Plutonium(IV) oxalate
Plutonium oxalate is a compound consisting of plutonium and oxalate with the formula. It is produced by addition of oxalic acid to plutonium solution, and is widely used in the synthesis of plutonium(IV) oxide for nuclear reprocessing, plutonium recovery from radioactive waste, or lab use. It is also a starting material for the production of other plutonium compounds, such as plutonium(III) fluoride, plutonium(IV) fluoride, or plutonium(III) chloride.
Synthesis
Plutonium oxalate is prepared by the combination of oxalic acid solution and plutonium-nitric acid solution, after which it precipitates as the hexahydrate,. Hydrogen peroxide can added to prevent reduction to plutonium:There are three ways that these solutions can be combined: direct strike, reverse strike, and continuous.
Properties
Plutonium oxalate forms several hydrates, notably the hexahydrate,, which has been variously described as tan or yellow-green. Other hydrates are known, such as the monohydrate and dihydrate, and the compound can also be found without water as.Decomposition
The thermal decomposition of plutonium oxalate hexahydrate starts by it losing water. It goes through the dihydrate,, and the monohydrate,, as intermediates before arriving at anhydrous plutonium oxalate:The anhydrous form loses carbon dioxide to produce anhydrous plutonium(III) oxalate,. Upon heating, it loses carbon monoxide, going through several carbonate oxalate phases with compositions and, before arriving at plutonium(IV) oxycarbonate. finally releases carbon dioxide to form plutonium dioxide:
Plutonium oxalate also slowly degrades under ambient conditions. The end product is proposed to be either a colloidal polymer or.
Structure
Two structures are predicted for anhydrous. In the first one, each plutonium atom is at the center of a cube formed by eight oxygen atoms coming from four oxalate groups. The plutonium atoms are bonded with both oxygen atoms coming from each oxalate. In the second one, each plutonium atom is at the center of a distorted square antiprism formed by eight oxygen atoms coming from four oxalate groups. Unlike in the first one, only one oxygen from each oxalate group bonds with the plutonium center, as the other oxygen atom is too far away to form a bond. In both structures, each oxalate group bridges between two plutonium atoms, and both structures consist of two-dimensional plutonium-oxalate layers, though layer-layer interactions are stronger in the second one than in the first one. The second structure has been calculated to be more stable.The structure of plutonium hexahydrate consists of alternating layers of and interstitial water molecules. Within the layers, each plutonium atom is coordinated to ten oxygen atoms, eight from four oxalate groups and two from two water molecules. Three-quarters of the oxalate groups lie perpendicular to the layers, while one quarter of them lie parallel to the plane, providing enough space to fit the two water molecules.
Uses
Plutonium oxalate is widely used to produce plutonium(IV) oxide via thermal decomposition for applications such as nuclear reprocessing, recovery of plutonium from waste and residues, laboratory use, or plutonium(III) chloride production. The related compound plutonium(III) oxalate can also be used to produce. After it is synthesized, it is first slowly heated up to 700 °C, and then heated afterwards at 1000 °C to remove any leftover carbon. Plutonium oxide produced by this method appears as a yellow-buff bulky powder. In addition, it can also be converted to plutonium oxide by hydrothermal methods. This has been proposed as an alternative to thermal decomposition. Because it can be synthesized from nitrate solution and then be converted to the oxide, it can be used in the conversion of plutonium(IV) nitrate to as an intermediate.It can also be used for the production of plutonium fluorides. Upon reaction with hydrogen fluoride, it either produces plutonium(III) fluoride or plutonium(IV) fluoride. When reducing agents such as hydrogen gas are present, is formed: