Polonium acids

Metallic polonium is not affected by 15% bromic acid, even at 70°C, and polonium dioxide or polonium(IV) hydroxide are only slightly soluble (2.5 mg Po02/liter) in 10% bromic acid. Polonium tetrachloride is converted to a white solid of unknown composition by 15% bromic acid this could be a basic chloride (12). 

The more metallic nature of polonium is shown by the fact that it dissolves not only in concentrated nitric and sulphuric acids but also in hydrofluoric and hydrochloric acids. 

This has been made in trace quantities by the action of dilute hydrochloric acid on magnesium plated with polonium. As expected, it is extremely unstable and decomposes even at 100 K,... 

Polonium is readily dissolved in dilute acids, but is only slightly soluble in alkali. Polonium slats of organic acids char rapidly halide amines are reduced to the metal. 

The maximum permissible body burden for ingested polonium is only 0.03 microcuries, which represents a particle weighing only 6.8 x IO-12 g. Weight for weight it is about 2.5 x lOii times as toxic as hydrocyanic acid. The maximum allowable concentration for soluble polonium compounds in air is about 2 x lO-ii microcuries/cnu. 

PoS forms as a black precipitate when H2S is added to acidic solutions of polonium compounds. Its solubility product is 5 X 10-2 The... 

Metals typically form basic oxides and nonmetals typically form acidic oxides, but what about the elements that lie on the diagonal frontier between the metals and nonmetals Along this frontier from beryllium to polonium, metallic character blends into nonmetallic character, and the oxides of these elements have both acidic and basic character (Fig. 10.7). Substances that react with both acids and bases are classified as amphoteric, from the Greek word for both. For example, aluminum oxide, A1203, is amphoteric. It reacts with acids ... 

Metals form basic oxides, nonmetals form acidic oxides the elements on a diagonal line from beryllium to polonium and several d-block metals form amphoteric oxides. 

The chemistry of sulfur is a broad area that includes such chemicals as sulfuric acid (the compound prepared in the largest quantity) as well as unusual compounds containing nitrogen, phosphorus, and halogens. Although there is an extensive chemistry of selenium and tellurium, much of it follows logically from the chemistry of sulfur if allowance is made for the more metallic character of the heavier elements. All isotopes of polonium are radioactive, and compounds of the element are not items of commerce or great use. Therefore, the chemistry of sulfur will be presented in more detail. 

Radiometric methods are unique for their ability to provide directly the surface concentration of the adsorbate. A method for in situ study of electrochemical reactions on solid electrodes was invented by Joliot. ° He used a thin gold foil as an electrode which at the same time served as the window of the radiation counter. Johot determined the kinetics and the effect of tartaric acid on polonium electrodeposition on gold. The method was later further developed and improved (e.g.. Refs. 102,103). 

After neutron irradiation bismuth (canned in aluminum jackets) is dissolved in a mixture of hydrochloric and nitric acids and excess NO3 is removed by adding a reducing agent, such as, urea or formic acid. If bismuth is used as an anode, the reducing agent is dissolved in HCl. Various methods are applied for concentration of polonium in the acid mixture and its subsequent separation from bismuth. Such processes include spontaneous deposition of polonium over a less electropositive metal and coprecipitation with tellurium. In the latter method, a Te + or Te + salt is added to the extract, followed by addition of stannous chloride, which reduces both the tellurium and polonium to their metallic state, coprecipitating them from bismuth in the extract mixture. 

Polonium may be purified by various processes. Such purification methods include precipitation of polonium as sulfide and then decomposing the sulfide at elevated temperatures spontaneous decomposition of polonium onto a nickel or copper surface and electrolysis of nitric acid solutions of polonium-bismuth mixture. In electrolytic purification polonium is electrodeposited onto a platinum, gold, nickel, or carbon electrode. 

The metal dissolves in dilute hydrochloric acid forming pink-red polonium dichloride ... 

For the chemical separation, the irradiated bismuth is dissolved in acid, tellurium carrier is added, and metallic polonium and bismuth are precipitated from solution with stannous chloride (96, 117). The metals are dissolved in acid and the tellurium reprecipitated with sulfur dioxide (76), leaving polonium in solution in the bipositive state. 

Polonium, however, can be readily recovered from aged silver foils by dissolving them in nitric acid and precipitating the silver with hydrochloric acid little or no polonium is lost by adsorption on the precipitated chloride provided the acidity is high. An insoluble black residue, left after the bulk... 

The deposition of polonium on to copper does not give a good separation of the element from bismuth (83, 111), but bismuth powder itself provides a quite successful process (25). In practice, the irradiated bismuth is dissolved in a mixture of hydrochloric and nitric acids, and after elimination of the latter, the solution is stirred with a few grams of powdered bismuth the polonium is deposited completely on to the bismuth. The product is dissolved in acid and the whole process repeated with decreasing amounts of metallic bismuth, until the proportion of polonium to bismuth is high enough for the former to be precipitated as the metal with stannous chloride. 

In the final purification, polonium is either dissolved in nitric acid and clectrodeposited onto platinum, or, better, gold (6, 25) the polonium is sublimed in a vacuum from the support metal or dissolved off the latter in dilute hydrochloric acid and precipitated as the monosulfide. Either hydrogen sulfide itself or the sulfide ion produced by the hydrolysis of thioacetamide may be used. The monosulfide is decomposed by heating under vacuum and the pure metal sublimed (14). 

An interesting method (88) for the separation of trace amounts of polonium makes use of the volatility of some, as yet unidentified, organic compounds. Polonium complexes with diphenylearbazonc, diphenylear-bazide and diphenylthiocarbazone sublime below 100°C under atmospheric pressure and those with thiourea, 8-hydroxyquinoline, s-diphenylthiourea, thioseinicarbazide and other related compounds sublime below 160°C under the same conditions. Thus trace polonium has been separated from dilute nitric acid in the presence of diphenyl carbazide by steam distillation. 

The electrochemical separation of polonium from irradiated bismuth has not been investigated to any extent it appears, however, that electrodeposition from hydrofluoric acid solution offers a practical means of separation (131). 

Solvent extraction by tributyl phosphate (TBP) (13, 96), dithizone (20, 71, 72), cupferron (89), thenoyl trifluoroacetone (TTA) (55), diiso-propyl ketone (26), mesityl oxide (92), tri-n-benzylamine and methyl di-n-octylamine (99), diisopropyl and diisobutyl carbinol (100) have all found some application on the trace scale. Acetylaeetone and methyl isobutyl ketone extract milligram amounts of polonium almost quantitatively from hydrochloric acid, but the stable polonium-organic compounds which are formed make it difficult to recover the polonium in a useful form from solutions in these ketones (7). Ion exchange (22, 115, 119) and paper chromatography (44, 87) have also been used for trace scale separations of polonium, but the effects of the intense alpha-radiation on organic com-... 

The alpha radiation chemical effects at the curie level are severe, leading to the self-decomposition of most polonium compounds thus solid polonium salts of organic acids char rapidly and polonium iodate evolves free iodine. 

The trace level work with polonium was bedeviled by its radioeolloidal behavior in neutral or weakly acid solution. This led to the deposition of polonium on the wall of containing vessels, a behavior which is much less evident with macroscopic amounts. The conflicting views as to the cause of this phenomenon are outside the scope of this article and further information may be obtained from recent reviews and papers (4, 41, 57, 127). 

The precipitated metal is a grey-black powder, but when sublimed, polonium is silvery in thick layers [ 0.2 mg (1 curie)/cm2] and a transparent smoked film in thin ones. When the thicker metal mirrors, obtained by vacuum sublimation onto a glass surface, are treated with a little 8 N nitric acid, a part of the metal can be detached from the glass as a thin foil. 

The physical properties of the metal (Table II) resemble those of thallium, lead and bismuth, its neighbors in the Periodic Table, rather than those of tellurium, its lower homologue. The low melting and boiling points are particularly noteworthy an attempted study of the Hall effect in polonium metal has also been reported (90). In chemical properties the metal is very similar to tellurium, the most striking resemblance being in its reactions with concentrated sulfuric acid (or sulfur trioxide) and with concentrated selenic acid. The products are the bright red solids, PoSOs and... 

The treatment of polonium(lV) with nitric acid/potassium permanganate under reflux yields a sludge of manganese dioxide which contains all the polonium originally present the valency state is uncertain. Polonium (IV) in weighable amounts is not oxidized by persulfate, ceric salts or chlorine in alkaline solution (12), although trace scale work indicates that both ceric salts and dichromate do oxidize polonium to polonium(VI) (94). 

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