Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Reexamination Certificate
2000-04-10
2002-06-25
King, Roy (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
C075S010540, C075S398000, C373S142000, C373S144000
Reexamination Certificate
active
06409791
ABSTRACT:
TECHNICAL FIELD
This invention relates to the metallothermy and continuous drawing off of metals or alloys, in cold inductive crucibles. The metals or alloys are produced from metallic oxides or salts. The invention particularly concerns the preparation of uranium metal from a uranium oxide or salt. It also concerns the preparation of an alloy of uranium or another metal.
State of Prior Art
Conventionally, uranium metal is obtained after transformation of UO
2
oxide into UF
4
, followed by a step to reduce the tetrafluoride into uranium metal. No current industrial process is capable of directly producing solid uranium metal ingot from the dioxide. The action of a reducing metal such as Ca or Mg on uranium dioxide, despite its very strong exothermal nature, cannot melt the lime or magnesia, and uranium metal is obtained divided in an unmeltable solid. The slag may be dissolved in an acid, but the processing cost is prohibitive for large scale production and there is a risk that the divided metal could be attacked. On the other hand, the slag composed of fluorite or sellaite formed during reduction of UF
4
by these metals is relatively meltable. The uranium assembles in situ in the form of an ingot. Slag generates a solid waste, treated by a wet method before being permanently stored in a controlled tip.
At the present time, constraints necessary for the reduction of waste involve the use of recycling processes, for example using electrolysis.
Patent U.S. Pat. No. 5,290,337 divulges a process for the reduction of uranium oxide by magnesium capable of recovering uranium metal and regenerating the metallic reduction agent. Uranium oxide (for example UO
2
) is reduced in the presence of molten salts, for example MgCl
2
/MgF
2
or MgCl
2
/NdCl
3
in order to improve the settlement of uranium metal, as recommended by C. MORANVILLE and J. DUBUISSON in
Le Nouveau Traité de Chimie Minérale
(The New Treatise of Inorganic Chemistry) published under the management of P. PASCAL, Volume XV, book 1, 1960, Masson and Company, page 187, and J. H. BUDDERY in Metallurgy and Fuels, 1956, vol. 4, pages 24-32. The metal is recovered in a layer of molten ZnMg or CuMg alloy. UO
2
is added into the two-phase medium composed of the molten alloy (ZnMg) and the mix of molten salts (MgCl
2
/NdCl
3
), stirred and heated to 750° C. Some of the magnesium reduces UO
2
by forming U and MgO. The MgO then reacts with neodymium chloride to produce magnesium chloride and neodymium oxide. The uranium metal is incorporated in the ZnMg phase. When the reactional medium is no longer stirred, the phases separate. The denser metallic phase settles at the bottom of the crucible. After cooling and solidification, the phases are mechanically separated. The uranium metal is then separated by evaporation of ZnMg. Mg is regenerated by electrolysis of the salt.
Thus according to U.S. Pat. No. 5,290,337, reduction of UO
2
by Mg takes place in a two-phase mix while being stirred. The principle of two separate phases only appears after the end of the process that can only be a discontinuous system (“batch process”). Therefore, this process has the disadvantage that it cannot directly and continuously produce uranium metal at the output from the crucible. Two additional steps are necessary to separate the constituents, firstly a mechanical separation of the phases and then a distillation. Furthermore, the bath is necessarily remelted before electrolysis and regeneration of Mg, and it cannot subsequently be recycled unless an additional step is added to convert the neodymium oxide into chloride.
Since the 1960s, many studies, publications and patents have been made on continuous melting and drawing off of ingots. The metal is usually added directly into the drawing off crucible, after being produced in other structures, for example by electrolysis, metallothermy or reduction by a metalloid (carbon, sulfur).
The “Economically Producing Reactive Metals by Aerosol Reduction” article by J. D. LELAND, published in the J.O.M. review, pages 52-55, October 1996, divulges a process for obtaining titanium, hafnium or zirconium semi-continuously from their precursor salts (chlorides). The reduction process by aerosols consists of a reaction between two jets of products.
The reducing metal (for example Na or Mg) is in the form of an aerosol between 400 and 600° C., and the metal chloride to be reduced is in vapor form. Due to the exothermal nature of the reaction, the chloride formed is vaporized whereas the solid metal drops to the bottom of a liquid metal bath. The temperature of the medium is stabilized at about the boiling point of the salt formed, typically 1100-1200° C. The metal is collected and molten starting from the bottom of the bath in an inductive cold crucible. This process has two main disadvantages, firstly the necessity to have an exothermal reaction in order to vaporize the slag and the initial product that has not reacted, and the difficulty in controlling feed flows. Furthermore, this process would not be applicable in the case of exothermal reactions in which there is a risk of reaching the thermodynamic inversion temperature or if the slag boiling temperature exceeds the thermodynamic inversion temperature.
DESCRIPTION OF THE INVENTION
The invention overcomes the disadvantages of prior art mentioned above by proposing a solution that enables complete and continuous production as far as the preformed metal, starting from the metal salt or oxide.
Therefore, the purpose of the invention is a metallothermy and continuous drawing off process for a metal product, composed of at least one metal, comprising:
a metal production step in a first cold crucible heated by induction in which reduction of the oxide or salt of the said metal is provoked in a reducing medium composed of a floating layer of melting material and in which the formed metal settles in a solvent medium consisting of a bath composed of at least one molten salt that absorbs the slag resulting from the reduction reaction, the maximum input flow of the floating layer of oxide or salt of the said metal being determined by the thickness of the floating layer and the temperature of its top surface such that the reduction of the oxide or salt of the said metal takes place entirely in the floating layer;
a step in which the settled metal is collected and melted, that takes place in a second cold crucible heated by induction located under the first cold crucible, in order to enable continuous drawing off of the metallic product.
This determination of the maximum feed flow may depend on test results and/or a model to produce nomograms. The floating reducing medium can be used to perfectly control the temperature and avoid reversibility of the reactions.
Induction heating of the first crucible and the second crucible can take place at different frequencies.
The reducing medium may include a material chosen among a metal, a mix of metals, a metalloid or a mix of metalloids.
The oxide or the salt of the said metal to be produced may be added into the first cold crucible above the layer if this oxide or salt is in the solid state or the liquid state. The oxide or salt of the said metal to be produced may be added into the first cold crucible under the layer if this oxide or salt is in the gaseous state.
If the metallic product to be produced is an alloy of at least two metals, the first cold crucible may be fed by a mix of oxide(s) or salt(s) of these two metals. As a variant, one of these metals may be added into the first cold crucible directly in its metallic form, the other of these metals being added in the form of an oxide or salt.
Advantageously, the process also comprises a step in which the reducing medium is regenerated by electrolysis of the slag present in the solvent medium. The solvent medium is drawn off continuously.
Another purpose of the invention is a device for embodiment of the process described above, characterized in that it comprises:
a first crucible with cold walls equipped with induction heating means and means of adding the oxide or salt of
Hurbin Véronique
Petit Jany
Philippe Laurent
Compagnie Generale des Matieres Nucleaires
King Roy
McGuthry-Banks Tima
Pearne & Gordon LLP
LandOfFree
Metallothermal process and continuous drawing, in cold... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Metallothermal process and continuous drawing, in cold..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Metallothermal process and continuous drawing, in cold... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2932395