Removal of Thorium

The filtrate from (A) (which contains H , SO4 , H2P04, Th , La+ , Ce , Nd , etc.) is diluted to a total volume of 168 1. in a stoneware jar or wooden barrel and stirred for at least 1 hour. Then the pale, blue-gray, heavy, gelatinous precipitate is allowed to settle for 8 to 12 hours. This precipitate consists of thorium phosphate together with some cerium and other rare earth phosphates. To be certain that all the thorium has been removed, a sample is filtered and tested by further dilution. This simple test is sufficient to determine whether the removal of thorium has been complete, since a tremendously greater dilution would be necessary to cause precipitation of rare earth phosphates. The main precipitate is removed by filtration and washed free of rare earth ions. If it is desired to obtain the thorium from this phosphate precipitate, the material should be washed free of sulfuric acid and air-dried. If the phosphate is allowed to dry with sulfuric acid present, it will become hard and glassy in character. It is then almost entirely unreactive toward concentrated acids and bases and yields only to a basic fusion. 

After the thorium has been removed, the rare earths are recovered from the solution. Finely ground solid sodium 

If the original material contained any considerable quantity of xenotime, the yttrium earths (which will be present) will not be precipitated completely by sodium sulfate. In such a case, solid oxahc acid may be substituted for the sodium sulfate or. added to the filtrate from the sulfate precipitation. Otherwise, the filtrate may be discarded. Solid oxalic acid is preferable to the saturated solution in that it does not further dilute the solution and does not form any troublesome gummy precipitates, which must be heated or allowed to stand for some time before effective filtration may be obtained. Ordinarily, the use of oxalic acid is not justified because of the greater expense involved. 

Although the rare earths are conveniently stored as oxalates or double sulfates, they are frequently converted to oxides for storage and, particularly, for use in reactions. However, if the sample of rare earth material contains an unusually large amoimt of cerium, it is not advisable to convert it to oxides because of the difficulty of dissolving cerium(IV) oxide in common reagents. 

The oxalates or double sulfates are made into a thick paste with water, and then sodium hydroxide ffakes or 

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Bacon MP, Rutgers van der Loeff MM (1989) Removal of Thorium-234 by scavenging in the bottom nepheloid layer of the ocean. Earth Planet Sci Lett 92 157-164 Bacon MP, Cochran JK, Hirschberg DJ, Hammar TR, Fleer AP (1996) Export flux of carbon at the equator during the EqPac time-series cruises estimated from " Th measurements. Deep-Sea Res II 43 1133-1153... 

The removal of thorium from the body has been achieved by the use of chelating agents, primarily ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) (Fried and... 

Peter-Witt E, Volf V. 1984. Efficacy of different diethylenetriaminepentaacetic acid treatment schedules for removal of thorium-234 from simulated wounds in rats. Int J Radiat Biol Relat Stud Phys Chem Med 45 45-50. 

Table 6.19 lists distribution coefficients for amines considered [C5] for extracting uranium from monazite sulfate solutions after removal of thorium. Except for Primene JM, all coefficients were judged [C5] to be large enough and sufficiently greater than those of the rare earths to provide efficient solvent extraction separation of uranium. 

For many years fluorine has been deterrnined by the Willard-Winters method in which finely ground ore, after removal of organic matter, is distilled with 72% perchloric acid in glass apparatus. The distillate, a dilute solution of fluorosiUcic acid, is made alkaline to release fluoride ion, adjusted with monochloroacetic acid at pH 3.4, and titrated with thorium nitrate, using sodium a1i2arine sulfonate as indicator. 

The sohds are treated with hydrochloric acid at 70°C at pH 3—4. The thorium hydroxide [13825-36-0] remains iasoluble and can be filtered off. Small amounts of trace contaminants that carry through iato solutioa, such as uranium and lead as well as some thorium, are removed by coprecipitation with barium sulfate ia a deactivatioa step. The resultiag product, after SX-removal of the heavy La fractioa, is a rare-earth/lanthanide chloride,... 

The application of the Chelex 100 resin separation and preconcentration, with the direct use of the resin itself as the final sample for analysis, is an extremely useful technique. The elements demonstrated to be analytically determinable from high salinity waters are cobalt, chromium, copper, iron, manganese, molybdenum, nickel, scandium, thorium, uranium, vanadium, and zinc. The determination of chromium and vanadium by this technique offers significant advantages over methods requiring aqueous final forms, in view of their poor elution reproducibility. The removal of sodium, chloride, and bromide allows the determination of elements with short and intermediate half-lives without radiochemistry, and greatly reduces the radiation dose received by personnel. This procedure was successfully applied in a study of... 

Livingston and Cochran [50] collected large seawater samples by using a cable-supported electrical pumping system for subsequent determination of thorium, americium, and plutonium isotopes. Particles were removed by filtration and actinides were collected by absorption on manganese dioxide-coated filters. The samples were then analysed by standard radiochemical and a spec-trometric techniques. 

The fluoride solution is diluted to 100 ml. with water, 8 drops of the indicator are added and the pink coloration just removed with 1/200 hydrochloric acid solution. Then 1 ml. of the monochloroacetate buffer solution is added and the solution is titrated with the thorium nitrate solu -tion to a faint pink coloration. This may be seen more easily by allowing the precipitate of thorium fluoride to settle, when the pink coloration collects at the bottom of the beaker. It is essential to use either bright sunlight or mercury vapour illumination, otherwise the end-point is indistinct. 

Radium, thorium, and other radionuclides accumulate in uranium mill tailings. The potential environmental effects of these radionuclides has become of increasing concern to the public. In the future, it may be necessary to modify existing uranium recovery processes to accommodate removal of radium and perhaps other radioactive decay products of uranium. 

Data regarding the fate and transport of thorium in the air are limited. Wet and dry deposition are expected to be mechanisms for removal of atmospheric thorium. The rate of deposition will depend... 

Tried JF, Schubert J. 1961. Effect of chelating agent administration on the removal of monomeric and polymeric thorium. Rad Res 15 227-235. 

The actual discovery was made by Mile. Marguerite Perey at the Curie Institute in Paris. In 1939 she purified an actinium preparation by removing all the known decay products of this element. In her preparation she observed a rapid rise in beta activity which could not be due to any known substance. She was able to show that, while most of the actinium formed radioactinium, an isotope of thorium, by beta emission, 1.2 0.1 per cent of the disintegration of actinium occurred by alpha emission and gave rise to a new element, which she provisionally called actinium K, symbol AcK (35, 36). This decayed rapidly by beta emission to produce AcX, an isotope of radium, which was also formed by alpha emission from radioactinium. Thus AcK, with its short half-life, had been missed previously because its disintegration gave the same product as that from the more plentiful radioactinium. 

The uranium and thorium ore concentrates received by fuel fabrication plants still contain a variety of impurities, some of which may be quite effective neutron absorbers. Such impurities must be almost completely removed if they are not seriously to impair reactor performance. The thermal neutron capture cross sections of the more important contaminants, along with some typical maximum concentrations acceptable for fuel fabrication, are given in Table 9. The removal of these unwanted elements may be effected either by precipitation and fractional crystallization methods, or by solvent extraction. The former methods have been historically important but have now been superseded by solvent extraction with TBP. The thorium or uranium salts so produced are then of sufficient purity to be accepted for fuel preparation or uranium enrichment. Solvent extraction by TBP also forms the basis of the Purex process for separating uranium and plutonium, and the Thorex process for separating uranium and thorium, in irradiated fuels. These processes and the principles of solvent extraction are described in more detail in Section 65.2.4, but the chemistry of U022+ and Th4+ extraction by TBP is considered here. 

The disadvantages are reduced hardness (HV = 1250) and the fact that it is impossible to remove traces of thorium from the raw material. Due to this impurity the surroundings of the implant are exposed to radiation. 

Cation exchange in nitric acid for preferential sorption and removal of tet-ravalent thorium (192). 

Thiourea, mercury(II) chloride complexes with, 6 26 Thorium, powder by reduction of oxide with calcium, 6 50 removal of, in extraction of... 

The four commonly used isotopes of thorium (234Th,228Th, 230Th, and 232Th) are produced from the decay of uranium and radium parents (figure 7.5). Thorium is present in highly insoluble forms and can be rapidly removed by scavenging of particulate matter. 

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