Volume 104, Issue 6

The aqueous chemistry of Np(V) in alkaline 0.01 to 5.5 M CaCl 2 solutions at T  = 23 ± 2 ℃ was thoroughly studied by long-term batch solubility experiments from both over- and undersaturation. Applying a comprehensive set of experimental and spectroscopic techniques including Vis/NIR and Np L3-edge EXAFS, the solubility controlling Np(V) solid phases and the predominant aqueous Np(V) species were identified. The results demonstrate that the solubility behavior of Np(V) in alkaline CaCl 2 solutions differs completely from the one reported for alkaline NaCl and NaClO 4 solutions: as solubility limiting solid phases, three so far not considered Ca-Np(V)-OH compounds were identified and their solubility and stability in CaCl 2 solutions analyzed: CaNpO 2 (OH) 2.6 Cl 0.4  · 2H 2 O(s) (I) (metastable), Ca 0.5 NpO 2 (OH) 2  · 1.3H 2 O(s) (II) (long-term metastable) and Ca 0.5 NpO 2 (OH) 2 (s) (III) (stable). The considerably higher stability of these (qua)ternary phases which readily form in alkaline CaCl 2 solutions from oversaturation (addition of NpO 2 + ) and undersaturation (addition of binary NpO 2 OH(am)) limit the Np(V) equilibrium concentrations to values that are up to 3 log-units lower compared to those for NpO 2 OH(am) in NaCl and NaClO 4 systems. Based on systematic evaluation of the pH dependence (solubility curve slopes), Vis/NIR and EXAFS spectroscopic information, unhydrolysed NpO 2 + and innersphere chloro complexes, NpO 2 Cl(aq) and Ca z [NpO 2 Cl] 2 z + with z  = 1 (EXAFS, Vis/NIR), were identified as prevailing Np(V) species in less alkaline solutions with pH m  < 10.5 for [CaCl 2 ] ≤ 2.0 M and [CaCl 2 ] > 2.0 M, respectively. The steep increase of the Np(V) solubility for pH m  > 11 with slopes of approximately + 2.5 (for solid phase (I) ) and + 3 (for solids (II) and (III) ) as well as the Np L3-edge EXAFS results for the aqueous Np(V) species in 4.5 M CaCl 2 /pH m  ≈ 12 confirm the presence of ternary Ca-Np(V)-OH complexes Ca x [NpO 2 (OH) 2 ] 2 x– 1 ( x  ≈ 1 is estimated within the thermodynamic evaluation in a subsequent paper (Fellhauer, D., Altmaier, M., Gaona, X., Lützenkirchen, J., Fanghänel, Th., Np(V) solubility, speciation and solid phase formation in alkaline CaCl 2 solutions. Part II: Thermodynamics and implications for source term estimations of nuclear waste disposal (Radiochim. Acta, DOI 10.1515/ract-2015-2490), in the following referred to as “Part II” [1]) and Ca y [NpO 2 (OH) 5 ] 2 y– 4 with y  ≈ 2.4 ± 1.5 (EXAFS result) as predominant Np(V) hydrolysis species in solution for [CaCl 2 ] ≥ 0.25 and pH m  > 10.5. The thermodynamic evaluation and implications of the new findings with respect to source term estimations for nuclear waste disposal scenarios are discussed in “Part II” [1]).

The results of comprehensive solubility experiments with Np(V) in dilute to concentrated CaCl 2 solutions which included the spectroscopic investigation of the predominant aqueous Np(V) species and the thorough analysis of the solubility controlling Np(V) solid phases [1](Fellhauer, D., Rothe, J., Altmaier, M., Neck, V., Runke, J., Wiss, T., Fanghänel, Th., Np(V) solubility, speciation and solid phase formation in alkaline CaCl 2 solutions. Part I: Experimental solubility (Radiochim. Acta, DOI 10.1515/ract-2015-2489), in the following referred to as “Part I”), showed that the concentration of Np(V) in these systems is limited by equilibrium reactions between previously unknown (qua)ternary solid compounds, CaNpO 2 (OH) 2.6 Cl 0.4  · 2H 2 O(s) (I) , Ca 0.5 NpO 2 (OH) 2  · 1.3H 2 O(s) (II) and Ca 0.5 NpO 2 (OH) 2 (s) (III) , and ternary aqueous complexes of Np(V) with the general formulae Ca x [NpO 2 (OH) 2 ] 2 x– 1 , Ca y [NpO 2 (OH) 5 ] 2 y– 4 with y  ≈ 2.4 ± 1.5 (EXAFS result) and innersphere Np(V) chloro complexes, Ca z [NpO 2 Cl] 2 z + with z  = 0 and 1 (EXAFS result). A systematic thermodynamic evaluation of the experimental solubility data based on the specific ion interaction theory (SIT) and the Pitzer approach is performed. The stoichiometries of the ternary hydrolysis complexes are assessed as Ca[NpO 2 (OH) 2 ] + and Ca 3 [NpO 2 (OH) 5 ] 2+ . The corresponding thermodynamic solubility and complex formation constants at I  = 0 as well as the ion interaction parameters (SIT and Pitzer) were derived yielding a comprehensive geochemical model for the Np(V) solubility behavior in pH neutral and alkaline CaCl 2 solutions over a large range of ionic strengths. This significantly improves source term estimations for scenarios with calcium dominated aquatic systems. The principally different behavior of Np(V) in NaCl and CaCl 2 solutions is highlighted, and the impact of the new findings on geochemical modelling of systems relevant for nuclear waste disposal is discussed.

Radionuclides should be separated from the waste streams before their discharge due to their undesired effects on human physiology and ecological systems. In this work, the feasibility of using Dowex-HCR-S/S(HCR), a strong acid cation-exchange resin as sorbent for 134 Cs and 152+154 Eu ions removal was examined. Sorption experimental data were analyzed by kinetic and isotherm models. The distribution coefficients of 134 Cs and 152+154 Eu were studied as a function of pH; 3525.6 mL/g and 393.1 mL/g were obtained in case of 152+154 Eu and 134 Cs at pH 4.1, respectively. Four isotherm models; Freundlich, Langmuir, Tempkin and Dubinin-Radushkevich, were used to fit the sorption equilibrium data. The results indicated that the sorption of both 134 Cs and 152+154 Eu onto HCR resin is highly fit with the pseudo-second order model. The sorption kinetic for 134 Cs and 152+154 Eu onto polymeric resin takes 90 and 120 min to reach equilibrium which is considered as a fast kinetic process. The results of sorption experiments indicate that the maximum sorption capacity of 134 Cs and 152+154 Eu are 102.84 and 161.93 mg/g. The amount of radionuclides removed increased with increasing temperature, which indicates the endothermic nature of the sorption process. The negative values of ΔG ○ indicated the spontaneity of the sorption process. The proposed procedure has been successfully applied for the removal of 134 Cs, 152+154 Eu and other radionuclides from real liquid radioactive waste. The present study concludes that the commercial HCR resin used under these conditions, has a considerable potential as an effective sorbent for the removal of 134 Cs and 152+154 Eu from real radioactive wastewater. It can therefore have a place in the treatment of cationic radionuclides from radioactive wastewater since it is of a low-cost and commercially available adsorbent.

Antimony oxide was synthesized by a simple method involving the mixing of 6 M HCl and antimony pentachloride, adjusting the synthesis pH with 25% ammonia. The obtained material was characterized using X-ray diffraction, field emission scanning electron microscopy, and surface area and pore size analysis. The material structure resembled that of Sb 6 O 13 . The cobalt sorption efficiency of the synthesized antimony oxide was tested in the dark and under UV-C irradiation. The 0.01 M NaNO 3 test solution contained varying concentrations of Co 2+ and EDTA and was traced with 57 Co. The cobalt concentration in the solutions was determined by gamma spectroscopy. The synthesized material proved to have a high cobalt uptake. In the presence of 20 μM EDTA, 99.7% of cobalt was removed from the solution after 2 h of UV-C irradiation.

The composite of magnetic Fe(hydr) Oxide and cobalt potassium ferrocyanide with excellent adsorption capacity of cesium has been prepared by chemical coprecipitation method. The results of structural testing confirm the successful preparation of magnetic material K 2 [CoFe(CN) 6 ]. It is applied as adsorbent for the separation of cesium from water solution. At pH 7 and 293 K, the maximum adsorption capacity for cesium can achieve to 141.44 mg/g. Adsorption of cesium on magnetic K 2 [CoFe(CN) 6 ] surface is an spontaneous process. The as-synthesized adsorbent can be separated from aqueous solution in the magnetic field. The results of adsorption process show that it has the potential to be an effective adsorbent for practical use.

The measurements of activity concentrations in soil of the lignite belt and soil of the villages surrounding the lignite belt have been carried out in order to present the radiological health hazards due to gamma radiation levels of the soil to general public. A low- background Pb-shielded gamma spectroscopic counting assembly utilizing NaI(Tl) detector was employed for the measurements. The activity concentration of radionuclides have been determined and compared with the international and national recommended values. A correlation analysis was also performed in order to predict the contribution of the respective nuclides towards the measured dose rate and to the find the existence of these radioactive nuclides together in the study area.