Thorium peroxide

The hydrated thorium peroxide sulfate, Th(02)S04-3H20, is very stable to heat, and thorium(IV) peroxo compounds of variable composition, approximating to... 

Hydrogen peroxide white precipitate of hydrated thorium heptoxide (thorium peroxide), Th207.4H20 in neutral or faintly acid solution. 

Thirty percent hydrogen peroxide precipitates thorium peroxide Th207 from solutions of thorium salts. As few cations other than thorium and uranium precipitate under these conditions, this method has been used to purify thorium. 

Oxide and Hydroxide. The only oxide, Th02, is obtained by ignition of oxo acid salts or of the hydroxide. The latter is-insoluble in an excess of alkali hydroxides, although it is readily peptized by heating it with Th4+ or Fe3+ ions or dilute acids the colloid exists as fibers that are coiled into spheres in concentrated sols but uncoil on dilution. Addition of hydrogen peroxide to Th4+ salts gives a highly insoluble white precipitate of variable composition which contains an excess of anions in addition to peroxide the composition is approximately Th(02)3.2X0.500. 5 but it is usually referred to as thorium peroxide. 

Actinide Peroxides. Many peroxo compounds of thorium, protactinium, uranium, neptunium, plutonium, and americium are known (82,89). The crystal stmctures of a number of these have been deterrnined. Perhaps the best known are uranium peroxide dihydrate [1344-60-1/, UO 2H20, and, the uranium peroxide tetrahydrate [15737-4-5] UO 4H2O, which are formed when hydrogen peroxide is added to an acid solution of a uranyl salt. 

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. 

For example, when coned sulfuric acid is brought in contact with a mixt of KMn04 and some org substances, such as glycerin or sugar, the temp is raised to inflammation point and the detonator fires the main chge. The same happens when coned hydrogen peroxide is added to A1 + C or to thorium or when fuming nitric acid is added to triethylamine... 

One method of preparation consists in a modification of the Goldschmidt process. Niobium pentoxide is mixed with an alloy of the rare earths, called mixed metal, obtained in the manufacture of thorium nitrate, and consisting roughly of 45 per cent, of cerium, 20 per cent, of lanthanum, 15 per cent, of didymium, and about 20 per cent, of other rare-earth metals. The reaction is carried out in a magnesia-lined crucible, and is started with a firing mixture of barium peroxide, potassium chlorate, and aluminium powder. Considerable evolution of heat takes place and the reduction is extremely rapid a button of niobium is obtained 4 which, however, is not pure. 

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Actinide Peroxides. Many peroxo compounds of thorium, protactinium, uranium, neptunium, plutonium, and americium are known. Uranium peroxide has found several applications in the nuclear energy industry . 

The compound is not a true peroxide, but an associate compound of thorium dioxide and hydrogen peroxide 2Th02.3H202.H20. 

Plutonium Purification. The same purification approach is used for plutonium separated from sediments or seawater. In case reduction may have occurred, the plutonium is oxidized to the quadrivalent state with either hydrogen peroxide or sodium nitrite and adsorbed on an anion exchange resin from 8M nitric acid as the nitrate complex. Americium, curium, transcurium elements, and lanthanides pass through this column unadsorbed and are collected for subsequent radiochemical purification. Thorium is also adsorbed on this column and is eluted with 12M hydrochloric acid. Plutonium is then eluted from the column with 12M hydrochloric acid containing ammonium iodide to reduce plutonium to the non-adsorbed tervalent state. For seawater samples, adequate cleanup from natural-series isotopes is obtained with this single column step so the plutonium fraction is electroplated on a stainless steel plate and stored for a-spectrometry measurement. Further purification, especially from thorium, is usually needed for sediment samples. Two additional column cycles of this type using fresh resin are usually required to reduce the thorium content of the separated plutonium fraction to insignificant levels. 

The APT is calcined to AMT at 220 °C and dissolved in water while adding hydrogen peroxide and sulfuric acid. The traces of uranium and thorium are extracted selectively by 0.5 M di-2-ethylhexyl phosphoric acid and 0.125 M tri-n-octyl-phosphine oxide dissolved in kerosene. 

Separation. — The separation of thorium from the rare earth metals with which it is still mixed may be accomplished by three methods (1) the carbonate separation depends on the fact that thorium carbonate is much more soluble in sodium carbonate than the carbonates of the rare earth metals (2) by the fractional crystallization of the mixed sulfates at 15°-20°, crystals of Th(S04)2 8 H20 are obtained at the insoluble end of the series (3) thorium oxalate forms a soluble double salt with ammonium oxalate, while the rare earth oxalates are almost insoluble in this reagent. Some other methods which have been suggested are fractionation of the chromates,4 of the hydrogen alkyl sulfates,5 of the acetates, by the use of sebacic add 6 and hydrogen peroxide. 

The peroxide is obtained as hydrated Th2C>7 when ammonia and hydrogen peroxide are added to the solution of a thorium salt. It is unstable and loses oxygen readily, forming the relatively stable ThO>. This is a very useful means of detecting and estimating thorium, by which it may be distinguished from both zirconium and the rare earths. 

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