Extraction of Thorium

In the acid route, the phosphate ore is digested with sulfuric acid at 230 °C for some hours and thorium phosphate is precipitated on adjusting the pH to 1. This is purified by first converting it into Th(OH)4, thence into thorium nitrate, purified as above. 

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The possibility of dissolving the mixed hydroxide in HNOs and obtaining direct extraction of thorium (and uranium) from the nitrate solution has been studied [155,156], but does not seem to be too promising, possibly due to the partial oxidation of tripositive cerium to the tetrapositive state. Kraitzer [157] was able to separate thorium from the mixed hydroxide cake by extracting the cake with sodium carbonate buffer at pH 9.5—10. Thorium was found to form a soluble carbonate complex and a recovery of better than 99% of thorium was claimed after only four extractions. 

There are various modifications of the process just described. Direct extraction of thorium from monazite after conversion to the sulphate has been considered. Recovery of thorium by selective precipitation as oxalate [145, 146], sulphate [147] or fluoride [148] has been attempted. 

It has been shown that the extraction of thorium(IV) by organophosphoric adds involves the mechanisms... 

Figure 21 An outline flowsheet for the alkaline extraction of thorium from its ore...

Even though in the THOREX process 233U can be preferentially recovered from irradiated thorium fuel by using an extraction flowsheet based on 5% TBP n-dodecane as the extractant, further lowering of the concentration of TBP in the solvent has certain advantages in terms of reduced co-extraction of thorium and fission products (195, 196). Ramanujam et al. reported a sequential precipitation technique... 

Otu, E.O. The synergistic extraction of thorium(lV) and uranium(VI) by 2-ethylhexyl phenylphosphonic acid and micelles of dinonylnaphthalene sulphonic acid, Solvent Extr. Ion Exch. 15 (1997) 1-13. 

Mohapatra, P.K. Veeraraghavan, R. Manchanda, V.K. Extraction of thorium(IV) by a mixture of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone and tri-n-octyl phosphine oxide, J. Radioanal. Nucl. Chem. 240 (1999) 31-38. 

Yaftian, M.R. Hassanzadeh, L. Eshraghi, M.E. Matt D. Solvent extraction of thorium (IV) and europium (III) ions by diphenyl-N,N-dimethylcarbamoylmethylphosphine oxide from aqueous nitrate media, Sep. Purif. Tech. 31 (2003) 261-268. 

Lin, Y. Wai, C.M. Jean, F.M. Brauer, R.D. Supercritical fluid extraction of thorium and uranium ions from solid and liquid materials with fluorinated P-Diketones and tributyl... 

Kumar, R Pal, A. Saxena, M.K. Ramakumar, K.L. Supercritical fluid extraction of thorium from tissue paper matrix employing organophosphorous reagents, Radiochim. Acta 95 (2007) 701-708. 

Extraction of thorium nitrate and europium nitrate 0 0 4 M) from 1 M HN03 into dichloromethane was carried out for 19 calixarenes totally or partially substituted on the lower rim by phosphine oxide moieties (CPol-CPol7-CPol9-CPo20) and for one calixarene substituted by phosphinate (CP0I8) (see Section 4.7).IM 152 154... 

Extraction of thorium and europium by these same compounds shows an increase from 051 to Os5 (Table 4.26). Thorium is equally extracted by the linear tetramer and pentamer, whereas europium is even better extracted by linear tetramer than by the linear pentamer. Most of the CMPO calixarenes extract europium better than TOPO and OOCMPO. All these extractants are stronger extractants of thorium than europium, because similar efficiencies require ligand concentrations of 10-3 M for... 

The equilibrium constants for the equilibria involving the formation of Th(TTA)4 B are summarised in Table 11. The extraction of thorium by TBP in presence of different betadiketones was studied109 and while no synergism was observed for HA A, with others the extraction order HBA < HDFM < HTFA was observed, the species extracted being ThA4 TBP in all the systems. 

Synergism was also observed110 in the extraction of thorium by HTTA in presence of bipyridyl, a bidentate neutral donor. However, the nature of the species extracted has not been investigated. 

Synergism in the extraction of thorium with HIPT-B mixtures was studied48,1U. The extraction of Th(IPT)4 B in these systems was well established. The formation of earlier... 

Table 11. Equilibrium constant data for the extraction of thorium by chelating acid - neutral donor combinations...

Synergism was also reported1125 in the extraction of thorium with mixtures of HDMPP and TBP. 

Thorium is known1135 to get extracted by oxine and several 1 1 neutral donor adducts of thorium oxinate were synthesised1145. Thus, mixtures of oxine and neutral extractants should provide a good combination for the synergic extraction of thorium. 

It was reported115,1165 that by the use of MIBK or n-BA as diluents, the extraction of thorium by cupferron can be accomplished at a lower pH, which suggests that cupferron and neutral extractants can be good partners for the synergic extraction of thorium. 

Mixtures of H2MEHP with neutral donors showed only antagonistic behaviour169 in the extraction of thorium from dil. HC1 and this was exploited in stripping thorium from the organic phase. 

The extraction of thorium by mixture of HTTA and TOA was studied198 and the observed synergism was attributed to the equilibrium,... 

As thorium is known to form pentakis oxinates193 or pentakis tropolonates114, extraction of thorium by oxine or tropolones in combination with amines or other cation... 

Mixtures of HIPT and HTTA were shown201 to give synergism in the extraction of thorium. In addition to the mixed chelates, several HIPT adducts of the mixed chelates were suggested to be responsible for the synergism. 

As tetravalent ions are extracted by amines as M(N03)6 synergism in combination with neutral extractants was expected203) and it was in fact observed207) in the extraction of thorium by mixtures of TDA with TBP or TOPO. 

Synergism by mixtures of different neutral donors was observed in the extraction of thorium from nitrate media101,207) and chloride media211) and that of Pu(IV) from nitric acid medium212), and the mixed solvates were assumed to be responsible for it. 

Selenophene /3-diketones can be used as extractants for the separation and isolation of metals. The advantages of selenophene /3-dike-tones were revealed by comparison of their dissociation and distribution constants with those of acetylacetone, benzoylacetone, thenoyl-trifluoromethylacetone, etc. Selenophene /3-diketones containing a trifluoromethyl group and a pyridyl radical were of particular interest. 2-Acetoacetylselenophene127 is better for the extraction of thorium from water than acetylacetone, previously extensively used. 

Kumar, R, Rao, A., and Ramakumar, K.L. (2009) Supercritical flirid extraction of thorium from tissue paper matrix employing 3-diketones. Radiochimica Acta, 97, 105-112. 

Case 1. Lower chelates in aqueous phase (hydroxyl complexes, masking effects, and adducts negligible) Particularly with multivalent metals, an appreciable fraction of the metal ion in the aqueous phase may exist as lower complexes. Thus Rydberg, in studying the extraction of thorium acetylacetonate from water... 

Using Rydberg s data for the extraction of thorium acetylacetonate (Example 23-5), calculate the complete extraction curve of E against pH for [HL] =... 

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