Uranium IV Oxalate

Uranium(IV) oxalate has been prepared by the reaction of uranium(IV) chloride,sulfate, and hydroxide with a saturated solution of oxalic acid, or by the reduction of a water-soluble uranyl compound with copper, zinc, or sodium dithionite (Na2S204), followed by treatment with oxalic acid. It is prepared conveniently by the reduction of the readily available uranyl acetate 2-hydrate with sodium dithionite. 

The reduction of the uranyl ion by the dithionite ion in acid solution may be assumed to t e place substantially in accordance with the following equations  

However, some colloidal sulfur is also formed, possibly because of the following side reactions  

Consequently, twice the amount of dithionite calculated from the above equation is used to ensure complete reduction. 

Five grams (0.012 mol) of powdered uranyl acetate 2-hydrate is dissolved in 100 ml. of warm (80°) dilute hydrochloric acid (10 ml. of concentrated hydrochloric acid and 90 ml. of water). Five grams (0.024 mol) of powdered sodium dithionite 2-hydrate is added in small amounts while the solution is stirred. As the dithionite comes in contact with the solution a brown material is formed that quickly changes to a whitish-green precipitate. Five milliliters of concentrated hydrochloric acid is added and the mixture is then heated on a steam bath for at least 10 minutes mtil solution has been effected. The solution is usually cloudy due to the formation and presence of a small amount of free sulfur. The latter is easily removed by filtration, yielding a filtrate that possesses the characteristic dark green color of the uranium(IV) ion. 

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Uranium(VI) dioxydichloride, 5 148 Uranium (VI) hydrogen dioxyortho-phosphate 4-hydrate, 6 150 analysis of, 5 151 Uranium(IV) oxalate, 3 166 Uranium (IV) oxide, formation of, by uranyl chloride, 6 149 Uranium (IV) (VI) oxide, U3Oa, formation of, by uranyl chloride, 5 149... 

Uranium(IV) oxalate 6-hydrate commonly crystallizes in dark green microcrystals, which are not reactive toward the water vapor and oxygen of the air, in contrast to the rapid atmospheric oxidation of solutions of uranium(IV) ion. Four molecules of water are lost when the compound is dried in a vacuum at room temperature. When ura-nium(IV) oxalate 6-hydrate is heated to 100 to 110°, five molecules of water are lost the sixth is lost at 200°. The anhydrous compound is blue-violet. 

The compound is only slightly soluble in water and dilute acids but is soluble in warm concentrated hydrochloric acid to form a dark green solution. It can be reprecipitated by cooling or by diluting such a solution. Concentrated nitric acid effects oxidation to the uranyl salt. With solutions of the alkali carbonates or hydrogen carbonates, uranium(IV) hydroxide is formed. With an excess of a solution of potassium carbonate and by atmospheric oxidation, potassium uranyl carbonate results. Uranium(IV) oxalate 6-hydrate is also soluble in solutions of alkali and ammonium oxalates to form the tetraoxalatouranate(IV)... 

Potassium tetraoxalatouranate(IV) 5-hydrate has been prepared by the reaction of a potassium oxalate solution with an excess of uranium(IV) oxalate 6-hydrate.This excess prevents contamination of the product by potassium oxalate, since both potassium tetraoxalatouranate(IV) and potassium oxalate are precipitated from aqueous solution by absolute alcohol. 

A solution of 5 g. (0.027 mol) of potassium oxalate 1-hydrate in 20 ml. of water is added to a slurry of 6 g. (0.014 mol) of uranium(IV) oxalate 6-hydrate in 50 ml. of water. The reaction is complete after the mixture has been heated on a steam bath for 1 hour. The dark green filtrate is treated with 200 ml. of absolute alcohol, which is added drop by drop from a separatory funnel while the mixture is stirred. J Small light green crystals are obtained, which are quickly dried by washing them several times with absolute alcohol and finally with ether. To avoid oxidation, potassium tetraoxalatouranate(IV) is stored in a desiccator over phosphorus (V) oxide. 

On the basis of these facts, it was speculated that plutonium in its highest oxidation state is similar to uranium (VI) and in a lower state is similar to thorium (IV) and uranium (IV). It was reasoned that if plutonium existed normally as a stable plutonium (IV) ion, it would probably form insoluble compounds or stable complex ions analogous to those of similar ions, and that it would be desirable (as soon as sufficient plutonium became available) to determine the solubilities of such compounds as the fluoride, oxalate, phosphate, iodate, and peroxide. Such data were needed to confirm deductions based on the tracer experiments. 

In their manufacture uranium(IV) oxide is mixed with the appropriate quantity of plutonium(IV) oxide, the mixture pressed into pellets and then sintered (termed coprocessing in the USA). Uranium(IV) oxide is produced by one of the above-described processes and plutonium(IV) oxide from the aqueous nitrate solution produced during reprocessing by precipitating it as plutonium oxalate and calcining the oxalate. 

Extraction of columbate-tantalates, titanocolumbates, and titanosilicates may also be initiated by treatment of the mineral with hydrofluoric acid. The procedure has the advantage that columbium, tantalum, uranium(VI), scandium, titanium, zirconium, and hafnium are dissolved, while silica is volatilized as silicon tetrafluoride and the rare earth elements, together with thorium and uranium(IV), remain as slightly soluble fluorides. The residue is then heated with concentrated sulfuric acid to remove hydrogen fluoride and to oxidize uranium (IV), the thorium is separated by precipitation of the phosphate (synthesis 12), and the rare earths are precipitated as oxalates. 

Uranium(lV) oxalate, synthesis 45 Potassium tetraoxalatouranate (IV), synthesis 46 Barium thiocyanate, synthesis 5 Potassium octacyanomolybdate (IV) 2-hydratc, synthesis 43 Bis(lV,lV -disallcylalethylenedia-mine)-/t-aquodicobalt(II), synthesis 53... 

Oxalic acld precipitates uranium (IV) fran acidic... 

Uranium (IV), In general, should behave similarly as neptunium (IV) and plutonium (IV). These are carried by lanthanum fluoride, ceric and zirconium lodates, ceric and thorium oxalates, barium sulfate, zlrconliun phosphate, and bismuth fifrsonate.- Uranium (Vl) does not carry with these agents providing the concentration of either carrier or uranlxun Is not too large. 

Sulphuric acid is not recommended, because sulphate ions have a certain tendency to form complexes with iron(III) ions. Silver, copper, nickel, cobalt, titanium, uranium, molybdenum, mercury (>lgL-1), zinc, cadmium, and bismuth interfere. Mercury(I) and tin(II) salts, if present, should be converted into the mercury(II) and tin(IV) salts, otherwise the colour is destroyed. Phosphates, arsenates, fluorides, oxalates, and tartrates interfere, since they form fairly stable complexes with iron(III) ions the influence of phosphates and arsenates is reduced by the presence of a comparatively high concentration of acid. 

Carrier (TOPO)-mediated transport of uranium(Vl) has been studied by Akiba and Hashrmoto [94] who have observed that uranium was extracted in the liquid membrane as U02(N03)2 2TOPO and stripped into the carbonate solutions as U02(C03)3. Using TOPO and HDEHP mixmre, liquid membrane technique was apphed for the recovery of uranium from WPPA [95]. Carrier-facilitated Pu(IV) pertraction through an SLM was standardized for its decontamination from oxalate wastes employing a commercially available Cyanex-923 (TOPO analog) in dodecane as the receptor [96,97]. More than 95% of plutonium could be easily recovered from Pu oxalate wastes solution during Pu reconversion operations. 

The Arsenazo III method for determining thorium is highly selective. In the presence of oxalic acid as a masking agent, thorium can be determined in 2.5-3.5 M HCl in the presence of Zr, Hf, and Nb. Iron(III), which interferes, is reduced to Fe(II) by ascorbic acid, and U(IV) is oxidized to U(VI) by adding some KMn04 (followed by ascorbic acid to decolorize the solution). At high concentrations of chloride (HCl -1- LiCl) Th can be determined in the presence of a 100-fold amount of uranium(Vl). The effect of Ti on the determination of Th has been discussed [55,56],... 

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