigned to MoO2 and MoO3, respectively, due to surface oxidation of molybdenum carbide upon exposure to air [Wan 2014; Ma 2015]. Quantitative analysis of the ratio of Mo chemical states was performed using η-MoC 1-x High oxidation state in (Mo 4+ and Mo 6+ ) but β-Mo2C and α-MoC 1-x Since it showed a larger value than that in α-MoC, β-Mo2C is the phase with the highest oxidation resistance, and α-MoC 1-x This indicates that it will be followed by [something else].

[0073]

[0143] Morphological characterization using scanning electron microscopy (SEM) revealed the fine powder characteristics of all three carbide phases. Energy-dispersive spectroscopy (EDS) mapping images showed a uniform distribution of Mo and C.

[0074]

[0144] The size and crystallinity of molybdenum carbide were characterized using transmission electron microscopy (TEM) and XRD. The particle size of the molybdenum carbide phase was determined by FJH voltage. β-Mo2C synthesized at the lowest voltage had the largest average size of approximately 26.4 nm, followed by α-MoC 1-x (approximately 21.2 nm) and η-MoC 1-x (The size is approximately 20.1 nm). Smaller particle sizes obtained under higher voltages may be due to faster nucleation rates at higher temperatures [Jang 1995].

[0075]

[0145] The particle size values ​​measured by TEM agree well with the crystal size determined by XRD using the Halder-Wagner method (see Table I), which indicates the single-crystal characteristics of the synthesized carbide particles.

[0076] [Table 1]

[0077]

[0146] Typical bright-field TEM (BF-TEM) images of β-Mo2C nanocrystals show regular hexagonal nanoplates (depicted by hexagons 201) with a transverse size of approximately 20 nm supported on carbon (Figure 2D). High-resolution TEM (HRTEM) images show fringes of the crystal lattice (Figure 2E, top), in which case the interplanar spacing (d) of 0.26 nm corresponds to the (300) plane of β-Mo2C. According to atomic-resolved images and the corresponding fast Fourier transform (FFT) patterns (Figure 2E, bottom), the orientation of the nanoplates is assigned to β-Mo2C (001). High-angle annular dark-field (HAADF) scanning transmission electron microscope (STEM) images and EDS elemental maps under STEM conditions reveal a uniform spatial distribution of Mo, C, and O (Figure 2F). It should be noted that the O is due to surface contamination and is consistent with the XPS results (Figure 2C). Also, α-MoC 1-x (Figure 2G) and η-MoC 1-x The HRTEM image and corresponding FFT pattern in (Figure 2H) also show α-MoC in the identified sample. 1-x (110) and η-MoC 1-x The carbide nanocrystals were obtained with orientation (116). Nevertheless, XRD results showed no favorable orientation for these carbide nanocrystals (Figure 2A).

[0078] Phase transformation process of molybdenum carbide

[0147] To explain voltage-dependent phase formation, the current flowing through the sample and the temperature under different FJH voltages were first recorded. Higher voltages result in higher temperatures and energy input. The maximum temperatures at FJH voltages of 30V, 60V, and 120V were measured at 839K, 1468K, and 3242K, respectively.

[0079]

[0148] β-Mo2C and α-MoC with altered carbon content 1-x , and η-MoC 1-xThe formation energy was calculated using first-principles density functional theory (DFT) (Figure 3A, curves 301-303, respectively). It was found that the β-Mo2C phase is the most stable phase with the lowest formation energy, and therefore, β-Mo2C is formed at relatively low voltages and temperatures (point 301).

[0080]

[0149] In contrast, α-MoC 1-x and η-MoC 1-x α-MoC is a metastable phase [Hugosson 1999], and according to the Mo-C phase equilibrium diagram, it is formed and stabilized at higher temperatures. 1-x The (x=1 / 2) structure has a slightly higher formation energy and the same stoichiometric composition as β-Mo2C (Figure 3B). Therefore, when the carbon content is slightly increased, β-Mo2C is converted to α-MoC 1-x A topotactic transition to is predicted (see line 304, which represents the predicted phase transition pathway). As more carbon is incorporated into the Mo-C system, α-MoC 1-x The formation energy increases continuously (curve 302), and the energy curve is η-MoC 1-x It intersects with the energy curve of (curve 303).

[0081]

[0150] η-MoC 1-x The phase becomes relatively stable near x=3 / 8 (Figure 3B), and remains stable up to higher carbon content. This result indicates that carbon vacancies dominate the energy landscape of the Mo-C system, transitioning from β-Mo2C to α-MoC 1-x Next to, η-MoC 1-x We demonstrated that it functions as a driving factor for topotactic transition pathways to the phase.

[0082]

[0151] The FJH process, with its widely adjustable energy input, allows for the acquisition of metastable phases at higher formation energies than thermodynamically stable phases, and subsequently, the ultrafast cooling rate of the FJH process (>10 4 (K / sec) is α-MoC 1-x and η-MoC 1-xIt helps to kinetically maintain the metastable phase containing the phase down to room temperature. For comparison, at the same temperature, metastable α-MoC 1-x When the phase was produced by FJH, synthesis using a conventional tubular furnace at its slow cooling rate of approximately 10 K / min produced only the thermodynamically stable β-Mo2C phase. This explicitly demonstrates the role of the ultrafast cooling rate of the FJH process in kinetically obtaining the metastable phase.

[0083] Phase-dependent HER performance of molybdenum carbide

[0152] A side-by-side electrochemical comparison of the three molybdenum carbide phases elucidates their individual unique characteristics and the effect of phase control on catalytic behavior. To demonstrate their catalytic properties, the HER performance of the three molybdenum carbide phases in 0.5 M H2SO4 was measured using a standard three-electrode configuration. Figure 4A shows linear scanning voltammogram (LSV) curves relative to Pt / C, in addition to the different electrocatalysts (curves 401-405 represent Pt / C, β-Mo2C, and α-MoC). 1-x η-MoC 1-x (and for flash graphene (FG)). When flash graphene (FG) obtained from carbon black FJH was used as a control, negligible HER activity was shown. [Luong 2020].

[0084]

[0153] Phase-dependent HER activity of molybdenum carbide was observed. β-Mo2C, α-MoC 1-x , and η-MoC 1-x Regarding 10mA / cm 2 The overpotentials (η) against the reversible hydrogen electrode (RHE) at geometric current densities were -220 mV, -310 mV, and -510 mV, respectively (Figure 4A). β-Mo2C, α-MoC 1-x , and η-MoC 1-x The calculated Tafel slopes (b) were 68 mV / dec, 84 mV / dec, and 113 mV / dec, respectively (curves 411-413 in Figure 4B), thus demonstrating the phase-dependent HER reaction kinetics.

[0085]

[0154] The high electrode velocity of the β-Mo2C phase is reflected in a small charge transfer resistance of approximately 60Ω at a potential of -0.5V versus RHE, as measured by electrochemical impedance. (See Figure 4C; curves 421-423 represent β-Mo2C and α-MoC, respectively.) 1-x , and η-MoC 1-x (This indicates the alternating current (AC) impedance.)

[0086]

[0155] The durability of the three molybdenum carbide phases was evaluated by sweeping the electrode catalyst every 1000 cycles using cyclic voltammetry. Figure 4D shows the LSV curves for the first and 1000th cycles for each of the three molybdenum carbide phases (curves 431-432, respectively). No significant current degradation was observed in any of the three phases, at 10 mA / cm². 2 The overvoltage hardly decreased (Graph 433), demonstrating excellent long-term stability.

[0087]

[0156] We performed DFT calculations to elucidate the phase-dependent HER performance. The Gibbs free energy (ΔG) of hydrogen adsorption was used. H ) is a descriptor in the selection of HER electrode catalysts [Mavrikakis 2006], and the optimal catalyst is one with a ΔG close to 0 eV according to Sabatier's principle. H [Greenley 2006] has β-Mo2C(001), α-MoC 1-x (110), and η-MoC 1-x (001) ΔG H The calculated values ​​were 0.48 eV, 0.71 eV, and 1.09 eV, respectively (Figure 4E). These results are for β-Mo2C and α-MoC 1-x However, η-MoC 1-x This demonstrates a lower hydrogen adsorption energy, consistent with previous reports. [Fan 2017; Matanovic 2018] ΔG H In addition, the electronic structure provides useful insights into the metallic characteristics of the carbide phase. [Politi 2013]

[0088]

[0157] Figure 4F illustrates the partial densities of the Mo and C states (DOS) in molybdenum carbide. The DOS of β-Mo2C near the Fermi level is α-MoC 1-x and η-MoC 1-x The DOS is substantially larger than that of the other two phases. The higher Mo content in β-Mo2C results in a higher support density and enhanced metallicity, which is beneficial for charge transfer during electrochemical reactions (Figure 4C). The larger surface area of ​​β-Mo2C compared to the other two phases, as measured by the Brunauer-Emmett-Teller (BET) method, also contributes to the higher current density. The best observed HER performance of β-Mo2C was the combined effect of relatively low hydrogen adsorption energy, enhanced metallic characteristics, and high surface area. In addition, the flash graphene support provided conductive pathways and prevented aggregation of carbide nanocrystals, thus contributing to the improvement of HER performance [Li 2019].

[0089] Generalized strategies for carbide nanocrystal synthesis

[0158] Due to the extremely high usable temperature of the FJH process, a variety of TMCs can be easily 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 (Figures 5A-5D). The uniform temperature distribution allows for phase-pure synthesis across the entire sample. (The peak at approximately 26°C in all samples (marked with asterisks) is attributed to the graphene support).

[0090]

[0159] The reduction temperatures of metal oxides were calculated according to the Ellingham diagram. Since the reaction between metal and carbon is exothermic, it serves as a reference value for evaluating carbide formation (Figure 5A). The ultra-high temperatures (approximately 3000 K) of the FJH process, up to approximately 2510 K, enable the reduction of all enumerated oxides, including the most difficult HfO2, to their elemental metals. Because almost all low-cost metals or metal compounds, including oxides, hydroxides, and chlorides, can be used as precursors, FJH is a promising low-cost production method compared to previous methods that relied on the availability of volatile compounds. [Kolel-Veetil 2005; Wolden 2011; Pol 2009].

[0091]

[0160] Only the IVB group carbides, including TiC, ZrC, and HfC, possess a stable rock salt crystal structure, and these were readily synthesized (Figure 5B). The particle sizes of TiC, ZrC, and HfC were measured to be approximately 30.4 nm, 38.6 nm, and 30.6 nm, respectively. These values ​​were in good agreement with the crystal sizes determined by XRD (see Table I above), demonstrating that the as-synthesized carbide nanoparticles are largely single crystals. For VB group carbides, a competing M2C (M=V, Nb, and Ta) phase may exist at lower C content [Hugosson 1999]. Nevertheless, by using a large C / M molar ratio, pure phases of VC, NbC, and TaC nanocrystals with cubic structures and particle sizes in the range of approximately 20–30 nm were successfully synthesized (Figure 5C). In contrast, the phases of VIB group carbides (Cr, Mo, and W) are more complex. [Hugosson 2001] In this case, orthorhombic Cr3C2 phases and hexagonal W2C phases were synthesized with particle sizes of approximately 14.2 nm and 18.7 nm, respectively (Figure 5D). According to the WC phase equilibrium phase diagram, W2C is thermodynamically less favorable than the WC phase below 1250°C. [Kurlov 2006] The success of synthesizing metastable W2C is attributed to the high energy input and ultrafast cooling rate of the ultrafast electrothermal reaction, again demonstrating the excellent phase manipulation capability of the FJH process. The generality of the FJH process was demonstrated when covalent carbides of B4C and SiC were synthesized separately from TMCs.

[0092] System and Synthesis Process

[0161] Therefore, for the synthesis of metal carbides, the present invention offers, among many others, (i) ultrafast synthesis thousands of times faster than previously reported methods; (ii) phase control capabilities difficult to achieve by other methods; and (iii) generality demonstrated by the synthesis of up to 13 types of carbides that are impossible by any other method.

[0093]

[0162] The metal carbides obtained by the present invention, particularly molybdenum carbide and tungsten carbide, can be used as electrode catalysts, for example, as electrode catalysts for hydrogen generation, which is important for applications in fuel cells in clean energy. Furthermore, nanoscale carbides are important precursors for the fabrication of high-performance carbide ceramics.

[0094]

[0163] Figures 6A-6B show the electrical circuit diagram of the FJH system and an exemplary system and process used in its setup. (Further details on additional electrical components can be found in Luong 2020). A capacitor bank with a total capacitance of 60 mF was used as the power source. Metal precursors and carbon black (Table I) were mixed in specific weight ratios by gliding using a mortar and pestle. The reactant (approximately 50 mg) was packed into a quartz tube with an inner diameter (ID) of 4 mm and an outer diameter (OD) of 8 mm. When scaling up the process, a quartz tube with an ID of 8 mm and an OD of 12 mm was used for a sample of approximately 200 mg, and a quartz tube with an ID of 16 mm and an OD of 20 mm was used for a sample of approximately 1 g. Further scaling up the mass to the kilogram scale is expected to require containers that do not necessarily have to be quartz. Graphite rods were used as electrodes at both ends of the quartz tube. The electrodes were loosely fitted into the quartz tube to allow for gas generation. The resistance was controlled by the compressive force of the electrodes across the sample. The tube was then placed on the reaction stage (Figure 6C). The reaction stage was placed in a sealed reaction chamber and degassed to a gentle vacuum (approximately 10 mmHg) to prevent oxidation of the sample (Figure 6D). The reaction stage was then connected to the FJH system.

[0095]

[0164] The condenser bank was charged with a DC power supply capable of reaching a maximum voltage of 400V. Discharge time was controlled using relays with programmable millisecond-level delay times. Charging, flash Joule heating, and discharge were automatically controlled using a combination of National Instruments multifunction I / O (NI USB-6009) and a customized LabView program. After the FJH reaction, the apparatus was rapidly cooled to room temperature. Before removing the sample, it was confirmed that the condenser bank was completely discharged. Table I lists the detailed conditions for the synthesis of various carbides.

[0096] Features and Applications

[0165] In this embodiment, as-synthesized carbide nanocrystals were supported on flash graphene. The need for graphene and carbide separation depends on the further application. In the case of applications of nanocrystalline carbides in electrocatalysts, a graphene support is beneficial to improve performance by providing conduction and particle aggregation prevention. In another major application of nanocrystalline carbides as precursors for ultra-high-strength ceramics, removal of excess carbon is required.

[0097]

[0166] For SiC, simple firing in air; for TiC, ZrC, HfC, VC, NbC, TaC, Cr3C2, β-Mo2C, and W2C, Ca metal etching [Dyjak 2013]; and for metastable molybdenum carbide, α-MoC 1-x and η-MoC 1-x In this case, efficient purification of the carbide was achieved through post-synthesis processes, including a density-in-liquid purification procedure. In addition, significantly improved purity of B4C was demonstrated by using a controlled feed during synthesis.

[0098]

[0167] Due to its ultrafast heating / cooling rates, direct sampling heating characteristics, and short reaction duration of less than one second, the FJH process for carbide synthesis is highly energy-efficient compared to heating in conventional furnaces, where large amounts of energy are used to maintain the chamber temperature. Carbide nanocrystals were synthesized with electrical energy of only 2.2–8.6 kJ / g. FJH synthesis has excellent scalability, with constant temperature values ​​and uniformity across different mass scales obtainable by adjusting the discharge voltage and / or capacitance.

[0099]

[0168] The synthesis of carbide nanocrystals down to the gram scale was demonstrated by increasing the FJH voltage. The FJH process can be extended to the synthesis of carbide alloys [Sarker 2018], heteroatom-modified carbides [Song 2019], and crystalline phase engineering of metastable carbides [Demetriou 2002], providing a powerful technique for carbide production.

[0100]

[0169] The controlled synthesis of metastable phases is attractive in the synthesis of inorganic materials [Chen 2020]. The FJH process, combined with a kinetically controlled ultrafast cooling rate (>10 4 It provides a widely tunable energy input (K / sec), potentially exceeding 3000K. Therefore, the FJH process serves as a potential tool for manipulating metastable phases of various materials, such as metallic nanomaterials [Chen 2020], layered oxides [Bianchini 2020], metallic nitrides [Sun W 2017], and two-dimensional materials, as it provides access to many non-equilibrium phases and then maintains them at room temperature.

[0101] Ultrafast synthesis of corundum nanoparticles

[0170] The present invention further includes flash Joule heating for the synthesis of metallic corundum nanoparticles [see Luong 2020; Stanford 2020; Tour PCT '000], i.e., an ultrafast process for ultrafast phase conversion from γ-Al2O3 (in addition to γ-AlOOH) to α-Al2O3 by flash Joule heating. In short, carbon black (or other carbon additives such as those discussed above) is mixed with γ-Al2O3 (or γ-AlOOH) nanoparticles, and this is then subjected to flash Joule heating. The phase conversion is ultrafast, taking less than one second, which is thousands of times faster than other state-of-the-art methods.

[0102]

[0171] Accordingly, embodiments of the present invention include a pulsed direct current (PDC) based Joule heating process that completes the phase conversion from γ-Al2O3 to α-Al2O3 at a significantly reduced average bulk temperature and reaction duration (approximately 573 K, <1 second). Rapid conversion may be possible by localized heating induced by resistant hot spots in the PDC process, when appropriate volume fractions of the γ-Al2O3 precursor and carbon black conductive additive are used. Pulsing and localized heating reduce aggregation and reduce the average particle size of approximately 23 nm and approximately 65 nm. 2 This leads to the synthesis of α-Al2O3 NPs with a surface area of ​​ / g. First-principles calculations reveal that the topotactic phase transition process (from γ-Al2O3, δ'-Al2O3, to α-Al2O3) is determined by the surface energy difference of the three phases. A thermodynamic limit of approximately 21 nm was achieved for the synthesis of dehydrated α-Al2O3 NPs containing δ'-Al2O3 as an intermediate phase through a thermal process.

[0103]

[0172] Furthermore, based on Joule heating technology, an alternating current (ACS) sintering process was developed that demonstrates ultrafast and atmospheric pressure sintering of these α-Al2O3NPs into alumina ceramics with nanoscale particle size and improved strength and hardness.

[0104]

[0173] A firing process for completely removing carbon black or formed flash graphene was also developed, and a pure phase of α-Al2O3 was obtained. In an embodiment, the synthesized α-Al2O3 has a surface area of 65 m 2 / g, which means that these materials are useful in applications of catalyst supports and high-strength ceramics.

[0105] Phase conversion synthesis

[0174] A method for ultra-fast synthesis of corundum nanoparticles (i.e., the conversion from γ-Al2O3 (in addition to γ-AlOOH) to α-Al2O3) may include the following.

[0106]

[0175] Since the γ-Al2O3NP precursor is electrically insulating, commercial carbon black (CB) was used as a conductive additive in an embodiment. For example, a mixture of γ-Al2O3NP and CB was compressed inside a quartz tube between two graphite electrodes. See FIG. 7 (showing the PDC device 701 and the resistive hot spots 702 in and around the gap of the insulating γ-Al2O3NP, with arrows depicting the current lines) and FIG. 13A (including an aluminum electrolytic capacitor (450V, 13mF) having a total capacitance of 0.624F used for charging).

[0107]

[0176] CB also functions as a separator to avoid aggregation of Al2O3NP during heating. The resistance is controlled by the compressive force at the two electrodes, as shown in Table II.

[0108]

Table 2

[0109]

[0177] The electrodes were connected to a capacitor bank with a capacitance of C=0.624F and a maximum charging voltage of V0=500V. The discharge circuit was a series resistor-inductor-capacitor circuit with a natural time of τ=0.1ms, which enabled a PDC with a frequency of f=1000Hz. Figure 13B shows the generation of a pulse voltage that can be used by the system to generate a PDC, with a frequency of 1000Hz and the ON state set to 20%, thereby producing a 0.2ms voltage pulse.

[0110]

[0178] Joule heating affects the entire conductor; in the case of a uniform conductor, the current density is uniform, so resistive losses allow for a uniform temperature distribution across the sample. [Johnson 2011] However, when the electric field is applied to a non-uniform medium, such as in the case of a composite material of conductive CB and insulating Al2O3, the current and powder density vary greatly in space. [Soderberg 1987] Power dissipation is substantially greater in some areas than in adjacent areas, which is called a resistive hotspot 702 (illustrated in Figure 7A). Even at low mean bulk temperatures, hotspots allow for localized heating, initiating conversions that occur at considerably higher temperatures.

[0111]

[0179] By using this mechanism, phase conversion from γ-Al2O3 to α-Al2O3 with an intermediate t-phase of δ'-Al2O3 was achieved in <1 second at an average bulk temperature of approximately 573 K. See the pulsed DC method 814 shown in Figure 8. As shown in Figure 8, this pulsed DC method 814 is comparable to representative phase conversion methods reported in the literature, namely the flame spray pyrolysis method 811 [Laine 2006], the furnace annealing method 812 [Steiner 1971], and the high-energy ball mill method 813 [Amrute 2019].

[0112]

[0180] The liquid-feed flame spray pyrolysis method 811 produced α-Al2O3 at temperatures close to 1873K; however, the kinetically controlled process can make it difficult to obtain a pure phase (α-phase with a purity of 80-85%). [Laine 2006]. Conventional heating methods that supply heat through the sample boundary, such as furnace annealing method 812, require a long period of time to heat uniformly, and therefore require 1473K and 10-20 hours to complete the phase conversion. [Steiner 1971]. Other room-temperature non-equilibrium processes, such as high-energy ball milling method 813, have been reported to form α-Al2O3. [Amrute 2019]. Nevertheless, γ-Al2O3 can aggregate, thereby causing a loss of surface area during long-duration and high-energy collisions. [Zielinski 1993; Chauruka 2015].

[0113]

[0181] The detailed phase transformation process of γ-Al2O3 was investigated using the PDC approach. See Figures 9-11. (In Figure 9, the symbols represent γ-Al2O3 (black square), δ'-Al2O3 (black triangle), α-Al2O3 (black circle), and γ-AlOOH (white circle); the precursor was γ-Al2O3, containing a small amount of the γ-AlOOH phase (crystal system: monoclinic; space group: P21 / n; PDF number 07-0324); samples processed for 0.8 seconds were calcined). Particle size was approximately 10 nm and approximately 156 nm. 2Commercial γ-Al2O3NP with a surface area of ​​1 / g was used as a precursor. A small amount of γ-AlOOH phase appeared in the precursor (Figure 9, 0 sec). The mass ratio of γ-Al2O3NP to CB was 4:1, which resulted in a sample resistance of approximately 8 Ω (Table II). A discharge voltage of 60 V was applied along with different discharge times controlled by a relay. Figure 9 shows the X-ray diffraction (XRD) patterns of the product at different PDC on-state times. As the discharge time increased, γ-AlOOH disappeared first at 0.3 sec; then γ-Al2O3 transitioned to the δ' and α-Al2O3 phases at 0.4–0.5 sec; and finally, after a discharge of 0.8 sec, the intermediate δ'-Al2O3 phase was completely converted to the α-Al2O3 phase (Figure 11 shows curves 1121–1123 for γ-Al2O3, δ'-Al2O3, and α-Al2O3, respectively). Orthorhombic δ'-Al2O3 was observed as a single intermediate phase (Figure 10), which differs from other thermal processes in which δ and θ-Al2O3 typically appear before the final α-Al2O3 phase (Figure 8). [Steiner 1998; Levin 1998; Lamouri 2017].

[0114]

[0182] Unlike previous reports on graphene synthesis by high-voltage flash Joule heating at high temperatures of approximately 3000K [Luong 2020], a 60V PDC did not provide sufficient energy to graphitize the carbon ions (CBs). Figure 13C (no 2D peaks are observed in the product after Joule heating at 60V). Consequently, according to thermogravimetric analysis (TGA), the CBs were readily removed by heating in air. Here, the as-synthesized mixture of α-Al2O3 NPs and CBs was calcined in air at 700°C for 1 hour to purify the product. The X-ray photoelectron emission spectrum (XPS) of the α-Al2O3 product after calcination showed a very faint carbon signal, which may be due to carbon adsorption in air.

[0115]

[0183] Raman spectra are sensitive to carbon monolayers [Wang 2008]; interestingly, no characteristic carbon Raman bands were detected after calcination at 700°C (in Figure 12, curves 1224-1226 for 700°C calcination and CB / Al2O3 for 650°C calcination), demonstrating efficient carbon removal. In contrast, it was determined that the calcination process itself does not initiate phase transformation and has only a negligible effect on the coarsening or aggregation of the γ-Al2O3 phase.

[0116] Characterization of corundum nanoparticles

[0184] The α-Al2O3 NPs obtained by PDC and subsequent gentle calcination were further characterized in detail. Bright-field transmission electron microscopy (BF-TEM) images showed well-dispersed particles. See Figure 14A. High-resolution TEM (HRTEM) showed the high crystallinity of the α-Al2O3 NPs. See Figure 14B. Interplane spacing values ​​of approximately 2.57 Å and 2.09 Å correspond to d(10⁴) and d(11³) of α-Al2O3, respectively. Some α-Al2O3 NPs exhibited surface roughness at the level of several nanometers, which is similar to the particle size of the γ-Al2O3 precursor. This explains that while the fast PDC process caused phase conversion, significant aggregation of NPs did not occur. TEM images show particle sizes ranging from 14 to 36 nm, with an average particle size of 25.4 nm and a standard deviation (σ) of 5.8 nm. See Figure 14C.

[0117]

[0185] The Brunauer-Emmett-Teller (BET) measurement indicates that the surface area of ​​α-Al2O3NP is approximately 65 m². 2 It was shown that the value was / g. See inset 1401 in Figure 14D (this inset shows the N2 adsorption / desorption isotherm of α-Al2O3NP at 77K). The average particle size (D) is estimated to be approximately 23 nm by equation (1): D=6 / (ρS) Equation (1) In the formula, ρ is the density of α-Al2O3 (3.96 g / cm³). 3), where S is the specific surface area [Karagdov 1999].

[0118]

[0186] Pore ​​sizes determined from N2 adsorption / desorption isotherms using a density functional theory (DFT) model show a high-probability distribution between 3 and 10 nm. See Figure 14D. The observed surface area was attributed to nanoscale particle size, as well as pore and surface roughness characteristics within the NP. The crystal size of α-Al2O3NP was estimated to be approximately 22 nm based on the Halder-Wagner method. The crystal size (approximately 22 nm) is in good agreement with the particle size measured from TEM statistics (approximately 25 nm) and BET estimation (approximately 23 nm), demonstrating the single-crystal characteristics of the NP.

[0119]

[0187] Unlike the initial γ-Al2O3NP, which had a hydrated surface, the surface of the synthesized α-Al2O3NP was highly dehydrated due to the thermal process. Figure 14E, curves 1411–1412 show the α-Al2O3 product and γ-Al2O3 precursor, respectively (the black arrow 1413 further indicates the absorbance of the hydroxyl group).

[0120]

[0188] The XPS fine spectrum shows a dominant O from α-Al2O3NP at a binding energy of approximately 531.2 eV. 2- Peak, and single Al at a binding energy of approximately 74.0 eV. 3+ A peak was observed. See Figure 14F. This suggests that the ultrafast PDC process is probably Al 3+ Due to its high reduction potential, the presence of CB did not result in obvious oxygen deficiency or carbonothermal reduction of Al2O3. The absence of other peaks in the full XPS spectrum demonstrates the high purity synthesis capability of the electrothermal process. For this reason, this process is superior to solvent-based methods, including ball milling [Amrute 2019] or coprecipitation [Guo 2016], which are plagued by lengthy purification processes and chemical contaminants.

[0121] Resistant hotspot effect

[0189] The composition of the non-uniform medium can be important due to 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 ratios of γ-Al2O3 and CB were treated by PDC at the same voltage and time. Figure 15A (Symbols: γ-Al2O3 (black squares), δ’-Al2O3 (black triangles), and α-Al2O3 (black circles), and the numbers are the mass ratios of γ-Al2O3 to CB); Table II. Due to the densities of γ-Al2O3 and CB, the volume fraction (f) of γ-Al2O3 was obtained (shown in Table III), and the phase mass ratios that change f(γ-Al2O3) after the PDC process were calculated. Figure 15B (showing curves 1501 - 1502 for α-Al2O3 and δ’-Al2O3 respectively).

[0122]

Table 3

[0123]

[0190] When f(γ-Al2O3) increased from 0.41 to 0.73, the degree of phase transformation increased; at f(γ-Al2O3) of about 0.73, phase-pure α-Al2O3 was obtained. A further increase in f(γ-Al2O3) to >0.78 did not result in phase transformation.

[0124]

[0191] To explain the f(γ-Al2O3)-dependent phase transformation, the electrical conductivity and temperature were measured. The conductivity was determined based on the measured resistance (R) and the characteristic size of the sample. Table II; Figure 15C (Curves 1503 - 1504 are the conductivity and temperature for f(γ-Al2O3) respectively. Since γ-Al2O3 is electrically insulating, it was reasonable that the conductivity was inversely proportional to f(γ-Al2O3) (curve 1504 in Figure 15C). The real-time temperature was measured using an infrared (IR) thermometer. The average bulk temperature decreased with the increase in f(γ-Al2O3) (curve 1503 in Figure 15C). This can be explained by the power (P) equation of Joule heating according to Equation (2): P = V 2 / R = V 2 σ Equation (2) In the formula, V is the voltage and σ is the conductivity of the sample.

[0125]

[0192] Since the initial voltage was fixed at V0 = 60V, the power was proportional to the conductivity of the sample. Interestingly, phase-pure α-Al2O3NP was obtained at a low average bulk temperature of approximately 573K, with f(γ-Al2O3) being approximately 0.73. Figure 15C.

[0126]

[0193] Such low temperatures were not expected to initiate the phase conversion from γ-Al2O3 to α-Al2O3 with a high activation energy of approximately 485 kJ / mol [Steinr 1971]. Furthermore, the higher degree of phase conversion at even lower temperatures was counterintuitive. Figure 15C.

[0127]

[0194] To explain this phenomenon, numerical simulations based on the finite element method (FEM) were performed on the current density distribution of the γ-Al2O3 / CB composite material during the PDC process. As shown in Figures 15D–15F, the current density is non-uniform in the γ-Al2O3 and CB composite material; the current density in the region of the vertical gap between γ-Al2O3NPs is greater than in the bulk region. (In Figures 15D–15F, the spheres are γ-Al2O3, the continuous phase is CB, and the vertical sidebars indicate the current density values). The gap narrows as f(γ-Al2O3) increases, resulting in significantly higher current densities in these regions. Assuming that the resistivity (R) of the conductive CB phase is constant, the heat per unit volume (Q) produced by the PDC is proportional to the square of the current density (j) by equation (3): Q∝j 2 R equation (3)

[0195] The large heat dissipation in the region with high current density results in hot spots near the γ-Al2O3 NPs at a temperature higher than the bulk region, which initiates the phase transformation. As shown in Fig. 16, the quantitative analysis of the current density reveals that as f(γ-Al2O3) increases, the bulk temperature decreases (curve 1601), while the hot spot temperature increases (curve 1602), which is in good agreement with the temperature measurements shown in Fig. 15C.

[0128] Topotactic transition pathways

[0196] To provide deeper insights into the topotactic transition pathway, a thermodynamic analysis of the three Al2O3 phases was performed based on DFT. The bulk energies and surface energies of the three Al2O3 phases were calculated. Fig. 17A. The bulk energy of α-Al2O3 is the lowest, followed by δ’-Al2O3 and then γ-Al2O3, indicating that α-Al2O3 is the most stable phase as a high-density bulk crystal. In contrast, the surface energies are reversed: γ-Al2O3(100) has the lowest surface energy, followed by δ’-Al2O3(100), α-Al2O3(1-10) and (001) with low surface energies. The surface energy difference determines the thermodynamic stability of the three Al2O3 phases when the surface area is increased. Fig. 17B, curves 1701-1703 are α-Al2O3, δ’-Al2O3, and γ-Al2O3 respectively. When the surface area is smaller than about 79 m 2 / g or the particle size is larger than about 21 nm, the α-Al2O3 phase becomes more stable than the δ’ phase. Therefore, a particle size of about 21 nm was suggested as the thermodynamic limit for the synthesis of dehydrated α-Al2O3 by thermal processes involving the intermediate δ’ phase. The particle size of α-Al2O3 synthesized by PDC (about 23 nm) approaches the thermodynamically limited value and is smaller than that obtained by most other thermal processes (Table IV).

[0129]

Table 4

[0130]

[0197] Ultrafast pulsed and low-temperature PDC processes significantly avoid mass transfer and particle coarsening during phase conversion processes.

[0198] To gain insight into the structural causes of phase-dependent bulk and surface energies, partial charge density contours were plotted in the highest band (0.3 eV below the Fermi level) of the surface states of the three Al2O3 phases (Figures 17C-17D). While all surface atoms on α-Al2O3(001) are active, the Al atom-deficient sites on the δ'-Al2O3(100) and γ-Al2O3(100) surfaces are relatively active (Figure 17C). More detailed analysis showed that in the case of δ'-Al2O3(100) and γ-Al2O3(100), the active state penetrates deep into the bulk, but not in α-Al2O3(001) (Figure 17D). This explains the order of surface energies in addition to bulk energies for the three Al2O3 phases and identifies Al vacancies in the γ and δ' phases as structural causes of their thermodynamic stability / instability relative to the α phase.

[0131] Application

[0199] Therefore, for the synthesis of corundum nanoparticles, the present invention provides an ultrafast synthesis that is faster than any reported method, taking less than one second and requiring at least several hours. The corundum (α-Al2O3) nanoparticles obtained by the present invention have a small particle size and a high surface area and can be used in a variety of applications, for example, as a stable catalyst support or in ceramics with high fracture strength and toughness.

[0132]

[0200] For example, one important application of α-Al2O3NP is as a precursor for sintering alumina ceramics with nanometer-level grain size (i.e., ultrafast ACS for nanograin-sized alumina ceramics). Typical alumina ceramic sintering processes are carried out under high-pressure, high-temperature (HP-HT) conditions such as hot hydrostatic pressurization [Mizuta 1992], electrostatic discharge plasma sintering [Balima 2019], and pulsed current sintering [Zhou 2004]. The high pressure, typically several GPa, preserves grain growth and promotes densification [Wang 2013], which can be a major factor for high-density ceramic sintering using coarse-grained precursors. However, HPHT processes are not suitable due to the complex structure. Nanocrystalline precursors could undergo pressureless sintering, but this would be plagued by increased sintering temperatures and prolonged sintering times (>10 hours) [Guo 2016; Cao 2017; Li 2006]. Very recently, an ultrafast high-temperature sintering method based on DC heating for high-speed sieving of ceramics was reported [Wang 2020].

[0133]

[0201] Based on Joule heating technology, an alternative current sintering (ACS) process was developed for ultrafast sintering of alumina ceramics. The ACS system is suitable for sintering structural ceramics because it can provide a stable and high energy output at voltages as high as 63V and currents as high as 100A (Figure 18A). In the ACS system, the total capacitance was 1.5F, and the maximum usable voltage was 63V. The capacitors were simultaneously charged by the AC power supply, and energy output was provided to the sample through discharge. The energy output was continuous, enabling long-term sintering of several seconds at high energy output.

[0134]

[0202] Two separate, highly graphitized carbon papers 1801a-1801b, connected to electrodes in Figure 18C, were used as heating elements. See Figure 18B (wherein carbon papers 1801a-1801b are attached to a glass slide and bonded with copper tabs). Pellet 1802 was obtained by pressing α-Al2O3NP [Taktak 2011] mixed with polyethylene glycol (PEG) binder at 500 MPa. Commercial α-Al2O3 nanopowder (approximately 300 nm) was used as a control. After removing the binder (from 5°C / min, held at 500°C for 2 hours; in air), pellet 1802 was placed between the carbon papers and subjected to ACS at approximately 15 V.

[0135]

[0203] Figure 19A shows rapid heating 1901, stable sintering 1902, and rapid cooling 1903. Temperature was recorded by fitting blackbody radiation. The temperature was approximately 10 3 The temperature rapidly increased to approximately 2250K at a heating rate of K / second. After a stable sintering period of 5 seconds, the sample similarly rose to approximately 10 3 Cooling was performed at a high cooling rate of K / sec. See Figure 19B. Figure 19C shows sintered ceramic pellets 1911-1912 supported on carbon paper 1913.

[0136]

[0204] XRD patterns confirm the pure α-phase of the alumina ceramic (Figure 19D). Scanning electron microscopy (SEM) microstructure revealed equally sized grains and tightly bonded grain boundaries with polyhedral morphology (Figure 19E), demonstrating well-developed sintering. The average grain size of the alumina ceramic was approximately 270 nm (Figure 19F). In comparison, alumina ceramics sintered from commercially available α-Al2O3 powder showed high residual porosity with a grain size of approximately 1200 nm, demonstrating that sintering was an early stage. This result suggests that the fine grain size of α-Al2O3NP facilitates ultrafast sintering, which is expected to be promoted by grain growth at high temperatures [Guo 2016]. Mechanical properties of the ceramic were measured. See Figures 19G-19H. Ceramics sintered with α-Al2O3NP precursors demonstrated a Young's modulus of approximately 11.7 GPa, which is significantly higher than that of commercially available α-Al2O3 powder (approximately 1.5 GPa). It is expected that the mechanical properties of alumina ceramics obtained from α-Al2O3NP will likely be improved by using conventional high-pressure-based sintering processes [Mizuta 1992; Balima 2019; Zhou 2004] or by extending the sintering time [Guo 2016; Laine 2006].

[0137]

[0205] Therefore, the ACS process can be used in the sintering of functional ceramics, porous ceramics, or for material sieving. [Wang 2020] Effectiveness and scalability

[0206] Joule heating is a highly efficient energy supply technique with an operating coefficient of 1.0. Localized heating by resistive hotspots in the PDC makes the process more efficient because most of the electrothermal energy is directed directly to the phase conversion, enabling synthesis with a low energy input of approximately 4.77 kJ / g or an electrical energy cost of $0.027 / kg. Furthermore, the PDC process can be scaled by adjusting the sample cross-sectional area and PDC voltage. Synthesis of α-Al2O3NP down to 1.4 g scale was performed. See Figures 20A-20B and 21A-21B (in Figures 20A and 21A, the black powder is the as-synthesized mixture of CB and α-Al2O3, and the white powder is α-Al2O3 after calcination). The combination of the PDC process and the resistive hotspot effect significantly reduces the temperature required for a reaction that would originally require a high energy input, serving as an alternative technique for cost-effective synthesis.

[0138] Metal recovery from electronic waste

[0207] The present invention includes flash Joule heating for an ultrafast process for recovering metals (precious metals) from waste (e.g., electronic waste) [see Luong 2020; Stanford 2020; Tour PCT '000]. The waste may be mixed with carbon black and then subjected to ultrafast Joule heating flushing. According to the Ellingham diagram, multiple types of precious metals are reduced to elemental metals by a carbon-thermal reaction. The recycling process is ultrafast, taking less than a few seconds. Importantly, the process is a completely dry process requiring no solvents and is therefore extremely environmentally friendly.

[0139] Synthesis process

[0208] A method for ultrafast synthesis to recover metals from waste may include the following:

[0140]

[0209] This method may include the preparation of electronic waste for flushing. For example, printed circuit boards (PCBs) from used electronic printers were used as the starting material. First, the PCB boards were cut into small pieces and then ground into small particles. Using a ball mill, this was ground into a microscale fine powder, which was then made available for flash Joule heating by adding carbon black (or other carbon materials as discussed above) and processed in a flash Joule heating apparatus as described later.

[0141] Evaporation separation

[0210] It has been discovered that the difference in vapor pressure between metals and substrate materials (carbon, ceramics, and glass) allows for the separation of metals from electronic waste. This is called "evaporative separation." The high vapor pressure of precious metals is achieved by an ultrafast flash Joule heating (FJH) process in a vacuum. A current pulse of less than one second passes through the precursor, raising the sample to an ultra-high temperature of approximately 3400K, enabling the evaporation separation of precious metals. Halide additives are used to improve recovery yields by more than 80% for Rh, Pd, and Ag, and more than 60% for Au, which are abundant in the electronic waste tested. Alternatively, recovery yields are significantly improved by leaching the residual solid after FJH compared to directly leaching the electronic waste raw materials, with increases of several tens of times for Ag and several times for Rh, Pd, and Au. Toxic heavy metals, including Cd, Hg, As, Pd, and Cr, may also be removed and collected to minimize health risks and environmental impacts in the recycling process.

[0142]

[0211] The FJH process for recovering precious metals from electronic waste consists of three stages. See Figure 22, which shows a schematic diagram of system 2200. In the metal evaporation stage 2201 (including an FJH apparatus with a capacitor bank 2205 and porous Cu electrodes 2206), the metals in the electronic waste were heated and evaporated by ultra-high temperature FJH. Then, in the material transport stage 2202, the metal vapor was transported in a vacuum (using a vacuum system with a pump 2207), and in the condensation stage 2203, it was collected by condensation (using a cold trap 2208). Printed circuit boards (PCBs) from discarded computers, which are typical electronic waste, were used as the starting material. See Figure 23. The PCBs were glided into a fine powder and mixed with carbon black (CB) to be used as a conductive additive. Insertion 2310 of Figure 23.

[0143]

[0212] To establish baseline concentrations, PCBs were digested using dilute aqua regia [Hong 2020], and the concentrations of precious metals were determined by inductively coupled plasma mass spectrometry (ICP-MS). As shown in Figure 24, among the precious metals, Rh, Pd, Ag, and Au were abundant at concentrations ranging from a few ppm to tens of ppm (parts per million).

[0144]

[0213] In the FJH process, a mixture of PCB powder and approximately 30 wt% CB was slightly compressed inside a quartz tube between two sealed electrodes. Figure 22. Figure 29A shows a photograph of the system including the flash stage 2901, power source 2902, pump 2903, and cold trap 2904 (liquid nitrogen, dewar). One electrode was a porous Cu electrode to facilitate gas diffusion, and the other was a graphite rod. Figure 30. The resistance of the sample was adjustable by adjusting the compression force at the two electrodes. The two electrodes were connected to a condenser bank with a total capacitance of 60 mF. Table V shows the detailed separation conditions.

[0145] [Table 5]

[0146]

[0214] The high-voltage discharge of the capacitor bank raises the reactants to a high temperature. The current passing through the sample was measured under different FJH voltages using a fixed sample resistor of approximately 1 Ω. See Figure 25, which shows curves 2521–2523 for 150V, 120V, and 100V, respectively. The real-time temperature of the sample was estimated by fitting blackbody radiation at 600–1100 nm emission. The temperature varied with the FJH voltage, reaching approximately 3400K at 150V, <50 ms. See Figure 26, which shows curves 2631–2633 for 150V, 120V, and 100V, respectively.

[0147]

[0215] Because the resistance of the sample is considerably greater than that of the graphite and porous Cu electrodes, the voltage drop was primarily imposed on the sample. Therefore, the high-temperature range is limited to the sample, and the FJH setup, although capable of reaching temperatures of >3000K, exhibits excellent durability. Such high temperatures (>3000K) volatilize most of the non-carbon components. According to the calculated vapor pressure-temperature relationship (Figure 27), noble metals have a higher vapor pressure than carbon, and carbon does not sublimate up to approximately 3900K. [Abrahamson 1974].

[0148]

[0216] As a result, the metal evaporated and carbonized the main carbon-containing components, such as plastics. [Luong 2020; Algozeeb 2020] In a cold trap, the evaporated metal vapor was captured by condensation (Figures 22 and 29A). Some of the vapor remained in gaseous form even at liquid N2 temperature (77K); these gases were presumed to be H2 and CO. [Algozeeb 2020].

[0149]

[0217] The content of precious metals in the condensed solid was measured, and the recovery yield was calculated (Figure 28). The recovery yield of Ag was approximately 40%, while Rh, Pd, and Au had relatively lower recovery yields of approximately 3%. This is because Ag has a high vapor pressure and a relatively low boiling point. The concentration of precious metals in commercial CB at the start is 1-2% in PCB, and therefore their presence in CB is not expected to introduce significant error. Furthermore, precious metals tend not to form a stable carbide phase even at high temperatures due to their extremely low carbon solubility [Okamoto 2016]. Therefore, the use of CB as a conductive additive is not expected to affect the evaporation behavior of precious metals.

[0150] Improvement of recovery yields facilitated by halogens

[0218] High recovery yields in evaporation separation rely on the generation of more volatile components. To improve recovery, halides were used as additives due to their higher vapor pressure compared to elemental metals. [Lide 2005]. Initially, fluorine-containing components such as sodium fluoride (NaF) and polytetrafluoroethylene (PTFE, Teflon®) were used as additives. With the use of additives, the recovery yields of Rh and Pd improved to >80% and 70%, respectively. See Figures 31A-31B, which demonstrate an improvement of approximately 20 times compared to experiments without additives. The concentration of precious metals in the additives was <2% of the concentration in the PCB, thus ruling out the additives introducing a significant error in the recovery of precious metals.

[0151]

[0219] Compounds containing chlorine were tested for their generation amount and low cost. Both sodium chloride (NaCl) and potassium chloride (KCl) were used (Figure 31C). The recovery amounts of Rh, Pd, and Ag increased with both the NaCl and KCl additives. In addition, both polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC) plastics were used (Figure 31D). The recovery amounts of all four noble metals increased, especially the recovery amount of Ag, which was improved to >80%. Since the plastic additives were shredded post-consumer samples with very low or negative value, they were expected not to introduce significant material costs during the e-waste recycling process.

[0152]

[0220] Even with F and Cl additives, the recovery amount of Au is <10%. Interestingly, when sodium iodide (NaI) was used as an additive, the recovery amounts of all four noble metals were improved, and the recovery amount of Au was improved to >60% (Figure 31E). The I additive has the best performance regarding Au recovery among the halides. 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 - and AuI is preferred. By using an additive mixture of NaF, NaCl, and NaI, all the noble metals had excellent recovery amounts, >60% for Rh, >60% for Pd, >80% for Ag, and >40% for Au (Figure 31F). According to the compositional analysis of the raw materials and the remaining solids after FJH by X-ray photoelectron spectroscopy (XPS), it was shown that 10 - 40% of the halide additives evaporated during the FJH process, which can be recovered and reused by washing and precipitation processes with water.

[0153]

[0221] A total compositional analysis of the metals collected in the cold trap was performed. In addition to precious metals, the most abundant metal, both with and without chemical additives, was Cu at a mass ratio of >60 wt%, followed by other notable metals in the electronic waste, such as Al, Sn, Fe, and Zn. Further purification and refining may be carried out by selective precipitation, solvent extraction, and solid-phase extraction, which are commercially well-established and conventional methods and are well known in the art. [Ueda 2016]

[0154]

[0222] The morphological and chemical composition of the condensed solid was characterized using scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS). Elemental maps showed clustered alloy particles of Rh, Pd, Ag, and Au (Figure 31G), formed by the ultrafast heating and rapid cooling of the FJH process. This is analogous to the case of carbothermic shock synthesis of high-entropy alloy nanoparticles, which may be used in catalysts [Yao 2018]. In other regions, noble metals were also observed spread throughout the product. Furthermore, XPS analysis of collected volatiles indicated that Ag and Au were primarily in elemental states, while Rh and Pd coexisted in both elemental and higher oxidation states, presumably due to their different chemical reactivity.

[0155] Improved leaching efficiency of precious metals

[0223] Apart from the condensation of volatile compositions, another route for recovering precious metals was by leaching the residual solid obtained by FJH. See Figure 32A. Unlike the use of vacuum to facilitate metal volatilization in the evaporation separation scheme (Figure 22), a pressurized setup was constructed to capture the metal in a reactor (Figure 33A). An inert gas (N2) cylinder was connected to the FJH reactor, where the pressure was monitored by a pressure gauge. The internal pressure (P0) in the FJH was estimated to be approximately 5 atm from the amount of gas collected.

[0156]

[0224] Based on the pressure drop and the size of the FJH chamber, gas diffusion is controlled at different pressures (P out ) Simulated below (Figure 33B). When using a vacuum (P out At 0 atm, as in the case of evaporation separation (Figure 22), the gas velocity reached a maximum of 800 m / s. Such a high gas velocity facilitated the rapid diffusion of volatile components into the cold trap, preventing losses due to condensation on the tube sidewalls. In contrast, the gas velocity decreased significantly with increasing pressure (Figure 33B). As a result, more of the originally volatile components were captured in the residual solids in the reactor. Table VI shows the detailed reaction conditions for pressurized FJH.

[0157] [Table 6]

[0158]

[0225] Leaching of residual solids after FJH (indicated as PCB-flash) was initiated at 120 V and atmospheric pressure using dilute acids (1 M HCl, 1 M HNO3). The elutable content of Rh, Pd, and Ag in the PCB-flash was substantially higher than that in the PCB raw material (Figure 33C). The ratio of recovery yields from leaching the PCB-flash (Y) and leaching the PCB raw material (Y0) was calculated. FJH with leaching was far more effective than leaching alone. Recovery yields of Rh, Pd, and Ag increased by 4.17 ± 0.48, 2.90 ± 0.31, and 56.0 ± 18.1 times, respectively (Figure 33C). (In Figure 33C, Y0 and Y represent the recovery yields from leaching the printed circuit board (PCB) and PCB-flash, respectively. The dotted line indicates Y / Y0 = 1. Error bars represent the standard deviation for n=3). The deviation may be due to the non-uniform distribution of precious metals in the electronic waste. Interestingly, the Au recovery yield decreased after the FJH process. The reason is probably the formation of covalent bonds between Au and carbon [Olavarria-Contreras 2016], which may significantly increase the difficulty of acid leaching.

[0159]

[0226] Thermogravimetric analysis (TGA) of the PCB flash showed that carbon could be removed in air at approximately 700°C (Figure 32B). (The TGA curve in Figure 32B shows that the PCB flash began to lose weight at approximately 400°C and remained stable at approximately 800°C). Therefore, the PCB flash solid was calcined at 700°C for 1 hour (indicated as PCB-flash-calcined). Insertion 3201 shows a photograph of the PCB flash, and for control, the PCB flash-calcined PCB raw material was also calcined (indicated as PCB-calcined in Figure 32C).

[0160]

[0227] XPS analysis demonstrated efficient carbon removal by calcination (Figure 32D). (In Figure 32D, the XPS of the PCB shows a signal that is mostly C and some inorganic substances. The XPS of the PCB-flash shows a signal that is mostly C, indicating that O was removed by the FJH process, and no inorganic element peaks are detected, which is presumably because the inorganic substances were coated with carbon during the FJH process. The XPS of the PCB-flash-calcination shows abundant elemental signals, which demonstrates the removal and exposure of inorganic materials.) Using the FJH and calcination processes, the recovery yields of Rh, Pd, Ag, and Au increased by 3.11±0.37, 2.64±0.39, 28.5±9.8, and 7.24±2.22 times, respectively (Figure 33D). (In Figure 33D, Y0 and Y represent the recovery yields from leaching PCB and PCB-flash-calcination, respectively. The dotted line means Y / Y0=1. The error bars represent the standard deviation for n=3). The values ​​are greater than those achieved by the calcination-only process (Figures 32E-32F).

[0161]

[0228] Figures 34A–34E illustrate the mechanism of improved leaching efficiency by FJH. Modern electronic devices are fabricated and packaged by planar processes and have a layered structure in which useful metals are embedded in a polymer or ceramic matrix (Figure 34A). [Sun Z 2017] Even after grinding, the particle size was approximately 5 μm (Figure 34B). The layered structure hinders metal extraction in typical hydrochemical processes, resulting in long leaching times and low leaching efficiency. [Sun Z 2017] During the FJH process, the matrix becomes an ultrafine powder at ultra-high temperatures (Figures 34C–34D), exposing the metal (Figure 34E), which significantly increases the leaching rate and the degree of metal extraction.

[0162]

[0229] The effects of FJH voltage and pressure on recovery yield were evaluated. A moderate FJH voltage between 30 and 50 V was found to yield the best recovery (Figure 33E, curves 3301–3304 show Rh, Pd, Ag, and Au, respectively; the shaded region in Figure 33E represents the approximate optimal voltage for all metal recovery). Voltages that were too low did not provide enough energy to thermally decompose the matrix, while voltages that were too high were expected to result in evaporation losses. Higher ambient pressure was found to be beneficial (Figure 33F, curves 3311–3314 show Rh, Pd, Ag, and Au, respectively). This was because volatile components were trapped in the residual solid, as predicted by gas flow simulations (Figure 33B). The slow acid leaching conditions (1M HCl, 1M HNO3) used in the process of the present invention are more cost-effective and environmentally friendly compared to other wet metallurgical processes that use highly concentrated mineral acids such as aqua regia [Sun Z 2017; Park 2009] or toxic cyanides [Sethurajan 2019; Quinet 2005] as extraction solvents to achieve high recovery yields.

[0163] Removal and collection of toxic heavy metals

[0230] The removal of toxic components is another major concern regarding electronic waste treatment. [Ogunseitan 2009; Leung 2008; Julander 2014; Sun 2020]. The heavy metal removal capability of the FJH process was evaluated. Compared to precious metals, heavy metals such as Cr, Pb, Cd, As, and Hg have even higher vapor pressures and lower boiling points (Figure 35A). In particular, for the most toxic Cd, As, and Hg, the separation coefficients between them and precious metals are approximately 10 based on theoretical analysis. 5 The levels of heavy metals in PCB waste range from 0.1 to 20 ppm (Figure 35B). These values ​​exceed the safe limits for heavy metals in soil for agriculture recommended by the World Health Organization (WHO). [Kinuthia 2020]

[0164]

[0231] After one FJH (Flash-Jack-Heat) treatment, the heavy metal content in the remaining solid (PCB-flash) was significantly reduced (Figure 35C). The removal efficiencies for Hg and Cd were calculated to be >80%, followed by Pb and As (>50%), and Cr (>35%) (Figure 35D). These efficiencies were consistent with their vapor pressure values ​​(Figure 35A). Heavy metals were collected by condensation in a cold trap, similar to the method used in evaporation separation, and the collected yield was calculated (Figure 35D). The collected yield was in good agreement with the removal efficiencies, demonstrating that most of the evaporated heavy metals were captured by the cold trap, minimizing the leakage of heavy metals into the environment during recycling.

[0165]

[0232] The concentrations of heavy metals in the solid residue can be further reduced by multiple FJH reactions. After one FJH reaction, the concentration of Hg was reduced to below the safe limit for Hg in agricultural soil (0.05 ppm), which is the highest standard for waste treatment (Figure 35E) [Kimuthia 2020]. Similar to Cd, three consecutive FJH cycles reduced the concentration to below the safe limit (0.003 ppm) (Figure 35F) [Kimuthia 2020]. The concentrations of As, Pb, and Cr all decreased with increasing numbers of FJH reactions. Multiple flushes are easily achieved because each FJH takes only 1 second.

[0166] Metal separation

[0233] The process described above, utilizing an evaporation separation scheme, is discussed for the recovery of metals from electronic waste. Nevertheless, such a process can demonstrate the capability of metal separation. According to calculations, approximately 10 5 It is shown that large separation coefficients up to can be achieved for most metals with large vapor pressure differences. The chart in Figure 36 provides theoretical separation coefficients for the vapor pressure difference-based evaporation separation process. The coefficients represent practical values ​​for the separation of trace metals from abundant metals. For the separation of abundant metals, the values ​​should be adjusted according to their activity in the aggregate solution.

[0167]

[0234] The FJH process, based on vapor pressure difference, demonstrated different precious metal recovery yields (Figure 28). As shown in Figure 28, without the use of chemical additives, the precious metal recovery yields 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 capability of the FJH process. See Table VII below.

[0168] [Table 7]

[0169]

[0235] Chemical additives (Figures 31A-31F) also controlled the separation of noble metals, presumably due to their different chemical reactivity. See Tables VIII-X below.

[0170] [Table 8]

[0171] [Table 9]

[0172] [Table 10]

[0173]

[0236] The separation capability of the evaporation separation scheme can be further improved by gradually increasing the FJH temperature. Carbon-thermal reduction

[0237] The flash Joule heating process can also be used for the carbon thermal reduction of metals from oxides. Before recovery, various metal oxides were used to demonstrate the applicability of metal recovery by the flash Joule heating method. As shown in Figures 37A-37F, it was found that Al can be recovered from Al2O3, Fe from Fe2O3, Cu from CuSO4, Ni from NiSO4, Mn from MnO2, and Pb from PbNO3. During the flash Joule heating process, carbon from carbon black reduces metal oxides and metal salts back to metals, while simultaneously oxidizing carbon to carbon dioxide and carbon monoxide.

[0174]

[0238] In certain embodiments of the present invention, the process may include a mechanism used to capture metals in the waste. For example, the mechanism may use reduced pressure and, upon flash joule heating of the feed source, volatilize metals, metal carbides, metal oxides, or other metal complexes from the reaction chamber and place them in a cold trap. The cold trap may be, but is not limited to, liquid N2. These can be collected in the trap even at room temperature.

[0175]

[0239] Furthermore, for example, the mechanism can use atmospheric pressure or higher pressure (e.g., 10 or 20 atmospheres) to leave the metal in the newly formed graphene. The graphene can be sintered away (e.g., in air at 700-800°C), leaving the metal (or metal oxide, etc.) separated. Alternatively, the graphene can be chemically oxidized away, as in the case of using HNO3. With regard to this latter mechanism, a pressure relief valve can be used at the end of the electrode-hole assembly for the flash Joule heating process. Some of the recovered metal has an extremely high boiling point, and they are expected to remain with the carbon, especially at the higher pressures at which they are utilized.

[0176] Design and scalability

[0240] Figure 38 shows a flash Joule heating pressure and gas collection system 3800 that can be used in embodiments of the present invention. System 3800 includes the following: (a) Timing sprocket and belt 3801; (b) Manual or motor-driven 3802; (c) Driver 3803 (e.g., twin screw drive); (d) Power supply 3804 (e.g., AC or DC from a flash power supply); (e) Sample compression 3805; (f) Nuts 3807a~3807b and soft spacers 3806a~3806b; (g) Electrode 3808a (e.g., a solid brass electrode with threads) and electrode 3808b (e.g., a brass electrode with threads and drilled holes); (h) Tube 3809 (e.g., quartz tube); (i) Copper wool 3810; (j) Torsion spring compression 3811; (k) Electrode 3812 (e.g., a brass electrode having an O-ring seal and an axial hole); (l) Sample 3813; (m) Conduit 3814 (e.g., PTFE tube) inside electrode 3812; (n) Pressure seal 3815 (e.g., having a reducing union from Swagelok); (o) Particle collection device 3816; (p) Adjustable pressure relief valve 3817; (q) Gas collection device 3818; (r) Flow to vacuum or gas analysis 3819; (s) Ventilation hole 3820; (t) Safety relief valve 3821; (u) Conduit 3822 (e.g., PFE pipe material); (v) Flow into vacuum 3823; (w) Pressurized input 3824 from the gas supply; and (x) Pressure gauges 3825~3826.

[0177]

[0241] System 3800 is a pressurizable flash Joule heating cell having a gas collector 3818 for use in cases where gas overpressure occurs. In some embodiments, System 3800 utilizes electrodes having a diameter of 5 / 16 inch or 8 mm. The conduit may have an outer diameter of 1 / 8 inch (approximately 3 mm).

[0178]

[0242] In System 3800, two brass electrodes with O-ring grooves are inserted into a quartz tube that is compressed by tightly winding a compression spring to resist outward pressure forces. One electrode is hollow, and a PTFE tube is inserted to provide a smooth, continuous exit passage. A reducing swagelok fitting provides a pressure and vacuum airtight seal to the PTFE tube exiting the electrode without a joint. System 3800 can withstand tens of atmospheres. Generally, with respect to pressure, the limiting elements are the quartz tube and how strong the spring can be to prevent breakage. The twin-screw support frame is also expected to be robust enough to withstand the thrust when the sample is pressurized or when pressure is generated by flashing. The quartz tube can be replaced with any non-conductive tube, and cross-linked polyethylene has also been used, as the temperature reached in the tube is generally less than 250°C in less than 1 second. Although not shown in Figure 38, a motor drive may be added and utilized. Furthermore, because the system is completely sealed, it does not require an external vacuum chamber surrounding the flash assembly.

[0179]

[0243] When short-duration flashes are used, a rubber bushing between the nut and the support frame may be useful for shock absorption.

[0244] System 3800 can be sealed with O-rings. Silicone O-rings are heat-resistant and will not melt even when overheated, but they tend to harden, so the seals should be maintained. Normally, hot gases cannot pass through the O-rings, so the O-rings do not overheat. Discoloration was observed in the first O-ring, but the double O-rings maintained their seal.

[0180]

[0245] System 3800 may be completely degassed and is expected to maintain pressure as the gas exits into a heavy-walled glass pressure tube after flushing of sample 3813. In some embodiments, right-angle fittings may be used so that the exhaust of the gas does not interfere with the electrode end connections. However, a straight outlet tube is generally preferred when particulate or nanoparticles are being discharged. System 3800 shows a straight, continuous conduit 3814 (PTFE outlet tube), and the wire is connected to the ring with threaded brass electrodes 3808a-3808b.

[0181]

[0246] System 3800 utilizes a twin-screw relay, which provides consistent electrode alignment. In the case of a single-screw relay, it was found that when pressure or force was applied, the electrode angle was upward, followed by distortion in the quartz tube 3809. The twin screws are connected by a timing sprocket and belt 3801 for simultaneous thrust, and can be driven either manually or with a stepper motor.

[0182]

[0247] As in the case of vacuum and gas supply, the tubular material extending from the end of the hollow electrode can be connected via valves to vacuum 3823, gas supply 3824, and pressure gauge 2925. The gas supply may be inert or may be used to impregnate the sample with reagents such as hydrogen, methane, or other reactants such as halocarbons, ammonia, or boron compounds. These can be added to porous carbon / graphene in subsequent flushes.

[0183]

[0248] The pressure release can be preset according to the system 3800. An adjustable pressure relief valve 3817 determines the target pressure for the sample 3813. The cell may be sufficiently pressurized before flushing, or it may be flushed to produce high pressure. The release pressure can be set by a spring and threaded cover on the valve, and when the pressure exceeds the set force of the spring, the valve opens and the gas enters a gas collector that has been previously degassed. The gas may then be analyzed or simply pumped out. The pressure gauge 3826 and the volume of the gas collector 3818 provide information regarding the total gas yield. In case of excess gas production, the gas collector 3818 also has a pressure relief valve 3821 connected to a vent 3820.

[0184]

[0249] Similar to the effects of the wide range of pressures available with System 3800, the effects of various pressures on flash yield were evaluated using a sealed flash chamber and an adjustable relief valve. Due to the pressure, volatile additives may be incorporated into the sample and are not expected to volatilize until the relief valve is opened.

[0185]

[0250] System 3800 can be used for various particle / metal collection methods. For example, if it is desirable to collect fine particles, the PTFE tube can be inserted straight into the particle collection device 3816 (i.e., a test tube impactor) without bending. This is expected to be inside a larger degassed container (not shown), where the propulsion of the particles will cause them to adhere to the tube, while non-agglutinating gases can be removed by pumping. This can be used to collect volatile metals and metallic compounds, such metals and metallic compounds which, when cooled, will agglutinate and form nanoparticles that adhere to the particle collection device 3816.

[0186]

[0251] This design can be modified or altered as needed, depending on the intended use, by changing materials or modifying the design itself.

[0252] The costs and benefits of FJH treatment were evaluated because economic incentives are the primary driving force for waste recycling. [Awasthi 2019]. FJH is a highly efficient heating process due to its ultrafast heating / cooling rates, direct sample heating characteristics, and short reaction duration compared to conventional melting furnaces, which use large amounts of energy to maintain the temperature throughout the chamber. [Khaliq 2014]. The FJH method consumes approximately 939 kWh / ton of energy, which is about 1 / 500th the energy consumption of an experimental-scale tubular furnace [Balaji 2020] and about 1 / 80th the energy consumption of a commercially used Kaldo furnace on an industrial scale [Theo 1998]. Thus, the FJH process for electronic waste treatment has advantages over conventional dry metallurgy methods.

[0187]

[0253] The FJH process is scalable. According to analyses performed, the FJH voltage and / or capacitance of the capacitor bank may be increased when scaling up the sample mass. Figures 39A–39D show the scale-up of the flash Joule heating (FJH) process. Figure 39A is a photograph of samples treated under the following conditions: m0=0.2g, V0=150V, and C0=0.06F (sample 3901), m1=2g, V1=150V, and C1=0.6F (sample 3902), and m2=4g, V2=300V, and C2=0.6F (sample 3903). Figures 39B–30D are real-time temperature curves for samples 3901–3903, respectively.

[0188]

[0254] Figure 40A shows a scheme of a continuous flash Joule heating (FJH) reactor 4000, which has a continuous feed 4001 (e.g., electronic waste and carbon black), Cu electrodes 4002-4003 (including Cu electrodes with holes), porous electrode 4004, graphite electrode 4005, O-ring 4006, and partition wall 4007. Volatile components may be sent to a collection system 3108 for collection using a cooling trap, and non-volatile components can be collected in a collection device 4009.

[0189]

[0255] Figure 40B shows a scheme of a continuous flash Joule heating (FJH) reactor 4020 having a continuous feed of feed material 4021 (e.g., electronic waste and carbon black) flowing from bin 4022. In step 4031, the feed material 4021 is filled into chamber 4023 on a conveyor belt 4024. In step 4032, the feed material 4021 in chamber 4023 is compressed to a predetermined resistance (using a compressor 4025). In step 4033, the feed material 4021 then undergoes an FJH reaction using an FJH system 4026 having a Cu electrode 4027 and a graphite electrode 4028. In step 4034, the product 4034 then is removed from a collection device 4029.

[0190]

[0256] The schemes for supplying electronic waste and carbon fragments are shown in Figures 40A-40B, but these can also be used for other materials utilized in the FJH reaction.

[0257] Through the use of the FJH setup and integrated automation system, a production rate of >10 kg / day has already been achieved.

[0191]

[0258] Therefore, for metal recovery from electronic waste, the present invention provides, among many, the following: (i) flash joule heating is a dry process that does not use any solvents and is therefore considered environmentally friendly; (ii) flash joule heating can recover most of the metallic elements in the waste in one step, which is difficult to achieve by other methods; (iii) the flash joule heating process is also expected to remove almost all harmful materials in the waste and therefore not cause secondary contamination; and (iv) the flash joule heating process uses far less electrical energy than a furnace because the heating duration is short and only a small amount of energy escapes from the sample being flash joule heated.

[0192]

[0259] Precious metals recovered from electronic waste are extremely important raw materials for various industries. In fact, such metal mixtures are very useful, as many mining companies have already introduced automated systems for separating base metals.

[0193]

[0260] Furthermore, the recovery process removes harmful materials such as heavy metals from the waste, which is important in solving the environmental problems caused by this waste. Ore, fly ash, and bauxite residue (red mud)

[0261] A situation similar to that of electronic waste is equally relevant to ore, fly ash, and bauxite residue (recently referred to as bauxite residue), because rare earth elements (REEs) are strategic resources in the modern electronics, clean energy, and automotive industries. Therefore, the methods and systems described above can also be implemented for the recovery of metals from ore, fly ash, and bauxite residue (bauxite residue).

[0194]

[0262] Embodiments of the present invention include an ultrafast electrothermal process (FJH) based on flash Joule heating for activating ore, fly ash, and red mud to improve the acid extraction rate of REE using a mild acid such as 0.1 M HCl. A pulsed voltage raises the raw material to a temperature of approximately 3000°C in seconds, causing the thermal decomposition of REE phosphates, which are difficult to dissolve in CFA, into highly soluble REE oxides, and the carbonthermal reduction of REE components into highly reactive REE metals. The activation process allows for an increase in REE recovery yield to approximately 206% for Class F CFA (CFA-F) and approximately 187% for Class C CFA (CFA-C) compared to directly leaching the raw material with more concentrated acid. Activation strategies for various secondary wastes are feasible, as demonstrated with coal fly ash (CFA) and red mud (bauxite residue (BR)). The high-speed FJH process is scalable and highly energy-efficient with low electrical energy consumption (e.g., 600 kWh / ton or $12 / ton), enabling profit margins of more than 10 times.

[0195] FJH Systems and Processes

[0263] The available FJH systems are similar to those described and discussed above. For example, Figure 41A shows an electrical circuit diagram of an FJH system that can be used for fly ash (this is similar to the FJH systems described above, such as those shown in Figures 6A, 13A, and 30).

[0196]

[0264] In a typical experiment, secondary waste (CFA, BR) was mixed with carbon black in a predetermined mass ratio (e.g., 2:1) using a ball mill (MSE supplies, PWV1~0.4L). The carbon black acted as a conductive additive. 200 mg of the mixture (133 mg of waste and 67 mg of CB) was added to a quartz tube (8 mm inner diameter and 12 mm outer diameter). Resistance was controlled by compressing the two electrodes. The sample was packed into a jig (Figures 41B~41C), and the electrodes were connected to a capacitor bank. In this embodiment, ten aluminum electrolytic capacitors (450V, 6 mF, Mauser #80-80-PEH200YX460BQU2) were used for charging, and a capacitor bank with a total capacitance of 60 mF was charged by a DC power supply. Discharge time was controlled using a relay with a programmable ms-level relay. Table XI reflects the detailed parameters of some of the secondary waste used. After FJH, the samples were rapidly cooled to room temperature.

[0197] [Table 11]

[0198] Acid-extractable REE content in CFA

[0265] There are two types of CFA classified by their chemical composition: CFA-F has a total content of >70 wt% SiO2, Al2O3, and Fe2O3, while CFA-C has a higher amount of CaO. [Liu 2019]. In the examples evaluated herein, both CFA-F and CFA-C were collected from the Appalachian Basin (App) and Powder River Basin (PRB) in the United States, respectively. [Taggart 2016]. Figure 42 shows photographs of CFA-C 4201 and CFA-F 4202 (scale bar, 4 cm).

[0199]

[0266] CFA is composed of a primary amorphous phase (60–90%) [Zhang 2020], with the remainder of the crystalline material consisting mainly of quartz and mullite, as shown by the X-ray diffraction pattern (XRD) (Figure 43A). In addition to the enrichment of Ca in CFA-C, elemental analysis by X-ray photoelectron spectroscopy (XPS) (Figure 43B) and energy-dispersive X-ray spectroscopy (EDS) showed a high C content in CFA-F, which may have been caused by the incomplete combustion of the coal feed. The high C content in CFA-F was also evident by thermogravimetric analysis (TGA) from a large weight loss at approximately 700°C.

[0200]

[0267] The total amount of REE in CFA was quantified using the HF:HNO3 digestion method. [Taggart 2016]. The total REE content is c totalThe (CFA raw material) content was 516±48 mg / kg for CFA-F and 418±71 mg / kg for CFA-C. Figure 43C. CFA from App had a higher REE content than that from PRB, consistent with Taggart 2016. The acid-extractable REE content c0 (CFA raw material), which is the REE content from the CFA raw material, was measured using 1M HCl or 15M HNO3 [Taggart 2016; Middleton 2020]. For CFA-F, the HNO3 and HCl-extractable REE content was 144±32 mg / kg and 160±50 mg / kg, respectively (Figure 43C), which corresponded to REE extraction rates (Y0) of approximately 28% and 31%, respectively. In the case of CFA-C, the REE extractable content for HNO3 and HCl was 246±71 mg / kg and 231±81 mg / kg, respectively (Figure 43C), which corresponded to REE extraction rates of approximately 59% and 55%, respectively. It was concluded that the effect of acid concentrations above 1 M on REE leaching was limited. Therefore, a standard protocol for subsequent evaluation utilized leaching with 1 M HCl.

[0201]

[0268] The acid extraction rate of REE from CFA-C was higher than that from CFA-F. This is consistent with [Liu 2019], and the higher extraction rate is thought to be due to a higher content of readily soluble REE species, such as REE oxides, in CFA-C. Morphological images of CFA-F by scanning electron microscopy (SEM) are shown in Figure 43D, and the high carbon content may hinder the accessibility of the acid aqueous solution to the REE-containing species, resulting in a lower extraction rate ranging from 21% to 42% per individual REE, Figure 43E. In contrast, CFA-C consists of fine, uncoated spherical particles (Figure 43F), which is favorable for the acid leaching process, resulting in a relatively higher extraction rate ranging from 33% to 67% per individual REE (Figure 43G).

[0202] Improvement of REE recovery yield from CFA through electrothermal activation

[0269] In the electrothermal activation process using FJH, the CFA raw material was first mixed with carbon black (CB), which acted as a conductive additive. The mixture of CFA and CB (approximately 30% CB) was packed inside a quartz tube between two graphite electrodes. Figures 41A and 44A. The resistance (R) of the sample was adjustable by adjusting the compressive force between the two electrodes connected to a 60 mF capacitance bank. The sample was heated by high-voltage discharge of the capacitor. Table XI shows the detailed experimental parameters.

[0203]

[0270] In a typical discharge process with a 120V FJH voltage, a 1Ω resistor, and a discharge time (t) of 1 second, the current curve passing through the sample was recorded using a peak current of approximately 120A followed by a current plateau at approximately 7A (Figure 44B). The corresponding real-time temperature curve shows a peak temperature up to approximately 3000°C, followed by stable heating at approximately 1150°C (Figure 44C). The solid obtained after FJH is called activated CFA (Figure 45). (Fluid table showing REE recovery from CFA4501 to activated CFA4503 from synthesized CFA+CB4502 (via FJH)). The acid-leached REE content from activated CFA (c(activated CFA)) was measured by a leaching procedure with 1M HCl. The REE recovery yield (Y) from activated CFA was calculated and compared to the recovery yield (Y0) of the CFA raw material.

[0204]

[0271] A series of FJH voltages in the range of 50V to 150V were applied (Figure 44D). At approximately 120V, the HCl-elutable content of total REE from activated CFA-F (1M HCl, 85°C) improved to 329±14 mg / kg (Figure 44D). This corresponds to a recovered yield of approximately 64% Y, representing an increase to approximately 206% (approximately 31% Y0), exceeding the recovered yield of CFA-F raw material. The kinetics of pH-dependent leaching of REE from CFA-F raw material and activated CFA-F were investigated (Figure 44E; curves 4401-4402 represent CFA-F raw material and activated CFA-F, respectively). Generally, yields decreased as acid pH increased. Surprisingly, the REE recovery yield from activated CFA-F remained at approximately 45% Y at pH 2 (or 0.01 M HCl), which was significantly higher than that of the CFA raw material, even under higher acid concentrations (approximately 31% Y0 at pH 0), compared to the same leaching conditions (approximately 9% Y0 at pH 2).

[0205]

[0272] In the case of CFA-C, when the acid leaching of REE from activated CFA-C was measured under optimized FJH conditions, using an HCl leaching procedure (1M HCl, 85°C), the Y was approximately 103% (Figure 44F, curves 4403-4404 represent CFA-F raw material and activated CFA-F, respectively), which corresponds to approximately 187% of that from CFA-C raw material (approximately 55% Y0).

[0206]

[0273] Even with the use of dilute acid (pH 1, 0.1M HCl), the REE recovery yield from activated CFA-C remained at approximately 94% Y0, which is significantly higher than that of CFA-C raw material (approximately 54% Y0). This is expected to make wastewater streams more manageable.

[0207]

[0274] For individual REEs, using the FJH activation process, acid leaching was improved in the range of 170%–230% for CFA-F (Figure 44G) and 170%–210% for CFA-C (Figure 44H) using the same leaching procedure (1M HCl, 85°C). Similar improvements were achieved using dilute acid leaching (0.1M HCl, 85°C). Since no significant deviations were observed between REEs, it is demonstrated that the FJH activation process works largely similarly for all REEs.

[0208]

[0275] As a control, the REE content in carbon black was measured using the same digestion method. The total REE content in carbon black was approximately 5 mg / kg, which was equivalent to about 1% of the REE content in CFA. Therefore, the use of carbon black does not introduce significant error into these measurements. In practical applications, carbon black can be replaced with anthracite or any other inexpensive source of weakly conductive carbon, but the REE content in the source should be taken into account in yield calculations.

[0209] Mechanism of improved REE extraction rate

[0276] The mechanism of improved REE leaching by an electrothermal activation process was investigated. REE species formation and distribution in CFA determine the REE extraction rate. REE phosphates such as monazite and xenotime are among the main counterions of REE in coal. [Liu 2019; Stuckman 2018]. REE phosphates are relatively stable components and do not melt or thermally dissociate in air up to approximately 2000°C. [Ushakov 2001; Hikichi 1987]. Coal flame combustion temperatures are typically in the range of 1300°C to 1700°C. [Stuckman 2018]. As a result, a trace phase containing REE such as monazite and xenotime remains in the CFA. [Kolker 2017; Smolka-Danielowska 2010]. REE may also be partitioned and encapsulated in the glass fraction of CFA by diffusion into a molten material (e.g., aluminosilicate) formed at coal boiler temperatures [Dai 2014]. Such difficult-to-dissolve REE phosphates and glass phases are detrimental to REE extraction [Liu 2019], while REE oxides and carbonates in CFA are relatively easier to extract than by acid leaching.

[0210]

[0277] The high temperature of approximately 3000°C generated by the FJH process is significantly higher than the temperature of a coal boiler, allowing for the thermal decomposition of REE species. Lanthanum phosphate (LaPO4) and yttrium phosphate (YPO4) were used as representative examples of REE phosphates. As shown in Figure 46A, the La2O3 phase was observed after FJH of the LaPO4 precursor. Similarly, YPO4 was thermally decomposed to Y2O3 after the FJH process. Figure 46B. REE oxides are found in the log of REE phosphates (-27 to -24). 10 K sp ) has a considerably higher solubility (5-33 log 10 K sp ). Please refer to Table XII.

[0211] [Table 12]

[0212]

[0278] To provide further insights into the solubility of REE phosphates and oxides, dissolution curves as a function of pH were calculated in Figure 46C (curves 4601–4604 represent La2O3, Y2O3, LaPO4, and YPO4, respectively). It was found that LaPO4 and YPO4 showed significant solubility only when the pH approached 0, while their oxide counterparts dissolved readily at low acidity levels of around pH 6. This partially explains the pH-dependent dynamics of REE leaching, where higher REE leaching is achieved with activated CFA than with raw materials using dilute acids, as shown in Figures 46E–46F. (In the case of Figure 46E, the Si signal may be from the quartz tube in FJH).

[0213]

[0279] In addition to the thermal decomposition of REE phosphates, ultra-high temperatures can also initiate the thermal reduction of REE compounds. According to the Ellingham diagram (Figure 46D), the carbonothermal reduction temperature of REE oxides is estimated to be between approximately 1900°C (for Eu2O3) and approximately 2500°C (for Dy2O3). FJH at approximately 120V generates temperatures up to approximately 3000°C (Figure 44C), which allows for the reduction of REE oxides.

[0214]

[0280] Y2O3 and La2O3 were used as representative examples to verify the carbonothermal reduction of REE oxides by the FJH process. The fitting of the XPS fine spectrum of Y2O3 after FJH shows four peaks. Figure 46E and Table XIII. The peaks at 157.5 and 159.6 eV are the 3d Y in Y2O3. 5 / 2 and 3D 3 / 2 Assigned to [Barreca 2001], the peaks at 156.4 and 158.5 eV are the 3d of Y at Y(0). 5 / 2 and 3D 3 / 2 [Cole 2020] will be assigned to [Cole 2020].

[0215] [Table 13]

[0216]

[0281] XPS analysis demonstrated the reduction of Y2O3 to Y metal by the FJH process, although a small proportion of Y2O3 may have been due to surface oxidation. Similarly, fitting of XPS fine spectra of La2O3 precursor and La2O3 after FJH (Figure 46F, Table XIII) verifies the reduction of La2O3 to La metal [Deasha 1995; Li 2019]. Reduced REE species in low oxidation states are highly reactive materials that readily react even with pure water [Greenwood 1997]. The calculated Gibbs free energy change (ΔG) values ​​for the REE metal dissolution reaction are far more negative than those for REE oxides (Figure 46G, Table XII), demonstrating the much greater thermodynamic solubility of REE metals than that of their oxide counterparts.

[0217]

[0282] This suggests that the temperatures required for thermal activation are >2000°C for the thermal decomposition of REE phosphate and >2500°C for the carbothermal reduction of REE oxide, which also provides insight into voltage-dependent REE leaching. Figure 44D. An FJH voltage of ≥120V may be necessary to achieve a temperature of >2000°C, while voltages <100V may have limited their effect on REE leaching. Nevertheless, FJH voltages that are too high, such as ≥150V, may result in prolonged high temperatures >3000°C, which in turn may cause evaporation losses of REE during the FJH process.

[0218]

[0283] In addition to seed formation, REE distribution also affects extraction rates, and REE encapsulated in or distributed across the glass phase is difficult to dissolve. [Liu 2019]. FJH is ultrafast heating and rapid cooling (>10 4 Allowing a temperature of K / sec (Figure 44C) is expected to induce thermal stress and cracking of the glass phase in CFA, thus contributing to improved leaching.

[0219] An overview of electrothermal activation processes

[0284] The electrothermal activation process is applicable to other wastes for REE recovery, such as BR [Deady 2016; Rivera 2018; Reid 2017] and electronic waste (including those discussed above) [Maroufi 2018; Deshmane 2020; Peelman 2018].

[0220]

[0285] BR (Red Mud) is a waste product of the Bayer Act for alumina production. BR is one of the most abundant industrial wastes, with 3 billion tons already stored in waste ponds, an additional 150 million tons produced annually, and currently only 3% recycled [Service 2020]. BR contains significant amounts of REE; for example, a total REE content of approximately 1000 ppm is found in BR from Mytilineos' "Aluminum of Greece" [Deady 2016]. BR is a dry powder with fine particle size and its main components include Fe2O3, CaCO3, FeO(OH), and SiO2. Figures 47A-47B. 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. Figures 47C and 48A-48B.

[0221]

[0286] Similar to CFA, the REE extraction rate of BR after the electrothermal activation process also depends on the FJH voltage. Figure 48A. At an optimized FJH voltage of 120V, the extractable REE content increased to 757±30 mg / kg (Figure 48B), which corresponds to approximately 177% of the Y / Y0 of that from the BR raw material (Figure 47C). The mechanism of improvement in REE extraction rate from BR by the FJH process is presumed to be similar to that of CFA, since phosphate is one of the dominant counterions for BR (Figures 46A-46G). [Boni 2013].

[0222]

[0287] This FJH strategy is also applied to revitalize electronic waste, and is presented herein as a complement to the described method which does not use slow acid leaching. More than 40 million tons of electronic waste are produced worldwide each year for the rapid upgrade of personal electronic devices, and less than 20% is recycled. [Zeng 2018]. REE is widely used in electronic devices as permanent magnets [Deshmane] and capacitors [Alam 2012]. Similarly, the recovery of REE from high-grade electronic waste has its economic viability compared to the extraction of REE from ore.

[0223]

[0288] The electronic waste used in this FJH process was printed circuit boards (PCBs) from discarded computers. Figure 49A shows the electronic waste glided into powder. As shown in Figure 49B, the abundant metals in the electronic waste include Cu and Al, which are primarily used as interconnects. REE was extracted from the PCB waste by a 1M HCl leaching process at 85°C. The acid-leached REE content from the electronic waste raw material was 61±4 mg / kg. Figures 50A-50B. After the activation process at an optimized voltage (Figures 50A-50B), the extractable REE content increased to 94.6±0.2 mg / kg, which corresponds to approximately 156% of the Y / YO from the electronic waste raw material. Figures 49C and 50A-50B.

[0224]

[0289] Unlike CFA or BR, REE species in electronic waste are typically in the form of readily soluble REE metals or oxides. [Alam 2012] However, REE is usually embedded in the matrix material due to the laminated structure of electronics, which can hinder REE extraction by wet metallurgical processes. The FJH process can expose the metal by fracturing the matrix, accelerating the leaching rate and the degree of metal extraction.

[0225] Scalability and usefulness

[0290] The FJH process for REE recovery is scalable. To maintain a constant temperature, the FJH voltage or the total capacitance of the capacitor bank can be increased when scaling up the sample mass per batch. Production rates of >10 kg / day by batch processes have already been achieved. The FJH process can also be integrated into a continuous production system for further automation by using the scheme shown in Figures 40A-40B, for example. Commercial expansion of the FJH process to several tons per day on a continuous basis paves the way for future large-scale REE recovery from waste.

[0226]

[0291] Economically, what often drives recycling is profit margins. Due to its direct sample heating characteristics, short duration, and rapid heating / cooling rates, embodiments of the FJH process are highly energy-efficient with low electrical energy consumption of 600 kWh / ton or $12 / ton, enabling profit margins more than 10 times higher compared to directly leaching raw materials.

[0227]

[0292] For further refinement, it is necessary to remove and subsequently separate dissolved impurities, mainly Al, Si, Fe, Ca, and Mg, from the REE-containing leachate. In most cases, the ratio of REE to impurities in the leachate (c(REE) / c(impurities)) was observed to improve with the FJH process, indicating that the FJH process is also beneficial for subsequent REE separation.

[0228] ore

[0293] Since monazite, (Ce,La,Y,Th)PO4, and xenotime, YPO4 are the primary commercial sources for REE production [Cheisson 2019], embodiments for REE mining can also be used to improve leaching from REE ore. Commercially, alkaline digestion (70% NaOH, 140-150°C) is the primary leaching technique for monazite [Peelman 2016], or acid baking (concentrated H2SO4, 200°C) is the primary leaching technique for monazite and xenotime [Kim 2016]. This FJH process may be faster or slower depending on the use of concentrated bases and acids. Since the REE mixture obtained by FJH is often less contaminated than that produced through conventional mining methods, existing individual element separation techniques, such as solvent extraction and ion exchange [Xie 2014], can be utilized in conjunction with it.

[0229]

[0294] While embodiments of the present invention have been shown and described, those skilled in the art can modify them without departing from the essence and teachings of the invention. The embodiments described and the examples provided herein are merely illustrative and not intended to limit. Many variations and modifications of the invention disclosed herein are possible and within the scope of the invention. The scope of protection is not limited by the foregoing description but is limited only by the claims set forth below, the scope of which includes all equivalents of the subject matter of the claims.

[0230]

[0295] All patents, patent applications, and publications cited herein are incorporated herein by reference in their entirety to the extent that they provide exemplary, procedural, or other details that supplement those described herein.

[0231]

[0296] Quantitative and other numerical data may be presented in the form of ranges as described herein. Such ranges, which are expected to be understood as being used merely for convenience and brevity, should be interpreted flexibly to include not only the numbers explicitly listed as range limits, but also all individual numbers or subranges within that range, as if each number and subrange were explicitly listed. For example, a numerical range from approximately 1 to approximately 4.5 should be interpreted to include not only the explicitly listed limits from 1 to approximately 4.5, but also individual numbers, e.g., 2, 3, 4, and subranges, e.g., 1 to 3, 2 to 4, etc. The same principle applies to ranges that list only one number, such as "less than approximately 4.5," which should be interpreted to include all the values ​​and ranges listed above. Furthermore, such interpretations should apply regardless of the width or characteristics of the range described.

[0232]

[0297] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the subject matter of this disclosure. Any methods, devices, and materials similar to or equivalent to those described herein may be used in carrying out or testing the subject matter of this disclosure, but representative methods, devices, and materials are described herein.

[0233]

[0298] In accordance with long-standing patent law practice, the terms “one (a)” and “one (an)” mean “one or more” when used in this application, including the claims.

[0234]

[0299] Unless otherwise specified, all numerical values ​​representing quantities of components, reaction conditions, etc., used in the specification and claims shall be understood in all examples to be modified with the term “approximately.” Therefore, unless otherwise indicated, the numerical parameters described herein and in the appended claims are approximations, which may vary depending on the desired properties to be achieved by the subject matter of this disclosure.

[0235]

[0300] Where used herein, the terms “about” and “substantially” mean, when spoken of in terms of a value, or in terms of a quantity of mass, weight, time, volume, concentration, or percentage, to include variations of ±20%, ±10%, ±5%, ±1%, ±0.5%, and ±0.1% from the specified quantity, in some embodiments, to be appropriate for carrying out the disclosed method.

[0236]

[0301] As used herein, the terms “substantially perpendicular” and “substantially parallel” mean, in some embodiments, a variation of ±10° in the perpendicular and parallel directions, in some embodiments, a variation of ±5° in the perpendicular and parallel directions, in some embodiments, a variation of ±1° in the perpendicular and parallel directions, and in some embodiments, a variation of ±0.5° in the perpendicular and parallel directions.

[0237]

[0302] As used herein, the term "and / or," when used in the context of enumerating entities, means that the entities may exist individually or in combination. Thus, for example, the phrase "A, B, C, and / or D" includes not only A, B, C, and D individually, but also every possible combination and subcombination of A, B, C, and D. [1] A method for recovering metal, (a) A step of mixing a material with a conductive additive to form a mixture, wherein the material is prepared from ore, fly ash, and / or bauxite residue; (b) A step of applying a voltage to the mixture to recover the metal from the material, where, (i) The voltage is applied in one or more voltage pulses, (ii) The duration of each of the one or more voltage pulses shall be over the duration of the duration; and (c) A step of collecting the recovered metal, wherein the recovery and collection of the metal includes applying a voltage to the mixture and then performing a leaching process; The above method, including. [2] The method according to [1], wherein the conductive additive is a carbon source. [3] The method according to [1], wherein the material is prepared from ore. [4] The method according to [1], wherein the material is prepared from fly ash. [5] The method according to [1], wherein the material is prepared from bauxite residue. [6] The method according to [1], wherein the material is prepared by performing a mechanical process to convert the material into a fine powder. [7] The method according to [6], wherein the mechanical process is selected from the group consisting of cutting the material into pieces, crushing the material, gliding the material, grinding the material, and combinations thereof. [8] The method according to [6], wherein the fine powder is a microscale fine powder. [9] The method according to [1], wherein the conductive additive is selected from the group consisting of elemental carbon, carbon black, graphene, flash graphene, coal, anthracite, coke, metallurgical coke, calcined coke, activated carbon, biochar, carbon from natural gas stripped of hydrogen atoms, activated carbon, shungite, plastic waste, carbon char derived from plastic waste, food waste, carbon char derived from food waste, biomass, carbon char derived from biomass, hydrocarbon gas, and mixtures thereof.

[10] The method according to [1], wherein the conductive additive is carbon black.

[11] The method according to [1], wherein the conductive additive is mainly elemental carbon.

[12] The method according to [1], wherein the material and the conductive additive are mixed in a weight ratio in the range of 1:2 to 25:1.

[13] The method according to [1], wherein the applied voltage is within the range of 15V to 300V.

[14] (a) The mass of the mixture to which the voltage is applied is greater than 1 kg; (b) The method according to [1], wherein the applied voltage is between 100V and 100,000V.

[15] The method according to

[14] , wherein the mass of the mixture to which the voltage is applied is greater than 100 kg.

[16] (a) The mass of the mixture to which the voltage is applied is greater than 1 kg; (b) The method according to [1], wherein the applied current is between 1,000 amp and 30,000 amp.

[17] The method according to

[16] , wherein the mass of the mixture to which the voltage is applied is greater than 100 kg.

[18] The method according to [1], wherein the mixture has a resistance in the range of 0.1 ohms to 25 ohms when a voltage is applied.

[19] The method according to [1], wherein the duration of each of the one or more voltage pulses is between 1 microsecond and 25 seconds.

[20] The method according to [1], wherein the duration of each of the one or more voltage pulses is between 1 microsecond and 10 seconds. [twenty one] The method according to [1], wherein the duration of each of the one or more voltage pulses is between 1 microsecond and 1 second. [twenty two] The method according to [1], wherein the duration of each of the aforementioned one or voltage pulses is between 100 microseconds and 500 microseconds. [twenty three] The method according to [1], wherein the one or more voltage pulses are between two voltage pulses and 100 voltage pulses. [twenty four] The method according to [1], wherein the voltage pulse is performed using direct current (DC). [twenty five] The method described in [1], which is performed using a pulsed direct current (PDC) Joule heating process.

[26] The method according to [1], wherein the voltage pulse is performed using alternating current (AC).

[27] The method according to [1], wherein the voltage pulse is performed by using both direct current (DC) and alternating current.

[28] The method described in

[27] , wherein the use of direct current (DC) and alternating current (AC) is switched alternately.

[29] The method described in

[27] , wherein direct current (DC) and alternating current (AC) are used simultaneously.

[30] The method according to [1], wherein the one or more voltage pulses increase the temperature of the mixture to at least 3000K.

[31] The method according to [1], wherein the metal comprises a rare earth element.

[32] The method according to [1], wherein the metal includes a precious metal.

[33] (a) The material includes a metal oxide; (b) The method according to [1], wherein applying a voltage to the mixture brings about a carbonothermal reaction of the metal oxide and recovers the metal.

[34] The method according to [1], wherein the application of the voltage to the mixture for recovering the metal from the material is performed at a pressure of 0.001 to 25 atmospheres.

[35] The method according to

[34] , wherein the pressure is approximately 1 atmosphere.

[36] The method according to

[34] , wherein the pressure is at least 2 atmospheres.

[37] The method according to

[34] , wherein the pressure is at least 10 atmospheres.

[38] The method according to

[34] , wherein the pressure is at least 20 atmospheres.

[39] The method described in

[34] , which is performed using a pressurized cell.

[40] The method according to

[39] , wherein the application of the voltage to the mixture for recovering the metal from the material causes the majority of the metal to remain in the graphene produced by the method.

[41] The method according to

[40] , wherein the collection of the recovered metal is further comprising separating the metal from the graphene.

[42] The method according to [1], wherein the collecting step comprises collecting a gas stream containing volatile products produced by applying the voltage to the mixture.

[43] The method according to

[42] , wherein the collecting step further comprises cooling the gas stream.

[44] The method according to [1], wherein the leaching of the metal in the mixture after applying voltage to the mixture is greater than twice the leached content of the metal in the mixture before applying voltage to the mixture, when the aqueous treatment is carried out using the same pH and the same volume.

[45] The method according to [1], wherein the leaching process is carried out using a dilute acid.

[46] The method according to

[45] , wherein the dilute acid is at most 1 M of the acid.

[47] The method according to

[45] , wherein the dilute acid is the acid at a maximum of 0.1 M.

[48] The method according to

[45] , wherein the dilute acid is at least 1 M of the acid.

[49] The method according to [1], wherein the method is performed in a continuous process or an automated process.

[50] A system for performing a method for recovering metals using at least one of the methods described in any one of items [1] to

[49] , (a) A source of a mixture containing materials and conductive additives; (b) A cell into which the mixture can be poured and held under compression, operably connected to the source; (c) Electrodes operably connected to the pressure cell; and (d) A flash power supply for the process of applying voltage to the mixture to recover metal from the material; The above system, including.

[51] The system performs a method for recovering metal using at least one of the methods described in any one of

[34] to

[41] , and the system (a) A pressure cell, a cell; and (b) A gas supply for pressurizing the pressure cell; The system described in

[50] further includes the following:

[52] The system according to

[51] further includes an adjustable relief valve.

[53] The system according to

[51] further includes a particle collection device.

[54] The system according to

[51] further includes a gas collection device.

[55] The system described in

[50] , which can perform a continuous process or an automated process.

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[0239] 101 Route (i) 102 Route (ii) Figure 7 701 PDC device 702 Resistant Hotspot Figure 18C 1801a~1801b Carbon paper 1802 pellets 1901 Fast heating 1902 Stable sintering 1903 Fast cooling 1911-1912 Sintered ceramic pellets 1913 Carbon paper Figure 22 2200 System 2201 Metal Evaporation Stage 2202 Material transport stage 2203 Condensation stage 2205 Capacitor Bank 2206 Porous Cu electrode 2207 Pump 2208 Cold Trap 2310 Insert Diagram Figure 29A 2901 Flash stage 2902 Power source 2903 Pump 2904 Cold Trap Figure 38 3800 Gas Collection System 3801 Timing sprocket and belt; 3802 Manual or motor-driven; 3803 Driver 3804 Power supply 3805 sample compression; 3806a~3806b Soft Spacer 3807a~3807b Nut 3808a electrode 3808b electrode 3809 tube 3810 Copper Wool 3811 Torsion spring compression 3812 Electrode 3813 samples 3814 Conduit 3815 Pressure seal 3816 Particle collection device; 3817 Adjustable pressure relief valve; 3818 Gas collection device; 3819 Flow to vacuum or gas analysis; 3820 Ventilation holes; 3821 Safety relief valve; 3822 Conduit (e.g., PFE pipe material); 3823 Flow into vacuum; 3824 Pressurized input from gas supply 3825~3826 Pressure gauge Figure 40A 4000 Continuous Flash Joule Heating (FJH) Reactors 4001 Continuous Feed 4002~4003 Cu electrode 4004 Porous electrode 4005 Graphite Electrode 4006 O-ring 4007 Bulkhead 3108 Collection System 4009 Collection device Figure 40B 4020 Continuous Flash Joule Heating (FJH) Reactor 4021 Supply materials 4022 bottles 4023 Chamber 4024 Conveyor Belt 4025 Compressor 4026 FJH System 4027 Cu electrode 4028 Graphite Electrode 4029 Collection device 4031~4034 Process

Claims

1. A method for recovering metals containing precious metals and / or rare earth elements using flash Joule heating, (a) A step of mixing a material with a conductive additive to form a mixture, wherein the material is prepared from ore, fly ash, and / or bauxite residue; (b) A step of recovering metals containing noble metals and / or rare earth elements from the material by utilizing flash Joule heating, which includes applying a voltage to the mixture, (i) The voltage is applied in one or more voltage pulses, (ii) The duration of each of the one or more voltage pulses is over the duration; and (c) A step of collecting the recovered metal, wherein the recovery and collection of the metal includes applying a voltage to the mixture and then performing a leaching process; The above method, including.

2. The method according to claim 1, wherein the material is prepared from ore.

3. The method according to claim 1, wherein the material is prepared from fly ash.

4. The method according to claim 1, wherein the material is prepared from bauxite residue.

5. The method according to claim 1, wherein the material is prepared by performing a mechanical process to convert the material into a fine powder.

6. The method according to claim 1, wherein the conductive additive is selected from the group consisting of elemental carbon, carbon black, graphene, flash graphene, coal, anthracite, coke, metallurgical coke, calcined coke, activated carbon, biochar, carbon from natural gas from which hydrogen atoms have been stripped, activated carbon, shungite, plastic waste, carbon char derived from plastic waste, food waste, carbon char derived from food waste, biomass, carbon char derived from biomass, hydrocarbon gas, and mixtures thereof.

7. The method according to claim 1, wherein the material and the conductive additive are mixed in a weight ratio in the range of 1:2 to 25:

1.

8. The method according to claim 1, wherein the mass of the mixture to which the voltage is applied is greater than 1 kg; and the applied current is between 1,000 amp and 30,000 amp.

9. The method according to claim 1, wherein the metal includes a rare earth element.

10. The method according to claim 1, wherein the metal includes a precious metal.

11. The method according to claim 1, wherein the material comprises a metal oxide; and applying a voltage to the mixture brings about a carbon-thermal reaction of the metal oxide, thereby recovering the metal.

12. The application of the voltage to the mixture for recovering the metal from the material is performed at a pressure of 0.001 to 25 atmospheres; It is performed using a pressurized cell; By applying the voltage to the mixture for recovering the metal from the material, the majority of the metal remains in the graphene produced by the method; further, The method according to claim 1, wherein the collection of the recovered metal includes separating the metal from the graphene.

13. The method according to claim 1, wherein the collecting step includes collecting a gas stream containing volatile products produced by applying the voltage to the mixture.

14. The method according to claim 1, wherein the leaching of the metal in the mixture after applying a voltage to the mixture is greater than twice the leached content of the metal in the mixture before applying a voltage to the mixture, when the treatment is carried out using the same pH and the same volume of aqueous treatment.

15. A system for carrying out a metal recovery method using the method described in claim 1, A source of a mixture containing materials and conductive additives; A cell operably connected to the source, which can receive the mixture and hold the mixture under compression; Electrodes operably connected to a pressure cell; and A flash power supply for the process of applying voltage to the mixture to recover metal from the material; The system comprises a material derived from ore, fly ash, and / or bauxite residue, and in which metals, including precious metals and / or rare earth elements, are recovered using flash Joule heating.

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