Thermodynamics of Curium(III) in Concentrated Electrolyte Solutions : Formation of Sulfate Complexes in NaCl/Na<sub>2</sub>SO<sub>4</sub> Solutions

111

Europium / TRLFS / Clay minerals / Surface complexation / Ternary complexesSummary. The surface sorption process of Eu(III) onto smectite and kaolinite was investigated by time-resolved laser fluorescence spectroscopy (TRLFS) in the trace concentration range. The experiments were performed in 0.025 M and 0.45 M NaClO 4 . The sorption process of Eu(III) onto smectite was obtained by TRLFS under atmospheric conditions and in absence of CO 2 . The pH was varied between 3.5 and 9 at a fixed metal ion concentration of 3.3 × 10 −6 mol/L Eu(III). At low pH (< 4) the metal ion keeps its complete hydration sphere indicating outer-sphere complexation. With increasing pH the formation of an inner-sphere Eu(III) surface complex was observed. The differences in the spectra and the fluorescence emission lifetimes of the surface sorbed Eu(III) in presence and absence of carbonate indicate the formation of ternary clay/Eu(III)/carbonate complexes. The different europium/clay surface complexes were characterized by their fluorescence emission spectra ( 5 D 0 → 7 F 1 / 5 D 0 → 7 F 2 intensity ratio) and their fluorescence emission lifetime.

Section: Lifetime (Fluorescence Decay) Of Eu(iii) Emissionmentioning

confidence: 90%

Section: Experimental Set-upmentioning

confidence: 99%

Inner-sphere, outer-sphere and ternary surface complexes: a TRLFS study of the sorption process of Eu(III) onto smectite and kaolinite

Stumpf¹,

Bauer²,

Coppin³

et al. 2002

111

“…5b), log K 0 1:1 = 6.21, is smaller than the complexation with carbonate (log K 0 1:1 = 8.30; [19]) and clearly stronger than complexation with sulfate (log K 0 1:1 = 3.28; [19]). The strength of Cm(III) complexes with divalent complexing inorganic ligands thus follows the line: CO 3 2− > HPO 4 2− SO 4 2− . The results of our study showed that HPO 4 2− belongs to the strong inorganic complexing ligands.…”

Section: Thermodynamic Speciation and Strength Of The Complexesmentioning

confidence: 95%

“…Using ion exchange, an indirect speciation technique, stability constants log K of Ln/AnH 2 PO 4 2+ species between 1.52 and 1.69 at ionic strengths of 0.2 and 0.5 M were determined. Later many speciation studies of Cm(III) in several of inorganic systems, e.g., silicate [2]; sulfate [3]; dihydrogenphosphate [4], hydroxide [5][6][7]; chloride [5,6]; carbonate [5,6] and nitrate [8] applied TRLFS. All these investigations demonstrated that the characteristic luminescence emission band of Cm 3+ at 593.7 ± 0.1 nm is sensitive to changes in its first coordination sphere.…”

Section: Introductionmentioning

confidence: 99%

Aqueous curium(III) phosphate species characterized by time-resolved laser-induced fluorescence spectroscopy

Moll¹,

Brendler

Bernhard

2011

The formation of aqueous Cm(III) phosphate complexes was studied at room temperature by time-resolved laser-induced fluorescence spectroscopy (TRLFS) in 0.1 M NaClO 4 solutions. The experiments were perfomed at a fixed total Cm(III) concentration of 3 × 10 −7 or 2 × 10 −8 M by varying the phosphoric acid concentration (3 × 10 −5 -0.1 M) and the pH (1.4-6.0). The red shift of the excitation and emission spectra, as well as the increase of luminescence lifetimes clearly showed the influence of phosphate on the aqueous Cm(III) speciation. In acidic phosphate solutions ([H 3 PO 4 ] ≤ 0.1 M, pH 1.4-2.6) an increase in luminescence intensity was detected due to complexation with H 2 PO 4 − . At [H 3 PO 4 ] ≥ 4 × 10 −4 M and between pH 4.0 and 6.0 in general a decrease in luminescence intensity affiliates the complexation with HPO 2− 4 . Two Cm(III)-phosphate complexes could be identified from the emission data, CmH 2 PO 4 2+ and CmHPO 4 + , having peak maxima at 599.6 and 600.8 nm, respectively. TRLFS in combination with ultra-filtration (1 kD) showed that the formation of CmHPO 4 + is accompanied by the generation of Cm(III)-phosphate colloids especially at [H 3 PO 4 ] ≥ 0.002 M and pH ≥ 5. Cm(III)-phosphate colloids formed at pH 5 and 6 are characterized by an emission maximum at 603.1 nm. Based on the factor analysis of the emission data the stability constants of the two complexes were calculated to be log β 121 = 20.23 ± 0.13 and log β 111 = 16.54 ± 0.80 at an ionic strength of 0.1 M (NaClO 4 ).

“…The interaction of Cm(in) with main natural inorganic ligands Cl", SOJ", and COi~ was investigated and appropriate thermodynamic models were developed which are valid from low to high ionic strength [1][2][3][4], The goal of the present contribution is to develop a thermodynamic model describing the chemical behaviour of trivalent actinides in high Chloride concentrations. Recently published experimental data for the Chloride complexation of Cm(III) in CaClj solutions, determined by time-resolved laser fluorescence spectroscopy (TRLFS) [1], are used to parameterize the ion interaction (Pitzer) approach.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics of Trivalent Actinides in Concentrated Electrolyte Solutions: Modelling the Chloride Complexation of Cm(III)

Könnecke¹,

Fanghänel²,

Kim³

1997

Self Cite

Curium / Neodymium / Chloride complexes / Modelling / Pitzer parameters SummaryA thermodynamic model describing the Chloride complexation of trivalent actinides in solutions of high Chloride concentration is developed on the basis of the ion interaction (Pitzer) approach using recently published spectroscopic data for Cm(III). The experimentally confirmed complex species CmCP"^ and CmClJ are included in the model. The complex formation constants at zero ionic strength and a set of Pitzer parameters are evaluated. The model is verified by calculating solubilities in the analogous system NdClj-CaCU-HaO and comparing them with literature data. Applying the new parameters, a revised model describing the hydrolysis of trivalent actinides is presented.