Hydrolysis of thorium

The compound also can be prepared by many other methods including thermal decomposition of thorium oxalate, hydroxide, carbonate, or nitrate. Heating thorium metal in oxygen or air, and hydrolysis of thorium halides also yield thorium dioxide. 

Tetravalent. The hydrolysis of tetravalent actinide ions can begin to occur in solutions with pH levels < 2. Under dilute conditions, species of the form An(OH) " (n = 1 4) are predicted however, most hydrolysis studies have only been able to identily the first hydrolysis product, An(OH) +. It should be noted that in all of these compounds the remainder of the coordination sphere is made up of bound H2O molecules. The end member of the speciation is the neutral An(OH)4 or An02-2H20. This complex has low solubihty but has been postulated to exist in solutions from solubihty experiments when using the isolated solid as the starting material. Under more concentrated conditions, polymeric materials have been postulated. In modeling the hydrolysis of thorium at concentrations greater than mM, polynuclear species of the form Th2(OH)2 +, Th2(OH)4 +, Th4(OH)g +, Th6(OH)i4 +, and so on, have been included. 

Similarly, the hydrolysis of thorium(IV) can be accounted for on the assumption of a series of polynuclear complexes Th[(OOH)Th] ", where n has values exceeding 6 in certain cases. ... 

A number of papers give only quahtative information on the hydrolysis of thorium [1930CHA/SOU], [1947SCH/FAU], [1948SOU], [1954FAU], [1960MAT/ABR],... 

Bilinski, H., Ingri, N., Precipitation and hydrolysis of thorium(lV) in aqueous solution. V. Studies of the system thorium nitrate-ammonium oxalate, Croat. Chem. Acta, 39, (1967), 235-243. Cited on pages 156,502,503. 

Sergeev, G. M., Almazova, V. D., Reaction of thorium(IV) with organic acids in aqueous solutions. I. Hydrolysis of thorium ions, Tr. Khim. Khim. TekhnoL, 1, (1970), 31-35. Cited on pages 135, 527. 

PER] Pershin, A. S., Hydrolysis of thorium nitrate, Sov. Radiochem., 14,... 

Davydov, Yu. P., Toropov, I. G., Hydrolysis of thorium(4+) cations with formation of polynuclear hydroxo complexes in solutions, Dokl. Akad. Nauk Belarusi, 36, (1992), 229-233, in Russian. Cited on page 593. 

Table 21.1 Hydrolysis of thorium (/y) and uranium (iv) in solutions of various ionic strengths I and temperatures t. M ium NaJl)ClO, if not otherwise stated. Constants pPZm listed refer to the acid dissociation equilibria + n H2O M (OH) + IIH. ...

Hydrolysis of thorium(IV) ions in lithium and potassium chloride media. Bull. Soc. Chim. Beograd, 46, 657-661. 

Alkoxide gels, 23 60 Alkoxide gels, in optical fiber manufacturing, 11 145 Alkoxide initiators, 14 259 Alkoxide ligands, thorium, 24 770 Alkoxides, 12 190 25 72-86 controlled hydrolysis of, 23 56 iron, 14 533 mixed-metal, 25 100 titanium, 25 82 uranium complexation with,... 

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. 

Although the exact extentis not known accurately, hydrolysis of various salts is known to occur. Since the hydroxide is not precipitated it is assumed that the hydrolysis product is some ion on the form Th(OH)2++ orThOHJ+. The solution chemistry of thonum is made more complicated because of the hydrolytic phenomena observed and the polynuclear complex ions that are formed at low acidities and higher thorium concentrations. 

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. 

More recently a flowsheet has been developed which employs 30% TBP/OK as the solvent.349-446 447 This involves the use of an acid feed to the first cycle to assist in zirconium decontamination and suppress hydrolysis. An acid-deficient partition cycle then follows in which the U-Th separation is effected. A pilot plant (JUPITER) has been constructed at Julich in Germany to process Th02/U02 fuel using this flowsheet. Although a complete separation of thorium, uranium and FPs is possible using TBP in the Thorex process,448 alternative approaches... 

A different type of bridging occurs in hydrolysis complexes of tho-rium(IV) (219) and uranium(IV) (130). Here a distinct peak at 3.94(2) A in the hydrolyzed solutions can be ascribed to the metal-metal distances in the hydrolysis complexes. Discrete dinuclear complexes with a very similar metal-metal distance, 3.988(2) A, in which the metal atoms are joined by double hydroxo bridges have been found in crystals ofTh2(OH2)(N03)6(H20)8 (229). The same type of bridging, therefore, must occur in solution. When hydrolysis is increased, however, the number of metal-metal distances per metal atom increases beyond a value of 0.5, valid for a dinuclear complex, and larger hydrolysis complexes are obviously formed. These structures are unknown but an extensive X-ray investigation of highly hydrolyzed thorium(IV) solutions has shown that there is probably no close relation between the structures of the hydrolysis complexes in solution and the structure of thorium dioxide, which is the ultimate product of the hydrolysis process (230). 

Lieser K. H. and Hill R. (1992) Hydrolysis and colloid formation of thorium in water and consequences for its migration behavior comparison with uranium. Radiochim. Acta 56(1), 37-45. 

Early work" established that Cu", Ni" and Co" promote the hydrolysis of glycinamide in the pH range 9.35 to 10.35 at temperatures of 6.5 to 75 °C. Bamann and his collaborators carried out an extensive series of studies on the metal ion-promoted hydrolysis of peptides and related compounds" and a review of this early work is available." Highly charged ions such as thorium(IV) were found to promote the hydrolysis of leucylglycylglycine at pH values as low as 5. The thorium(IV) species is very extensively hydrolyzed at this pH and the reaction is presumably heterogeneous. Gel hydrolysis is effective at relatively low temperatures (37 °C), whereas observable effects were only obtained with such ions as copper(II) at temperatures of ca. 70 °C. 

The release of uranium and thorium from minerals into natural waters will depend upon the formation of stable soluble complexes. In aqueous media only Th is known but uranium may exist in one of several oxidation states. The standard potential for the oxidation of U in water according to equation (2) has been re-evaluated as E° - 0.273 0.005 V and a potential diagram for uranium in water at pH 8 is given in Scheme 3. This indicates that will reduce water, while U is unstable with respect to disproportionation to U and U Since the Earth s atmosphere prior to about 2 x 10 y ago was anoxic, and mildly reducing, U " would remain the preferred oxidation state in natural waters at this time. A consequence of this was that uranium and thorium would have exhibited similar chemistry in natural waters, and have been subject to broadly similar redistribution processes early in the Earth s history. Both U " and Th are readily hydrolyzed in aqueous solutions of low acidity. A semiquantitative summary of the equilibrium constants for the hydrolysis of actinide ions in dilute solutions of zero ionic strength has been... 

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