Solubility Of Am Research Articles

Americium solubility and solubility limiting solid phase (SLSP) analysis in groundwater of Beishan, a proposed site for the disposal of high-level radioactive waste in China

The disposal of high-level radioactive waste (HLW) in deep geological repository requires reliable data including the solubility and speciation of americium and other actinides in safety assessment. In this work, a generic thermodynamic equilibrium model using the geochemical codes PHREEQC-3 and PhreePlot was used to investigate the solubility of americium in the groundwaters of Beishan in the possible ranges of pH (6–11) and PCO2 (10−5.5 - 10−2.5 bar). The pH-logPCO2 diagram of solid phases and aqueous species of Am was computed and plotted with Am solubility contour lines. The results indicate that the solubility of Am under the repository far-field conditions is dependent on pH and under the near-field conditions on pH and PCO2. Based on our calculations, we have determined that AmCO3OH·0.5H2O(cr) is thermodynamically stable in both the near- and far-field conditions, leading to an Am solubility of 4.0 × 10−9 mol/kg and 1.5 × 10−8 mol/kg under, respectively, the near- and far-field conditions of the proposed Beishan repository. However, the amorphous AmCO3OH(am, hyd) phase, while thermodynamically metastable, is expected to persist for an extended period of time, possibly hundreds of years or more after the closure of a repository. As such, it is assumed to be the solid phase that limits the solubility of americium, leading to much enhanced Am solubilities of 6.3 × 10−7 and 2.4 × 10−6 mol/kg for the Beishan near- and far-field conditions, respectively. Therefore, solely based on the solubility data, Am could be more toxic than the natural uranium in the Beishan granitic groundwater within ∼5000 years after the proposed repository's closure. It is thus important to ensure that Am is well contained by the engineered barriers within this timeframe. Since Am solubilities in Beishan groundwater are rather low, the effect of sorption and colloidal formation could be potentially more important for Am migration in groundwaters, however further studies are required before these processes can be properly evaluated.

Physicochemical and biological properties of nanochitin—abamectin conjugate for Noctuidae insect pest control

Abamectin (Am) is an excellent biopesticide for insect pests control but environmental sensitivity and a short duration in conventional formulations limit its application in agriculture. In order to promote the dispersity, stability, and biological activity of Am, well-monodisperse nanochitin (NCh) and Am-loaded nanoparticles (NCh-Am) were prepared and examined in this study. NCh was prepared by ultrasonication combining with low concentration acidic hydrolysis and NCh-Am nanoparticles were combined by conjugation in dispersion naturally. The effective particle size of NCh was 110.6 ± 18.6 nm with cationic nature, while those of NCh-Am conjugates ranged from 160 to 700 nm based on the mixing ratio. The binding efficiency of Am to NCh in the conjugates reached 53.7 ± 7.6% in DI water at pH 6.2. The thermal stability and water solubility of Am were greatly promoted by NCh. The photodegradation of Am in the conjugates decreased 48% when exposed to UV light for 56 h. The conjugate containing half of Am showed significant control efficiency in larva growth and enhanced mortality against 2 instar larvae of noctuid. The results suggested that NCh significantly promoted Am water dispersity, thermal stability, and photostability, and effectively reduced pesticides dosage in insect pest control. This finding indicates that NCh-Am can be used as a new bioactive delivery system in future pest management.

Radionuclide release from research reactor spent fuel

Numerous investigations with respect to LWR fuel under non oxidizing repository relevant conditions were performed. The results obtained indicate slow corrosion rates for the UO 2 fuel matrix. Special fuel-types (mostly dispersed fuels, high enriched in 235U, cladded with aluminium) are used in German research reactors, whereas in German nuclear power plants, UO 2-fuel (LWR fuel, enrichment in 235U up to 5%, zircaloy as cladding) is used. Irradiated research reactor fuels contribute less than 1% to the total waste volume. In Germany, the state is responsible for fuel operation and for fuel back-end options. The institute for energy research (IEF-6) at the Research Center Jülich performs investigation with irradiated research reactor spent fuels under repository relevant conditions. In the study, the corrosion of research reactor spent fuel has been investigated in MgCl 2-rich salt brine and the radionuclide release fractions have been determined. Leaching experiments in brine with two different research reactor fuel-types were performed in a hot cell facility in order to determine the corrosion behaviour and the radionuclide release fractions. The corrosion of two dispersed research reactor fuel-types (UAl x -Al and U 3Si 2-Al) was studied in 400 mL MgCl 2-rich salt brine in the presence of Fe 2+ under static and initially anoxic conditions. Within these experimental parameters, both fuel types corroded in the experimental time period of 3.5 years completely, and secondary alteration phases were formed. After complete corrosion of the used research reactor fuel samples, the inventories of Cs and Sr were quantitatively detected in solution. Solution concentrations of Am and Eu were lower than the solubility of Am(OH) 3(s) and Eu(OH) 3(s) solid phases respectively, and may be controlled by sorption processes. Pu concentrations may be controlled by Pu(IV) polymer species, but the presence of Pu(V) and Pu(IV) oxyhydroxides species due to radiolytic effects cannot completely be ruled out. Solution concentrations of U were within the range of the solubility limits of the solid phase U(OH) 4(am). The determined concentrations of U and Am in solution were about one order of magnitude higher for the U 3Si 2-Al fuel sample. Here, the formation of U/Si containing secondary phase components and their influence on radionuclide solubility cannot be ruled out. Results of this work show that the U 3Si 2-Al and UAl x -Al dispersed research reactor spent fuel samples dissolved completely within the test period of 3.5 years in MgCl 2-rich brine in the presence of Fe 2+. In view of final disposal this means that these fuel matrices represent no barrier. The radionuclides will be released instantaneously. Cs (the long-lived isotope 135Cs is of special concern with respect to final disposal) and Sr were classified as mobile radionuclide species. For U, Am, Pu and Eu, a reimmobilization was observed. Sorption is the process which is assumed to be responsible for the reimmobilization of the long-lived actinide Am and the lanthanide Eu. Solution concentrations of U and Pu seem to be controlled by their solubility controlling solid phases.

Thermodynamics of trivalent actinides and neodymium in NaCl, MgCl2, and CaCl2 solutions: Solubility, hydrolysis, and ternary Ca-M(III)-OH complexes

Abstract Known data on the solubility of Am(OH)3(s) and the hydrolysis of Am(III) and Cm(III), additional information from an extensive solubility study with Nd(OH)3(s) in NaCl, MgCl2, and CaCl2 media of various ionic strengths and spectroscopic (time-resolved laser fluorescence spectroscopy, TRLFS) data for Cm(III) in alkaline CaCl2 solutions are used to evaluate a comprehensive set of standard-state equilibrium constants and ion interaction parameters for the specific ion interaction theory (SIT) and Pitzer equations at 25 °C. The thermodynamic model takes into account the analogous solubility and hydrolysis behavior of trivalent actinides and Nd(III) and covers the entire pH range in dilute to concentrated NaCl, MgCl2, and CaCl2 solutions. In alkali chloride/hydroxide solutions, the formation of the tetrahydroxide complex M(OH)4 – requires OH– concentration above 3 mol l–1, whereas in alkaline CaCl2 solutions (at pHc < 12) M(III) complexes with four and six hydroxide ligands are formed. Similar as the recently detected ternary Ca–M(IV)–OH complexes Ca3[Zr(OH)6]4+ and Ca4[Th(OH)8]4+, these complexes are stabilized by the association of Ca2+ ions. The solubility and hydrolysis of Am(III), Cm(III), and Nd(III) in both Ca-free and -containing solutions is consistently described with a model including the ternary Ca–M(III)–OH complexes Ca[M(OH)3]2+, Ca2[M(OH)4]3+, and Ca3[M(OH)6]3+.

Actinide speciation in the environment

Nuclear test explosions and nuclear reactor wastes and accidents have released large amounts of radioactivity into the environment. Actinideions in waters often are not in a state of thermodynamic equilibrium and their solubility and migration behavior is related to the form in which the nuclides are introduced into the aquatic system. Chemical speciation, oxidation state, redox reactions, and sorption characteristics are necessary in predicting solubility of the different actinides, their migration behaviors and their potential effects on marine biota. The most significant of these variables is the oxidation state of the metal ion as the simultaneous presence of more than one oxidation state for some actinides in a solution complicates actinide environmental behavior. Both Np(V)O2 + and Pu(V)O2 +, the most significant soluble states in natural oxic waters, are relatively noncomplexing and resistant to hydrolysis and subsequent precipitation. The solubility of NpO2 + can be as high as 10−4M while that of PuO2 + is much more limited by reduction to the insoluble tetravalent species, Pu(OH)4, (pKsp≥56) but which can be present in the pentavalent form in aqautic phases as colloidal material. The solubility of hexavalent UO2 2+ in sea water is relatively high due to formation of carbonate complexes. The insoluble trivalent americium hydroxocarbonate, Am(OH)(CO3) is the limiting species for the solubility of Am(III) in sea water. Thorium(IV) is present as Th(OH)4, in colloidal form. The chemistry of actinide ions in the environment is reviewed to show the spectrum of reactions that can occur in natural waters which must be considered in assessing the environmental behavior of actinides. Much is understood about sorption of actinides on surfaces, the mode of migration of actinides in such waters and the potential effects of these radioactive species on marine biota, but much more understanding of the behavior of the actinides in the environment is needed to allow proper and reliable modeling needed for disposition of nuclear waste over many thousands of years.

Precipitation polymerization of acrylamide with quaternary ammonium cationic monomer in potassium carbonate solution initiated by plasma

AbstractPrecipitation polymerization of 2‐(methacryloyloxyethyl) trimethyl ammonium chloride (DMC)‐co‐acrylamide (AM) [poly(AM‐DMC)] has been successfully performed in potassium carbonate (K2CO3)‐water media by plasma initiation. K2CO3 solution was selected because not only the higher solubility of AM and DMC comparing with that of poly(AM‐DMC), but the higher intrinsic viscosity of poly(AM‐DMC) could be obtained. A set of experiments was performed using different K2CO3 concentration (from 50 down to 10% (w/w)), thus the precipitation architecture was not obtained below 20% (w/w). And particles size, particles size distribution (7–120 μm), and intrinsic viscosity of poly(AM‐DMC) (ranging up to 455 cm3/g) were also summarized in this article. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4060–4067, 2007

Actinide speciation in aquatic systems

Nuclear test explosions and reactor wastes have deposited an estimated 16 × 10 15 Bq of plutonium into the world's aquatic systems. However, plutonium concentration in open ocean waters is on the order 10 − 5 Bq/kg, indicating that most of the plutonium is quite insoluble in marine waters and has been incorporated into sediments. Actinide ions often are not in a state of thermodynamic equilibrium and their solubility and migration behavior is related to the form in which the nuclides were introduced into the aquatic system. Actinide solubility depends on such factors as the pH (hydrolysis), Eh (oxidation state), reaction with complexants (e.g., carbonate, phosphate, humic acid, etc.), sorption to surfaces of minerals and/or colloids etc., in the water. The most significant of these variables is the oxidation state of the metal ion. The simultaneous presence of more than one oxidation state for some actinides (e.g., plutonium) in a solution complicates actinide environmental behavior. Both Np(V)O 2 + and Pu(V)O 2 +, the most significant states in natural, oxic waters are relatively noncomplexing and resistant to hydrolysis and subsequent precipitation. The solubility of NpO 2 + can be as high as 10 − 4 M while that of PuO 2 + is limited by reduction to the insoluble tetravalent species, Pu(OH 4), (pK sp = 56). The net solubility of hexavalent UO 2 2+ in sea water is also limited by hydrolysis; however, it has a relatively high concentration due to formation carbonate complexes. The insoluble trivalent americium hydroxocarbonate, Am(CO) 3(OH), is limiting species for the solubility of Am(III) in sea water. Thorium is found exclusively as the tetravalent species and its solubility is limited by the formation of quite insoluble Th(OH) 4. The chemistry of actinide ions in the environment is reviewed to show the spectrum of reactions that can occur in natural waters which must be considered in assessing the environmental behavior of actinides. While much is understood about sorption of actinides on surfaces, the mode of migration of actinides in such waters and the potential effects of these radioactive species on marine bioto, much more is needed for a satisfactory understanding of the behavior of the actinides in the environment.

Acrylic-melamine modified DGEBA-epoxy coatings and their anticorrosive behavior

Acrylic acid modified melamine resin (AM) was synthesized and used as a curing agent, in different compositions (10–40 wt.%), for DGEBA-epoxy resin (EAM). EAM resins were applied on mild steel strips of standard size to study their coating properties. The structures of AM and EAM were established by IR and 1 H NMR spectroscopies. The physico-mechanical and anticorrosive behavior of these coatings was evaluated by standard methods. The solubility of AM was determined in various organic solvents at room temperature. TGA and DSC techniques were used to analyze the thermal properties and curing aspects of the resin. The sample with 30 wt.% loading of AM (EAM-30), among all EAM resins gave better physico-mechanical and corrosion resistance performance under various corrosive media. The acrylic-melamine modified DGEBA-epoxy coatings were compared with the reported DGEBA-polyamide coating system. It was found that EAM-30 exhibited better anticorrosive properties than the reported DGEBA-polyamide coating system.

Reactions of Am(III) and Eu(III) with potassium ferricyanide in nitric acid solutions

Summary The reactions between Am or Eu present in 0.1 M nitric acid solutions, alone or both together, with 0.25 M K3Fe(CN)6, were studied at room temperature. When Am was the only trivalent metal ion in solution, precipitation of AmFe(CN)6 occurs and the residual Am concentration is about equal to 0.95 mM. However, when Am initial concentration is less than the above specified value for AmFe(CN)6 solubility, Am residual concentration measured is lower that its concentration in the initial solutions. The solubility of EuFe(CN)6 was found to be equal to 30 mM. However, when precipitate formation occurs, the Eu residual concentration after phase separation is about in average 8 mM. When Am and Eu were simultaneously present at the same concentration in solution, the solubility of Am differs little from that measured with Am alone. For initial Am concentrations below 1 mM, the solubility of Am is higher than that observed in the absence of Eu. For initial concentrations of about 8 mM, the Am solubility is lower (about 0.7 mM) than that observed for Am alone. When the initial Eu concentration is constant at 29 mM, the Am precipitation efficiency is much higher than observed in the absence of Eu, for Am concentrations between 30 and 0.5 mM. The residual Am concentratixon in solution thus drops considerably in the presence of Eu (29 mM), and is about 0.04 mM for initial Am concentrations below 4 mM.

Processes Controlling Radionuclide Release from Spent Fuel

AbstractDissolution of spent fuel has been studied in saline, anaerobe, carbonate free solutions. Processes controlling spent fuel dissolution and associated radionuclide release are radiolytically controlled oxidative dissolution, sorption on container, solubility and coprecipitation. Upper limits for oxidative dissolution rates are given by the production rates of oxidative radiolysis products. This limitation leads to a strong decrease in surface area normalized reaction rates with increasing surface to volume ratio (S/V) and imposes geometric constraints on prediction of spent fuel behavior in a repository. Solution concentrations of Am during spent fuel corrosion were about 5 orders of magnitude lower than the solubility of Am(OH)3(s) and are likely controlled by coprecipitation. Pu concentrations may be controlled by Pu(VI) or Pu(IV) (hydr)oxides.

Am(lll) Hydrolysis Constants and Solubility of Am(lll) Hydroxide

Americium(III) hydroxide solubility was measured in dilute salt solutions under an argon atmosphere. The equilibrium, attained in < 23 days, was approached from both over and undersaturation. Thermodynamic equilibrium constants (K/sub S10//sup 0/) for the solubility of Am(OH)/sub 3/ (amorphous) (Am(OH)/sub 3/ (amorphous) + 3 H/sup +/ in equilibrium Am/sup 3 +/ + 3 H/sub 2/O in equilibrium Am(OH)/sub n//sup 3-n/ + nH/sup +/) were calculated from the solubility data. The measured value of log K/sub S10//sup 0/ was 17.5 +/- 0.3. The values of log ..beta../sub 1//sup 0/, log ..beta../sub 2//sup 0/, and log ..beta../sub 3//sup 0/ were less than or equal to -8.2, -17.1 +/- 0.5, and less than or equal to -27.0, respectively. Contrary to predictions in the literature, Am(III) does not show amphoteric behavior in the pH range studied (i.e., no evidence for the existance of Am(OH)/sub 4//sup -/ species). 18 references, 2 figures, 5 tables.

Influence of an americium solid phase on americium concentrations in solutions

Americium-241 concentrations in solutions contacting contaminated sediments for up to 2 yr were measured as a function of pH. Steady-state concentrations were reached within a few days. The solubility-limited Am concentration was found to decrease approximately 10-fold with one unit increase in pH. The log equilibrium constant for the solubility of Am (soil) solid [Am (soil) + H + ⇌ Am (aq complex) +] was found to be −4.12. The predictions based upon thermodynamic data suggest that Am (aq complex) + is likely to be Am(OH) 2 +. Although the chemical formula of Am (soil) was not determined, it does not appear to be Am(OH) 3(a). Published data on sorption coefficients of Am by different rocks, soils, and minerals were critically evaluated. Final Am solution concentrations calculated from the sorption coefficients of a variety of earth materials with several solutions agreed well with the concentrations predicted from the solubility of Am (soil) solid, indicating that the sorption coefficient data are controlled by Am precipitation.