Protactinium chemistry

Progress in the preparative and structural fields of protactinium chemistry has been rapid during the past 6 years and there is now sufficient information available, particularly in the halide and oxide fields, to permit a more balanced comparison than has previously been possible with the properties of the actinide elements, on the one-hand, and those of niobium and tantalum, on the other. In this connection one must, of course, bear in mind the fact that the ionic radii of protactinium in its various valence states [Pa(V), 0.90 A and Pa(IV), 0.96 A] are appreciably larger than those of niobium or tantalum and this itself will have a considerable influence on the chemical and crystallographic properties of the elements. 

While this article was in press the Third International Conference on Protactinium Chemistry was held at Schloss Elmau, Mittenwald, West Germany in April, 1969. Many of the papers presented at this meeting... 

Protactinium as 231Pa occurs in pitchblende, but even the-richest-ores contain only about 1 part of Pa in 107. The isolation of protactinium from residues in the extraction of uranium from its minerals is difficult, as indeed is the study of protactinium chemistry generally, owing to the" extreme tendency of the compounds to hydrolyze. In aqueous solution, polymeric ionic species and colloidal particles are formed, and these are carried on precipitates and adsorbed on vessels in solutions other than those containing appreciable amounts of mineral acids or complexing agents or ions such as F , the difficulties are almost insuperable. 

The actinium decay series consists of a group of nuclides whose mass number divided by 4 leaves a remainder of 3 (the 4n + 3 series). This series begins with the uranium isotope which has a half-life of 7.04 X 10 y and a specific activity of 8 X 10 MBq/kg. The stable end product of the series is ° Pb, which is formed after 7 a- and 4 /3-decays. The actinium series includes the most important isotopes of the elements protactinium, actinium, ftancium, and astatine. Inasmuch as U is a conqx>nmt of natural uranium, these elem ts can be isolated in the processing of uranium minerals. The longest-lived protactinium isotope, Pa (ti 3.28 X 10 y) has been isolated on the 100 g scale, and is the main isotope for the study of protactinium chemistry. Ac (t 21.8 y) is the longest-lived actinium isotope. 

As the parent of actinium in this series it was named protoactinium, shortened in 1949 to protactinium. Because of its low natural abundance its chemistry was obscure until 1960 when A. G. Maddock and co-workers at the UK Atomic Energy Authority worked up about 130g from 60 tons of sludge which had accumulated during the extraction of uranium from UO2 ores. It is from this sample, distributed to numerous laboratories throughout the world, that the bulk of our knowledge of the element s chemistry was gleaned. 

The most interesting elements of the seventh row are those following actinium. For some of these elements a large amount of chemistry is known. The first four, actinium, thorium, protactinium, and uranium, used to be shown in the periodic... 

Some recent preparative chemistry of protactinium. D. Brown, Adv. Inorg. Chem. Radiochem., 1969, 12, 1-51 (138). 

Some Recent Preparative Chemistry of Protactinium D. Brou n... 

Otto Hahn, 1879-. President of the Max Planck Society for the Promotion of Science. Discoverer with F. Strassmann, in 1938, of the splitting of uranium and of thorium by neutron irradiation into two elements of medium weight. Discoverer of radioactinium, radiothorium, mesotliorium, uranium Z, and (with Miss Lise Meitner) protactinium. He has devised radioactive methods for determining the geologic and biologic age of materials. In 1945 he received the Nobel Prize for Chemistry for the year 1944. 

Exhaustive accounts of the chemistry of thorium, protactinium, uranium and the transuranium elements appear in the most recent supplementary volumes of the Gmelin series.12 Unless otherwise indicated by the inclusion of references to specific papers, further information on the compounds discussed in this chapter will be found in the Gmelin volumes and in the work cited in reference 2. 

First identified in 1913 (the first compound, Pa20s, was isolated in 1927 by von Grosse, who isolated the element in 1931), protactinium is not generally extracted. Most of what is known about the chemistry of protactinium ultimately results from the extraction in 1960 by the UK Atomic Energy Authority of some 125 grams of Pa, from 60 tons of waste material left over from the extraction of uranium, at a cost of about 500,000 (very roughly, 1,250,000 at today s exchange rate). 

Protactinium-231, an a-emitter, is the only isotope suitable for macrochemical studies [fj/2 = 32,340 years (36)] and in view of the radiochemical hazards associated with weighable amounts of this isotope, it is necessary to perform all manipulations in glove boxes or, in the case of solution chemistry, in well-ventilated fume hoods. An indication of the toxicity of protactinium-231 is given by the fact that the maximum permissible concentration in air is 10 mg/m whereas that of hydrogen cyanide is 10 mg/m. Details of suitable handling procedures are adequately dealt with in other publications (11, 136). 

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