Separation of Polonium

The extraction of polonium from uranium ores is now only of historical interest. The trace level amounts used in the earlier work were usually obtained either from the lead residues of uranium ore processing, which contained lead-210, or, more commonly, from aged radon ampoules which, after the complete decay of the radon, contained Pb210, Bi210, Po210, and 

but were often contaminated with mercury from the pumps used to convey the radon from its radium parent. 

Much of the early literature of polonium describes methods for separating it from these mixtures many of these have subsequently been adapted to the separation of milligram amounts of polonium from irradiated bismuth and to its purification. The methods range from a simple chemical separation of the element with a tellurium carrier to its electrodeposition on to a more noble metal or its spontaneous electrochemical replacement on the surface of a less noble metal. 

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 

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Hydrazine sulfate is used as a reducing agent in analytical chemistry for gravimetric measurement of nickel, cobalt, and other metals, and in peptide analysis in the separation of polonium from tellurium as an antioxidant in... 

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-... 

Reactions used for the preparation of polonium compounds are straightforward, but the experimental techniques are strictly determined by the small amount of the commonly used polonium-210 which is available and by the exceptionally high specific activity of the isotope (4.5 curics/mg, i.e., 1013 disintegrations/min/mg). Apart from the major effects of the alpha bombardment to be described, the separation of polonium-210 from its lead daughter, which grows in at a rate of 0.5%/day, constitutes a major chemical problem. It calls for rapid and efficient methods of purifying the polonium stock before each experiment the best of these is the sulfide process described in Section III. 

The vapor pressures of lead and polonium iodides have been investigated. The metals were heated in an atmosphere of iodine in a closed system. The pressure of the products was determined by a statistical method. At less than 80 atomic percent iodine, P0I4 forms in the condensed phase. At 473°K P0I4 dissociates into P0I2. Above 80 atomic percent iodine, the condensed phase exhibits the presence of Pole. The enthalpy of evaporation of Pole is 116kj mole. These experiments suggest that the separation of polonium from lead can be accomplished by their volatization in iodine vapors at elevated temperatures. 

The separation of polonium from lead is an important procedure in radiochemistry. It was proposed,based upon studies of the vapor pressure of the iodides of lead and polonium, that polonium diiodide should serve for the pyrochemical separation of Po from Pb. 

Use Manufacture of chemicals, condensation reactions, catalyst in making acetate fibers. Analysis of minerals, slags, and fluxes determination of arsenic in metals separation of polonium from tellurium fungicide, germicide. 

Polonium (ii) The radioisotopes of polonium (usually Po) have been difficult to analyze with accuracy using the conventional methods. The procedure outlined here is, however, simple, rapid, and accurate. With the sample in solution, add 3 to 5 mL of concentrated phosphoric acid and evaporate to remove other acids. Transfer this phosphoric acid solution to a small equilibration vessel using 3 to 5 mL of water. Add 1 mL of 0.1 M HCl. Add a measured volume, 1.2 to 1.5 mL, of a solution of TOPO, 0.1 to 0.2 M, in toluene and equilibrate. This is a highly selective separation of polonium from other radionuclides with the possible exception of the beta/gamma emitting bismuths. Quantitative stripping and transfer of the polonium to a plate is difficult but the use of an extractive scintillator and counting on a PERALS spectrometer is rapid and simple and the results are quite accurate. Because of the minimal chemical manipulations required, the accuracy of this determination can easily be better than 1%. 

Since Mosander thus fractioned the gadolinite earths in 1839, the method has been extensively employed by W. Crookes (Ghem. News, 54, 131, 155, 1886), in some fine work on the yttria and other earths. The recent separations of polonium, radium and other curiosities have attracted some attention to the process. The mathematics of the reactions follows directly from the law of mass action. Let only sufficient C be added to partially precipitate A and B and let the solution originally contain a of the salt A, b of the salt B. Let x and y denote the amounts of A and B precipitated at the end of a certain time t, then a - x and b - x will represent the amounts of A and B respectively remaining in the solution. The rates of precipitation are, therefore,... 

OTHER COMMENTS used as a solvent for mineral oils, waxes, and resins used to extract acetic acid from aqueous solutions also is used as a solvent in the separation of polonium from lead and bismuth a fuel additive. 

As only small absolute amounts of radionuclides are to be determined, and thus only small amounts of elements are to be separated, separation cannot usually be properly performed by methods whose success depends on the amount of the component to be isolated (e.g., as in precipitation). Therefore, methods that are independent of amount (such as liquid-liquid extraction and ion-exchange methods) are more advantageous. Extraction procedures very often take advantage of additions of chelating components. For separating volatile radionuclides (such as iodine or ruthenium) from the sample matrix, distillation methods can be used advantageously. Electrolytic deposition has been shown to be applicable in the separation of polonium. 

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. 

At trace levels, polonium can be separated effectively by solvent extraction, ion exchange, paper chromatography, and other techniques. Diisopropyl ketone, di-n-octylamine, and tri-n-butylphosphate are suitable solvents for extraction. Trace amounts of polonium in solutions or sohd mixtures containing no other emitters can be determined by measuring its alpha activity. 

The rarity of polonium is evident from a calculation (1) which shows that the outermost mile of the earth s crust contains only 4000 tons of the element, whereas radium, usually classed as rare, is present to the extent of 1.8 X 107 tons. The abundance of polonium in uranium ores is only about 100 Mg per ton and hence separation of the element from such mineral sources cannot seriously be considered. However, radium, at equilibrium with its daughters, contains 0.02 wt % of polonium and, until recently, most of the element was obtained either from radium itself or, more usually, from expended radon ampoules which, after the radon decay is complete, contain radium-D and its daughters. Fortunately, however, the parent of polonium in these sources, bismuth-210, can be synthesized by neutron bombardment of natural bismuth [Bi209 (n,y) Bi210] and with the advent of the nuclear reactor it has become practicable to prepare milligram amounts of polonium. Almost all of the chemistry of the element recorded in the recent literature has been the result of studies carried out with polonium-210 prepared in this way. 

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. 

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. 

Complexes with organic compounds have been reported. Solubility studies with tributyl phosphate (TBP) indicate the formation of a complex PoC14-2TBP (IS). Weighable amounts of polonium tetrachloride in dilute hydrochloric acid can be titrated to a colorless end point with ethylene-diamine tetra-acetic acid (EDTA) the results suggest a complex with two molecules of EDTA, but solubility studies favor a 1 1 complex. The EDTA complex is soluble in alkali and is more stable in alkaline than in acid media, but the ligand is rapidly destroyed by the radiation and solvent radiolysis products 12). However, EDTA can apparently be used to complex trace polonium in the separation of radium D-E-F mixtures (129). 

Separation and Determination of Polonium 210Po and Lead 210Pb... 

After separation and purification, the pure fractions of uranium and plutonium are electroplated on polished stainless discs and the activities of their radionuclides measured using alpha spectrometry. The distribution value of alpha detectors, which is between 17 and 20 kev, is very important. Two radionuclides ( Pu and " °Pu) are measured together because the difference between the energy of their alpha particles is less than 15 keV [1, 14]. Figures 15.3, 15.4, and 15.5 present typical spectra for the alpha measurement of polonium, uranium, and plutonium [ 1 ]. 

Becquerel s student Marie Sklodowska Curie (1867-1934) and her husband, Pierre Curie (1859-1906), began to investigate this new phenomenon and were aided in their examination of the elements for radioactivity by the loan of some rare elements such as thorium. Only uranium and thorium seemed to have this property, but this led them to investigate the components of the mineral pitchblende. Pitchblende was composed primarily of uranium oxide, but the results of the ionization tests seemed to indicate that it had was more ionizing power than could be accounted for by uranium alone. After months of purification and separation work, in July 1898 they announced the discovery of polonium, named after Poland, Marie Curie s homeland. By December, further work led to the discovery of a second new element, which they named radium. The Curies, along with Becquerel, were awarded the Nobel Prize for... 

Their early researches led to the isolation of polonium, named after the country of Marie s birth, and radium, and she later developed methods for separating radium from radioactive residues in sufficient quantities to allow for the study of its properties, and especially its therapeutic properties. 

Already in the early days of radiochemistry some radionuclides were isolated from matrices and their mixtures were separated, making use of different volatility of various elements and compounds. Well-known is the role of the extreme volatility of radon in the discovery of emanations by Dorn and Rutherford (see a detailed story in Reference [1]). In her logbooks Mme. Curie noted purification of polonium by sublimation, when collecting deposits obtained at different temperatures [2], After the discovery of nuclear fission, the volatile species — Kr and Xe in the elemental state, As and Sb as gaseous ASH3 and SbH3, as well as Ru in the... 

By 1898 Madame Curie and her husband Pierre, in collaboration with Bequerel, had isolated two new elements from the radioactive decay of uranium in pitchblende ore. Both were more radioactive than uranium itself. They named the first element polonium (Po) after Madame Curie s native land (Poland), and the second was named radium (Ra). Isolation of these two elements required chemical separation of very small amounts of Po and Ra from tons of pitchblende. Radium was found to be over 300,000 times more radioactive than uranium. 

Polonium is separated from Bi by sublimation or in a variety of chemical ways. The study of polonium chemistry is difficult owing to the intense a radiation, which causes damage to solutions and solids, evolves much heat, and makes necessary special handling techniques for protection of the chemist. 

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