Sodium uranyl carbonate

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. 

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. 

Sodium Uranyl Carbonate, Na4U02(C03)g, is obtained by evaporation of a solution of freshly precipitated sodium uranate in sodium bicarbonate solution or by the addition of sodium carbonate in excess to a solution of uranyl acetate. It separates as a yellow crust. 

The sodium uranyl carbonate is very soluble in the aqueous phase, but the sodium salt of EHPA has only limited solubility in the organic phase and tends to form a third liquid phase containing the salt, some diluent, and water. To prevent this, the organic phase is also made 0.1 M in TBP, in which the sodium salt of EHPA is soluble. 

Uranyl solutions are easily prepared by dissolution of water-soluble salts the nitrate, fluoride, chloride, bromide, iodide, sulfate, and acetate. Other water-soluble uranyl salts Include those of other organic acids the formate, propionate, butyrate, emd valerate and certain double salts such as potassliun uranyl sulfate, sodium uranyl carbonate, sodium uranyl chromate, etc. Uranyl solutions may be prepared also by dissolution of a uranium(VI) compound in an appropriate solvent, by dissolution of a lower valence uranium compound in an oxidizing medium, or by oxidation of lower valence uranium ions already in solution. Uranyl solutions are yellow in color. They are the most stable of uranlvim solutions. As indicated in preceding paragraphs, the... 

Goishi and Libby have investigated the extraction of pertechnetate from alkali solutions with pyridine. Later work showed that a better extraction is obtained using a mixture of sodium hydroxide and sodium carbonate as the aqueous phase. Since the uranyl carbonate complex is not extracted into pyridine, this system may be used for the separation of technetium from uranium. Distribution coefficients of fission products in pyridine are given in Table 4. Substituted pyridine such as 2,4-dimethylpyridine or 4-(5-nonyl)pyridine ) are useful for separating technetium from solutions containing appreciable amounts of aluminum nitrate. 

In the Dapex process, uranium is usually stripped from the loaded organic phase with a solution of sodium carbonate, which converts the extractant to the sodium salt form, while retaining uranium in solution as sodium uranyl tricarbonate ... 

Ammonium (or sodium) carbonate solution white precipitate of uranyl carbonate, U02C03, soluble in excess of the reagent forming a clear, yellow solution containing the tricarbonatouranylate(VI) ion (cf. reaction 1). 

For the mierochemical detection of uranium, the formation of either thallium uranyl carbonate or sodium uranyl acetate may be employed. 

Some uranium ore bodies are high in limestone and dolomitic content which is wasteful on acid employed for leaching. Such sources are successfully treated by an alkaline mixed sodium carbonate and bicarbonate leach, the later being required to buffer the pH so as not to precipitate the uranium. Sorption occurs as the uranyl carbonate complex anion, U02(C03)3 , but elution is with sodium nitrate since acid would cause evolution of carbon dioxide gas. 

Uranium is extracted from pitchblende, essentially UgOg. The ore is washed, then fused with sodium carbonate and sodium nitrate. From the mass, dilute sulphuric acid extracts uranyl sulphate, UO2SO4. The addition of ammonium carbonate enables ammonium uranyl carbonate, (NH4)4U02 (003)3, to be crystallised which, on ignition, yields pure U3O3. 

Leaching with alkali always takes place at high temperatures, either under pressure (5 to 6 bar, 95 to 120°C) or at atmospheric pressure (75 to 80°C). The leaching agent used is sodium carbonate, sodium hydrogen carbonate or ammonium carbonate. Uranium(Vl) oxide is converted in this process into uranyl tricarbonato-complexes ... 

Most leaching described in the literature has followed the lines described above. Strongly basic ores, usually those containing abundant carbonate, are not well suited to bacterial leaching since a low pH is not as readily obtained as in other cases. For such ores, leaching with sodium carbonate solution has been used successfully, the uranium being transported as an anionic uranyl carbonate complex (Merritt, 1971). 

Simple uranyl carbonates arc not known, but double carbonates arc easily formed as, for example, a salt of the composition U02C03 2 NajCOj is obtained as a yellow crust, when freshly precipitated sodium uranate is treated with sodium bicarbonate, or when an excess of sodium carbonate is added to a solution of uranyl acetate. 

Uranyl carbonate complexes, like sodium uranyl tricarbonate, Na4[U02(C03>3], that is obtained when uranium ore is leached with sodium carbonate solutions and ammonium uranyl carbonate (AUC), (NH4)4[U02(C03)3l, that is used to precipitate the uranium in the UCF, are important in the NFC. These carbonates serve to purify the uranium from several metals (like Fe, Al, Cr, Ni, and other metals) that are precipitated as hydroxides or oxycarbonates, as well as aUcaline-earth elements. These purification methods utilize the effect of the ammonium carbonate concentration on the solubility of uranium. Upon heating of AUC to 300°C-500°C, it decomposes to UO3, ammonia, CO2, and water and at temperatures of 700°C-800°C, without air, UO2 may be formed (the ammonia serves as the reducing agent). The solubility of AUC decreases markedly in the presence of ammonium carbonate, for example, from 119.3 g L" at 50°C without ammonium carbonate to 0.5 g L" with 35% ammonium carbonate (Galkin 1966). The carbonate complexes also play a role in biological systems and affect clearance by the blood after exposure to uranium compounds. 

The reduced mobility of radium in comparison with uranium is explained by the solubility difference between the two elements, which occur in nature as sulphates and carbonates at 18°C radium sulphate = 1.410" g/1 uranyl sulphate = 205 g/1 radium carbonate is insoluble and uranyl carbonate = 60g/l. With the acidity and alkalinity of water, however, radium solubility changes. The radium content of water also depends on the salt concentration of certain elements—mainly alkaline chloride (radium replaces sodium). Radium precipitates with complexes of barium (S04Ba) and with calcium carbonates (travertine). Radium is also fixed by clay, organic matter, iron and manganese hydroxides. 

The solvent, a solution of either sulfuric acid or sodium carbonate, forms the stable complex uranyl ions U02(S04) "2) U02(SO ) )... 

These can be converted to their uranyl nitrate addition compounds. The crude or partially purified ester is saturated with uranyl nitrate solution and the adduct filtered off. It is recrystallised from -hexane, toluene or ethanol. For the more soluble members crystallisation from hexane using low temperatures (-40°) has been successful. The adduct is decomposed by shaking with sodium carbonate solution and water, the solvent is steam distilled (if hexane or toluene is used) and the ester is collected by filtration. Alternatively, after decomposition, the organic layer is separated, dried with CaCl or BaO, filtered, and fractionally distilled under high vacuum. 

Alkaline leaching is carried out by using sodium carbonate solution. In this case any U(IV) present in the ore must also be oxidized to U(VI). The uranium species soluble in carbonate leach solutions in the uranyl tricarbonate ion. The formation of this ion by solubilization of a hexavalent uranium mineral such as camotite, or a tetravalent uranium mineral such as uraninite, may be represented by the following reactions ... 

Dapex [Di-alkylphosphoric acid extraction] A process for the solvent extraction of uranium from sulfuric acid solutions using di-(2-ethylhexyl) phosphoric acid (HDEHP). The HDEHP is dissolved in kerosene containing 4 percent of tributyl phosphate. The uranium is stripped from the organic phase by aqueous sodium carbonate and precipitated as uranyl peroxide (yellow cake). The process was no longer in use in 1988. See also Amex. 

IJmnate. Sodium uranate, uranium yellow, Na2U04, yellow solid, insoluble, formed by reaction of soluble uranyl salt solution and excess sodium carbonate solution. Used (1) in the manufacture of yellowish-green fluorescent glass, (2) in ceramic enamels, (3) as a source of uranium for chemical reactions. 

There are several uranium ore-bodies in the world that cannot be leached economically with sulfuric acid because of the high limestone content of the ore. Such ore-bodies are generally leached with an alkaline solution of sodium carbonate and bicarbonate. Carbonate also forms anionic complexes with the uranyl ion the predominant species being UC fCC 4- — and may therefore also be treated with anion-exchange resins. 

Anion Resin Exchange to Separate Sodium Carbonate from - p Ammonium Uranyl Tricarbonate... 

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