pH = 11 - SKB

PDF rendering: DokumentID 1415884, Version 1.0, Status Godkänt, Sekretessklass Öppen4.2.16 Actinides (Th, Pa, U, Np, Pu, Am, Cm)4.2.16.1 ThoriumA comprehensive Th-phosphate data selection was recently performed by NEA (Randet al., 2009). The data selected by Rand et al. (2009) was obtained mainly from liquidliquiddistribution and solubility studies, although also results from qualitative studieswhere used for justifying their selection. Rand et al. (2009) also reported the lack ofrelevant data regarding Th phosphate solid phases, being then difficult to perform areliable thermodynamic data selection.For this element it is recommended to include in the Simple Functions Spreadsheettool the whole set of species selected by Rand et al. (2009) (Table 4-15). Nothermodynamic data is selected in the present work for the formation of Th phosphatesolid phases.Table 4-15. Thermodynamic data for the Th -P system as reported by Rand et al.(2009).Species Reaction Log Kº eqTh(H 2 PO 4 ) 22+Th 4+ + 2H 2 (PO 4 ) - ↔ Th(H 2 PO 4 ) 22+10.48Th(H 2 PO 4 ) 3+ Th 4+ + H 2 (PO 4 ) - ↔ Th(H 2 PO 4 ) 3+ 5.59Th(H 3 PO 4 )(H 2 (PO 4 ) 3+ Th 4+ + 2H 2 (PO 4 ) - + H + ↔ Th(H 3 PO 4 )(H 2 (PO 4 ) 3+ 9.70Th(H 3 PO 4 ) 4+ Th 4+ + H 2 (PO 4 ) - + H + ↔ Th(H 3 PO 4 ) 4+ 4.03Figure 4-18 shows a Th predominance diagram obtained by using Rand et al. (2009)data selection.34