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.     

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.     

Adsorption and desorption of Am(III) on calcareous soil and its parent material

Summary The adsorption and desorption of Am(III) on a calcareous soil (sierozem) and its parent material (loess) were studied by batch technique. The molarities of the Am(III) aqueous solutions were less than 5 ^. 10^-9 mol/l. High adsorbability was found of Am(III) on the calcareous soil and its parent material. In order to decrease the adsorption and, hence, to investigate the adsorption characteristics properly, stable Eu³⁺ as hold back carrier and analogue was added to the aqueous solution. The relative contributions of CaCO₃, organic matter (OM) to the Am(III) adsorption on calcareous soil and its parent material were investigated. The adsorption and desorption isotherms of Am(III) on untreated soil and loess and the three kinds of treated soils and three kinds of treated loesses to remove CaCO₃, OM and both CaCO₃ and OM were determined, respectively. It was found that all isotherms were linear, the average distribution coefficients (K^-_d) for the untreated soil and for the untreated loess were almost equal, while there was an obvious difference between the values of the average distribution coefficients (K^-_d) for the treated soil and the treated loess to remove CaCO₃ or OM. The adsorption-desorption hysteresis on the untreated and treated soils and loesses actually occurred and there was an obvious difference between the hysteresis coefficients on both the corresponding treated soil and loess. It can be concluded that the adsorbability of Am(III) on calcareous soil is similar to that on its parent material, and that the contributions of CaCO₃ and OM to the Am(III) adsorption by the untreated soil are different from those by the untreated parent material.     

Migration characteristics of radionuclides 85+89Sr2+, 134Cs+, 125I-, 75SeO3 2- and 152+154Eu(III) in Chinese soils

The migration of radionuclides ⁸⁵⁺⁸⁹Sr²⁺, ¹³⁴Cs⁺, ¹²⁵I^- and ⁷⁵SeO₃ ^2- in calcareous soil from Yuzhong county of Gansu Province (China) at pH 7.8±0.2 and ^152+154Eu(III) in red earth from Yingtan county of Jiangxi Province (China) at pH 4.6±0.2, in presence of CaCl₂ was studied using column experiments. Results indicate that the negative anions, iodide and selenide are mobile nuclides while the migration of positive cations is related to the sorption capacity for the element. Iodide can be assumed to be non-reactive in calcareous soil. The breakthrough curves (BTCs) were fitted to the analytical solution or numerical solution of one-dimensional convection-dispersion transport models. Good agreements were obtained between the measured and predicted concentration profiles.     

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.     

Uptake behavior of titanium molybdophosphate for cesium and strontium

This study investigates uptake of cesium and strontium from aqueous solution similar to nuclear waste on three samples of titanium molybdophosphate (TMP) synthesized under various conditions. Effects of concentration of sodium nitrate, pH and contact time on the uptake of cesium and strontium have been studied by bath method. The results showed that TMP has high affinity toward cesium and strontium at pH > 2 and relatively low concentration of sodium nitrate. Kinetic data indicated that cesium uptake process to achieve equilibrium was faster than strontium. Cesium and strontium breakthrough curves were examined at 25 °C using column packed with H₃O⁺ form of TMP and breakthrough curves showed symmetrical S-shaped profiles. At the same time, the calculated breakthrough capacity for cesium was higher than strontium. The results of desorption studies showed that over 99% of cesium and strontium was washed out of column by using 4 M NH₄Cl solution. This study suggests that TMP can have great potential applications for the removal of strontium and specially cesium from nuclear waste solution.     

Extraction of radiostrontium from the mixture of radionuclides in milk using dicarbolide of cobalt

The possibilities of radiostrontium extraction from milk after the isolation of radiocesium were investigated. The polyhedral complex of the type H⁺[(π-/3/-1,2-C₂B₉H₁₁)₂Co⁻], further referred to as dicarbolide-H⁺, in nitrobenzene was used for the extraction. The increase of values and larger differentiation of distribution ratios in the extraction of ion associates of radionuclides were achieved by hydrophobizing with polyethyleneglycol (PEG). The changes of the distribution ratios of⁹⁰Sr,⁸⁹Sr and⁹⁰Y with PEG concentration were studied, and ranges of the highest synergic effect, changing with different extraction agent concentrations in extraction from water solutions and a fresh milk were determined. The influence of milk dilution and nitric acid concentration upon the value of distribution ratio in radiostrontium extraction using dicarbolide-H⁺ and the optimum PEG concentration were investigated. Under suitably selected conditions of radiostrontium isolation, the distribution ratios of some potential contaminants were determined. The influence of nonisotopic carrier Ca²⁺ upon radiostrontium extraction was examined. The possibilities of purification of isolated radiostrontium using reextraction were investigated. A selective and quick analytical procedure was suggested for radiostrontium isolation after the separation of radiocesium from a mixture of fission and activated radionuclides in milk using extraction by dicarbolide-H⁺. The chemical yield is about 98% and⁹⁰Sr is determined by liquid scintillation technique.     

Breakup promotion of deformed EPDM droplets by the migration of nanoparticles during extrusion

The effect of migration of calcium carbonate (CaCO₃) nanoparticles on the breakup dynamics of Ethylene-Propylene-Diene Monomer (EPDM) droplets in Polypropylene (PP) matrix during melt extrusion was investigated in situ. The breakup process of EPDM droplets was sped up dramatically when the migration of CaCO₃ nano-particles from dispersed phase to matrix was introduced to PP/EPDM melts. It was found that both the total breakup time and the shape stability of slender EPDM droplets decreased with the increase of CaCO₃ concentration. Both the maximum value in equivalent diameter d and aspect ratio AR of EPDM droplets were also reduced by increasing the composition of CaCO₃ nanoparticles. Results were discussed in consideration of interfacial tension and migration of CaCO₃ nanoparticles. Reduction in interfacial tension is mainly responsible for the improved breakup process in the two-step composites with CaCO₃ nanoparticles (<2 wt%). Higher composition of CaCO₃ (≥2 wt%) induced the CaCO₃ aggregates in the EPDM phase. These aggregates acted as stress concentration when the EPDM droplets break up.     

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 radiocesium on calcareous soil: Results from batch and column investigations

The sorption and desorption of radiocesium on a calcareous soil from Jiuqian County of Gansu Province (China) were studied by using batch and column experiments. The sorption-desorption isotherms and the breakthrough curves, displacement curves on the whole soil and two treated soils were determined. Based on these results, it was found that the sorption and retention of cesium are mainly determined by the clay minerals, that the sorption-desorption hysteresis of cesium on the calcareous soil is obvious and that the organic matter has a little positive contribution and the calcium carbonate has a little negative contribution to the sorption of cesium on the whole soil. The results from batch experiments were consistent with the results from column experiments.     

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.     

Factors affecting interaction of radiostrontium with river sediments

Uptake of radiostrontium by sediments from two small streams was studied as a function of pH and composition of aqueous phase, of the concentration of strontium, of contact time, temperature and liquid-to-solid ratio (V/m), using laboratory model experiments. Between pH 5 and 12 the uptake increased with pH and shifted to higher pH values with increasing V/m ratio. Addition of cations suppressed the uptake in the order Na⁺<K⁺<Ca²⁺. Increase in strontium concentration had negligible effect up to 10^–5–10^–4 mol·dm^–3 concentration due to high concentrations of dissolved and exchangeable strontium present in the systems. The V/m ratio had no influence on K_d in the range of V/m=20–446 cm³ · g^–1 but K_d value for V/m=0.79 cm³ · g^–1 was significantly lower. Two-step kinetics of the uptake was observed in most cases with a rapid first step (<100 min) followed by a slow increase. No difference was found between the uptake at 10°C and 22°C. Adsorbed radiostrontium could be easily desorbed with river water. The easiness of desorption decreased with repeated desorption. Drying of sediment did not affect the first desorption, repeated desorptions slightly decreased. Conclusions were drawn on the mechanism of radiostrontium uptake and on the importance of the factors studied for modelling of radiostrontium migration in rivers.     

Adsorption of Sulfur Dioxide from Pseudo Binary Mixtures on Hydrophobic Zeolites: Modeling of the Breakthrough Curves

The adsorption of SO₂ from pseudo binary mixtures with water and CO₂ on hydrophobic zeolites (MFI and MOR type) was investigated using the breakthrough curve method. The SO₂ and water breakthrough curves were compared with theoretical ones based on an axially dispersed plug flow through the column and the linear driving force rate equation. In addition, different semi-predictive multi-component equilibrium equations were used for the breakthrough modeling: Langmuir 1, Langmuir 2 and Langmuir-Freundlich extended models. The overall mass transfer coefficients were derived by matching theoretical with experimental breakthrough curves for single component systems, i.e., water vapor or SO₂ in a carrier gas. They were also predicted from a simplified bi-porous adsorbent model and compared with experimentally derived values. The presence of CO₂ species in ternary mixtures with water vapor and SO₂, even at relatively high concentrations of 9 vol%, had no significant effect on the breakthrough behavior of the other two species. For that reason the CO₂ species was ignored in the analysis of the resulting pseudo binary mixtures. The breakthrough model was solved by finite element orthogonal collocation method using the commercial software gPROMS. Both extended Langmuir 1 and Langmuir 2 based models gave reasonable predictions of the water and SO₂ breakthrough curves for pseudo binary mixtures involving a mordenite sample for all water concentration levels used in this study (up to 3.5 vol%). However, the same models were successfully used to predict SO₂ breakthrough curves for a MFI sample only at low water concentrations, i.e., 1.5 vol%. At the higher water levels both models failed to describe equilibrium behavior in the MFI sample due to the introduction of multi-layer adsorption in the interstices between small MFI-26 crystals.     

Stability of modified surface CaCO3 in the non-polar medium

The adsorption isotherm of methacrylic acid (MAA) and polymethacrylic acid (PMAA) molecules on CaCO₃ were studied. The isotherm of (MAA) adsorption from cyclohexane was found formed from two steps, while that of (PMAA) from ethanol is formed from one step. The effects of surface modification of CaO₃ with (MAA) and (PMAA) in the sedimentation properties in a non-polar medium (cyclohexane) have been studied. It was found that the most stable suspension formed is concerned with monolayer surface coverage for the two adsorptives. Also, studies were made for the rheological properties of concentrated suspension of CaCO₃ modified with (MAA) and (PMAA) in a paraffin oil. The equilibrium flow curves of CaCO₃ modified with (PMAA) suspensions exhibit pseudoplastic characteristics, accompanied by some degree of complex thixotropy, while that modified with (MAA) exerts a thickening effect with rheopexy characteristics.     

Role of Na-Montmorillonite on Microbially Induced Calcium Carbonate Precipitation

The use of additives has generated significant attention due to their extensive application in the microbially induced calcium carbonate precipitation (MICP) process. This study aims to discuss the effects of Na-montmorillonite (Na-MMT) on CaCO₃ crystallization and sandy soil consolidation through the MICP process. Compared with the traditional MICP method, a larger amount of CaCO₃ precipitate was obtained. Moreover, the reaction of Ca²⁺ ions was accelerated, and bacteria were absorbed by a small amount of Na-MMT. Meanwhile, an increase in the total cementing solution (TCS) was not conducive to the previous reaction. This problem was solved by conducting the reaction with Na-MMT. The polymorphs and morphologies of the CaCO₃ precipitates were tested by using X-ray diffraction and scanning electron microscopy. Further, when Na-MMT was used, the morphology of CaCO₃ changed from an individual precipitate to agglomerations of the precipitate. Compared to the experiments without Na-MMT in the MICP process, the addition of Na-MMT significantly reduced the hydraulic conductivity (HC) of sandy soil consolidated.     

Dynamic Adsorption of H2S onto a Goethite-Based Material

The use of adsorption technology to remove H₂S from synthetic gas (H₂S and N₂) using a goethite-based adsorbent was investigated. The influence of the H₂S feed concentration (150–600 mg), the adsorbent dosage (1–4 g), and the gas flow rate (210–540 cm³/min) on the breakthrough curves and H₂S adsorption on the adsorbent at the breakthrough point was investigated. Dynamic column experiments were performed to provide data for the theoretical models and to verify the performance of the system in the adsorption process. The theoretical models used in the present work were found to predict the adsorption breakthrough performance reasonably well.     

Kinetics of carbon dioxide absorption from air in a flow reactor with a fixed bed of K<Subscript>2</Subscript>CO<Subscript>3</Subscript>-based sorbent

Sorption of carbon dioxide from air in a flow reactor with a bulky fixed bed of the K₂CO₃/Al₂O₃ composite sorbent was studied. The dynamic sorption capacity of the material was shown to depend on the relative humidity of the inlet air. A numerical model was constructed for evaluating the profile of СО₂ concentration in the layer and kinetic curves of CO₂ breakthrough at the outlet of the reactor. The results of simulation allowed us to adequately describe the experimental kinetic curves at 20–40% humidity.     

Crystallization of calcium carbonate controlled by Pluronic P123 in room-temperature ionic liquid

The crystallization of calcium carbonate (CaCO₃) controlled by Pluronic P123 in a room-temperature ionic liquid, ethylamine nitrate (EAN), was investigated. The CaCO₃ aggregates were obtained by rapid mixing of ammonium carbonate ((NH₄)₂CO₃) and calcium chloride (CaCl₂). Cubic calcite, spherical vaterite, and bagel-like vaterite were obtained easily by changing P123 concentration and reaction temperature. The morphologies of the as-prepared CaCO₃ aggregates were investigated by transmission electron microscopy and scanning electronic microscopy. The phase change of the obtained crystals was confirmed by X-ray diffraction and Fourier transform infrared spectroscopy. It was shown that higher P123 concentration and higher reaction temperature favor the formation of vaterite in EAN. Unusual bagel-like vaterite was first obtained at 60 °C in the presence of 5 g/L P123 in EAN. Mineralization of CaCO₃ regulated by P123 in EAN is a simple, novel, and environment-friendly strategy for vaterite synthesis.     

Preparation of superhydrophobic nanocalcite crystals using Box–Behnken design

Superhydrophobic nanocalcite crystals were prepared via an adjusted aqueous reaction of CaO, CO₂ gas and sodium oleate. Box–Behnken design was used to optimize the preparation parameters such as CaO concentration, CO₂ gas flow rate and surfactant concentration. The results revealed that the produced CaCO₃ is indexed to the calcite phase. The crystallite size, particle size, morphology, hydrophobicity and surface charge of CaCO₃ are significantly affected by changing the preparation parameters. The addition of sodium oleate helps in reducing the crystallite size from 101 nm to 48 nm, reducing the particle size from 1.5 μm length scalenohedral particles to 40 nm rhombohedral particles and modifying the properties of pure CaCO₃ from highly hydrophilic to superhydrophobic.     

Sorptive elimination of fluoride from contaminated groundwater in a fixed bed column: A kinetic model validation based study

The current investigation involves a continuous adsorption experiment in a packed bed column for the sorptive elucidation of fluoride from contaminated groundwater using an activated soil-clay mixture. Through the combination of naturally accessible laterite soil with silica enriched clay (3:1 ratio), a low-cost Al–Si heterogeneous material has been developed. Following detailed characterization, the developed materials were employed in a long-time column process to achieve a high degree of fluoride separation from real-world groundwater. In a packed bed column investigation, the effect of bed height, initial fluoride concentration, and flow rate on the breakthrough properties of the adsorption system were investigated. By using a non-linear regression equation, three model kinetics, such as the Thomas Model, Adams-Bohart Model, and Yoon-Nelson Model, were fitted to validate the column-based experimental data, by analysing the breakthrough curves profiles, and distinct kinetic parameters. The Bed Depth Service Time Analysis (BDST) model was tested to express the effect of bed height on breakthrough curves, as well as to predict the time for breakthrough, and material depletion under optimal conditions. The Thomas and Yoon-Nelson models were identified to be the most appropriate ones for describing the entire breakthrough curve, whereas the Adams-Bohart model was only utilised to predict the first half of the dynamic process. With correlation coefficients (R²) 0.96, the experimental results were well suited to Thomas, Yoon-Nelson, and Adams-Bohart models. Finally, regeneration assessment was carried out where even after four cycles of operation, regenerated adsorbent showed a rejection efficacy of 78% to fluoride that proves the viability of the material and methodology.