Thorium dissolved

I. In this method, Th is quantitatively precipitated as the phosphate, together with a small amoimt of rare earth phosphates this is accomplished by neutralization and dilution of the solution. The phosphates are dissolved in cone, hydrochloric acid and precipitated with oxalic acid, and the thoroughly washed precipitate is extracted with warm aqueous NagCOa. Most of the rare earths stay in the residue, while the thorium dissolves in the form of a carbonate complex, NaeTh(C03)s. The material is freed of the remaining traces of rare earths by repeated crystallization in the form of the sulfate Th(S04,)a 8H3O. The procedure consists of precipitation of the hydroxide with ammonia and solution of the latter in sulfuric acid to re-form the sulfate. The precipitate from the last purification stage is dissolved in nitric acid to yield the nitrate. 

Oxidized chalcogens. Thorium dissolves as Th", but not readily, in H2SO4. Metallic Pa is attacked, but only briefly, by 2.5-M H2SO4. Uranium dissolves slowly... 

Mona.Zlte, The commercial digestion process for m on a site uses caustic soda. The phosphate content of the ore is recovered as marketable trisodium phosphate and the rare earths as RE hydroxide (10). The usual industrial practice is to attack finely ground m on a site using a 50% sodium hydroxide solution at 150°C or a 70% sodium hydroxide solution at 180°C. The resultant mixed rare-earth and thorium hydroxide cake is dissolved in hydrochloric or nitric acid, then processed to remove thorium and other nonrare-earth elements, and processed to recover the individual rare earths (see... 

There are a number of minerals in which thorium is found. Thus a number of basic process flow sheets exist for the recovery of thorium from ores (10). The extraction of mona ite from sands is accompHshed via the digestion of sand using hot base, which converts the oxide to the hydroxide form. The hydroxide is then dissolved in hydrochloric acid and the pH adjusted to between 5 and 6, affording the separation of thorium from the less acidic lanthanides. Thorium hydroxide is dissolved in nitric acid and extracted using methyl isobutyl ketone or tributyl phosphate in kerosene to yield Th(N02)4,... 

Most mineral acids react vigorously with thorium metal. Aqueous HCl attacks thorium metal, but dissolution is not complete. From 12 to 25% of the metal typically remains undissolved. A small amount of fluoride or fluorosiUcate is often used to assist in complete dissolution. Nitric acid passivates the surface of thorium metal, but small amounts of fluoride or fluorosiUcate assists in complete dissolution. Dilute HF, HNO, or H2SO4, or concentrated HCIO4 and H PO, slowly dissolve thorium metal, accompanied by constant hydrogen gas evolution. Thorium metal does not dissolve in alkaline hydroxide solutions. 

Assay of beryUium metal and beryUium compounds is usuaUy accompHshed by titration. The sample is dissolved in sulfuric acid. Solution pH is adjusted to 8.5 using sodium hydroxide. The beryUium hydroxide precipitate is redissolved by addition of excess sodium fluoride. Liberated hydroxide is titrated with sulfuric acid. The beryUium content of the sample is calculated from the titration volume. Standards containing known beryUium concentrations must be analyzed along with the samples, as complexation of beryUium by fluoride is not quantitative. Titration rate and hold times ate critical therefore use of an automatic titrator is recommended. Other fluotide-complexing elements such as aluminum, sUicon, zirconium, hafnium, uranium, thorium, and rate earth elements must be absent, or must be corrected for if present in smaU amounts. Copper-beryUium and nickel—beryUium aUoys can be analyzed by titration if the beryUium is first separated from copper, nickel, and cobalt by ammonium hydroxide precipitation (15,16). 

Like many chemical species, thorium exhibits a great affinity for particle surfaces in the marine environment. These other species and thorium are referred to as particle reactive because they are readily removed from the dissolved phase onto the particulate phase. Thorium exists as a hydrolyzed species in seawater, Th(OH) " , and is thus extremely particle reactive. Because of its particle-reactive nature, thorium has been used to examine scavenging as an analog for other... 

Thorinm-232 is the only non-radiogenic thorium isotope of the U/Th decay series. Thorinm-232 enters the ocean by continental weathering and is mostly in the particulate form. Early measurements of Th were by alpha-spectrometry and required large volume samples ca. 1000 T). Not only did this make sample collection difficult, but the signal-to-noise ratio was often low and uncertain. With the development of a neutron activation analysis " and amass spectrometry method " the quality of the data greatly improved, and the required volume for mass spectrometry was reduced to less than a liter. Surface ocean waters typically have elevated concentrations of dissolved and particulate 17,3 7,62... 

The separation of basic precipitates of hydrous Th02 from the lanthanides in monazite sands has been outlined in Fig. 30.1 (p. 1230). These precipitates may then be dissolved in nitric acid and the thorium extracted into tributyl phosphate, (Bu"0)3PO, diluted with kerosene. In the case of Canadian production, the uranium ores are leached with sulfuric acid and the anionic sulfato complex of U preferentially absorbed onto an anion exchange resin. The Th is separated from Fe, A1 and other metals in the liquor by solvent extraction. 

Figure 1. Schematic diagram showing a TRU-spec extraction chromatography method for separation of uranium, thorium, protactinium, and radium from a single rock aliquot. Further purification for each element is normally necessary for mass spectrometric analysis. Analysis of a single aliquot reduces sample size requirements and facilitates evaluation of uranium-series dating concordance for volcanic rocks and carbonates. For TIMS work where ionization is negatively influenced by the presence of residual extractant, inert beads are used to help remove dissolved extractant from the eluant.

Bacon MP, Anderson RF (1982) Distribution of thorium isotopes between dissolved and particulate forms in the deep sea. J Geophys Res 87 2045-2056... 

Bacon MP, Spencer DW, Brewer PG (1976) Pb-210/Ra-226 and Po-210/Pb-210 disequilibria in seawater and snspended particulate matter. Earth Planet Sci Lett 32 277-296 Bacon MP, Anderson RF (1982) Distribution of thorium isotopes between dissolved and particulate forms in the deep sea. J Geophys Res 87 2045-2056... 

McKee BA, DeMaster DJ, Nittrouer CA (1984) The use of Th-234/U-238 disequilibrium to examine the fate of particle-reactive species on the Yangtze continental shelf. Earth Planet Sci Lett 68 431-42 McKee BA, DeMaster DJ, Nittrouer CA (1986) Temporal variability in the portioning of thorium between dissolved and particulate phases on the Amazon shelf Implications for the scavenging of particle-reactive species. Cont Shelf Res 6 87-106... 

Figure 9. Variations of uranium (a) and thorium (b) contents in the filtrates of a sample as a function of the filtration size, and relation with the variations of the dissolved organic carbon (DOC). Data sources (1) Viers et al. (1997), (2) Dupre et al. (1999), (3) Porcelh et al. (1997, 2001), (4) Riotte et al. (2003). Filtrates are recovered by tangential ultra-filtration. Low filtration sizes are usually given in Dalton—a molecular weight unit of 1 g/mol—and are ranging between 3 and 300 kD. These filtration sizes have been converted here into an approximate rm pore size.

Chen JH, Edwards RL, Wasserburg GJ (1992) Mass spectrometry and applications to uranium-series disequilibrium. ln Uranium-series Disequilibrium Applications to Earth, Marine and Environmental Sciences. Ivanovich M, Harmon RS (eds) Clarendon Press, Oxford, p 174-206 Cheng H, Edwards RL, Hoff J, Gallup CD, Richards DA, Asmerom Y (2000) The half lives of manium-234 and thorium -230. Chem Geol 169 17-33Church TM, Sarin MM, Fleisher MQ, Ferdelman TG (1996) Salt marshes An important coastal sink for dissolved uranium. Geochim Cosmochim Acta 60 3879-3887... 

In most uranium ores the element is present in several, usually many diverse minerals. Some of these dissolve in sulfuric acid solutions under mild conditions, while others may require more aggressive conditions. Thus, while it may be comfortable to recover 90-95% of the uranium present, it may be tough or impractical to win the balance amount of a few percent economically. Some of the most difficult uranium minerals to leach are those of the multiple oxide variety, most commonly brannerite and davidite. These usually have U(IV) as well as U(VI), together with a number of other elements such as titanium, iron, vanadium, thorium, and rare earths. To extract uranium from these sources is not as easy as other relatively simpler commonly occurring sources. 

Baskaran et al. [30] pumped seawater at 35l/min and collected dissolved species on cartridges prior to determining radium, thorium, and lead by y counting methods. 

Bacon and Anderson [42] determined 230thorium and 228thorium concentrations, in both dissolved and particulate forms, in seawater samples from the eastern equatorial Pacific. The results indicate that the thorium isotopes in the deep ocean are continuously exchanged between seawater and particle surfaces. The estimated rate of exchange is fast compared with the removal rate of the particulate matter, suggesting that the particle surfaces are nearly in equilibrium with respect to the exchange of metals with seawater. 

---