Patent Grant
9039885
This disclosure relates to the field of electrolytic chemistry. More particularly, this disclosure relates to the production of metal halides for electrorefining of metals.
Metal halides are useful for electrorefining metals. However, the production of many metal halides is difficult. In particular, current methods for the production of uranium trichloride (UCl3) on a large scale require handling of highly pyrophoric uranium/uranium hydride fines or the use of toxic cadmium chloride as an oxidizer in a molten salt bath. It is desirable to eliminate the need for both of these reagents. Moreover, it is desirable in some circumstances to provide in-situ production of metal halides such as UCl3. Consequently, improved systems and methods are needed for making metal halides, and in particular for making UCl3 for electrorefining uranium.
In some embodiments, the present disclosure provides an electrochemical cell for producing a metal halide. A typical electrochemical cell includes a container, a source of an acid of a halogen, and an electrolyte in the container. The composition of the electrolyte includes a molten salt of (a) the halogen and (b) an alkali metal. The electrochemical cell typically also includes an anode in the electrolyte where the anode includes a non-alkali metal. There is an anolyte portion of the electrolyte adjacent the anode. Generally there is a tube in the electrolyte, and the tube establishes a catholyte portion of the electrolyte and the tube has a permeable portion for ionic transportation. Typically a cathode is in the catholyte portion, and the cathode has a chemical feed passageway for flowing the hydrogen halide gas into the catholyte portion of the electrolyte. It is generally important that a portion of the hydrogen halide dissolves in the electrolyte that is in the catholyte portion of the electrolyte. The electrochemical cell typically includes a direct current power source that has an anode terminal that is in electrical connectivity with the anode and has a cathode terminal that is in electrical connectivity with the cathode. With this configuration, the hydrogen halide is electrolyzed adjacent the cathode to produce hydrogen and to produce anions of the halide that migrate to the anode and form the metal compound as a halide of the non-alkali metal adjacent the anode.
Another embodiment provides an electrochemical cell for producing an electrorefined non-alkali metal. This embodiment has a container and an electrolyte is in the container. The composition of the electrolyte includes a molten salt of (a) a halogen and (b) an alkali metal. In this embodiment there is an anode disposed in the electrolyte. An anolyte portion of electrolyte is adjacent the anode, and a halide consisting of (a) the halogen and (b) a non-alkali metal is disposed in the anolyte portion. There is a cathode disposed in the electrolyte. Further in this embodiment there is a direct current power source having an anode terminal that is in electrical connectivity with the anode and there is a cathode terminal that is in electrical connectivity with the cathode such that cations of the non-alkali metal migrate from the anolyte portion and are electro-deposited adjacent the cathode as the electrorefined non-alkali metal.
Method embodiments are provided for producing a non-alkali metal halide that includes a halogen and a non-alkali metal where the hydrogen halide has a solubility of at least 1 mmol/L in a molten salt of (a) the halogen and (b) an alkali metal. A typical method involves electrolytically dissociating at a cathode the hydrogen halide dissolved in the molten salt such that halogen anions and gaseous hydrogen are formed at the cathode. Such methods typically further involve electrolytically charging a metal at an anode in the molten salt such that cations of the non-alkali metal are formed at the anode. Such methods typically further involve combining the halogen anions and the cations of the non-alkali metal to form the metal compound adjacent the anode as a non-alkali metal halide.
Method embodiments are provided for producing an electrorefined non-alkali metal. Such methods generally involve disposing in a electrochemical cell having an anode and a cathode a mixture of (1) a halide consisting of a halogen and a non-alkali metal and (2) a molten salt of the halogen and an alkali metal. Then, typically, the methods involve applying a direct current potential across the anode and the cathode wherein cations of the non-alkali metal migrate from a region adjacent the anode and are electro-deposited adjacent the cathode as the electrorefined non-alkali metal.
In the various embodiments disclosed herein the halide is chlorine, the alkali metal is lithium and the non-alkali metal is uranium, such that UCl3 is produced and/or electrorefined.
Various advantages are apparent by reference to the detailed description in conjunction with the figures, wherein elements are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein:
In the following detailed description of the preferred and other embodiments, reference is made to the accompanying drawings, which form a part hereof, and within which are shown by way of illustration the practice of specific embodiments of an electrochemical cell for making a metal halide and embodiments of methods for making metal halides. It is to be understood that other embodiments may be utilized, and that structural changes may be made and processes may vary in other embodiments.
Various embodiments disclosed herein provide systems and methods for the electrolysis of a hydrogen halide in a molten salt of (a) an alkali metal and (b) the halogen, to produce that halide of a non-alkali metal. For example, anhydrous hydrogen chloride may be electrolyzed in a molten lithium chloride salt in order to convert elemental uranium metal to uranium trichloride.
As used herein the term “halogen” refers to any of the elements of Table 1.
As used herein the term “alkali metal” refers to any of the elements in Table 2.
Note that the “alkali metals” of Table 2 include elements that are sometimes elsewhere referred to as “alkaline earth metals.”
As used herein the term “non-alkali metal” refers to any of the elements in Table 3.
A direct current (DC) power supply 30 is provided. An anode terminal 34 of the DC power supply 30 is in electrical connectivity with the anode 22, and a cathode terminal 38 of the DC power supply 30 is in electrical connectivity with the cathode 18.
A catholyte portion 50 of the electrolyte 14 is proximate to the cathode 18, and an anolyte portion 54 of the electrolyte 14 is proximate to the anode 22. The anolyte portion 54 is not isolated from the bulk of the electrolyte 14 by any physical barrier, but the catholyte portion 50 and the cathode 18 are isolated from the anolyte portion 54 and the anode 22 and by a tube 70. Typically, the tube 70 is fabricated from quartz. The tube 70 has a permeable portion 74 for ionic transport, as subsequently described herein. Typically, the permeable portion 74 is formed with porous frits. A source 90 of a hydrogen halide is provided. For example, if the halogen is chlorine then the hydrogen halide may be anhydrous hydrogen chloride (HCl).
To operate the electrochemical cell 10, gas bubbles 94 of the hydrogen halide (e.g., bubbles of anhydrous HCl) are flowed into the catholyte portion 50 through the hollow tube 70 of the anode 18. Some of the hydrogen halide (from source 90) is dissolved into the electrolyte 14. In order for the process to operate, the solubility of the acid of the halogen into the molten salt (i.e., the molten salt of (a) the alkali metal and (b) the halogen) should be at least 1 mmol/L. Then, with the DC power supply 30 energized, the following reactions occur:
Cathode: 3HHn→3H++3Hn− (Reaction 1a)
3H++3e−→3/2H2 (g) (Reaction 1b)
Anode: M+3Hn−→MHn3+3e− (Reaction 2)
where the symbols “M”=the non-alkali metal and “Hn”=the halogen.
Thus, when the non-alkali metal is uranium and the halogen is chlorine, Reactions 1a, 1b and 2 are:
Cathode: 3HCl→3H++3Cl− (Reaction 3a)
3H++3e−→3/2H2 (g) (Reaction 3b)
Anode: U+3Cl−→UCl3+3e− (Reaction 4)
The net reaction is:
M+3HHn→MHn3+3/2H2 (g) (Reaction 5)
such that when the non-alkali metal is uranium and the halogen is chlorine, Reaction 5 is:
U+3HCl→UCl3+3/2H2 (g) (Reaction 6)
A halide of a non-alkali metal (e.g., UCl3) is formed at the anode and hydrogen gas is formed at the cathode. The halide of the non-alkali metal (e.g., UCl3) is produced as a mixture with molten salt of (a) the alkali metal and (b) the halogen (e.g., LiCl).
It is important to note that the same halogen is used in the hydrogen halide (from source 90) and in the molten salt of the alkali metal that is the electrolyte 14. Thus, if the non-alkali metal is uranium and the molten salt of the alkali metal is LiCl, then the hydrogen halide that is used is HCl such that UCl3 is produced as the halide of the non-alkali metal.
The electrochemical cell 100 of
The electrochemical cell 100 has two DC power sources. The DC power source 30 in
The electrochemical cell 100 has an electrical switching system 170 that includes a first electrical switch 174 and a second electrical switch 178. These switches permit the electrochemical cell 100 to be operated in either production mode (for producing a halide of the alkali metal) or a refining mode (for electrorefining the halide of the alkali metal).
When the electrochemical cell 100 is in the electrorefining mode, the first electrical switch 174 is open and the second electrical switch 178 is closed. In this configuration the second anode terminal 154 is in electrical connectivity with the anode 22 and the second cathode terminal 158 is in electrical connectivity with the second cathode 124, and the following reactions occur:
Anode: M+3Hn−→MHn3+3e− (Reaction 7)
Cathode: MHn3+3e−→M+3Hn− (Reaction 8)
where the symbol “M”=the non-alkali metal and “Hn”=the halogen.
Thus, when the non-alkali metal is uranium and the halogen is chlorine, reactions 7 and 8 are:
Anode: U+3Cl−→UCl3+3e− (Reaction 9)
Cathode: UCl3+3e−→U+3Cl− (Reaction 10)
The net reaction is:
M+MHn3→MHn3+M (Reaction 11)
such that when the non-alkali metal is uranium and the halogen is chlorine, Reaction 11 is:
2U+UCl3→3U+3Cl− (Reaction 12)
In other words, cations of the non-alkali metal in the anolyte portion 108 of the mixture 104 migrate from the anolyte portion 108 and are electro-deposited adjacent the second cathode 124. The halogen ions act as a mechanism for transporting ions of the non-alkali from the anode to the cathode. When the non-alkali metal is deposited on the cathode, the halogen ions are released back into the salt so that they are free to grab another non-alkali metal ion from the anode. In the case where the halogen is chlorine and the non-alkali metal is uranium, U3+ ions migrate from the anolyte portion 108 and are electro-deposited adjacent the second cathode 124 as uranium metal while the chlorine items shuttle back and forth between the anode and the cathode.
When the electrochemical cell 100 is in the non-alkali metal halide production mode, a non-alkali metal (such as the non-alkali metal 26 of
It is important to note that the net reaction in Reaction 6 (shown above) is spontaneous at elevated temperatures. However, that reaction is kinetically slow due to the formation of UCl3 that presents a barrier to the HCl reactant. In a molten salt bath the UCl3 is dissolved, so uranium may be converted to UCl3 in a molten salt bath by simply bubbling HCl over the uranium metal. A key advantage of making the UCl3 using methods described herein is the ability to keep the HCl contained in the catholyte compartment. By equipping the catholyte compartment with a low porosity membrane that allows primarily ionic conduction, the HCl will remain confined. This also mitigates potential corrosion of the electrorefiner structural materials without a need to remove dissolved HCl from the molten salt prior to electrorefining.
While the electrochemical cell 100 is depicted with two DC power supplies 130 and 150, in some embodiments a single power supply may be used with an electrical switching system that switches its anode terminal and cathode terminal to the configurations described for the production mode and the electrorefining mode.
In summary, embodiments disclosed herein provide systems and methods for producing a halide of a non-alkali metal and for electrorefining the halide of the non-alkali metal. The foregoing descriptions of embodiments have been presented for purposes of illustration and exposition. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of principles and practical applications, and to thereby enable one of ordinary skill in the art to utilize the various embodiments as described and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
The U.S. Government has rights to this invention pursuant to contract number DE-AC05-00OR22800 between the U.S. Department of Energy and Babcock & Wilcox Technical Services Y-12, LLC.
| Number | Name | Date | Kind |
|---|---|---|---|
| 2534677 | Newton et al. | Dec 1950 | A |
| 2943033 | Blue et al. | Jun 1960 | A |
| 4880506 | Ackerman et al. | Nov 1989 | A |
| 5009752 | Tomczuk et al. | Apr 1991 | A |
| 6689260 | Ahluwalia et al. | Feb 2004 | B1 |
| 6800262 | Miller et al. | Oct 2004 | B1 |
| 7267754 | Willit | Sep 2007 | B1 |
| 7638026 | Willit et al. | Dec 2009 | B1 |
| Entry |
|---|
| S. Yoshizawa, et al.; The Recovery of Chlorine From Hydrogen Chloride Part 1; New Method Using a Molten Salt as the Electrolyte; Journal of Applied Electrochemistry 1 (1971) pp. 245-251. |
