Uranous hydroxide

Urano-hydroxyd, n. uranous hydroxide, ura-nium(IV) hydroxide, -reihe, /. uranous series, -salz, n. uranous salt, -uranat, n. uranous uranate, uranium(IV,VI) oxide, UaOa. -verbindung, /. uranous compound, Uran-oxyd, n. uranium oxide, specif, uranic oxide, uranium(VI) oxide, UOa. -ozydhydrat, n. uranium hydroxide, -oxydoxydul, n. = Uranoxyduloxyd. -oxydrot, n. uranium oxide red- -oxydul, n. uranous oxide, ura-nium(IV) oxide, UO2. -oxyduloxyd, n. uranoso-uranic oxide, uranium (I V,VT) oxide, UaOa. -oxydulsalz, n. uranous salt, uranium-(IV) salt, -pechblende, /., -pecherz, n. pitchblende, -phosphat, n, uranium phosphate. -rot, n. uranium red. -salz, n. uranium salt. 

If insufficient acid is added, basic salts result while if the reaction is allowed to proceed further, a black precipitate of uranous hydroxide is obtained. 

It is formed in solution by oxidising uranous chloride with nitric acid by dissolving uranic oxide in concentrated hydrochloric acid or by adding barium chloride to a concentrated solution of uranyl sulphate until precipitation is complete. Its aqueous solution on evaporation yields the monohydrate, UOaClj.HaO." The solution is unstable at ordinarj temperatures and slowly deposits uranic hydroxide, which after a time partly redissolves. The uranyl chloride may be reduced in solution to black uranous oxide by the action of magnesium or aluminium powder. The densities of aqueous solutions of uranyl chloride have been determined as follows ... 

Uranous oxide is also obtained in the form of black microscopic crystals when urano-uranic oxide is reduced uith carbon or heated with a little hydrofluoric acid when crystallised uranic hydroxide is heated in hydrogen when uranyl chloride is heated with potassium in a current of hydrogen, or with a mixture of ammonium and sodium... 

Uranous Hydroxide.—The addition of alkali to a solution of a uranous salt produces a reddish-brown gelatinous precipitate, which darkens in colour on boiling the solution. If dried in vacuo it becomes black and has the composition UOg.HgO. This rapidly oxidises in the air and readily dissolves in dilute acids, forming uranous salts. It acts upon a neutral solution of silver nitrate, first precipitating silver oxide and forming a green solution which, however, soon turns yellow, and the oxide is reduced to metallic silver as the uranyl salt forms in solution, thus ... 

It has been observed that colloidal uranic hydroxide, in very dilute solution, acts as a powerful catalyst in the synthesis of formaldehyde %vhen an aqueous solution of carbon dioxide is exposed to direct sunlight. 

Uranous Nitrate has not been obtained in the solid form. It appears to exist in the unstable green solution obtained on the addition of uranous hydroxide to a neutral solution of silver nitrate (see p. 302). A light green basic nitrate has been obtained by short exposure to light of an eoholic solution of uranyl nitrate, and rapid filtration of the product. ... 

Uranous hydroxide is obtained as a bulky reddish brown precipitate when alkalies are added to uranous solutions. The precipitate darkens on boiling and is easily oxidized by air in the presence of excess alkali, forming uranyl compounds. The formula for the compound is written either U02 2 H20 or U(OH)4. 

Some bicarbonate or other acid cation, therefore, is required to be present in a leach solution, and the sole purpose is to buffer the hydroxide produced and prevent thereby uranate formation. 

When alkali metal bases are used to raise the solution pH to moderate levels, the uranium will precipitate from the solution in the form of hydrous uranyl hydroxides or uranates, for example, Na2U207. However, through judicious choice of a base, for example, tetramethylammonium hydroxide, (TMA)OH, or tetramethylaimnoirium trifluoromethansulfonate, the study of the amphoteric behavior of uranyl hydroxides can be undertaken. Polynuclear anions of the form (U02)3(0H)7, (U02)3(0H)g, and (U02)3(OH)io are examples of soluble species in solutions where the pH < 14. When the concentration of the (TMA)OH is increased (>0.6 M OH ), highly soluble ( 0.1M) monomers ofthe form U02(0H) "(n = 3, 4,5) have been reported. These three species are in equilibrium with each other however, in solutions where the [OH ] is greater that 1M, the pentahydroxo complex predominates the speciation. 

According to Aloy, a black crystalline hydrate, of composition UO2.2H2O, is obtained when crystallised uranous sulphate is treated with hot potassium or sodium hydroxide solution. The product, when thoroughly w ashed, remains stable in air for several days. It dissolves in dilute acids, yielding uranous salts. On heating, it is completely converted to the green oxide. 

Ammonium Diuranate, (NH4)2U207, is obtained as a yellow voluminous precipitate when solutions of uranyl salts are treated with ammonia. It is prepared commercially (see p. 277) by boiling a solution of sodium uranyl carbonate with ammonium sulphate, or by boiling a solution of sodium diuranate with concentrated ammonium chloride solution. It is a deep yellow powder, which may be dried at 100° C. at higher temperatures it yields urano-uranic oxide. When fused with ammonium chloride, uranous oxide is formed. It is known commercially as uranium yellow (see also sodium diuranate) and is used in making fluorescent uranium glass. It is insoluble in ammonium hydroxide solution, and this fact is sometimes made use of (see p. 388) in the analytical separation of uranium. 

Potassium Uranyl Carbonate, K4U02(C03)a, may be prepared by the action of carbon dioxide on potassium uranyl cyanide, or by evaporating at moderate temperature a solution containing potassium bicarbonate and potassium uranate. It crystallises in small hexagonal prisms, which are stable in dry air and dissolve in cold water without decomposition. The solution is hydrolysed on warming, and the addition of alkali causes j recipitation of uranyl hydroxide. 

Uranous and uranyl cyanides have not been prepared. The addition of potassium cyanide to solutions of uranous or uranyl salts causes evolution of hydrogen cyanide and precipitation of hydroxide. If, however, an excess of potassium cyanide is added to a solution of a uranyl salt, a clear solution results, which on further addition of the cyanide yields a microcrystalline precipitate of the double cyanide, Iv2U02(CN)4. The solution is unstable in the air and gradually releases hydrogen cyanide. The precipitate is also very unstable, and is transformed to a double carbonate by tlie atmospheric carbon dioxide. 

Uranium and Hydrogen—Halogen and Oxyhalogen Compounds—Oxide. and. Hydroxides—Uranic Acid—Salts of Uranic Acid—Peruranic Acid and Peruranates—Compounds with Sulphur, Selenium, and Tellurium. 

Both uranium(VI) and plutonium(VI) form oxoanions. Uranium gives mono-, di-, tri-, tetra-, penta- and hexa-uranates the common diuranates, MgUgOy, correspond only formally to the dichromates. Barium hydroxide precipitates the triplutonate, BaPugO o, from solutions containing PuOg. ... 

The Haynes-Engle process consists in digesting the coarsely ground ore with a solution of sodium carbonate until the uranium and vanadium are extracted. Sodium hydroxide is added to precipitate sodium uranate and slaked lime to precipitate the vanadium. 

Pure uranous compounds may be prepared by precipitating U(OH)4 from aqueous solution with ammonium hydroxide and dissolving the precipitate in the appropriate acid. Uranous sulfate, the most common salt, is soluble in water, as are the chloride, bromide, and iodide. Uranous nitrate is unstable, gradually undergoing oxidation to uranyl nitrate with liberation of oxides of nitrogen. 

Other deviations from a simple elution process can also be beneficial. For example, recovery of eluate is generally a practical proposition, i.e. the uranium is precipitated from sodium chloride solution by the addition of sodium hydroxide, or from ammonium nitrate solution by the addition of ammonia. After filtration of the yellow sodium di-uranate or ammonium di-uranate, the filtrates can be reconstituted as an eluting agent by the addition of hydrochloric or nitric acid respectively. 

It is usual to take advantage of the alkali addition to separate off ferric iron and other metallic ions which precipitate at a lower pH than uranium. Furthermore, this can often be done with lime. This is normally the cheapest alkali and also has the advantage that it precipitates the sulphate ion impurity at the same time as the iron. A pH of 3 -6 is used for this impurity precipitation, followed by the first-stage filtration. Then the addition of extra alkali, e.g. ammonia, sodium hydroxide or magnesia, to pH 6 7 precipitates the uranium. The second-stage filtration finally removes the uranium from solution as ammonium, sodium or magnesium di-uranates. 

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