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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Iodide Sorption to Clays and the Relationship to Surface Charge and Clay Texture - 12356

Iodine is assumed to behave conservatively in clay barriers around nuclear waste repositories and in natural sediments. Batch experiments tend to show little to no sorption, while in column experiments iodine is often retarded relative to tritiated water. Current surface complexation theory cannot account for negatively charged ion sorption to a negatively charged clay particle. Surface protonation and iodide sorption to clay minerals were examined using surface titrations and batch sorption experiments with a suite of clay minerals. Surface titrations were completed spanning a range of both pH values and ionic strengths. For reference, similar titrations were performed on pure forms of an Al-O powder. The titration curves were deconvoluted to attain the pKa distribution for each material at each ionic strength. The pKa distribution for the Al-O shows two distinct peaks at 4.8 and 7.5, which are invariant with ionic strength. The pKa distribution of clays was highly variable between the different minerals and as a function of ionic strength. Iodide sorption experiments were completed at high solid:solution ratios to exacerbate sorption properties. Palygorskite and kaolinite had the highest amount of iodide sorption and montmorillonite had the least. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Effect of Water Content on Sodium Chloride Sorption in Cross-Linked Cation Exchange Membranes

Ion exchange membranes used for energy generation and water purification selectively transport ions, and this characteristic is strongly influenced by ion sorption in such membranes. Although water content and fixed charge group concentration are key factors affecting ion sorption in ion exchange membranes, their individual effects on ion sorption are not often studied. Here, a series of cross-linked cation exchange membranes (CEMs) were synthesized with different water uptake values and similar fixed charge group concentrations to study the effect of water content on ion sorption in such materials. Equilibrium co-ion concentrations in all membranes were very similar at a given external salt concentration, suggesting that co-ion sorption in these materials was mainly influenced by fixed charge group concentration rather than water content per se. Equilibrium co-ion sorption data were interpreted using a thermodynamic model based on Donnan theory and Manning’s counterion condensation theory. The inhomogeneous morphology of the membranes was characterized by small-angle X-ray scattering (SAXS). The Manning parameter was used as an adjustable constant to account for morphological heterogeneity. The Manning parameter was less than the critical value for these CEMs, suggesting no counterion condensation occurred. Good agreement was observed between the model and experimental co-ion sorption data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Effects of Radiation and Temperature on Iodide Sorption by Surfactant-Modified Bentonite

Bentonite, which is used as an engineered barrier in geological repositories, is ineffective for sorbing anionic radionuclides because of its negatively charged surface. This study modified raw bentonite using a cationic surfactant (i.e., hexadecyltrimethylammonium [HDTMA]-Br) to improve its sorption capability for radioactive iodide. The effects of temperature and radiation on the iodide sorption of surfactant-modified bentonite (SMB) were evaluated under alkaline pH condition similar to that found in repository environments. Different amounts of surfactant, equivalent to the 50, 100, and 200% cation-exchange capacity of the bentonite, were used to produce the HDTMA-SMB for iodide sorption. The sorption reaction of the SMB with iodide reached equilibrium rapidly within 10 min regardless of temperature and radiation conditions. The rate of iodide sorption increased as the amount of the added surfactant was increased and nonlinear sorption behavior was exhibited. However, high temperature and γ-irradiation (60Co) resulted in significantly (~2–10 times) lower iodide Kd values for the SMB. The results of Fourier transform infrared spectroscopy analysis suggested that the decrease in iodide sorption may be caused by weakened physical electrostatic force between the HDTMA and iodide, and by the surfactant becoming detached from the SMB during the heating and irradiation processes.

bentonite↗
DOE OSTI2013

“Multi-temperature” method for high-pressure sorption measurements on moist shales

A simple and effective experimental approach has been developed and tested to study the temperature dependence of high-pressure methane sorption in moist organic-rich shales. This method, denoted as “multi-temperature” (short “multi-T”) method, enables measuring multiple isotherms at varying temperatures in a single run. The measurement of individual sorption isotherms at different temperatures takes place in a closed system ensuring that the moisture content remains constant. The multi-T method was successfully tested for methane sorption on an organic-rich shale sample. Excess sorption isotherms for methane were measured at pressures of up to 25 MPa and at temperatures of 318.1 K, 338.1 K, and 348.1 K on dry and moisture-equilibrated samples. The measured isotherms were parameterized with a 3-parameter Langmuir-based excess sorption function, from which thermodynamic sorption parameters (enthalpy and entropy of adsorption) were obtained. Using these, we show that by taking explicitly into account water vapor as molecular species in the gas phase with temperature-dependent water vapor pressure during the experiment, more meaningful results are obtained with respect to thermodynamical considerations. The proposed method can be applied to any adsorbent system (coals, shales, industrial adsorbents) and any supercritical gas (e.g., CH{sub 4}, CO{sub 2}) and is particularly suitable for sorption measurements using the manometric (volumetric) method.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Quantification of Cation Sorption to Engineered Barrier Materials Under Extreme Conditions

The objective of this research is to examine mechanisms and thermodynamics of actinide sorption to engineered barrier materials (iron (oxyhydr)oxides and bentonite clay) for nuclear waste repositories under high temperature and high ionic strength conditions using a suite of macroscopic and microscopic techniques which will be coupled with interfacial reaction models. Gaining a mechanistic understanding of interfacial processes governing the sorption/sequestration of actinides at mineral-water interfaces is fundamental for the accurate prediction of actinide behavior in waste repositories. Although macroscale sorption data and various spectroscopic techniques have provided valuable information regarding speciation of actinides at solid-water interfaces, significant knowledge gaps still exist with respect to sorption mechanisms and the ability to quantify sorption, particularly at high temperatures and ionic strengths. This objective is addressed through three major tasks: (1) influence of oxidation state on actinide sorption to iron oxides and clay minerals at elevated temperatures and ionic strengths; (2) calorimetric titrations of actinide-mineral suspensions; (3) evaluation of bentonite performance under repository conditions. The results of the work will include a qualitative conceptual model and a quantitative thermodynamic speciation model describing actinide partitioning to minerals and sediments, which is based upon a mechanistic understanding of specific sorption processes as determined from both micro-scale and macroscale experimental techniques. The speciation model will be a thermodynamic aqueous and surface complexation model of actinide interactions with mineral surfaces that is self-consistent with macroscopic batch sorption data, calorimetric and potentiometric titrations, X-ray absorption Spectroscopy (XAS, mainly Extended X-ray Absorption Fine Structure (EXAFS)), and electron microscopy analyses. The novelty of the proposed work lies largely in the unique system conditions which will be examined (i.e. elevated temperature and ionic strength) and the manner in which the surface complexation model will be developed in terms of specific surface species identified using XAS. These experiments will thus provide a fundamental understanding of the chemical and physical processes occurring at the solid-solution interface under expected repository conditions. Additionally, the focus on thermodynamic treatment of actinide ion interactions with minerals as proposed will provide information on the driving forces involved and contribute to the overall understanding of the high affinity many actinide ions have for oxide surfaces. The utility of this model will be demonstrated in this work through a series of advective and diffusive flow experiments.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Influence of Borate on Sorption of Strontium and Barium to Calcium Silicate Hydrate - 20148

Radioactive waste with the decommissioning process at the Fukushima Daiichi Nuclear Power Plant (FDNPP), contains borate with relatively high concentration. As with general low-level wastes, such waste is also assumed the solidification with cementitious materials which calcium silicate hydrate (C-S-H) is one of the main components. In this study, the sorption behavior of strontium (Sr) ions and barium (Ba) ions to C-S-H in the presence of borate was examined by the sorption experiments without drying process. In the sorption experiments, C-S-H was synthesized by the mixture of calcium oxide, fumed silica and a solution with setting the Ca/Si molar ratios to 0.4, 0.8, 1.2 and 1.6. The total amount of a solid phase was 1.5 g, and the total volume of the solution containing borate and adsorbed ions (Sr or Ba) was 30 mL. The concentration of borate was set to 0 M or 0.6 M and the sodium/boron (Na/B) ratios was set to 0.2 or 1.0 by mixing boric acid and sodium hydroxide. The concentration of Sr ions or Ba ions was adjusted to 1 mM. The sorption period was set to 7 days. In the results, the sorption ratios of Sr ions and Ba ions for C-S-H exceeded 80% under all experimental conditions, although the sorption competition of cations with Na ions and the inhibition of the C-S-H formation with generating borate compounds observed by Raman spectroscopy might slightly reduce the sorption of them. These suggest that cationic radionuclides will be immobilized by C-S-H contained in the cements even in the presence of borate. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Sorption and oxidation of Co(II) at the surface of birnessite: Impacts of aqueous Mn(II)

The sorption of aqueous Mn(II) (1 mM) and Co(II) (50 and 200 μM) onto hexagonal birnessite (0.1 g L –1 ) was studied under anoxic conditions at pH 6.5 and 7.5 in binary and ternary experiments using batch kinetic experiments and XRD, ATR-FTIR, and Co K-edge EXAFS analyses. In the binary systems, sorption of Co(II) was accompanied by partial oxidation to Co(III) yielding a mixture of corner-sharing Co(II) and edge-sharing Co(III) complexes at both pH values, while Mn(II)-birnessite interaction resulted in coordination of Mn(II/III) at layer vacancy sites at pH 6.5, and led to reductive transformation of birnessite into feitknechtite at pH 7.5. In the ternary systems, strong mutual interferences between Co(II) and Mn(II) co-sorbates reduced the rate and extent of sorption relative to the binary experiments. The introduction of Mn(II) aq into the high-Co systems (200 μM) halted the slow sorption of Co(II) that was attributed to the incorporation of Co(III) into layer vacancies, while Co(II) aq prevented Mn(II)-driven transformation of birnessite into feitknechtite at pH 7.5. In the low-Co system (50 μM), reductive transformation of birnessite by Mn(II) aq at pH 7.5 produced Co(II)-substituted feitknechtite, a conversion that was accompanied by reduction of sorbed Co(III) to Co(II) which was partially released to solution. The strong effects of co-sorption are attributed to the similarity in sorption mechanisms of Co(II) and Mn(II), which both sorb as a mixture of di- and trivalent species. Finally, the results of this work demonstrate that aqueous Mn(II) may significantly affect the reactivity of phyllomanganate sorbents towards dissolved Co(II), and therefore impact the speciation and solubility of this trace metal in anoxic and suboxic geochemical environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

A mechanistic model for multi-scale sorption dynamics in shale

Evidence from experimental studies related to sorption on nanoporous materials, coals, and most recently on shales suggests that the sorption of gas in these targets is not instantaneous, i.e. the time it takes for the gas to adsorb to its maximum capacity is not negligible. Here, a recent experimental study showed that the sorption in shale rocks is non-instantaneous, i.e. there is a delayed effect in adsorption due to different mechanisms of sorption in different materials of shale, for e.g. in inorganic and organic matter. The current suite of models used to predict sorption in shale (e.g. Langmuir, BET, etc.) assumes an instantaneous equilibrium, which is not justifiable for sorption in shales.

58 GEOSCIENCES↗
DOE OSTI2020

Macroscopic and microscopic behaviors of Mn(II) (ad)sorption to goethite with the effects of dissolved carbonates under anoxic conditions

Manganese and its compounds have been extensively researched because of their far-reaching roles in a wide range of biogeochemical processes in natural systems. The (ad)sorption behavior of Mn(II), however, is poorly understood despite its important role as the primary reaction step for surface-catalyzed Mn(II) oxidation that is the principal abiotic process forming various Mn (oxyhydr)oxides in nature. Here, we systematically examined Mn(II) (ad)sorption to one of the most common natural sorbents, goethite, in oxygen- and carbonate-free systems. Traditional sorption edge and isotherm experiments were conducted by varying sorbate-to-sorbent ratio (0.027–15 μmol∙m -2 ) and solution pH (pH 5.0–9.0). The effects of dissolved carbonates on Mn(II) sorption were also assessed in a range of naturally prevalent concentrations (0.5–10 mM NaHCO 3 ). The Mn(II) uptake on goethite followed a typical Langmuir isotherm in the absence of dissolved carbonates, with increasing maximum adsorption capacities (Γ max ) from 0.19 at pH 6.5 to 3.4 μmol∙m -2 at pH 9.0. The presence of dissolved carbonates raised the extent of Mn(II) adsorption, which appeared to be directly correspondent to that of the adsorption of dissolved carbonates. Extended X-ray absorption fine structure (EXAFS) analysis indicated that Mn(II) predominantly formed inner-sphere binuclear bidentate surface complexes. Mn(II) uptake became deviated from the Langmuir model and showed a clear indication of surface precipitation when the Mn(II) sorption density (Γ) exceeded a threshold value in a given solution composition. This secondary Mn(II) phase was identified as rhodochrosite using X-ray diffraction (XRD) and transmission electron microscope (TEM). Furthermore, it would be plausible that a minor fraction of adsorbed Mn(II) coexisted with the secondary rhodochrosite according to a linear combination fitting (LCF) of the X-ray absorption near edge structure (XANES) spectra of Mn reference and samples. These systematic investigations of the macroscopic and microscopic behaviors of Mn(II) (ad)sorption to goethite provide a critical avenue for disentangling surface-catalytic Mn(II) oxidation processes, which ultimately lead to the formation of diverse Mn (oxyhydr)oxides in the environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Methylmercury sorption onto engineered materials

Four commercially available sorbents (BioChar (BC), ThiolSAMMS® (TS), SediMite (SM), and Organoclay™ PM-199 (OC-199)) were tested for their ability to sorb methylmercury (MeHg) and MeHg complexed with dissolved organic matter (DOM). Testing sorption behavior with DOM is more representative of the environmental conditions and mercury speciation expected during in-situ remediation efforts. Isotherms were fit using a robust, iterative re-weighting scheme. This fitting method improves upon the traditionally used indirect sorption method by removing the dependence between aqueous and solid phase concentrations in isotherm fitting. Developed isotherms reflect that without DOM, BC, TS, and SM adsorbed similar amounts of MeHg while OC-199 sorbed substantially less MeHg. Below an equilibrium concentration of 5.6 ng L -1 BC was the best performing sorbent, between 5.6 and 20. ng L -1 SM sorbed the most MeHg, and above an equilibrium concentration of 20.9 ng L -1 TS outperformed the other sorbents. BC and OC-199 showed indication of MeHg sorption saturation over the tested concentration range of 3.5–680 ng L -1 . With DOM, SM outperformed the other sorbents at equilibrium concentrations less than 0.98 ng L -1 and TS was the superior MeHg:DOM sorbent at higher concentrations. MeHg:DOM sorption was controlled by DOM-sorbent interactions. DOM decreased MeHg sorption onto BC and SM whereas TS exhibited similar sorption with and without DOM. OC-199 had slightly higher MeHg uptake with DOM. East Fork Poplar Creek (EFPC), an industrially Hg contaminated site, was used as a case study example to build a relationship between aqueous and fish MeHg concentrations and subsequently compare the cost of sorbent materials required to meet regulatory objectives. For this case study, SM provided the most cost-effective sorbent option for in-situ remediation efforts to reduce aqueous MeHg concentrations.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Arsenic sorption on TiO[subscript 2] nanoparticles: Size and crystallinity effects

Single solute As (III) and As (V) sorption on nano-sized amorphous and crystalline TiO{sub 2} was investigated to determine: size and crystallinity effects on arsenic sorption capacities, possible As (III) oxidation, and the nature of surface complexes. Amorphous and crystalline nanoparticles were prepared using sol-gel synthesis techniques. For amorphous TiO{sub 2}, solute pH in the range of 4-9 had a profound impact on only As (V) sorption. As (III) and As (V) sorption isotherms indicated that sorption capacities of the different TiO{sub 2} polymorphs were dependent on the sorption site density, surface area (particle size) and crystalline structure. When normalized to surface area, As (III) surface coverage on the TiO{sub 2} surface remained almost constant for particles between 5 and 20 nm. However, As (V) surface coverage increased with the degree of crystallinity. X-ray absorption spectroscopic analysis provided evidence of partial As (III) oxidation on amorphous TiO{sub 2} rather than crystalline TiO{sub 2}. The data also indicated that As (III) and As (V) form binuclear bidentate inner-sphere complexes with amorphous TiO{sub 2} at neutral pH.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2011

Effect of Aqueous Fe(II) on Arsenate Sorption on Goethite and Hematite

Biogeochemical iron cycling often generates systems where aqueous Fe(II) and solid Fe(III) oxides coexist. Reactions between these species result in iron oxide surface and phase transformations, iron isotope fractionation, and redox transformations of many contaminant species. Fe(II)-induced recrystallization of goethite and hematite has recently been shown to cause the repartitioning of Ni(II) at the mineral-water interface, with adsorbed Ni incorporating into the iron oxide structure and preincorporated Ni released back into aqueous solution. However, the effect of Fe(II) on the fate and speciation of redox inactive species incompatible with iron oxide structures is unclear. Arsenate sorption to hematite and goethite in the presence of aqueous Fe(II) was studied to determine whether Fe(II) causes substantial changes in the sorption mechanisms of such incompatible species. Sorption isotherms reveal that Fe(II) minimally alters macroscopic arsenate sorption behavior except at circumneutral pH in the presence of elevated concentrations (10{sup -3} M) of Fe(II) and at high arsenate loadings, where a clear signature of precipitation is observed. Powder X-ray diffraction demonstrates that the ferrous arsenate mineral symplesite precipitates under such conditions. Extended X-ray absorption fine structure spectroscopy shows that outside this precipitation regime arsenate surface complexation mechanisms are unaffected by Fe(II). In addition, arsenate was found to suppress Fe(II) sorption through competitive adsorption processes before the onset of symplesite precipitation. This study demonstrates that the sorption of species incompatible with iron oxide structure is not substantially affected by Fe(II) but that such species may potentially interfere with Fe(II)-iron oxide reactions via competitive adsorption.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Precise Modulation of CO 2 Sorption in Ti 8 Ce 2 –Oxo Clusters: Elucidating Lewis Acidity of the Ce Metal Sites and Structural Flexibility

Investigating the structure-property correlation in porous materials is a fundamental and consistent focus in various scientific domains, especially within sorption research. Metal oxide clusters with capping ligands, characterized by intrinsic cavities formed through specific solid-state packing, demonstrate significant potential as versatile platforms for sorption investigations due to their precisely tunable atomic structures and inherent long-range order. This study presents a series of Ti 8 Ce 2 -oxo clusters with subtle variations in coordinated linkers and explores their sorption behavior. Notably, Ti 8 Ce 2 -BA (BA denotes benzoic acid) manifests a distinctive two-step profile during CO 2 adsorption, accompanied by a hysteresis loop. This observation marks a new instance within the metal oxide cluster field. Of intrigue, the presence of unsaturated Ce(IV) sites was found to be correlated with the stepped sorption property. Moreover, the introduction of an electrophilic fluorine atom, positioned ortho or para to the benzoic acid, facilitated precise control over gate pressure and stepped sorption quantities. Advanced in-situ techniques systematically unraveled the underlying mechanism behind this unique sorption behavior. The findings elucidate that robust Lewis base-acid interactions are established between CO 2 molecules and Ce ions, consequently altering the conformation of coordinated linkers. Conversely, the F atoms primarily contribute to gate pressure variation by influencing the Lewis acidity of the Ce sites. This research advances the understanding in fabricating metal-oxo clusters with structural flexibility and provides profound insights into their host-guest interaction motifs. Furthermore, these insights hold substantial promise across diverse fields and offer valuable guidance for future adsorbent designs grounded in fundamental theories of structure-property relationships.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Estimation of Sorption Behavior of Europium(III) Using Biotite Flakes - 13272

The interaction of biotite and Eu(III) (europium (III)) was examined by using secondary ion-microprobe mass spectrometer (SIMS), fluorescence emission spectrum and decay behavior of fluorescence emission spectrum in addition to the time-changes of Eu(III) and potassium ions concentrations in a solution, using the flake form samples. The results of SIMS showed that the intensity of Eu was gradually decreasing with depth, while the intensity of Eu in the case shaken for 30 days exceeded that in the case for 1 day. Furthermore, the spatial distribution of Eu(III) and potassium ions in the flake of biotite suggested that Eu ions diffuse mainly from the edges of biotite flake, while Eu ions can slightly diffuse through some small cracks existing on the flake surface far from the edges. Besides, the elution amount of potassium from the biotite flakes into a solution was proportional to the sorption amount of Eu(III). The changes nearly revealed ion exchange between these ions, while muscovite flake sample did not show such ion exchange reaction. In addition, from the time-change of Eu(III) concentration, an apparent diffusion coefficient was estimated to be 8.0x10{sup -12} m{sup 2}/s, by using two-dimensional diffusion model coupled with a film between the solid phase and the liquid phase. Furthermore, the fluorescent intensity decreased with the shaking (contacting) time. This means that Eu(III) gradually diffuses into the inside of biotite edges of the biotite flakes, after the sorption of Eu(III) in the edges. This tendency was observed also in the powder samples. The observed fluorescence decay (at 592 nm in wave length) showed almost similar curve in any samples, indicating a certain sorption form of Eu(III) onto the edges of the biotite flakes. These results mentioned above suggest that the diffusion processes through internal layer in biotite mainly control the sorption behavior of multivalent ions. Such diffusion processes affect the retardation-effects on fracture surfaces in the rock matrix, depending on the fluid flow velocity of groundwater. That is, a more reliable model considering the mass transfer in the internal layer of biotite may be required to estimate the sorption behavior of RNs with biotite which controls the whole sorption behavior of granite. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Bio-sorption of uranium, Am-241 and Cs-137 by Rice Husk - 15437

New techniques involving the treatment of radioactive waste which combine simplicity and low cost have directed attention to bio-sorption. The bio-sorption term is used to describe the removal of metals, non-metals and/or radionuclides by a material from a biological source, regardless of its metabolic activity. Among the potential biomass, agricultural residues have very attractive features, as they allow for the removal of radionuclides present in the waste using a low cost bio-sorbent. The aim of this study was to evaluate the capacity of rice husk to remove uranium, Am-241 and Cs-137 in real radioactive liquid organic waste. This work was divided into two stages: i) Preparation and physical characterization of the rice husk and ii) Batch bio-sorption experiments. The parameters evaluated for physical characterization of biomass were morphological characteristics of rice husk, real and apparent density and surface area. The adopted contact times were 30 min, 1, 2 and 4 hours and the concentrations tested ranged between 10% and 100%. The results were evaluated by maximum experimental sorption capacity and isotherm and kinetics ternary models. The maximum capacity of the bio-sorption for the rice husk with approximate values was of 0.5 mg/g of U (total), 14 x10{sup -6} mg/g of Am-241 and 20 x10{sup -9} mg/g of Cs-137. These results suggest that bio-sorption with rice husk can be applied in the treatment of radioactive liquid organic waste. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

The influence of humic acid and colloidal silica on the sorption of U(VI) onto SRS Sediments Collected from the F/H Area - 15499

Between 1955 and 1988, the F/H Area Seepage Basins located in the center of SRS received approximately 6,814,000 m{sup 3} of acidic waste solutions containing radionuclides and dissolved metals. Uranium (VI) is a key contaminant of concern in groundwater associated with the basins. The pump-and-treat water treatment unit designed and built in 1997 to remove metals and radionuclides eventually became less effective, prompting research for new remedial alternatives. The pump-and-treat system was discontinued in 2004, replaced with a funnel-and-gate system in which base solutions are injected at the gates to raise pH. To take advantage of the potential formation of uranium silicate minerals, Florida International University - Applied Research Center (FIU-ARC), in collaboration with Savannah River National Laboratory (SRNL), is conducting an investigation into a base containing sodium silicate to evaluate whether these solutions have sufficient alkalinity to correct the acidic nature of the aquifer sediments. The research was extended to investigate if U(VI) is bound to colloidal silica and if any synergy exists between humic acid (HA) and colloidal Si that would influence the removal of uranium. Humic substances (HS) are a major component of soil organic matter and are known for their abilities to influence the migration behavior and fate of heavy metals. Studies showed that HA function as an important ion exchange and metal-complexing ligand, carrying a large number of functional groups with high complexing capacity that can greatly affect the mobility behavior of actinides in natural systems. The study investigates if there are any synergistic interactions between U(VI) ions, humic acid and colloidal silica under oxidized conditions and studies the influence of HA and Si on the sorption of U(VI) onto sediments collected from the F/H Area. The experiments also evaluated the effects of different environmental variables such as pH, presence of U(VI) and varying concentrations of HA on the sorption behavior of U(VI) in multi-component batch systems in the pH range between 3 and 8. Several background sediment samples were collected at SRS from archived cores obtained during installation of the well FSB 91C and used for preparation of triplicate samples. The experimental matrix was set up as follows: - Batch 1: Si (3.5 mM) + U (VI) (0.5 ppm) (no sediments and no HA); - Batch 2: Si (3.5 mM) + U (VI) (0.5 ppm) + HA (10 ppm) (no sediments); - Batch 3: U (VI) (0.5 ppm) + HA (10 ppm) (no Si and no sediments); - Batch 4: Sediments + Si (3.5 mM) + U (VI) (0.5 ppm) (no HA); - Batch 5: Sediments + Si (3.5 mM) + U (VI) (0.5 ppm) + HA; - Batch 6: Sediments + U (VI) (0.5 ppm) + HA, (no Si); - Batch 7: Sediments + U (VI) (0.5 ppm) (no Si and no HA). All samples were prepared in triplicate 50-mL conical tubes. All control and experimental tubes were vortexed and kept on a shaker for 24 h at 100 rpm and room temperature. Results showed that the sediment-bearing batches typically exceeded the performance of non-sediment batches. Results showed that the sorption of U(VI) onto sediments was influenced by the pH and the presence of HA. At low pH 3, the addition of HA slightly enhances U(VI) sorption compared to the HA-free samples. This result is consistent with other studies; in the acidic pH range, the addition of HA slightly enhances U(VI) sorption relative to the HA-free system. Conversely, in the pH range of 4 to 7, the sorption of U(VI) on Si was reduced in the presence of HA in comparison to the system without HA. In subsequent experiments the concentration of HA will be increased to 50 ppm. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Sorption of Anionic Iodine and Molybdenum to Multi-sorbing Barrier (MSB) Materials - 20030

A multi-sorbing barrier (MSB) material containing sodium bentonite (NaB), organoclay, and anion resin is being evaluated for containment of anionic radionuclides. Batch tests on the MSB were conducted using two non-radioactive analog isotopes ({sup 127}I, {sup 95}Mo) as surrogates for {sup 129}I and {sup 99}Tc due to their similar valence and molecular weight relative to the radionuclides. Tests were conducted on the organoclay, anion resin, and NaB individually and on NaB-resin blends with resin contents of 1% and 5% by mass. The anion resin exhibits very strong sorption of {sup 127}I and {sup 95}Mo relative to the other materials. The organoclay exhibited modest sorption of {sup 95}Mo and {sup 127}I, and NaB little sorption. The sorption isotherms follow a linear model for NaB, a Freundlich model for the organoclay, and a Langmuir model for the anion resin and NaB-resin mixtures. Combining resin with NaB significantly enhances sorption relative to NaB alone, with a larger resin fraction yielding greater sorption. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Study of optimal sizing for residential sorption heat pump system

Gas-driven sorption heat pumps (GDSHP) show significant potential to reduce primary energy use, associated emissions and energy costs for space heating and domestic hot water production in residential applications. This study considered a bivalent heating system consisting of a sorption heat pump and a condensing boiler, and focuses on the optimal heating capacity of each of these components relative to each other. Two bivalent systems were considered: one based on a solid chemisorption cycle (GDSHPA), and one based on a resorption cycle (GDSHPB). Simulations of year-round space heating loads for two single-family houses, one in New York and the other Minnesota, were carried out and the seasonal gas coefficient of performance (SGCOP) calculated. The sorption heat pump’s design heating capacity as a fraction of the bivalent system’s total heating capacity was varied from 0 to 100%. Results show that SGCOP was effectively constant for sorption heat pump design capacity greater than 41% of the peak bivalent GDSHPA design capacity in Minnesota, and 32% for GDSHPB. In New York, these values were 42% and 34% for GDSHPA and GDSHPB respectively. The payback period was also evaluated based on postulated sorption heat pump component costs. The fastest payback was achieved with sorption heat pump design capacity between 22 and 44%.

42 ENGINEERING↗