Actinium separation

With the exception of actinium, which is found naturally only in traces in uranium ores, these elements are by no means rare though they were once thought to be so Sc 25, Y 31, La 35 ppm of the earth s crustal rocks, (cf. Co 29ppm). This was, no doubt, at least partly because of the considerable difficulty experienced in separating them from other constituent rare earths. As might be expected for class-a metals, in most of their minerals they are associated with oxoanions such as phosphate, silicate and to a lesser extent carbonate. 

Lin [ 1 ] used coprecipitation with lead sulfate to separate 237-actinium from sea water samples. The 237-actinium was purified by extraction with HDEHP, and determined by alpha spectrometry via Si (Au) surface barrier detection. The method has a sensitivity of 10 3 pCig"1 of ashed sample. 

Ac, actinium, was initially identified in 1899 by Andr6-Louis Debierne, a French chemist, who separated it from pitchblende. He dissolved the mineral in acid, then added NH4OH, and found that a radioactive species was carried down with the rare earth hydroxides. He named the element actinium after the Greek aktinos which means ray. Because of its low abundance in U, the element is usually not obtained by isolation from U. It can be obtained in mlligram amounts by irradiation of Ra-226 in a nuclear reactor. The preparation of Ac metal involves reduction of AcFs by Li at high temperature. 

The aqueous chemistry of the two rows of f-block elements, the lanthanides (lanthanum to lutetium) and the actinides (actinium to lawrencium), are sufficiently different from each other to be dealt with in separate sections. Similarities between the two sets of elements are described in the actinide section. 

Daughters of alpha emitters The recoil method can also be useful for the separation of daughter products produced by a decay of a parent. This technique has been applied to studies of short-lived daughters In the radioactive decay series of uranium, thorium, and actinium (175) ... 

The Group 3 elements are scandium, yttrium, and lanthanum. Strictly speaking actinium should also be included, but it is the general practice to associate it with the elements that follow it (the actinides) and treat them all separately, as we do in this book in Chapter 20. 

Actinium occurs in traces in uranium minerals, but it is made on a milligram scale by neutron capture in radium (Table 20-2). The actinium +3 ion is separated from... 

Since the chemistry of actinium is confined to the Ac + ion, it can readily be separated from thorium (and the lanthanides, for that matter) by processes like solvent extraction with thenoyltrifluoroacetone (TTFA) and by cation-exchange chromatography. The latter is an excellent means of purification, as the Ac + ion is much more strongly bound by the resin than its decay products. 

In natural U, the radionuclides of the uranium family and the actinium family are present, and sometimes also radionuclides of the thorium family. Therefore, direct determination of U in ores without chemical separation is difficult, especially since the absorption of the radiation depends on the nature of the minerals. Generally, the samples are dissolved and Th is separated, e.g. by coprecipitation or by extraction with thenoyltrifluoroacetone (TTA). Radioactive equilibrium between " Th and the daughter nuclide 234mp jg rather quickly attained, and the high-energy yS" radiation of the latter can easily be measured. A prerequisite of the determination of U by measuring the activity of either " Th or 234mp jg establishment of radioactive equilibrium. This means that the uranium compound must not have been treated chemically for about 8 months. 

In the case of Th, the attainment of radioactive equilibrium with the daughter nuclides is very slow, because of the long half-life of Ra (q/2 = 5.75 y). Th can be determined directly by measuring its a radiation, but the measurement of Po is more sensitive (about 10 g Th can be determined in this way in 1 g of rock material). Other methods are based on the separation and measurement of Ra or Rn. In all determinations of Th, the possibility of the presence of radioactive impurities, mainly of members of the uranium and actinium families, has to be taken into account. 

The solution photochemistry of the actinides begins with uranium none has been reported for actinium, thorium, and protactinium. Spectra have been obtained for most of the actinide ions through curium in solution (5). Most studies in actinide photochemistry have been done on uranyl compounds, largely to elucidate the nature of the excited electronic states of the uranyl ion and the details of the mechanisms of its photochemical reactions (5a). Some studies have also been done on the photochemistry of neptunium (6) and plutonium (7). Although not all of these studies are directed specifically toward separations, the chemistry they describe may be applicable. 

From this mineral it was formerly customary to extract the uranium and discard the residue. The chemical study of such a complex mixture is an exceedingly difficult task, but by patient effort M. and Mme. Curie succeeded > in 1898 in separating two new radioactive substances to which the names radium and polonium were applied. The latter is now commonly called radium F. Later Debieme discovered 2 a third radioactive constituent of pitchblende residues and named the new substance actinium. 

Actinium and the actinide elements (thorium, etc.) also are listed separately at the bottom. Each actinide element is somewhat similar to actinium and to the lanthanide element with which it is paired. The discovery of hafnium (Hf) in 1923 and rhenium (Re) in 1925 completed the Periodic Table through uranium except for four blank spaces. 

Seaborg s theory was that these elements heavier than actinium might constitute a second series similar to the series of rare earth or lanthanide elements the "lanthanides are chemically very similar and are usually listed in a separate row below the main part of the Periodic Table. 

The so-called rare earth elements, which are all metals, usually are displayed in a separate block of their own located below the rest of the periodic table. The elements in the first row of rare earths are called lanthanides because their properties are extremely similar to the properties of lanthanum. The elements in the second row of rare earths are called actinides because their properties are extremely similar to the properties of actinium. The actinides following uranium are called transuranium elements and are not found in nature but have been produced artificially. 

Radium. Ra at. wt 226 (mass number of most stable isotope) at. no. 88 valence 2. A radioactive alkaline earth meta], Occurrence in earth s crust approx ]0-d% by wt. Natural isotopes 223, actinium X 224, thorium X 226 228, mesothorium 1. 22 Ra is a product of disintegration of uranium and is present in al] ores contg uranium. Separated in the form of a salt by P. and M. S. Curie from the pitchblende nf Joachimsthal, Bohemia Curie et at.. Compt. Rend. 127, 12]5 (1898). [soln of the element by electrolysis of an aq soln of radium chloride Curie, Debierne. ibid. 151, 523 (1910). 12 Ra iT, 6.7 years) produced by disintegration of thorium (I12Th) discovered in 1907 by O. Hahn in monazite residues from isolating thorium. Zaire (Congo) is the main producer of radium, Canada next. Clinical evaluation in... 

U/Ac ratio was found to be constant, but the amount of actinium present was nevertheless less than would be expected if it were a direct disintegration product of uranium. This was the reason for assuming it to lie in a separate chain. By the Group Displacement Law protactinium should belong to Group v and thus resemble tantalum. It was this consideration that led to its discovery. 

The actinides are a row of radioactive elements from thorium to lawrencium. They were not always separated into their own row in the periodic table. Originally, the actinides were located within the d-block following actinium. In 1944, Glenn Seaborg proposed a reorganization of the periodic chart to reflect what he knew about the chemistry of the actinide elements. He placed the actinide series elements in their own row directly below the lanthanide series. Seaborg had played a major role in the discovery of plutonium in 1941. His reorganization of the periodic table made it possible for him and his coworkers to predict the properties of possible new elements and facilitated the synthesis of nine additional transuranium elements. 

Following a brief period with Haber, Georg Hevesy began work with Rutherford at Manchester in 1910. In 1913, he began work with Fritz Paneth in Vienna and conducted the first radiotracer experiments. At that time, it was known that one of the products of radium decay was a substance, having its own unique decay signature, called radium-D. Hevesy tried unsuccessfully to separate radium-D from lead. In 1913, Alexander Fleck (1889-1968), working with Soddy, found that radium-D, radium-B, thorium-B, and actinium-B were chemically inseparable from lead and were, therefore, isotopes of lead. 

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