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Iodine radioisotopes released during nuclear fuel reprocessing must be removed from the off-gas stream before discharge. One promising material for iodine capture is reduced silver mordenite (Ag0Z). Nevertheless, the adsorbent's capacity will degrade, or age, over time when the material is exposed to other off-gas constituents. Though the overall impact of aging is known, the underlying physical and chemical processes are not. To examine these processes, Ag0Z samples were prepared and aged in 2% NO2 in dry air and in 1% NO in N2 gas streams at 150 °C for up to six months. Aged samples were then characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray absorption spectroscopy. These techniques show that aging involves two overarching processes: (i) oxidation of the silver nanoparticles present in Ag0Z and (ii) migration of oxidized silver into the mordenite's inner network. Silver on the nanoparticle's surface is oxidized through adsorption of O2, NO, and NO2. Raman spectroscopy and X-ray absorption spectroscopy indicate that nitrates are the primary products of this adsorption. Most of these nitrates migrate into the interior of the mordenite and exchange at framework binding sites, returning silver to its unreduced state (AgZ). The remaining nitrates exist at a persistent concentration without aggregating into bulk-phase AgNO3. X-ray absorption spectroscopy results further indicate that iodine adsorption occurs on not just Ag0Z but also on AgZ and a portion of the nitrates in the system. AgZ adsorbs a sizable quantity of iodine early in the aging process, but its capacity drops rapidly over time. For well-aged samples, nitrates are responsible for up to 95% of mordenite's iodine capacity. These results have enhanced our understanding of the aging process in silver mordenite and are expected to guide the development of superior adsorbents for the capture of radioactive iodine from reprocessing off-gas.

Global demand for nuclear energy is expected to rise in the coming decades. To meet these growing needs, new uranium resources must be explored. One of the potential alternatives to traditional ura...

The salt removal capacity (SRC) of the carbon electrodes in membrane capacitive deionization (MCDI) is limited by the applied potential (

Self-charging of radioactive uranium oxide particles was measured by comparing the electrostatic surface-charge characteristics of the uranium particles to various airborne dust particulates. Though radioactive aerosols can gain charge through various decay mechanisms, researchers have traditionally assumed that the radioactive aerosols do not carry any additional charge relative to other atmospheric dust particles as a consequence of charge neutralization over time. In this work, we evaluate this assumption by directly examining the surface charge and charge density on airborne uranium oxide particles and then comparing those characteristics with charging of other natural and engineered airborne dust particles. Based on electric field–assisted particle levitation in air, the surface charge, charge distribution as a function of particle size, and surface charge density were determined for uranium oxide aerosols (

Oceanic uranium represents a vast fuel resource that could ensure the long-term sustainability of nuclear power. A new study seeks to harness that potential by developing a bioinspired adsorbent membrane capable of capturing uranium from seawater.

With global demand for nuclear power expected to rise, new nuclear fuel resources must be explored to ensure the viability and sustainability of nuclear power. Uranium recovery from seawater is one potential source, though the low concentration of uranium in seawater is a significant obstacle. As a concentrate of seawater, desalination brine reject would have a significantly higher uranyl concentration. In this work, the adsorption of uranium and competing ions in brine reject is investigated. Adsorption experiments were performed over 84 days in 5-gallon batch tanks with amidoxime adsorbents and samples taken from the feed seawater and reverse osmosis brine reject of the Tampa Bay Desalination Plant. The aqueous concentration and adsorbed mass of uranium, zinc, copper, iron, vanadium, calcium, and magnesium were determined through inductively coupled plasma mass spectroscopy. Aqueous adsorption modeling was used to simulate speciation and adsorption of these ions under the experimental conditions. The ad...

Neutralization of the bio-oil pH has been shown to generate a neutralized bio-oil aqueous phase (NBOAP) that includes most of the acidic components and a neutralized bio-oil organic phase (NBOOP) that includes hydrophobic organics, such as phenols. NBOOP can be used for fuel production, while NBOAP can be fed to microbial electrolysis cells (MECs) for hydrogen production. After pH neutralization, some organic acidic components remain in NBOOP. This work is focused on capturing acidic compounds from NBOOP through water extraction and electrosorption, and demonstrating hydrogen production via MECs. Capacitive deionization (CDI) is proven effective in capturing ions from NBOOP-contacted water and NBOAP via electrosorption. Captured acidic compounds enable the MEC application to effectively produce renewable hydrogen. Chemical oxygen demand (COD) removal of 49.2%, 61.5%, and 60.8% for 2, 4, and 10 g/L-anode/day loading were observed, corresponding to a total COD degradation of 0.19 g/L, 0.79 g/L, and 1.3 g/L, respectively. A maximum hydrogen productivity of 4.3 L-H2/L-anode/day was obtained. Major compounds in the water phase such as fatty acids, sugar derivatives, furanic and phenolic compounds were converted to hydrogen with an efficiency of 80–90%. This approach may lead the entire biomass pyrolysis process to be an overall carbon-neutral process.

This work is related to the removal of tritiated water and radioactive iodine from off-gases released during spent nuclear fuel reprocessing. Specifically, it is focused on the adsorption equilibrium of water on reduced silver mordenite (Ag0Z), which is the state-of-art solid adsorbent for iodine retention in the off-gas treatment. As the off-gases contain different gas species, including iodine and water, Ag0Z would take up iodine and water simultaneously during the adsorption process. Therefore, understanding the adsorption of water on Ag0Z is important and necessary for studying the performance of Ag0Z in off-gas treatment processes. The isotherms of water (nonradioactive water) on Ag0Z were obtained at temperatures of 25, 40, 60, 100, 150, and 200 °C with a continuous-flow adsorption system. The data were analyzed using the Heterogeneous Langmuir and generalized statistical thermodynamic adsorption (GSTA) models, and thermodynamic parameters of the isotherms were obtained from both models. Both models...

One of the current barriers to achieving fast and stable performance for flow-electrode capacitive deionization (FCDI) is determining optimal operating parameters. To date, however, no consensus has been reached for universal conditions for FCDI. Through experimental and modeling approaches in this study, we systematically evaluated the influence of applied potential (V = 1.2–2.4 V) and electrolyte concentration (C0 = 0.05–0.5 M) on the FCDI and electrodialysis (ED) desalination processes. Evaluation indicators include the concentration decrease in the desalinated solution, salt removal rates, pH fluctuations, charge efficiency, and energy consumption. Results demonstrated that the dynamic curves of concentration decrease at 2.0 V nearly overlapped with the response at 1.6 V at certain electrolyte concentrations, while the salt removal rates at 0.2 M salt concentration were the best among all concentrations tested at a range of applied potential. It was thus concluded that the optimum conditions for FCDI operation are 1.6 V applied potential and 0.2 M initial salt concentration, under which faradaic reactions are not being triggered, and concentration polarization does not significantly affect ion transfer. Furthermore, a comparative study between FCDI and ED indicated that ED has a different dependence on the electrolyte concentration and applied potential, in which the desalination can be linearly enhanced with increasing potential but greatly limited at high concentrations. Due to the presence of carbon particles in FCDI, the enhanced charge/ion transfer is probably the main reason for the different desalination performance of FCDI and ED. The optimal operating parameters obtained in this work could be used as basic test conditions for further development of new carbon-based materials for FCDI.

Seawater contains uranium at an average concentration of 3.3 ppb, as well as a variety of other ions at either overwhelmingly higher or similar concentrations, which complicate the recovery of uranium. This report describes an investigation of the effects of various factors such as uranium speciation and presence of salts including sodium, calcium, magnesium, and bicarbonate, as well as trace elements such as vanadium on uranium adsorption kinetics in laboratory experiments. Adsorption models are also developed to describe the experimental data of uranium extraction from seawater. Results show that the presence of calcium and magnesium significantly slows down the uranium adsorption kinetics. Vanadium can replace uranium from amidoxime-based adsorbent in the presence of sodium in the solution. Results also show that bicarbonate in the solution strongly competes with amidoxime for binding uranium, and thus slows down the uranium adsorption kinetics. Developed on the basis of the experimental findings, the ...

Recovering uranium from seawater has been the subject of many studies for decades, and has recently seen significant progress in materials development since the U.S. Department of Energy (DOE) has become involved. With DOE direction, the uranium uptake for amidoxime-based polymer adsorbents has more than tripled in capacity. In an effort to better understand how these new adsorbent materials behave under different environmental stimuli, several experimental and modeling based studies have been employed to investigate impacts of competing ions, salinity, pH, and other factors on uranium uptake. For this study, the effect of temperature and type of comonomer on uranium adsorption by three different amidoxime adsorbents (AF1, 38H, AI8) was examined. Experimental measurements of uranium uptake were taken in 1-L batch reactors from 10 to 40 °C. A chemisorption model was developed and applied in order to estimate unknown system parameters through optimization. Experimental results demonstrated that the overall uranium chemisorption process for all three materials is endothermic, which was also mirrored in the model results. Model simulations show very good agreement with the data and were able to predict the temperature effect on uranium adsorption as experimental conditions changed. This model may be used for predicting uranium uptake by other amidoxime materials.

The influence of low-amplitude, high-frequency, pulsed electrical potential on ion transport in mesoporous carbon electrodes has been investigated. Mesoporous carbon electrodes of approximately 10-nm average pore size were synthesized based on a soft-template method. The carbon electrodes were used in capacitive deionization experiments with salt solutions consisting of a mixture of ions of concentrations ranging from 5000 ppm to 10,000 ppm to investigate the effect of a pulsed potential on the ion removal rate. Higher rates of sorption and regeneration were observed when the pulsed potential was superimposed on a direct current (DC) offset of 1.2 V that is typically applied in capacitive deionization (CDI). The rate of ion sorption in CDI experiments was dependant on the amplitude and frequency of the pulsed potential. Conductivity measurements showed enhancement in transport rates due to the pulsed potential up to 130%. The effect was stronger during regeneration. Neutron imaging, a visualization technique, was also employed to quantify the diffusion of ions through mesoporous carbon electrodes under different conditions. Sequences of neutron images showed enhanced transport of gadolinium ions under the influence of pulsed potential. From the concentration histories of gadolinium ions inside the carbon electrodes, the effective diffusion coefficient of gadolinium ions was estimated at 8.3 ± 0.4 × 10−11 m2/s at 1.2 V DC and 1.1 × 10−10 m2/s at 1.2 V DC with pulsed potential added.

Neutron imaging was used to study cathode water content over time in a three-dimensional-cathode enzyme fuel cell (EFC). A porous carbon felt cathode allowed air to flow through the electrode. A solution with laccase and a mediator formed an aqueous layer on the electrode surface. Water loss was observed in situ via neutron imaging for varying experimental conditions, including flow rates of hydrogen and air, cathode inlet humidity, volume of enzyme solution, and its composition. Cathode water loss occurred for all experimental conditions, but the loss rate was noticeably reduced when a high-salt-concentration enzyme solution was used in the cathode in conjunction with increased humidity in the air feed stream. Results from neutron imaging and power density analysis were used in analyzing the causes that could contribute to EFC water loss. An increase in temperature due to the exothermic cathode reaction is considered a plausible cause of cathode water loss via evaporation. This is the first reported application of neutron imaging as a technique to study EFC water management. The results suggest that neutron imaging can be employed to provide a better understanding of EFC phenomena and thereby contribute to design and operational improvements of EFCs.

Proton-exchange-membrane fuel cells (PEMFC) are highly dependent on operating conditions, such as humidity and temperature. This study employs electrochemical impedance spectroscopy (EIS) to measure the effects of operating parameters on internal proton and electron transport resistance mechanisms in the PEMFC. Current-density experiments have been performed to measure the power production in a 25 cm2 Nafion 117 PEMFC at varying operating conditions. These experiments have shown that low humidity and low temperature contribute to decreased power production. EIS is currently employed to provide a better understanding of the mechanisms involved in power production by calculating the specific resistances at various regions in the PEMFC. Experiments are performed at temperatures ranging from 30 to 50°C, feed humidities from 20 to 98%, and air stoichiometric ratios from 1.33 to 2.67. In all experiments, the hydrogen feed stoichiometric ratio was approximately 4.0. EIS is used to identify which transpo...

Unfavorable aggregation and deposition of colloidal particles in natural and engineered systems is still a subject of debate. Complicating factors such as surface roughness, secondary minimum aggregation, and the nature of discrete surface charge and surface potential make it difficult to attribute a specific cause to these phenomena. The presence of surface charge heterogeneity and its influence on interaction forces, which are responsible for aggregation and deposition, are studied in this work through the application of atomic force microscopy (AFM). Force-volume-mode AFM was used to map interaction forces on a surface and relate them to surface charge heterogeneities. The experimental system consisted of a silica plate and a standard silicon nitride AFM tip. Copper ions were used for sorption on the silica surface in order to modify the surface charge and cause charge reversal. Different concentrations of copper ions were selected to identify conditions of partial coverage of the silica surface. The pH and ionic strength of the solutions were varied, and the extension of the surface charge modification and its influence on the resulting interaction forces were monitored via AFM force measurements. Depending on the pH and ionic strength, the interaction force was found to change at certain regions on the surface from attraction to either weak or strong repulsion. Force imaging allowed the visual localization of zones of strong repulsive interaction that diminished in size with increasing ionic strength. X-ray photoelectron spectroscopy analysis was used to confirm the presence of copper on the surface. Local charge differences on a surface result in local differences in surface forces, not only in magnitude but also in direction. This behavior may explain the aggregation, deposition, and transport of colloidal particles under unfavorable chemical conditions.

A sorption modeling approach based on surface complexation concepts was applied to predict copper uptake and its effects on the surface electrostatic potential of ferric oxide and silica colloids. Equilibrium modeling of copper uptake by ferric oxide using the traditional surface complexation model (SCM) was reasonably successful with some discrepancies especially in the acidic pH ranges and high colloid concentration cases. Good predictions of the ferric oxide charge reversals during uptake were obtained from the modeling. Based on the SCM predictions, copper removal from solution is due to the outer-sphere complexation of the first hydrolysis product, resulting in the surface-metal complex SO − CuOH + . The SCM was found to be insufficient to describe copper uptake by silica particles. To address discrepancies between experimental data and SCM predictions, the SCM was modified to include attributes of the surface polymer model (SPM), which incorporates sorption of the dimeric copper species Cu 2 (OH) 2 2+ . The continuum model (CM) was also studied as a second modification to the SCM to include formation of surface precipitates. Both the SPM and the CM were successful in modeling copper uptake and ζ potential variations as a function of pH at various solution conditions and colloid concentrations. From the SPM and CM predictions, it was concluded that for systems with high surface loadings, copper removal from solution occurs due to the formation of both monomeric and dimeric surface complexes, as well as through precipitation mechanisms.

Experimental studies were carried out to determine the effects of influent pH, ionic strength, metal concentration, and empty-bed contact time (EBCT) on copper sorption in the activated carbon fixed-bed columns. As the influent pH was increased, the column performance significantly improved. An overshoot of the effluent concentration was observed at pH 3.0 due to desorption of copper from the surface–metal complexes. The uptake enhanced as the ionic strength was increased; however, this role was much weaker than that of pH. An increase in metal concentration resulted in a decrease in the bed volumes at the breakthrough. In the beginning of all the experiments, the effluent pH increased dramatically and then dropped and approached lower values. Less sorption was observed when prewashed columns were used, in which the pH in the columns was kept constant. Modelling of the metal sorption in the prewashed columns was performed using a metal ion transport model hydrogeochem and a fixed-bed model.

This study is focused on the formation of the electrical double layer (EDL) inside uniform platinum nanochannels. Strong hysteresis of adsorption/desorption of protons observed in cyclic voltammetry experiments suggests that adsorption is controlled by ion diffusion through the charged nanochannels whereas desorption is controlled by the electrical potential. It was determined that the nanostructured platinum electrodes prepared in this study were selective for halogen ions. The sorption capacity decreased in the order of F- > Cl- > Br-.

Atomic force microscopy (AFM) is employed to directly measure colloidal surface forces between a silica particle and a smooth glass plate in an aqueous solution with or without the presence of copper ions. Without the presence of copper ions, results show that the force between these two surfaces is repulsive and that its magnitude decreases with increasing ionic strength and decreasing pH. The surface forces are calculated based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for constant surface charge and are then compared with AFM force measurements. A good agreement between theory and experimental data is reported except at very small separation distances (3 nm) between the silica particle and the glass plate. This behavior may be attributed to non-DLVO forces, such as the hydration effect that results from the bounded water molecules on the surface of the silica particle, or to surface roughness. When copper ions are present in acidic aqueous solutions, the magnitude of the force is found to be the same as that without the presence of copper ions, which indicates that no sorption of copper ions by the silica particle occurs under these conditions. Near neutral pH, sorption of copper ions causes charge reversal for the silica particle from negative to positive. Therefore, the force between the silica particle and the glass plate changes from repulsive to attractive. The transient zeta-potential of the silica particle during sorption of copper ions is determined by representing the experimental data with the DLVO theory. In alkaline solutions, where removal of copper ions is known to occur mainly by bulk precipitation, the measured force is similar to that without the presence of copper ions, which suggests that sorption does not occur under such conditions.

Groundwater and soil contamination with depleted uranium (DU) isan important public concern because of its long-term toxicity. In this study, the DU risk in groundwater was assessed through modeling of its sorption equilibrium and kinetics, as well as modeling of its transport in natural subsurface systems. Wheneverpossible, simulation results were compared with published experimental and field data. Equilibrium modeling studies showedthat DU sorption increased sharply from 0 to 100% in the pH range of 3.5 to 5.0 and maximum immobilization was established at pH > 5. Kinetic simulations indicated that the sorption of DUin subsurface systems is a rapid process. Simulations of DU mobility due to groundwater flow and due to infiltration, as wellas modeling of DU fate, were carried out by using a metal ion transport model, which included aqueous speciation, redox, precipitation, and sorption reactions. The results showed that the DU mobilization is a relatively slow process. Precipitation,redox, and sorption reactions resulted in the immobilization of DU. Among these reactions, sorption played a major role, and thepH of soils was critical in the immobilization; higher pH in soils resulted in greater immobilization of DU. The impact of DUtransport from infiltration was estimated based on four extremecases of climate and existing conditions of uranium penetrator fragments. The simulations demonstrated that the transport of DU in groundwater is slow due to the low infiltration rate and lowDU concentration resulted from the penetrators. Finally, modelingof DU fate showed that the natural cleanup of the DU-contaminatedsites is a slow process.

Desalination of high-salinity solutions has been studied using a novel experimental technique and a theoretical model. Neutron imaging has been employed to visualize lithium ions in mesoporous carbon materials, which are used as electrodes in capacitive deionization (CDI) for water desalination. Experiments were conducted with a flow-through CDI cell designed for neutron imaging and with lithium-6 chloride ((6)LiCl) as the electrolyte. Sequences of neutron images have been obtained at a relatively high concentration of (6)LiCl solution to provide information on the transport of ions within the electrodes. A new model that computes the individual ionic concentration profiles inside mesoporous carbon electrodes has been used to simulate the CDI process. Modifications have also been introduced into the simulation model to calculate results at high electrolyte concentrations. Experimental data and simulation results provide insight into why CDI is not effective for desalination of high ionic-strength solutions. The combination of experimental information, obtained through neutron imaging, with the theoretical model will help in the design of CDI devices, which can improve the process for high ionic-strength solutions.

Copper uptake by ferric oxide and silica particles is studied through batch kinetic experiments. Copper uptake rates are found to be strongly dependent on pH and on the sorbate/sorbent molar concentration ratio. Dramatic changes to the zeta potential of both colloids from baseline values are observed. Modeling of copper uptake and zeta potential charge reversals using the surface complexation model (SCM) yields poor descriptions under high surface coverage conditions. The conventional SCM, modified in the recent literature to (i) the surface polymer model (SPM), which additionally incorporates uptake of dimeric copper species; and (ii) the continuum model (CM), which includes formation of surface precipitates, is extended here to model uptake kinetics. Both the SPM and the CM are successful in modeling copper uptake rates as well as zeta potential variations over a wide range of solution conditions. For systems with high surface loadings, copper removal from solution appears to result from the formation of monomeric and dimeric surface complexes, as well as through precipitation mechanisms. It is further concluded that a kinetic model incorporating diffusion through the surface film of sorbed and precipitated copper species as the rate-limiting process, in association with the SPM and CM, successfully describes the effect of pH and colloid concentration on copper uptake and oxide particle zeta potential histories.

An electrical double-layer model is developed to predict electrosorption of ions from aqueous solutions by carbon aerogel electrodes. The carbon aerogel electrodes are treated as electrical double-layer capacitors, and electrosorption is modeled using classical electrical double-layer theory. Because of the porous characteristics of the electrodes, the total capacity of the system is obtained by summing the contributions of the individual pores. The pore size distribution of the carbon aerogel is measured by the physical adsorption of N2 and CO2 as well as by mercury intrusion porosimetry. When a pore has a width smaller than a specific value (cutoff pore width), it does not contribute to the total capacity because of the electrical double-layer overlapping effect. This effect greatly reduces the electrosorption capacity for electrodes with significant numbers of micropores, such as carbon aerogel; thus, it is considered in the electrical double-layer model. The model in this study focuses on the electros...

X-ray photoelectron spectroscopy (XPS) is employed to study chemical interactions between three metal ions — Cu(II), Mo(VI), and Cr(VI) — and chitosan, a natural biopolymer extracted from crab shells. Three forms of chitosan are used — flakes, beads, and modified beads obtained by glutaraldehyde cross-linking. XPS provides identification of the sorption sites involved in the accumulation of metals, as well as the forms of species sorbed on the biopolymer. It is found that sorption occurs on amine functional groups for all the three metals. With copper, the sorption step is not followed by reduction of the metal. More complex phenomena are involved in molybdate removal. A partial reduction (about 20–25% of the total molybdenum content) occurs with chitosan beads and flakes. The distribution of reduced Mo(V) on the surface of the sorbent differs from that in the bulk of the sorbent for raw chitosan beads, while the glutaraldehyde cross-linking allows uniform distribution of reduced Mo(V) throughout the sorbent. The difference between these two forms of chitosan can be related to a complementary photoreduction step occurring on the surface of the biopolymer. For chromium, a similar trend with molybdenum is followed but to a greater extent; with cross-linked sorbents all chromate previously sorbed is reduced to Cr(III), while with raw chitosan beads Cr(VI) reduction does not exceed 60%.

Copper uptake by ferric oxide and silica particles is studied through batch equilibrium and kinetic experiments under different conditions of pH and ionic strength. Acid–base titrations of the oxide particles indicate that the point of zero charge is 3.0 for the ferric oxide and 4.7 for the silica particles used in this study. For the same particles, electrokinetic measurements show an isoelectric point of 2.2 for ferric oxide and 2.7 for silica. The extent of metal removal is found to strongly depend on solution conditions and to increase with an increase in pH. Changes in ionic strength cause little or no significant change in the pH dependence of ion uptake. From control experiments, as well as from copper hydrolysis and speciation calculations, copper precipitation (as CuO) is evident above pH 6. In the acidic and neutral pH ranges, a marked increase in the ζ potential of both sorbents from baseline values is found during equilibrium copper uptake. Size distribution measurements show an increase in the number of flocculated sorbent particles at pH values corresponding to the steep increase in copper uptake. Further, at highly acidic pH ranges silica particles are found to be well stabilized and non-flocculating in equilibrium uptake studies. Similar findings are observed with ferric oxide particles at highly alkaline pH values. Kinetic studies indicate that copper uptake by ferric oxide is a much slower process as compared with uptake by silica under the conditions studied here. Also, the lower the sorbate/sorbent molar concentration ratio, the faster is the rate of copper uptake. With both particles, a rapid increase in ζ potential is observed within the first few minutes. Floc formation and breakage are evident from size distribution measurements. These findings indicate a possible role of metal ion uptake in particle flocculation kinetics through alteration of the ζ potential of sorbent particles.

Ozone is widely used to deactivate microorganisms and remove organic contaminants in water industries. However, interest also exists in using radical species, which are stronger oxidants than ozone...

Equilibrium and kinetic experiments of copper ion uptake by calcium alginate beads were carried out under different values of pH, ionic strength, initial concentration of copper ion, and amount of calcium alginate. The removal efficiency increases with increasing pH and decreasing ionic strength and initial concentration. The removal of copper occurs rapidly in the first hour, followed by a slow process that takes about 15 h. The copper ion uptake becomes faster with increasing pH and decreasing initial copper concentration and ionic strength. Mass transport of copper ions plays an important role in the kinetics of uptake. Equilibrium experiments show that surface complex formation is the major mechanism for copper ion uptake. Modeling of equilibrium and kinetics was also conducted based on a surface complexation approach. Modeling results showed that the two-pK Basic Stern model can successfully describe the effect of pH on equilibrium uptake. A diffusion-controlled model can also predict the effect of p...

Copper biosorption from aqueous solutions by calcium alginate is reported in this paper. The experimental section includes potentiometric titrations of biosorbents, batch equilibrium and kinetic studies of copper biosorption, as well as fixed-bed biosorption experiments. The potentiometric titration results show that the surface charge increases with decreasing pH. The biosorption of copper strongly depends on solution pH; the metal ion binding increases from 0 to 90 percent in pH ranging from 1.5 to 5.0. In addition, a decrease in ionic strength results in an increase of copper ion removal. Kinetic studies indicate that mass transfer plays an important role in the biosorption rate. Furthermore, a fixed-bed biosorption experiment shows that calcium alginate has a significant capacity for copper ion removal. The two-pK Basic Stern model successfully represents the surface charge and equilibrium biosorption experimental data. The calculation results demonstrate that the copper removal may result fr...

Neutron imaging is presented as a tool for quantifying the diffusion of ions inside porous materials, such as carbon electrodes used in the desalination process via capacitive deionization and in electrochemical energy-storage devices. Monolithic mesoporous carbon electrodes of ∼10 nm pore size were synthesized based on a soft-template method. The electrodes were used with an aqueous solution of gadolinium nitrate in an electrochemical flow-through cell designed for neutron imaging studies. Sequences of neutron images were obtained under various conditions of applied potential between the electrodes. The images revealed information on the direction and magnitude of ion transport within the electrodes. From the time-dependent concentration profiles inside the electrodes, the average value of the effective diffusion coefficient for gadolinium ions was estimated to be 2.09 ± 0.17 × 10(-11) m(2) s(-1) at 0 V and 1.42 ± 0.06 × 10(-10) m(2) s(-1) at 1.2 V. The values of the effective diffusion coefficient obtained from neutron imaging experiments can be used to evaluate model predictions of the ion transport rate in capacitive deionization and electrochemical energy-storage devices.

Copper adsorption by granular activated carbon is reported in this paper. The experimental section includes titrations of activated carbon, as well as equilibrium and kinetic studies of copper adsorption. The potentiometric titration results show that the point of zero charge is 9.5, and that the surface charge increases with decreasing pH. The adsorption of copper strongly depends on solution pH and increases from 10 to 95% at pH ranging from 2.3 to 8. A dramatic increase in pH and emission of small gas bubbles are observed during the experiments, which may result from adsorption of hydrogen ion and/or reduction-oxidation reactions. The two-pK triple-layer model is employed to describe copper adsorption. KINEQL, an adsorption kinetics algorithm, is used to represent the experimental data, and it is found that the model can describe reasonably well the experimental measurements of surface charge, adsorption equilibrium, and adsorption kinetics. Calculations show that formation of the surface-metal complexes SO−Cu2+ and SO−CuOH+ (a hydrolysis product of SO−Cu 2+) in the outer layer around the surface of carbon results in removal of copper ion. It is also found that mass transfer controls the adsorption rate, and that adsorption occurs in the micropore region where both external mass transfer and diffusion are important.

Self-assembled mesoporous carbon (MC) materials have been synthesized and tested for application in capacitive deionization (CDI) of saline water. MC was prepared by self-assembly of a triblock copolymer with hydrogen-bonded chains via a phenolic resin, such as resorcinol or phloroglucinol in acidic conditions, followed by carbonization and, in some cases, activation by KOH. Carbon synthesized in this way was ground into powder, from which activated MC sheets were produced. In a variation of this process, after the reaction of triblock copolymer with resorcinol or phloroglucinol, the gel that was formed was used to coat a graphite plate and then carbonized. The coated graphite plate in this case was not activated and was tested to serve as current collector during the CDI process. The performance of these MC materials was compared to that of carbon aerogel for salt concentrations ranging between 1000 ppm and 35,000 ppm. Resorcinol-based MC removed up to 15.2 mg salt per gram of carbon, while carbon aerogel removed 5.8 mg salt per gram of carbon. Phloroglucinol-based MC-coated graphite exhibited the highest ion removal capacity at 21 mg of salt per gram of carbon for 35,000 ppm salt concentration.