Thorium production

The physical and chemical properties of elemental thorium and a few representative water soluble and insoluble thorium compounds are presented in Table 3-2. Water soluble thorium compounds include the chloride, fluoride, nitrate, and sulfate salts (Weast 1983). These compounds dissolve fairly readily in water. Soluble thorium compounds, as a class, have greater bioavailability than the insoluble thorium compounds. Water insoluble thorium compounds include the dioxide, carbonate, hydroxide, oxalate, and phosphate salts. Thorium carbonate is soluble in concentrated sodium carbonate (Weast 1983). Thorium metal and several of its compounds are commercially available. No general specifications for commercially prepared thorium metal or compounds have been established. Manufacturers prepare thorium products according to contractual specifications (Hedrick 1985). 

There are several processes for commercial thorium production from monazite sand. They are mostly modifications of the acid or caustic digestion process. Such processes involve converting monazite to salts of different anions by combination of various chemical treatments, recovery of the thorium salt by solvent extraction, fractional crystallization, or precipitation methods. Finally, metalhc thorium is prepared by chemical reduction or electrolysis. Two such industrial processes are outlined briefly below. 

Iodine is obtained by oxidizing iodides from seawater or brines using Cl2, concentrated H2S04, Fe3+, or other oxidizing agents. Astatine is produced naturally by the radioactive decay of uranium or thorium. Production of At is also accomplished by bombarding Bi with alpha particles,... 

Figure 5.59. Thorium production assumed in the safe nuclear scenario, given as kt of thorium oxide per year for each country (Sorensen, 1999).

The world s consumption of monazite is estimated at about 3000 tons per year. Three-fourths of the world s supply of monazite in 1915 came from India, and since this ore contains a higher per cent of thoria, this corresponds to 90 per cent of the thorium production. This is used for its thorium content, which determines the price of the mineral. During 1920 monazite sand with a guaranteed minimum of 6 per cent Th02 ranged in price from 25 to 30 per unit,1 duty paid. Thorium nitrate sold wholesale for 3.75 to 4 per pound,... 

Until recently, most U.S. thorium production has been as a by-product of monazite processing from placer deposits in Florida, Georgia, and South Carolina. Some bastnaesite has been mined at Mountain Pass, San Bernardino, California. 

Table 6.15 summarizes two sources of information on the annual rate of thorium production, by country. The first three columns give the production rate of monazite concentrates for the more recent years of 1976, 1977, and 1978 [El]. We have estimated total thorium production from a typical monazite thorium content of 6 weight percent (w/o). These columns do not include monazite production in the United States or Soviet Union, nor the small production of other thorium minerals. The last two columns give the U.S. Bureau of Mines figures [Ul] for total thorium production in 1973 and an estimate of total thorium production capacity in 1980, if demand were such as to support it. 

In the second contacting unit, thorium is stripped from the rich solvent by 0.1 A HNO3 uranium is scrubbed from the thorium product by additional solvent. 

Heat balances for Iowa process. To show the need for addition of the booster ZnCl2 tCT the charge, Table 6.23 shows that when 1 mol Thp4 and 2 mol CaCl2 at 475°C (748 K) react to produce 1 mol liquid Th and 2 mol liquid CaF2 at the melting point of thorium (1750°C or 2023 K), there is an enthalpy deficiency of 12.84 kcal/g-mol thorium. It would thus be impossible to melt the thorium product and obtain massive thorium metal free of CaF2 from these reactants preheated to 475°C. 

Table 6.25 gives the material balance for the Iowa process as described by Wilhelm [W2], Table 6.26 gives the heat balance for this process, with reactants at 475°C (748 K) and products molten at 1360 C (1633 K). An excess of 17.7 kcal/mol thorium product was available to compensate for heat losses. 

R2. Ross, A. M. Quoted by F. L. Cuthbert, Thorium Production Technology, Addison-Wesley, Reading, Mass., 1958, p. 128. 

Uranium in the partially stripped thorium stream IBXT leaving the IBX column was extracted from the thorium in the IBS column by additional 30 v/o TBP in dodecane containing 0.01 M HNO3. The aqueous stream leaving IBX was the crude thorium product IBT. The organic stream HAO leaving IBS contained some uranium and thorium and was recycled to the HA column. 

Process results. Decontamination factors observed by Kuchler et al. [K7] in processing 54,000 MWd/MT fuel with thorium/uranium ratio of 5.9, cooled 346 days, are listed in Table 10.19. Uranium losses were 0.012 percent to thorium product, 0.004 percent to solvent from 2C, and... 

Thorium Iodide, Thorium tetraiodide. I4Th mol wt 739.69. I 68.63%, Th 31,37%. Thl4. Prepd hy passing iodine vapors in an inert gas over the metal at elevated temp Allen, Yost, J. Chem. Phys. 22, 855 (1954). See also Cuthbert, Thorium Production Technology (Addison-Wesley, Reading, Mass., 1958). 

Fig. S.8. Stirred bed plant for the production of thorium tetrafluoride (From F. L. Cnthbert, Thorium Production Technology, 1958, Addison-Weslq, ...

Impurity ppm in Thorium product ppm in crude Thorium feed... 

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