Polonium separation

Poland, native country of Mme. Curie) Polonium, also called Radium F, was the first element discovered by Mme. Curie in 1898 while seeking the cause of radioactivity of pitchblend from Joachimsthal, Bohemia. The electroscope showed it separating with bismuth. 

In 1898, Marie and Pierre Curie isolated two new radioactive elements, which they named radium and polonium. To obtain a few milligrams of these elements, they started with several tons of pitchblende ore and carried out a long series of tedious separations. Their work was done in a poorly equipped, unheated shed where the temperature reached 6°C (43°F) in winter. Four years later, in 1902, Marie determined the atomic mass of radium to within 0.5%, working with a tiny sample. 

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... 

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. 

Another method to separate polonium from bismuth involves heating at 650°C to convert the metals into their oxides. This is followed by further heating to about 800° C at reduced pressure in which polonium metal is removed by volatilization. 

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. 

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. 

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. 

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. 

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). 

Radium is chemically similar to barium it displays a characteristic optical spectrum its salts exhibit phosphorescence in the dark, a continual evolution of heat taking place sufficient in amount to raise the temperature of 100 times its own weight of water 1°C every hour and many remarkable physical and physiological changes have been produced. Radium shows radioactivity a million times greater than an equal weight of uranium and. unlike polonium, suffers no measurable loss of radioactivity over a short period of time (its half life is 1620 years). From solutions of radium salts, there is separable a radioactive gas radium emanation, radon, which is a chemically ineit gas similai to xenon and disintegrates with a half life of 3.82 days, with the simultaneous formation of another radioactive element, Radium A (polonium-218). 

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

Polonium crystals have a simple cubic structure with atoms separated by d = 336.6 pm. If a polonium crystal is exposed to X-rays with k = 154 pm (the most common source wavelength), find the angle 20 which corresponds to the deflection of the strongest scattered component. 

When small amounts of isotopes are thus synthesized and must be separated from other chemical elements in a mixture, chemical periodicity helps for example, radioactive francium (group 1) can be extracted from its mixture with radium (group 2) or polonium (group 16) by adding cesium or rubidium (group 1). 

This chapter describes the chemistry of sulfur, selenium, and tellurium. Polonium will be mentioned only briefly in keeping with the fact that all of the isotopes of the element are radioactive. As a result, the chemistry of such an element is too specialized for inclusion in a survey book of this type. The plan followed in this chapter will be to discuss some of the topics of sulfur chemistry separately from those of selenium and tellurium because in several regards sulfur is somewhat different from the other two elements. 

Pb-Bl-Po tracers in 2 ml of 1 M hydrochloric acid were added to the column. The lead activity was eluted by passing through 3 ml of 1 M hydrochloric acid in 1 ml portions. Then by eluting with 4 ml of concentrated hydrochloric acid in 2 ml portions, the bismuth activity was recovered. Finally, the polonium was eluted with concentrated nitric acid. The entire separation can be effected in 10-15 minutes and the products, are obtained in carrier-free form. 

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. 

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 ]. 

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