Plutonium(III) chloride
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| IUPAC name
Plutonium(III) chloride
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| Other names
Plutonium trichloride
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| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |
| Cl3Pu | |
| Molar mass | 350.322 g/mol |
| Appearance | Green solid |
| Density | 5.71 g/cm3, solid[1] |
| Melting point | 767 °C (1,413 °F; 1,040 K)[1] |
| Boiling point | 1,767 °C (3,213 °F; 2,040 K)[1] |
| Related compounds | |
Other anions
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Plutonium(III) fluoride Plutonium(III) bromide Plutonium(III) iodide |
Other cations
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Samarium(III) chloride |
Related plutonium chlorides
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Plutonium(IV) chloride |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Plutonium(III) chloride or plutonium trichloride is a chemical compound with the formula PuCl3.[1] It is the only stable solid chloride of plutonium, though another plutonium chloride, plutonium tetrachloride, is known in the gas phase.[2]: 1092 It can either be found as an anhydrous solid (containing no water), or in the form of hydrates (solids containing water), such as the hexahydrate, PuCl3·6H2O.[2]: 1100 It is used in the processing of plutonium metal[2]: 864, 870 and in molten-salt reactors.[3][4]
Synthesis
[edit]Multiple different methods have been used to synthesize plutonium(III) chloride, which all involve the chlorination of plutonium or plutonium compounds. Many of these methods use plutonium(III) oxalate, which can be prepared by carefully adding oxalic acid to an acidic plutonium(III) solution, resulting in the decahydrate, Pu2(C2O4)3·10H2O.[2]: 1092–1093
After it is synthesized, it is advised that it be purified by sublimation in a sealed quartz tube.[2]: 1092–1093
Using hydrogen chloride
[edit]For medium-scale reactions (between 1 to 10 grams), the best method of preparing plutonium(III) chloride is by reacting plutonium(III) oxalate with hydrogen chloride, HCl. The reaction proceeds like so:[2]: 1093
- Pu2(C2O4)3·10H2O + 6 HCl → 2 PuCl3 + 3 CO2 + 3 CO + 13 H2O
For processing 100 gram quantities of plutonium, plutonium hydride can be reacted with hydrogen chloride in a fluidized bed reactor at 450 °C. To remove oxychlorides, the resulting PuCl3 is melted at 800 °C and sparged with HCl.[2]: 1093
Plutonium(III) chloride can also be formed from aqueous solutions of hydrogen chloride (hydrochloric acid). Upon evaporation of the HCl solution, a residue of plutonium(III) chloride hexahydrate, PuCl3·6H2O, is formed. The hexahydrate can then be dehydrated in a stream of HCl to give the anhydrous solid.[2]: 1093
Using hexachloropropene
[edit]Due to the difficulty in handling hazardous gases, hexachloropropene (C3Cl6) can be used as a chlorinating agent instead of more dangerous compounds. Plutonium(III) oxalate (Pu2(C2O4)3) has been reported to be an efficient initial source of plutonium. To produce plutonium(III) chloride, Pu2(C2O4)3 is heated with C3Cl6:[3]
- Pu2(C2O4)3·10H2O + 3 C3Cl6 → 2 PuCl3 + 3 C3Cl4O + 3 CO2 + 3 CO + 10 H2O
Using chlorine gas
[edit]Plutonium(III) chloride can be produced via reacting plutonium metal with chlorine gas at temperatures between 300°C and 500°C, followed by sublimation at 600–800°C.[2]: 1093 Chlorine can also be used to chlorinate plutonium(IV) oxide (PuO2). For PuO2 chlorination, carbon is used as a reducing agent. The reaction proceeds as follows:[4]
Using other gaseous fluorinating agents
[edit]Plutonium(IV) oxide can also be chlorinated with phosgene (COCl2) or carbon tetrachloride, yielding analytically pure samples of PuCl3. This method has been used at Los Alamos National Laboratory. One method for the continuous production of PuCl3 using phosgene is as follows:[2]: 1093
Plutonium(IV) oxalate hydrate (Pu(C2O4)2·6H2O) is precipitated from plutonium(IV) solution, dried, and calcined (heated to decomposition without oxygen) to form plutonium(IV) oxide (PuO2). The resulting PuO2 is then heated with phosgene in a tube furnace at 500 °C. This method produces plutonium at a rate of 250 grams / hour.[2]: 1093
Using ammonium chloride
[edit]To ensure a high-purity product, plutonium(III) chloride can be prepared by reacting plutonium metal with ammonium chloride at high temperature. The ammonium chloride sublimes, producing ammonia and hydrogen chloride. The hydrogen chloride subsequently reacts with the plutonium metal to form PuCl3. The overall reaction follows like so:[5]
- 2 Pu + 6 NH4Cl → 2 PuCl3 + 6 NH3 + 3 H2
Formation
[edit]Plutonium(III) chloride is formed unintentionally from the corrosion of plutonium metal by hydrogen chloride gas:[6]
- 2 Pu + 6 HCl → 2 PuCl3 + 3 Cl2
Properties
[edit]The color of plutonium(III) chloride depends on its method of production. Plutonium(III) chloride produced via dehydration of the hexahydrate is slate-blue, while when prepared by one of the anhydrous methods the compound is blue-green to emerald green. When condensated from the gas phase, it appears as an emerald green solid.[2]: 1093 It is incredibly hygroscopic, and is readily hydrated by atmospheric moisture.[4] This leads to the formation of several hydrates, or compounds containing water. These include the monohydrate (PuCl3·H2O), dihydrate (PuCl3·2H2O), and hexahydrate (PuCl3·6H2O). Which hydrate is formed depends on the partial pressure of water in the atmosphere.[2]: 1100 . Plutonium(III) chloride hexahydrate has a melting point of 94 °C, at which it in its own waters of crystallization, forming a solution. In a vacuum at 27 °C, it decomposes to give the monohydrate, and upon heating between 400–520 °C, it gives plutonium oxychloride, PuOCl.[7]: 130, 140
When heated with chlorine at high temperatures, plutonium(III) chloride reacts to form the compound plutonium tetrachloride, increasing its volatility. Upon condensing, it reverts back to PuCl3.[2]: 1094
- 2 PuCl3 + Cl2 ⇌ 2 PuCl4
The compound is antiferromagnetic below around 4.5 K.[8]
Structure
[edit]Anhydrous PuCl3 is isostructural with (has the same structure as) the related uranium(III) chloride, UCl3, having a hexagonal structure. Each plutonium atom is surrounded by nine chlorine atoms. Six of the nine chlorine atoms form a triangular prism, which have Pu-Cl bond lengths of 2.886 Å. Each of three rectangular sides of the triangular prism are capped off by chlorine atoms, which have Pu-Cl distances of 2.919 Å. This gives each plutonium atom a coordination geometry of tricapped trigonal prismatic. The prisms' triangular bases connect to form infinite chains. This structure is related to the structures of plutonium(III) bromide (PuBr3) and plutonium(III) iodide (PuI3); however, one of the three bromine or iodine atoms that would have capped off one of the rectangular sides of the triangular prism is too far away from the plutonium atom to bond.[2]: 1096–1097 Unlike in PuBr3, where the Pu-Br bonds are predominantly covalent, the Pu-Cl bonds within PuCl3 are predominantly ionic.[2]: 1100
Plutonium(III) chloride hexahydrate, PuCl3·6H2O, adopts the GdCl3·6H2O-type structure,[note 1] which is seen across all the lanthanide chlorides except those of lanthanum and cerium. In this structure, each plutonium atom is bonded to six water ligands and two chloride ligands, forming monomeric PuCl2(H2O)+6 groups. The PuCl2(H2O)+6 groups are linked together by chloride ions via hydrogen bonding.[10]
Plutonium(III) chloride trihydrate (PuCl3·3H2O) adopts the same structure as the corresponding neodymium compound, NdCl3·3H2O.[4]
Uses
[edit]Plutonium metal processing
[edit]Plutonium(III) chloride is an important intermediate in the production of plutonium metal. Plutonium metal produced from the reduction of plutonium tetrafluoride and plutonium(IV) oxide can be impure, notably with americium created via the beta decay of plutonium-241. To separate americium impurities from plutonium, the impure plutonium metal is placed in a mixture of molten magnesium chloride, sodium chloride, and potassium chloride. Plutonium(III) chloride is produced when plutonium metal is oxidized by the magnesium chloride, but is subsequently reduced back to plutonium metal by americium. The reactions that occur are:[2]: 869–870
- 2 Am + 3 MgCl2 → 2 AmCl3 + 3 Mg
- 2 Pu + 3 MgCl2 → 2 PuCl3 + 3 Mg
- Am + PuCl3 → AmCl3 + Pu
After the americium is oxidized, the americium(III) chloride and molten salt mixture can be separated, leaving a plutonium metal button behind.[2]: 870
Molten-salt reactors
[edit]Plutonium(III) chloride is a common nuclear material for use in molten-salt reactors, reactors which use molten salts in which actinides are dissolved as their fuel, such as a mixture of sodium chloride and plutonium(III) chloride. Molten salts containing chlorides, like plutonium(III) chloride, are often used, as they have low melting points and can dissolve high concentrations of actinides.[3][4][5]
Handling and storage
[edit]As with all plutonium compounds, it is subject to control under the Nuclear Non-Proliferation Treaty. Due to the radioactivity of plutonium, all of its compounds, PuCl3 included, are warm to the touch. Such contact is not recommended, since touching the material may result in serious injury.[citation needed] Due to plutonium(III) chloride's high hygroscopicity, it must be kept in an controlled, dehumidified atmosphere.[4]
Notes
[edit]References
[edit]- ^ a b c d www.webelements.com: Plutonium(III) chloride.
- ^ a b c d e f g h i j k l m n o p q r Clark, David L.; Hecker, Siegfried S.; Jarvinen, Gordon D.; Neu, Mary P. (2011). "Plutonium". The Chemistry of the Actinide and Transactinide Elements (PDF). doi:10.1007/978-94-007-0211-0_7. ISBN 978-94-007-0211-0.
- ^ a b c https://inis.iaea.org/records/h3p87-hyf93/preview/53064563.pdf
- ^ a b c d e f https://airdrive.eventsair.com/eventsairseasiaprod/production-ausimm-public/ab4ca63977fa48b5b15a71d641db7c1f
- ^ a b Karlsson, Toni Y.; Middlemas, Scott C.; Nguyen, Manh-Thuong; Woods, Michael E.; Tolman, Kevin R.; Glezakou, Vassiliki-Alexandra; Herrmann, Steven D.; Schorne-Pinto, Juliano; Johnson, Ryan D.; Reddish, Shawn E.; Warmann, Stephen A.; Paviet, Patricia D. (2023). "Synthesis and thermophysical property determination of NaCl-PuCl3 salts". Journal of Molecular Liquids. 387 122636. doi:10.1016/j.molliq.2023.122636.
- ^ Burgess, M.; Haschke, J. M.; Allen, T. H.; Morales, L. A.; Jarboe, D. M.; Puglisi, C. V. (April 1998). "Chloride-catalyzed corrosion of plutonium in glovebox atmospheres".
- ^ Brown, David (1972). "Compounds with Chlorine". Transurane. pp. 129–147. doi:10.1007/978-3-662-11547-3_7. ISBN 978-3-662-11548-0.
- ^ Jones, E. R.; Hendricks, M. E.; Stone, J. A.; Karraker, D. G. (1974). "Magnetic properties of the trichlorides, tribromides, and triiodides of U(III), Np(III), and Pu(III)". The Journal of Chemical Physics. 60 (5): 2088–2094. Bibcode:1974JChPh..60.2088J. doi:10.1063/1.1681318.
- ^ Lemire, R. J. et al., Chemical Thermodynamics of Neptunium and Plutonium, Elsevier, Amsterdam, 2001.
- ^ a b Kandabadage, Thimira; Legnon, Beau; Baranets, Sviatoslav (2024). "Comprehensive structural study of lanthanide(III) chloride hydrates: [RECl3·xH2O (RE = La–Nd, Sm–Lu; x = 6, 7)]". Acta Crystallographica Section e Crystallographic Communications. 80 (12): 1342–1349. Bibcode:2024AcCrE..80.1342K. doi:10.1107/S2056989024011319.