WO2013052753A1 - Procédés et dispositif pour production et distillation efficaces de métaux comprenant une électrolyse d'oxydes - Google Patents

Procédés et dispositif pour production et distillation efficaces de métaux comprenant une électrolyse d'oxydes Download PDF

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Publication number
WO2013052753A1
WO2013052753A1 PCT/US2012/058882 US2012058882W WO2013052753A1 WO 2013052753 A1 WO2013052753 A1 WO 2013052753A1 US 2012058882 W US2012058882 W US 2012058882W WO 2013052753 A1 WO2013052753 A1 WO 2013052753A1
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Prior art keywords
metal
molten salt
magnesium
cathode
gas
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Application number
PCT/US2012/058882
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English (en)
Inventor
Uday B. Pal
Eric GRATZ
Xiaofei GUAN
Peter A. ZINK
Soobhankar Pati
Adam Clayton Powell
John Strauss
Aaron TAJIMA
R. Steve TUCKER
Original Assignee
Metal Oxygen Separation Technologies, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Application filed by Metal Oxygen Separation Technologies, Inc. filed Critical Metal Oxygen Separation Technologies, Inc.
Priority to CN201280059607.6A priority Critical patent/CN104204306A/zh
Priority to EP12837979.9A priority patent/EP2764136A4/fr
Publication of WO2013052753A1 publication Critical patent/WO2013052753A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/001—Dry processes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B26/00—Obtaining alkali, alkaline earth metals or magnesium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B4/00—Electrothermal treatment of ores or metallurgical products for obtaining metals or alloys
    • C22B4/02—Light metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B4/00—Electrothermal treatment of ores or metallurgical products for obtaining metals or alloys
    • C22B4/04—Heavy metals
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/02—Electrolytic production, recovery or refining of metals by electrolysis of melts of alkali or alkaline earth metals
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/04—Electrolytic production, recovery or refining of metals by electrolysis of melts of magnesium
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the invention relates to production and recycling of metals.
  • Magnesium and calcium have sufficient solubility in molten salts that they both react with gases formed at the anode, such as C0 2 or oxygen, also reducing current efficiency to below 50% (J. Phys. Chem. 74(22):3896-3900, 1970; herein incorporated by reference in its entirety).
  • This invention describes methods to prevent metal dissolution in the molten salt and/or to remove it from the molten salt, thereby improving current efficiency and membrane lifetime. Such methods can be useful for removing dissolved metal from the molten salt, which can be useful for separation of metals due to differential solubility in the molten salt.
  • a method for recovering a target metal comprising: (a) providing a molten salt; (b) dissolving a portion of a mixed metal scrap into the molten salt to form a molten salt and metal mixture, the mixed metal scrap including a target metal species and at least one contaminant metal species; (c) bubbling a gas through the molten salt and metal mixture to form a gas and metal vapor mixture, the gas and metal vapor mixture including target metal vapors; and (d) condensing at least a portion of the target metal vapors.
  • the mixed metal scrap comprises an oxide of the target metal.
  • an apparatus for recovering a target metal comprising: (a) a housing including a lower wall and a plurality of side walls; (b) a divider at least partially disposed within the housing, the divider forming within the housing at least a first chamber, a second chamber, and a fluid conduit between the first and second chambers; (c) a top wall cooperating with the lower wall and at least one of the plurality of side walls to enclose the second chamber; (d) a plurality of gas inlets disposed in the second chamber; and (e) a gas outlet in fluid communication with the second chamber.
  • the divider forms floating metal piers.
  • the gas inlets are positioned between the piers.
  • the apparatus further comprises (f) a
  • a method for recovering a target metal comprising: (a) providing a cathode in electrical contact with a molten salt; (b) providing an anode in electrical contact with the molten salt; (c) dissolving an oxide of a target metal into the molten salt to form a molten salt and metal ion mixture; (d) establishing an electrical potential between the cathode and the anode to form target metal at the cathode; (e) bubbling a gas through the molten salt and metal ion mixture to form a gas and metal vapor mixture, the gas and metal vapor mixture including target metal vapors comprised at least in part by a portion of the target metal formed at the cathode; and (f) condensing at least a portion of the target metal vapors.
  • the bubbling the gas through the molten salt and metal ion mixture includes bubbling the gas in immediate proximity to the cathode.
  • the bubbling the gas through the molten salt and metal ion mixture includes providing the gas through at least one opening in the cathode. In some embodiments, the bubbling the gas through the molten salt and metal ion mixture includes providing the gas across a current path through the molten salt between the cathode and the anode. In some
  • the gas is an inert gas.
  • the inert gas is argon.
  • the cathode includes perforations or other means of introducing the gas immediately adjacent to the cathode reaction location, such that the reduced metal first forms as a dilute vapor in the gas, instead of a pure or concentrated metal vapor or liquid.
  • the method further comprises measuring the quantity of target metal in the molten salt.
  • the method further comprises providing a SOM between the cathode and the anode.
  • the oxide of the target metal further comprises at least one contaminant metal.
  • an apparatus for recovering a target metal comprising: (a) a container for holding a molten salt; (b) a cathode disposed to be in electrical contact with the molten salt when the molten salt is disposed in the container; (c) an oxide ion-conducting membrane disposed to be in ion-conducting contact with the molten sale when the molten salt is disposed in the container; (d) an anode in electrical contact with the oxide ion-conducting membrane; (e) a power source for generating an electric potential between the anode and the cathode; (f) a gas inlet having at least one end disposed within the container to be below a level of the molten salt when the molten salt is disposed in the container; and (g) a gas outlet in fluid communication with a volume defined by the container.
  • the at least one end of the gas inlet is in immediate proximity to the cathode.
  • the cathode includes the at least one end of the gas inlet.
  • the at least one end of the gas inlet is disposed in the container to form gas bubbles in the molten salt, when the salt is disposed in the container, across a current path through the molten salt between the cathode and the anode.
  • the gas inlet is a nozzle.
  • the gas inlet is disposed at the bottom of the container.
  • the cathode forms at least portion of container.
  • a method for recovering a target metal comprising: (a) providing a molten salt; (b) dissolving a portion of a mixed metal scrap into the molten salt to form a molten salt and metal mixture, the mixed metal scrap including a target metal species and at least one contaminant metal species; (c) reducing a pressure of the molten salt and metal mixture to remove, as vapors of the target metal, at least a portion of the target metal species dissolved in the molten salt and metal mixture; and (d) recovering at least a portion of the target metal vapors.
  • the reducing a pressure of the molten salt and metal mixture comprises creating a partial vacuum in an atmosphere overlying the molten salt and metal mixture.
  • the scrap comprises an oxide of the target metal.
  • the dissolving step comprises melting the scrap metal mixture.
  • the method further comprises providing SOM elements and performing SOM electrolysis.
  • the method further comprises dissolving an oxide of a second metal subsequent to production of at least some of the first metal in the salt.
  • an apparatus for recovering a target metal comprising: (a) a container for holding a molten salt; (b) a cathode disposed to be in electrical contact with the molten salt when the molten salt is disposed in the container; (c) an oxide ion-conducting membrane disposed to be in ion-conducting contact with the molten salt when the molten salt is disposed in the container; (d) an anode in electrical contact with the oxide ion-conducting membrane; (e) a power source for generating an electric potential between the anode and the cathode; (f) a gas outlet in fluid communication with a volume defined by the container; (g) a condenser in fluid communication with the gas outlet for condensing at least a portion of the target metal vapor in a gas stream exiting the container; and (h) the vacuum source in fluid communication with the gas outlet and/or the container for creating at least a
  • a method for recovering a metal from an oxide of said metal comprising: (a) providing a cathode in electrical contact with a molten salt; (b) providing an anode in electrical contact with the molten salt; (c) dissolving an oxide of a first metal into the molten salt to form a molten salt and metal ion mixture; (d) establishing an electrical potential between the cathode and the anode to form first metal at the cathode; (e) dissolving an oxide of a second metal into the molten salt, the second metal being more electronegative than the first metal, and the second metal being less soluble in the molten salt than the first metal; (f) subsequent to dissolving the oxide of the second metal into the molten salt, establishing an electrical potential between the cathode and the anode to form first metal at the cathode; and (g) recovering at least a portion of the first metal formed at the catho
  • the metal charge comprises contaminant metals and/or the target metal.
  • Figure 1 shows the theoretical electrorefming potential for magnesium bubble nucleation versus magnesium-aluminum scrap anode composition for several values of activity coefficient ⁇ (from equation 1).
  • Figure 2 shows an illustrative embodiment of the recycling process, showing electrodes for electrolysis and for measuring magnesium content in scrap anode and molten salt.
  • FIG. 3 shows current-voltage relationships for an illustrative refining process at various times.
  • the open circuit voltage and two electrorefming potentials (OCV, E ERI , and E ER2 ) for the last scan PDS5 are indicated by arrows.
  • Figure 4 shows electrorefming potentials for bubble nucleation (triangles) and OCV
  • Figure 5 shows a schematic illustration of embodiments of cathode configurations according to embodiments of the invention.
  • C mesh/screen
  • D porous material.
  • Figure 6 shows a schematic illustration of embodiments of a single-tube electrolysis apparatus operating at low pressure according to embodiments of the invention.
  • Figure 7 shows a schematic illustration of embodiments of a production and recycling apparatus according to embodiments of the invention.
  • Figure 8 shows a schematic illustration of embodiments of a production and recycling apparatus according to embodiments of the invention.
  • Figure 9 shows a schematic illustration of embodiments of a production and recycling apparatus according to embodiments of the invention.
  • Figure 10 shows a schematic illustration of embodiments of a production and recycling apparatus according to embodiments of the invention.
  • Figure 11 shows a schematic illustration of embodiments of a production and recycling apparatus according to embodiments of the invention.
  • Figure 12 shows potentiodynamic scans before electrolysis, after electrolysis, and after electrolysis and argon stirring.
  • Figure 13 shows potentiodynamic scans before electrolysis, after each of two electrolysis runs using a notched argon tube as cathode, and after a third electrolysis run using the crucible as the cathode.
  • Figure 14 shows potentiodynamic scans (5mV/s) after 3 hours of electrolysis at 1 atm pressure and after 7.5 hours of electrolysis at 0.08 atm pressure.
  • Figure 15 shows a schematic illustration of embodiments of a production and recycling apparatus according to embodiments of the invention.
  • Figure 16 shows an initial potentiodynamic scan (5mV/s).
  • Figure 17 shows impedance before electrolysis 1.
  • Figure 18 shows electrolysis 1 at 2 V for 3 hours.
  • Figure 19 shows a potentiodynamic scan at the cathode after electrolysis 1.
  • Figure 20 shows a potentiodynamic scan at the anode after electrolysis 1.
  • Figure 21 shows electrolysis 2.
  • Figure 22 shows potentiodynamic scans after electrolysis 2 using the stirring tube as cathode or the steel crucible as cathode.
  • Figure 23 shows electrolysis 3 using the steel crucible as cathode.
  • Figure 24 shows potentiodynamic scans after electrolysis 3 using the stirring tube as cathode or the steel crucible as cathode.
  • Figure 25 shows current vs. cathode potential after electrolysis 3.
  • Figure 26 shows current vs. anode potential after electrolysis 3.
  • Figure 27 shows a schematic illustration of embodiments of a refining and SOM electrolysis method according to embodiments of the invention.
  • Figure 28 shows a schematic experimental setup of a refining and SOM electrolysis apparatus according to embodiments of the invention.
  • Figure 29 shows temperature steps at the center of an electrorefmer chamber according to embodiments of the invention.
  • Figure 30 shows a potentiodynamic scan taken at 13 minutes after the maximum operating temperature was reached.
  • Figure 31 shows impedance spectroscopy measured 20 minutes after the maximum operating temperature was reached.
  • Figure 32 shows potentiodynamic scans taken at 13 and 38 minutes after the maximum operating temperature was reached.
  • Figure 33 shows potentiodynamic scans taken at 13, 38, and 58 minutes after the maximum operating temperature was reached.
  • Figure 34 shows potentiodynamic scans taken at 13, 38, 58, and 68 minutes after the maximum operating temperature was reached.
  • Figure 35 shows a potentiostatic scan taken at 74 minutes after the maximum operating temperature was reached.
  • Figure 36 shows potentiodynamic scans taken at 13, 38, 58, 68, and 79 minutes after the maximum operating temperature was reached.
  • Figure 37 shows potentiodynamic scans taken at 13, 38, 58, 68, 79 and 83 minutes after the maximum operating temperature was reached.
  • Figure 38 shows a potentiostatic scan taken at 85 minutes after the maximum operating temperature was reached.
  • Figure 39 shows potentiodynamic scans taken at 13, 38, 58, 68, 79, 83 and 96 minutes after the maximum operating temperature was reached.
  • Figure 40 shows potentiodynamic scans taken at 13, 38, 58, 68, 79, 83, 96 and 113 minutes after the maximum operating temperature was reached.
  • Figure 41 shows a potentiostatic scan taken at 115 minutes after the maximum operating temperature was reached.
  • Figure 42 shows potentiodynamic scans taken at 13, 38, 58, 68, 79, 83, 96, 113 and 148 minutes after the maximum operating temperature was reached.
  • Figure 43 shows potentiodynamic scans taken at 13, 38, 58, 68, 79, 83, 96, 113, 148 and 172 minutes after the maximum operating temperature was reached.
  • Figure 44 shows a potentiostatic scan taken at 187 minutes after the maximum operating temperature was reached.
  • Figure 45 shows potentiodynamic scans taken at 13, 38, 58, 68, 79, 83, 96, 113, 148, 172 and 218 minutes after the maximum operating temperature was reached.
  • Figure 46 shows a potentiostatic scan taken at 228 minutes after the maximum operating temperature was reached.
  • Figure 47 shows potentiodynamic scans taken at 13, 38, 58, 68, 79, 83, 96, 113, 148, 172, 218 and 259 minutes after the maximum operating temperature was reached.
  • Figure 48 shows impedance spectroscopy measured at 267 minutes after the maximum operating temperature was reached.
  • Figure 49 shows a potentiostatic scan taken at 274 minutes after the maximum operating temperature was reached.
  • Figure 50 shows potentiodynamic scans taken at 13, 38, 58, 68, 79, 83, 96, 113, 148, 172, 218, 259 and 285 minutes after the maximum operating temperature was reached.
  • Figure 51 shows a potentiostatic scan taken at 287 minutes after the maximum operating temperature was reached.
  • Figure 52 shows potentiodynamic scans taken at 13, 38, 58, 68, 79, 83, 96, 113, 148, 172, 218, 259, 285 and 298 minutes after the maximum operating temperature was reached.
  • Figure 53 shows first and second impedance spectroscopy measurements.
  • Figure 54 shows a potentiodynamic scan taken at 11 minutes after the SOM process was started.
  • Figure 55 shows a potentiostatic scan taken at 17 minutes after the SOM process was started.
  • Figure 56 shows a potentiodynamic scan taken at 82 minutes after the SOM process was started.
  • Figure 57 shows impedance spectroscopy measured at 111 minutes after the SOM process was started.
  • Figure 58 shows a potentiostatic scan taken at 119 minutes after the SOM process was started.
  • Figure 59 shows a potentiodynamic scan taken at 181 minutes after the SOM process was started.
  • Figure 60 shows potentiodynamic scans taken at before the SOM was started and during the first hour of electrolysis.
  • Figure 61 shows for the first hour of electrolysis and the second hour of electrolysis. Both electrolyses were performed at 3 V.
  • Figure 62 shows EDS results for the collected magnesium.
  • Figure 63 shows EDS results for the scrap residue inside the alloy crucible.
  • Figure 64 shows SEM of a piece of remaining alloy taken from its center.
  • Figure 65 shows EDS results for the center gray zone of the remaining alloy taken from its center.
  • Figure 66 shows EDS results for the center black zone of the remaining alloy taken from its center.
  • Figure 67 shows the yttrium profile for a 32 hour overlay using no yttrium fluoride, 2.5 wt% yttrium fluoride, 1.5 wt% yttrium fluoride and 5 wt% yttrium fluoride.
  • Figure 68 shows the system diagram for LiF-MgF 2 .
  • Figure 69 shows an apparatus for determination of metal concentration in the salt.
  • Described herein are methods and apparatuses for primary production and recycling of metals soluble in molten salts, including but not limited to magnesium, calcium, and rare- earths including samarium and dysprosium.
  • primary production is by oxide electrolysis
  • recycling is by molten salt-assisted separation of metallic mixtures, and combining with electrolysis to recycle oxidized metals.
  • the invention further describes methods for manipulating the metal concentration in a molten salt in order to achieve high rate, energy efficiency, and long component lifetime.
  • immediate proximity means that the gas inlet is disposed close to the cathode such that the gas contacts the cathode and the molten salt.
  • Magnesium developed a system for continuous melting with a molten salt in order to remove oxides from the liquid metal (U.S. Patent No. 5,167,700; and H. E. Friedrich, B. L. Mordike, Magnesium Technology: metallurgy, design data, applications (Springer, 2006), 638; each herein incorporated by reference in its entirety).
  • this process cannot separate magnesium from other metals.
  • Molten salt fluxes such as, for example, CaF 2 -MgF 2 -MgO, CaCl 2 -MgCl 2 , CaO, etc.
  • metals such as Ca, Mg, etc.
  • SOM solid oxide membrane
  • a less stable oxide that can react with and oxidize the soluble metal in the salt.
  • metallic magnesium concentration in a molten salt one can add iron oxide to the molten salt. The dissolved magnesium in the salt will react with and reduce the iron oxide.
  • the metal solubility in the molten salt can be advantageously utilized for designing novel refining process that employ gas bubbling to recover metal species from partially oxidized scrap alloys.
  • Mg can be refined and separated from automotive scrap alloys via conversion of the alloy to Mg in the molten salt, and in turn converted to gaseous Mg.
  • the oxide scale and the metal species will dissolve in the molten salt, and the dissolved metal species will be removed in the vapor phase via gas bubbling.
  • a lower solubility of the metal benefits SOM electrolysis while metal solubility in general can be utilized to design novel refining processes.
  • a larger metal solubility aids the refining and/or separation processes.
  • the alloys comprise magnesium.
  • the alloys comprise magnesium and aluminum.
  • the alloys comprise scrap automotive alloys, AZ91, AM50 or AM60.
  • magnesium is discussed herein as an exemplary target metal, the methods and apparatuses herein can also be used to separate other reactive metals soluble in molten salts, including but not limited to calcium and rare-earth metals such as samarium and dysprosium.
  • Rare earth metals comprise metals from the lanthanide series in the chemical periodic table from lanthanum to lutetium as well as scandium and yttrium. Scandium is considered a rare earth element, though it usually occurs in minor amounts. Yttrium is considered a rare earth element because it often occurs with rare earth metals in nature and has similar chemical properties.
  • the target metal is magnesium, calcium, or a rare-earth metal.
  • the rare earth metal is from the lanthanide series. In some embodiments, the rare earth metal is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu. In some embodiments, the rare earth metal is samarium or dysprosium. In some embodiments, the target metal is magnesium, calcium, samarium or dysprosium. In some embodiments, the target metal is magnesium, calcium, or samarium. In some embodiments, the target metal is magnesium or calcium. In some embodiments, the target metal is calcium. In some embodiments, the target metal is magnesium.
  • the methods and apparatuses described herein use dissolution in a molten salt to efficiently separate magnesium from aluminum and other metals, and recover nearly all of the magnesium from heavily-oxidized scrap.
  • the methods also use the same principle to recover samarium or dysprosium, or other rare-earth metals or combinations of rare-earth metals from rare-earth magnets, industrial magnet scrap, and other products.
  • the apparatuses and methods described herein can thus meet an important need in the metal recycling ecosystem in general, and recycling of fast-growing automotive magnesium and rare-earth metals in particular.
  • the methods and apparatuses provide a mechanism for in situ measurement of the metal remaining in the scrap charge, that is which has not been removed, which one can use to maximize equipment productivity or to create an alloy with a specific composition.
  • the methods and apparatuses described herein entail the use of modified SOM processes that enable extraction of metals from metal oxides.
  • Representative embodiments of the SOM apparatus and process may be found, for example, in U.S. Patent Nos. 5,976,345; 6,299,742; and Mineral Processing and Extractive Metallurgy 117(2): 118-122 (June 2008); JOM Journal of the Minerals, Metals and Materials Society 59(5):44-49 (May 2007); Metall. Mater. Trans. 36B:463-473 (2005); Scand. J. Metall. 34(5):293-301 (2005); and
  • methods further comprise collecting the metallic species.
  • Methods of collecting metallic species are known (See, e.g., Krishnan et al, Metall. Mater.
  • the methods comprise manipulating metal solubility in a molten salt to improve the rate or efficiency of electrolysis or refining.
  • the methods comprise differential dissolution in a molten salt and distillation to separate magnesium, calcium, samarium or dysprosium, or another high-vapor pressure metal soluble in a molten salt, herein called the "target metal", from other metals, as shown for a preferred embodiment in Figure 2.
  • the apparatus (200) consists of a cathode (201), a molten salt bath (202) in electrical contact with a cathode, and a solid oxygen ion conducting membrane (SOM) (203) anode (204) in contact with the molten salt bath.
  • SOM solid oxygen ion conducting membrane
  • the scrap charge is introduced into the scrap chamber (205), where heat is applied to melt it.
  • the liquid scrap metal (217) contacts the molten salt where the target metal preferentially dissolves into the salt.
  • Several metals such as magnesium, calcium, rare-earth elements and others, have much higher solubility in molten salts than iron, nickel, aluminum, silicon, copper, zinc, manganese and others, so the target metals preferentially dissolve into the salt, leaving the other metals behind.
  • magnesium cations Mg 2+
  • magnesium alloy scrap liquid is oxidixed from magnesium metal to Mg 2+ , and at the SOM anode 0 2 ⁇ is oxidized to 1 ⁇ 2 0 2 + 2 e " .
  • the target metal then evaporates from the molten salt, leaving behind the salt, any dissolved oxides, and metals with lower vapor pressure.
  • the target metal vapor condenses in a condenser.
  • argon or other gas bubbled through the salt provides high surface area for one mechanism of rapid mass transfer from the salt into the gas.
  • a gas can be used that does not react strongly with the target metal such as forming gas, or form a gas in situ, such as boiling zinc or other low-boiling point metal or causing a chemical reaction to create another gas in the salt, in place of or with the inert gas, in order to both agitate the melt and provide high surface area for rapid mass transfer.
  • the higher vapor pressure of the target metal vs. others further refines the target metal product, e.g. magnesium exhibits higher vapor pressure and evaporates faster than calcium and rare-earths.
  • the carrier gas-metal gas mixture travels to a condenser, where the metal vapor condenses to a liquid or solid.
  • a condenser where the metal vapor condenses to a liquid or solid.
  • Methods for condensing magnesium vapor to liquid are described by Schoukens et al. (U.S. Patent No. 7,641,711; herein incorporated by reference in its entirety) for high magnesium vapor pressure and Powell et al. (U.S. Patent Application No. 13/543,575; herein incorporated by reference in its entirety) for low magnesium or other metal vapor pressure.
  • the target metal content of the scrap charge such as magnesium
  • the target metal is sufficiently low, as measured by electrodes or as inferred by the reaction time, then one can drain the remaining scrap liquid metal for collection of material depleted of the target metal, for example aluminum and other metals after magnesium has been removed.
  • electrodes inserted into the liquid scrap metal and molten salt, with the anode in the scrap and cathode preferably at the inert gas introduction locations in the molten salt can measure the amount of the target metal, illustratively magnesium, remaining in the scrap charge, as follows.
  • a potentiodynamic sweep illustratively from -0.05 V to 0.15 V and illustratively at a rate of 5 mV/sec as shown in Figure 3, provides information such as: the open circuit voltage (OCV), voltages at two sudden increases corresponding to electrochemical transitions which can be called E ERI and E ER2 , and the slope away from the transitions.
  • the transition voltages E ERI and E ER2 change with time as shown in Figure 4 and with magnesium composition in the scrap metal.
  • the voltage E ER2 in particular is related to magnesium mole fraction in the scrap metal XMg(attoy) according to equation 1 as displayed in Figure 1.
  • Accurately estimating XMg(aiioy) requires either calibration by measuring E ER2 at known values of XMg(aiioy), or knowledge of the activity coefficient in the particular alloy system.
  • E ER2 and E ERI are calculated as E(reduction at anode) minus E(reduction at cathode). This assumes that the nucleating pressure of magnesium bubbles at E ER2 is approximately 1 atm. and the fact that the standard vapor pressure of magnesium over pure magnesium ⁇ P° M g(g)) is known.
  • This method presents several benefits over direct distillation by heating the liquid metal mixture.
  • distillation hindrance by oxide film formation is not a problem because the molten salt dissolves any oxide present at the metal-salt interface.
  • the molten salt catalyzes magnesium removal from the alloy, facilitating near perfect separation as described below.
  • volatile metals such as zinc and other volatiles in the scrap charge do not contaminate the magnesium product because their solubility in the molten salt is much lower than that of magnesium.
  • in situ monitoring of the scrap alloy composition and magnesium content of the molten salt permit precise timing of the duration of distillation, reducing mean cycle time.
  • the anode is preferably separated from the molten salt and inert gas-target metal vapor by a solid oxygen ion-conducting membrane (SOM), as shown in Figure 2.
  • SOM solid oxygen ion-conducting membrane
  • the SOM can be made illustratively of zirconia with high oxygen ion conductivity, illustratively zirconia stabilized by yttria, calcia, or magnesia, or can take on multiple other embodiments as discussed by Pal and Britten (See, e.g., U.S.
  • This membrane serves two purposes: it separates the anode and cathode products, such that dissolved magnesium in the molten salt does not react with oxygen or combustion products such as C0 2 or H 2 0 which form at the anode, resulting in high current efficiency, and it prevents fluoride ions from reaching the anode, resulting in zero fluorine or perfluorocarbon emissions and in some embodiments a high purity oxygen by-product.
  • This embodiment includes all of the prior benefits, but can also increase the recycling yield by capturing all of the target metal oxide in the scrap.
  • Figure 5 shows four geometries for accomplishing this. Holes (506) in the cathode (501) (Fig. 5A) distribute the inert gas over its surface, promoting uptake of the target metal at or near where it is reduced, such that less of the metal dissolves. Sharp notches (507) on holes, or at the bottom of a tube, promote formation of small bubbles with high surface area, toward the same end (Fig. 5B). Another embodiment incorporates a mesh surface (508) (Fig.
  • the cathode configuration is selected from a tube comprising holes, a tube comprising notches at the tube end, a tube comprising notched holes, a tube comprising a mesh screen, and/or a porous tube material.
  • the notches, holes or pores are about 0.5-2 mm in diameter. In some embodiments, the notches, holes or pores are less than about 0.5 mm in diameter.
  • target metal oxide to the molten salt, in order to better utilize the electrodes which are in the salt for oxide reduction.
  • electrodes used for electrolysis can measure the dissolved target metal content of the molten salt as follows.
  • anode gases such as oxygen, or CO or water when using a fuel in the anode
  • Faradaic current indicates the Faradaic current in the system.
  • Subtracting this from the total current gives the electronic current in the cell. This in turn is proportional to the electronic conductivity of the molten salt, which is related to its dissolved metal concentration.
  • the oxide electrolysis can be carried out at lower pressure (below atmospheric pressure), illustratively at 0.001-0.2 atmospheres (about 1-200 mbar).
  • An exemplary configuration is shown in Figure 6 comprising an anode exhaust (610) and a cathode exhaust (611) are connected in line to vacuum gauges (612), valves (613), liquid nitrogen traps (614) and a vacuum pump (615) which is run at about 59 to about 61 torr.
  • This approach lowers the metal solubility in the salt considerably (Mg dissolved in the salt ⁇ Mg vapor) thereby increasing current efficiency and lowering membrane degradation during electrolysis.
  • the lower pressure also reduces the target metal condensation dew point, allowing the process to run at lower temperature, as low as 900-1000 °C for magnesium, or 1100-1300 °C for calcium and samarium.
  • the oxide of the more electronegative metal is soluble in the molten salt.
  • the oxide of the more electronegative metal is insoluble in the molten salt.
  • the more electronegative metal is insoluble in the molten salt. This causes a reaction between the target metal in the salt and the more electronegative oxide, producing the target metal oxide and the more electronegative metal. This reduces the amount of dissolved metal in the molten salt, thereby increasing the current efficiency and lowering membrane degradation during electrolysis.
  • oxide free energies of formation for cation species in the molten salt must be more negative than the target metal for production, such that the process does not reduce molten salt cations along with the product.
  • exemplary cation species include calcium, strontium, barium, lithium, potassium, cesium and ytterbium. Though sodium has lower electronegativity than rare earth elements and some others, its oxide free energy is less negative so sodium oxide present in the molten salt is reduced and evaporates at the cathode before rare earths and magnesium.
  • the molten salt must exhibit very low vapor pressure and evaporation rate in the process temperature range. Combining thermo-gravimetric analysis (TGA) with differential scanning calorimetry (DSC) or differential thermal analysis (DTA) experiments can efficiently evaluate the molten salt for this criterion. In some embodiments, fluoride salts are preferable over chloride salts. [0137] The molten salt must also have a relatively low melting point. In some embodiments, the temperature range of from about 1000 °C to about 1200 °C provides a balance between good energy efficiency and apparatus stability at lower temperature, and good oxide ion conductivity in stabilized zirconia at higher temperature.
  • the molten salt must not be a solid, and is preferably not partially solid or semi-solid in this temperature range.
  • Differential scanning calorimetry (DSC) or differential thermal analysis (DTA) experiments can efficiently evaluate the flux for this criterion by measuring the temperature at which the flux becomes partially solid (the liquidus temperature) and the temperature at which it becomes completely solid (the solidus or eutectic temperature).
  • the molten salt should preferably also dissolve the target metal oxide to at least about 2-3 weight % in order to achieve reasonable ionic current densities at the anode and cathode. In some embodiments, dissolution of the target metal oxide at least about 2-3% by weight achieves sufficient ionic current densitites. For some metals, the target metal oxide need only be dissolved as little as 0.5%> by weight to render the process economically viable. In some embodiments, dissolution of the target metal oxide at 0.5% by weight achieves sufficient ionic current densitites. DSC or DTA experiments at various compositions can efficiently
  • the molten salt must not appreciably dissolve or corrode the solid electrolyte, illustratively zirconia.
  • evaluation of stability can be made via immersion of zirconia in the molten salt at the process temperature for several hours, for example tens to hundreds or thousands of hours, followed by sectioning and characterization of the zirconia, to determine the minimum corrosion rate of zirconia in the molten salt, without any applied current.
  • Species in the molten salt must have high mobility, i.e., high ionic conductivity and low viscosity, in order to support high current density without significant transport limitation.
  • a high viscosity molten salt would inhibit mass transfer to the zirconia electrolyte and the cathode; at the zirconia, oxygen ions would be depleted in the boundary layer, thereby reducing the current, and at the cathode the target metal ions would be depleted in the boundary layer, thereby leading to reduction and co-deposition of molten salt cations.
  • molten salts without silica or alumina and with high fluoride/oxide ratio have sufficient mobility.
  • the molten salt must also have low electronic conductivity so as not to function as an extended cathode and reduce or corrode the zirconia. In part, conductivity depends on solubility of the reduced metal in the molten salt. The skilled artisan will be able to determine molten salt conductivity during electrolysis experiments.
  • the target metal must be highly soluble in the molten salt, that is, with higher solubility and/or higher rate of dissolution than the other metals present in the scrap alloy, and/or with higher evaporation rate than the other metals present.
  • the aluminum and calcium both preferentially dissolve into the molten salt leaving the aluminum in the scrap liquid, and the magnesium preferentially evaporates leaving the calcium in the molten salt.
  • the electronegative metal produced must be lowly soluble in the molten salt such that the metal precipitates out of solution.
  • nickel oxide is added to remove magnesium from the salt by generation of nickel and magnesium oxide, the nickel should precipitate out of solution.
  • These embodiments differ from that of Pal and Britten (See, e.g., U.S. Patent Nos. 5,976,345 and 6,299,742; each herein incorporated by reference in its entirety) in the use of one or more of the methods described above to prevent the dissolution of metal and/or to remove it from the molten salt after it has dissolved; those methods are:
  • the oxide reduction embodiments can operate continuously with repeated or continuous additions of target metal oxide to the molten salt as the reduced target metal comes out of the salt in the gas phase.
  • Methods 1 and/or 3 can continuously prevent newly-produced metal from dissolving in the molten salt, and methods 2, 3 and/or 4 can periodically remove dissolved metal from the molten salt as needed.
  • Each of the methods can be performed independently; however combinations of two or more of the methods are also within the scope of the invention.
  • the inert gas or carrier gas creates high surface area.
  • the high surface area promotes mass transfer of the target metal into the gas.
  • reduced pressure prevents dissolution of the metal into the salt.
  • reduced pressure removes the magnesium from the molten salt surrounding the cathode.
  • the layer of molten salt surrounding the cathode is less electronically conductive.
  • the layer of molten salt surrounding the cathode becomes non-electronically conductive.
  • reduced dissolution of the metal in the salt results in increased current efficiency in the salt.
  • the molten salt is at least about 90% liquid. In some embodiments, the molten salt is at least about 92% liquid. In some embodiments, the molten salt is at least about 95% liquid. In some embodiments, the molten salt is at least about 98% liquid. In some embodiments, the molten salt is at least about 99% liquid.
  • a physical barrier can be used to separate target metal dissolution region from the evaporation region.
  • Exemplary embodiments for such purposes include two chambers with salt circulating between the dissolution region and the evaporation region.
  • the regions are held at two different temperatures. Not only can this reduce the rate of unwanted target metal evaporation from the scrap/alloy target metal dissolution region, but, in some embodiments, further allows operating at different pressures in the two regions.
  • the barrier comprises a plurality of gas bubbles to create a region between the anode and the cathode wherein the metal concentration and electronic conductivity are low.
  • the oxide cannot block the process because it is dissolved in the molten salt, whereas an oxide layer can block distillation.
  • the refining process also has improved selectivity over distillation due to differential dissolution in the salt. In many cases, the refining process also occurs at a high rate, whereas distillation does not.
  • FIG. 7 shows an exemplary design concept for scrap metal with density lower than that of the molten salt.
  • Scrap metal is introduced into the scrap chamber (705) through the opening (716) shown in the top left visualization of a rear view into the scrap chamber (Fig. 7A).
  • the scrap melts, and the scrap alloy liquid (717) floats on the molten salt.
  • the scrap is held in floating "piers” (718) resting on the molten salt by a metal gate (719), which creates "inlets” of exposed molten salt between the piers.
  • a carrier gas illustratively argon
  • Figs. 7B-D are cross-sectional views shown without the chamber.
  • Fig. 7B shows a cross-sectional view with the scrap alloy liquid (717) floating on the molten salt (702), the metal gate (719) configured angularly toward the molten salt, steel tubes (720), and zirconia tubes with anodes (721).
  • Translucent cones (722) visualize the plumes of argon bubbles rising through the molten salt.
  • FIG. 7C shows another cross-sectional view with the scrap alloy liquid (717) floating on the molten salt (702), the metal gate (719) configured angularly toward the molten salt, steel tubes (720), and zirconia tubes with anodes (721).
  • Fig. 7D shows another cross-sectional view with the steel tubes (720), zirconia tubes with anodes (721) and translucent cones visualizing plumes of argon (722).
  • the goal of this design is to facilitate transport of the target metal, illustratively magnesium, from the liquid alloy through the molten salt to the carrier gas bubblers.
  • the alternating liquid metal piers and exposed salt inlets give a large "coastline” with relatively short distance for the target metal to travel.
  • the proximity between argon bubble plumes and liquid scrap metal also enable the salt to perform some stirring along that metal-salt coastline, further enhancing transport of target metal into and through the salt.
  • the system can have multiple sets of floating liquid alloy "piers" on the molten salt.
  • the liquid metal will be below the molten salt.
  • the system addresses any liquid metal leaks under the metal gate. Liquid which leaks would float on the molten salt, and could either reduce evaporation rate, or possibly short-circuit the electrolysis operation.
  • a simple weir system manages this contingency by creating a pathway for the floating metal to spill out of the molten salt, removing it from the system such that it does not prevent evaporation or lead to short circuiting.
  • the most energy-efficient distillers use "compression distillation", in which a pump between the evaporator and condenser maintains a pressure difference between them.
  • the condenser is at a higher pressure, thus has a higher boiling point, and the temperature at the condensing surface is higher than in the evaporator.
  • This energy-efficient distiller design and operation are described in, for example, U.S. Patent Nos. 2,899,366 and 4,082,616; each herein incorporated by reference in its entirety.
  • the carrier gas and target metal flow through, and condense in, tubes or other conduits in or below the molten salt, and holes, tuyeres, pores, or similar openings between the conduit and molten salt allow some of the carrier gas to escape into the molten salt, providing direct bubbling. This would require that the holes be small enough to maintain a pressure difference between the condenser tubes/conduits and the molten salt.
  • FIG. 8 Another illustrative embodiment is shown in Figure 8, wherein the target metal is more dense than the molten salt.
  • exemplary target metals may include samarium, neodymium and other lanthanides.
  • the target metal product (825) is held between a side of the apparatus (800) and a barrier in the form of a lower portion (840) and an upper portion (841).
  • an interface (842) separates the molten salt (802) from the metal (825).
  • Other exemplary apparatuses for target metals having density higher than the molten salt are described in U.S. Patent Publication No.
  • FIG. 9 An illustrative industrial embodiment is shown in Figure 9, showing a magnesium oxide feed introduced into a crucible (900) that contains a molten salt electrolyte (902) via a plurality of feed tubes (905), a plurality of SOM anodes (903), a plurality of cathodes/argon feed tubes (901).
  • Ar/Mg bubbles (923) are generated and Ar/Mg migrates to a condenser (924) where condensation of Mg occurs to provide liquid Mg (925).
  • a tap (926) enables removal of the condensed Mg.
  • An argon recycling pump (927) collects argon from the condenser and recirculates the argon back into the crucible. Oxygen gas is removed from the system, which is connected to a gas/power/raw material manifold (928).
  • FIG. 10 Another illustrative industrial embodiment is shown in Figure 10, showing scrap material feed from Al and Mg, optionally Mg dross (1005), a plurality of stabilized zirconia tubes/anodes (1003), a plurality of cathodes/argon feed tubes (1001) and the molten salt electrolyte (1002).
  • Aluminum is separated from the anodes via a barrier (1029) and a first tap (1030) enables removal of aluminum.
  • Ar/Mg bubbles (1023) are generated and Ar/Mg migrates to a condenser (1024) where condensation of Mg occurs to provide liquid Mg (1025).
  • a second tap (1026) enables removal of the condensed Mg.
  • An argon recycling pump (1027) collects argon from the condenser and recirculates the argon back into the crucible (1000). Oxygen gas is removed from the system, which is connected to a gas/power/raw material manifold (1028).
  • FIG. 11 Another illustrative embodiment is shown in Figure 11, showing an assembly for reduction of volatile metals such as magnesium.
  • the perforated cathode tube on the outside is solid along its length (1101) until it extends below the level of the molten salt.
  • a downward gas purge (1136) (illustratively argon gas) is used to keep magnesium vapor produced by electrolysis from rising into the annulus, and forces the magnesium to exit through the perforations (1106) in the lower section of the cathode.
  • a boron nitride spacer (1137) at or above the salt level (1138) further impedes vapors from rising along the zirconia, and aids in creating a region of slight positive pressure to protect the zirconia outside of the salt.
  • the nozzle provides an argon bubble stream that contributes to mixing of the salt and the magnesium oxide, and provides good oxide mass transfer to the zirconia tube.
  • the argon bubble stream also absorbs magnesium metal dissolved in the molten salt, and carries the magnesium vapor outward through the perforations in the cathode.
  • the entire cathode-anode assembly can be replaced and inserted as a unit, thus facilitating replacement of cathodes and/or anodes.
  • the closed end of the cathode allows it to be used as a basket, which prevents the zirconia pieces from escaping and eventually building up in the salt. Removing the cathode will thus remove any large zirconia shards in an efficient manner.
  • this assembly also provides a very short anode-cathode distance.
  • the short anode-cathode distance provides very low resistance due to the molten salt.
  • this assembly also results in low cathode current density (illustratively about 1 ⁇ 4 to about 1 ⁇ 2 of the maximum current density in the zirconia tube) due to the large area. Current density is substantially uniform along the cathode due to the concentricity with the anode.
  • multiple zirconia tubes with anodes can be inserted into a single large perforated cathode tube.
  • a plurality of zirconia/anode tubes may be inserted into a single cathode tube.
  • zirconia/anode tubes are inserted. In some embodiments, more than four zirconia/anode tubes are inserted. In these embodiments, the cathode current density is not necessarily uniform, but the high resistivity of zirconia (generally 5-30 times higher than that of the molten salt) results in substantially uniform current density in the zirconia tubes.
  • Example 1 The experimental set up is shown in Figure 15.
  • a stainless steel crucible cathode/reference (1500) was fitted with a YSZ tube (1503), an Ar stirring tube/cathode (1501) was isolated from the crucible with an alumina tube (1531).
  • a molten salt of magnesium fluoride-calcium fluoride (1502) was added to the crucible.
  • the anode (1504) was tin with a molybdenum current collector (1532). Steel tubes to vent Mg and Ar vapor to the condenser are not shown. Hydrogen was bubbled through room temperature water before being bubbled in the tin. The cell temperature was 1190 °C.
  • Electrolysis 1 was run at 2 V for 3 hours with isolated argon stirring tube as the cathode. No evidence of mass transfer limitations were observed (Figure 18). After electrolysis 1, PDS plots of cathode potential versus current (Figure 19) and anode potential versus current ( Figure 20) were performed. No current was observed until 1 V was applied.
  • Electrolysis 2 was run at 3 V for 1 hour with isolated argon stirring tube as the cathode. Again, no mass transfer limitations were observed (Figure 21). After electrolysis 2, PDS plots of potential versus current showed very small to no leakage current ( Figure 22). A potential dynamic scan with the crucible was as the cathode was then used and no leakage current was recorded. High current at larger cathodes suggests cathodic mass transfer limitations.
  • Electrolysis 3 was run at 2.75 V for 2 hours using the steel crucible as the cathode ( Figure 23). After electrolysis 3, PDS plots of potential versus current after using the steel crucible as the cathode showed noticable leakage current (Figure 24). Cathode potential appeared to leverl off at 0.7 V ( Figure 25), whereas anode potential continued to increase ( Figure 26).
  • Example 2 A method for recycling Mg from Mg scrap by combining a refining process and an SOM electrolysis process is shown in Figure 27.
  • the magnesium and its oxide were dissolved from scrap (2717) into a molten salt (2702), followed by vapor phase removal of dissolved magnesium.
  • the SOM electrolysis process when applied potential reaches the dissociation potential of MgO, oxygen ions are pumped out of the molten salt through a yttria-stabilized zirconia (YSZ) SOM (2703) toward a carbon rod current collector (2732) and are oxidized by the carbon to produce carbon monoxide gas and electrons.
  • YSZ yttria-stabilized zirconia
  • the setup consists of an upper reaction chamber (2800), heated to 1175 °C and a lower condensing chamber (2824) with a temperature gradient of 1 100 - 200 °C.
  • the setup was fabricated using grade 304 stainless steel (SS-304) and heated in an argon atmosphere.
  • the starting Mg scrap is slightly oxidized 50.5wt% Mg-Al alloy, prepared by melting a 9.624 g piece of magnesium (Mg > 99.8%) and a 9.4 g piece of aluminum (Al > 97.9%) together inside a small SS-304 crucible. To form the alloy, the mixture was stirred with a SS-304 rod for 15 minutes at 800 °C in an argon atmosphere, held at the same temperature without stirring for about 15 minutes and quenched.
  • a result of melting the molten salt at the top of alloy crucible (2805) is that some of magnesium in the alloy becomes oxidized. This magnesium oxide is later reduced with the SOM electrolysis process.
  • the crucible was fitted with an electrorefiner (anode 1), a graphite rod (anode 2) (2832) in a SOM (2803), the Mg-Al alloy, venting tube (2834), bubbling tube (2801), 2 g iron powder, and 680 g of molten salt.
  • the alloy crucible and inverted crucible (2835) served as the anode, and the reaction chamber wall and bubbling tube served as the cathode.
  • the SOM tube was held above the molten salt.
  • An alumina spacer was used to insulate the rod connecting the inverted crucible and the reaction chamber. Potentiodynamic scans were performed to determine the electrorefining potential for magnesium, as the refining of magnesium proceeded.
  • an yttria stabilized zirconia (YSZ) tube was used for recycling magnesium from magnesium oxide.
  • the stainless steel wall of the reaction chamber still served as the cathode, but silver inside the YSZ tube served as the anode, and a carbon rod acted as the anodic current collector.
  • YSZ yttria stabilized zirconia
  • the reaction chamber is continually purged with 95%Ar-H 2 at 15cc/min through a bubbling tube, and at 30cc/min through the two annuli at the top of the reaction chamber. This is done to lower the partial pressure of magnesium vapor over the molten salt and to carry the magnesium vapor to the condensing chamber.
  • the inlet of the venting tube is well above the molten salt surface, to prevent any molten molten salt from entering the condenser.
  • Electrochemical measurements were performed.
  • a Solartron SI 1280B potentiostat was used for potentiodynamic scans and impedance spectroscopy during the refining process; an Agilent Technologies N5743A power supply was used for potentiodynamic scans and electrolysis. Temperature steps at the center of the electrorefmer chamber are shown in Figure 29. Time of day versus temperature is plotted. The temperature reached maximum after ⁇ 5 h (4:00 PM) and was held at 1175 °C.
  • a PDS scan was run at 13 minutes after the maximum operating temperature was reached (4: 13 PM) at electrorefining (ER) potential of 0.018 V, Faradic current of 0.629 A and open circuit voltage (OCV) of -0.0003 V ( Figure 30). Impedance spectroscopy (IS) was measured at 4:20 PM, indicating a cell ohmic resistance of 0.066 ohms Figure 31.
  • PES potentiostatic scan
  • a PDS was added at 5: 19 PM, with ER potential of 0.0041 V, OCV of -0.0242 V, and Faradic current (second jump) 0.0592 A ( Figure 36).
  • a potentiostatic scan (PSS) was done at 5:25 PM, with applied potential of 0.057 V, OCV of -0.043 V, current typical value of 0.42 A and Faradic current 0.1154 A ( Figure 38). Magnesium electrorefmed was 0.0087 g.
  • a PDS was added at 5:36 PM, with ER potential of -0.0018 V, OCV of -0.031 V, and Faradic current (second jump) 0.0659 A (first jump N/A) ( Figure 39).
  • a PDS was added at 5:53 PM, with ER potential of -0.0047 V, OCV of -0.0504 V, and Faradic current 1 st jump at 0.0622 A and 2 nd jump at 0.0838 A ( Figure 40).
  • a potentiostatic scan was done at 5:55 PM, with applied potential of 0.106 V, OCV of -0.0439 V, current typical value of 0.46 A and Faradic current 0.146 A ( Figure 41). Magnesium electrorefmed was 0.0328 g.
  • a PDS was added at 6:28 PM, with ER potential of 0.017 V, OCV of -0.0269 V, and
  • a PDS was added at 6:52 PM, with ER potential of 0.045 V, OCV of 0.0124 V, and
  • Magnesium electrorefmed was 0.032 g.
  • a potentiostatic scan was done at 7:48 PM, with applied potential of 0.221 V, OCV of 0.021 V, current typical value of 0.45 A and Faradic current 0.1208 A ( Figure 46). Magnesium electrorefmed was 0.0271 g.
  • a PDS was added at 8: 19 PM, with ER potential of 0.103 V, OCV of 0.0394 V, and Faradic current 1 st jump at 0.0462 A and 2 nd jump at 0.0597 A ( Figure 47).
  • Impedance spectroscopy (IS) was measured at 8:27 PM, indicating a cell ohmic resistance of 0.09 ohms ( Figure 48).
  • a potentiostatic scan was done at 8:34 PM, with applied potential of 0.2656 V, OCV of 0.0154 V, current typical value of 0.51 A and Faradic current 0.1059 A (Figure 49). Magnesium electrorefmed was 0.008 g.
  • a potentiostatic scan (PSS) was done at 8 :47 PM, with applied potential of 0.288 V, OCV of 0.038 V, current typical value of 0.5 A and Faradic current 0.1309 A ( Figure 51).
  • Magnesium electrorefmed was 0.0096 g.
  • a PDS was added at 8:58 PM, with ER potential of 0.132 V, OCV of 0.0824 V, and Faradic current 1 st jump at 0.0593 A and 2 nd jump at 0.0823 A ( Figure 52).
  • the magnesium solubility inside the molten salt after the experiment was found to be 0.03wt% as measured with a manometer. Dilute acid was added to powdered salt in a closed container and the volume of gas produced due to the hydrogen evolution was measured. The salt was powdered in a glove box to avoid the oxidation of magnesium in the salt.
  • the magnesium solubility inside a molten salt of similar composition (55%MgF 2 -45%CaF 2 -10%MgO) was reported to be 0.02-0.05wt.% [E.
  • ⁇ is the activity coefficient of magnesium in Mg-Al alloy
  • XMg(aiioy) is the magnesium molar content in Mg-Al alloy
  • PM g (moiten salt) is the partial pressure of magnesium vapor in equilibrium with liquid magnesium dissolved in molten salt at the cathode, where PM g (moiten sait ) ⁇ latm.
  • the first electrorefinmg potential and the open circuit voltage depend on the ratio of activity of magnesium dissolved in the molten salt and the activity of magnesium in the alloy. There is a minor difference between the open circuit voltage and the first electrorefinmg potential in the experimental measurement caused by the fluctuating value of
  • ⁇ is the activity coefficient of magnesium in Mg-Al alloy
  • XMg(aiioy) is the magnesium molar content in Mg-Al alloy
  • the electrorefinmg potential depends on the ratio of magnesium vapor activity at the cathode and magnesium activity in the alloy.
  • Impedance spectroscopy (IS) was measured at 1 1 :07 PM, indicating a cell ohmic resistance of 1.28 ohms ( Figure 57).
  • Electrolysis was performed for a total of two hours at a potential of 3V.
  • the lower curve in Figure 60 shows the initial potentiodynamic scan before any SOM electrolysis was performed, and shows an electronic current of 0.35 A due to the dissolution of magnesium from the scrap into the molten salt.
  • the lower curve in Figure 61 shows the current-time relationship during the first hour of electrolysis. Current efficiency is defined as the ratio of Faradic current to total current, and was calculated to be approximately 41% for the first hour of electrolysis. This is done by measuring the flow rate of carbon monoxide produced from the reaction of the carbon rod and oxygen on the anode side of the YSZ membrane. Based on the volume of carbon monoxide generated, magnesium reduced at the cathode was calculated to be 0.18g during the first hour of SOM electrolysis.
  • Leakage current for the SOM process is high right after electrorefining. Magnesium obtained from the SOM process is about 0.4101 g.
  • a piece of collected Mg was characterized by EDS, which indicated that the collected magnesium is pure ( Figure 62).
  • the atomic percent of magnesium was 99.6%> and aluminum was 0.4%.
  • Current efficiency of SOM is 41% at first electrolysis and 39% at second electrolysis. Current efficiency of SOM is low because of electronic conductivity in the molten salt due to dissolved magnesium. The SOM efficiency can be improved after removing the dissolved magnesium. Pure Mg was collected and the remaining amount of Mg in the alloy is negligible.
  • Example 3 The stability of YSZ in MgO-MgF 2 -CaF 2 molten salt containing YF 3 and on Mg solubility as a function of temperature in MgO (MgF 2 -CaF 2 ) molten salt were studied. YSZ stability was examined with impurities and with 2% YF 3 . The yttrium profile for a 32 hour overlay is shown in Figure 67. The solid line in Figure 67 is the control with no yttria. Negative position corresponds to flux, while positive position values correspond to membrane. Impurity compositions are shown in Table 1 : [0250] Table 1 : Impurity Composition
  • a 1.5% YF 3 in solution is close, but a higher concentration is needed to prevent the yttrium from diffusing into the molten salt.
  • a new molten salt made from LiF-MgF 2 was also tested for lower Mg solubility.
  • the system diagram showing the eutectic melting temperature of LiF-MgF 2 is shown in Figure 68 and in J. Am. Ceram. Soc. 1953, 36(1), 15; herein incorporated by reference in its entirety).
  • the eutectic melting temperature is approx. 730 °C.
  • the eutectic melting temperature of 45% CaF 2 - 55MgF 2 is 975 °C.
  • a manometer was used for solubility measurements, determination of which was conducted in an enclosed chamber ( Figure 69). Magnesium and molten salt (6944) were placed in a beaker and acid and water (6945) were added.
  • Tosoh zirconia powder 700 mg was added to Aremco 552 alumina paste (20 mL), and the resulting seal (2 applications) reduced the flow from 24 mL/min to 5 mL/min at 4 psi. Glass pastes, gold and silver o-rings were not sufficient.
  • When magnesium is mixed with dilute acid in the flask, hydrogen gas evolves and pressure on the sample side increases. The difference in pressure between the two sides is ⁇ pgh.
  • Moles of hydrogen produced in the test equal the moles of magnesium in the sample.
  • Mg solubility as a function of T is shown in Table 3.
  • Solubility of Mg can also be measured at 1250 °C and 1300 °C.

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Abstract

Dans un aspect, la présente invention concerne des procédés et dispositifs de récupération de métaux cibles à partir de riblons. Dans certains modes de réalisation, ces procédés comprennent les étapes consistant à dissoudre une portion de riblons métalliques mixtes dans un sel fondu afin de former un mélange de sel fondu et de métal, les riblons contenant une espèce métallique cible et au moins une espèce métallique contaminante, à faire barboter un gaz dans le mélange de sel fondu et de métal afin de former un mélange de gaz et de vapeurs métalliques contenant des vapeurs du métal cible, et condenser une partie au moins des vapeurs de métal cible.
PCT/US2012/058882 2011-10-07 2012-10-05 Procédés et dispositif pour production et distillation efficaces de métaux comprenant une électrolyse d'oxydes WO2013052753A1 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115747523A (zh) * 2022-11-18 2023-03-07 昆明理工大学 一种真空碳热还原炼镁的方法

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