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Municipal sewage carries degraded and intact viral particles and RNA (ribonucleic acid) of SARS-CoV-2 (severe acute respiratory coronavirus 2), shed by COVID-19 (coronavirus disease 2019) patients, to sewage and eventually to wastewater treatment plants. Proper wastewater treatment can prevent uncontrolled discharges of the virus into the environment. However, the role of different wastewater treatment stages in reducing viral RNA concentrations is, thus far, unknown. Here, we quantified SARS-CoV-2 RNA in raw sewage and during the main stages of the activated sludge process from two wastewater treatment plants in Israel, on three different days during the 2020 COVID-19 outbreak. To reduce the detection limit, samples were concentrated prior to quantification by real-time polymerase chain reaction by a factor of 2–43 using ultrafiltration. On average, ∼1 log RNA removal was attained by each of the primary and secondary treatment steps; however, >100 copies of SARS-CoV-2 RNA/mL remained in the secondary effluents. Following chlorination, SARS-CoV-2 RNA was detected only once, likely due to an insufficient chlorine dose. Our results emphasize the capabilities and limitations of the conventional wastewater treatment process in reducing the SARS-CoV-2 RNA concentration and present preliminary evidence for the importance of tertiary treatment and chlorination in reducing dissemination of the virus to the environment., We present data on SARS-CoV-2 RNA concentration and removal rates during the different stages of the activated sludge wastewater treatment process with implications for controlling environmental viral dissemination.

We describe a new electro-enhanced sorption approach, where an electric field is applied across an ion-selective nano-composite membrane. Unlike capacitive deionization, here the membrane rather th...

Ion-exchange membranes hybridized with laser-induced graphene (LIG) might lead to membranes with functional surface effects such as antifouling, antibacterial, or joule heating effects; however, understanding the change in the electrical properties of the membrane is essential. Here we studied LIG-modified ion-exchange polymeric membranes using electrochemical impedance spectroscopy (EIS). The conductivity of the anionic sulfonated poly(ether sulfone) membranes and the effective capacitance of the membrane-electrolyte interface were obtained by fitting the EIS spectra to an electrochemical equivalent circuit and compared with LIG-modified nonionic poly(ether sulfone) films. The transport selectivity (as the relative permeability) of counterions (K

Phosphogypsum–a byproduct of phosphoric acid production–piled near eco-sensitive regions, poses both environmental and health risks. By reacting phosphogypsum with NaOH, Ca(OH)2 is produced, which ...

Using the 90–105 keV gamma-rays for determining Pu isotopic composition is studied for dilute Pu solutions (0.0001–0.05 μg/mm3) as well as Pu-U mixed solutions. It is shown that for concentrations higher than 0.001 μg/mm3 Pu, results match well with those of mass spectrometric results. However, in mixed solutions, beyond 0.005 mg/mm3 U concentration, the errors on isotopic compositions of Pu increased as U content increased.

This work addresses a key challenge of tailoring the ion selectivity of a thin-film composite nanofiltration membrane to a specific application, such as water softening, without altering the water permeability. We modified the active surface of a commercial NF270 membrane by molecular layer deposition (MLD) of ethylene glycol-Al (EG-alucone). With increasing deposition cycles, we found that the MLD precursors first infiltrated and deposited in the active layer of NF270, then inflated the active layer, and finally deposited on the surface as a distinct EG-alucone layer. The deposition process changed the morphology of the membrane active layer and decreased the overall density of its fixed negative charge by embedding the positively charged EG-alucone. Filtration experiments revealed that these modifications affected the ion separation properties of the membrane without significantly hindering the water permeability. Specifically, the permeation of Na+ increased relative to that of Mg2+, as indicated by the permselectivity of Na+ salts over Mg2+ salts. The changes in permselectivities with an increasing number of MLD cycles were rationalized using the dielectric, steric, and electrostatic ion exclusion mechanisms, which are related to the membrane material, pore size, and fixed charge, respectively. These relations open a path for the rational design of nanofiltration membranes with tailored selectivity by tuning the properties of the MLD layer. Filtration results of natural brackish groundwater using the MLD modified membranes agreed with the single salt experiments. As a result, water hardness was 26% lower for the permeate obtained using the MLD-modified membranes, which were found stable even during a 24 h filtration run. These results highlight the practical potential of this approach in enhancing water softening efficiency.

Poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA) and poly(ethylene oxide)-b-poly(isopropyl methacrylate) (PEO-b-PiPMA) diblock copolymers of different block ratios have been synthesized using atom transfer radical polymerization with functionalized PEO monomethylether as macroinitiator. The phase separation between the constituent blocks of the copolymers has been investigated by differential scanning calorimetry (DSC). In PEO-b-PMMA, the constituent blocks are completely miscible irrespective of their molar mass and block ratios. This behaviour remains the same for PEO-b-PiPMA with ≤15% PEO fraction; phase separation could only be observed for PEO-b-PiPMA with higher PEO content. These observations are supported by results of atomic force microscopy studies of films of two copolymers with comparable molecular weight and PEO fraction (≥24% PEO); a very well developed lamellar morphology was only observed for PEO-b-PiPMA, while the block domains were randomly dispersed in PEO-b-PMMA. Interestingly, the phase separation behaviour in PEO-b-PMMA with >30% PEO fraction has been found to be strongly dependent on its processing and thermal history. On the contrary, phase separation in PEO-b-PiPMA BCPs with ≥24% PEO fraction has not been affected by its processing or thermal history. Results indicate that the use of a block-selective solvent for the precipitation of the diblock copolymer promotes the formation of microphase separated structures even for copolymers with miscible blocks. The findings are relevant for ongoing attempts to utilize the microphase separation of such polymers to obtain well-defined nanoporous membranes and other materials.

The present work describes a novel and cleaner approach for large scale (litre) separation of cesium from simulated nuclear waste solutions by electrodriven transport through a hollow fiber supported liquid membrane (HFSLM) containing chlorinated cobalt dicarbollide as the carrier. To the best of our knowledge, this is the first report on electrodriven cation transport through HFSLM. The transport selectivity of Cs + over Na + and other fission products was studied from synthetic nuclear waste solutions. An attempt has also been made to pre-concentrate radio-cesium from an environmental sample containing very low level of 137 Cs (≤ 10 –12 M) with excellent transport efficiency. A very high decontamination factor of cesium over Na + other metal ions have been obtained for all types of feed solution. For neutral feed solution, the current efficiency for the Cs + transport has been found to be 100%. The present work certainly adds a new dimension to the ongoing membrane based separations.

The ion-exchange kinetics of Az+sol ⇆ Na+mem (Az+ = Cs+/Ba2+/Eu3+) in Nafion-117 have been measured using non-stationary radiotracer technique for trace concentrations of Az+ ions in external solution. A method based on non-steady state Nernst–Planck approach has been developed and used to fit the experimental ion-exchange profiles to obtain the diffusion coefficients (DCs) of these ions. The DCs, thus obtained, have been found to be appreciably lower than the literature-reported self-diffusion coefficients, indicating slower rate of ion-exchange. The results show that membrane DCs of these ions are modified by bulk electrolyte solution.

In the present work, the algebraic reconstruction technique (ART) combined with Monte Carlo method has been proposed for image reconstruction in gamma ray transmission tomography, which is generally used for the nondestructive assay of special nuclear materials. The Monte Carlo method has been explored to generate the weight matrix, which is required for executing ART algorithm. The method has been successfully demonstrated using a two-dimensional tomographic set-up with circular sample. The advantage of the method is that it is generalized, with no assumptions regarding weight matrices and is easily extendable to three dimensional systems, where other classical approaches become cumbersome. Moreover, the method is computationally simple and less time consuming unlike full scale Monte Carlo simulations.

In our earlier work, we reported [Env. Sci. Technol. 2014, 48, 12994] a novel electrodialysis based selective separation of Cs+ from nuclear waste solution using chlorinated cobalt dicarbollide (HCCD) loaded polymer inclusion membrane (PIM). In continuation with that work, the mechanism of electrodriven transport of Cs+ through HCCD loaded polymer inclusion membranes has been explored. PIMs containing fixed amount of cellulose triacetate and nitrophenyl octyl ether (NPOE) but different concentrations of the carrier have been prepared. The experimental flux of Cs+ across the PIMs, for two different concentrations of the metal ion in the initial feed solution, has been measured using the radiotracer technique. On the basis of the Nernst–Planck equation, an attempt has been made to calculate the time dependence of concentration changes of the metal ion in the feed compartment. The experimental parameters of the membrane., viz., length, self-diffusion coefficient, distribution ratio, electrical resistance, an...

Large volume radioactive waste drums with low/intermediate level of alpha activity, generated in radiochemical laboratories, are in general screened for special nuclear materials (SNM) in a segmented gamma scanner (SGS) before disposal. The assay methodology traditionally requires a standard drum of identical geometry and thereby making the procedure relying on the availability of a true standard, which is often difficult to organize. Here, we report a non-conventional absolute segmented gamma scanning (ASGS) methodology for the assay of 200 L waste drums, avoiding the use of a standard drum. The present analysis employ the full energy peak (FEP) efficiency, ingeniously determined using a standard 152Eu point source. From combined experiment and Monte Carlo simulation, it has been established that, the FEP efficiencies of the detector for a 200 L cylindrical sample can be well reproduced using a point source. While verifying the applicability of the point source FEP efficiencies for the assay of plutonium in 200 L drums, an energy dependent bias has been seen, which confirms the presence of lump attenuation in addition to the general matrix attenuation. An infinite energy extrapolation of apparent mass approach has been adopted for the assay of large volume waste drums which takes care of the gamma-ray attenuation from all sources that is otherwise difficult to correct for in a sample drum of unknown history.

For the first time, the use of a membrane based copper ferrocyanide loaded sorbent for removal of Cs+ from neutral aqueous solution is reported in this work. The results indicated high Cs+ exchange capacity (1.75 mmol/g), large distribution coefficient, as well as fast absorption of the cation in the membrane. The membrane, inspite of presence of other metal ion, exclusively absorbed 137Cs from a simulated nuclear waste solution, though the absorption rate is affected due to their presence. This composite membrane showed promising properties for Cs+ removal from nuclear waste solution.

The ion-exchange kinetics of a tracer ion (Cs+ and Ba2+) in presence of a bulk ion (Na+/H+) has been measured in Nafion-117 membrane for a range of concentrations of NaCl/HNO3 using the nonstationary radiotracer method. A systematic increase in the ion-exchange rate and decrease in the partition coefficients of the tracer ions between membrane and solution have been observed with the increase in bulk ion concentration. The sigmoidal nature of experimental profiles indicates film-diffusion-controlled kinetics even for well-stirred solutions. In the absence of an existing analytical or numerical solution, a simple empirical approach has been proposed to find the variable membrane surface concentration and has been used to solve the membrane diffusion equation by the finite difference method. The fitting of the experimental curves with a single diffusion coefficient for Cs+/Ba2+ has been achieved. The exchange rate has been found to be independent of the stirring speed beyond a limiting speed.

Two types of Cs+ ion-selective crown ether–Nafion composite membranes have been prepared. In one case, the dibenzo-21-crown-7 (DB21C7) has been incorporated uniformly in the Cs+ form of Nafion-117 membrane in varying molar ratio with respect to Cs+, and in the other case, Cs+ driven loading of DB21C7 has been confined (ion gating) to a very small thickness (25 μm) from one of the surfaces of the Nafion-117 membrane. The surface confinement of Cs+ in the ion-gated membrane has been studied by energy dispersive X-ray spectroscopy and secondary ion mass spectrometry. The cation (Cs+/Na+) transport properties of the membranes have been studied under application of electric field. In the uniformly crown-ether-loaded membranes (Cs-Naf-CR), the decrease in crown ether molar ratio has been found to increase the mobility of Cs+ through the membrane at the cost of mutual cationic selectivity (Cs+ over Na+). On the other hand, enhanced selectivity of Cs+ over Na+ with significant cationic transport at room temperatu...

The polyelectrolyte-filled (PF) cation-exchange membranes were prepared by in situ photo-polymerization in pores of the host membranes. It is expected that cationic-gel confined in pores would provide close proximity of exchange-sites leading to better diffusional-transport properties. The host membrane provides mechanical support to cationic-microgel. Poly(propylene), poly(ethersulfone) and poly(vinylidene fluoride) microporous membranes were used as the host membranes. In situ polymerization in pores was carried out by filling pores of the microporous host membrane with polymerizing solution and irradiating with 365 nm UV light. The polymerizing solution filled in pores of the host membranes consisted of required amounts of functional monomer (2-acrylamido-2-methyl-1-propane sulfonic acid), spacer ((3-acryloxypropyl)trimethoxysilane), crosslinker (ethylene glycol dimethacrylate) and UV-initiator (α,α′-dimethoxy-α′-phenyl acetophenone) dissolved in DMF and methanol (1:1) mix solvent. These PF-membranes were found to have ion-exchange capacities in the range of 1.40–1.85 meq g −1 . The proton conductivity of PF-membrane was found to be 13×10 −2 S cm −1 that is higher than proton conductivity (7.4×10 −2 S cm −1 ) in Nafion-117 membrane. The diffusional-transport properties of the PF-membrane were studied by measuring the self-diffusion coefficient (D) of different valence counterions like Ag + , Na + , Cs + , Ba 2+ and Eu 3+ ions using radiotracer method. The D values in PF-membranes varied from 0.79×10 −6 cm 2 s −1 (Na + ion) to 0.19×10 −6 cm 2 s −1 (Eu 3+ ). Contrary to this, the D values in Nafion-117 membrane varied from 1.03×10 −6 cm 2 s −1 (Na + ion) to 0.045×10 −6 cm 2 s −1 (Eu 3+ ). The wide variation of the D values in Nafion was attributed to its higher variation in water content in different ionic forms as compared to PF-membranes.

Interference of high amount of americium in the plutonium isotopic composition analysis has been studied by simulating gamma-ray spectra for Am-Pu samples over a wide composition range (5-97% (241)Am) for both power and research reactor grade plutonium. An alternate way for isotopic composition analysis has been proposed by correlating the isotopic ratios available in our old database with the experimentally obtained (241)Pu/(239)Pu isotopic ratio. The proposed method has been validated using simulated spectra of known isotopic compositions.

Copper ferrocyanide (CFCN) crystals, well known for its selectivity for Cs+ ions, have been synthesized within the pores of a polycarbonate track etched membrane (PTEM) by two compartment permeation method using CuSO4 and K4Fe(CN)6. The synthesized material has been characterized by X-ray Diffraction (XRD), Small Angle X-ray Scattering (SAXS), Energy Dispersive X-ray Fluorescence (EDXRF) and Transmission Electron Microscopy (TEM) techniques. X-ray techniques confirmed the presence of nanosized ferrocyanide particles (radius ∼40 nm) within the pores of the PTEM. It has been observed from TEM analysis that the CFCN crystals are almost uniformly filling the conical shaped pores of the PTEM with the dimension of each conical shaped structure being ∼300 nm diameter at surface and ∼140 nm diameter inside. This CFCN loaded PTEM (CFCNm) has been used to study the selective transport of Cs+ over Na+ in presence of nitric acid. The rate of cation transport has been enhanced (∼300%) by application of electric field across the membrane. A cation exchange membrane (Nafion-1135) has been coupled with the CFCNm to protect the ferrocyanide crystals from early degradation. The transport behavior of the Nafion-CFCNm composite system under different experimental conditions has been studied and explanation has been given for the differential transport of Cs+ over Na+ through this membrane. The Cs+ transport rate of the membrane has been found to be limited by the ion exchange capacity of the CFCNm.

Isotopic composition of dilute Pu solutions (1–3900 μg/mL) has been determined by analysis of HPGe detector response function in the 90–105 keV region of gamma ray spectra. Results are in excellent agreement with that obtained from mass spectrometric measurements. The present method has been successfully applied for samples of low Pu concentrations, which otherwise is not possible using the conventional 120–415 keV region of plutonium γ ray spectra.

The transport rate of ions across Nafion-117 ion-exchange membrane in a Donnan dialysis process has been measured for mono–monovalent (Na + –Cs + ) and mono–bivalent (Na + –Ba 2+ , Na + –Mg 2+ ) ion-exchange process. This has been carried out for different salt concentrations (0.01 M, 0.1 M and 0.5 M). The transport rate has also been calculated using appropriate form of Nernst–Planck equation. The self-diffusion coefficients of the ions and the ion-exchange capacity of the membrane have been given as input parameters in the calculations. The concentration of ions at the solution/membrane interface has been obtained from solution concentrations by the use of Donnan relation. The calculated time profile has been found to match with the experimental time profile at 0.1 M and 0.5 M salt concentrations. At 0.01 M concentration, there is significant deviation between the two profiles, probably showing the change in selectivity of the membrane with decrease in salt concentration. The experimental and the NP calculations have been compared with the calculations based on mass balance approach as given by Miyoshi (1996, 1997, 1998) [17–19] . The NP calculations coupled with the experimental time profile, have been used to obtain the self-diffusion coefficient of Mg 2+ ion in Nafion-117 membrane.

The self-diffusion coefficients (SDCs) of Na(+), Cs(+), and Ba(2+) have been determined in Nafion-117 membrane having mixed cationic compositions. Membranes with different proportions of Na(+)-Cs(+), Cs(+)-Ba(2+), Na(+)-Ba(2+), and Ag(+)-Ba(2+) cations have been prepared by equilibrating with solutions containing different ratios of these cations. The SDCs of the cations (D(Na), D(Cs), D(Ba)) and the ionic compositions of the membrane have been determined using a radiotracer method. For the Na-Cs and Cs-Ba systems, the SDCs of the cations have been found to be independent of the ionic compositions of the membrane. In the case of the Na-Ba system, D(Na) does not change with ionic composition, while D(Ba) has been found to be strongly dependent on the ionic composition of the membrane and decreases continuously with increasing Na(+) content in the membrane. Similar results have also been obtained for D(Ba) in the case of the Ag-Ba system. The specific conductivities (κ(imp)) of the membrane in mixed cationic forms have also been obtained from ac impedance measurement and compared with that (κ(cal)) calculated from the SDC data. For the Na-Ba system, the increment of κ(imp) with increase in the Na(+) content of the membrane has been found to be parabolic, whereas for the Na-Cs system the increment is linear. The reason behind the different behaviors for different types of ionic systems has been qualitatively explained based on different transport pathways of the cations in the membrane.

The Donnan membrane equilibrium experiments using two compartment cell have been carried out to understand the effect of speciation on the transport behavior of mercury ion through Nafion-117 ion-exchange membrane. The mercury ions have been observed to rapidly permeate to Cl− side from Hg(NO3)2 solution, showing the extraordinary preference of mercury ions for Cl− ion in aqueous solution. On the other hand, from HgCl2 solution, slow permeation of mercury ions through the membrane has been observed. Also the transport of mercury ion from HgCl2 solution has been found to be higher than expected based on Donnan membrane equilibrium principle considering the ionic concentration of HgCl2 calculated using speciation diagram. This has been attributed to the leakage of neutral HgCl2 molecules through the membrane. The leakage of neutral HgCl2 species through Nafion-117 membrane has been confirmed in different cationic forms of the membrane. An attempt has been made to determine the concentration of cati...

An activated concrete sample was counted at different source to detector distances with CdZnTe and HPGe detectors. The experimental count rates for different radionuclides were converted to dose rate using Monte Carlo code and compared with the Measured dose rates obtained using digital survey meter. The results agreed well for both the detectors. This indicates that CdZnTe detector having a better portability but poorer resolution than HPGe detector can be effectively used for online monitoring of radioactivity as well as dose rate calculations.

Monte Carlo simulation is important to get efficiencies for cases where the experimental efficiencies are difficult to get such as for samples with nonstandard geometries and for large samples. In this paper, efficiency of the HPGe detector, routinely used in our lab for a variety of samples, has been computed for point source geometry and its parameters has been optimized to match MCNP and experimental efficiencies within 5% at different sample to detector distances. This optimized geometry was then validated by efficiency transfer to other geometries.

CdZnTe detector was used to monitor the radioactivity at several locations of primary heat transport (PHT) system of the Tarapur Atomic Power Station-III & IV reactor during shut down as well as operating condition of the reactor. Dose measurements at the same locations were also carried out using a teletector. MCNP code was used to simulate the detector efficiency for the required counting geometry. The efficiencies were then used to convert the experimental count rates (cps) to corresponding activity concentration (Bq/mL) of different radionuclides in coolant water. The total dose rates in these locations were also calculated by summing up the simulated dose rates of individual γ ray energy. The simulated and the measured total dose rates were found to be in reasonably good agreement.

The transport characteristics of multivalent cations like Ba(2+) and Eu(3+) have been studied in bi-ionic form of the Nafion-117 membrane. The membranes have been prepared by loading different proportions of H(+)-Ba(2+)/Mg(2+)-Ba(2+)/Ba(2+)-Eu(3+)/H(+)-Eu(3+)/Na(+)-Eu(3+). The cationic compositions of the membranes have been determined from the measured ion exchange isotherms. Results show that the self-diffusion coefficient of Ba(2+) (D(Ba)) in H-Ba/Mg-Ba systems as well as the self-diffusion coefficient of Eu(3+) (D(Eu)) in H-Eu/Na-Eu systems are strongly dependent on the membrane ionic compositions and decreased continuously with increasing concentration of the highly hydrated ions (H(+)/Na(+)/Mg(2+)) in the membrane. Increase in the proportion of H(+)/Na(+)/Mg(2+) ions in the membrane increases the effective charge on the membrane matrix. This causes stronger electrostatic interaction of the less hydrated multivalent ions (Ba(2+)/Eu(3+)) with the membrane matrix charges, which ultimately results in their slower self-diffusion coefficients. The higher the valence, the stronger the electrostatic interaction is with the fixed ionic charges; hence, in general, D(Eu) is affected more as compared to D(Ba). On the basis of the free-volume theory for polymers, the effective interaction potential (Φ) of the Ba(2+) with the fixed ionic sites in the membrane has been calculated and found to be on the order of approximately millivolts. The higher the proportion of hydrated ion in the membrane, the higher the Φ is and the stronger the ion pair formation is with the fixed ionic sites in the membrane. However, in the Ba-Eu system, as the electrostatic interactions of the two ions with the membrane matrix are close, D(Ba) and D(Eu) are independent of the membrane ionic composition. The ionic composition dependence of D(Ba) in the H-Ba system is reflected in the transport rate of Ba(2+), showing the importance of such measurements in understanding the transport characteristics of the membrane.

The work describes a novel and cleaner approach of electrodriven selective transport of Cs from simulated nuclear waste solutions through cellulose tri acetate (CTA)/poly vinyl chloride (PVC) based polymer inclusion membrane. The electrodriven cation transport together with the use of highly Cs+ selective hexachlorinated derivative of cobalt bis dicarbollide, allows to achieve selective separation of Cs+ from high concentration of Na+ and other fission products in nuclear waste solutions. The transport selectivity has been studied using radiotracer technique as well as atomic emission spectroscopic technique. Transport studies using CTA based membrane have been carried out from neutral solution as well as 0.4 M HNO3, while that with PVC based membrane has been carried out from 3 M HNO3. High decontamination factor for Cs+ over Na+ has been obtained in all the cases. Experiment with simulated high level waste solution shows selective transport of Cs+ from most of other fission products also. Significantly fast Cs+ transport rate along with high selectivity is an interesting feature observed in this membrane. The current efficiency for Cs+ transport has been found to be ∼100%. The promising results show the possibility of using this kind of electrodriven membrane transport methods for nuclear waste treatment.

To study the possibility of modifying diffusional-transport properties of the poly(perfluorosulfonic) acid (Nafion-117) membrane, the silica particles were incorporated in its matrix by in situ sol-gel method. The amount of silica incorporated in the membrane samples was varied by controlling the equilibrating time of the membrane sample in solution containing fixed proportion of precursor tetraethylorthosilicate (TEOS), methanol and water. The silica contents in the membrane samples were characterized by gravimetry, energy dispersive X-ray analysis (EDXRF) and transmission electron microscopy (TEM). Differential scanning calorimetry (DSC) studies showed that there were no significant difference in transition peak temperatures of both samples (Nafion-117 and Nafion/SiO(2)) in same ionic form except that enthalpies were increased in Nafion/SiO(2) samples in all the ionic forms. The increase in enthalpy was due to higher water content in Nafion/SiO(2) as compared to Nafion-117 in given ionic form as enthalpies normalized with water content of the respective membrane were comparable. The ion-exchange capacity, water uptake capacity and ion-exchange isotherms of the Na(+) + Cs(+) and Na(+) + Ba(2+) binary systems in silica embedded membrane samples were experimentally measured using appropriate radiotracers, and compared with that of pristine Nafion-117 membrane. The specific conductivities of the membrane samples with and without silica were studied in Na(+), Cs(+) and Ba(2+) ionic forms by electrochemical impedance spectroscopy (EIS). The self-diffusion coefficients of Na(+), Cs(+) and Ba(2+) ions in the Nafion/SiO(2) were measured by the radiotracer method. It was observed from the experimentally measured specific conductivities and self-diffusion coefficients data that diffusion mobility of Cs(+) and Ba(2+) counter-ions were enhanced significantly after incorporation of SiO(2) in the Nafion-117 matrix. Contrary to this, diffusion mobility of Na(+). counter-ion decreased in Nafion/SiO(2) sample. The selectivity of Cs(+) and Ba(2+) counter-ions was reduced in Nafion/SiO(2) sample with respect to pristine Nafion-117. (C) 2011 Elsevier B.V. All rights reserved.

Studies on isotopic and ion-exchange kinetics of mercury ions in Nafion-117 membrane have been carried out with (203)Hg radiotracer in the presence of Cl(-) and NO(3)(-) in solution. The results of isotopic-exchange kinetics indicate that mercury ions diffuse into the membrane as monovalent cation from HgCl(2) solution while as divalent ion from Hg(NO(3))(2) solution. The studies on the kinetics of ion exchange of Hg(2+) with Na(+) follow the prediction of the Nernst-Planck equation when NaNO(3) is used as an external salt solution. The Nernst-Planck equation fails to predict the kinetics when NaCl is used as an external salt solution, indicating that the complexation of Cl(-) with Hg(2+) in the membrane influences the kinetics. Permeation studies using (203)Hg and (36)Cl radiotracer between two HgCl(2) solutions show that the permeability coefficients of mercury and chloride ions are the same, indicating the cotransport of mercury and chloride ions through the membrane. Ion-exchange equilibrium studies using a mixture of HgCl(2) and HNO(3) solution were carried out to ascertain the species transporting through the membrane. The equilibrium sorption of mercury in the membrane shows the uptake of an ionic species, presumably HgCl(+), not a neutral salt. The speciation diagrams, calculated as a function of pH, show wide divergence of species present in HgCl(2) and Hg(NO(3))(2) solution and explain the difference in membrane transport behavior for HgCl(2) and Hg(NO(3))(2) solution. The results show that any ion-exchange-membrane-based separation of Hg(2+) needs careful consideration regarding the anions present in the solution, as it influences the speciation of mercury and hence its transport behavior through the membrane.