Ultrafast flash vaporization joule heating synthesis method and system for implementing the same

Abstract

Ultrafast flash evaporation joule heating synthesis methods and systems, and more particularly, ultrafast synthesis methods for recovering precious and other metals from electronic waste (e-waste).

Description

[0001] This application claims priority to U.S. Patent Application Serial No. 63 / 082,592, filed September 24, 2020, entitled "Ultrafast Flash Joule Heating Synthesis Methods and Systems For Performing Same," which is jointly owned by the owners of this invention. The entire contents of this patent application are hereby incorporated by reference. Technical Field

[0002] This invention relates to an ultrafast flash joule heating synthesis method and system, and more particularly to an ultrafast synthesis method for recovering precious metals and other metals from electronic waste. Background Technology

[0003] Efficient and low-cost synthesis of nanomaterials is a prerequisite for their commercial application.

[0004] carbide

[0005] Nanoscale transition metal carbides (TMCs) have been widely used as precursors for superhard and superstrong ceramics [Zou 2013; Zhang 2019; Reddy 2012], high-performance electrochemical catalysts (due to their platinum-like electronic structure) [Li 2018; Zhong 2016; Gao 2019; Gong 2016; Han 2018], and catalyst supports (due to their strong metal-substrate interactions) [Lin 2017; Yao 2017]. Conventional methods for the synthesis of bulk carbides include carburizing of metal precursors with gaseous carbon precursors or sintering of metal precursors with graphitic carbon at high temperatures [Rosa 1983]. These procedures can be problematic because they lead to coking of the carbide surface due to an excessive supply of carbon source, as well as large particle sizes and low surface areas detrimental to catalytic performance [Chen 2013; Zeng 2015].

[0006] Significant efforts have been devoted to the synthesis of carbides with fine particle sizes, including temperature-programmed reduction [Oyama 2992], carbothermic reduction of metal precursors [Wu 2020; Wang K 2019], laser-spray pyrolysis of metal complexes [Kolel-Veetil 2005], and solution-based precipitation and carburizing [Wan 2014]. The TPR method is general for the synthesis of high surface area metal carbides, but requires a well-optimized reaction window [Claridge 2000]. Carbothermic reduction of metal precursors in a furnace is common in the synthesis of TMCs [Wu 2020]; however, prolonged high-temperature conditions are necessary to compensate for the slow solid-solid reaction kinetics, which inevitably leads to sintering or agglomeration [Wang K 2019].

[0007] To avoid severe agglomeration, a microwave combustion method was developed for the rapid synthesis of Mo2C and WC nanodots within 2 minutes [Wan 2019]. The pyrolysis of metal complexes involves the use of expensive and toxic organometallic compounds, such as Cp2Mo2(CO)6 for the synthesis of Mo2C [Kolel-Veetil 2005; Wolden 2011] and W(CO)6 for the synthesis of WC [Pol 2009].

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

[0009] Recently, several unconventional electrothermal methods have been developed for high-efficiency high-temperature synthesis [Wang 2020; Giorgi 2018; Yan 2018]. Thermal shock (CTS) processes use short current pulses to synthesize high-entropy alloy nanoparticles on carbon supports at ~2000 K [Yan 2018]. Ultra-high temperature sintering (UHS) based on current induction heating has been proposed for sintering and screening ceramics within 10 seconds [Wang 2020]. Spark flash sintering (SPS) applies current for reactive carbothermal synthesis of zirconium carbide (ZrC) within 10 minutes [Giorgi 2018]. However, these methods target the sintering of bulk ceramics and lack the ability to synthesize fine nanocrystals.

[0010] Furthermore, phase and crystal surface structure play important roles in carbide behavior, such as in their hydrogen adsorption / desorption energies [Gong 2016; Politi 2013]. However, procedures for selectively designing the phase and crystal surface of carbides for maximum performance are extremely rare [Gong 2016; Wan 2014].

[0011] Electrocatalytic hydrogen evolution (HER) reactions depend on the availability of low-cost electrocatalysts. Metal carbide nanoparticles (TMCs) are very promising for HER due to their platinum-like electronic structure [Gao 2019]. However, existing techniques for synthesizing metal carbide nanoparticles are limited by high cost and low productivity [Gong 2016]. Crucially, most methods are too specific and lack generality, and phase control is also difficult to achieve [Wan 2014].

[0012] Corundum

[0013] High-surface-area corundum nanoparticles (α-Al₂O₃ NPs) have a wide range of applications. For example, corundum is widely used in ceramics for prosthetic implants [De Aza 2002] and high-speed cutting tools [Kumar 2003]. α-Al₂O₃ NP precursors provide a pathway to obtain nanocrystalline alumina ceramics with significantly improved fracture toughness [Ighodaro 2008], wear resistance [Krell 1996], and high density at reduced sintering temperatures [Guo 2016]. Even though γ-Al₂O₃ NPs are primarily used as catalyst supports due to their high surface area [Peterson 2014], α-Al₂O₃ NPs are also used as catalyst supports, exhibiting higher mechanical stability in automotive exhaust Pt-Mo-Co catalytic converters [Frank 1998], as well as enhanced Ru catalyst activity for ammonia synthesis [Lin 2019].

[0014] Numerous efforts have been made to improve the synthesis of α-Al₂O₃, but few methods have been available to provide high surface area (NP) due to inherent thermodynamic limitations [Guo 2016; McHale 1997; Amrute 2019]. Even though corundum is the thermodynamically stable phase of coarse-crystalline alumina (Al₂O₃), the synthesis of nanocrystalline Al₂O₃ typically results in γ-Al₂O₃ because when the surface area is greater than 125 m², the synthesis yields higher NP. 2 g -1 Its surface energy is relatively low [McHale 1997].

[0015] Another reason is the phase transition from the cubic close-packed structure of the γ phase to the hexagonal close-packed structure of the α phase, which is approximately 485 kJ / mol. -1 The high activation energy barrier [Steiner 1971]. As a result, heat treatment typically requires temperatures >1470 K and extended annealing times of 10 to 20 hours to promote the transformation [Steiner 1971; Levin 1998]. Due to the large amount of mass transfer, high energy input, and extended high-temperature annealing, the surface area is <10 m². 2 g -1 [Amrute 2019]. Furthermore, the polymorphism of Al2O3 during the phase transition further increases the complexity and may lead to mixed transition (t)-alumina with undesirable δ- and θ-Al2O3 [Steiner 1971; Chang 2001; Laine 2006]. Representative methods for corundum nanoparticles are quite time-consuming and energy-intensive, such as annealing γ-Al2O3 at 1473–1673 K for 10–20 hours [Lodziana 2004], and hydrothermal reaction of γ-AlOOH at 723 K and 1200 bar for 35 days [McHale 1997; Loffler 2003].

[0016] Therefore, the production of α-Al2O3 via a phase transition from the cubic close-packed γ phase ((γ-Al2O3)) is typically subject to a high activation energy barrier (~485 kJ / mol). -1 The high-temperature annealing process (~1500K, 10 to 20 hours) presents a significant obstacle, hindering the widespread application of α-Al2O3 nanoparticles. Therefore, developing ultrafast and energy-efficient methods is crucial for their broad application.

[0017] e-waste

[0018] Recovering valuable metals from waste is important for the circular economy and crucial for addressing environmental issues. Specifically, this includes electronic waste (e-waste), which contains a wealth of valuable elements.

[0019] E-waste originates from discarded electrical or electronic devices. Recovering precious metals from e-waste (known as "urban mining") is important for the circular economy. Current methods used in urban mining (primarily smelting and leaching) are hampered by lengthy refining processes and adverse environmental impacts.

[0020] More than 40 million tons of electronic waste (e-waste) are generated globally each year [Zhang 2012; Zeng 2018], making it the fastest-growing component of solid waste due to the rapid upgrading of personal electrical and electronic devices [Ogunseitan 2009; Wang 2016]. Most e-waste ends up in landfills [Ghosh 2015], which can lead to adverse environmental impacts due to the widespread use of heavy metals in electronic devices [Leung 2008; Julander 2014; Awasthi 2019].

[0021] E-waste can be a sustainable resource due to its rich content of valuable metals [Kaya 2016]. The concentration of some precious metals in e-waste is higher than that in ores [Zhang 2012]. Recovering precious metals from e-waste, i.e., urban mining, has become more cost-effective than primary mining [Zeng 2018] and is important for the circular economy [Awasthi 2019].

[0022] Similarly, due to the widespread use of heavy metals in electronic devices, including Cd, Co, Cu, Ni, Pb, and Zn, e-waste can lead to significant health risks and adverse environmental impacts [Leung 2008; Julander 2014; Awashthi 2019]. Heavy metal leaks due to improper landfill disposal cause environmental damage [Zhang 2012; Awashthi 2019]. The release of hazardous components as dust or fumes during recycling [Leung 2008] deteriorates the health of recycling workers and local residents. For example, significantly higher concentrations of Pb have been found in the blood of e-waste workers [Julander 2014; Popoola 2019].

[0023] The lack of high-yield and environmentally friendly recycling processes is a major obstacle to urban mining [Kaya 2016]. Traditional methods of e-waste recycling are based on pyrometallurgical processes [Hall 2007], in which metals are melted by heating at high temperatures. Pyrometallurgy is energy-intensive, lacks selectivity, and requires high-grade precursors [Cui 2008]. Pyrometallurgical processes also produce harmful fumes containing heavy metals, especially those with low melting points such as Hg, Cd, and Pb [Kaya 2016]. Hydrometallurgical processes are more selective and are carried out by leaching metals using acids, alkalis, or cyanides [Sun Z 2017]. Leaching kinetics are generally slow. The use of highly concentrated leaching agents makes hydrometallurgical processes difficult to scale up and generates large amounts of liquid waste and sludge, which can lead to secondary pollution [Jafhav 2015]. Biometallurgy can be highly selective and environmentally sustainable, but it is still in its early stages [Zhuang 2015]. Separating valuable metals from a variety of material matrices, including 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 non-ferrous metal waste [Yamane 2011]. Hydrometallurgical separation is based on the chemical reactivity of the metal with the leaching agent [Sethurajan 2019].

[0024] Electronic components contain potentially highly hazardous materials, including lead (Pd), cadmium (Cd), beryllium (Be), and chromium (Cr). If released into the environment, these hazardous materials can cause numerous waterborne or even airborne diseases. Meanwhile, circuit boards contain many precious metals, such as gold (Au), silver (Ag), and platinum (Pt), as well as rare earth elemental metals, neodymium (Nd) and dysprosium (Dy), which are difficult to mine and are considered key elements in the manufacture of electronic devices and electric motors. One method of e-waste recycling involves melting the circuit boards and leaching out valuable metals [Sthiannopkao 2013]. Conventional recycling methods often expose workers to hazardous and carcinogenic substances. Therefore, there is a strong need for ultra-clean and efficient methods to recover valuable metals from e-waste.

[0025] Ore, fly ash, and bauxite residue (red mud)

[0026] Similar situations involve ores, fly ash, and red mud (which has recently been 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]. Leaching REE minerals with concentrated acid solutions followed by two-phase solvent extraction is the mainstream approach for large-scale REE production [Cheisson 2019]. However, resource-intensive and pollution-intensive production has a large environmental footprint, necessitating the search for sustainable solutions [Lee 2018]. Extraction of REEs from industrial waste has gained more attention due to the depletion of readily available REE minerals [Jyothi 2020]. Applicable secondary wastes include fly ash (CFA) [Taggart 2016; Smith 2019; Zhang 2020; Liu 2019; Sahoo 2016; Middleton 2020], bauxite residue (BR, also known as red mud) from bauxite processing for aluminum production [Deady 2016; Rivera 2018; Reid 2017], and e-waste (electronic waste) from consumer electronics and electric vehicles [Maroufi 2018; Deshmane 2020; Peelman 2018]. Red mud is a highly alkaline waste, primarily composed of oxides, including Fe2O3, Al2O3, TiO2, CaO, SiO2, and Na2O. In addition, red mud contains valuable rare earth elements, including La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y [Deady2016]. Therefore, similar situations regarding the need to recover metals from e-waste, as discussed above, also involve ores, fly ash, and bauxite residue (red mud).

[0027] The reuse of these wastes reduces the environmental burden of disposing of them [Sahoo 2016]. However, the REE content in these secondary wastes is usually lower than that in REE minerals, and the recycling yield remains extremely low, which exacerbates the need for establishing circular economy initiatives [Taggart 2016].

[0028] For example, CFA (coal ash) is a byproduct of coal combustion, with an annual production of approximately 750 million tons worldwide [Sahoo 2016]. The average total REE content of CFA is approximately 500 ppm, which varies depending on the geological origin of the raw coal [Taggart 2016; Middleton 2020]. However, acid-extractable REE content is typically much lower and highly dependent on the CFA feedstock. REE extractability in CFA depends on the type of REE, such as oxides, phosphates (cerium phosphate, xenotime, monazite, etc.), apatite, zircon, and the glassy phase [Liu 2019]. The low REE extractability in most CFA resources is attributed to a large proportion of poorly soluble REEs, such as REE phosphates, zircon, and the glassy phase [Liu 2019].

[0029] Optimizing acid leaching processes can improve extractability to some extent, achieving 70% extractability using highly concentrated inorganic acids, such as 15M HNO3 at 85-90°C [Taggart 2016], and 35-100% extractability at 85°C using 12M HCl, depending on the feedstock [King 2018]. However, the use of concentrated acids inevitably increases extraction costs and disposal burden. Pretreatment of CFA with chemicals or heat prior to acid leaching helps achieve high REE recovery rates [Wang Z 2019; Taggart 2018]. For example, hydrothermal treatment with NaOH followed by acid leaching achieved a total REE recovery rate of 88% [Wang Z 2019]. Alkali roasting with NaOH resulted in recovery rates >90% [Taggart 2018]. However, these pretreatment processes are typically lengthy and energy-intensive, significantly reducing profit margins and incentives.

[0030] Furthermore, there are environmental hazards associated with the discharge of these materials. Red mud is extremely harmful to the environment due to its alkalinity. In fact, given the large amounts of acid used, developed methods for separating and recovering rare earth elements, such as leaching and cation exchange chromatography [Ochsenkuhn-Petropulu 1995], can lead to secondary pollution.

[0031] Therefore, existing methods for REE recovery are hampered by long purification times, low extraction rates, and high wastewater flows. Consequently, there remains a need for rapid and energy-efficient pretreatment to recover REEs from ores, fly ash, and bauxite residues (red mud). This further necessitates the development of a "dry" method for the direct recovery of rare earth elements from ores, fly ash, and bauxite residues (red mud). Summary of the Invention

[0032] This invention relates to an ultrafast flash Joule heating synthesis method, and more particularly, embodiments of the invention include an ultrafast synthesis method for recovering precious metals and other metals from electronic waste.

[0033] This solvent-free method, based on flash Joule heating, offers a solvent-free and sustainable approach to recover precious metals from electronic waste and remove harmful heavy metals within one second. Sample temperatures can be raised to ~3400 K within milliseconds via an ultrafast electrothermal process. This high temperature enables the evaporation and separation of precious metals from the supporting matrix, with recoveries greater than 80% for Rh, Pd, Ag, Ir, Ru, and Pt, and greater than 60% for Au. Heavy metals, some of which are highly toxic, including Cr, As, Cd, Hg, and Pb, are also removed from the electronic waste, leaving final waste with minimal metal content acceptable even for agricultural soil levels. Urban mining using FJH will consume 80 to 500 times less energy than recovering metal components using conventional smelting furnaces and is more environmentally friendly.

[0034] Typically, in one embodiment, the invention is characterized by a method for recovering metals. The method includes mixing a material with a conductive additive to form a mixture. The material is prepared from electronic waste. The method further includes applying a voltage through the mixture to recover metals from the material. The voltage is applied in the form of one or more voltage pulses. The duration of each of the one or more voltage pulses is a duration period. The method further includes collecting the recovered metals.

[0035] Embodiments of the present invention may include one or more of the following features:

[0036] The conductive additive can be a carbon source.

[0037] This electronic waste can be printed circuit boards.

[0038] This electronic waste may include plastic.

[0039] This e-waste can be waste material from devices selected from computers, smartphones, electronic devices, and displays.

[0040] This material can be prepared by mechanically converting it into fine powder.

[0041] The mechanical process can be selected from cutting the material into small pieces, crushing the material, grinding the material, milling the material, and combinations thereof.

[0042] This fine powder can be micron-sized.

[0043] The conductive additive can be selected from elemental carbon, carbon black, graphene, flash graphene, coal, anthracite, coke, metallurgical coke, calcined coke, activated carbon, biochar, natural gas carbon that has had its hydrogen atoms removed, activated carbon, sub-graphite, plastic waste, carbon derived from plastic waste, food waste, carbon derived from food waste, biomass, carbon derived from biomass, hydrocarbon gases and mixtures thereof.

[0044] The conductive additive can be carbon black.

[0045] This conductive additive can be primarily elemental carbon.

[0046] The conductive additive can be selected from metals, metal salts, metal oxides, quasi-metals, metal complexes, conductive phosphorus, and non-metallic conductive materials.

[0047] The conductive additive can be selected from metals, metal salts, metal oxides, metalloids, and metal complexes.

[0048] The conductive additive can be a quasi-metal.

[0049] The metalloid can be selected from B, Si, As, Te, and At.

[0050] The material and the conductive additive can be mixed in a weight ratio ranging from 1:2 to 4:1.

[0051] The applied voltage can be in the range of 15V to 300V.

[0052] The mass of the mixture to which the voltage is applied can exceed 1 kg. The applied voltage can range from 100V to 100,000V.

[0053] The mass of the mixture to which voltage is applied can exceed 100 kilograms.

[0054] The mass of the mixture to which the voltage is applied can exceed 1 kg. The applied current can be from 1,000 amps to 30,000 amps.

[0055] The mass of the mixture to which voltage is applied can exceed 100 kilograms.

[0056] When a voltage is applied, the mixture can have a resistance of 0.1 ohms to 25 ohms.

[0057] The duration of each of the one or more voltage pulses can be from 1 microsecond to 25 seconds.

[0058] The duration of each of the one or more voltage pulses can be from 1 microsecond to 10 seconds.

[0059] The duration of each of the one or more voltage pulses can be from 1 microsecond to 1 second.

[0060] The duration of each of the one or more voltage pulses can be from 100 microseconds to 500 microseconds.

[0061] One or more voltage pulses can be from 2 voltage pulses to 100 voltage pulses.

[0062] This voltage pulse can be generated using direct current (DC).

[0063] This method can be carried out using pulsed direct current (PDC) Joule heating.

[0064] This voltage pulse can be generated using alternating current (AC).

[0065] This voltage pulse can be generated using direct current (DC) or alternating current (AC).

[0066] This method allows switching between using direct current (DC) and alternating current (AC).

[0067] This method can use both direct current (DC) and alternating current (AC) simultaneously.

[0068] The one or more voltage pulses can raise the temperature of the mixture to at least 3000K.

[0069] The metal may include rare earth elements.

[0070] The metal may include precious metals.

[0071] The metal may include toxic heavy metals.

[0072] The material may include metal oxides. Applying voltage through the mixture can cause a carbothermic reaction of the metal oxides to recover the metal.

[0073] A voltage can be applied through the mixture at pressures ranging from 1 to 25 atmospheres to recover metals from the material.

[0074] This pressure can be below 0.5 atmospheres.

[0075] This pressure can be below 0.001 atmospheres.

[0076] This pressure can be approximately 1 atmosphere.

[0077] This pressure can be at least 2 atmospheres.

[0078] This pressure can be at least 10 atmospheres.

[0079] This pressure can be at least 20 atmospheres.

[0080] This method can be implemented using a pressurized cell.

[0081] Applying voltage through the mixture to recover metals from the material can result in most of the metals being retained along with the graphene produced by this method.

[0082] Collecting the recovered metal may include separating the metal from the graphene.

[0083] The separation of the metal from the graphene may include chemical oxidation to remove the graphene.

[0084] This graphene can be oxidized using an oxidizing agent.

[0085] The oxidant can be HNO3 or H2O2.

[0086] The oxidant can be HNO3 or H2O2 and H2SO4.

[0087] The separation of the metal from the graphene may include calcination to remove the graphene, leaving a metallic substance selected from metals, metal oxides, metal carbides, metal salts, and combinations thereof.

[0088] The mixture of the material and the conductive additive may further include halogen-containing compounds.

[0089] The halogenated compound can be selected from NaCl, NaF, KCl, NaI, halogenated polymers, halogenated organic compounds, halogenated inorganic compounds, halogenated salts, and combinations thereof.

[0090] The halogenated compound may include halogenated polymers selected from PTFE, PVDF, PVC and CPVC.

[0091] The collection step may include collecting a gas stream containing volatile products generated by applying a voltage through the mixture.

[0092] The volatile products may include metal halides.

[0093] The collection step may further include cooling the gas stream.

[0094] The step of applying voltage through the mixture can heat and evaporate the metal from the mixture, forming metal vapor. The step of collecting the recovered material may include conveying the metal vapor at low pressure. The step of collecting the recovered material may also include using a condenser or cold trap to condense the metal vapor for collection.

[0095] The metal vapor contains metal halides.

[0096] Metal vapor can be transported under vacuum.

[0097] The collection step may further include a leaching process following the application of voltage through the mixture.

[0098] When treated with the same pH and the same volume of water, the leaching of metals in the mixture after voltage is applied through the mixture can be more than twice the leaching content of metals in the mixture before voltage is applied through the mixture.

[0099] This leaching process can be carried out using dilute acid.

[0100] The dilute acid can be at least 1M.

[0101] Applying voltage through the mixture to recover metals from the material can be carried out at pressures above 1 atmosphere, such that the volatile components of the electronic waste are trapped in the residual solids of the material after the voltage is applied.

[0102] This method can be performed as a continuous process or an automated process.

[0103] Typically, in another embodiment, the invention is characterized by a system for a method of recovering metals using at least one of the methods described above. The system includes a source comprising a mixture of the material and a conductive additive. The system further includes a unit operatively connected to the source, allowing the mixture to flow into the unit and remain under compression. The system further includes electrodes operatively connected to the pressure unit. The system further includes a flash power source for applying a voltage through the mixture to recover metals from the material.

[0104] Embodiments of the present invention may include one or more of the following features:

[0105] The unit may be a pressure unit. The system may further include a gas supply for pressurizing the pressure unit.

[0106] The system may further include an adjustable safety valve.

[0107] The system may further include a particle collector.

[0108] The system may further include a gas collector.

[0109] The system can be operated to perform continuous or automated processes. Attached Figure Description

[0110] Figure 1A-1E The ultrafast synthesis of carbides via flash joule heating (FJH) was demonstrated. Figure 1A This is a schematic diagram of FJH synthesis of carbides, where route (i) shows a high-temperature FJH process according to one embodiment of the present invention, while route (ii) shows a conventional carburizing process. Figure 1B The current measurement during the FJH process is shown. Figure 1C Real-time spectral radiation in the wavelength range of 640–1000 nm is shown. The insets are photographs of the samples before, during, and during rapid cooling of the FJH (Frequency-Journal-Hydrogen). Figure 1D The real-time temperature measurement is shown by fitting the blackbody radiation from the sample during the FJH process. Figure 1E The temperature-vapor pressure relationships of various metallic precursors and carbon are shown.

[0111] Figure 2A-2H This demonstrates the phase-controlled synthesis of molybdenum carbides. Figure 2A β-Mo2C and α-MoC were synthesized at voltages (V) of 30V, 60V, and 120V, respectively. 1-x and η-MoC 1-x X-ray diffraction (XRD) patterns. The respective PDF reference cards are β-Mo₂C, 35-0787; α-Mo₂C... 1-x ,65-8092;η-MoC 1-x , 08-0384. Figure 2B It is a crystal structure of three phases of molybdenum carbide. β-Mo₂C is a hexagonal crystal system with ABAB stacking, α-MoC... 1-x It is a cubic crystal system, η-MoC 1-x It is a hexagonal crystal system with ABCABC stacking. Figure 2C It is the X-ray photoelectron emission spectrometry (XPS) spectrum of the three phases of molybdenum carbide. Figure 2D This is a bright-field transmission electron microscope (BF-TEM) image of β-Mo2C nanocrystals loaded on graphene. 0.339 nm corresponds to the interplanar spacing (d) of graphene. Figure 2E These are high-resolution transmission electron microscopy (HRTEM) images of β-Mo2C and the corresponding fast Fourier transform (FFT) patterns. Figure 2F These are high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) images and energy-dispersive X-ray spectroscopy (EDS) elemental spectra of β-Mo2C. Figure 2G It is α-MoC 1-x HRTEM images and corresponding FFT patterns. Figure 2H It is η-MoC 1-x HRTEM images and corresponding FFT patterns.

[0112] Figures 3A-3BThe phase transition process of molybdenum carbides is shown (which is revealed by density functional theory (DFT) calculations). Figure 3A β-Mo2C and α-MoC with different carbon contents were shown. 1-x and η-MoC 1-x The formation energy. Figure 3B It is β-Mo2C, α-MoC 1-x (x=1 / 2), α-MoC 1-x (x = 3 / 8) and η-MoC 1-x Calculated crystal structure of (x = 3 / 8) (dashed circles represent carbon vacancies).

[0113] Figures 4A-4F The phase-dependent hydrogen evolution reaction (HER) performance of molybdenum carbides was demonstrated. Figure 4A Polarization curves for the three phases of molybdenum carbide are shown. Pt / C and pure flash graphene (FG) were used as controls. Properties were normalized to the same mass loading of molybdenum carbide. Figure 4B Tafel curves for the three phases of molybdenum carbide are shown. Figure 4C The alternating current (AC) impedances of the three phases of molybdenum carbide are shown. Figure 4D This demonstrates the durability of molybdenum carbides. α-MoC 1-x Polarization curves for the first and 1000th cycles. Figure 4D The illustration shows the overpotential changes of the three phases of molybdenum carbide. Figure 4E The results show that under a single-layer hydrogen adsorption coverage, β-Mo2C(001) and α-MoC... 1-x (110) and η-MoC 1-x (001) Free energy diagram of HER. Figure 4F The results show that in β-Mo2C(001), α-MoC 1-x (110) and η-MoC 1-x (001) The calculated partial density of states of Mo and C, with the dashed line indicating the location of the Fermi level.

[0114] Figures 5A-5D This demonstrates a general strategy for carbide synthesis. Figure 5A It is the carbothermic reduction temperature of the oxide derived from the Ellingham diagram. Figure 5B These are X-ray diffraction (XRD) patterns and high-resolution transmission electron microscopy (HRTEM) images of group IVB metal carbides. PDF reference cards are TiC, 65-7994; ZrC, 65-8834; and HfC, 65-7326. Figure 5C These are XRD patterns and HRTEM images of group VB metal carbides. The respective PDF reference cards are VC, 65-8825; NbC, 65-8780; and TaC: 65-0282. Figure 5D These are XRD patterns and HRTEM images of group VIB metal carbides. The respective PDF reference cards are Cr3C2, 65-0897; Mo2C, 35-0787; and W2C, 20-1315. Figures 5B-5D The scale bar in the image is 5 nm.

[0115] Figures 6A-6D The flash joule heating (FJH) apparatus is shown. Figure 6A This is an electrical schematic diagram of the FJH system. Ten aluminum electrolytic capacitors (450V, 6mF, Mouser #80-PEH200YX460BQU2) are used for charging, with a total capacitance of 60mF. Additional details of the electrical components can be found in this publication. [Luong, 2020]. Figure 6B This is a photo of the FJH equipment. Figure 6C These are photos of the reaction phase. Figure 6D This is a photo of the reaction chamber.

[0116] Figure 7-12 The ultrafast phase transition of alumina via pulsed DC Joule heating is demonstrated. Figure 7 The scheme demonstrates pulsed DC Joule heating and resistive hotspot effect. Figure 8 This demonstrates a representative method for the phase transition from γ- to α-Al2O3. Figure 9 These are XRD patterns of γ-Al2O3 and α-Al2O3 products after different PDC durations and calcination. Figure 10 The crystal structure of the alumina phase is shown: 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). For γ-Al₂O₃, all Al sites are depicted to show the crystal structure, whereas in the actual structure, not all sites are occupied. Figure 11 The phase mass ratio of alumina polymorphs as a function of PDC duration is shown. Figure 12 Raman spectra of the synthesized α-Al₂O₃ / CB mixture and the purified α-Al₂O₃ NP obtained by calcination in air are shown.

[0117] Figures 13A-13B The PDC Joule heating system is shown. Figure 13A This is the electrical diagram of the system. Figure 13B The pulse voltage generation that can be used in this system to generate PDC is shown.

[0118] Figure 13C The Raman spectra of the CB precursor and product are shown after PDC Joule heating at 60V for 0.8 seconds.

[0119] Figure 14A-14F Characterization of α-Al2O3 NP is shown. Figure 14A This is a BF-TEM image of α-Al2O3 NP. Figure 14B This is an HRTEM image of α-Al2O3 NP. Figure 14C This is a bar chart and distribution of α-Al2O3 NP particle size determined by TEM. Figure 14D The pore width distribution determined by applying the DFT model is shown. Figure 14E These are the Fourier transform infrared spectra of the γ-Al₂O₃ NP precursor and the α-Al₂O₃ NP product. Figure 14F These are the fine XPS spectra of Al and O in α-Al₂O₃ NP.

[0120] Figure 15A-15F The resistive hotspot effect in the PDC method is shown. Figure 15A These are XRD patterns of γ-Al2O3 / CB with different mass ratios after the PDC method. Figure 15B It is the phase mass ratio of the product after PDC method, which varies with the volume fraction f(γ-Al2O3). Figure 15C It is a graph of conductivity versus temperature as a function of f(γ-Al2O3). Figure 15D-15F The current density diagrams are for samples in the PDC process with different γ-Al2O3 volume fractions of f = 0.41, f = 0.73 and f = 0.78, respectively.

[0121] Figure 16 The current density is shown in the body region and the hot spot region.

[0122] Figures 17A-17D The topological phase transition process revealed by DFT calculations is shown. Figure 17A The bulk cohesive energy (μ, eV / Al2O3) and surface formation energy of the three Al2O3 phases are shown. Figure 17B The free energies of the three phases of Al2O3 nanocrystals are shown relative to their specific surface area. Figure 17C-17D It is from the top view ( Figure 17C ) and side view ( Figure 17D ) of γ-Al2O3(100), δ ′ Contour plot of partial charge density at the highest energy band (0.3 eV below the Fermi level) of the surface states of -Al2O3(100) and α-Al2O3(001).

[0123] Figures 18A-18C The ultrafast alternating current sintering (ACS) system and sample holder are shown. Figure 18A This is the electrical diagram of the ACS system. Figure 18B-18CThese are the top and side views of the carbon paper holder used for sintering.

[0124] Figures 19A-19H The ultrafast ACS of alumina ceramics was demonstrated. Figure 19A The image shows photographs of carbon paper during the heating, sintering, and cooling process. Figure 19B The real-time temperature measurement during the ACS process is shown. Figure 19C An image showing sintered ceramic particles loaded on carbon paper is displayed. Figure 19D The XRD patterns of alumina ceramics using α-Al₂O₃ NP or commercially available α-Al₂O₃ nanopowder as precursors are shown. Figure 19E The image is a SEM image of a ceramic produced using α-Al₂O₃ NP as a precursor.

[0125] Figure 19F The grain size distribution of alumina ceramics is shown. Figure 19G Statistics on the Young's modulus of alumina ceramics using α-Al2O3 NP precursors are shown. Figure 19H Statistics on the Young's modulus of alumina ceramics using commercially available α-Al2O3 precursors are shown.

[0126] Figures 20A-20B and Figures 21A-21B This demonstrates the scalability of the PDC method. Figure 20A This is a photograph of a 700 mg sample synthesized using a tube (D=15 mm) and a PDC voltage of 60 V. Figure 20B yes Figure 20A The XRD pattern of the product shown is shown. Figure 21A This is a photograph of a 1.4-gram sample synthesized using a tube (D=15mm) and a PDC voltage of 120V. Figure 21B yes Figure 21A The XRD pattern of the product shown is shown.

[0127] Figure 22-28 The study demonstrates the recovery of precious metals via flash joule heating (FJH). Figure 22 This is a schematic diagram of the FJH and evaporation separation system. Figure 23 The image shows a printed circuit board (PCB) (scale bar, 5 cm), and the illustration shows a mixture of carbon black (CB) and PCB powder (scale bar, 2 cm). Figure 24 The concentration of noble metals in PCBs is shown by inductively coupled plasma mass spectrometry (ICP-MS). Figure 25 The current vs. time data recorded at different FJH voltages are shown. Figure 26 The real-time temperature measurements at different FJH voltages are shown by fitting the blackbody radiation emitted from the sample. Figure 27 The vapor pressure-temperature relationship of precious metals and carbon is shown. Figure 28The recovery rate of precious metals from gaseous components obtained through condensation and evaporation is shown.

[0128] Figures 29A-29E This is a photograph of a system for collecting evaporated metal vapor. Figure 29A This is a photo of an evaporation collection system. Figures 29B-29C These are photographs of the vacuum gauge before and after flash Joule heating (FJH). Figures 29D-29E These are photos of the condensate container before and after the FJH reaction.

[0129] Figure 30 This is a circuit diagram of the flash Joule heating (FJH) system used in the system shown in Figure 29.

[0130] Figure 31A-31G Halogen-assisted improvements show recovery rates. Figures 31A-31F They respectively showed the use of ( Figure 31A NaF, ( Figure 31B PTFE, ( Figure 31C NaCl, ( Figure 31D CPVC, ( Figure 31E )NaI and ( Figure 31F The recovery rate of precious metals using a mixture of NaF, NaCl, and NaI as additives. Y0 and Y represent the recovery rates of precious metals with and without additives, respectively. The dashed line indicates that Y / Y0 = 1, meaning that if Y / Y0 ≤ 1, there is no advantage of the additive. Figure 31G These are scanning transmission electron microscope (STEM) images of the collected solids, and energy dispersive X-ray spectra (EDS) of Rh, Pd, Ag, and Au in rectangular regions (scale bar in STEM images, 0.5 μm; scale bar in EDS images, 100 nm).

[0131] Figures 32A-32F The study demonstrates the recovery of precious metals via flash joule heating (FJH) and calcination. Figure 32A Different methods for recovering precious metals from printed circuit boards (PCBs) are shown. Figure 32B The thermogravimetric analysis (TGA) curves of the PCB after FJH (PCB-flash evaporation) in air are shown. The inset shows photographs of the PCB after FJH and calcination (PCB-flash evaporation-calcination) and the PCB itself. Figure 32C It is the TGA curve of the PCB. Figure 32D The X-ray photoelectron emission spectra (XPS) of PCB, PCB-flash evaporation, and PCB-flash evaporation-calcination are shown. Figure 32E The concentration of precious metals in the PCB after calcination (PCB-calcination) is shown. Figure 32F The results show that calcination improves the leaching yield. Y0 and Y represent the recovery rates obtained by leaching PCB and PCB-calcination, respectively.

[0132] Figures 33A-33F This demonstrates how flash joule heating (FJH) can improve the leaching efficiency of precious metals. Figure 33A A schematic diagram of the pressurization device for FJH is shown. Figure 33B The airflow simulations at different pressures are shown. The internal pressure (P0) in the FJH process is calculated to be ~5 atmospheres. P0 at 0 atmospheres, 1 atmosphere, and 4 atmospheres are also shown. out FJH corresponds to vacuum, atmospheric pressure, and positive pressure of 3 atmospheres. Figure 33C The results showed improvements in precious metal concentration and recovery rate via FJH. Figure 33D The results showed improvements in precious metal concentration and recovery rate via FJH and calcination. Figure 33E The improved recovery rate with varying FJH voltage at atmospheric pressure is shown. Figure 33F This shows an improvement in recovery rate as pressure changes. For Figure 33E-33F The recovery rates of Rh, Pd, and Ag were calculated using PCB-flash evaporation, while the recovery rate of Au was calculated using PCB-flash evaporation-calcination.

[0133] Figures 34A-34E The mechanism by which flash Joule heating (FJH) improves leaching efficiency is demonstrated. Figure 34A A schematic diagram of the lamination configuration for several types of electronic devices is shown. Figure 34B This is a scanning electron microscope (SEM) image of printed circuit board (PCB) powder. Figure 34C This is a SEM image of a PCB flash. Figure 34D This is a SEM image of a PCB after flash evaporation and calcination. Figure 34E A schematic diagram showing the morphological and structural changes of the PCB during the FJH and calcination process is presented.

[0134] Figures 35A-35F The method of removing heavy metals from electronic waste by flash joule heating (FJH) was demonstrated. Figure 35A The vapor pressure-temperature relationship of toxic heavy metals and carbon is shown. Figure 35B This shows the concentration of toxic heavy metals in the printed circuit board (PCB). Figure 35C The concentration of toxic heavy metals in the PCB after FJH is shown. Figure 35D The results show the removal efficiency and collection yield of heavy metals. Figure 35E The concentration of Hg in the residue after multiple FJH reactions is shown. Figure 35F The concentration of Cd in the residue after multiple FJH reactions is shown. Figure 35E-35F The dashed line in the figure represents the initial content and the World Health Organization (WHO) level of the approved agricultural soil safety limit.

[0135] Figure 36It is a graph showing the theoretical separation factor of the evaporation separation method.

[0136] Figures 37A-37F The carbothermic reaction for recovering metals from metal oxides is shown. Figure 37A This is the XRD pattern of Al recovered from Al2O3. Figure 37B This is the XRD pattern of Fe recovered from Fe2O3. Figure 37C This is the XRD pattern of Cu recovered from CuSO4. Figure 37D This is the XRD pattern of Ni recovered from NiSO4. Figure 37E This is the XRD pattern of Mn recovered from MnO2. Figure 37F This is the XRD pattern of Pb recovered from PbNO3. This is the same as that that occurs in bauxite residue (red mud).

[0137] Figure 38 This is a schematic diagram of a flash Joule heating pressure and gas collection system that can be used in embodiments of the present invention.

[0138] Figures 39A-39D A scaled-down version of the flash joule heating (FJH) method is shown. Figure 39A These are photographs of the processed samples. The samples were treated under the following conditions: m0 = 0.2 g, V0 = 150 V and C0 = 0.06 F (left), m1 = 2 g, V1 = 150 V and C1 = 0.6 F (middle), m2 = 4 g, V2 = 300 V and C2 = 0.6 F (right). Figures 39B-39D This is the real-time temperature curve of the sample.

[0139] Figures 40A-40B This is a diagram of a continuous flash Joule heating (FJH) reactor.

[0140] Figures 41A-41C The FJH system for fly ash is shown. Figure 41A The electrical diagram of the FJH system is shown. Figure 41B-41C These are photographs of the ligation samples synthesized at 200 mg and 2 g, respectively, with the FJH fixture of the FJH system.

[0141] Figure 42 These are photos of CFA-C and CFA-F. The scale bar is 4 cm.

[0142] Figure 43A-43G The content of acid-extractable REEs in CFA is shown. Figure 43A These are the XRD patterns of CFA-F and CFA-C. Figure 43B It is the full XPS spectrum of CFA-F and CFA-C. Figure 43C The concentrations of total REEs in CFA-F and CFA-C were obtained through HNO3 leaching (15M, 85℃), HCl leaching (1M, 85℃), and total quantification. Figure 43D It is a CFA-F (scale bar, 2μm) SEM image. Figure 43E The results show the REE content that can be extracted with HCl (1M, 85°C) and the total amount of REE in CFA-F, as well as the REE recovery rate. Figure 43F It is a CFA-C (scale bar, 5μm) SEM image. Figure 43G The REE content extractable by HCl (1M, 85°C) and the total REE amount in CFA-C, as well as the REE recovery rate, are shown. (All error bars represent standard deviations, where N = 3).

[0143] Figures 44A-44H The improved REE recovery from CFA by electrothermal activation is shown. Figure 44A It is a diagram of the CFA FJH (Foreign Language Teaching and Research). Figure 44B The current curve is under the conditions of 120V and 1 second. Figure 44C The real-time temperature measurement is displayed. Figure 44D The relationship between the HCl-leached REE content (1M, 85°C), the improvement in recovery rate, and the FJH voltage from CFA-F is shown. Figure 44E The pH-dependent REE leaching properties from CFA-F feedstock and activated CFA-F were shown. Figure 44F The pH-dependent REE leaching properties from CFA-C feedstock and activated CFA-C were shown. Figure 44G The results show the HCl leaching REE content (1M, 85°C) from activated CFA-F, as well as the improved recovery rate. Figure 44H The results show the REE content (1M, 85°C) that can be leached by HCl from activated CFA-C, as well as the improvement in recovery rate. (Y0 represents the REE recovery rate of CFA feedstock leached by HCl, and Y represents the REE recovery rate of activated CFA leached by HCl. All error bars show the standard deviation, where N=3).

[0144] Figure 45 This is a flowchart of the process for recovering REE from secondary waste through electrothermal activation.

[0145] Figure 46A-46G The mechanism by which electrothermal activation improves REE extractability was demonstrated. Figure 46A These are XRD plots of YPO4 (bottom) with reference PDF (YPO4, #11-0254) and YPO4 (top) after FJH with reference PDF (Y2O3, #43-0661).

[0146] Figure 46BThese are XRD patterns of LaPO4 (bottom) with reference PDF (LaPO4, #35-0731) and LaPO4 (top) after FJH with reference PDF (La2O3, #05-0602). Figure 46C This is the calculated solubility curve of 1 gram of Y₂O₃, YPO₄, La₂O₃, and LaPO₄ in 100 mL of solution. - Used to balance charges. Figure 46D This is an Ellingham diagram of carbon monoxide and REE oxides. The vertical dashed line represents the temperature at which Sc2O3 is reduced. Figure 46E This is the fine XPS spectrum of Y2O3 after FJH. Figure 46F This is the fine XPS spectrum of La2O3 after FJH. Figure 46G It is the Gibbs free energy change of the dissolution reaction of REE oxides and REE metals.

[0147] Figures 47A-47C This shows the REE recovered from the BR. Figure 47A This is a photo of BR (scale bar is 5 cm). Figure 47B This is the XRD pattern of BR. Figure 47C This represents the acid-leached REE content (0.5M HNO3) from BR feedstock and 120V FJH activated BR, as well as the improvement in recovery rate. (Y0 represents the REE recovery rate obtained by acid leaching the feedstock, and Y represents the REE recovery rate obtained by acid leaching the activated material. All error bars show the standard deviation, where N=3).

[0148] Figures 48A-48B The FJH voltage-dependent REE recovery rate from BR is shown. Figure 48A It is the acid-leaching content of total REE (0.5M HNO3) from BR, and the increase in REE yield as a function of FJH voltage. Figure 48B The values ​​represent the acid-leached REE content (0.5 MH NO3) and the improvement in recovery rate at 120V FJH. (Y0 represents the REE recovery rate by direct leaching of BR feedstock. Y represents the REE recovery rate by leaching activated BR. Error bars indicate the standard deviation, where N = 3).

[0149] Figures 49A-49C The image shows the recycling of REEs from electronic waste. Figure 49A It is a photo of electronic waste ground into powder, with a scale bar of 5 centimeters. Figure 49B This is an XRD pattern of electronic waste. Figure 49CThis represents the acid-leaching REE content (1M HCl) of e-waste raw materials and 50V FJH activated e-waste, as well as the improvement in recovery rate. (Y0 represents the REE recovery rate through acid leaching of raw materials, and Y represents the REE recovery rate through acid leaching of activated materials. All error bars show the standard deviation, where N=3).

[0150] Figures 50A-50B The study demonstrated that FJH activation improves the recycling rate of REEs from electronic waste. Figure 50A It is the acid leaching content of total REE (1M HCl) from electronic waste, and the increase in REE recovery rate as a function of FJH voltage. Figure 50B This represents the acid-leaching content of total REE (1MHCl) and the improvement in REE recovery at 50V FJH. (Y0 represents the REE recovery rate by direct leaching of e-waste raw materials. Y represents the REE recovery rate by leaching activated e-waste. Error bars show the standard deviation, where N=3). Invention Details

[0152] This invention relates to an ultrafast flash joule heating synthesis method. More particularly, embodiments of this 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, and an ultrafast synthesis method for recovering metals from ores, fly ash, and bauxite residues (red mud).

[0153] Ultrafast synthesis of carbides

[0154] Synthesis method

[0155] This invention comprises flash Joule heating for an ultrafast method of synthesizing metal carbide nanoparticles [see Luong 2020; Stanford 2020; Tour PCT'000 application]. Metal carbides are synthesized in seconds, hundreds of times faster than previous methods [Gong 2016; Wan 2014; Ma 2015]. Therefore, in some embodiments, this invention provides phase-controlled synthesis of transition metal carbide nanocrystals via ultrafast flash Joule heating.

[0156] This solvent-free method based on flash Joule heating can provide ultrafast synthesis of coke-free carbide nanocrystals within 1 second. A millisecond current pulse can pass through the precursor, bringing the sample to ultra-high temperatures (>3000 K), which are then rapidly cooled to room temperature (>10 °C). 4 K·s -1It can synthesize carbides of thirteen elements, including interstitial TMCs of TiC, ZrC, HfC, VC, NbC, TaC, Cr2C3, MoC, and W2C, as well as covalent carbides of B4C and SiC, providing excellent versatility. Furthermore, by controlling the FJH pulse voltage, it can selectively synthesize β-Mo2C and metastable α-MoC. 1-x and η-MoC 1-x The pure-phase molybdenum carbides demonstrated phase design capabilities for synergistic electrothermal processes. Phase-dependent HER performance of molybdenum carbides was also discovered; β-Mo₂C exhibited the best HER performance (overpotential of -220 mV, Tafel slope of 68 mV dec). -1 (and good durability).

[0157] Figure 1A This is a schematic diagram of FJH synthesis using various precursor carbides. Route (i) 101 illustrates the ultra-high temperature FJH method 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 the reverse gas-solid reaction interface. Route (ii) 102 shows a conventional carburizing process referred to as the solid-gas reaction interface.

[0158] Methods for ultrafast synthesis of carbides may include the following.

[0159] Select a reaction precursor (or multiple precursors) and mix it with a conductive carbon additive such as carbon black. Alternatively, the conductive additive can be other carbon sources (combined with or substituted for carbon black, as these temperatures convert any carbon source into nearly pure carbon at these temperatures). Carbon black can be replaced with graphene, flash graphene, coal, anthracite, coke, metallurgical coke, calcined coke, activated carbon, biochar, natural gas carbon with its hydrogen atoms removed, activated carbon, sub-graphite, plastic waste, carbon derived from plastic waste, food waste, carbon derived from food waste, biomass, carbon derived from biomass, hydrocarbon gases, and mixtures thereof. As described herein, carbon black represents a conductive additive that can be used in this invention. In some embodiments of the invention, the weight ratio of the precursor to the conductive additive is from 1:2 to 15:1, and in other embodiments, the weight ratio is from 1:2 to 2:1.

[0160] like Figure 1A As shown, general precursors, including elemental metals and metallic components such as metal oxides, metal chlorides, and metal hydroxides, can be used as precursors. The carbon black (or other conductive additives) and the metallic precursors are thoroughly mixed by hand grinding or ball milling.

[0161] A mixture of carbon black (or other conductive additives) and a metal precursor is subjected to flash joule heating. For example... Figure 1A As shown, the mixture can be packed into a quartz tube and compressed to a resistance of 0.5 to 20 ohms. Two copper or graphite rods are placed on either side as electrodes. A high voltage of 30V to 150V is applied through a capacitor bank (this can also be done using AC, sometimes even with an advantage). However, the voltage will be much higher, up to several thousand volts (and can exceed 10,000 amperes) if the reaction scale is larger, because as the scale increases, the voltage (and current) must increase to induce the same reaction temperature. For example, if the reaction scale is several kilograms or hundreds of kilograms of material, the voltage can be 10,000 volts, and even up to 100,000 volts (and the current can be 10,000 amperes, and up to 30,000 amperes).

[0162] In one embodiment, a mixture of a metal precursor and commercially available carbon black is slightly compressed within a quartz tube between two graphite electrodes. Figure 1A The widely applicable metal precursors can be elemental metals (M) and metal oxides (MO). x ), chloride (MCl) x ) and hydroxide (M(OH) x Carbon black is used simultaneously as a carbon source for carbothermal reduction and as a conductive additive. Two electrodes are connected to a capacitor bank, which is first charged by a power source and then discharged at a high voltage to bring the precursor to a high temperature. In a typical FJH process with a voltage of 100V and a sample resistance of 1Ω, the current passing through the sample within a ~50ms discharge time was recorded to be ~100A. Figure 1B ).

[0163] Fast light emission was observed during the FJH process (see [link]). Figure 1C (Photos 110-112). Temperature was measured by fitting the blackbody radiation spectrum of the sample. Figure 1C The highest estimated temperatures obtained at 80V and 100V FJH are ~2700K and ~3000K, respectively (e.g. Figure 1D (As shown in curves 121-122 in the figure).

[0164] The cooling rate is extremely fast, and it is 10. 4 K·s -1 The magnitude of the temperature distribution was measured using the finite element method (FEM) to simulate the temperature distribution of the sample, which further provided insights into the influence of FJH parameters on the achievable temperature. It was found that higher temperature values ​​could be obtained by applying a larger FJH voltage and an appropriate sample conductivity. In contrast, the higher thermal conductivity of the sample resulted in lower temperatures due to faster heat dissipation. The temperature plots showed that the temperature distribution was uniform throughout the sample, demonstrating the uniform heating characteristics of the FJH process.

[0165] Exposing sample FJH to such high temperatures (~3000K) caused most of the non-carbon components to volatilize. Based on the temperature-vapor pressure relationship ( Figure 1E All representative metal precursors, including elemental metals and metal oxides with chlorides, have higher vapor pressures than carbon, which sublimates at ~3900 K [Abrahamson 1974]. As a result, the metal precursor is the volatile component, and the carbon source remains solid during the reaction. In this case, the metal precursor vapor reacts with carbon to form metal carbides; this reaction 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 through the solid-gas interface is typically rapid, and the surface of the carbide, due to the excessive supply of carbon source, results in coking. Figure 1A (ii) 102), which would passivate the catalytic activity of the final product [Gong 2016].

[0166] Phase-controlled synthesis of molybdenum carbide nanocrystals

[0167] Catalyst-attractive molybdenum carbides were synthesized using embodiments of the present invention [Yao 2017; Wan 2014; Li 2016; Ma 2015]. The phases of molybdenum carbides are complex due to their temperature, composition, and vacancy-dependent stability [Hugosson 1999]. Different phases have different geometries and electronic structures [Politi 2103; Baek 2019], with catalytically relevant phases being hexagonal β-Mo₂C [Wan 2014; Ma 2015; Fan 2017] and cubic α-Mo₂C. 1-x [Yao 2017; Baek 2019; Song 2019] and hexagonal η-MoC 1-x 34 [Song 2019].

[0168] MoCl3 was chosen as the precursor due to its high vapor pressure. Figure 1E It was discovered that by adjusting the FJH voltage, three pure phases of molybdenum carbide could be selectively synthesized. Figure 2A-2B According to X-ray diffraction (XRD), a β-Mo2C phase is generated at a voltage of 30V. Figure 2A (bottom); when the voltage is increased to 60V, pure α-MoC is obtained. 1-x Mutually( Figure 2A (middle); further increasing the voltage to 120V to obtain η-MoC 1-x ( Figure 2A (Top). Note the diffraction peak at ~26° (shown as a star) attributable to the graphene support.

[0169] From hexagonal β-Mo2C to cubic α-MoC 1-x Then to hexagonal η-MoC 1-x The phase transition is a newly discovered topological transformation pathway, which differs from previous reports [Wan 2019], in which α-MoC 1-x After annealing at 850℃ for 24 hours, it transforms into β-Mo2C, while η-MoC... 1-x It is stabilized at higher temperatures by using only NiI2 additives.

[0170] To investigate the electronic structure, X-ray photoelectron spectroscopy (XPS) spectra at the Mo 3d nucleus level were collected. Figure 2C The Mo3d spectrum is divided into 3d... 3 / 2 and 3D 5 / 2 Peaks. Peak fitting revealed the four chemical states of Mo in molybdenum carbide, including Mo2O3. 0 Mo 2+ Mo 4+ and Mo 6+ Mainstream Mo 0 Feng and Mo 2+ The smaller peak is attributed to molybdenum carbides, due to the coexistence of Mo-Mo and Mo-C bonds within them [Wan 2014]. This is due to surface oxidation of the molybdenum carbides upon exposure to air. 4+ and Mo 6+ They were respectively assigned to MoO2 and MoO3 [Wan 2014; Ma 2015]. Quantitative analysis of the Mo chemical state ratio showed that η-MoC 1-x High oxidation state (Mo) 4+ and Mo 6+ Greater than β-Mo2C and α-MoC 1-x Those in the diagram indicate that β-Mo2C is the most antioxidant phase, followed by α-MoC. 1-x .

[0171] Morphological characterization by 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.

[0172] The size and crystallinity of molybdenum carbides 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 ~26.4 nm, followed by α-MoC. 1-x (~21.2nm) and η-MoC 1-x(Size ~20.1 nm). The smaller particle size obtained at higher voltages can be attributed to the faster nucleation kinetics at higher temperatures [Jang 1995].

[0173] The particle size values ​​measured by TEM matched well with the crystal size determined by XRD using the Halder-Wagner method (see Table I), indicating the single-crystal characteristics of the synthesized carbide particles.

[0174] Table I

[0175] Parameters of carbide synthesis

[0176]

[0177] Typical bright-field TEM (BF-TEM) images of β-Mo2C nanocrystals show regular hexagonal nanoplates with lateral dimensions of ~20 nm (depicted by hexagon 201) loaded on carbon. Figure 2D High-resolution TEM (HRTEM) images show lattice fringes ( Figure 2E (top), where the 0.26 nm interplanar spacing (d) corresponds to the (300) plane of β-Mo2C. Based on the atomic resolution image and the corresponding Fast Fourier Transform (FFT) pattern ( Figure 2E (bottom), the nanosheet orientation was specified as β-Mo2C(001). High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) images and EDS elemental spectra in STEM mode revealed a uniform spatial distribution of Mo, C, and O ( Figure 2F Note that O is attributed to surface contamination, consistent with XPS results. Figure 2C For a specific sample, α-MoC 1-x ( Figure 2G ) and η-MoC 1-x ( Figure 2H The HRTEM image and corresponding FFT mode are also in α-MoC 1-x (110) and η-MoC 1-x (116) orientation was obtained. However, according to the XRD results ( Figure 2A No preferred orientation of these carbide nanocrystals was observed.

[0178] Phase transition process of molybdenum carbides

[0179] To explain the voltage-dependent phase formation, the current and temperature passing through the sample were first recorded at different FJH voltages. Higher voltages resulted in higher temperatures and energy inputs. The highest temperatures measured at FJH voltages of 30V, 60V, and 120V were 839K, 1468K, and 3242K, respectively.

[0180] β-Mo2C and α-MoC as a function of carbon content were calculated using first-principles density functional theory (DFT). 1-x and η-MoC 1-x The formation energy ( Figure 3A (See curves 301-303). It was found that the β-Mo2C phase is the most stable phase with the lowest formation energy; therefore, β-Mo2C forms at relatively low voltage and temperature (point 301).

[0181] In contrast, α-MoC 1-x and η-MoC 1-x It is a metastable phase [Hugosson 1999], and according to the Mo-C phase diagram, it forms and stabilizes at higher temperatures. α-MoC 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 increases slightly, a shift from β-Mo2C to α-MoC is expected. 1-x The topological transformation (see line 304, which shows the expected phase transition pathway). With the introduction of more carbon into the Mo-C system, α-MoC... 1-x The formation energy continues to increase (curve 302), and this energy curve is consistent with η-MoC 1- The energy curve of x (curve 303) intersects.

[0182] The η-MoC 1-x The phase becomes relatively stable around x = 3 / 8. Figure 3B The process continues to stabilize at higher carbon contents. This result indicates that carbon vacancies dominate the energy picture of the Mo-C system and act as a transitional phase from β-Mo₂C to α-MoC. 1-x Then to η-MoC 1-x The driving factors of the topological transition pathway of a phase.

[0183] The FJH process, with its widely adjustable energy input, allows for the production of metastable phases with higher formation energies than thermodynamically stable phases; subsequently, the ultrafast cooling rate of the FJH process (>10) 4 K·s -1 This helps to dynamically maintain metastable phases (including α-MoC). 1-x and η-MoC 1-x (phase) to room temperature. As a control, metastable α-MoC prepared by FJH was obtained. 1-x At the same temperature, using a conventional tube furnace with a temperature of ~10K min -1 Synthesis conducted at a slow cooling rate yielded only the thermodynamically stable β-Mo2C phase. This clearly demonstrates the role of the ultrafast cooling rate in the FJH process in kinetically obtaining metastable phases.

[0184] Phase-dependent HER performance of molybdenum carbides

[0185] A side-by-side electrochemical comparison of the three molybdenum carbide phases reveals the influence of phase control on their respective intrinsic properties and catalytic behavior. To demonstrate their catalytic performance, the HER performance of the three molybdenum carbide phases was measured in 0.5 M H₂SO₄ using a standard three-electrode configuration. Figure 4A The figure shows linear sweep voltammograms (LSV) of different electrocatalysts and Pt / C as the reference (Pt / C, β-Mo2C, α-MoC). 1-x η-MoC 1-x The curves for flash graphene (FG) are 401-405. Flash graphene (FG) obtained from carbon black FJH was used as a control and showed negligible HER activity [Luong 2020].

[0186] Phase-dependent HER activity was observed in molybdenum carbides. For β-Mo₂C and α-Mo₂C... 1-x and η-MoC 1-x At 10mA cm -2 At geometric current densities, the overpotentials (η) relative to the reversible hydrogen electrode (RHE) are -220 mV, -310 mV, and -510 mV, respectively. Figure 4A Calculate β-Mo2C and α-MoC. 1-x and η-MoC 1-x The Tafel slope (b) is 68mV dec -1 84mV dec -1 and 113mV dec -1 ( Figure 4B The curves 411-413 show the phase-dependent HER reaction kinetics.

[0187] According to electrochemical impedance spectroscopy measurements, the rapid electrode kinetics of the β-Mo₂C phase are reflected in a small charge transfer resistance of ~60 Ω at a potential relative to RHE of -0.5 V. (See also...) Figure 4C Curves 421-423 show the β-Mo2C and α-MoC, respectively. 1-x and η-MoC 1-x (AC impedance).

[0188] The durability of three molybdenum carbide phases was evaluated by scanning the electrocatalyst for 1000 cycles using cyclic voltammetry. The LSV curves for the three molybdenum carbide phases at the 1st and 1000th cycles (curves 431-432, respectively) are shown below. Figure 4D In the middle. No significant current drop was observed in any of the three phases at 10 mA cm. -2The overpotential hardly decreased (curve 433), demonstrating excellent long-term stability.

[0189] DFT calculations were performed to interpret the phase-dependent HER performance. The Gibbs free energy (ΔG) of hydrogen adsorption was calculated. H () has become a descriptive term for HER electrocatalyst selection [Mavrikakis 2006], and according to the Sabatier principle, the optimized catalyst has a ΔG close to 0 eV. H [Greenley2006]. β-Mo2C(001), α-MoC 1-x (110) and η-MoC 1-x The ΔGH of (001) was calculated to be 0.48 eV, 0.71 eV, and 1.09 eV, respectively. Figure 4E These results show that β-Mo2C and α-MoC 1-x Having the same properties as η-MoC 1-x Compared to the smaller hydrogen adsorption energy, this is consistent with previous reports [Fan 2017; Matanovic 2018]. Except for ΔG H In addition, the electronic structure provides valuable insights into the metallic properties of carbide phases. [Politi 2013].

[0190] Figure 4F The partial density of states (DOS) of Mo and C in molybdenum carbides is shown. The DOS of β-Mo₂C near the Fermi level is significantly greater than that of α-MoC. 1-x and η-MoC 1-x The higher Mo content in β-Mo₂C leads to higher carrier density and enhanced metallicity, which is beneficial for charge transfer during electrochemical reactions. Figure 4C As measured by the Brunauer-Emmett-Teller (BET) method, the larger surface area of ​​β-Mo2C compared to the other two phases also contributes to a higher current density. The best HER performance observed in β-Mo2C is a combination of relatively small hydrogen adsorption energy, enhanced metallic properties, and high surface area. Furthermore, the flash-evaporated graphene support provides a conductive pathway and prevents the agglomeration of carbide nanocrystals, which is beneficial for improving HER performance [Li 2019].

[0191] General strategies for the synthesis of carbide nanocrystals

[0192] Due to the ultra-high usable temperature of the FJH process, various TMCs can be easily synthesized regardless of the availability of metal precursors with high vapor pressures. A series of carbide nanocrystals from the IVB, VB, and VIB transition groups were successfully synthesized. Figures 5A-5DThe uniform temperature distribution allowed for pure-phase synthesis throughout the sample. (The star-shaped peaks at ~26°C in all samples are attributed to the graphene support.)

[0193] Based on the Ellingham diagram, the reduction temperature of the metal oxide is calculated. Since the reaction between the metal and carbon is exothermic, this reduction temperature is used as a reference value for evaluating carbide formation. Figure 5A The ultra-high temperatures (~3000 K) of the FJH process allow for the reduction of all listed oxides to elemental metals, including the most challenging HfO2 at temperatures up to ~2510 K. Almost all low-cost metals or metal compounds, including oxides, hydroxides, and chlorides, can be used as precursors, making FJH 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].

[0194] Group IVB carbides possess only stable rock salt crystal structures, including TiC, ZrC, and HfC, and are readily synthesized. Figure 5B The particle sizes of TiC, ZrC, and HfC were measured to be ~30.4 nm, ~38.6 nm, and ~30.6 nm, respectively. These values ​​match well with the crystal sizes determined by XRD (see Table I above), indicating that the synthesized carbide nanoparticles are mainly single crystals. For group VB carbides, the competitive M2C (M = V, Nb, and Ta) phase can exist at lower C contents [Hugosson 1999]. However, by using a large C / M molar ratio, pure phases of VC, NbC, and TaC nanocrystals with cubic structures and particle sizes of ~20 to ~30 nm were successfully synthesized. Figure 5C In contrast, the phases of group VIB carbides (Cr, Mo, and W) are much more complex [Hugosson 2001]. Here, orthorhombic Cr3C2 and hexagonal W2C phases with particle sizes of ~14.2 nm and ~18.7 nm, respectively, were synthesized. Figure 5D According to the WC phase diagram, below 1250℃, W₂C is thermodynamically not superior to the WC phase [Kurlov 2006]. The successful synthesis of metastable W₂C is attributed to the high energy input and ultrafast cooling rate of the ultrafast electrothermal reaction, further demonstrating the excellent phase design capability of the FJH process. In addition to TMC, covalent carbides of B₄C and SiC were synthesized, proving the versatility of the FJH process.

[0195] System and synthesis process

[0196] Therefore, for the synthesis of metal carbides, the present invention provides in particular (i) ultrafast synthesis that is thousands of times faster than previously reported methods; (ii) phase control capabilities that are difficult to achieve by other methods; and (iii) universality, as demonstrated by the synthesis of up to 13 carbides, which is impossible by any other method.

[0197] The metal carbides derived from this invention, particularly molybdenum and tungsten carbides, can be used as electrocatalysts, such as for hydrogen evolution, which are crucial for the application of fuel cells in clean energy. Furthermore, nanoscale carbides are important precursors for the manufacture of high-performance carbide ceramics.

[0198] Figures 6A-6B The exemplary system and process used are shown, including circuit diagrams and the equipment of the FJH system. (Additional details of the electrical components can be found at Luong 2020). A capacitor bank with a total capacitance of 60 mF is used as the power source. The metal precursor and carbon black are mixed in a specific weight ratio (Table I) by grinding with a mortar and pestle. The reactants (~50 mg) are loaded 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 is used for samples of ~200 mg, and a quartz tube with an ID of 16 mm and an OD of 20 mm is used for samples of ~1 g. Further scaling up the mass to the kilogram level will require a container that does not require quartz. Graphite rods are used as electrodes at both ends of the quartz tube. The electrodes are loosely fitted into the quartz tube to allow degassing. The resistance is controlled by the compressive force of the electrodes through the sample. The tube is then loaded onto the reaction stage. Figure 6C Place the reaction platform into the sealed reaction chamber, and evacuate the chamber to a suitable vacuum (~10 mmHg) to allow for degassing and prevent sample oxidation. Figure 6D The reaction station was then connected to the FJH system.

[0199] The capacitor bank is charged using a direct current (DC) power supply capable of reaching voltages up to 400V. Discharge time is controlled using a relay with a programmable millisecond-level delay. Charging, flash Joule heating, and discharging are automated using a National Instruments Multifunction I / O (NIUSB-6009) integrated with a custom LabVIEW program. After the FJH reaction, the apparatus itself is rapidly cooled to room temperature. The capacitor bank is ensured to be fully discharged before sample removal. Detailed conditions for the synthesis of various carbides are listed in Table I.

[0200] Features and Applications

[0201] In the implementation scheme, the synthesized carbide nanocrystals are supported on flash-evaporated graphene. The necessity of separating the graphene and carbide depends on the further application. For the application of nanocrystalline carbides in electrocatalysts, the graphene support is beneficial for improving performance by providing conductivity and preventing particle agglomeration. For another major application of nanocrystalline carbides as precursors for ultra-strong ceramics, the removal of excess carbon is essential.

[0202] It has been recognized that carbides can be effectively purified through post-synthetic processes, including simple calcination in air for SiC; Ca metal etching for TiC, ZrC, HfC, VC, NbC, TaC, Cr3C2, β-Mo2C, and W2C [Dyjak2013]; and for metastable molybdenum carbides α-MoC. 1-x and η-MoC 1-x A liquid density purification method was developed. Furthermore, the use of controlled feed during synthesis demonstrated significantly improved B4C purity.

[0203] Due to its ultrafast heating / cooling rate, direct sampling heating characteristics, and short reaction duration of less than 1 second, the FJH process for carbide synthesis is highly energy-efficient compared to conventional furnace heating, which uses a large amount of energy to maintain the furnace chamber temperature. In terms of electrical energy, it consumes only 2.2 to 8.6 kJ / g. -1 Synthesized carbide nanocrystals. The FJH synthesis exhibits good scalability; constant temperature values ​​and uniformity across different mass scales can be obtained by adjusting the discharge voltage and / or capacitance.

[0204] By increasing the FJH voltage, the synthesis of carbide nanocrystals up to gram scale was confirmed. This FJH process can be extended to the synthesis of carbide alloys [Sarker 2018], heteroatom-modified carbides [Song 2019], and phase design of metastable carbides [Demetriou 2002], which provides a powerful technique for carbide production.

[0205] Controlled synthesis of metastable phases is challenging in the synthesis of inorganic materials [Chen2020]. The FJH process offers a wide range of tunable energy inputs exceeding 3000 K, combined with kinetically controlled ultrafast cooling rates (>10 K). 4 K s -1 Therefore, the FJH process can yield many non-equilibrium phases and subsequently retain them at room temperature, thus serving as a potential tool for designing metastable phases of various materials, such as metal nanomaterials [Chen 2020], layered oxides [Bianchini 2020], metal nitrides [Sun W 2017], and two-dimensional materials.

[0206] Ultrafast synthesis of corundum nanoparticles

[0207] This invention further includes flash Joule heating [see Luong 2020; Stanford 2020; Tour PCT'000 application] for an ultrafast process for synthesizing metallic corundum nanoparticles, namely, an ultrafast phase transition from γ-Al₂O₃ (and γ-AlOOH) to α-Al₂O₃ via flash Joule heating. In short, carbon black (or other carbon additives, as described above) is mixed with γ-Al₂O₃ (or γ-AlOOH) nanoparticles, followed by flash Joule heating. The phase transition is ultrafast, occurring within one second, thousands of times faster than other prior art methods.

[0208] Embodiments of the present invention thus include a Joule heating method based on pulsed direct current (PDC) to achieve the phase transition from γ- to α-Al₂O₃ at a significantly reduced average bulk temperature and reaction duration (~573 K, <1 second). When using a suitable volume fraction ratio of γ-Al₂O₃ precursor and carbon black conductive additive, rapid transition can be achieved through localized heating induced by resistive hotspots in the PDC process. Pulsed and localized heating reduces agglomeration, resulting in the synthesis of particles with an average particle size of ~23 nm and a surface area of ​​~65 m². 2 g -1 α-Al₂O₃ NPs. Ab initio calculations revealed the determination of the topological phase transition process (from γ- to δ-) through the surface energy difference of the three phases. ′ -to α-Al2O3). Particle sizes of ~21 nm were achieved through thermal synthesis with δ... ′ -Al2O3 is the thermodynamic limit of dehydration of α-Al2O3 NP as an intermediate phase.

[0209] Furthermore, based on Joule heating technology, an alternating current sintering (ACS) process has been developed, which has demonstrated the ability to sinter these α-Al2O3 NPs ultrafast and pressureless into alumina ceramics with nanoscale grain size and improved strength and hardness.

[0210] A calcination process was also developed to completely remove carbon black or the formed flash graphene, yielding pure-phase α-Al₂O₃. In the embodiments, the synthesized α-Al₂O₃ exhibited a high α-phase content of up to 65 μm. 2 / g surface area, which means these materials can be used in catalyst supports and high-strength ceramic applications.

[0211] Phase transition synthesis

[0212] Methods for the ultrafast synthesis of corundum nanoparticles (i.e., the transformation from γ-Al2O3 (and γ-AlOOH) to α-Al2O3) may include the following.

[0213] Because the γ-Al₂O₃ NP precursor is electrically insulating, commercially available carbon black (CB) is used as a conductive additive in the embodiments. For example, a mixture of γ-Al₂O₃ NP and CB is compressed inside a quartz tube between two graphite electrodes. See also Figure 7 (This shows a PDC device 701 and a resistive hot spot 702 surrounding and situated within an insulating γ-Al₂O₃ NP gap, with arrows depicting current lines.) Figure 13A (Among them, aluminum electrolytic capacitors with a total capacitance of 0.624F (450V, 13mF) are used for charging.)

[0214] The CB also serves as a separator to prevent the agglomeration of Al2O3 NPs during heating. The resistance is controlled by the compressive force on the two electrodes, as shown in Table II.

[0215] Table II

[0216] PDC Joule heating parameters final quality

[0217]

[0218] Note: V0: initial voltage, V1: voltage after Joule heating.

[0219] The electrodes are connected to a capacitor bank with a capacitance of C = 0.624F and a charging voltage as high as V0 = 500V. The discharge circuit is a series resistor-inductor-capacitor circuit with a characteristic time of τ = 0.1ms and a PDC with an allowable frequency of f = 1000Hz. Figure 13B The pulse voltage generation that can be used in this system to generate PDC is shown, with a frequency of 1000Hz and the ON state set to 20%, which gives a 0.2ms voltage pulse.

[0220] Joule heating affects the entire electrical conductor; for a homogeneous conductor, the current density is uniform, and therefore ohmic dissipation allows for a uniform temperature distribution throughout the sample [Johnson 2011]. However, when an electric field is applied to a non-homogeneous medium, such as in a composite of conductive CB and insulating Al₂O₃, the current and powder density exhibit strong spatial variations [Soderberg 1987]. In some regions, power dissipation is significantly greater than in adjacent regions, which are referred to as resistive hotspots 702 (shown in...). Figure 7 (Middle). Even with a low average bulk temperature, this hot spot allows for localized heating and triggers transitions that occur at much higher temperatures.

[0221] By utilizing this effect, it was achieved that, within <1 second at an average bulk temperature of ~573K, accompanied by δ ′The phase transition from γ-Al₂O₃ to α-Al₂O₃ in the intermediate t phase of Al₂O₃. See also Figure 8 The pulsed DC method 814 is shown in the figure. (As shown in the figure...) Figure 8 As shown, the pulsed DC method 814 is compared with representative phase change methods reported in the literature, namely flame spray pyrolysis 811 [Laine 2006], furnace annealing 812 [Steiner 1971] and high-energy ball milling 813 [Amrute 2019].

[0222] Liquid-feed flame spray pyrolysis 811 produces α-Al₂O₃ at temperatures close to 1873 K; however, the kinetically controlled process may make it difficult to obtain a pure phase (80-85% pure α-phase) [Laine 2006]. Conventional heating methods that supply heat through the sample boundary, such as furnace annealing 812, require extended times to allow for uniform heating; therefore, 1473 K and 10 to 20 hours are needed to complete the phase transformation [Steiner 1971]. Other room-temperature non-equilibrium methods, such as high-energy ball milling 813, have been reported to form α-Al₂O₃ [Amrute 2019]. However, γ-Al₂O₃ may agglomerate, leading to a loss of surface area during prolonged high-energy collisions [Zielinski 1993; Chauruka 2015].

[0223] The detailed phase transition process of γ-Al₂O₃ was investigated using the PDC method. See [link to PDC study]. Figure 9-11 (exist Figure 9 In the diagram, the symbols represent: γ-Al₂O₃(■), δ′-Al₂O₃(▲), α-Al₂O₃(●), and γ-AlOOH(○); the precursor is γ-Al₂O₃ (crystal system: monoclinic; space group: P21 / n; PDF No. 07-0324) with a small amount of γ-AlOOH phase; and the sample was calcined for 0.8 seconds. Particles with a size of ~10 nm and a surface area of ​​~156 m² were used. 2 g -1 Commercially available γ-Al₂O₃ NP was used as a precursor. A small proportion of the γ-AlOOH phase appeared in the precursor. Figure 9 (0 seconds). A sample resistance of ~8 Ω was obtained with a γ-Al₂O₃ NP to CB mass ratio of 4:1 (Table II). A discharge voltage of 60 V was applied, and different discharge times were controlled by a relay. X-ray diffraction (XRD) patterns of products with different PDC on-state times are shown in... Figure 9 In the middle stage, as the discharge time increases, γ-AlOOH disappears first at 0.3 seconds; subsequently, γ-Al2O3 transforms into δ-Al2O3 between 0.4 and 0.5 seconds. ′ - and α-Al2O3 phase; finally, after 0.8 seconds of discharge, the intermediate δ′ -Al2O3 phase is completely transformed into α-Al2O3 phase. Figure 11 In the figure, curves 1121-1123 represent γ-Al2O3 and δ... ′ -Al₂O₃ and α-Al₂O₃). Orthogonal δ ′ -Al2O3 as a single intermediate phase ( Figure 10 This differs from other thermal processes where δ- and θ-Al2O3 typically appear before the final α-Al2O3 phase. Figure 8 )[Steiner1998; Levin 1998; Lamouri 2017].

[0224] Unlike previous reports on the synthesis of graphene by high-voltage flash Joule heating at ~3000K [Luong 2020], the 60V PDC did not provide sufficient energy to graphitize the CB. Figure 13C (No 2D peak was observed in the product after Joule heating at 60V). As a result, according to thermogravimetric analysis (TGA), CB could be easily removed by heating in air. Here, the synthesized mixture of α-Al₂O₃ NP and CB was calcined in air at 700°C for 1 hour to purify the product. The X-ray photoelectron emission spectrum (XPS) of the calcined α-Al₂O₃ product showed a very small carbon signal, which is likely due to the adsorption of carbon from the air.

[0225] Raman spectroscopy is even sensitive to carbon monolayers [Wang 2008]; interestingly, no characteristic Raman bands of carbon were detected after calcination at 700 °C. Figure 12 Curves 1224-1226, representing calcination at 700℃, 650℃, and CB / Al2O3 respectively, confirm the effective removal of carbon. As a control, it was determined that the calcination process itself does not trigger a phase transition, and its effect on the coarsening or agglomeration of the γ-Al2O3 phase is negligible.

[0226] Characterization of corundum nanoparticles

[0227] Further detailed characterization of the α-Al₂O₃ NPs obtained via PDC and subsequent mild calcination. Bright-field transmission electron microscopy (BF-TEM) images show well-dispersed particles. See also Figure 14A High-resolution TEM (HRTEM) revealed the high crystallinity of α-Al₂O₃ NP. See also... Figure 14B . and The interplanar spacing values ​​correspond to d(104) and d(113) for α-Al₂O₃, respectively. Some α-Al₂O₃ NPs were observed to have surface roughness characteristics of several nanometers, similar to the particle size of the γ-Al₂O₃ precursor. This indicates that the rapid PDC method triggers the phase transition without significant NP agglomeration. 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 also Figure 14C .

[0228] Brunauer-Emmett-Teller (BET) measurements show that the surface area of ​​α-Al₂O₃ NP is ~65 m². 2 g -1 See also Figure 14D Illustration 1401 (this illustration shows the N2 adsorption-desorption isotherm of α-Al2O3 NP at 77 K). The average particle size (D) is estimated to be ~23 nm by equation (1):

[0229] D = 6 / (ρS) Equation (1)

[0230] Where ρ is the density of α-Al₂O₃ (3.96 g cm⁻¹). -3 ), where S is the specific surface area [Karagdov 1999].

[0231] Pore ​​size measurements from N2 adsorption-desorption isotherms, using a density functional theory (DFT) model, indicate a high-probability distribution in the 3–10 nm range. See also... Figure 14D The observed surface area is attributed to the nanoscale grain size, as well as the porosity and surface roughness characteristics of the NP. Based on the Halder-Wagner method, the crystal size of α-Al₂O₃ NP is estimated to be ~22 nm. This crystal size (~22 nm) is in excellent agreement with the particle size measured by TEM statistics (~25 nm) and BET estimation (~23 nm), confirming the single-crystal nature of the NP.

[0232] Unlike the initial γ-Al2O3 NP with a hydrated surface, the synthesized α-Al2O3 NP surface is highly dehydrated due to the thermal process. Figure 14E Curves 1411-1412 show the α-Al2O3 product and the γ-Al2O3 precursor, respectively (black arrow 1413 points to the absorbance of the hydroxyl group).

[0233] XPS fine spectroscopy revealed that O2- from α-Al2O3 NPs predominates at a binding energy of ~531.2 eV. 2- The peak and Al at a binding energy of ~74.0 eV 3+ Single peak. See also Figure 14FThis indicates that the ultrafast PDC process did not lead to significant oxygen defects or carbothermic reduction of Al2O3 even in the presence of CB, likely due to the fact that Al... 3+ The high reduction potential. No other peaks were detected in the XPS full spectrum, indicating the high-purity synthesis capability of the electrothermal process. This makes it superior to solvent-based methods, including ball milling [Amrute 2019] or coprecipitation [Guo 2016], which are hampered by lengthy purification processes and chemical contaminants.

[0234] Resistive hotspot effect

[0235] The composition of heterogeneous media can be important for local power dissipation during PDC processes. To quantitatively demonstrate the effect of this composition on the phase transition, a series of precursors with different γ-Al₂O₃ to CB mass ratios were treated by PDC at the same voltage and time. Figure 15A (With labels: γ-Al2O3(■), δ′-Al2O3(▲) and α-Al2O3(●), the numbers are the mass ratio of γ-Al2O3 to CB); Table II. Based on the densities of γ-Al2O3 and CB, the volume fraction (f) of γ-Al2O3 was obtained (shown in Table III), and the phase mass ratio as a function of f(γ-Al2O3) after the PDC process was calculated. Figure 15B (showing α-Al₂O₃ and δ) ′ -Al2O3 curves 1501-1502).

[0236] Table III

[0237] Volume fraction of γ-Al2O3

[0238]

[0239] The degree of phase transition increased as f(γ-Al2O3) increased from 0.41 to 0.73; pure phase α-Al2O3 was obtained at f(γ-Al2O3) ~ ​​0.73. Further increasing f(γ-Al2O3) to > 0.78 resulted in no phase transition.

[0240] To explain the f(γ-Al₂O₃)-dependent phase transition, conductivity and temperature were measured. Conductivity was determined based on the measured resistance (R) and the characteristic dimensions of the sample. Table II; Figure 15C (Curves 1503 and 1504 represent conductivity and temperature vs. f(γ-Al₂O₃), respectively). Conductivity is inversely proportional to f(γ-Al₂O₃). Figure 15C The curve 1504 in the figure is reasonable because γ-Al₂O₃ is electrically insulating. Real-time temperature was measured using an infrared (IR) thermometer. The average bulk temperature decreases with increasing f(γ-Al₂O₃). Figure 15CThe curve 1503 in the figure can be explained by equation (2) from the power (P) equation of Joule heating:

[0241]

[0242] Where V is the voltage and σ is the conductivity of the sample.

[0243] Since the initial voltage is fixed at V0 = 60V, the power is proportional to the conductivity of the sample. Interestingly, pure-phase α-Al2O3 NPs were obtained using f(γ-Al2O3) of ~0.73 at a low average bulk temperature of ~573K. Figure 15C .

[0244] Such low temperatures should not trigger a reaction with ~485kJ / mol. -1 The phase transition from γ- to α-Al₂O₃ with high activation energy [Steinr 1971]. Furthermore, the higher degree of phase transition at lower temperatures is counterintuitive. Figure 15C .

[0245] To explain this phenomenon, the current density distribution of the γ-Al₂O₃ / CB composite material during the PDC process was numerically simulated using the finite element method (FEM). For example... Figure 15D-15F As shown, the current density is non-uniform in the γ-Al₂O₃ and CB composite; the current density is greater in the vertical gap region between γ-Al₂O₃NPs than in the bulk region. Figure 15D-15F In the diagram, the sphere is γ-Al₂O₃, the continuous phase is CB, and the vertical side pillars represent the current density values. The gap narrows as f(γ-Al₂O₃) increases, resulting in significantly larger current densities in those regions. Considering that the resistivity (R) of the conductive CB phase is constant, according to equation (3), the heat (Q) generated per volume by the PDC is proportional to the square of the current density (j):

[0246] Q∝j 2 Equation (3)

[0247] Large heat dissipation in regions with high current density leads to hot spots near γ-Al₂O₃ NPs, which have much higher temperatures than the bulk region, triggering a phase transition. For example... Figure 16 As shown in the figure, quantitative analysis of current density indicates that as f(γ-Al2O3) increases, the bulk temperature decreases (curve 1601), but the hotspot temperature increases (curve 1602), which is consistent with... Figure 15C The temperature measurement results shown are very consistent.

[0248] Topological transformation pathways

[0249] To gain a deeper understanding of the topological transformation pathway, thermodynamic analysis of three Al2O3 phases was performed based on DFT. The bulk energy and surface energy of the three Al2O3 phases were calculated. Figure 17A α-Al₂O₃ has the lowest bulk energy, followed by δ-Al₂O₃. ′ -Al₂O₃, followed by γ-Al₂O₃, indicates that α-Al₂O₃ is the most stable phase as a dense, massive crystal. In contrast, surface energies are reversed: γ-Al₂O₃(100) has the lowest surface energy, followed by δ-Al₂O₃. ′ -Al2O3(100), α-Al2O3(1ī0), and (001). As the surface area increases, the difference in surface energy determines the thermodynamic stability of the three Al2O3 phases. Figure 17B α-Al2O3, δ ′ -Al₂O₃ and γ-Al₂O₃ are curves 1701-1703, respectively. When the surface area is less than ~79m²... 2 When the particle size is greater than ~21 nm, the α-Al₂O₃ phase transformation is more pronounced than δ. ′ - The phase is more stable. Therefore, it is recommended to use a particle size of ~21 nm as the threshold through the intermediate δ phase. ′ Thermodynamic limit of the thermal process synthesis of dehydrated α-Al₂O₃. The particle size of α-Al₂O₃ synthesized by PDC (~23 nm) is close to the thermodynamic limit and smaller than the particle size obtained by most other thermal processes (Table IV).

[0250] Table IV

[0251] Synthesis of α-Al2O3 via thermal process

[0252]

[0253] This ultrafast, pulsed, and low-temperature PDC process largely avoids mass transfer and grain coarsening during phase transition.

[0254] To gain insight into the structural origins of phase-dependent bulk and surface energy, partial charge density contours were plotted at the highest energy bands (0.3 eV below the Fermi level) of the surface states of the three Al2O3 phases. Figure 17C-17D All surface atoms on α-Al₂O₃(001) are active, while δ ′ The sites on the surface of -Al2O3(100) and γ-Al2O3(100) that lack Al atoms are relatively active. Figure 17C Closer analysis shows that the active state affects δ ′ -Al2O3(100) and γ-Al2O3(100) penetrate the bulk, while α-Al2O3(001) does not. Figure 17DThis explains the bulk and surface energy sequences of the three Al2O3 phases and identifies the γ- and δ-phases. ′ Al vacancies in the - phase relative to the α phase are the structural source of their thermodynamic stability / instability.

[0255] application

[0256] Therefore, for the synthesis of corundum nanoparticles, this invention provides, in particular, an ultrafast synthesis that takes less than one second and is much faster than any previously reported method that requires at least several hours. The corundum (α-Al₂O₃) nanoparticles obtained by this invention have small particle size and high surface area, and can be used in many applications, such as for stable catalyst supports and for ceramics with high fracture strength and toughness.

[0257] For example, a prominent application of α-Al₂O₃ NPs is as a precursor for sintering nanocrystalline alumina ceramics (i.e., ultrafast ACS for nanocrystalline alumina ceramics). Typical alumina ceramic sintering processes are carried out under high pressure and high temperature conditions (HP-HT), such as hot isostatic pressing [Mizuta 1992], spark plasma sintering [Balima 2019], and pulsed current sintering [Zhou 2004]. High pressure (typically several GPa) sustains grain growth and promotes densification [Wang 2013], which is likely the main factor in the sintering of dense ceramics using coarse-grained precursors. However, HPHT processes are not suitable for complex structures. Nanocrystalline precursors can undergo pressureless sintering, but they will be hampered by elevated sintering temperatures and extended times (>10 hours) [Guo 2016; Cao 2017; Li 2006]. Recently, an ultrafast high-temperature sintering method based on DC heating [Wang 2020] was reported for the rapid screening of ceramics.

[0258] Here, based on Joule heating technology, an alternative AC sintering (ACS) process for ultrafast sintering of alumina ceramics has been developed. The ACS system can provide stable and high energy output with voltages up to 63V and currents up to 100A. Figure 18A This makes it suitable for sintering structural ceramics. For the ACS system, the total capacitance is 1.5F, and the maximum usable voltage is 63V. The capacitor is simultaneously charged by an AC power supply and provides energy output to the sample through discharge. The energy output is continuous, enabling extended sintering of several seconds with high energy output.

[0259] Connected to the electrode Figure 18C Two separate, highly graphitized carbon papers, 1801a-1801b, are used as heating elements. See also Figure 18B(Carbon paper 1801a-1801b is attached to the glass slide and adhered via copper tabs). α-Al₂O₃NP [Taktak 2011] mixed with polyethylene glycol (PEG) binder was pressed into granules 1802 at 500 MPa. Commercially available α-Al₂O₃ nanoparticles (~300 nm) were used as a control. The binder was removed (5°C min). -1 After reaching 500°C and holding for 2 hours (in air), place the granules 1802 between carbon paper and under ACS at ~15V.

[0260] Figure 19A The rapid heating at 1901, stable sintering at 1902, and rapid cooling at 1903 are shown. Temperatures were recorded by fitting blackbody radiation. These temperatures are in the range of ~10. 3 K s -1 The heating rate rapidly increased the temperature to ~2250K. After sintering for 5 seconds, it was further heated at ~10... 3 Ks -1 The sample was cooled at a rapid cooling rate. See also Figure 19B . Figure 19C The image shows sintered ceramic granules 1911-1912 loaded on carbon paper 1913.

[0261] The XRD pattern confirms that the alumina ceramic is a pure α-phase. Figure 19D The microstructure determined by scanning electron microscopy (SEM) revealed uniformly sized grains and tightly bound grain boundaries with polyhedral morphology. Figure 19E This indicates good sintering. The average grain size of the alumina ceramic is ~270 nm. Figure 19F In contrast, alumina ceramics sintered from commercially available α-Al₂O₃ powder exhibited high residual porosity and a grain size of ~1200 nm, indicating that sintering was in its initial stage. This result suggests that the fine grain size of α-Al₂O₃ NPs facilitates ultrafast sintering, presumably aided by grain growth at high temperatures. [Guo2016]. Measurement of the mechanical properties of the ceramics. See also... Figure 19G-19H Ceramics sintered from α-Al₂O₃ NP precursors exhibit a Young's modulus of ~11.7 GPa, significantly higher than that from commercially available α-Al₂O₃ powders (~1.5 GPa). The mechanical properties of alumina ceramics derived from α-Al₂O₃ NPs may be improved by using conventional high-pressure sintering processes [Mizuta 1992; Balima 2019; Zhou 2004] or by extending the sintering time [Guo 2016; Laine 2006].

[0262] Therefore, the ACS method can be used for the sintering of functional ceramics and porous ceramics, or for material screening [Wang 2020].

[0263] Effectiveness and scalability

[0264] As a highly efficient energy supply technology, Joule heating has a coefficient of performance of 1.0. Localized heating via resistive hotspots in PDC makes this process even more efficient because most of the electrothermal energy is directly targeted at the phase transition, enabling a yield rate of ~4.77 kJ / g. -1 Low energy input or 0.027 kg -1 The synthesis was carried out at a low energy cost. Furthermore, the PDC process can be scaled up by adjusting the sample cross-sectional area and the PDC voltage. Synthesies of α-Al₂O₃ NPs up to 1.4 g in scale have been achieved. See [link to documentation]. Figures 20A-20B and 21A-21B (in Figure 20A and 21A In the image, the black powder is a synthetic mixture of CB and α-Al2O3, and the white powder is calcined α-Al2O3. The PDC process, combined with the resistive hotspot effect, significantly reduces the temperature required to trigger the reaction, which should otherwise be triggered under high energy input, serving as a cost-effective alternative to the synthesis.

[0265] Recycling metals from e-waste

[0266] This invention includes a flash Joule heating method for recovering metals (precious metals) from waste (such as e-waste) using an ultrafast method [see Luong 2020; Stanford 2020; Tour PCT'000 application]. The waste can be mixed with carbon black and then subjected to ultrafast Joule heating flash evaporation. According to the Ellingham diagram, various precious metals are reduced to elemental metals via a carbothermal reaction. This recovery process is ultrafast, taking only seconds. Importantly, this method is a completely dry method without any solvents, and is therefore extremely environmentally friendly.

[0267] Synthesis method

[0268] Methods for ultrafast synthesis of metals for recycling from waste may include the following.

[0269] This method may include preparing electronic waste for flash evaporation. For example, printed circuit boards (PCBs) from used electronic printers are used as starting materials. The PCBs are first cut into small pieces, then crushed into small particles. They are then ground into micron-sized fine powder using a ball mill, and then made usable for flash evaporation Joule heating by adding carbon black (or other carbon materials as described above), and processed in a flash evaporation Joule heating apparatus as described below.

[0270] Evaporation Separation

[0271] It has been discovered that the different vapor pressures of metals compared to substrate materials (carbon, ceramics, and glass) enable the separation of metals from e-waste. This is known as "evaporative separation." High vapor pressures of precious metals are achieved through an ultrafast flash Joule heating (FJH) process under vacuum. A second current pulse passes through the precursor, bringing the sample to an ultra-high temperature of ~3400 K, enabling the evaporative separation of precious metals. Halogen additives are used to improve the recovery rates of Rh, Pd, and Ag, which are abundant in the tested e-waste, to greater than 80%, and the recovery rate of Au to greater than 60%. Alternatively, compared to directly leaching the raw e-waste materials, leaching the residual solids after FJH significantly improves recovery rates, increasing Ag recovery by tens of times and Rh, Pd, and Au recovery by several times. Toxic heavy metals, including Cd, Hg, As, Pd, and Cr, can also be removed and collected, minimizing the health risks and environmental impact of the recycling process.

[0272] The FJH process for recovering precious metals from electronic waste involves three stages. See also Figure 22 A schematic diagram of system 2200 is shown. In the metal evaporation stage 2201 (which includes an FJH device with capacitor bank 2205 and porous Cu electrode 2206), metals in electronic waste are heated and evaporated by ultra-high temperature FJH heating. Subsequently, in the mass transfer stage 2202, the metal vapor is transported under vacuum (using a vacuum system with pump 2207), and in the condensation stage 2203, the metal vapor is collected by condensation (using cold trap 2208). Printed circuit boards (PCBs) from discarded computers, a representative form of electronic waste, are used as starting materials. See also Figure 23 The PCB is ground into a fine powder and mixed with carbon black (CB) as a conductive additive. Figure 23 Illustration 2310.

[0273] To determine the baseline concentration, PCB [Hon2020] was digested with dilute aqua regia, and the concentration of noble metals was determined by inductively coupled plasma mass spectrometry (ICP-MS). Figure 24 As shown, among the precious metals, Rh, Pd, Ag and Au are abundant, ranging from a few parts per million to tens of parts per million (ppm).

[0274] In the FJH process, a mixture of PCB powder and ~30% by weight of CB is slightly compressed inside a quartz tube between two sealed electrodes. Figure 22 . Figure 29A A photograph of the system is shown, which includes a flash stage 2901, a power supply 2902, a pump 2903, and a cold trap 2904 (liquid nitrogen, Dewar). One electrode is a porous Cu electrode to facilitate gas diffusion, and the other electrode is a graphite rod. Figure 30The resistance of the sample is adjustable by adjusting the compressive force on the two electrodes. The two electrodes are connected to a capacitor bank with a total capacitance of 60 mF. Detailed separation conditions are shown in Table V.

[0275] Table V

[0276] Parameters of FJH under vacuum

[0277]

[0278]

[0279] The high-voltage discharge of the capacitor bank brought the reactants to a high temperature. The current through the sample was measured at different FJH voltages with a fixed sample resistance of ~1Ω. See [link to relevant documentation]. Figure 25 Curves 2521-2523 are shown for 150V, 120V, and 100V, respectively. The real-time temperature of the sample was estimated by fitting blackbody radiation emitted in the 600-1100nm range. This temperature varies with the FJH voltage, reaching ~3400K at 150V within <50ms. See [link to documentation]. Figure 26 The curves 2631-2633 are shown for 150V, 120V and 100V respectively.

[0280] Because the resistivity of the sample is much higher than that of the graphite and porous Cu electrodes, the voltage drop is primarily applied to the sample. Therefore, the high-temperature region is confined to the sample, and the FJH device exhibits good durability, even at temperatures >3000 K. Such high temperatures (>3000 K) volatilize most of the non-carbon components. Based on the calculated vapor pressure-temperature relationship ( Figure 27 Noble metals have higher vapor pressures than carbon, which does not sublimate before ~3900K. [Abrahamson 1974].

[0281] As a result, the metal is evaporated, and the predominantly carbon-containing components, such as plastics, are carbonized. [Luong 2020; Algozeeb 2020]. The evaporated metal vapor is captured by condensation in a cold trap. Figure 22 and 29A Some vapors remain gaseous even at liquid N2 temperatures (77 K); these gases are assumed to be H2 and CO. [Algozeeb 2020].

[0282] The content of precious metals in the condensed solids was determined and the recovery rate was calculated. Figure 28The recovery rate of Ag was ~40%, while Rh, Pd, and Au had relatively low recovery rates of ~3%. This is because Ag has a high vapor pressure and a relatively low boiling point. The concentration of noble metals in the initial commercially available CB is 1-2% of that in PCBs, so their presence in CB does not introduce significant errors. Furthermore, due to the extremely low carbon solubility of noble metals, they tend not to form stable carbide phases even at high temperatures [Okamoto 2016]. Therefore, using CB as a conductive additive does not affect the evaporation behavior of noble metals.

[0283] Halogen-assisted improvement in recovery rate

[0284] High recovery rates in evaporative separation rely on generating more volatile components. To improve recovery rates, halides are used as additives because metal halides have much higher vapor pressures compared to elemental metals [Lide 2005]. Fluorine-containing components, including sodium fluoride (NaF) and polytetrafluoroethylene (PTFE, Teflon), were initially used as additives. Using these additives, the recoveries of Rh and Pd improved to >80% and 70%, respectively. See also Figures 31A-31B This indicates 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 PCBs, thus ruling out the possibility that the additives would introduce significant errors in the recovery of precious metals.

[0285] Chlorine-containing compounds were tried because they are abundant and inexpensive. Sodium chloride (NaCl) and potassium chloride (KCl) were used. Figure 31C For NaCl and KCl additives, the recovery rates of Rh, Pd, and Ag were all improved. Furthermore, polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC) plastics were used. Figure 31D The recovery rates of all four precious metals improved, especially Ag, with a recovery rate improved to >80%. Plastic additives are pulverized post-consumer samples with very low or negative value, so they will not introduce significant material costs in the e-waste recycling process.

[0286] Even with the use of F and Cl additives, the recovery rate of Au was <10%. Interestingly, when sodium iodide (NaI) was used as an additive, the recovery rates of all four precious metals improved; the recovery rate of Au improved to >60%. Figure 31E Among halides used for Au recovery, additive I exhibits the best performance. According to the hard-soft acid-base (HSAB) theory, Au... + It is a soft Lewis acid, I - It is a soft Lewis base, while F - and Cl - Than I -Hard [Pearson 1963], favorable for AuI. With the use of additive mixtures of NaF, NaCl, and NaI, good recovery rates were achieved for all noble metals: Rh > 60%, Pd > 60%, Ag > 80%, and Au > 40%. Figure 31F Compositional analysis of the raw materials and residual solids after FJH by X-ray photoelectron spectroscopy (XPS) showed that 10-40% of the halide additives evaporated during the FJH process, and could be recovered and reused through water washing and precipitation processes.

[0287] Overall composition analysis was performed on the metals collected in the cold trap. In both cases, with and without chemical additives, the most abundant metal, besides precious metals, was Cu at >60 wt%, followed by other major metals in e-waste, including Al, Sn, Fe, and Zn. Further purification and refining can be performed by selective precipitation, solvent extraction, and solid-phase extraction, which are commercially established practices and known in the art. [Ueda 2016].

[0288] The morphology and chemical composition of the condensed solids were characterized using scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS). The elemental diagram shows clustered alloy particles of Rh, Pd, Ag, and Au. Figure 31G This process, known as FJH, involves ultrafast heating and rapid cooling to form high-entropy alloy nanoparticles. This is similar to the carbon thermal shock synthesis of high-entropy alloy nanoparticles, which could potentially be used as catalysts [Yao 2018]. Noble metals were also observed throughout the product in other regions. Furthermore, XPS analysis of the collected volatiles showed that Ag and Au were primarily in elemental form, while Rh and Pd coexisted in both elemental and higher oxidation states, likely due to their different chemical reactivity.

[0289] Improved precious metal leaching efficiency

[0290] Besides condensing volatile compositions, another route to recover precious metals is by leaching the residual solids obtained from FJH. See also Figure 32A Unlike evaporation separation schemes that use vacuum to promote metal volatilization (…), this method… Figure 22 ), and establish a pressurization device to capture metal in the reactor ( Figure 33A An inert gas (N2) cylinder is connected to the FJH reactor, where the pressure is monitored by a pressure gauge. Based on the amount of gas collected, the internal pressure (P0) in the FJH process is estimated to be ~5 atmospheres.

[0291] Based on the pressure drop and size of the FJH chamber, at different pressures (P out Simulated gas diffusion () Figure 33B When using vacuum (P) out=0 atmospheres), as in evaporation separation ( Figure 22 The gas velocity reached as high as 800 m / s. -1 Such high gas velocities facilitate the rapid diffusion of volatile components into the cold trap and prevent condensation losses at the tube sidewalls. In contrast, gas velocities decrease significantly with increasing pressure. Figure 33B As a result, more of the initially volatile components are retained in the residual solids within the reactor. Detailed reaction conditions for pressurized FJH are shown in Table VI.

[0292] Table VI

[0293] Parameters of FJH under pressure

[0294]

[0295] The leaching of residual solids after initiating FJH (referred to as PCB-flash evaporation) using dilute acids (1M HCl, 1M HNO3) at 120V and atmospheric pressure. The leaching content of Rh, Pd, and Ag in PCB-flash evaporation is significantly higher than that in PCB raw materials. Figure 33C The recovery rates of PCB leaching-flash evaporation (Y) and leaching of PCB raw materials (Y0) were calculated. FJH, combined with leaching, was significantly more effective than leaching alone. The recoveries of Rh, Pd, and Ag increased by 4.17±0.48, 2.90±0.31, and 56.0±18.1 times, respectively. Figure 33C ).(exist Figure 33C In the figure, Y0 and Y represent the recovery rates by leaching printed circuit boards (PCBs) and PCB-flash evaporation, respectively. The dashed line indicates that Y / Y0 = 1. The error bars represent the standard deviation (where n = 3). This deviation may be due to the uneven distribution of precious metals in e-waste. Interestingly, the Au recovery rate decreases after the FJH process. This is likely because Au forms covalent bonds with carbon [Olavarria-Contreras 2016], which significantly increases the difficulty of acid leaching.

[0296] Thermogravimetric analysis (TGA) of PCB flash evaporation showed that carbon could be removed in air at ~700°C. Figure 32B ). ( Figure 32B The TGA curves show that PCB-flash evaporation begins to lose weight at ~400℃ and remains stable at ~800℃. Therefore, the PCB-flash evaporation solid was calcined at 700℃ for 1 hour (referred to as PCB-flash evaporation-calcination). Figure 32B Illustration 3210 shows photographs of PCB flash evaporation and PCB flash evaporation-calcination. PCB raw material was also calcined as a control (denoted as PCB-calcined). Figure 32C ).

[0297] XPS analysis showed that calcination effectively removed carbon ( Figure 32D ).(exist Figure 32D In the PCB XPS, the main signals were C and some inorganic substances. The PCB-flash evaporation XPS mainly showed C signals, indicating that O was removed by the FJH method, and no inorganic element peaks were detected, likely because inorganic substances were covered by carbon during the FJH process. The PCB-flash evaporation-calcination XPS showed abundant elemental signals, demonstrating the removal and exposure of inorganic materials. Using the FJH and calcination processes, the recoveries 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 ).(exist Figure 33D In the diagram, Y0 and Y represent the recovery rates of PCB leaching and PCB-flash evaporation-calcination, respectively. The dashed line indicates that Y / Y0 = 1. The error bars represent the standard deviation (where n = 3). This value is greater than the value obtained from the calcination process alone. Figure 32E-32F ).

[0298] The mechanism by which FJH improves leaching efficiency is shown in Figures 34A-34E Modern electronic devices are manufactured and packaged using planar processes and have laminated structures, in which useful metals are embedded in polymer or ceramic matrices. Figure 34A [Sun Z2017]. Even after pulverization, the particle size is still as large as ~5μm. Figure 34B The laminated structure hinders metal extraction in typical hydrochemical processes, leading to prolonged leaching times and low leaching efficiency. [Sun Z 2017]. In the FJH process, the matrix is ​​made into an ultrafine powder at ultra-high temperatures. Figure 34C-34D ), and exposed metal ( Figure 34E This greatly accelerates the leaching rate and the degree of metal extraction.

[0299] The effects of FJH voltage and pressure on recovery rate were evaluated. A moderate FJH voltage of 30 to 50 V was found to provide the optimal recovery rate. Figure 33E Curves 3301-3304 are shown for Rh, Pd, Ag and Au respectively. Figure 33E The shaded area represents the approximate optimal voltage for all metal recycling. Too low a voltage will not provide enough energy to thermally decompose the matrix, while too high a voltage may result in evaporation losses. It was found that higher ambient pressure was beneficial. Figure 33F Curves 3311-3314 are shown for Rh, Pd, Ag, and Au, respectively. This is because volatile components are trapped in the residual solids, as predicted by gas flow simulations. Figure 33BCompared to other hydrometallurgical processes that use high-concentration inorganic acids such as aqua regia [Sun Z 2017; Park 2009] or toxic cyanides [Sethurajan 2019; Quinet 2005] as extractants to achieve high recovery rates, the mild acid leaching conditions (1M HCl, 1M HNO3) used in the method of this invention are more cost-effective and environmentally friendly.

[0300] Removal and collection of toxic heavy metals

[0301] Removing toxic components is another major concern in e-waste treatment. [Ogunseitan 2009; Leung 2008; Julander 2014; Sun 2020]. The heavy metal removal capacity of the FJH method was evaluated. Compared to precious metals, heavy metals (including Cr, Pb, Cd, As, and Hg) have much higher vapor pressures and much lower boiling points. Figure 35A In particular, for the most toxic elements Cd, As, and Hg, theoretical analysis shows that their separation factors from precious metals can reach ~10. 5 The levels of heavy metals in PCB waste range from 0.1 to 20 ppm. Figure 35B These values ​​are higher than the safe limits for heavy metals in agricultural soils recommended by the World Health Organization (WHO) [Kinuthia 2020].

[0302] After one FJH (Flash Evaporation), the heavy metal content in the remaining solids (PCB-flash evaporation) 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 are consistent with their vapor pressure values. Figure 35A Heavy metals were collected by condensation in a cold trap, as is done for evaporative separation, and the collection yield was calculated. Figure 35D The good match between collection yield and removal efficiency indicates that most of the evaporated heavy metals are trapped by the cold trap, minimizing the leakage of heavy metals into the environment during the recovery process.

[0303] The concentration of heavy metals in the residue solids can be further reduced through multiple FJH reactions. After one FJH reaction, the concentration of Hg decreased to below the safe limit for Hg in agricultural soils (0.05 ppm). Figure 35E [Kimuthia 2020], the safety limit is the highest standard for waste disposal. For Cd, three consecutive FJH cycles reduce the concentration to below the safety limit (0.003 ppm). Figure 35F[Kimuthia 2020]. With increasing FJH reaction times, the concentrations of As, Pb, and Cr all decreased. Since each FJH reaction takes only 1 second, multiple flash evaporations are easily achievable.

[0304] Metal separation

[0305] The aforementioned method utilizing an evaporation separation scheme, relating to the recovery of metals from electronic waste, has been discussed. However, such methods can exhibit the ability to separate metals. Calculations show that for most metals with large vapor pressure differentials, separation rates as high as ~10 can be achieved. 5 A large separating factor. Figure 36 The charts provide theoretical separation factors for evaporative separation processes based on vapor pressure differentials. These factors represent the practical value of separating trace metals from abundant metals. To separate abundant metals, these values ​​should be corrected for their activity in the alloy melt.

[0306] Separation using the FJH process based on vapor pressure difference has demonstrated varying recoveries of precious metals. Figure 28 ).like Figure 28 As shown, without chemical additives, the recoveries of precious metals are Y(Rh) = 4.0%, Y(Pd) = 3.1%, Y(Ag) = 38.0%, and Y(Au) = 1.3%. These different recovery rates demonstrate the separation capability of the FJH process. See Table VII below.

[0307] Table VII

[0308] Separation factor of precious metals

[0309]

[0310] Chemical additives ( Figures 31A-31F It also regulates the separation of precious metals, likely due to their different chemical reactivity. See Tables VIII-X below.

[0311] Table VIII

[0312] Separation factor of noble metals by using NaCl additive

[0313]

[0314] Table IX

[0315] Separation factor of noble metals using NaF additive

[0316]

[0317]

[0318] Table X

[0319] Separation factor of noble metals by using NaI additive

[0320]

[0321] The separation capability of the evaporation separation scheme can be further improved by gradually increasing the FJH temperature.

[0322] Carbothermic reduction

[0323] Flash Joule heating can also be used for the carbothermic reduction of metals from oxides. Various metal oxides have been used prior to recovery, demonstrating the applicability of metal recovery via flash Joule heating. For example... Figures 37A-37F As shown, 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 the carbon black reduces metal oxides and metal salts to metals, while carbon is approximately oxidized to carbon dioxide and carbon monoxide.

[0324] In some embodiments of the invention, the process may include a mechanism for trapping metals in the waste. For example, this mechanism may utilize reduced pressure and, during flash Joule heating of the source, cause volatile metals, metal carbides, metal oxides, or other metal complexes to evaporate from the reaction chamber and enter a cold trap. The cold trap may be, but is not necessarily, liquid N2. These can be collected in the trap even at room temperature.

[0325] Furthermore, for example, this mechanism can utilize atmospheric pressure or higher (e.g., 10 or 20 atmospheres) and retain the metal within the newly formed graphene. The graphene can then be burned off (e.g., in air at 700-800°C), leaving the separated metal (or metal oxides, etc.). Alternatively, the graphene can be chemically oxidized, such as with HNO3. For the latter mechanism, a pressure relief valve can be used at the end of the electrode-hole assembly used in the flash Joule heating process. Some of the recovered metals have very high boiling points and will remain with carbon, especially at the higher pressures used.

[0326] Design and scalability

[0327] Figure 38 A flash Joule heating pressure and gas collection system 3800, which can be used in embodiments of the present invention, is shown. System 3800 includes the following:

[0328] (a) Timing sprocket and belt 3801;

[0329] (b) Manual or motor driven 3802;

[0330] (c) Driver 3803 (e.g., twin screw driver);

[0331] (d) Power supply 3804 (such as AC or DC from a flash power supply);

[0332] (e) Sample compression 3805;

[0333] (f) Nuts 3807a-3807b and flexible spacers 3806a-3806b;

[0334] (g) Electrode 3808a (such as a solid brass electrode with threads) and electrode 3808b (such as a brass electrode with threads and a drilled hole);

[0335] (h) Tube 3809 (e.g., quartz tube);

[0336] (i) Copper wool 3810;

[0337] (j) Torsion spring compression 3811;

[0338] (k) Electrode 3812 (such as a brass electrode with an O-ring seal and an axial bore);

[0339] (l) Sample 3813;

[0340] (m) The conduit 3814 (such as a PTFE tube) inside the electrode 3812;

[0341] (n) Pressure seal 3815 (e.g., using a Swagelok reducer);

[0342] (o) Particle collector 3816;

[0343] (p) Adjustable pressure safety valve 3817;

[0344] (q) Gas collector 3818;

[0345] (r) Flow to vacuum or gas analysis 3819;

[0346] (s) Exhaust port 3820;

[0347] (t) Safety valve 3821;

[0348] (u) Conduit 3822 (e.g., PFE conduit);

[0349] (v) Flow to vacuum 3823;

[0350] (w) Pressurized input 3824 from the gas supply; and

[0351] (x) Pressure gauge 3825-3826.

[0352] System 3800 is a pressurized flash Joule heating unit with a gas collector 3818, which should ensure gas overpressure. In some embodiments, System 3800 utilizes electrodes with a diameter of 5 / 16 inch or 8 mm. The conduit may have an outer diameter of 1 / 8 inch.

[0353] In System 3800, two brass electrodes with O-ring grooves are inserted into a quartz tube tightly wound with a compression spring to compress the quartz and resist outward pressure. One electrode is hollow and inserted into a PTFE tube to provide a smooth and continuous outlet path. A reducing Swagelok fitting provides pressure and vacuum sealing for the PTFE tube, which exits the electrode without a joint. System 3800 is capable of withstanding tens of atmospheres of pressure. Typically, the limiting factors regarding pressure are the quartz tube and how well the robust spring can prevent breakage. The twin-screw support frame should also be robust enough to resist the thrust when the sample is pressurized or when pressure is generated by flash evaporation. The quartz tube can be replaced with any non-conductive tube, and cross-linked polyethylene has also been used because the temperatures reached on the tube are typically below 250°C and typically less than 1 second. Although in Figure 38 It is not shown in the diagram, but a motor driver can be added and utilized. Furthermore, because the system is completely sealed, an external vacuum chamber surrounding the flash assembly is not required.

[0354] When using short-duration flash evaporation, the rubber bushing between the nut and the support frame can be used to absorb vibration.

[0355] System 3800 can be sealed with O-rings. Silicone O-rings are heat-resistant and do not melt even under overheating; instead, they tend to harden and maintain a seal. Because no hot gases typically flow through the O-rings, they do not overheat. Although discoloration of the first O-ring has been observed, the double O-rings maintain a seal.

[0356] System 3800 can be completely evacuated and will maintain pressure after the sample 3813 flashes as the gas exits into the thick-walled glass pressure tube. In some embodiments, right-angle connectors can be used so that venting does not interfere with the end connections of the electrodes. However, if particles or nanoparticles are being ejected, a straight outlet tube is generally preferred. System 3800 shows a straight and continuous tube 3814 (PTFE outlet tube), and the wires are connected to loops on the threaded brass electrodes 3808a-3808b.

[0357] System 3800 uses a twin-screw translation system, which provides consistent alignment of the electrodes. It has been found that with a single-screw translation system, when pressure or force is applied, the electrode angle is upward, which in turn induces strain in the quartz tube 3809. The twin screws are connected via a timing sprocket and belt 3801 for simultaneous propulsion and can be driven manually or by a stepper motor.

[0358] Regarding vacuum and gas supply, the conduit leading off the hollow electrode can be connected via valves to vacuum 3823, gas supply 3824, and pressure gauge 2925. The gas supply can be inert or used to inject reagents into the sample, such as hydrogen, methane, or other active substances like halogenated hydrocarbons, ammonia, boron compounds, etc. These can then be added to the porous carbon / graphene in a subsequent flash evaporation.

[0359] A preset pressure release can be provided for system 3800. An adjustable pressure relief valve 3817 determines the ultimate pressure on sample 3813. The unit can be fully pressurized before flash evaporation, or high pressure can be allowed to be generated during flash evaporation. The opening pressure is set by a spring and a threaded cap on the valve; when the pressure exceeds the set force of the spring, the valve opens, and gas enters a previously emptied gas collector. The gas can then be analyzed, or simply evacuated. The volume of pressure gauge 3826 and gas collector 3818 provides information about the total gas yield. Gas collector 3818 also has a pressure relief valve 3821 connected to exhaust port 3820 in case of excess gas.

[0360] The impact of the wide range of pressures available in the system 3800, which features a sealed flash chamber and an adjustable safety valve, on flash yield has been evaluated. Due to pressure, volatile additives can be incorporated into the sample and will not leave until the safety valve is opened.

[0361] System 3800 can be used for various particle / metal collection methods. For example, when particle collection is desired, the PTFE tube can be inserted straight (without bends) into particle collector 3816 (i.e., a test tube impactor). This will be inside a larger evacuated container (not shown), and the momentum of the particles will cause them to adhere to the tube, while non-condensable gases are evacuated. This can be used to collect volatile metals and metal compounds that will agglomerate and form nanoparticles that will adhere to particle collector 3816 as they cool.

[0362] This design can be changed and modified as needed, depending on the materials and design, and the intended use.

[0363] The cost and benefits of FJH treatment were evaluated, as economic incentives are the primary driver of waste recycling [Awasthi 2019]. Compared to conventional furnaces that use large amounts of energy to maintain the temperature of the entire chamber, FJH is a highly efficient heating process due to its ultrafast heating / cooling rates, direct sample heating characteristics, and short reaction duration [Khaliq 2014]. The energy consumption of the FJH process is ~939 kWh / ton, which is ~1 / 500 of the energy consumption of a laboratory-scale tubular furnace [Balaji 2020] and ~1 / 80 of the energy consumption of an industrial-scale commercial Kaldo furnace [Theo 1998]. Therefore, the FJH process for e-waste treatment has advantages over conventional pyrometallurgical processes.

[0364] The FJH process is scalable. Based on the analysis conducted, the FJH voltage and / or the capacitance of the capacitor bank can be increased when the sample mass is scaled up. Figures 39A-39D This shows a scaled-up version of the flash joule heating (FJH) process. Figure 39A These are photographs of samples treated with 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-39D These are the real-time temperature curves of samples 3901-3903.

[0365] Figure 40A The design is for a continuous flash Joule heating (FJH) reactor 4000, which includes a continuous feed 4001 (such as electronic waste and carbon black), Cu electrodes 4002-4003 (porous Cu electrodes), a porous electrode 4004, a graphite electrode 4005, an O-ring 4006, and a baffle 4007. Volatile components can enter a collection system 3108 for collection using a cold trap, and non-volatile components can be collected in a collector 4009.

[0366] Figure 40B This is a scheme for a continuous flash Joule heating (FJH) reactor 4020 with a continuous feed of raw material 4021 (such as e-waste and carbon black) flowing from a hopper 4022. In step 4031, the raw material 4021 is loaded onto chamber 4023 of conveyor belt 4024. In step 4032, the raw material 4021 in chamber 4023 is compressed (using compressor 4025) to a predetermined resistance. In step 4033, the raw material 4021 is subjected to an FJH reaction using an FJH system 4026 with Cu electrode 4027 and graphite electrode 4028. In step 4034, the product 4034 is subsequently unloaded in collector 4029.

[0367] Although the raw materials for electronic waste and carbon black are described Figures 40A-40B These are schemes, but they can be used with other materials used in the FJH reaction.

[0368] By using an automated system integrated with FJH equipment, a production rate of >10 kg per day has been achieved.

[0369] Therefore, for the recovery of metals from electronic waste, the present invention particularly provides: (i) flash Joule heating is a dry process that does not use any solvents, making it environmentally friendly; (ii) flash Joule heating can recover most of the metal elements in the waste in one step, which is difficult to achieve by other methods; (iii) the flash Joule heating process also removes almost all harmful substances from the waste, so it does not cause secondary pollution; and (iv) the flash Joule heating process uses far less electrical energy than a furnace due to the short heating duration and the fact that almost no energy escapes from the flash Joule heated sample.

[0370] Precious metals recovered from e-waste are vital raw materials for various industries. In fact, such metal mixtures are quite valuable, as many mining companies have implemented automated systems for separating base metals.

[0371] In addition, this recycling process removes harmful substances such as heavy metals from the waste, which is important for addressing the environmental problems caused by these wastes.

[0372] Ore, fly ash, and bauxite residue (red mud)

[0373] Similar to the situation with e-waste, this also involves ores, fly ash, and red mud (recently known as bauxite residue), because rare earth elements (REEs) are strategic resources in modern electronics, clean energy, and the automotive industry. Therefore, the methods and systems described above can also be used to recover metals from ores, fly ash, and bauxite residue (red mud).

[0374] Embodiments of this invention include an ultrafast electrothermal process based on flash Joule heating (FJH) to activate ores, fly ash, and red mud, using a mild acid (e.g., 0.1 M HCl) to improve the acid extractability of REEs. Pulsed voltages measured in seconds bring the feedstock to ~3000°C, causing the thermal decomposition of sparingly soluble REE phosphates in CFA into highly soluble REE oxides, and carbothermally reducing the REE components to highly reactive REE metals. Compared to direct leaching of the feedstock with a more concentrated acid, this activation method can increase REE recovery rates to ~206% for Class F CFA (CFA-F) and ~187% for Class C CFA (CFA-C). This activation strategy is feasible for a variety of secondary wastes, as demonstrated by fly ash (CFA) and red mud (bauxite residue (BR)). The rapid FJH process is scalable and energy efficient, with low power consumption (e.g., 600 kWh / ton or $12 / ton), resulting in a profit margin greater than 10 times.

[0375] FJH System and Process

[0376] The FJH systems that can be used are similar to those described and discussed above. For example, Figure 41A The diagram shows the electrical diagram of an FJH system that can be used for fly ash (similar to the one described above). Figure 6A , 13A (and the aforementioned FJH system shown in 30).

[0377] In a typical experiment, secondary waste (CFA, BR) is mixed with carbon black at a mass ratio (e.g., 2:1) using a ball mill (MSEsupplies, PWV1-0.4L). Carbon black acts as a conductive additive. 200 mg of the mixture (133 mg waste and 67 mg CB) is added to a quartz tube (8 mm inner diameter, 12 mm outer diameter). Resistance is controlled by compressing two electrodes. The sample is loaded into a fixture (…). Figure 41B-41C The electrodes are then connected to a capacitor bank. In this embodiment, ten aluminum electrolytic capacitors (450V, 6mF, Mouser #80-80-PEH200YX460BQU2) are used for charging, and the capacitor bank with a total capacitance of 60mF is charged via a direct current (DC) power supply. The discharge time is controlled using a relay with a programmable millisecond-level relay. Table XI reflects detailed parameters of some of the secondary waste materials used. After FJH, the sample is rapidly cooled to room temperature.

[0378] Table XI

[0379] FJH parameters for activating secondary waste

[0380]

[0381] *The results on printed circuit boards are shown as a comparison of methods for dealing with electronic waste.

[0382] The acid in CFA can be used to extract REE content.

[0383] There are two types of CFA classified by chemical composition: CFA-F, with a total content of SiO2, Al2O3, and Fe2O3 > 70 wt%, and CFA-C, with a higher CaO abundance [Liu 2019]. In the examples evaluated herein, CFA-F was collected from Appalachian Basin (App), and CFA-C was collected from Powder River Basin (PRB), both in the United States [Taggart 2016]. Figure 42 These are photographs of CFA-C 4201 and CFA-F 4202 (scale bar, 4 cm).

[0384] CFA consists of a predominantly amorphous phase (60-90%) [Zhang 2020], with the remaining crystalline material mainly consisting of quartz and mullite, as shown in the X-ray diffraction (XRD) pattern. Figure 43A In addition to Ca enrichment in CFA-C, X-ray photoelectron spectroscopy (XPS) was also observed. Figure 43B Elemental analysis by energy dispersive X-ray spectroscopy (EDS) revealed a high carbon content in CFA-F, which is likely due to incomplete combustion of the coal feedstock. The high carbon content in CFA-F was also evident through thermogravimetric analysis (TGA) showing significant weight loss at ~700°C.

[0385] The total REE content in CFA was determined by HF:HNO3 digestion. [Taggart 2016]. Total REE content c 总计 (CFA Raw) for CFA-F is 516±48 mg kg -1 The CFA-C content was 418 ± 71 mg / kg. -1 . Figure 43C CFA from App has a higher REE content than CFA from PRB, consistent with Taggart 2016. The acid-leaching REE content c0 (CFA Raw) from CFA feedstock was measured using 1M HCl or 15M HNO3 [Taggart 2016; Middleton 2020]. For CFA-F, the REE content extractable by HNO3 and HCl was 144 ± 32 mg kg, respectively. -1 and 160±50mg kg -1 ( Figure 43CThe extractable REE contents for CFA-C were ~28% and ~31% respectively (Y0). The extractable REE contents for HNO3 and HCl were 246 ± 71 mg / kg. -1 and 231±81mg kg -1 ( Figure 43C These correspond to REE extractability of ~59% and ~55%, respectively (Y0). The conclusion is that once the acid concentration exceeds 1M, its impact on REE extractability is limited; therefore, 1M HCl leaching is used in the standard protocol for subsequent evaluation.

[0386] The acid extractability of REEs from CFA-C is higher than that from CFA-F. This is consistent with [Liu 2019], who attributed the higher extractability to the higher content of readily soluble REEs, such as REE oxides in CFA-C. Morphological images of CFA-F obtained by scanning electron microscopy (SEM) are shown... Figure 43D Furthermore, high carbon content hinders the accessibility of aqueous acids to REE-containing substances, resulting in low extractability of individual REEs ranging from 21% to 42%. Figure 43E In contrast, CFA-C consists of fine, uncovered spherical particles. Figure 43F This is beneficial to the acid leaching process, resulting in a relatively high extractability of 33% to 67% for individual REEs. Figure 43G ).

[0387] Improving REE recovery from CFA through electrothermal activation

[0388] In the electrothermal activation process via FJH, CFA raw material is first mixed with carbon black (CB) as a conductive additive. The mixture of CFA and CB (~30% CB) is then loaded into a quartz tube between two graphite electrodes. Figure 41A and 44A The sample's resistance (R) is adjustable by regulating the compressive force between the two electrodes, which are connected to a 60 mF capacitor bank. High-voltage discharge through the capacitor raises the sample to a high temperature. Detailed experimental parameters are shown in Table XI.

[0389] During a typical discharge process with an FJH voltage of 120V, R of 1Ω, and a discharge time (t) of 1 second, the current curve passing through the sample was recorded, with a peak current at ~120A, followed by a current plateau at ~7A. Figure 44B The corresponding real-time temperature profile shows a peak temperature as high as ~3000℃, followed by stable heating at ~1150℃. Figure 44C The solid obtained after FJH is called activated CFA. Figure 45(A flowchart is shown for REE recovery from CFA 4501 to CFA+CB 4502 synthesized (via FJH) to activated CFA 4503). The acid-leaching REE content c (activated CFA) from activated CFA was measured using a 1M HCl leaching procedure. The REE recovery rate (Y) from activated CFA was calculated and compared with the REE recovery rate (Y0) from the CFA feedstock.

[0390] Apply a series of FJH voltages from 50V to 150V. Figure 44D At ~120V, the total REE content (1M HCl, 85℃) from activated CFA-F that can be leached with HCl was improved to 329±14 mg kg. -1 . Figure 44D This corresponds to a recovery rate of Y ~64%, representing an improvement of ~206% compared to the recovery rate of CFA-F feedstock (Y 0 ~31%). The pH-dependent leaching kinetics of REEs from CFA-F feedstock and activated CFA-F were investigated. Figure 44E (CFA-F feedstock and activated CFA-F are curves 4401-4402, respectively). Generally, the yield decreases with increasing acid pH. Notably, at pH 2 (or 0.01M HCl), the REE recovery from activated CFA-F remains Y–45%, significantly higher than the REE recovery from CFA feedstock under the same leaching conditions (Y 0–9% at pH 2), and even at much higher acid concentrations (Y 0–31% at pH 0).

[0391] For CFA-C, under optimized FJH conditions, the acid leaching capacity of REEs from activated CFA-C, measured using an HCl leaching program (1M HCl, 85°C), was Y ~ 103%. Figure 44F The CFA-F raw material and activated CFA-F are curves 4403-4404, respectively, corresponding to a proportion of ~187% of the acid leaching property (Y0~55%) from the CFA-C raw material.

[0392] Even with dilute acid (pH 1, 0.1M HCl), the recovery rate of REE from activated CFA-C remains at approximately 94%, significantly higher than the recovery rate of the CFA-C feedstock (0–54%). This will make the wastewater stream easier to manage.

[0393] For a single REE, using the FJH activation process and the same leaching procedure (1M HCl, 85℃), the acid leaching properties of CFA-F ( Figure 44G The improvement was from 170% to 230% for CFA-C ( Figure 44HThe efficiency improved from 170% to 210%. A similar improvement was achieved using dilute acid leaching (0.1M HCl, 85°C). No significant deviation was observed in the REEs, indicating that the FJH activation process works indiscriminately for all REEs.

[0394] As a control, the REE content in carbon black was measured using the same digestion method. The total REE content in carbon black was ~5 mg / kg. -1 This corresponds to approximately 1% of the REE content in CFA. Therefore, using carbon black will not introduce significant errors in these measurements. In practical applications, carbon black can be substituted with any other inexpensive source of anthracite or moderately conductive carbon, but the REE content of that source should be taken into account in yield calculations.

[0395] Mechanism of improved REE extractability

[0396] The mechanism by which REE leaching is improved through electrothermal activation was investigated. The morphology and distribution of REE in coal flasks (CFAs) determine REE extractability. REE phosphates, including monazite and xenotime, are among the major counterions of REE in coal [Liu 2019; Stuckman 2018]. REE phosphates are relatively stable components and do not melt or thermally dissociate in air at temperatures up to ~2000 °C [Ushakov 2001; Hikichi 1987]. Coal combustion temperatures are typically 1300 °C to 1700 °C [Stuckman 2018]. As a result, trace phases containing REE, including monazite and xenotime, persist in CFAs [Kolker 2017; Smolka-Danielowska 2010]. REEs can also be partitioned and coated into the glassy portion of CFAs by diffusion into melts (e.g., aluminosilicates) formed at coal-fired boiler temperatures [Dai 2014]. Those sparingly soluble REE phosphates and glass are detrimental to REE extraction [Liu2019], while REE oxides and carbonates in CFA are relatively easier to extract by acid leaching.

[0397] The FJH process generates temperatures of ~3000℃, significantly higher than that of coal-fired boilers, which can thermally degrade REE substances. Lanthanum phosphate (LaPO4) and yttrium phosphate (YPO4) are used as representative REE phosphates. Figure 46A As shown, the La2O3 phase was identified after the FJH process on the LaPO4 precursor. Similarly, YPO4 thermally decomposes into Y2O3 after the FJH process. Figure 46B REE oxides have a higher oxidation state than REE phosphates (log 100%). 10 K sp Much higher solubility (log 27 to -24) 10 K sp(5 to 33). See Table XII.

[0398] Table XII

[0399] Gibbs free energy change and solubility product constant of REE metal, oxide and phosphate dissolution reactions at 25℃

[0400]

[0401]

[0402] To provide further insight into the solubility of REE phosphates and oxides, solubility profiles as a function of pH were calculated. Figure 46C (La₂O₃, Y₂O₃, LaPO₄, and YPO₄ are curves 4601-4604, respectively). It was found that LaPO₄ and YPO₄ only exhibited significant solubility near pH 0, while their oxide counterparts dissolved readily at low acidity levels (pH ~ 6). This partially explains the pH-dependent REE leaching kinetics, i.e., using dilute acid resulted in higher REE leaching capacity for activated CFAs compared to the feedstock. Figure 46E-46F (right Figure 46E The Si signal may originate from the quartz tube during the FJH process.

[0403] Besides the thermal decomposition of REE phosphates, ultra-high temperatures can also trigger the thermal reduction of REE compounds. (According to Ellingham diagram...) Figure 46D The carbothermic reduction temperature of REE oxides is estimated to be ~1900℃ (Eu₂O₃) to ~2500℃ (Dy₂O₃). FJH at ~120V produces temperatures as high as ~3000℃. Figure 44C This temperature can reduce REE oxides.

[0404] Y₂O₃ and La₂O₃ were used as representatives to verify the carbothermic reduction of REE oxides via the FJH process. Fine XPS spectral fitting of Y₂O₃ after FJH revealed four peaks. Figure 46E And Table XIII. In Y₂O₃, the peaks at 157.5 and 159.6 eV are designated as the 3d peaks of Y. 5 / 2 and 3D 3 / 2 [Barreca 2001], and in Y(0), the peaks at 156.4 and 158.5 eV are designated as the 3d peaks of Y. 5 / 2 and 3D 3 / 2 [Cole 2020].

[0405] Table XIII

[0406] XPS peak fitting of La and Y

[0407]

[0408] XPS analysis confirmed that Y₂O₃ was reduced to Y metal via the FJH process, while a small proportion of Y₂O₃ likely originated from surface oxidation. Similarly, after FJH, the XPS fine-fit spectra of the La₂O₃ precursor and La₂O₃ were obtained (…). Figure 46F Table XIII) verifies the reduction of La₂O₃ to La metal. [Deasha 1995; Li 2019]. Reduced REEs with low oxidation states are highly reactive materials that readily react with even pure water. [Greenwood 1997]. The calculated Gibbs free energy change (ΔG) for the REE metal dissolution reaction is more negative than that for REE oxides. Figure 46G Table XII shows that REE metals have greater thermodynamic solubility than their oxide counterparts.

[0409] This indicates that the required temperature for thermal activation is >2000℃ for the thermal decomposition of REE phosphates and >2500℃ for the carbothermic reduction of REE oxides, which also provides insight into the voltage-dependent REE leaching properties. Figure 44D To achieve temperatures >2000°C, an FJH voltage of ≥120V is required, while a voltage <100V has limited impact on REE leaching. However, excessively high FJH voltages of ≥150V can lead to prolonged high temperatures >3000°C, which can further result in REE evaporation loss during the FJH process.

[0410] Besides morphology, REE distribution also affects extractability, with REEs encapsulated in or distributed throughout the glass phase being difficult to dissolve [Liu 2019]. FJH allows for ultrafast heating and rapid cooling (>10). 4 K s -1 , Figure 44C This will cause thermal stress and cracking of the glass phase in the CFA, which helps to improve leachability.

[0411] The universality of electrothermal activation process

[0412] For recycling REE, the electrothermal activation process is applicable to other wastes, including BR [Deady 2016; Rivera 2018; Reid 2017] and e-waste (including as described above) [Maroufi 2018; Deshmane 2020; Peelman 2018].

[0413] Red mud (BR) is a waste product of the Bayer process for alumina production. BR is one of the most abundant industrial wastes, with 3 billion tons already stored in waste ponds and an additional 150 million tons generated annually, but currently only 3% is recycled [Service 2020]. BR contains significant amounts of REEs; for example, a total REE content of ~1000 ppm was found in BR from MYTILINEOS "Aluminum of Greece" [Deady 2016]. BR is a dry powder with a fine particle size and contains major components including Fe₂O₃, CaCO₃, FeO(OH), and SiO₂. Figures 47A-47B REEs were extracted from BR using a direct leaching method with 0.5M HNO3 [Ochsenkuhn-Petropulu 1996]. The acid-extractable REE content from the BR feedstock was 428 ± 9 mg / kg. -1 . Figure 47C and 48A -48B.

[0414] Similar to CFA, the REE extractability of BR after the electrothermal activation process also depends on the FJH voltage. Figure 48A Under an optimized FJH voltage of 120V, the extractable REE content was increased to 757±30 mg / kg. -1 ( Figure 48B ), corresponding to Y / Y0~177% from BR raw materials ( Figure 47C The mechanism by which the FJH process improves the REE extractability from BR is considered similar to the mechanism of CFA (…). Figure 46A-46G (This is because phosphate is one of the main counterions of BR. [Boni 2013].)

[0415] This FJH strategy is also applicable to the activation of e-waste and is shown here as a complement to the methods described without the use of mild acid leaching. Due to the rapid upgrading of personal electronic devices, more than 40 million tons of e-waste are generated globally each year, of which <20% is recycled [Zeng 2018]. REE is widely used in electronic devices such as permanent magnets [Deshmane] and capacitors [Alam 2012]. In turn, recycling REE from high-grade e-waste is economically feasible compared to mining REE from ore.

[0416] The electronic waste used in this FJH process is printed circuit boards (PCBs) from discarded computers. Figure 49A (This shows electronic waste ground into powder). For example... Figure 49BAs shown, the abundant metals in electronic waste include copper and aluminum, which are mainly used for interconnects. REEs in PCB waste were extracted via a 1M HCl leaching process at 85°C. The acid-leached REE content from the electronic waste raw material was 61 ± 4 mg / kg. -1 . Figures 50A-50B After optimizing the activation process under the voltage ( Figures 50A-50B The extractable REE content increased to 94.6 ± 0.2 mg / kg. -1 This corresponds to Y / Y0~156% from electronic waste raw materials. Figure 49C and 50A -50B.

[0417] Unlike CFA or BR, REEs in e-waste are typically in the form of readily soluble REE metals or oxides [Alam 2012]. However, due to the laminated structure of electronic devices, REEs are often embedded in the matrix material, which hinders REE extraction by hydrometallurgical processes. The FJH method can accelerate the leaching rate and extent of metal extraction by exposing the metal through matrix cracking.

[0418] Scalability and usability

[0419] The FJH process for REE recovery is scalable. To maintain a constant temperature while scaling up the sample quality of each batch, the FJH voltage or the total capacitance of the capacitor bank can be increased. A production rate of >10 kg / day has been achieved through the batch process. The FJH process can be integrated into continuous production for further automation, such as by using… Figures 40A-40B The scheme shown in the image. The continued commercial expansion of the FJH process to tons / day paves the way for the future recovery of REEs from large-scale waste products.

[0420] Economic viability, as profit margins are typically a strong supporter of recycling. Due to the direct sample heating characteristics, short duration, and rapid heating / cooling rate, the FJH process implementation is highly energy efficient, with low power consumption of 600 kWh / ton or $12 / ton, enabling a profit percentage >10× compared to direct leaching of feedstock.

[0421] For further refining, it is necessary to remove dissolved impurities (mainly Al, Si, Fe, Ca, and Mg) from the REE-containing leachate, as well as subsequent separation. It was observed that in most cases, the ratio of REE to impurities in the leachate (c(REE) / c(impurities)) improved with the FJH process, indicating that the FJH process will also benefit subsequent REE separation.

[0422] ore

[0423] Since monazite (Ce,La,Y,Th)PO4 and xenotime ore YPO4 are the main commercial sources of REE production [Cheisson 2019], the implementation scheme can also be used in REE mining to improve the leaching properties of REE ores. Commercially, alkali digestion (70% NaOH, 140-150°C) is the primary leaching technique for monazite [Peelman 2016], or acid roasting (concentrated H2SO4, 200°C) is the primary leaching technique for monazite and xenotime ore [Kim 2016]. This FJH process is faster and less dependent on the use of concentrated alkali and acid. Existing single-element separation techniques, such as solvent extraction and ion exchange [Xie 2014], can be used to process REE mixtures obtained through FJH, as these generally produce less contamination than those generated by conventional mining methods.

[0424] While embodiments of the invention have been shown and described, modifications can be made to them by those skilled in the art without departing from the spirit and teachings of the invention. The embodiments and examples provided herein are merely exemplary and not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. The scope of protection is not limited by the foregoing description but only by the appended claims, which include all equivalents of the subject matter of the claims.

[0425] All patents, patent applications and publications cited herein are incorporated herein in their entirety, to the extent that they provide exemplary, procedural or other details that supplement those set forth herein.

[0426] Quantities and other numerical data may be presented in range format herein. It should be understood that such range format is used for convenience and brevity only and should be flexibly interpreted to include not only the numerical values ​​explicitly described as the boundaries of the range, but also all individual numerical values ​​or subranges encompassed within that range, as if each numerical value and subrange were explicitly described. For example, a numerical range of approximately 1 to approximately 4.5 should be interpreted to include not only the explicitly described boundary of 1 to approximately 4.5, but also individual numbers such as 2, 3, 4, and subranges such as 1 to 3, 2 to 4, etc. The same principle applies to ranges describing only a single numerical value, such as “less than approximately 4.5,” which should be interpreted to include all the aforementioned values ​​and ranges. Furthermore, this interpretation should apply regardless of the width of the range or the characteristics described.

[0427] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the subject matter of this disclosure pertains. While any methods, apparatuses, and materials similar to or equivalent to those described herein may be used in the practice or testing of the subject matter of this disclosure, representative methods, apparatuses, and materials are described hereafter.

[0428] According to long-standing patent law practice, the terms "an" and "a" used in this application (including the claims) mean "one or more".

[0429] Unless otherwise indicated, all figures expressing quantities of ingredients, reaction conditions, etc., as used in the specification and claims shall be understood to be modified in all cases by the term “about.” Therefore, unless indicated to the contrary, the numerical parameters set forth in this specification and appended claims are approximate and may be varied according to the desired properties obtained from the subject matter view of this disclosure.

[0430] The terms “about” and “substantially” as used herein, when referring to a value or quantity of mass, weight, time, volume, concentration, or percentage, mean to cover variations from the specified quantity by ±20% in some embodiments, ±10% in some embodiments, ±5% in some embodiments, ±1% in some embodiments, ±0.5% in some embodiments, and ±0.1% in some embodiments, and such variations are appropriate for implementing the disclosed method.

[0431] As used herein, the terms “substantially vertical” and “substantially parallel” refer to variations within ±10° in some embodiments, ±5° in some embodiments, ±1° in some embodiments, and ±0.5° in some embodiments.

[0432] As used herein, the term "and / or" means, in the context of enumerating entities, that the entities exist individually or in combination. Thus, for example, the phrase "A, B, C and / or D" individually includes A, B, C, and D, but also includes any and all combinations and sub-combinations of A, B, C, and D.

[0433] References

[0434] PCT international patent application publication number WO / 2020 / 051000, entitled “Flash Joule Heating Synthesis Method And Compositions Thereof”, filed on August 23, 2019, and published on March 12, 2020, by James M. Tour et al. (“the Tour PCT'000 application”).

[0435] Abrahamson, J., “Graphite sublimation temperatures, carbon arcs and crystalline erosion,” Carbon, 1974, 12, 111 - 141 (“Abrahamson 1974”).

[0436] Alam, M. A. et al., “Economics of rare earth elements in ceramic capacitors,” Ceram. Int., 2012, 38, 6091 - 6098 (“Alam 2012”).

[0437] Algozeeb, W. A. et al., “Flash graphene from plastic waste,” ACS Nano, 2020, 14, 15595 - 15604 (“Algozeeb 2020”).

[0438] Amrute, A. P. et al., “High - surface - area corundum by mechanochemically induced phase transformation of boehmite,” Science, 2019, 366, 485 - 489 (“Amrute 2019”).

[0439] Awasthi, A. K. et al., “Circular economy and electronic waste,” Nat. Electron., 2019, 2, 86 - 89 (“Awasthi 2019”).

[0440] Baek, D. et al., “Ordered mesoporous metastable alpha - MoC 1-x with enhanced water dissociation capability for boosting alkaline hydrogen evolution activity,” Adv. Funct. Mater., 2019, 29, 1901217 - 1901225 (“Baek 2019”).

[0441] Balaji, R. et al., Urban Mining and Sustainable Waste Management Ch.7 (Springer, Singapore), 2020 (“Balaji 2020”).

[0442] Balima, F. et al., Phase transformation of alumina induced by high - pressure spark plasma sintering (HP - SPS),” Scripta Mater, 2019, 158, 20 - 23 (“Balima 2019”).

[0443] Barreca, D. et al., Y2O3 thin films characterized by XPS, Surf. Scid Spectra, 2001, 8, 234 - 239 (“Barreca 2001”).

[0444] Bianchini, M. et al., “The interplay between thermodynamics and kinetics in the solid - state synthesis of layered oxides,” Nat. Mater., 2020, 19, 1088 - 1095 (“Bianchini 2020”).

[0445] Blochl, P.E., “Projector Augmented - wave method,” Phys. Rev. B, 1994, 50, 17953 - 17979 (“Blochl 1994”).

[0446] Boni, M. et al., “Quantitative mineralogical characterization of karst bauxite deposits in the southern Apennines, Italy,” Econ. Geol., 2013, 108, 813 - 833 (“Boni 2013”).

[0447] Cao, W.B. et al., “Sintering of alpha-Al2O3 nanocrystalline ceramic from large alpha-Al2O3 polycrystalline nanoparticles,” Ceram Int, 2017, 43, 1378-1382 (“Cao 2017”).

[0448] Chang, P.L. et al., “Examinations on the critical and primary crystallite sizes during theta-to alpha-phase transformation of ultrafine alumina powders,” Nano Lett, 2001, 1, 253-261 (“Chang 2001”).

[0449] Chauruka, S.R. et al., “Effect of mill type on the size reduction and phase transformation of gamma alumina,” Chem Eng Sci, 2015, 134, 774-783 (“Chauruka 2015”).

[0450] Cheisson, T et al., “Rare earth elements: Mendeleev’s bane, modern marvels, Science, 2019, 363, 489-493 (“Cheisson 2019”).

[0451] Chen, W.F. et al., “Recent developments in transition metal carbides and nitrides as hydrogen evolution electrocatalysts,” Chem. Commun., 2013, 49, 8896-8909 (“Chen 2013”).

[0452] Chen, Y. et al., “Phase engineering of nanomaterials,” Nat.Rev.Chem., 2020, 4, 243-256 (“Chen 2020”).

[0453] Claridge, J.B. et al., “Study of the temperature-programmed reaction synthesis of early transition metal carbide and nitride catalyst materials from oxide precursors,” Chem. Mater., 2000, 12, 132-142 (“Claridge 2000”).

[0454] Cole, K.M. et al., “Surface Y2O3 layer formed on air exposed Y powder characterized by XPS,” Surf. Sci. Spectra, 2020, 27, 024010-024021 (“Cole 2020”).

[0455] Cui, J.R. et al., “Metallurgical recovery of metals from electronic waste: A review,” J. Hazard. Mater., 2008, 158, 228-256 (“Cui 2008”).

[0456] Dai, S.F. et al., “Petrology, mineralogy, and chemistry of size-fractioned fly ash from the Jungar Power Plant, Inner Mongolia, China, with emphasis on the distribution of rare earth elements,” Energy Fuels, 2014, 28, 1502-1514 (“Dai 2014”).

[0457] De Aza, A.H. et al., “Crack growth resistance of alumina, zirconia and zirconia toughened alumina ceramics for joint prostheses,” Biomaterials, 2002, 23, 937-945 (“De Aza 2002”).

[0458] Deady, E. A. et al., “A review of the potential for rare-earth element resources from European red muds: examples from Seydisehir, Turkey and Parnassus-Giona, Greece,” Mineral Mag, 2016, 80(1), 43-61 (“Deady 2016”).

[0459] Deasha, A. M. et al., “Oxidation of lanthanum overlayers on Cu(111),” Surf. Sci., 1995, 322, 41-50 (“Deasha 1995”).

[0460] Demetriou, M. D. et al., “Computation of metastable phases in tungsten-carbon system,” J. Phase Equilib., 2002, 23, 305-309 (“Demetriou 2002”).

[0461] Deshmane, V. G. et al., “Selective recovery of rare earth elements from a wide range of e-waste and process scalability of membrane solvent extraction,” Environ. Sci. Technol., 2020, 54, 550-558 (“Deshmane 2020”).

[0462] Dudarev, S. L. et al., “Electron-energy-loss spectra and the structural stability of nickel oxide: An LSDA+U study,” Phys. Rev. B, 1998, 57, 1505-1509 (“Dudarev 1998”).

[0463] Dyjak, S. et al., “A simple method of synthesis and surface purification of titanium carbide powder,” Int. J. Refract. Met. H, 2013, 38, 87 - 91 (“Dyjak 2013”).

[0464] Fan, X. J. et al., “Atomic H-induced Mo2C hybrid as an active and stable bifunctional electrocatalyst,” ACS Nano, 2017, 11, 384 - 394 (“Fan 2017”).

[0465] Frank, B. et al., “Kinetics and mechanism of the reduction of nitric oxides by H-2 under lean-burn conditions on a Pt-Mo-Co / alpha-Al2O3 catalyst,” Appl Catal B-Environ, 1998, 19, 45 - 57 (“Frank 1998”).

[0466] Gao, Q. S. et al., “Structural Design and Electronic Modulation of Transition-Metal-Carbide Electrocatalysts toward Efficient Hydrogen Evolution,” Adv Mater, 2019, 31(2) (“Gao 2019”).

[0467] Ghosh, B. et al., “Waste Printed Circuit Boards recycling: an extensive assessment of current status,” J. Clean. Prod., 2015, 94, 5 - 19 (“Ghosh 2015”).

[0468] Giorgi, E. et al., “Reactive carbothermal reduction of ZrC and ZrOC using Spark Plasma Sintering,” Adv. Appl. Ceram., 2018, 117, S34 - S47 (“Giorgi 2018”).

[0469] Greeley, J., Jaramillo et al., “Computational high - throughput screening of electrocatalytic materials for hydrogen evolution,” Nat. Mater., 2006, 5, 909 - 913 (“Greeley 2006”).

[0470] Greenwood, N.N. et al., Chemistry of the Elements (2nd ed., Butterworth - Heinemann), 1997, 299. (“Greenwood 1997”).

[0471] Gong, Q.F. et al., “Ultrasmall and phase - pure W2C nanoparticles for efficient electrocatalytic and photoelectrochemical hydrogen evolution,” Nat Commun, 2016, 7 (“Gong 2016”).

[0472] Guo, R.Y. et al., “Selective Corrosion Preparation and Sintering of Disperse - Al2O3 Nanoparticles,” J Am Ceram Soc, 2016, 99, 3556 - 3560 (“Guo 2016”).

[0473] Hall, W.J. et al., “Separation and recovery of materials from scrap printed circuit boards,” Resour. Conserv. Recycl., 2007, 51, 691 - 709 (“Hall 2007”).

[0474] Han, N. N. et al., “Nitrogen-doped tungsten carbide nanoarray as an efficient bifunctional electrocatalyst for water splitting in acid,” Nat. Commun., 2018, 9, 924 (“Han 2018”).

[0475] Hikichi, Y. et al., “Melting temperatures of monazite and xenotime,” J. Am. Ceram. Soc., 1987, 70, 252 - 253 (“Hikichi 1987”).

[0476] Hong, Y. et al., “Precious metal recovery from electronic waste by a porous porphyrin polymer,” P. Natl. Acad. Sci. USA, 2010, 117, 16174 - 16180 (“Hong 2020”).

[0477] Hugosson, H. W. et al., “Phase stability diagrams of transition metal carbides, a theoretical study,” Chem. Phys. Lett., 2001, 333, 444 - 450 (“Hugosson 2001”).

[0478] Hugosson, H. W. et al., “Theory of phase stabilities and bonding mechanisms in stoichiometric and substoichiometric molybdenum carbide,” J. Appl. Phys., 1999, 86, 3758 - 3767 (”Hugosson 1999”).

[0479] Ighodaro, O. L. et al., “Fracture toughness enhancement for alumina systems: A review,” Int J Appl Ceram Tec, 2008, 5(3), 313 - 323 (“Ighodaro 2008”).

[0480] Jadhav, U. et al., “Hydrometallurgical recovery of metals from large printed circuit board pieces,” Sci. Rep.-UK, 2015, 5, 14574 (“Jadhav 2015”).

[0481] Jang, H.D. et al., “The effects of temperature on particle-size in the gas-phase production of TiO2,” Aerosol. Sci. Tech., 1995, 23, 553-560 (“Jang 1995”).

[0482] Johnson, W.L. et al., “Beating Crystallization in Glass-forming metals by millisecond heating and processing,” Science, 2011, 332, 828-833 (“Johnson 2011”).

[0483] Johnston, G.P. et al., “Reactive Laser Ablation Synthesis of Nanosize Alumina Powder,” J Am Ceram Soc, 1992, 75, 3293-3298 (“Johnston 1992”).

[0484] Julander, A. et al “Formal recycling of e-waste leads to increased exposure to toxic metals: An occupational exposure study from Sweden,” Environ. Int., 2014, 73, 243-251 (“Julander 2014”).

[0485] Jyothi, R.K. et al., “Review of rare earth elements recovery from secondary resources for clean energy technologies: Grand opportunities to create wealth from waste,” J. Clean. Prod., 2020, 267, 122048 - 122073 (“Jyothi 2020”).

[0486] Karagedov, G.R. et al., “Preparation and sintering of nanosized alpha - Al2O3 powder,” Nanostruct Mater, 1998, 11, 559 - 572 (“Karagedov 1999”).

[0487] Kaya, M., “Recovery of metals and nonmetals from electronic waste by physical and chemical recycling processes,” Waste Manage., 2016, 57, 64 - 90 (“Kaya 2016”).

[0488] Khaliq, A. et al., “Metal extraction processes for electronic waste and existing industrial routes: a review and australian perspective,” Resources, 2014, 3, 152 - 179 (“Khaliq 2014”).

[0489] Kim, R. et al., “Optimization of acid leaching of rare - earth elements from Mongolian apatite - based Ore,” Minerals, 2016, 6, 63 (“Kim 2016”).

[0490] King, J.F. et al., “Aqueous acid and alkaline extraction of rare earth elements from coal combustion ash,” Int. J. Coal Geol., 2018, 195, 75 - 83 (“King2018”).

[0491] Kinuthia, G.K. et al., “Levels of heavy metals in wastewater and soil samples from open drainage channels in Nairobi, Kenya: community health implication,” Sci. Rep.-UK, 2020, 10, 8434 (“Kinuthia 2020”).

[0492] Kolel-Veetil, M.K. et al., “Formation of a superconducting mixture of beta-Mo2C nanoparticles and carbon nanotubes in an amorphous matrix of molybdenum compounds by the pyrolysis of a molybdenum derivative of a carboranylenesiloxane,” Chem. Mater., 2005, 17, 6101 - 6107 (“Kolel-Veetil 2005”).

[0493] Kolker, A. et al., “Distribution of rare earth elements in coal combustion fly ash, determined by SHRIMP-RG ion microprobe,” Int. J. Coal. Geol., 2017, 184, 1 - 10 (“Kolker 2017”).

[0494] Krell, A. et al., “Effects of grain size and humidity on fretting wear in fine-grained alumina, Al2O3 / TiC, and zirconia,” J Am Ceram Soc, 1996, 79, 1139-1146 (“Krell 1996”).

[0495] Kresse, G. et al., “Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set,” Phys. Rev. B, 1996, 54, 11169-11186 (“Kresse 1996”).

[0496] Kumar, A. S. et al., “Machinability of hardened steel using alumina based ceramic cutting tools,” Int J Refract Met H, 2003, 21, 109-117 (“Kumar 2003”).

[0497] Kurlov, A. S. et al., “Tungsten carbides and W-C phase diagram,” Inorg. Mater., 2006, 42, 121-127 (“Kurlov 2006”).

[0498] Laine, R. M. et al., “Nano-alpha-Al2O3 by liquid-feed flame spray pyrolysis,” Nat Mater, 2006, 5, 710-712 (“Laine 2006”).

[0499] Lamouri, S. et al., “Control of the gamma-alumina to alpha-alumina phase transformation for an optimized alumina densification,” Bol Soc Esp Ceram V, 2017, 56, 47-54 (“Lamouri 2))

[0500] Lee, J.C.K. et al., “Pathways for greening the supply of rare earth elements in China,” Nat. Sustain., 2018, 1, 598 - 605 (“Lee 2018”).

[0501] Leung, A.O.W. et al., “Heavy metals concentrations of surface dust from e - waste recycling and its human health implications in southeast China,” Environ. Sci. Technol., 2008, 42, 2674 - 2680 (“Leung 2008”).

[0502] Levin, I. et al., “Metastable alumina polymorphs: Crystal structures and transition sequences,” J Am Ceram Soc, 1998, 81, 1995 - 2012 (“Levin 1998”).

[0503] Li, J.G. et al., “Densification and grain growth of Al2O3 nanoceramics during pressureless sintering,” J Am Ceram Soc, 2006, 89, 139 - 143 (“Li 2006”).

[0504] Li, J.G. et al., “Synthesis and sintering behavior of an anocrystalline alpha - alumina powder,” Acta Mater, 2000, 48, 3103 - 3112 (“Li 2000”).

[0505] Li, J.P.H. et al., “Understanding of binding energy calibration in XPS of lanthanum oxide by in situ treatment,” Phys. Chem. Chem. Phys., 2019, 21, 22351 - 22358 (“Li 2019”).

[0506] Li, J. S. et al., “Coupled molybdenum carbide and reduced graphene oxide electrocatalysts for efficient hydrogen evolution,” Nat. Commun., 2016, 7, 11204 (“Li 2016”).

[0507] Li, Z. et al., “Two-dimensional transition metal carbides as supports for tuning the chemistry of catalytic nanoparticles,” Nat. Commun., 2018, 9, 5258 (“Li 2018”).

[0508] Lide, D. R., CRC Handbook of Chemistry and Physics Ch.4 (CRC Press, Internet Version), 2005 (“Lide 2005”).

[0509] Lin, B. Y. et al., “Ammonia Synthesis Activity of Alumina-Supported Ruthenium Catalyst Enhanced by Alumina Phase Transformation,” Acs Catal, 2019, 9(3), 1635 - 1644 (“Lin 2019”).

[0510] Lin, L. L. et al., “Low-temperature hydrogen production from water and methanol using Pt / alpha-MoC catalysts,” Nature, 2017, 544, 80 - 83 (“Lin 2017”).

[0511] Liu, P. et al., “Comprehensive understandings of rare earth element(REE)speciation in coal fly ashes and implication for REE extractability,” Environ. Sci. Technol., 2019, 53, 5369-5377 (“Liu2019”).

[0512] Lodziana, Z. et al., “A negative surface energy for alumina,” Nat Mater, 2004, 3(5), 289-293 (“Lodziana 2004”).

[0513] Loffler, L. et al., “Transformation mechanism of the dehydration of diaspore,” J Am Ceram Soc, 2003, 86(4), 534-540 (“Loffler 2003”).

[0514] Luong, D. X. et al., “Gram-scale bottom-up flash graphene synthesis,” Nature, 2020, 577(7792), 647-651 (“Luong 2020”).

[0515] Ma, R. G. et al., “Ultrafine Molybdenum Carbide Nanoparticles Composited with Carbon as a Highly Active Hydrogen-Evolution Electrocatalyst,” Angew Chem Int Edit, 2015, 54(49), 14723-14727 (“Ma 2015”).

[0516] Maroufi, S. et al., “Recovery of rare earth(i.e., La, Ce, Nd, and Pr)oxides from end-of-life Ni-MH battery via thermal isolation,” ACS Sustain. Chem. Eng., 2018, 6, 11811-11818 (“Maroufi 2018”).

[0517] Matanovic, I. et al., “Nitrogen electroreduction and hydrogen evolution on cubic molybdenum carbide: a density functional study,” Phys. Chem. Chem. Phys., 2018, 20, 14679-14687 (“Matanovic 2018”).

[0518] Mavrikakis, M., “Computational methods: A search engine for catalysts,” Nat. Mater., 2006, 5, 847-848 (“Mavrikakis 2006”).

[0519] McHale, J. M. et al., “Surface energies and thermodynamic phase stability in nanocrystalline aluminas,” Science, 1997, 277(5327), 788-791 (“McHale 1997”).

[0520] Middleton, A. et al., “Major element composition controls rare earth element solubility during leaching of coal fly ash and coal by-products,” Int. J. Coal Geol., 2020, 227, 103532-103539 (“Middleton 2020”).

[0521] Mizuta, H. et al., “Preparation of High-Strength and Translucent Alumina by Hot Isostatic Pressing,” J Am Ceram Soc, 1992, 75, 469-473 (“Mizuta 1992”).

[0522] Monkhorst,H.J., “Special Points for Brillouin-Zone Integrations,” Phys.Rev.B,1976,13,5188-5192(“Monkhorst 1976”).

[0523] Ochsenkuhn-Petropoulos, M. Baker, “Recovery of lanthanides and yttrium from red mud by selective leaching,” Anal.Chim.Acta., 1996, 319, 249-254.

[0524] Ochsenkuhn-Petropoulos, M. Beck, “Selective Separation and Determination of Scandium from Yttrium and Lanthanides in Red Mud by a Combined Ion Exchange / Solvent Extraction Method,” Anal Chem Acta, 1995, 315(1-2), 231-237(“Ochsenkuhn-Petropoulos 1995”).

[0525] Ogunseitan, OA General, “The electronics revolution: From e-wonderland to wasteland,” Science, 2009, 326, 670-671(“Ogunseit 2009”).

[0526] ASM Handbook Volume 3: Alloy Phase Diagrams(ASMInternational,Ohio),2016(“Okamoto 2016”).

[0527] Olavarria-Contreras, I.J. et al., “C-Au covalently bonded molecular junctions using nonprotected alkynyl anchoring groups,” J. Am. Chem. Soc., 2016, 138, 8465-8469 (“Olavarria-Contreras 2016”).

[0528] Oyama, S.T., “Preparation and catalytic properties of transition-metal carbides and nitrides,” Catal. Today, 1992, 15, 179-200 (“Oyama 1992”).

[0529] Park, Y.J. et al., “Recovery of high purity precious metals from printed circuit boards,” J. Hazard. Mater., 2009, 164, 1152-1158 (“Park 2009”).

[0530] Pearson, R.G., “Hard and soft acids and bases,” J. Am. Chem. Soc., 1963, 85, 3533-3539 (“Pearson 1963”).

[0531] Peelman, S. et al., “Hydrometallurgical recovery of rare earth elements from mine tailings and WEEE,” J. Sustain. Metall., 2018, 4, 367-377 (“Peelman 2018”).

[0532] Peelman, S. et al., in Rare Earths Industry (Borges, I. et al., Eds., Elsevier, Boston), 2016, 319-334 (“Peelman 2016”).

[0533] Perdew, J.P. et al., “Generalized gradient approximation made simple,” Phys. Rev. Lett., 1996, 77, 3865 - 3868 (“Perdew 1996”).

[0534] Peterson, E.J. et al., “Low-temperature carbon monoxide oxidation catalysed by regenerable atomically dispersed palladium on alumina,” Nat Commun, 2014, 5, 4885 (“Peterson 2014”).

[0535] Pinto, H.P. et al., “Ab initio study of gamma-Al2O3 surfaces,” Phys Rev B, 2004, 70, 125402 - 125412 (“Pinto 2004”).

[0536] Pol, V.G. et al., “One-step synthesis and characterization of SiC, Mo2C, and WC nanostructures,” Eur. J. Inorg. Chem., 2009, 6, 709 - 715 (“Pol 200�”).

[0537] Politi, J.R.D. et al., “Atomic and electronic structure of molybdenum carbide phases: bulk and low Miller-index surfaces,” Phys. Chem. Chem. Phys., 2013, 15, 12617 - 12625 (“Politi 2013”).

[0538] Popoola, O.E. et al., “Levels of awareness and concentrations of heavy metals in the blood of electronic waste scavengers in Nigeria,” J. Health Pollut., 2019, 9, 190311 (“Popoola 2019”).

[0539] Quinet, P. et al., “Recovery of precious metals from electronic scrap by hydrometallurgical processing routes,” Miner. Metall. Proc., 2005, 22, 17 - 22 (“Quinet 2005”).

[0540] Reddy, K.M. et al., “Enhanced mechanical properties of nanocrystalline boron carbide by nanoporosity and interface phases,” Nat. Commun., 2012, 3, 1052 (“Reddy 2012”).

[0541] Reid, S. et al., “Technospheric mining of rare earth elements from bauxite residue (red mud): process optimization, kinetic investigation, and microwave pretreatment,” Sci. Rep., 2017, 7, 15252 (“Reid 2017”).

[0542] Rivera, R.M. et al., “Extraction of rare earths from bauxite residue (red mud) by dry digestion followed by water leaching,” Miner. Eng., 2018, 119, 82 - 92 (“Rivera 2018”).

[0543] Rosa, C.J., “Carbon diffusion in Mo2C as determined from carburization of Mo,” Metall. Trans. A, 1983, 14, 199 - 202 (“Rosa 1983”).

[0544] Sahoo, P.K. et al., “Recovery of metals and other beneficial products from coal fly ash: a sustainable approach for fly ash management,” Int. J. Coal Sci. Technol., 2016, 3, 267 - 283 (“Sahoo2016”).

[0545] Sarker, P. et al., “High-entropy high-hardness metal carbides discovered by entropy descriptors,” Nat. Commun., 2018, 9, 4980 (“Sarker 2018”).

[0546] Sarvar, M. et al., “Characterization and mechanical separation of metals from computer Printed Circuit Boards (PCBs) based on mineral processing methods,” Waste Manage., 2015, 45, 246 - 257 (“Sarvar2015”).

[0547] Schatzmann, M.T. et al., “Synthesis of monoclinic monazite, LaPO4, by direct precipitation,” J. Mater. Chem., 2009, 19, 5720 - 5722 (“Schatzmann 2009”).

[0548] Sethurajan, M. et al., “Recent advances on hydrometallurgical recovery of critical and precious elements from end of life electronic wastes - a review,” Crit. Rev. Env. Sci. Tec., 2019, 49, 212 - 275 (“Sethurajan 2019”).

[0549] Service, R.F., “Red alert,” Science, 2020, 369, 910 - 911 (“Service2020”).

[0550] Smith, R.C. et al., “Selective recovery of rare earth elements from coal fly ash leachates using liquid membrane processes,” Environ. Sci. Technol., 2019, 53, 4490 - 4499 (“Smith 2019”).

[0551] Smolka - Danielowska, D., “Rare earth elements in fly ashes created during the coal burning process in certain coal - fired power plants operating in Poland - Upper Silesian Industrial Region,” J. Environ. Radioactiv., 2010, 101, 965 - 968 (“Smolka - Danielowska 2010”).

[0552] Soderberg, M., “Resistive breakdown of inhomogeneous - media,” Phys Rev B, 1987, 35, 352 - 357 (“Soderberg 1987”).

[0553] Song, H.J. et al., “Ultrafine alpha - phase molybdenum carbide decorated with platinum nanoparticles for efficient hydrogen production in acidic and alkaline media,” Adv. Sci., 2019, 6, 1802135 - 1802142 (“Song 2019”).

[0554] Stanford, M.G. et al., “Flash Graphene Morphologies,” ANS Nano, 2020, https: / / doi.org / 10.1021 / acsnano.0c05900 (“Stanford 2020”).

[0555] Steiner, C.J.-P. et al., “Kinetics of the gamma-to-alpha alumina phase transformation,” J Am Ceram Soc, 1971, 54, 412-413 (“Steiner 1971”).

[0556] Sthiannopkao, S. et al., “Handling e-waste in developed and developing countries: Initiatives, practices, and consequences,” Sci Total Environ, 2013, 463, 1147-1153 (“Sthiannopkao 2013”).

[0557] Stuckman, M.Y. et al., “Distribution and speciation of rare earth elements in coal combustion by-products via synchrotron microscopy and spectroscopy,” Int.J.Coal Geol., 2018, 195, 125-138 (“Stuckman 2018”).

[0558] Sun, G.L. et al., “Using yeast to sustainably remediate and extract heavy metals from waste waters,” Nat.Sustain., 2020, 3, 303-311 (“Sun 2020”).

[0559] Sun, W.H. et al., “Thermodynamic routes to novel metastable nitrogen-rich nitrides,” Chem.Mater., 2017, 29, 6936-6946 (“Sun W 2017”).

[0560] Sun, Z. et al., “Toward sustainability for recovery of critical metals from electronic waste: The hydrochemistry processes,” ACS Sustain. Chem. Eng., 2017, 5, 21 - 40 (“Sun Z 2017”).

[0561] Taggart, R.K. et al., “Effects of roasting additives and leaching parameters on the extraction of rare earth elements from coal fly ash,” Int. J. Coal Geol., 2018, 196, 106 - 114 (“Taggart 2018”).

[0562] Taggart, R.K. et al., “Trends in the rare earth element content of US - based coal combustion fly ashes,” Environ. Sci. Technol., 2016, 50, 5919 - 5926 (“Taggart 2016”).

[0563] Taktak, R. et al., “Effect of binders on microstructural and mechanical properties of sintered alumina,” Mater Charact, 2011, 62, 912 - 916 (“Taktak 2011”).

[0564] Teng, X.Y. et al., “Effect of Al2O3 particle size on the mechanical properties of alumina - based ceramics,” Mat SciEng a - Struct, 2007, 452, 545 - 551 (“Teng 2007”).

[0565] Theo, L., Proceedings of the 1998 IEEE International Symposium on Electronics and the Environment. ISEE-1998 (Cat. No. 98CH36145), 1998, 42-47 ("Theo1998").

[0566] Ueda, T., Ichiishi et al., Metal Sustainability: Global Challenges, Consequences, and Prospects, Ch. 15, (John Wiley & Sons Press, West Sussex), 2016 ("Ueda 2016").

[0567] Ushakov, S. V. et al., "Thermochemistry of rare-earth orthophosphates," J. Mater. Res., 2001, 16, 2623-2633 ("Ushakov2001").

[0568] Xie, F. et al., "A critical review on solvent extraction of rare earths from aqueous solutions," Miner. Eng., 2014, 56, 10-28 ("Xie 2014").

[0569] Wan, C. et al., "Multiple Phases of Molybdenum Carbide as Electrocatalysts for the Hydrogen Evolution Reaction," Angew Chem Int Edit, 2014, 53(25), 6407-6410 ("Wan 2014").

[0570] Wan, J. et al., "Rapid synthesis of size-tunable transition metal carbide nanodots under ambient conditions," J. Mater. Chem. A, 2019, 7, 14489-14495 ("Wan2019").

[0571] Wang, C.W. et al., “A general method to synthesize and sinter bulk ceramics in seconds,” Science, 2020, 368, 521-526 (“Wang 2020”).

[0572] Wang, K.F. et al., “Fabrication of ultrafine and high-purity tungsten carbide powders via a carbothermic reduction-carburization process,” J. Alloy Compd., 2019, 784, 362-369 (“Wang K 2019”).

[0573] Wang, S.F. et al., “Transparent ceramics: Processing, materials and applications,” Prog Solid State Ch, 2013, 41, 20-54 (“Wang 2013”).

[0574] Wang, Y.Y. et al., “Raman studies of monolayer graphene: The substrate effect,” J Phys Chem C, 2008, 112, 10637-10640 (“Wang 2008”).

[0575] Wang, Z. et al., “Rare earth elements and yttrium in coal ash from the Luzhou power plant in Sichuan, Southwest China: Concentration, characterization and optimized extraction,” Int. J. Coal Geol., 2019, 203, 1-14 (“Wang Z 2019”).

[0576] Wang, Z.H. et al., “Take responsibility for electronic-waste disposal,” Nature, 2016, 536, 23-25 (“Wang 2016”).

[0577] Wolden, C. A. et al., “Synthesis of beta-Mo2C Thin Films,” ACS Appl. Mater. Inter., 2011, 3, 517-521 (“Wolden 2011”).

[0578] Wu, K. H. et al., “Synthesis of high purity nano-sized transition-metal carbides,” J. Mater. Res. Technol., 2020, 9, 11778-11790 (“Wu 2020”).

[0579] Yamane, L. H. et al., “Recycling of WEEE: Characterization of spent printed circuit boards from mobile phones and computers,” Waste Manage., 2011, 31, 2553-2558 (“Yamane 2011”).

[0580] Yao, S. Y. et al., “Atomic-layered Au clusters on alpha-MoC as catalysts for the low-temperature water-gas shift reaction,” Science, 2017, 357, 389-393 (“Yao 2017”).

[0581] Yao, Y. G. et al., “Carbothermal shock synthesis of high-entropy-alloy nanoparticles,” Science, 2018, 359, 1489-1494 (“Yao 2018”).

[0582] Yoo, Y. S. et al., “Preparation of alpha-alumina nanoparticles via vapor-phase hydrolysis of AlCl3,” Mater Lett, 2009, 63, 1844-1846 (“Yoo 2009”).

[0583] Zeng, M. et al., “Recent advances in heterogeneous electrocatalysts for the hydrogen evolution reaction,” J. Mater. Chem. A, 2015, 3, 14942 - 14962 (“Zeng2015”).

[0584] Zeng, X. L. et al., “Urban mining of e - waste is becoming more cost - effective than virgin mining,” Environ. Sci. Technol., 2018, 52, 4835 - 4841 (“Zeng2018”).

[0585] Zhang, J. F. et al., “Biomorphic cellular silicon carbide nanocrystal - based ceramics derived from wood for use as thermally stable and lightweight structural materials, ACS Appl. Nano Mater., 2019, 2, 7051 - 7060 (“Zhang 2019”).

[0586] Zhang, K. et al., “E - waste recycling: where does it go from here?” Environ. Sci. Technol., 2012, 46, 10861 - 10867 (“Zhang 2012”).

[0587] Zhang, W. C. et al., “A comprehensive review of rare earth elements recovery from coal - related materials,” Minerals, 2020, 10, 451 - 478 (“Zhang 2020”).

[0588] Zhang, X. X. et al., “Nanocrystalline alpha - alumina with novel morphology at 1000 degrees C,” J Mater Chem, 2008, 18, 2423 - 2425 (“Zhang 2008”).

[0589] Zhao, Y.F. et al., “First-principles prediction of icosahedral quantum dots for tetravalent semiconductors,” Phys Rev Lett, 2004, 93, 015502 (“Zhao2004”).

[0590] Zhao, Y.F. et al., “What is the ground-state structure of the thinnest Si nanowires?” Phys Rev Lett, 2003, 91(3), 035501 (“Zhao2003”).

[0591] Zhong, L.S. et al., “Cobalt carbide nanoprisms for direct production of lower olefins from syngas,” Nature, 2016, 538, 84 - 87 (“Zhong 2016”).

[0592] Zhou, Y. et al., “Densification and grain growth in pulse electric current sintering of alumina,” J Eur Ceram Soc, 2004, 24, 3465 - 3470 (“Zhou 2004”).

[0593] Zhuang, W.Q. et al., “Recovery of critical metals using biometallurgy,” Curr. Opin. Biotech., 2015, 33, 327 - 335 (“Zhuang2015”).

[0594] Zielinski, P.A. et al., “Structural transformations of alumina by high-energy ball-milling,” J Mater Res, 1993, 8, 2985 - 2992 (“Zielinski1993”).

[0595] Zou, J. et al., “Spark Plasma Sintering of Superhard B4CZrB2 Ceramics by Carbide Boronizing,” J Am Ceram Soc, 2013, 96(4), 1055 - 1059 (“Zou 2013”).

Claims

1. A method for recycling metals, wherein the method includes: (a) The material is mixed with a conductive additive to form a mixture, wherein: (i) The material is prepared from electronic waste; and (ii) The electronic waste refers to waste material from one or more devices selected from computers, smartphones, electrical equipment, electronic devices, displays, and printed circuit boards; (b) Using a flash Joule heating process, a voltage is applied through the mixture to recover metals from the material, wherein... (i) The voltage is applied in one or more voltage pulses, and (ii) The duration of each of the one or more voltage pulses is a duration; and (c) Collect the recovered metals.

2. The method according to claim 1, wherein the conductive additive is a carbon source.

3. The method according to claim 1, wherein the electronic waste is a printed circuit board.

4. The method of claim 1, wherein the electronic waste comprises plastic.

5. The method of claim 1, wherein the electronic waste is waste material from devices selected from computers, smartphones, electronic devices, and displays.

6. The method of claim 1, wherein the material is prepared by mechanically converting the material into fine powder.

7. The method of claim 6, wherein the mechanical process is selected from cutting the material into small pieces, crushing the material, grinding the material, milling the material, and combinations thereof.

8. The method according to claim 6, wherein the fine powder is a micron-sized fine powder.

9. The method according to claim 1, wherein the conductive additive is selected from elemental carbon, carbon black, graphene, flash graphene, coal, anthracite, coke, metallurgical coke, calcined coke, activated carbon, biochar, natural gas carbon with its hydrogen atoms removed, sub-graphite, plastic waste, carbon derived from plastic waste, food waste, carbon derived from food waste, biomass, carbon derived from biomass, hydrocarbon gases, and mixtures thereof.

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

11. The method according to claim 1, wherein the conductive additive is primarily elemental carbon.

12. The method according to claim 1, wherein the conductive additive is selected from metals, metal salts, metal oxides, quasi-metals, metal complexes, conductive phosphorus, and non-metallic conductive materials.

13. The method of claim 12, wherein the conductive additive is selected from metals, metal salts, metal oxides, metalloids, and metal complexes.

14. The method of claim 12, wherein the conductive additive is a quasi-metal.

15. The method of claim 14, wherein the metalloid is selected from B, Si, As, Te and At.

16. The method of claim 1, wherein the material is mixed with the conductive additive in a weight ratio ranging from 1:2 to 25:

1.

17. The method of claim 1, wherein the applied voltage is in the range of 15V to 300V.

18. The method according to claim 1, wherein: (a) The mass of the mixture to which the voltage is applied exceeds 1 kg; and (b) The applied voltage is from 100V to 100,000V.

19. The method of claim 18, wherein the mass of the mixture to which the voltage is applied exceeds 100 kg.

20. The method of claim 1, wherein (a) The mass of the mixture to which the voltage is applied exceeds 1 kg; and (b) The applied current is between 1,000 amps and 30,000 amps.

21. The method of claim 20, wherein the mass of the mixture to which the voltage is applied exceeds 100 kg.

22. The method of claim 1, wherein the mixture has a resistance of 0.1 ohms to 25 ohms when a voltage is applied.

23. The method of claim 1, wherein the duration of each of the one or more voltage pulses is from 1 microsecond to 25 seconds.

24. The method of claim 1, wherein the duration of each of the one or more voltage pulses is from 1 microsecond to 10 seconds.

25. The method of claim 1, wherein the duration of each of the one or more voltage pulses is from 1 microsecond to 1 second.

26. The method of claim 1, wherein the duration of each of the one or more voltage pulses is from 100 microseconds to 500 microseconds.

27. The method of claim 1, wherein one or more voltage pulses are from 2 voltage pulses to 100 voltage pulses.

28. The method of claim 1, wherein a direct current (DC) is used to perform the voltage pulse.

29. The method according to claim 1, wherein the method is performed using pulsed direct current (PDC) Joule heating.

30. The method of claim 1, wherein alternating current (AC) is used to perform the voltage pulse.

31. The method of claim 1, wherein voltage pulses are generated using direct current (DC) and alternating current (AC).

32. The method of claim 31, wherein the method switches back and forth between direct current (DC) and alternating current (AC).

33. The method of claim 31, wherein the method uses both direct current (DC) and alternating current (AC).

34. The method of claim 1, wherein the one or more voltage pulses raise the temperature of the mixture to at least 3000 K.

35. The method of claim 1, wherein the metal comprises rare earth elements.

36. The method of claim 1, wherein the metal comprises a noble metal.

37. The method of claim 1, wherein the metal comprises a toxic heavy metal.

38. The method of claim 1, wherein (a) The material comprises a metal oxide; and (b) The step of applying voltage through the mixture leads to a carbothermic reaction of the metal oxide to recover the metal.

39. The method of claim 1, wherein a voltage is applied through the mixture at a pressure of 0.001 to 25 atmospheres to recover metal from the material.

40. The method of claim 39, wherein the pressure is less than 0.5 atmospheres.

41. The method of claim 39, wherein the pressure is less than 0.001 atmospheres.

42. The method of claim 39, wherein the pressure is about 1 atmosphere.

43. The method of claim 39, wherein the pressure is at least 2 atmospheres.

44. The method of claim 39, wherein the pressure is at least 10 atmospheres.

45. The method of claim 39, wherein the pressure is at least 20 atmospheres.

46. ​​The method of claim 39, wherein the method is performed using a pressurization unit.

47. The method of claim 46, wherein applying a voltage through the mixture to recover metals from the material results in most of the metals being retained along with the graphene produced by the method.

48. The method of claim 47, wherein collecting the recovered metal comprises separating the metal from the graphene.

49. The method of claim 48, wherein the separation of the metal from the graphene may include chemical oxidation to remove the graphene.

50. The method of claim 49, wherein the graphene is oxidized with an oxidizing agent.

51. The method according to claim 50, wherein the oxidant is HNO3 or H2O2.

52. The method according to claim 51, wherein the oxidant is HNO3 or H2O2 and H2SO4.

53. The method of claim 48, wherein the separation of the metal from the graphene comprises calcining to remove the graphene, leaving a metallic substance selected from metals, metal oxides, metal carbides, metal salts, and combinations thereof.

54. The method of claim 1, wherein the mixture of the material and the conductive additive further comprises a halogen-containing compound.

55. The method according to claim 54, wherein the halogen-containing compound is selected from NaCl, NaF, KCl, NaI, halogenated polymers, halogenated organic compounds, halogenated inorganic compounds, halide salts, and combinations thereof.

56. The method of claim 54, wherein the halogenated compound comprises a halogenated polymer selected from PTFE, PVC and CPVC.

57. The method of claim 1, wherein the collection step comprises collecting a gas stream containing volatile products generated by applying a voltage through the mixture.

58. The method of claim 57, wherein the volatile product comprises a metal halide.

59. The method of claim 1, wherein the collection step further comprises a cooling gas stream.

60. The method of claim 1, wherein (a) The mixture is heated and the metal evaporates from the mixture by applying voltage, forming metal vapor; (b) The steps for collecting recycled materials include: (i) Transporting metal vapor at low pressure, and (ii) Use a condenser or cold trap to condense metal vapor for collection.

61. The method of claim 60, wherein the metal vapor comprises a metal halide.

62. The method of claim 60, wherein the metal vapor is transported under vacuum.

63. The method of claim 1, wherein the collection step further comprises a leaching process following the application of voltage through the mixture.

64. The method of claim 63, wherein when water treatment is performed using the same pH and the same volume, the leaching of the metal in the mixture after voltage is applied through the mixture is more than twice the leaching content of the metal in the mixture before voltage is applied through the mixture.

65. The method of claim 63, wherein the leaching process is carried out using dilute acid.

66. The method of claim 65, wherein the dilute acid is an acid of at least 1 M.

67. The method of claim 63, wherein applying a voltage through the mixture to recover metals from the material is carried out at a pressure above 1 atmosphere, such that the volatile components of the electronic waste are trapped in the residual solids of the material after the voltage is applied.

68. The method of claim 1, wherein the method is performed as a continuous process or an automated process.

69. A system for recovering metals using the method of any one of claims 1-68, wherein the system comprises: (a) Sources comprising the mixture of the material and the conductive additive (i) The material contains electronic waste, and (ii) The electronic waste refers to waste material from one or more devices selected from computers, smartphones, electrical equipment, electronic devices, displays, and printed circuit boards; (b) A unit operably connected to the source, such that the mixture can flow into the unit and remain under compression; (c) Electrodes operably connected to the unit; and (d) A flash power source for applying voltage through a mixture to recover metals from the material.

70. The system of claim 69, wherein the system is used for a method of recovering metals using at least one of claims 40-53, and wherein the system further comprises: (a) The unit described is a pressure unit; and (b) Gas supply for pressurizing the pressure unit.

71. The system of claim 70, wherein the system further comprises an adjustable safety valve.

72. The system of claim 70, wherein the system further comprises a particle collector.

73. The system of claim 70, wherein the system further comprises a gas collector.

74. The system of claim 69, wherein the system is operable to perform a continuous process or an automated process.

Images