Thorium aqueous solutions

Oxo Ion Salts. Salts of 0x0 ions, eg, nitrate, sulfate, perchlorate, hydroxide, iodate, phosphate, and oxalate, are readily obtained from aqueous solution. Thorium nitrate is readily formed by dissolution of thorium hydroxide in nitric acid from which, depending on the pH of solution, crystalline Th(N02)4 5H20 [33088-17 ] or Th(N02)4 4H20 [33088-16-3] can be obtained (23). Thorium nitrate is very soluble in water and in a host of oxygen-containing organic solvents, including alcohols, ethers, esters, and ketones. Hydrated thorium sulfate, Th(S0 2 H20, where n = 9, 8, 6, or 4, is... 

With Acyl Halides, Hydrogen Halides, and Metallic Halides. Ethylene oxide reacts with acetyl chloride at slightly elevated temperatures in the presence of hydrogen chloride to give the acetate of ethylene chlorohydrin (70). Hydrogen haUdes react to form the corresponding halohydrins (71). Aqueous solutions of ethylene oxide and a metallic haUde can result in the precipitation of the metal hydroxide (72,73). The haUdes of aluminum, chromium, iron, thorium, and zinc in dilute solution react with ethylene oxide to form sols or gels of the metal oxide hydrates and ethylene halohydrin (74). 

The minerals on which the work was performed during the nineteenth century were indeed rare, and the materials isolated were of no interest outside the laboratory. By 1891, however, the Austrian chemist C. A. von Welsbach had perfected the thoria gas mantle to improve the low luminosity of the coal-gas flames then used for lighting. Woven cotton or artificial silk of the required shape was soaked in an aqueous solution of the nitrates of appropriate metals and the fibre then burned off and the nitrates converted to oxides. A mixture of 99% ThOz and 1% CeOz was used and has not since been bettered. CeOz catalyses the combustion of the gas and apparently, because of the poor thermal conductivity of the ThOz, particles of CeOz become hotter and so brighter than would otherwise be possible. The commercial success of the gas mantle was immense and produced a worldwide search for thorium. Its major ore is monazite, which rarely contains more than 12% ThOz but about 45% LnzOz. Not only did the search reveal that thorium, and hence the lanthanides, are more plentiful than had previously been thought, but the extraction of the thorium produced large amounts of lanthanides for which there was at first little use. 

Since transport by water is virtually the only available mechanism for escape, we will be predominantly concerned with the chemistry of aqueous solutions at the interface with inorganic solids - mainly oxides. These will be at ordinary to somewhat elevated temperatures, 20-200 C, because of the heating effects of radioactive decay during the first millennium. The elements primarily of interest (Table I) are the more persistent fission products which occur in various parts of the periodic table, and the actinides, particularly uranium and thorium and, most important of all, plutonium. 

Thorium sulfate, being less soluble than rare earth metals sulfates, can be separated by fractional crystallization. Usually, solvent extraction methods are applied to obtain high purity thorium and for separation from rare earths. In many solvent extraction processes, an aqueous solution of tributyl phosphate is the extraction solvent of choice. 

Finely-ground monazite is treated with a 45% NaOH solution and heated at 138°C to open the ore. This converts thorium, uranium, and the rare earths to their water-insoluble oxides. The insoluble residues are filtered, dissolved in 37% HCl, and heated at 80°C. The oxides are converted into their soluble chlorides. The pH of the solution is adjusted to 5.8 with NaOH. Thorium and uranium are precipitated along with small quantities of rare earths. The precipitate is washed and dissolved in concentrated nitric acid. Thorium and uranium are separated from the rare earths by solvent extraction using an aqueous solution of tributyl phosphate. The two metals are separated from the organic phase by fractional crystallization or reduction. 

Elemental composition (in anhydrous salt) Th 48.33%, N 11.67%, O 40.00%. The aqueous solution may be analyzed for thorium (See Thorium) and for nitrate ion by ion chromatography, nitrate ion-specific electrode, and colorimetric methods. The water of crystaUization can be determined by DTA, TGA, and other gravimetric methods. 

In aqueous solution, thorium exists as Th(IV), and no definitive data have been presented for the presence of lower-valent thorium ions in this medium. The standard potential for the Th(IV)/Th(0) couple has not been determined from experimental electrochemical data. The values presented thus far for the standard reduction potential have been calculated from thermodynamic data or estimated from spectroscopic measurements. The standard potential for the four-electron reduction of Th(IV) ions has been estimated as —1.9 V in two separate references 12. The reduction of Th(OH)4 to Th metal was estimated at —2.48 V in the same two publications. Nugent et al. calculated the standard potential for the oxidation ofTh(III) to Th(IV) as +3.7 V versus SHE, while Miles provides a value of +2.4 V [13]. The standard potential measurements from studies in molten-salt media have been the subject of some controversy. The interested reader is encouraged to look at the summary from Martinot [10] and the original references for additional information [14]. 

Thorium Dihydrogen Orihoarsenate, Th(H2As04)4.4H20, is obtained in a manner similar to the above, using 50 per cent, aqueous arsenic acid and thorium nitrate solution containing the equivalent of 5 per cent, thoria. It separates as colourless crystals. The salt is converted to the nronohydrogen salt by the action of water. 

Several attempts have been made to correlate the adsorptivity of hydrolyzable cations to the composition of the species in aqueous solution (1, 2, 20). In particular, the adsorption of thorium on silver halides indicated a very close relationship between the change in the amount of thorium adsorbed and the concentration of the hydrolyzed soluble species in solution (19). The major difficulty in this type of work is the lack of quantitative data on the hydrolysis of various metal ions. The other uncertainty is with regard to the knowledge of the true surface area of the adsorbent in aqueous solution. This latter information is needed if surface coverages are to be evaluated. 

Debye and Naumann first showed that Rayleigh scattering could be used to estimate the molecular weight of low molecular weight solutes in aqueous solution (9). Since then the technique has been used to estimate the degree of aggregation in solute metal hydrolysis products for many cation and anion systems (42). A recent example is the study of thorium reported by Hentz and Tyree (16). The reader is urged to compare the results of the two studies on the same system. 

It is of considerable interest to note that charge clusters can be formed in aqueous solutions and used to target dissolved radioactive materials. In experiments using low-level, naturally radioactive thorium, a considerable reduction of thorium from the solution has been achieved [6]. Charge clusters can be produced in air under various pressures [23]. However, not all arcs and sparks... 

In spite of considerable similarities between the chemical properties of lanthanides and actinides, the trivalent oxidation state is not stable for the early members of the actinide series. Due to larger ionic radii and the presence of shielding electrons, the 5f electrons of actinides are subjected to a weaker attraction from the nuclear charge than the corresponding 4f electrons of lanthanides. The greater stability of tetrapositive ions of actinides such as Th and Pu is attributed to the smaller values of fourth ionization potential for 5f electrons compared to 4f electrons of lanthanides, an effect that has been observed in aqueous solution of Th and Ce (2). Thus, thorium... 

Principle of Separation. Uranium forms a nitrate complex that is extractable into ethyl acetate (as well as other organic extractants). Thorium does not readily form an extractable nitrate complex. When ethyl acetate is contacted with an aqueous solution, the uranium-nitrate complex is partitioned favorably into the ethyl acetate whereas thorium nitrate is not. The distribution of the metal ion between the two phases is expressed as D = Corganic/Caqueous where C is the concentration in moles or dps per unit volume in the respective phases. The thorium remains in the aqueous phase and is precipitated as the hydroxide for counting. 

Step 5. Pipette 1 mL Nd carrier (1 mg/mL) into the aqueous solution in the centrifuge tube and mix. Add 1 mL 6 M NH4OH with stirring to precipitate Nd(OH)3 and co-precipitate thorium. 

Uranium and thorium can be determined by GC in aqueous solutions as ternary complexes with hexafluoroacetylacetone and dibutyl sulphoxide [645]. The extraction was performed with a solution of both reagents at concentrations 2—5-fold higher than the concentration of the ions. The best separation was obtained on a column packed with 17.8% of QF-1 on Chromosorb W. With a TCD, the detection limits were 0.4 mg/ml of thorium and 0.6 mg/ml of uranium. 

Examples of thenoyltrifluoroacetone (TTA) (in benzene) extraction can be found in the separation of. 3.8-minute V 2 in. neutron activation analysis (90), of zirconium activities in niobium bombarded by protons (128), and of 1.8-minute Pa22 from the reaction products of thorium bombarded.by a cyclotron (172,173,175)- 16-second Y89"1 (109) and 25-minute Am246 (74), the daughter products of Zr and Pu2 respectively, were separated by back extraction into acidic aqueous solution from the parent in TTA-benzene solution. 

---