Uranium, extraction properties

The Masurca waste exhibits the special property of high UO concentration (12 g/L), so that the first operation to be performed is TBP extraction of U(VI). This operation does not require prior feed adjustment, because the acidity and nitrate ion concentration are sufficiently high. The U(VI) concentration of the PuOprecycle waste,even after volume reduction by a factor of 50, does not require a specific uranium extraction cycle. 

In 1869, Mendeleev predicted the existence and certain properties of an element with atomic mass 45, terming it ekaboron within a decade, the Swede L. F. Nilsson and Frenchman P. T. Cleve independently isolated scandium oxide, subsequently preparing various other compounds. There are few ores where scandium is the main element (e.g. thortveitite, a silicate, Sc2Si207, and sterrite, SCPO4 2H2O) so that it is mainly obtained as a by-product from uranium extraction. 

Another SPE procedure for preconcentration of uranium in natural waters used octadecyl silica membrane disks modified by tri-n-octylphosphine oxide (TOPO) (Shamsipur et al. 1999). The high extractive properties of organic phosphorus compounds for uranyl ions are well known (e.g., TBP in the nuclear fuel cycle). 

TVEX-TBP properties were used to develop the biggest full-scale application of TVEX-TBP in the former USSR for uranium extraction at uranium ore-processing... 

The O or S atoms in P=0 and P=S groups may act as electron donors although these groups form relatively weak complexes with electron acceptor compounds such as nonpolarizable, more electropositive (ie, hard) acids, including protons (14). Use is made of this property in the recovery of uranium from wet-process phosphoric acid by extractants such as trioctylphosphine oxide [78-50-2] and di(2-ethylhexyl) hydrogen phosphate [298-07-7]. 

Depleted Uranium. In the natural state U is a mixt of isotopes from which two, U23s and U238> are extracted for use in nuclear reactors and weapons. What remains after the extraction is known as depleted uranium which now exists in large quantities and for which few uses have so far been found. One property of U is its high d -it is heavier than Pb — and this has led to the investigation of its military applications... 

Marie (NLP 1903, NLC 1911 ) and Pierre (NLP 1903 ) Curie took up further study of Becquerel s discovery. In their studies, they made use of instrumental apparatus, designed by Pierre Curie and his brother, to measure the uranium emanations based on the fact that these emanations turn air into a conductor of electricity. In 1898, they tested an ore named pitchblende from which the element uranium was extracted and found that the electric current produced by the pitchblende in their measuring instrument was much stronger than that produced by pure uranium. They then undertook the herculean task of isolating demonstrable amounts of two new radioactive elements, polonium and radium, from the pitchblende. In their publications, they first introduced the term radio-activity to describe the phenomenon originally discovered by Becquerel. After P. Curie s early death, M. Curie did recognize that radioactive decay (radioactivity) is an atomic property. Further understanding of radioactivity awaited the contributions of E. Rutherford. 

A primary goal of chemical separation processes in the nuclear industry is to recover actinide isotopes contained in mixtures of fission products. To separate the actinide cations, advantage can be taken of their general chemical properties [18]. The different oxidation states of the actinide ions lead to ions of charges from +1 (e.g., NpOj) to +4 (e.g., Pu" " ) (see Fig. 12.1), which allows the design of processes based on oxidation reduction reactions. In the Purex process, for example, uranium is separated from plutonium by reducing extractable Pu(IV) to nonextractable Pu(III). Under these conditions, U(VI) (as U02 ) and also U(IV) (as if present, remain in the... 

As noted earlier (see section 12.3.1), the Amex process, which uses long-chain amines, is preferred over the Dapex process, which uses HDEHP, for solvent extraction of uranium from H2SO4 leach solutions. Because the surfactant properties of amine sulfates are conducive to formation of objectionable emulsions, the Amex process is very sensitive to the presence of solids in the H2SO4 leachate. For acceptable phase coalescence in the Amex process, feeds should contain no more than 20 ppm solids. The Dapex process can tolerate feeds containing as much as 100 ppm solids. 

As mentioned, protactinium is one of the rarest elements in existence. Although protactinium was isolated, studied, and identified in 1934, little is known about its chemical and physical properties since only a small amount of the metal was produced. Its major source is the fission by-product of uranium found in the ore pitchblende, and only about 350 milligrams can be extracted from each ton of high-grade uranium ore. Protactinium can also be produced by the submission of samples of throrium-230 (g Th) to radiation in nuclear reactors or particle accelerators, where one proton and one or more neutrons are added to each thorium atom, thus changing element 90 to element 91. 

Protactinium is one of the rarest elements on Earth. It is formed when uranium and other radioactive elements break down. For many years, the only supply of protactinium of any size was kept in Great Britain. The British government had spent 500,000 to extract about 4 ounces (125 grams) of the element from about 65 short tons (60 metric tons) of radioactive waste. Relatively little is known about the properties of the element, and it has no commercial uses. 

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