Iron uranate

Iron Uranate.—Arfvcdson heated in hydrogen the precipitate obtained by passing ammonia into a solution containing ferric and uranyd salts, and obtained a product which he called iron uranate. It appears, however, to be a mixture of the oxides of iron and uranium. 

Sealed Tube Method. No evidence for compound formation was observed when mixtures of iron and uranium oxides were heated in air to temperatures as high as 1200°C. Substituting ferric and uranyl nitrates for the oxides as starting materials also proved unsuccessful. Ferric oxide and UO2.64 were the only product phases, thus giving an empirical formula of FeU04.i4 in the 1 1 mixture, and FeU309.42 in the 1 3 mixture. Unlike the situation encountered in the other double oxide systems, the iron uranates do not appear to have sufficient thermodynamic stability to be synthesized at ambient oxygen pressure. 

At the end of the eighteenth century, scientists thought that pitchblende was a mixture of iron and zinc compounds. In 1789 Martin Heinrich Klaproth (1743—1817) discovered a new metallic element in a sample of pitchblende, which he named uranus after the recently discovered planet. Although what he actually discovered was the compound uranous oxide (UOj), it was adequate to establish him as the discoverer of uranium. For almost a century, scientists believed that the compound uranous oxide (UO ) was the elemental metal uranium. In 1841 Eugene-Melchoir Pefigot (1811—1890) finally isolated the metal uranium from its compound. Even so, no one knew that both the compounds and metal of uranium were radioactive until 1896, when Henri Becquerel (1852—1908) mistakenly placed apiece of potassium... 

The spin-Hamiltonian of Equation (31) can also be used to describe EPR data (1 5, HO) of ions of the palladium and platinum transition groups, the rare earths, and the trans-uranic group. Experimental data, however, are not presently as plentiful for these elements as for those of the iron group. 

For the treatment of camotite several methods are available. The method recommended by the United States Bureau of Mines2 is as follows The ore is leached with concentrated nitric acid at 100° C., neutralised with caustic soda, and barium chloride and sulphuric acid added to the solution to precipitate the radium as barium-radium sulphate. The precipitate settles in three or four days, after which time the clear liquid is decanted into tanks and is treated with excess of boiling sodium carbonate solution in order to precipitate any iron, aluminium and chromium present. The solution now contains sodium uranyl carbonate and sodium vanadate. It is nearly neutralised with nitric acid, and caustic soda is added in sufficient quantity to precipitate the uranium as sodium uranate. After filtering, the remaining solution is neutralised with nitric acid and ferrous sulphate added, whereupon iron vanadate is thrown down. By this method it is claimed that 90 per cent, of the radium, all the uranium, and 50 per cent, of the vanadium in the camotite are recovered. 

Ignites on contact with antimony, arsenic, boron, iodine, phosphorus, selenium. Ignites when warmed with bismuth, carbon, chromium, lead, sulfur. Incandescent reaction with aluminum, cadmium, cobalt, iron, molybdenum, nickel, potassium, sodium, thorium, titanium, tungsten, uran-... 

The uranous compounds correspond to the basic oxide, UOj, and are usually green or blue in colour. They may be prepared by reduction of uranyl salts in solution under the influence of light (see below), but they are the more unstable and the solutions are readily oxidised back by air to uranyl compounds, especially in the presence of platinum black or of salts of iron or copper. In the uranous compounds uranium shows considerable chemical similarity to thorium, the terminal member of Group IV (see p. 4). 

On a commercial scale uranous oxide is prepared by fusing at red heat a mixture of 35 parts of common salt and 20 parts of sodium uranate with 1 part of powdered charcoal, the heating being continued until the escape of gas ceases. After cooling, the mass is lixiviated with water, and the residue of uranous oxide is washed by decantation. By washing with 5 per cent, hydrochloric acid, any iron, aluminium, or vanadium compounds may be removed, and a commercial product of purity equivalent to 97 per cent. U3O3 is obtained. If the uranous oxide is required for the production of ferro-uranium, the complete removal of iron is not necessary. 

Uranous sulphate, even in acid solutions, is a strong reducing agent and can precipitate silver and gold from solutions of their salts. The sulphate is readily oxidised in solution by atmospheric oxygen. Both these reactions are accelerated by the presence of catalysts, especially copper salts, and in less degree platinum black or traces of iron salts. -... 

Uranium Z, also thought to be a product of uranium X, was discovered by Hahn in 1921, who isolated it in the following manner. The mother-liquors from repeated fractional crj stallisations of uranous nitrate, containing uranium X and uranium Z, w ere treated with ferric chloride solution, and the iron precipitated by means of ammonia and ammonium carbonate. The precipitate, which contained both the uranium Xj and uranium Z, was treated with a solution of tantalum in hydrofluoric acid, lanthanum nitrate added, and the mixture digested on a water-bath with dilute hydrofluoric and sulphuric acids. Lanthanum fluoride was precipitated, and carried do%vn with it uranium The filtrate was evaporated to dryness and the residue ignited. The tantalum was thus rendered insoluble, whilst the iron could be removed by means of concentrated hydrochloric acid. The uranium Z remained with the tantalum. By this means Hahn obtained specimens of uranium Z which were 99-5 per cent, radioactively pure. 

All decomposition reactions are endothermal except that of FeU04, presumably because this is the only reaction which involves oxidation of the double oxide. No significant diflFerence was noted in the DTA or TGA curves of the two NiU04 phases. It is interesting to note the alternating pattern in the decomposition reactions of the uranates. The iron, nickel, and zinc double oxides tend to decompose directly into their constituent oxides, while the manganese, cobalt, and copper compounds decompose to other double oxides. The pattern is not carried over into the decomposition temperatures. In this instance, the thermal stability of the double oxides appears to vary directly with the characteristic transition element oxidation states Gr(III) > Mn, Go (III, II) > Ni, Zn(II) > Gu(II, I). The iron compounds constitute a definite exception to this pattern. 

In FIG. 18, A, B, and C represent individual particles of material containing natural uranium, but it is to be distinctly understood that. the entire chain may take place in one body, two bodies, or three, as shown, because of 60 the fact that the neutrons during the slowing down process are diffusing over random paths throughout the entire composite mass of ffie slurry, and are not nec sarily passing directly from one uranous body to the next adjacent body. The factor n represents any fixed number of neu-65 irons. 

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. 

The recently developed Excer process of the U.S.A.E.C. aims to extract uranium from low-grade ore, purify it up to nuclear specification and convert to uranium tetrafluoride ready for metal production. The process is shown in Fig. 3.15 and is based first upon a sulphuric acid leach of the ore and anion absorption of uranium from the pulp. Elution is then by 2M sulphuric acid to give a solution containing about 10 to 20 g U/1. The uranyl sulphate is then reduced by metallic iron to uranous sulphate, diluted to an acidity of 0-5M and a second cycle of anion-exchange carried out. Absorption behaves similarly to that with uranyl ion, but ferrous ion is not... 

A special procedure must be used when titanium is not present alone since chromotropic acid reacts also with other metal salts. Ferric salts give a deep green color, uranyl salts a brown. These colors can be easily discharged by the addition of a hydrochloric acid solution of stannous chloride the resulting ferrous and uranous salts do not react with chromotropic acid. Those mercury salts which dissociate give a yellow color and silver salts form a black stain on filter paper if spotted with chromotropic acid. The presence, however, of these two products does not materially interfere, since the titanium color is still perceptible. The same is true of iron, because the titanium color usually appears as a brown-red fleck in the center of the green iron stain. When there is uncertainty as to the identity of the other elements present, the following procedure should be used. 

The reaction is slow. The equivalence point is detected with diphenylamine sulfonic acid. Another methodology is to treat the uranous cation solution with an excess of iron + III chloride, which, in so doing, is reduced into iron + II ions ... 

---