Thorium cations

Thiol compounds 252, 254 Thione compounds 252, 254 Thiosemicarbazides, N-aryl- 248 Thiourea 107, 246,254, 269, 337 -, derivatives 322, 323 Thorium cations 144 Threonine 246 Thymol 153, 197, 198 -, derivatives 288 Tigogenin 59, 195 -, acetate 63 Tigogenone 59,60 Tillmans reagent 256 Tin, cations 144,311,398 -, organic derivatives see Organotin compounds... 

A successful process has been developed by the National Chemical Laboratory using cellulose phosphate as a cation-exchange material for the purification of thorium from rare earth elements. Monazite sand is broken with sulphuric acid and extracted with water to give a solution of thorium and rare earth sulphates and phosphates. This is first treated with metallic iron or aluminium to reduce the ferric iron impurity to the ferrous condition. The solution is then fed through a colunm of cellulose phosphate to absorb the thorium. Some of the thorium is present in solution as a cationic phosphate complex, rather than as simple thorium cations, but both forms are retained by the column to a high degree. Rare earth elements, which predominate in the feed solution, are not appreciably absorbed, and the ratio of thorium to rare earths is increased to about 450. ... 

Thorium was recently the focus of an environmental problem on extracting rare earths from ores, such as mon-azite. Actually thorium can be utilised for nuclear fertile material, thus the electrochemical process is one of the promising techniques of separation from rare earth elements. One of the systematic studies on the chemistry of the compounds containing thorium was the development of molten salt reactors [1]. To investigate the relationship between the electrochemical behaviour and physico-chemical properties of thorium is important for process design, but structural information of the related materials is still limited [2], Thus, EXAFS analysis of molten thorium fluoride in mono- and divalent cationic fluoride mixtures was systematically carried out to elucidate the variation in local structure of thorium cation in various melts. 

In contrast to the relatively simple tendency of the local structure around Th" in monovalent cationic fluoride mixtures, the additional effect of a divalent cation is slightly complicated. The CaF2 concentration dependence of local structural parameters derived from EXAFS of the constant concentration of %i,p4 = 0.25 are shown in Figure 6.7.4. Although the inter-ionic distance is independent from the concentration of CaF2, the coordination number, Debye-Waller factor and C3 cumulant parameter increase until the concentration of XcaF2 = 0.17, but these values decrease with increases at XcaF2 > 0.17. The local structure of thorium cation is unstabilised up to a certain concentration of calcium fluoride and is then stabilised by further addition of calcium fluoride. 

Phosphorus Donors. Phosphine coordination complexes of thorium are rare because the hard Th(IV) cation favors harder ligand donor types. The only stable thorium—phosphine coordination complexes isolated as of the mid-1990s contain the chelating ligand,... 

Complex salts of thorium fluorides have been generated by interaction of ThF with fluoride salts of aLkaU or other univalent cations under molten salt conditions. The general forms of these complexes are [ThF ] [15891 -02-8] ThFJ [1730048-0] and [ThF ] [56141-64-1], where typical countercations are LC, Na", K", Cs", NH" 4, and N2H" 3. Additional information on thorium fluorides can be found in the Hterature (81). 

Fluoride, in the absence of interfering anions (including phosphate, molybdate, citrate, and tartrate) and interfering cations (including cadmium, tin, strontium, iron, and particularly zirconium, cobalt, lead, nickel, zinc, copper, and aluminium), may be determined with thorium chloranilate in aqueous 2-methoxyethanol at pH 4.5 the absorbance is measured at 540 nm or, for small concentrations 0-2.0 mg L 1 at 330 nm. 

Even when modifiers are not necessary for cement formation, they can lead to improved cement properties. Kingery (1950b) also examined this effect. He found that optimum bonding was achieved with cations that had small ionic radii and were amphoteric or weakly basic, such as beryllium, aluminium, magnesium and iron. By contrast, cations that were highly basic and had large ionic radii, for example calcium, thorium and barium, had a detrimental effect on bonding. 

Spinels. There are limited experimental data on uranium and thorium partitioning between magnetite and melt (Nielsen et al. 1994 Blundy and Brooker 2003). Both studies find U and Th to be moderately incompatible. Blundy and Brooker s results for a hydrous dacitic melt at 1 GPa and 1025°C give Du and D h. of approximately 0.004. The accuracy of these values is compromised by the very low concentrations in the crystals and the lack of suitable SIMS secondary standards for these elements in oxide minerals. Nonetheless, these values are within the range of Djh of magnetites at atmospheric pressure 0.003-0.025 (Nielsen et al. 1994). It is difficult to place these values within the context of the lattice strain model, firstly because there are so few systematic experimental studies of trace element partitioning into oxides and secondly because of the compositional diversity of the spinels and their complex intersite cation ordering. 

As shown by Grandstaff (1976) the cations, thorium, lead and the rare earths, associated with uraninite retard the dissolution of UO2 significantly. 

Humic acids and fulvic acids interact with a wide variety of cations. In addition to interacting with iron and aluminium, the species with which they are complexed in soils (57), they also form stable complexes with zirconium, thorium, the lanthanides and the uranyl ion. In the case of uranium it has been suggested that humic acids could be of considerable importance in the geological formation of secondary deposits of uranium (58). 

The apparent failure of trivalent and tetravalent cations to enter plants could result from the interaction of the cations with the phospholipids of the cell membranes. Evidence for such interactions is provided by the use of lanthanum nitrate as a stain for cell membranes (143) while thorium (IV) has been shown to form stable complexes with phospholipid micelles (144). However, it is possible that some plant species may possess ionophores specific to trivalent cations. Thomas (145) has shown that trees such as mockernut hickory can accumulate lanthanides. The proof of the existence of such ionophores in these trees may facilitate the development of safeguards to ensure that the actinides are not readily transported from soil to plants. 

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. 

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