Adsorption of Am(III) on red earth and natural hematite

Summary The Am(III) adsorption isotherms on natural hematite, on a red earth and on three kinds of treated red earth samples were determined and compared. The treatment was performed to remove iron oxides, organic matter (OM) and both. The batch technique and aqueous Am(III) solutions with molarities less than 3 ^. 10^-9 mol/l were used. A very high adsorbability of Am(III) on hematite was found, and in order to decrease the adsorption percentage, stable Eu³⁺ as a hold back carrier was added to the aqueous solution. All the isotherms were found to be linear. The strong effects of pH, ionic strength and fulvic acid (FA) on the Am(III) adsorption on natural hematite were demonstrated. A positive contribution of OM and an unexpectedly high negative influence of iron oxides on the Am(III) adsorption by the untreated red earth were found too. The average distribution coefficients of Am(III) adsorption on natural hematite, on red earth and on three kinds of treated red earth samples were determined, respectively, from these linear isotherms. The very high adsorbability of Am(III) on hematite and the very strong negative influence of iron oxides on the Am(III) adsorption on untreated red earth were distinctly demonstrated as well. It appears that the adsorbability of composed natural materials cannot be predicted from the adsorbabilities of each of the mineral components alone, due to possible interactions between the mineral components and the different characteristics of the composite.     

Sorption and desorption of neptunium(V) on calcareous soil and its solid components: A comparative study

The sorption and desorption isotherms of untreated calcareous soil and three treated soils to remove CaCO₃, organic matter (OM) and both CaCO₃ and OM were determined and analyzed with the Freundlich equation at pH 7.8, moderate concentrations of NpO₂ ⁺ (~10^-5mol/l), in the presence of 0.01 mol/l CaCl₂ and under ambient aerobic conditions. The relative contribution of CaCO₃ and OM to the neptunium(V) sorption on calcareous soil and the sorption/desorption hysteresis is discussed. The effects of adding fulvic acid (FA) and carbonate in to the solution on the sorption of neptunium(V) on the soils were also studied. The sorption and desorption characteristics of NpO₂ ⁺, Zn²⁺, Sr²⁺ and Cs⁺ on the soils are compared.     

A multitracer study on the adsorption of 47 elements on a calcareous soil and its solid components

The distribution coefficients of 47 elements from Na to Bi on untreated calcareous soil, treated soil to remove CaCO₃ and treated soil to remove both CaCO₃ and organic matter, respectively, were determined by using a multitracer technique. The variation of the distribution coefficients of 47 elements was explained in terms of chemical bond formation and hydration. The effect of different solid components of the calcareous soil on the adsorption was investigated.     

Sorption and desorption of radioiodine and radioselenium on calcareous soil and its solid components

This paper is an extension of previous papers^1–3. The breakthrough curves and the displacement curves of¹²⁵I⁻ and⁷⁵SeO₃ on the calcareous soil, the treated soil to remove CaCO₃ and the treated soil to remove organic matter were determined at pH 7.8, at 20°C and in the presence of 1·10⁻³ or 1·10⁻⁴ mol/l CaCl₂. These results from column experiments and from batch experiments in the previous papers^1,2 were mutually complementary. It can be definitely concluded that iodide is retained to a very small degree and tetravalent-selenium is retained to a small degree by calcareous soil and that organic matter in calcareous soil acts as a significant trap of iodide and CaCO₃ acts as a trap of tetravalent selenium. Iodide and tetravalent-selenium would be expected to have relatively high dissemination in calcareous soil.     

Recovery of actinides extracted by Truex solvent from high level waste using complexing agents

The sorption and migration of radiostrontium in a calcareous soil from Yu Zhong county of Gansu province (China) was studied using batch and column experiments. Sorption isotherms, breakthrough curves and concentration profiles for the untreated soil and the soil treated to remove CaCO₃ were determined, respectively. It was found that radiostrontium is a relatively mobile nuclide in calcareous soil and removal of CaCO₃ from the soil slightly increases the retention ability for radiostrontium. The breakthrough curves were fitted to the analytical solution of a one-dimensional convection-dispersion transport model that assumes a reversible linear isotherm. Good agreement was obtained between the measured and predicted concentration profiles.     

Adsorption and migration of <Superscript>241</Superscript>Am in aerated zone soil

As an important radioisotope in nuclear industry and other fields, ²⁴¹ Am is one of the most serious contamination concerns due to its high toxicity and long half-life. In order to supply useful reference for disposal of ²⁴¹Am waste with low-medium radioactivity, the adsorption and migration behavior of ²⁴¹Am on aerated zone soil were investigated by the static experimental method and column experiments. The results showed that more than 98% of the total ²⁴¹Am could be adsorbed from ²⁴¹Am solution of 0.32·10⁻⁷−1.1·10⁻⁷ mol/l by the soil at pH 4–9. The adsorption of ²⁴¹Am on the soil was a pH-dependent process at pH<4, but for pH>4, the adsorption rate of ²⁴¹Am on the soil changed minutely. The adsorption equilibrium was achieved within 24 hours and no significant effect on adsorption of ²⁴¹Am was observed at liquid-solid ratios of 50:1–500:1. The relationship between concentration of ²⁴¹Am and adsorption capacities of ²⁴¹Am can be described by the Freundlich adsorption equation. Adsorption of ²⁴¹Am on the soil can be inhibited by humic acid, ferric hydroxide colloid, or some anions, such as citric acid anion, saturated EDTA solution, C₂O₄ ²⁻ and CO₃ ²⁻. It was also noted that the adsorption rate of ²⁴¹Am drops in solutions containing Eu³⁺ or Nd³⁺, even 0.5 times above the ²⁴¹Am concentration. A migration distance of 8 mm for ²⁴¹Am(III) is observed only in the aerated zone soil containing ferric colloid, while a migration distance of less than 2 mm is noted in other soil samples after more than 250 days. All these results indicate that the aerated zone soil is an efficient sorbent for ²⁴¹Am and can inhibit the migration of ²⁴¹Am.     

Am(III) adsorption on oxides of aluminium and silicon: effects of humic substances,pH, and ionic strength

The adsorption of Am(III) (total concentration 10(-9) mol/l) on alumina, silica, and hematite was studied by a batch technique. The effects of pH, ionic strength, and humic substances on the adsorption of Am(III) on alumina and silica were investigated, and the adsorption isotherms of Am(III) on alumina and silica at different pH values were determined. It was found that compared with the adsorption of Am(III) on alumina, the adsorbability of silica on the basis of mass is less, the relative adsorption rate on silica is slower, the sensitivity of adsorption on silica to ionic strength is less, the dependence of adsorption on silica on pH is gentler, and consequently that the adsorption characteristics of Am(III) on alumina and silica are distinctly different. The negative effect of fulvic acid on the adsorption on silica and the positive effect of humic acid on the adsorption on alumina were found. In contrast to the Am(III) adsorption on alumina and silica, a tremendously high adsorbability of Am(III) on hematite was found. The sequence of adsorbabilities of Am(III) on the basis of mass is Fe2O3 > Al2O3 > SiO2.     

Migration mechanisms of 237Np and 241Am through loess media

Migration experiments with ²³⁷Np(V) and ²⁴¹Am(III) have been performed using a column system, packed with loess, taken from Shanxi, China. The adsorption mechanism of ²³⁷Np and ²⁴¹Am on the loess was examined by a chemical extraction method. Most of ²³⁷Np was adsorbed on the influent edge of the column, and the adsorbtion was mainly controlled by surface complexation. However, the migration of ²³⁷Np in loess media could be roughly evaluated by the distribution coefficient. In the case of ²⁴¹Am, particulate, the ²⁴¹Am species was formed in the influent solution and moved in the column. The ²⁴¹Am adsorbed on loess was controlled by irreversible reactions. The migration behavior of particulate ²⁴¹Am in loess media could be expressed by the filtration theory.     

Sorption and desorption of radioselenium on calcareous soil and its solid components

The effect of different solid soil components of calcareous soils on the retention of SeO₃ has been investigated by a batch technique and selective extraction method. The sorption and desorption isotherms of SeO₃ on the untreated calcareous soil and the three treated soils were determined at 20°C, pH 7.8±0.2 and in the presence of 0.001M CaCl₂. It was found that all isotherms are linear, the sorption-desorption hysteresis for untreated soil and treated soils is obvious and the retention of SeO₃ in calcareous soil is mainly attributed to the oxides.     

Sorption and desorption of radioselenium on calcareous soil and its solid components

The effect of different solid soil components of calcareous soils on the retention of SeO₃ has been investigated by a batch technique and selective extraction method. The sorption and desorption isotherms of SeO₃ on the untreated calcareous soil and the three treated soils were determined at 20°C, pH 7.8±0.2 and in the presence of 0.001M CaCl₂. It was found that all isotherms are linear, the sorption-desorption hysteresis for untreated soil and treated soils is obvious and the retention of SeO₃ in calcareous soil is mainly attributed to the oxides.     

Americium(III) Adsorption on Polyethylene from very Dilute Aqueous Solutions

The Am(III) adsorption from very dilute aqueous solutions on polyethylene was studied as a function of the pH value, the composition of dissolved salts and the presence or absence of adsorbent SiO₂. It was found that the Am(III) adsorption on polyethylene is decreased with increasing H⁺ concentration and dissolved salt concentrations and in the presence of SiO₂ as an adsorbent. The mechanisms of Am(III) adsorption on polyethylene were discussed. Based on the observations in this paper, extreme care is necessary to minimize and correct the Am(III) adsorption on the container walls in order to improve the accuracy of Am(III) distribution coefficient (K _d) between a solid and an aqueous solution.     

Adsorption behavior of Me2-CA-BTP/SiO2-P adsorbent toward MA(III) and Ln(III) in nitrate solution

A porous Me₂-CA-BTP/SiO₂-P adsorbent was prepared to separate MA(III) from Ln(III) in high level liquid waste (HLLW). The adsorption behavior of Me₂-CA-BTP/SiO₂-P toward ²⁴¹Am(III) and Ln(III) in 0.01 M HNO₃-NaNO₃ solution was studied. Me₂-CA-BTP/SiO₂-P showed high adsorption and selectivity toward ²⁴¹Am(III) over Ln(III) fission products with the separation factor (SF) reaching to 557, 2355, 1952, 1082, 214, 105, 86, 14 for Y, La, Ce, Nd, Sm, Eu, Gd and Dy respectively in 0.01 M HNO₃-0.99 M NaNO₃ solution. The adsorption kinetics of both Dy(III) and Eu(III) on Me₂-CA-BTP/SiO₂-P was studied and followed pseudo-second-order rate equation indicating chemical sorption as the rate-limiting step of the adsorption, and the adsorption isotherm of Dy(III) and Eu(III) matched better with the Langmuir isotherm than the Freundlich isotherm with the adsorption amount around 0.22 and 0.20 mmol/g respectively. Thermodynamic study revealed that the adsorption of both Dy(III) and Eu(III) on Me₂-CA-BTP/SiO₂-P was spontaneous and endothermic processes with a positive entropy at 298, 308, 313 K.     

Sorption behavior of Am(III) onto granite

Sorption behavior of Am(III) onto granite was investigated. The distribution coefficient (K _d ) of Am(III) onto granite was determined in the solution of which pH was ranged from 2.9 to 11.4 and ionic strength was set at 10⁻² and 10⁻¹. TheK _d values were found to increase with increasing pH and with decreasing ionic strength. The obtained data were successfully analyzed by applying an electrical double layer model. The optimum parameter values of the double layer electrostatics and adsorption reactions were obtained, and the selective adsorption behavior of Am(III) onto the granite was discussed.     

Investigation of photo‐oxidative effect on morphology and degradation of mechanical and physical properties of nano CaCO3 silicone rubber composites

Photo‐oxidative degradation of treated and untreated nano CaCO₃: silicone rubber composite was studied under accelerated UV irradiation (≥290 nm) at different time intervals. Prolonged exposure to UV leads to a progressive decrease in mechanical and physical properties along with the change in behavior of filler‐matrix interaction. This was due to decrease in cross‐linking density with increase in mobility of rubber chains. Meanwhile, synthesized nano CaCO₃ was modified with stearic acid for uniform dispersion in rubber matrix. The increase in carbonyl (>CO), hydroxyl (? OH), CO₂, and alkene functional groups on the UV exposed surface of treated and untreated nano CaCO₃: silicone rubber composites at different time intervals was studied using Fourier transform infrared (FTIR) spectroscopy. The change in morphological behavior of filler‐matrix interaction after UV exposure was studied using SEM. Overall, the study showed that the treated nano CaCO₃: silicone composites were affected more by UV exposure than untreated nano CaCO₃: silicone composites and pristine composite after UV exposure. This effect was due to peeling of stearic acid from the surface of CaCO₃, which makes the rubber chains slippery and thus separation of filler and rubber chains takes place with initiation of fast‐degradation. Copyright © 2011 John Wiley & Sons, Ltd.     

Sorption and desorption of radioiodine on calcareous soil and its solid components

The effect of different solid components of calcareous soil on the retention of I was investigated by a batch technique and selective extraction method, and the effect of -irradiation was also investigated. The sorption and desorption isotherms of I on the one untreated, three treated soils and the calcareous soil irradiated with -rays were determined at 30 °C, pH 8.1±0.2 and in the presence of 1.0×10^–4M or 0.67×10^–5M CaCl₂. It was found that the sorption-desorption hysteresis on the calcareous soil actually occurs on the same time scale, that iodine can be easily transported in the calcareous soil and that the exceptionally high contribution of organic matter to the iodine sorption is demonstrated.     

Effect of fulvic acid and ionic strength on the sorption of radiostrontium on Chinese calcareous soil and its solid components

Summary The sorption and desorption of radionuclide ⁹⁰Sr²⁺were investigated on untreated calcareous soil and two treated soils to remove organic matter and calcium carbonate using batch technique. The experiments were carried out at ambient condition, pH 7.8±0.1 and in the presence of 0.001M NaCl. Effects of fulvic acid and ionic strength on the sorption of ⁹⁰Sr²⁺on calcareous soil were also studied. It was found that the sorption isotherms are linear in the strontium concentration range used herein, and the sorption of ⁹⁰Sr²⁺on the calcareous soil can be described as a reversible sorption process and the sorption mechanism is mainly ion-exchange. The sorption is dependent on ionic strength, and fulvic acid enhances the sorption of ⁹⁰Sr²⁺on calcareous soil. Organic matter present in the calcareous soil is a significant trap of ⁹⁰Sr²⁺and is responsible for the sorption.     

Americium and plutonium separation by extraction chromatography for determination by accelerator mass spectrometry

A simple method was developed to separate Pu and Am using single column extraction chromatography employing N,N,N′,N′-tetra-n-octyldiglycolamide (DGA) resin. Isotope dilution measurements of Am and Pu were performed using accelerator mass spectrometry (AMS) and alpha spectrometry. For maximum adsorption Pu was stabilized in the tetra valent oxidation state in 8 M HNO₃ with 0.05 M NaNO₂ before loading the sample onto the resin. Am(III) was adsorbed also onto the resin from concentrated HNO₃, and desorbed with 0.1 M HCl while keeping the Pu adsorbed. The on-column reduction of Pu(IV) to Pu(III) with 0.02 M TiCl₃ facilitated the complete desorption of Pu. Interferences (e.g. Ca²⁺, Fe³⁺) were washed off from the resin bed with excess HNO₃. Using NdF_3, micro-precipitates of the separated isotopes were prepared for analysis by both AMS and alpha spectrometry. The recovery was 97.7 ± 5.3% and 95.5 ± 4.6% for ²⁴¹Am and ²⁴²Pu respectively in reagents without a matrix. The recoveries of the same isotopes were 99.1 ± 6.0 and 96.8 ± 5.3% respectively in garden soil. The robustness of the method was validated using certified reference materials (IAEA 384 and IAEA 385). The measurements agree with the certified values over a range of about 1–100 Bq kg⁻¹. The single column separation of Pu and Am saves reagents, separation time, and cost.     

Adsorption behavior of trivalent americium and rare earth ions onto a macroporous silica-based isobutyl-BTP/SiO2-P adsorbent in nitric acid solution

To separate minor actinides from high level liquid waste (HLLW) of PUREX reprocessing, a silica-based macroporous isobutyl-BTP/SiO₂-P adsorbent was synthesized by impregnating isobutyl-BTP (2,6-di(5,6-diisobutyl-1,2,4-triazin-3-yl)pyridine) extractant into the macroporous SiO₂-P support with a mean diameter of 60 μm. A partitioning process using extraction chromatography for the treatment of HLLW was designed consisting five separation columns. As a partly work focused on isobutyl-BTP/SiO₂-P separation column, adsorption behavior of ²⁴¹Am and trivalent rare earth (RE) from simulated HLLW onto silica-based isobutyl-BTP/SiO₂-P adsorbent was investigated by batch method. Meanwhile, the chemical and radiolytic stabilities of isobutyl-BTP/SiO₂-P adsorbent against 0.01 M HNO₃ solution and γ-ray irradiation were studied. It was found that isobutyl-BTP/SiO₂-P adsorbent exhibited good adsorption selectivity for ²⁴¹Am over RE(III) in 0.01 M HNO₃ solution and showed weak or no adsorption affinity to light and middle RE(III) groups. In addition, in stability experiments, isobutyl-BTP adsorbent showed excellent stability against 0.01 M HNO₃ solution and γ-ray irradiation over 4 months contact time.     

Challenges to develop single-column MA(III) separation from HLLW using R-BTP type adsorbents

In order to directly separate trivalent minor actinides(MA:Am,Cm) from fission products(FP) containing rare earths(RE) in high level radioactive liquid waste(HLLW),the authors have challenged to develop a simplified MA separation process by extraction chromatography using a single column.Attention has been paid to a new type of nitrogen-donor ligands,R-BTP(2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl) pyridine,R:alkyl group) as an extractant because it shows high extraction selectivity for Am(Ⅲ) over RE(Ⅲ).It is known that the R-BTP ligands show different properties such as adsorbability and stability by having different alkyl groups.Therefore,some novel adsorbents were prepared by impregnating different types of R-BTP ligands(isohexyl-,isoheptyl-and cyheptyl-BTP) and a similar ligand to the R-BTP,ATP(2,6-bis(1-aryl-1H-tetrazol-5-yl)pyridines),into the porous silica/polymer support(SiO2-P particles).This work deals with comparison in adsorption and desorption properties of Am and some FP in HNO 3 solution onto such R-BTP type adsorbents,as well as chemical and radiolytic stability of the adsorbents.Then the possibility of a single-column separation of MA from main FP was pursued by evaluating the results of column experiments using the most promising adsorbent(isohexyl-BTP/SiO2-P) under temperature control.In addition,elution behaviors of U and Pd were also estimated.     

Influence of the physico-chemical properties of Selangor soil series on the distribution coefficient (<Emphasis Type="Italic">K</Emphasis><Subscript>d</Subscript>-value) of <Superscript>226</Superscript>Ra

²²⁶Ra is a member of the ²³⁸U natural decay series and is one of the most important isotope to be determined among the naturally occurring nuclides in environmental samples. In order to evaluate the radiation dose from ²²⁶Ra, it is important to know its mobility in different types of soils. The aim of the present study is to quantify the influence of physico-chemical soil properties on ²²⁶Ra adsorption. The distribution coefficients (K _d-value) of ²²⁶Ra in Selangor soil series samples were measured in one core, at three depth levels to evaluate the adsorbability of ²²⁶Ra. The soil samples were spiked with ²²⁶Ra tracer and the activities of ²²⁶Ra in the separated phase from batch sorption test were measured by a low background but high efficiency well-type HPGe detector. Several physico-chemical soil properties were also characterised for each soil samples. Pearson’s correlation and stepwise multiple regression test were applied at the 0.05 level of significance throughout all analysis to determine the relationships and influences between distribution coefficients (K _d-value) of ²²⁶Ra with physicochemical soil properties for the Selangor soil series. The observed K _d value was in the range of 50.55–172.28 mL g⁻¹ (mean: 93.20 ± 46.99 mL g⁻¹). The regression showed that the highest positive correlations were observed for organic matter (OM) and cation exchange capacity (CEC) (r = 0.96**, 0.81**, respectively) with K _d-values. The results indicate that the stepwise multiple regression model incorporating the soil’s OM and CEC accounts for 98% of the variability in distribution coefficients of ²²⁶Ra.