Complexation of thorium with phosphate

Abstract

Thorium / Phosphate / Stability constants / Solvent extraction / AKUFVESummary. Using liquid-liquid extraction and the AKUFVEtechnique developed by the Nuclear Chemistry Department at Chalmers University of Technology, Sweden, the complex formation equilibria of hydrogen phosphate (HPO 4 2− ) with thorium have been studied at different temperatures (15, 25 and 35 • C), varying pH (7, 8 and 8.7) and in 1 M (Na, H)ClO 4 . Evaluation of the acquired solvent extraction data indicated the formation of the ThHPO 4 2+ , Th(HPO 4 ) 2 (aq) and Th(HPO 4 ) 3 2− complexes. For Th(HPO 4 ) 2 (aq) and Th(HPO 4 ) 3 2− , the logarithm of the stability constants obtained at 25 • C were 17.0 ± 3.5 and 23.7 ± 0.2, respectively. Only an estimate of the stability of ThHPO 4 2+ could be obtained. Enthalpies and entropies of the complex formation reactions have been determined: Th(HPO 4 ) 2 (aq) (ΔH = 698 ± 27 kJ mol −1 , ΔS = 2669 ± 91 J mol −1 K −1 ) and Th(HPO 4 ) 3 2− (ΔH = 499 ± 4 kJ mol −1 , ΔS = 2137 ± 12 J mol −1 K −1 ).

Thermodynamic data provided through the FUNMIG project: Analyses and prospective

“…The topics of the work were: i) the analyses of previous data on americium and curium carbonates Am(CO3)n 3-2n and Cm(CO3)n 3-2n (Vercouter, 2004;, ii) europium carbonates Eu(CO3)n 3-2n (Vercouter, 2004;Vercouter et al, 2005c), iii) dedicated experiments on thorium phosphates Th(H2PO4)n 4-2n (Ekberg et al, 2010), iv) dedicated experiments on uranium(VI) sulphates UO2(SO4)n 2-2n (Vercouter et al, 2008), and analysis of previous trivalent lanthanide sulphates Ln(SO4)n 3-2n (Vercouter et al, 2005b), v) dedicated experiments on trivalent actinides and europium silicates (Vercouter et al, 2009a;2009c).…”

“…The resulting speciation is shown in Figure 6b, using the SIT, as function of pH at 0.1 mol/L (NaClO4) and [PO4]total = 10 -4 mol/L. Under these conditions, the phosphate complexes proposed by Ekberg et al (2010) would dominate over the hydroxo complexes of Th(IV) in a larger pH range.…”

“…It can be seen that the speciation changes completely. The adequacy or reliability of the constants obtained by Ekberg et al (2010) cannot be tested in front of analogue elements data given that no data for tetravalent actinide aqueous phosphate are available in the literature under circumneutral pH conditions, as pointed out by Rand et al (2009). The importance of ThHPO4 2+ can also be questioned as its log10β°1 value is only estimation.…”

“…Figure 12. Effect of the Th(HPO4)n 4-2n complexes proposed in Ekberg et al (2010), and extrapolated in Table 2 on the solubility at pH 8 and I = 0.1 mol NaClO4 /L of ThO2(am,hyd,aged) (dotted) and ThO2(am,hyd,fresh) (plain) from Rand et al (2009).…”

Is DTPA a good competing chelating agent for Th(IV) in human serum and suitable in targeted alpha therapy?

“…The second one corresponds to carbonate, CO 3 2-being the synergistic anion allowing the complexation with iron and other metal ions [21]. Finally, the third one is HPO 4 2-, phosphate ions being present in the blood serum and being known to be a strong complexing agent for Th(IV) in environmental samples [30].…”