TsingHai Wang

Cesium adsorption and distribution onto crushed granite under different physicochemical conditions

The adsorption of cesium onto crushed granite was investigated under different physicochemical conditions including contact time, Cs loading, ionic strength and temperature. In addition, the distribution of adsorbed Cs was examined by X-ray diffraction (XRD) and EDS mapping techniques. The results showed that Cs adsorption to crushed granite behaved as a first-order reaction with nice regression coefficients (R(2) > or = 0.971). Both Freundlich and Langmuir models were applicable to describe the adsorption. The maximum sorption capacity determined by Langmuir model was 80 micromol g(-1) at 25 degrees C and 10 micromol g(-1) at 55 degrees C. The reduced sorption capacity at high temperature was related to the partial enhancement of desorption from granite surface. In general, Cs adsorption was exothermic (DeltaH<0, with median of -12 kJ mol(-1)) and spontaneous (DeltaG<0, with median of -6.1 at 25 degrees C and -5.0 kJ mol(-1) at 55 degrees C). The presence of competing cations such as sodium and potassium ions in synthetic groundwater significantly reduces the Cs adsorption onto granite. The scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM/EDS) mapping method provided substantial evidences that micaceous minerals (biotite in this case) dominate Cs adsorption. These adsorbed Cs ions were notably distributed onto the frayed edges of biotite minerals. More importantly, the locations of these adsorbed Cs were coincided with the potassium depletion area, implying the displacement of K by Cs adsorption. Further XRD patterns displayed a decreased intensity of signal of biotite as the Cs loading increased, revealing that the interlayer space of biotite was affected by Cs adsorption.

Removal of cesium ions from aqueous solution by adsorption onto local Taiwan laterite

Utilization of local Taiwan laterite (LTL) to remove aqueous cesium was investigated in this work under the conditions of various contact time, cesium (Cs) loading and temperature. Experimental results show that adsorption is instantaneous. Freundlich and Langmuir simulation results demonstrate that local Taiwan laterite has high affinity and sorption capacity for Cs at low temperatures, which may be attributed to enhanced desorption as temperature increased. Thermodynamic parameters including DeltaH, DeltaG and DeltaS were calculated and it is indicated that Cs adsorption on LTL is an exothermic, spontaneous and physical adsorption reaction. Moreover, the adsorbed Cs is distributed evenly on the LTL surface, which is confirmed by SEM/EDS mapping images. Furthermore, the absence of apparent shifting or broadening of the kaolinite signal in XRD patterns after Cs adsorption is an indication of the non-expanding characteristic of kaolinite structure.

Bridging the gap between batch and column experiments: A case study of Cs adsorption on granite.

Both batch and column methods are conventionally utilized to determine some critical parameters for assessing the transport of contaminants of concern. The validity of using these parameters is somewhat confusing, however, since outputs such as distribution coefficient (Kd) from these two approaches are often discrepant. To bridge this gap, all possible factors that might contribute to this discrepancy were thoroughly investigated in this report by a case study of Cs sorption to crushed granite under various conditions. Our results confirm an important finding that solid/liquid (S/L) ratio is the dominant factor responsible for this discrepancy. As long as the S/L ratio exceeds 0.25, a consistent Kd value can be reached by the two methods. Under these conditions (S/L ratios>0.25), the sorption capacity of the solid is about an order of magnitude less than that in low S/L ratios (<0.25). Although low sorption capacity is observed in the cases of high S/L ratios, the sorption usually takes place preferentially on the most favorable (thermodynamically stable) sorption sites to form a stronger binding. This is verified by our desorption experiments in which a linear isotherm feature is shown either in deionized water or in 1M of ammonium acetate solutions. It may be concluded that batch experiment with an S/L ratio exceeding 0.25 is crucial to obtain convincing Kd values for safety assessment of radioactive waste repository.

Effect of Alkyl Properties and Head Groups of Cationic Surfactants on Retention of Cesium by Organoclays

Cationic surfactants modified clays exhibit high sorptive capability toward anionic radionuclides but retention of cationic radionuclides was concurrently reduced. In this study, organoclays were synthesized by intercalating a variety of primary/quaternary alkylammonium species (NH(2)R/(CH(3))(3)N(+)RBr(-), where R = benzyl, dodecyl, and octadecyl) into bentonite MX-80. The effect of surfactants properties on enhancing or limiting cationic sorption capability was investigated by performing Cs sorption experiments. Experimental results were analyzed using the MINEQL+ software by considering Cs uptake by structural and edge sorption sites. Bentonites that were intercalated with primary alkylammonium surfactants had a higher sorptive capacity than those intercalated with quaternary alkylammonium surfactants. Samples intercalated with octadecyl-bearing surfactants had the lowest sorption rate. XRD and FTIR analyses revealed that each organoclay had a characteristic arrangement of alkyl chains. The cation retention of organoclays was dominated by the extent of hydrophobic interactions affected by the local distribution and arrangement of surfactants. The intercalated primary alkylammoniun surfactants tended to transform into local clusters with a high packing density, leaving more structural sites available for Cs uptake. In contrast, the NH(3)R(+)-surfactants tended to form a denser monolayer over clay surface, inhibiting the retention of Cs at structural sites.

The in vivo biodistribution and fate of CdSe quantum dots in the murine model: a laser ablation inductively coupled plasma mass spectrometry study

Understanding the cytotoxicity of quantum dots strongly relies upon the development of new analytical techniques to gather information about various aspects of the system. In this study, we demonstrate the in vivo biodistribution and fate of CdSe quantum dots in the murine model by means of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). By comparing the hot zones of each element acquired from LA-ICP-MS with those in fluorescence images, together with hematoxylin and eosin-stained images, we are able to perceive the fate and in vivo interactions between quantum dots and rat tissues. One hour after intravenous injection, we found that all of the quantum dots had been concentrated inside the spleen, liver and kidneys, while no quantum dots were found in other tissues (i.e., muscle, brain, lung, etc.). In the spleen, cadmium-114 signals always appeared in conjunction with iron signals, indicating that the quantum dots had been filtered from main vessels and then accumulated inside splenic red pulp. In the liver, the overlapped hot zones of quantum dots and those of phosphorus, copper, and zinc showed that these quantum dots have been retained inside hepatic cells. Importantly, it was noted that in the kidneys, quantum dots went into the cortical areas of adrenal glands. At the same time, hot zones of copper appeared in proximal tubules of the cortex. This could be a sign that the uptake of quantum dots initiates certain immune responses. Interestingly, the intensity of the selenium signals was not proportional to that of cadmium in all tissues. This could be the result of the decomposition of the quantum dots or matrix interference. In conclusion, the advantage in spatial resolution of LA-ICP-MS is one of the most powerful tools to probe the fate, interactions and biodistribution of quantum dots in vivo.

Experimental and numerical investigations of effect of column length on retardation factor determination: A case study of cesium transport in crushed granite

This study investigated breakthrough curves (BTCs) from a series of column experiments, including different column lengths and flow rates, of a conservative tracer, tritium oxide (HTO), and a radionuclide, cesium, in crushed granite using a reactive transport model. Results of the short column, with length of 2cm, showed an underestimation of the retardation factor and the corresponding HTO BTCs cannot be successfully modeled even with overestimated fluid dispersivity. Column supporting elements, including filters and rings, on both ends of packed granite were shown to be able to induce additional dispersive mixing, thus significantly affecting BTCs of short columns while those of the long column, with length of 8cm, were less affected. By increasing flow rates from 1mL/min to 5mL/min, the contribution of structural dispersive mixing to the false tilting of short column BTCs still cannot be detached. To reduce the influence of structural dispersivity on BTCs, the equivalent pore volume of column supporting materials should be much smaller than that of packed porous medium. The total length of column supporting structures should be greatly shorter than that of porous medium column.

Influence of sodium halides (NaF, NaCl, NaBr, NaI) on the photocatalytic performance of hydrothermally synthesized hematite photoanodes.

It has been suggested that a high concentration of Fe(3+) in solution, a low pH, and noncomplexing ions of high ionic strength are all essential for developing a high-quality hematite array. Our curiosity was piqued regarding the role of the electrolyte ions in the hydrothermal synthesis of hematite photoanodes. In this study, we prepared hematite photoanodes hydrothermally from precursor solutions of 0.1 M FeCl3 at pH 1.55 with a background electrolyte of 1.0 M sodium halide (NaF, NaCl, NaBr, or NaI). We compared the structures and properties of the as-obtained hematite photoanodes with those of the material prepared in 1.0 M NaNO3, the most widely adopted electrolyte in previous studies. Among our studied systems, we found that the hematite photoanode prepared in NaCl solution was the only one possessing properties similar to those of the sample obtained from the NaNO3 solution-most importantly in terms of photoelectrochemical performance (ca. 0.2 mA/cm(2) with +0.4 V vs SCE). The hematites obtained from the NaF, NaBr, and NaI solutions exhibited much lower (by approximately 2 orders of magnitude) photocurrent densities under the same conditions, possibly because of their relatively less ordered crystallinity and the absence of rodlike morphologies. Because the synthetic protocol was identical in each case, we believe that these two distinct features reflect the environments in which these hematite photoanodes were formed. Consistent with the latest studies reported in the literature of the X-ray photoelectron spectra of fast-frozen hematite colloids in aqueous solutions, it appears that the degree of surface ion loading at the electrolyte-hematite interface (Stern layer) is critical during the development of hematite photoanodes. We suspect that a lower ion surface loading benefits the hematite developing relatively higher-order and a rodlike texture, thereby improving the photoelectrochemical activity.

Desorption of cesium from granite under various aqueous conditions

In this work the desorption of cesium ions from crushed granite in synthetic groundwater (GW) and seawater (SW) was investigated. Results were compared with those obtained in deionized water (DW) and in two kinds of extraction solutions, namely: MgCl(2) and NaOAc (sodium acetate). In general, the desorption rate of Cs from crushed granite increased proportionally with initial Cs loadings. Also, amounts of desorbed Cs ions followed the tendency in the order SW>GW>NaOAc approximately equal MgCl(2)>DW solutions. This indicated that the utilization of extraction reagents for ion exchange will underestimate the Cs desorption behavior. Fitting these experimental data by Langmuir model showed that these extraction reagents have reduced Cs uptake by more than 90%, while only less than 1% of adsorbed Cs ions are still observed in GW and SW solutions in comparison to those in DW. Further SEM/EDS mapping studies clearly demonstrate that these remaining adsorbed Cs ions are at the fracture areas of biotite.

Cs sorption to potential host rock of low-level radioactive waste repository in Taiwan: Experiments and numerical fitting study

A reliable performance assessment of radioactive waste repository depends on better knowledge of interactions between nuclides and geological substances. Numerical fitting of acquired experimental results by the surface complexation model enables us to interpret sorption behavior at molecular scale and thus to build a solid basis for simulation study. A lack of consensus on a standard set of assessment criteria (such as determination of sorption site concentration, reaction formula) during numerical fitting, on the other hand, makes lower case comparison between various studies difficult. In this study we explored the sorption of cesium to argillite by conducting experiments under different pH and solid/liquid ratio (s/l) with two specific initial Cs concentrations (100mg/L, 7.5 × 10(-4)mol/L and 0.01 mg/L, 7.5 × 10(-8)mol/L). After this, numerical fitting was performed, focusing on assessment criteria and their consequences. It was found that both ion exchange and electrostatic interactions governed Cs sorption on argillite. At higher initial Cs concentration the Cs sorption showed an increasing dependence on pH as the solid/liquid ratio was lowered. In contrast at trace Cs levels, the Cs sorption was neither s/l dependent nor pH sensitive. It is therefore proposed that ion exchange mechanism dominates Cs sorption when the concentration of surface sorption site exceeds that of Cs, whereas surface complexation is attributed to Cs uptake under alkaline environments. Numerical fitting was conducted using two different strategies to determine concentration of surface sorption sites: the clay model (based on the cation exchange capacity plus surface titration results) and the iron oxide model (where the concentration of sorption sites is proportional to the surface area of argillite). It was found that the clay model led to better fitting than the iron oxide model, which is attributed to more amenable sorption sites (two specific sorption sites along with larger site density) when using clay model. Moreover, increasing s/l ratio would produce more sorption sites, which helps to suppress the impact of heterogeneous surface on Cs sorption behavior under high pH environments.

CO2 uptake performance and life cycle assessment of CaO-based sorbents prepared from waste oyster shells blended with PMMA nanosphere scaffolds

In this paper, we demonstrate a means of simultaneously solving two serious environmental issues by reutilization of calcinated mixture of pulverized waste oyster shells blending with poly(methyl methacrylate) (PMMA) nanospheres to prepare CaO-based sorbents for CO2 capture. After 10 cycles of isothermal carbonation/calcination at 750°C, the greatest CO2 uptake (0.19 g CO2/g sorbent) was that for the sorbent featuring 70 wt% of PMMA, which was almost three times higher than that (0.07 g CO2/g sorbent) of untreated waste oyster shell. The greater CO2 uptake was likely a result of particle size reduction and afterwards surface basicity enhancement and an increase in the volume of mesopores and macropores. Following simplified life cycle assessment, whose all input values were collected from our experimental results, suggested that a significant CO2 emission reduction along with lesser human health and ecosystems impacts would be achieved immediately once waste is reutilized. Most importantly, the CO2 uptake efficiency must be greater than 20% or sorbents prepared from limestone mining would eventually produce a net positive CO2 emission.