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USH857H - Electrolytic process for preparing uranium metal - Google Patents

Electrolytic process for preparing uranium metal Download PDF

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Publication number
USH857H
USH857H US07/562,187 US56218790A USH857H US H857 H USH857 H US H857H US 56218790 A US56218790 A US 56218790A US H857 H USH857 H US H857H
Authority
US
United States
Prior art keywords
uranium
sub
anode
chlorides
cell
Prior art date
Legal status (The legal status 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 status listed.)
Abandoned
Application number
US07/562,187
Inventor
Paul A. Haas
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
US Department of Energy
Original Assignee
US Department of Energy
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.)
Filing date
Publication date
Application filed by US Department of Energy filed Critical US Department of Energy
Priority to US07/562,187 priority Critical patent/USH857H/en
Application granted granted Critical
Publication of USH857H publication Critical patent/USH857H/en
Assigned to UNITED STATES OF AMERICA, THE, AS REPRESENTED BY THE DEPARTMENT OF ENERGY reassignment UNITED STATES OF AMERICA, THE, AS REPRESENTED BY THE DEPARTMENT OF ENERGY ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: HAAS, PAUL A.
Abandoned legal-status Critical Current

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Classifications

    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25CPROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/34Electrolytic production, recovery or refining of metals by electrolysis of melts of metals not provided for in groups C25C3/02 - C25C3/32
    • GPHYSICS
    • G21NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21CNUCLEAR REACTORS
    • G21C19/00Arrangements for treating, for handling, or for facilitating the handling of, fuel or other materials which are used within the reactor, e.g. within its pressure vessel
    • G21C19/42Reprocessing of irradiated fuel
    • G21C19/44Reprocessing of irradiated fuel of irradiated solid fuel
    • G21C19/48Non-aqueous processes
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00Energy generation of nuclear origin
    • Y02E30/30Nuclear fission reactors
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02WCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00Technologies for solid waste management
    • Y02W30/50Reuse, recycling or recovery technologies

Definitions

  • This invention relates to a process for preparing uranium and more particularly an electrolytic process for preparing uranium using fluoride and chloride salt mixtures.
  • a standard method for making uranium metal is the reduction of UF 4 with magnesium as a reducing agent.
  • the high cost of such a process has directed efforts at alternatives.
  • One alternative is the use of electrochemical methods similar to the Hall-Heroult process used in making aluminum.
  • An additional object of this invention is to provide an electrolytic process for making uranium wherein current capacities are maximized.
  • a further object of this invention is to provide a process for making uranium that is safe, having no hazardous by products.
  • the process of this invention may comprise: in an electrolytic cell having an anode and cathode electrodes, contacting in the molten state uranium chloride and a mixture of salts comprising chloride salts of metals selected from the group consisting of K, Na and Ba, the fluoride salts of metals selected from the group consisting of K, Na and Ba in sufficient amounts to minimize volatility of uranium chlorides; and introducing an electric current across the electrodes thus resulting in the production of uranium metal.
  • This process is safer and more efficient than prior electrolytic processes.
  • the theory of this invention is to produce at one electrode a byproduct that can be recycled to a feed reactor containing UO 2 feed material to produce a uranium compound that can be electrolytically reduced, thus eliminating the problem of having UO 2 in the reaction vessel and also recycling a byproduct.
  • the composition of the reactants is formulated so that Cl 2 forms at the anode. This reacts with UO 2 in a the feed reactor to form uranium chlorides as the uranium compounds to be reduced.
  • the cell charge is a mixture of chloride and fluoride salts with one or more of the fluoride salts selected to give a high degree of conversion of uranium chlorides to uranium fluorides.
  • the preferred fluoride is KF and some conversion reactions are
  • Other possible fluoride salts for exchange with uranium chlorides are NaF and BaF 2 , however, NaCl is more volatile than KCl, and the exchange reaction with BaF 2 is less favorable thermodynamically.
  • the composition is selected so that UCl 4 concentration in the melt is low to enable the cell to be operated above the boiling point of UCl 4 without the production of excessive amounts of UCl 4 vapor. Because the chlorine is in the melt, as KCl, the anode product is Cl 2 in spite of the low UCl 4 concentration.
  • the electrode reaction depend on the ions present at the electrode and not on the melt constituents that do not ionize.
  • the KCl and UF 4 and UF 3 all ionize.
  • the anode reaction to form Cl 2 occurs first and the undesirable reaction of F - to form CF 4 requires a higher voltage and does not occur until the chloride at the anode is depleted to a low concentration.
  • U metal is formed in preference to K metal.
  • Uranium fluoride and chlorides are molten and soluble in the cell melt at 1200° C.; therefore, there are no interfering solids to foul the cell.
  • the cell can be operated without UF 4 feed material or having to deal with CF 4 waste.
  • the current efficiencies are higher since low efficiencies can be attributed to parasitic U(III) ⁇ U(IV) cycle and large amounts of UF 4 needed to give useful solubilities UO 2 .
  • Lower UF 4 concentrations and resulting higher current efficiencies are possible when the anode product is Cl 2 .
  • Higher anode current densities and higher cell capacities are possible with Cl 2 as the anode product since Cl 2 does not give the critical anode effect that occurs when CF 4 is a product.
  • the carbon anode is not consumed as it is when CO and CF 4 are the anode product. This allows for a continuous process for uranium manufacture since the anode does not need to be periodically replaced.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • High Energy & Nuclear Physics (AREA)
  • General Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)

Abstract

An electrolytic process for making uranium from uranium oxide using Cl2 anode product from an electrolytic cell to react with UO2 to form uranium chlorides. The chlorides are used in low concentrations in a melt comprising fluorides and chlorides of potassium, sodium and barium in the electrolytic cell. The electrolysis produces Cl2 at the anode that reacts with UO2 in the feed reactor to form soluble UCl4, available for a continuous process in the electrolytic cell, rather than having insoluble UO2 fouling the cell.

Description

This invention was developed pursuant to a contract with the U.S. Department of Energy.
This invention relates to a process for preparing uranium and more particularly an electrolytic process for preparing uranium using fluoride and chloride salt mixtures.
BACKGROUND OF THE INVENTION
A standard method for making uranium metal is the reduction of UF4 with magnesium as a reducing agent. The high cost of such a process has directed efforts at alternatives. One alternative is the use of electrochemical methods similar to the Hall-Heroult process used in making aluminum. These approaches presented major difficulties.
First, the high density and low solubility of uranium oxides resulted in fouled cells that prevented metal coalescence. Also, less than 50% of recovered metal is from uranium oxides, the rest being from UF4 which not only must first undergo conversion from the UO2 form before electrolytic reduction, but also produces an undesirable CF4 waste gas emission. The efficiencies are low, rarely exceeding 30% and usually lower than 20% for production from UO2. Cell capabilities are low due to low current efficiencies and because the maximum current is limited by the "critical current density" that gives an "anode effect" when CF4 is produced. Finally, in order to maintain continuous operation at 1200° C., consumed carbon anodes must be repeatedly replaced, a difficult and dangerous job.
Therefore there is a continuing need to develop new, safe and efficient process for making uranium metal.
SUMMARY OF THE INVENTION
In view of the above needs, it is an object of this invention to provide a process for making uranium that eliminates oxide fouling of the cell.
It is another object of this invention to provide a process for making uranium that has a high uranium yield and is thus more efficient than present processes.
An additional object of this invention is to provide an electrolytic process for making uranium wherein current capacities are maximized.
A further object of this invention is to provide a process for making uranium that is safe, having no hazardous by products.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the process of this invention may comprise: in an electrolytic cell having an anode and cathode electrodes, contacting in the molten state uranium chloride and a mixture of salts comprising chloride salts of metals selected from the group consisting of K, Na and Ba, the fluoride salts of metals selected from the group consisting of K, Na and Ba in sufficient amounts to minimize volatility of uranium chlorides; and introducing an electric current across the electrodes thus resulting in the production of uranium metal. This process is safer and more efficient than prior electrolytic processes.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The theory of this invention is to produce at one electrode a byproduct that can be recycled to a feed reactor containing UO2 feed material to produce a uranium compound that can be electrolytically reduced, thus eliminating the problem of having UO2 in the reaction vessel and also recycling a byproduct. The composition of the reactants is formulated so that Cl2 forms at the anode. This reacts with UO2 in a the feed reactor to form uranium chlorides as the uranium compounds to be reduced.
The anode reaction is
4Cl.sup.- →2Cl.sub.2 +4e
The reaction at the cathode is
U.sup.+4 +4e→U°
The net overall cell reaction is
UCl.sub.4 →2Cl.sub.2 +U°
The reactions listed using uranium chlorides are known and were used in batch-type processes to prepare dendritic uranium metal solids at 750° to 900° C. The process was inefficient and uneconomical because of the large amount of waste solids and the steps for recovery of the uranium metal powder. Operations to prepare molten uranium were not practical because of the excessive volatility of uranium chlorides.
To get around that problem, the cell charge is a mixture of chloride and fluoride salts with one or more of the fluoride salts selected to give a high degree of conversion of uranium chlorides to uranium fluorides. The preferred fluoride is KF and some conversion reactions are
4KF+UCl.sub.4 →4KCl+UF.sub.4
3KF+UCl.sub.3 →3KCl+UF.sub.3
Thermodynamic data shows a value of -255 Kj/mol UCl4 =f G°=-RT InKf at 1500° C. for the first reaction. This value indicates a very high equilibrium conversion to KCl and UF4 and results in a very fast conversion in the molten cell charge. Other possible fluoride salts for exchange with uranium chlorides are NaF and BaF2, however, NaCl is more volatile than KCl, and the exchange reaction with BaF2 is less favorable thermodynamically.
Another reason to use the salt mixture is that it will have a lower melting point resulting in easier more convenient operation. The composition is selected so that UCl4 concentration in the melt is low to enable the cell to be operated above the boiling point of UCl4 without the production of excessive amounts of UCl4 vapor. Because the chlorine is in the melt, as KCl, the anode product is Cl2 in spite of the low UCl4 concentration.
The electrode reaction depend on the ions present at the electrode and not on the melt constituents that do not ionize. The KCl and UF4 and UF3 all ionize. The anode reaction to form Cl2 occurs first and the undesirable reaction of F- to form CF4 requires a higher voltage and does not occur until the chloride at the anode is depleted to a low concentration. At the cathode, U metal is formed in preference to K metal. The net reactions in the cell when the uranium is mostly UF4 are
UF.sub.4 +4KCl→2Cl.sub.2 +U°+4KF
UF.sub.3 +3KCl→3/2Cl.sub.2 +U°+3KF
In combination with the exchange reactions for KF with uranium chloride feed, the net reactions starting with uranium chloride feed are
UCl.sub.4 →2Cl.sub.2 +U°
UCl.sub.3 →3/2Cl.sub.2 +U°
One reaction for chloride recycle in a chlorinator is
UO.sub.2 +2Cl.sub.2 +2CO→UCl.sub.4 +2CO.sub.2
Then the overall net process reaction is
UO.sub.2 +2CO→2CO.sub.2 +U°
This process provides many benefits over prior art processes. Uranium fluoride and chlorides are molten and soluble in the cell melt at 1200° C.; therefore, there are no interfering solids to foul the cell. The cell can be operated without UF4 feed material or having to deal with CF4 waste. The current efficiencies are higher since low efficiencies can be attributed to parasitic U(III)←→U(IV) cycle and large amounts of UF4 needed to give useful solubilities UO2. Lower UF4 concentrations and resulting higher current efficiencies are possible when the anode product is Cl2. Higher anode current densities and higher cell capacities are possible with Cl2 as the anode product since Cl2 does not give the critical anode effect that occurs when CF4 is a product. In addition, the carbon anode is not consumed as it is when CO and CF4 are the anode product. This allows for a continuous process for uranium manufacture since the anode does not need to be periodically replaced.

Claims (1)

I claim:
1. A process for making uranium comprising, in an electrolytic cell having anode and cathode electrodes, contacting in the molten state uranium chloride and a mixture of salts comprising chloride salts of metals selected from the group consisting of K, Na and Ba, and fluoride salts of metals selected from the group consisting of K, Na and Ba in sufficient amounts to minimize volatility of uranium chlorides; and introducing an electric current across the electrodes thus resulting in the production of uranium metal.
US07/562,187 1990-07-26 1990-07-26 Electrolytic process for preparing uranium metal Abandoned USH857H (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US07/562,187 USH857H (en) 1990-07-26 1990-07-26 Electrolytic process for preparing uranium metal

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
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Publications (1)

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USH857H true USH857H (en) 1990-12-04

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5164050A (en) * 1989-07-06 1992-11-17 Compagnie Europeenne Du Zirconium Cezus Method of obtaining uranium from oxide using a chloride process
US5380406A (en) * 1993-10-27 1995-01-10 The United States Of America As Represented By The Department Of Energy Electrochemical method of producing eutectic uranium alloy and apparatus
US5421855A (en) * 1993-05-27 1995-06-06 The United States Of America As Represented By The United States Department Of Energy Process for continuous production of metallic uranium and uranium alloys
WO2001041152A3 (en) * 1999-12-03 2002-03-21 British Nuclear Fuels Plc Actinide production
WO2002099815A3 (en) * 2001-06-06 2003-04-03 British Nuclear Fuels Plc Actinide production
US7011736B1 (en) * 2003-08-05 2006-03-14 The United States Of America As Represented By The United States Department Of Energy U+4 generation in HTER
US7097747B1 (en) * 2003-08-05 2006-08-29 Herceg Joseph E Continuous process electrorefiner

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5164050A (en) * 1989-07-06 1992-11-17 Compagnie Europeenne Du Zirconium Cezus Method of obtaining uranium from oxide using a chloride process
US5421855A (en) * 1993-05-27 1995-06-06 The United States Of America As Represented By The United States Department Of Energy Process for continuous production of metallic uranium and uranium alloys
US5380406A (en) * 1993-10-27 1995-01-10 The United States Of America As Represented By The Department Of Energy Electrochemical method of producing eutectic uranium alloy and apparatus
WO2001041152A3 (en) * 1999-12-03 2002-03-21 British Nuclear Fuels Plc Actinide production
WO2002099815A3 (en) * 2001-06-06 2003-04-03 British Nuclear Fuels Plc Actinide production
US20040244533A1 (en) * 2001-06-06 2004-12-09 Lewin Rober Glynn Actinide production
US7011736B1 (en) * 2003-08-05 2006-03-14 The United States Of America As Represented By The United States Department Of Energy U+4 generation in HTER
US7097747B1 (en) * 2003-08-05 2006-08-29 Herceg Joseph E Continuous process electrorefiner

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STCF Information on status: patent grant

Free format text: PATENTED CASE

AS Assignment

Owner name: UNITED STATES OF AMERICA, THE, AS REPRESENTED BY T

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:HAAS, PAUL A.;REEL/FRAME:005682/0396

Effective date: 19900424