Uranyl carbonates, ammonium salts

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. 

Ammonium Uranyl Carbonate, (NH4)4U0,(C03)3.2H20, is obtained by dissohnng freshly precipitated ammonium uranate in a solution of ammonium carbonate at 60° to 70° C. or by treating a soluble uranyl salt with ammonium carbonate and ammonia. In either case a yellow solution is formed which on evaporation deposits yellow monoclinic ery> stals of the double carbonate. The same compound results on mixing concentrated solutions of ammonium carbonate (3 molecules) and uranyl nitrate (1 molecule) at 50° to 55° C.,... 

Uranium minerals may be obtained in solution, in a suitable condition for estimation, by the following process. The ore is dissolved in aqua regia, or, if necessary, fused with alkali bisulphate and extracted mth hot hydrochloric acid. After evaporation to drjmess, the residue is taken up with dilute hydrochloric acid, and the solution saturated with hydrogeir sulphide in order to remove any copper, lead, bismuth, arsenic, antimony, or any other metal yielding an insoluble sulphide. The filtrate is concentrated and treated with ammonium carbonate, which precipitates the carbonates of the alkaline earths, iron, and most of the rare earths. The filtrate is neutralised by hydrochloric acid, evaporated to dryness, and the residue ignited to drive off ammonium salts, and then redissolved in dilute acid. The remaining rare earths, and particularly thorium, are next precipitated by the addition of oxalic acid. The filtrate, which contains the uranium in the uranyl condition, may now be precipitated by any of the methods described above. 

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)... 

In a much earlier patent, the removal of organics from exhaust gases by oxidation over a supported uranium oxide catalyst was reported by Hofer and Anderson [39]. The catalyst was 4% U3O8 supported on alumina spheres. The authors used the incipient wetness technique to impregnate alumina with uranyl nitrate solution. In this case the catalyst precursors were calcined at 700°C for 3 h to decompose the uranium salt. The use of other uranium compounds as starting materials was mentioned and these included uranyl acetate, uranium ammonium carbonate and uranyl chloride. The alumina-supported catalyst had a surface area of ca 400m g and further added components, such as copper, chromium and iron, were highlighted as efficient additives to increase activity. 

Uranium Pentoxide, U2O5.—The existence of this oxide is not definitely established. It has been described as the black product obtained when a uranium salt of a volatile acid is strongly ignited in air when uranyl sulphate, (U02)S04.3H20, is rapidly heated when ammonium diuranate, (NH4)2U207-6H20, is heated in a carbon crucible and when a solution of uranyl nitrate is electrolysed. 

In the first process the solution containing the uranyl salt is made slightly acid with hydrochloric or sulphuric acid and treated with a slight excess of ammonium hydroxide (free from carbonate) at the boiling-point. It is best to avoid the use of glass vessels as the... 

Sulfides. Ammonium sulfide or polysulflde precipitates brown, amorphous uranyl sulfide. Numerous other elements are precipitated under similar condltlons. Complexlng agents such as carbonate, pyrophosidiate, and citrate Interfere. Uranium (iv) salts are precipitated as UOg HgO by ammonium... 

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