Thermodynamic description of Tc(IV) solubility and hydrolysis in dilute to concentrated NaCl, MgCl 2 and CaCl 2 solutions

Transcription

1 Electronic Supplementry Mteril (ESI for Dlton Trnsctions. This journl is The Royl Society of Chemistry 2016 Thermodynmic description of Tc(IV solubility nd hydrolysis in dilute to concentrted NCl, MgCl 2 nd CCl 2 solutions Ezgi YALÇINTAŞ *, Xvier GAONA *, Mrcus ALTMAIER, Kthy DARDENNE, Robert POLLY, Horst GECKEIS Institute for Nucler Wste Disposl, Krlsruhe Institute of Technology, P.O. Box 3640, Krlsruhe, Germny *Corresponding uthor: ezgi.ylcints@kit.edu, xvier.gon@kit.edu 1

2 Supplementry Informtion Specific ion interction theory (SIT The SIT pproch is bsed on the extended Debye-Hückel lw, nd ccounts for the influence of electrosttic, non-specific long-rnge, binry interctions between oppositely chrged ions to clculte ctivity coefficients. SIT defines the ctivity coefficient of n ion j: log γ j = z 2 j D ε(j,k m k k (A1 where z j is the chrge of the ion j, D is the Debye-Hückel term ( D = A I m /1 + B j I m, ε(j,k is the specific ion interction coefficient of the ion j with the counter-ion k of the bckground electrolyte nd m k is the mollity of the ion k. The vlidity of SIT is considered to be limited to I 3.5 M 1. It is to note tht recent experimentl studies providing thermodynmic description of ctinide nd lnthnide systems hve demonstrted the good performnce of SIT in concentrted MgCl 2 nd CCl 2 solutions with I 13.5 M 2-4, lthough this observtion cnnot be generlized to other systems. 2

3 Pitzer model The Pitzer model describes the effect of ionic strength with short-rnge binry interctions, interctions between ions of the sme chrge, between chrged ions nd neutrl species s well s ternry interctions 5. This results in more relistic modelling of men ctivity coefficients especilly t medium nd high ionic strengths, t the cost of requiring significntly lrge number of prmeters for the clcultion of ctivity coefficients. In mixed electrolytes with ctions c, c nd nions,, the individul ctivity coefficients for ction M nd n nion X re described by equtions (A2 nd (A3, respectively: ln γ M = zm 2 F m (2 B M + Z C M c (2 Φ Mc m ψ Mc < ' m m ' ψ M' + z M c < m C c + 2 n m n nm (A2 ln γ X = zx 2 F (2 B cx + Z C cx c m (2 Φ X c ψ cx c < c' ' ψ cc'x + z X c < m C c + 2 n m n nx (A3 Z = where i m i z i, nd F includes the Debye-Hückel term nd the ionic strength dependence specific to the slt. The Pitzer model defines binry prmeters β (0 MX, β (1 MX, β (2 MX nd C (φ MX specific to the intercting ions. θ (or θ cc nd Ѱ c (or Ѱ cc re the mixing prmeters in the cse of ternry nd higher electrolyte systems nd their contribution is expected to be very smll except for mixing of non-identicl chrged species. The interctions between the ions nd the neutrlly chrged species re defined with nm (or nx. The formulism of the terms used in the Pitzer equtions re given elsewhere 5. 3

4 Comprison of Tc(IV solubility dt generted in this study nd reported in Hess et l. ( I = 0, NEA-TDB I = 0.8, 4 d, Hess et l., (2004 I = 0.8, d, Hess et l., (2004 I = 0.8, d, Hess et l., (2004 I = 1.0, 90 d, p.w I = 0, NEA-TDB I = 2.5, 3 d, Hess et l., (2004 I = 2.5, d, Hess et l., (2004 I = 2.5, 61 d, Hess et l., (2004 I = 3.0, 180 d, p.w I = 0, NEA-TDB I = 5.0, 4 d, Hess et l., (2004 I = 5.0, 11 d, Hess et l., (2004 I = 5.0, 29 d, Hess et l., (2004 I = 5.0, 520 d, p.w log [Tc(IV] slope of -1 log [Tc(IV] slope of -1 log [Tc(IV] slope of -1-9 slope of ph m -9 slope of ph m -9 slope of ph m Figure A1. Experimentl solubility dt of Tc(IV determined in the present work nd reported in Hess et l. (2004 for dilute to concentrted HCl NCl systems. Solid lines correspond to overll solubility curve of TcO 2 1.6H 2 O(s clculted for I = 0 with the current NEA TDB thermodynmic selection. Dshed lines indicte slopes of 2 nd 1 in the solubility digrm. 4

5 Liner SIT-regression plots of the solubility rections TcO 2 0.6H 2 O(s + n C H 2 O(l C n TcO(OH 5 (2n H + with n = log * K's,Cn[TcO(OH5 ]2n-3 - m D log w [TcO(OH 5 ] 3- C[TcO(OH 5 ] - C 2 [TcO(OH 5 ] + C 3 [TcO(OH 5 ] 3+ C 4 [TcO(OH 5 ] m CCl2 (mol kg -1 Figure A2. SIT-plot for the solubility rections TcO 2 0.6H 2 O(s + n C H 2 O(l C n TcO(OH 5 (2n-3 + log K 3 H + with n = 0 4 considering the conditionl equilibriuonstnts determined in dilute to concentrted CCl 2 solutions. ' s,c n TcO(OH (2n 3 5 5

6 Comprison of the plots for conditionl equilibriuonstnts for C n TcO(OH 5 (2n-3 (with n = 0 4 vs. m CCl2-30 TcO(OH 5 3- log * K' s,tco(oh Experimentl log * K' 3- s,tco(oh5-50 m (mol kg-1 CCl2 C[TcO(OH 5 ] - C 2 [TcO(OH 5 ] + log * K' s,c[tco(oh5] - Experimentl log * K' s,c[tco(oh5] - m (mol kg-1 CCl2 log * K' s,c2[tco(oh5] + Experimentl log * K' s,c2[tco(oh5] + m (mol kg-1 CCl2 log * K' s,c3[tco(oh5] 3+ C 3 [TcO(OH 5 ] 3+ Experimentl log * K' s,c3[tco(oh5] 3+ m (mol kg-1 CCl2 log * K' s,c4[tco(oh5] 5+ C 4 [TcO(OH 5 ] Experimentl log * K' s,c4[tco(oh5] m (mol kg-1 CCl2 Figure A3. Conditionl equilibriuonstnts for C n TcO(OH 5 (2n-3 (with n = 0 4 s function of CCl 2 mollity; experimentl vlues (symbols nd clculted functions bsed on the SIT (dshed line. 6

7 References 1. I. Grenthe, H. Wnner nd M. Östhols, Nucler Energy Agency, OECD, V. Neck, M. Altmier, T. Rbung, J. Lützenkirchen nd T. Fnghänel, Pure Appl Chem, 2009, 81, D. Fellhuer, V. Neck, M. Altmier, J. Lützenkirchen nd T. Fnghänel, Rdiochim Act, 2010, 98, B. Brendebch, M. Altmier, J. Rothe, V. Neck nd M. A. Denecke, Inorg Chem, 2007, 46, K. S. Pitzer, ed., Activity coefficients in electrolyte solutions, Boc Rton, FL,