Alekseev, E.

Altmaier, M.

Gaona, X.

Geckeis, H.

Hinz, K.

Rabung, Th.

Schild, D.

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KIT – Universität des Landes Baden-Württemberg und nationales Forschungszentrum in der Helmholtz-Gemeinschaft Interaction of An(III/IV/V/VI) with borate in dilute to concentrated alkaline NaCl, CaCl2 and MgCl2 solutions Solubility of Nd(III) // Cm(III)–TRLFS studies in NaCl, MgCl2 and CaCl2 solutions  6 7 8 9 10 11 12-9-8-7-6-5-4-3-2 pHclog[Nd]pHmax(MgCl2)pHmax(CaCl2)present work (2013) 3.5 M MgCl2 - 0.004 M [B]tot 3.5 M MgCl2 -   0.04 M [B]tot 3.5 M MgCl2 -   0.16 M [B]tot 3.5 M MgCl2 -     0.4 M [B]tot 3.5 M CaCl2 - 0.004 M [B]tot 3.5 M CaCl2 -   0.04 M [B]totNeck et al. (2009) [3] 3.5 M MgCl2 - no [B]tot 3.5 M CaCl2 - no [B]tot  3.5 M CaCl2 - no [B]tot calc.Clear decrease in Nd(III) solubility at [B]tot ≥ 0.04 M and pHc = 7‒9. No effect of borate at higher pHc-values. Similar effects observed in dilute systems. XPS confirms the presence of B in the solid phase (at [B]tot ≥ 0.16 M)  → Transformation of Nd(OH)3(am) into a “Nd-borate“ solid phase.  Solubility of Th(IV) and U(VI) in NaCl and MgCl2 solutions Clear indications of Np(V)–borate complex formation in conc. NaCl solutions.  Weaker complexation taking place in MgCl2 solutions => competition with Mg2+? [B]tot ≤  0.04 M: only slight peak shifts compared to the borate free system→ very weak borate complexation. [B]tot ≥ 0.16 M: clear red shift compared to low [B]tot → increasing Cm(III)-borate complex formation. Experimental Introduction Actinides relevant in the context of deep geological disposal: Am(III), Pu(III)/Pu(IV) especially important ( reducing conditions).  AIM: comprehensive assessment of actinide solubility and speciation      from dilute to highly concentrated brine solutions.  Presence of boron under repository-conditions: Component of intruding brines. Part of the emplaced waste.   This work: investigation of An-borate interactions relevant for assessing  long-term safety of repository.        Previous solubility study at pHc = 8.6 indicated complexation of Nd(III) with tetraborate in dilute to concentrated NaCl solutions [1]. Leaching experiments with boron-bearing glass showed no significant effect of An-solubility with borate [2]. Outlook  Conclusions  Actinide-borate interactions impact radionuclide solubility and speciation under repository relevant conditions. Cm(III)–TRLFS and Np(V) UV–vis indicate the formation of borate complexes with Cm(III) and Np(V) at pHc = 8–9, although these have only a minor impact on solubility. Hydrolysis outcompetes borate complexation at higher pH values. Borate has a minor impact on Th(IV) solubility. On the contrary, the solubility of U(VI) is significantly increased  at pHc = 8–9.  Strong decrease of An(III) and An(V) solubility within 7 ≤ pHc ≤ 9 related to formation of Ln/An(III)–borate and An(V)–borate  solid phases [→new retention mechanism].    Ln/An-borate interactions Comprehensive quantitative thermodynamic description of Ln/An–borate chemistry, including Ln/An–borate aqueous species and solid compounds forming in NaCl, CaCl2 and MgCl2 solutions. Continuation of 11B-NMR studies under saline conditions to achieve a better understanding of aqueous borate speciation in these systems.   Acknowledgements:  M. Böttle  (KIT-INE) F. Geyer (KIT-INE) D. Reed (LANL-CO)                                       M. Borkowski (LANL- CO) M. Richmann (LANL-CO)  All experiments conducted in Ar-glovebox [B4O7] 2-init = 0.001 M to 0.1 M    => [B] tot = 0.004 M to 0.4 M Background electrolytes:  NaCl : 0.1 to 5.0 M; MgCl2/CaCl2: 0.25 to 3.5 M  Nd(III),Th(IV), Np(V) and U(VI) -Solubility experiments: ca. 2-10 mg Nd(OH)3(am), Th(OH)4 (am), NpO2OH(am), UO3·2H2O(am) and Na2U2O71.6H2O(cr) per experiment (characterized by XRD) Equilibration time:  7d - 140 d Phase separation: 10 kD (2-3 nm) ultrafiltration Reference system without borate  Nd(III) [3], Np(V) [4], U(VI) [5] Cm(III)–TRLFS experiments:                            Np(V) UV–Vis:  [Cm] = 1·10-7 M per sample                                 Equilibration time: spectra taken at < 1 d    K. Hinz1,*, M. Altmaier1, X. Gaona1, Th. Rabung1, E. Alekseev2, D. Schild1, H. Geckeis1  1Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal, P. O. Box 3640, 76021 Karlsruhe, Germany 2Institute of Energy and Climate Research (IEK-6), Forschungszentrum Jülich, 52428 Jülich, Germany *katja.hinz@kit.edu 580 590 600 610 620  normalised intensityWavelength [nm]0.25 M MgCl2 0.04 M [B]tot 0.16 M [B]tot   0.4 M [B]tot3.5 M MgCl2 no borate 0.04 M [B]tot 0.16 M [B]tot   0.4 M [B]tot0.04 M 0.16 M0.4 MpHc = 84 5 6 7 8 9 10-8-7-6-5-4-3-2 0.1 M NaCl 0.16 M [B]tot 0.1 M NaCl 0.04 M [B]tot 0.1 M NaCl      0 M [B]tot 5.0 M NaCl 0.16 M [B]tot 5.0 M NaCl 0.04 M [B]tot 5.0 M NaCl      0 M [B]totAltmaier et al. (2003)   0.5 M NaCl   5.0 M NaCllog[U]pHc960 970 980 990 1000 1010 1020  norm. abs.Wavelength [nm] 0.1 M NaCl 0.04 M [B]tot 0.1 M NaCl 0.16 M [B]tot 5.0 M NaCl 0.04 M [B]tot 0.25 M MgCl2 0.04 M [B]tot 0.25 M MgCl2 0.16 M [B]tot 3.5 M MgCl2 0.04 M [B]tot 3.5 M MgCl2 0.16 M [B]tot 0.1 M NaCl  no borate 5.0 M NaCl  no borate979,8 988,3Solubility and UV–vis of Np(V) in NaCl and MgCl2 solutions  2 4 6 8 10 12 14-10-9-8-7-6-5-4-3-2-1without phase separation  log [Th]-log[H+]0.1 M NaCl 160 mM [B]tot14 d  60 d 138 d5.0 M NaCl 160 mM [B]tot14 d  60 d 138 d 0.1 M NaCl no [B]tot  5.0 M NaCl no [B]tot  Lit NaCl/NaClO4 (I< 1.0 M)Significant solubility increase at pHc = 7.5–9 Minor effect at pHc = 5–6  => key role of polyborates in complex formation (?) No significant effect of borate on Th(IV) solubility. Further studies in NaCl borate-free systems at elevated ionic strength needed. . Very clear shift of peak position in dil. and conc. NaCl  and MgCl2 solutions compared to borate-free systems => strong complex formation. Strong shift in peak position for conc. MgCl2 systems => formation of ternary Mg–Np(V)–Cl species suspected [4] => competition with Np(V)–borate complex formation. Very relevant drop in solubility (up to 3 log-units) observed in conc. NaCl and dil. MgCl2 solutions in the presence of [B]tot ≥ 0.16 M. New Np(V)–borate solid phase forming. 8 9 10 11-7-6-5-4-3-2NpO2OH(am,aged)  log[Np]pHc 5.0 M NaCl 0.04 M [B]tot 5.0 M NaCl 0.16 M [B]tot 5.0 M NaCl 0.16 M [B]totPetrov et al. (2011) 5.0 M NaCl Neck et al. (1992) 5.0 M NaClO4 5.0 M NaClO4 calc. 5.0 M NaClO4 corr.NpO2OH(am,fresh)Np(V)–boratecomplex formationNp(V)–borate solid phase formation (!)References:  [1]  Borkowski, M., Richmann, M., Reed, D. T., Xiong, Y., Radiochimica Acta 98, 577-582 (2010). [2]  Kienzler, B., Luckscheiter, B., Wilhelm, S.Waste Management 21, 741-752 (2001). [3]  Neck, V., Altmaier, M., Rabung, T., Lützenkirchen, J., Fanghänel, T., Pure and Applied Chemistry 81, 1555-1568 (2009). [4] V. G. Petrov, X. Gaona, D. Fellhauer, K. Dardenne, S. N. Kalmykov, M. Altmaier, Vortrag, Migration 2011, Peking, China. [5] M. Altmaier, V. Neck, V. Metz, R. Müller, M. Schlieker, T. Fanghänel, Vortrag, Migration 2003, Gyeongju, Korea Th(IV) U(VI) 900 ≤ λ [nm] ≤ 1200 Spectra taken after centrifugation . 

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Interaction of An(III/IV/V/VI) with borate in dilute to concentrated alkaline NaCl, CaCl₂ and MgCl₂ solutions

Interaction of An(III/IV/V/VI) with borate in dilute to concentrated alkaline NaCl, CaCl₂ and MgCl₂ solutions

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