Sorption Samples Research Articles

Isolation and identification of olive tree leaf phenols through a resin adsorption/desorption process

Agricultural by-products contain substantial amounts of phenolics with significant antioxidant properties. In this work, a method to recover high concentrations of phenolic substances from a typical agricultural by-product, such as olive tree leaves, was investigated. Phenolic compounds previously separated through extraction and fractionated on a membrane array: Ultrafiltration (UF)-Nanofiltration (NF)-Reverse Osmosis (RO), were examined, alongside standard compounds. More specifically, the NF concentrate fraction, which contained the low molecular weight organics (simple phenols, carbohydrates) was treated by sorption/desorption processes in a cylindrical column packed with XAD16 N resin. The aim of this study was to optimize the isolation and the enrichment of phenolic compounds through their selective adsorption on resin grains. Standard compounds such as gallic acid and glucose were tested to study the sorption and desorption kinetics of phenol and carbohydrate families and the sorption parameters were estimated using the Thomas model. The results showed that XAD16 N resin selectively adsorbed phenolic compounds over carbohydrates. This was evident by the adsorption capacity exhibited by the resin when treating the glucose and gallic acid solutions. Regarding the NF concentrate fraction of olive leaf phenols, after the adsorption step, the adsorbed hydrophilic carbohydrates were removed by desorption using pure water. Immediately afterwards, an alcohol/water mixture was introduced to recover and extract the phenolic compounds. To identify the distinct phenols, a thorough liquid chromatography study was performed on the sorption and desorption samples collected at the outlet of the packed column, identifying the different time frame each phenol left the system.

Technetium immobilization by chukanovite and its oxidative transformation products: Neural network analysis of EXAFS spectra

The uptake of the fission product technetium (Tc) by chukanovite, an FeII hydroxy carbonate mineral formed as a carbon steel corrosion product in anoxic and carbonate-rich environments, was studied under anoxic, alkaline to hyperalkaline conditions representative for nuclear waste repositories in deep geological formations with cement-based inner linings. The retention potential of chukanovite towards TcVII is high in the pH range 7.8 to 12.6, evidenced by high solid-water distribution coefficients, log Rd ~ 6, and independent of ionic strength (0.1 or 1 M NaCl). Using Tc K-edge X-ray absorption spectroscopy (XAS) two series of samples were investigated, Tc chukanovite sorption samples and coprecipitates, prepared with varying Tc loadings, pH values and contact times. From the resulting 37 XAS spectra, spectral endmembers and their dependence on chemical parameters were derived by self-organizing (Kohonen) maps (SOM), a neural network-based approach of machine learning. X-ray absorption near-edge structure (XANES) data confirmed the complete reduction of TcVII to TcIV by chukanovite under all experimental conditions. Consistent with mineralogical phases identified by X-ray diffraction (XRD), SOM analysis of the extended X-ray absorption fine-structure (EXAFS) spectra revealed the presence of three species in the sorption samples, the speciation predominately controlled by pH: Between pH 7.8 and 11.8, TcO2-dimers form inner-sphere sorption complexes at the surface of the initial chukanovite as well as on the surface of secondary magnetite formed due to redox reaction. At pH ≥ 11.9, TcIV is incorporated in a mixed, chukanovite-like, Fe/Tc hydroxy carbonate precipitate. The same species formed when using the coprecipitation approach. Reoxidation of sorption samples resulted in a small remobilization of Tc, demonstrating that both the original chukanovite mineral and its oxidative transformation products, magnetite and goethite, contribute to the immobilization of Tc in the long term, thus strongly attenuating its environmental transport.

(Invited) Hydrogen Storage Measurements; Protocols and Reproducibility

The transport and storage of hydrogen remains one of the critical challenges for hydrogen-based technologies. Specifically, the U.S. Department of Energy (DOE) has set forth hydrogen storage system targets for gravimetric and volumetric capacities in order to make light-duty polymer electrolyte membrane fuel cell vehicles viable alternatives to the current vehicle driving ranges. Hydrogen storage sorbent materials have shown continuous improvement in the past decade and many DOE targets have been met singularly, however, further advancements in materials development are needed to meet all of the performance targets simultaneously. The accuracy of hydrogen storage measurements is fundamental to identifying the potential of novel materials. Previous reports have called into question the reproducibility of hydrogen storage measurements. A round-robin report in 2009,[1] discovered large discrepancies among the different participating laboratories for H2 gravimetric capacity measurements on a standard material. This study brought attention to the challenges of H2 capacity measurements, provided recommendations, and discussed possible sources of errors. In a later study, we demonstrated an improved reproducibility amongst a smaller set of laboratories for the excess gravimetric capacity of standard sorption samples.[2] Both of these studies emphasized H2 gravimetric excess capacity. The volumetric capacity, however, is often not reported in the literature as determining volumetric capacities is not as straight-forward, especially for amorphous materials. Research efforts at the National Renewable Energy Laboratory, as a part of HyMARC, include characterization of thermodynamic and kinetic energetics, and hydrogen adsorption capacity measurements. In this talk, we will discuss the recommended measurement protocols and show the results from a recent comparative study of reproducibility of both volumetric and gravimetric H2 capacities. Common analysis protocols and figure of merits for reporting data[3] allow the materials to be compared on an equal basis, and provide insight into the uncertainty of measurements amongst the research community. We will also discuss the issues of approximating absolute capacities and calculating isosteric heats of adsorption at super critical conditions. [1] C. Zlotea, et.al. Int. J. Hydrog. Energy 34, 3044 (2009), [2] K.E. Hurst et.al. Appl. Phys. A2016, 122, 42.[3] P. Parilla, et.alAppl. Phys. A. 2016, 122, 201.

A Comparison of the Solubility Products of Layered Me(II)–Al(III) Hydroxides Based on Sorption Studies with Ni(II), Zn(II), Co(II), Fe(II), and Mn(II)

The precipitation of mixed metal–aluminum-layered double hydroxides (Me(II)–Al(III)-LDH)) may be an important control of the solubility of Mn(II), Fe(II), Ni(II), Zn(II), and Co(II) in soils, but assessment of this process is hindered by a lack of thermodynamic data. Here, we determined the solubility products (Ksp) of the Me(II)–Al(III)-LDHs formed by these metals based on long-term Me(II)–γAl2O3 sorption studies complemented with X-ray absorption spectroscopy (XAS) measurements. The LDH phases had the chemical formula Me(II)2/3Al1/3(OH)2Cl1/3. Solubility products were derived as Ksp = (Me2+)aq2/3(Al3+)aq1/3(OH−)aq2(Cl−)aq1/3, where brackets represent aqueous activity values determined from the equilibrium solution chemistry of the sorption samples. The Ksps are metal-dependent, with values increasing by two orders of magnitude in the order Ni(II) < Zn(II) < Co(II) < Fe(II) < Mn(II). Comparison to the solubility of β-Me(OH)2 suggests considerable thermodynamic preference of Me(II)–Al(III)-LDH over β-Me(OH)2 in soil environments and reveals a linear relation between the log-transformed Ksp values of Me(II)–Al(III)-LDH and β-Me(OH)2. Solubility plots suggest that Ni(II)–, Zn(II)–, and Co(II)–Al(III)-LDH may form in metal-polluted soils. Fe(II)–Al(III)-LDH may occur in riparian soils undergoing reduction, but precipitation of Mn(II)–Al(III)-LDH appears unlikely as it requires [Mn2+]aq much higher than commonly encountered in reducing soils. Additional thermodynamic and field studies are needed to further assess the importance of Me(II)–Al(III)-LDHs in soils and related geochemical systems.

Application of EXAFS with a bent crystal analyzer to study the pH-dependent microstructure of Eu(III) onto birnessite

Herein, Eu(III) retention mechanism and microstructure on δ-MnO2 as a function of solution pH were studied using both the conditional macroscopic method and molecular-level high resolution EXAFS technique with a bent crystal analyzer. The results suggested that the sorption Eu(III) onto δ-MnO2 was strongly dependent on pH but not on ionic strength, implying the formation of inner-sphere surface complexation for Eu(III) on δ-MnO2 surface. Molecular-level results from EXAFS methods showed that Eu was surrounded by ∼8O atoms in first coordination shell at REu-O ≈ 2.42 Å, and second shell of Mn atoms at REu-Mn ≈ 3.91 Å was found in four sorption samples from different solution pH. All this results reflected the formation of a bidentate surface complex with Eu(III) bonding by corner sharing to MnO6-octahedron on δ-MnO2 surface. Both the macroscopic findings and microstructure of Eu(III) at the δ-MnO2-water interface enhance our understanding for the reaction dynamics and states of Eu(III) and related radionuclides in natural environment.

Formation of CoAl layered double hydroxide on the boehmite surface and its role in tungstate sorption

Sorption of tungstate on boehmite (γ-AlOOH) is increased by co-sorption with Co2+ over the near-neutral pH range. Batch uptake experiments show up to a 3-fold increase in tungstate uptake over the range WO42−=50–1000μmol/L compared to boehmite not treated with Co2+. Desorption experiments reveal a corresponding decrease in sorption reversibility for tungstate co-sorbed with Co2+. Reaction of boehmite with Co2+ results in the formation of CoAl layered double hydroxide (LDH), as confirmed by X-ray diffraction and X-ray absorption spectroscopy. Tungsten L3-edge X-ray absorption near edge structure (XANES) reveals that W(VI) is octahedrally coordinated in all sorption samples, with polymeric tungstate species forming at higher tungstate concentrations. X-ray diffraction and X-ray absorption spectroscopy indicate that the mechanism for enhancement of tungstate uptake is the formation of surface complexes on boehmite at low tungstate concentrations, while exchange into the CoAl LDH becomes important at higher tungstate concentrations. The results provide a basis for developing strategies to enhance tungstate sorption and to limit its environmental mobility at near-neutral pH conditions.

Ni(II) immobilization by bio-apatite materials: Appraisal of chemical, thermal and combined treatments

Animal bones are natural and rich source of calcium hydroxyapatite (HAP), which was found to be a good sorbent material for heavy metals and radionuclides. Various treatments can reduce the content of bone organic phase and improve sorption properties. In this study, sorption capacities of raw bovine bones (B) and samples obtained by chemical treatment with NaOH (BNaOH), by heating at 400 oC (B400) and by combined chemical and thermal treatment (BNaOH+400), were compared, using Ni(II) ions as sorbates. Maximum sorption capacities increased in the order B<BNaOH<B400<BNaOH+400. Based on different sorption data and FT-IR analyses, the mechanism of Ni(II) sorption was found to be complex, with participation of both HAP and organic phase (when present). Sequential extraction analysis was applied for testing the stability of Ni(II) ions sorbed by BNaOH+400. Majority of Ni(II) was found in residual phase (65%) at lower level of sorbent loading, while with the increase of sorbent saturation carbonate fraction became dominant (39 %). According to the results, BNaOH+400 can be utilized in water purification systems. As an apatite based material with low organic content and high efficiency for Ni(II) sorption, it is also a good candidate for in-situ soil remediation, particularly at lower contamination levels.

Adsorption of methylantimony and methylarsenic on soils, sediments, and mine tailings from antimony mine area

Biogeochemical processes of antimony (Sb) – a chemically similar element as arsenic (As) – in a variety of environment is largely unexplored. Soil and sediment environment are known to control the geochemical fate of several contaminants via a multitude of processes, primarily adsorption. Here adsorption of organic Sb/As on soils, sediments, and mine tailings was investigated. Sorption studies showed that the methylarsenic sorption capacity and rate were greater than methylantimony sorption. For TMSb, MMA, and DMA sorption samples, the highest sorption capacity occurred in the Ferralsol, which contained the highest amount of Fe/Al-oxyhydroxides. The sorption capacity was proportional to the Fe/Al concentration in the environmental matrices (TMSb-Fe: R2=0.52, TMSb-Al: R2=0.69; MMA-Fe: R2=0.61, MMA-Al: R2=0.76; DMA-Fe: R2=0.42, DMA-Al: R2=0.59). The highest amount of TMSb, MMA, and DMA sorption rate was also observed for the Ferralsol with 82%, 97%, and 87%, respectively and that of the lowest values were the mine tailings. The other samples had similar amounts of TMSb/MMA/DMA sorption rate ranging from 5 to 60% of initially added organic species.

Liquid oil and residual characteristics of printed circuit board recycle by pyrolysis

Non-metal fractions of waste printed circuit boards (PCBs) were thermally treated (200–500°C) under nitrogen atmosphere. Carbon, hydrogen, and nitrogen were determined by elemental analyzer, bromine by instrumental neutron activation analysis (INAA), phosphorus by energy dispersive X-ray spectrometer (EDX), and 29 trace elements by inductively coupled plasma atomic emission spectrometer (ICP-AES) and mass spectrometry (ICP-MS) for raw material and pyrolysis residues. Organic compositions of liquid oil were identified by GC (gas chromatography)–MS, trace element composition by ICP system, and 12 water-soluble ions by IC (ionic chromatography). Elemental content of carbon was >450mg/g, oxygen 300mg/g, bromine and hydrogen 60mg/g, nitrogen 30mg/g, and phosphorus 28mg/g. Sulfur was trace in PCBs. Copper content was 25–28mg/g, iron 1.3–1.7mg/g, tin 0.8–1.0mg/g and magnesium 0.4–1.0mg/g; those were the main metals in the raw materials and pyrolytic residues. In the liquid products, carbon content was 68–73%, hydrogen was 10–14%, nitrogen was 4–5%, and sulfur was less than 0.05% at pyrolysis temperatures from 300 to 500°C. Phenol, 3-bromophenol, 2-methylphenol and 4-propan-2-ylphenol were major species in liquid products, accounting for >50% of analyzed organic species. Bromides, ammonium and phosphate were the main species in water sorption samples for PCB pyrolysis exhaust.

Retention mechanisms and microstructure of Eu(III) on manganese dioxide studied by batch and high resolution EXAFS technique

Abstract The batch experiment and high resolution EXAFS technique with bent crystal analyzer were combined to study Eu(III) retention mechanisms on β-MnO2 as a function of various environmental factors. The results indicated that the sorption of Eu(III) onto β-MnO2 was obviously dependent on pH but independent of ionic strength, suggesting the formation of inner-sphere surface complexes. Results of high resolution EXAFS analysis showed that Eu was surrounded by 8 ± 1 O atoms in the first shell at R Eu−O ≈ 2.40 Å for all sorption samples. A second shell of Mn atoms at R Eu−Mn ≈ 3.78 Å was observed for all sorption samples, which was associated with the formation of a bidendate inner-sphere complex with chemical bonding via edge sharing to MnO6-octahedron. This study shows the utility of high resolution EXAFS technique with bent crystal analyzer to discriminate the fluorescence peak of Eu(III) from that of manganese hydroxides, whose fluorescence peaks are too close in energy to be discriminated by the conventional EXAFS technique with a low resolving solid-state detector. Both the macroscopic interaction data and the molecular level evidence of Eu(III) surface speciation at the oxide-water interface should be factored into better evaluation of Eu(III) and related radionuclide mobility in the natural environment.

Mise en place de thérapies cognitivo-comportementales de groupe dans le traitement de l’insomnie chronique en cabinet libéral de ville : étude prospective

Non-metal fractions of waste printed circuit boards (PCBs) were thermally treated (200–500 °C) under nitrogen atmosphere. Carbon, hydrogen, and nitrogen were determined by elemental analyzer, bromine by instrumental neutron activation analysis (INAA), phosphorus by energy dispersive X-ray spectrometer (EDX), and 29 trace elements by inductively coupled plasma atomic emission spectrometer (ICP-AES) and mass spectrometry (ICP-MS) for raw material and pyrolysis residues. Organic compositions of liquid oil were identified by GC (gas chromatography)–MS, trace element composition by ICP system, and 12 water-soluble ions by IC (ionic chromatography). Elemental content of carbon was >450 mg/g, oxygen 300 mg/g, bromine and hydrogen 60 mg/g, nitrogen 30 mg/g, and phosphorus 28 mg/g. Sulfur was trace in PCBs. Copper content was 25–28 mg/g, iron 1.3–1.7 mg/g, tin 0.8–1.0 mg/g and magnesium 0.4–1.0 mg/g; those were the main metals in the raw materials and pyrolytic residues. In the liquid products, carbon content was 68–73%, hydrogen was 10–14%, nitrogen was 4–5%, and sulfur was less than 0.05% at pyrolysis temperatures from 300 to 500 °C. Phenol, 3-bromophenol, 2-methylphenol and 4-propan-2-ylphenol were major species in liquid products, accounting for >50% of analyzed organic species. Bromides, ammonium and phosphate were the main species in water sorption samples for PCB pyrolysis exhaust.

The surface reactions of U(VI) on γ-Al2O3 — In situ spectroscopic evaluation of the transition from sorption complexation to surface precipitation

The surface reactions of U(VI) on γ-Al2O3 were comprehensively investigated by a combined approach of in situ vibrational spectroscopy and X-ray absorption spectroscopy. The focus was set to micromolar U(VI) concentrations and a variety of sorption parameters which are relevant to most environmental scenarios, such as pH, ionic strength, different aluminum oxides, and solid-to-liquid ratios. Time-resolved IR spectroscopic sorption experiments at the alumina–water interface evidence the formation of three different species as a function of surface loading: a monomeric carbonate surface complex, an oligomeric surface complex, and a surface precipitate. EXAFS experiments of batch sorption samples different in their U(VI) surface loading, provided consistent results. Aluminum oxides and oxyhydroxides represent an essential structural component of many minerals and play a decisive role in regulating the mobility of contaminants in rocks and soils. Thus, the results presented in this study are of interest for the assessment of water contamination characterized by near neutral solutions. Additionally, the molecular-scale knowledge of the sorption reactions occurring at the water–alumina interface substantiates basic thermodynamic ideas of the formation and transition of surface complexes from sorption of monomers and oligomers to surface precipitation.

Inhibition Mechanisms of Zn Precipitation on Aluminum Oxide by Glyphosate: A 31P NMR and Zn EXAFS Study

In this research, the effects of glyphosate (GPS) on Zn sorption/precipitation on γ-alumina were investigated using a batch technique, Zn K-edge EXAFS, and (31)P NMR spectroscopy. The EXAFS analysis revealed that, in the absence of glyphosate, Zn adsorbed on the aluminum oxide surface mainly as bidentate mononuclear surface complexes at pH 5.5, whereas Zn-Al layered double hydroxide (LDH) precipitates formed at pH 8.0. In the presence of glyphosate, the EXAFS spectra of Zn sorption samples at pH 5.5 and 8.0 were very similar, both of which demonstrated that Zn did not directly bind to the mineral surface but bonded with the carboxyl group of glyphosate. Formation of γ-alumina-GPS-Zn ternary surface complexes was further suggested by (31)P solid state NMR data which indicated the glyphosate binds to γ-alumina via a phosphonate group, bridging the mineral surface and Zn. Additionally, we showed the sequence of additional glyphosate and Zn can influence the sorption mechanism. At pH 8, Zn-Al LDH precipitates formed if Zn was added first, and no precipitates formed if glyphosate was added first or simultaneously with Zn. In contrast, at pH 5.5, only γ-alumina-GPS-Zn ternary surface complexes formed regardless of whether glyphosate or Zn was added first or both were added simultaneously.

Microscopic level investigation of Ni(II) sorption on Na-rectorite by EXAFS technique combined with statistical F-tests

Extended X-ray absorption fine structure (EXAFS) spectroscopy combined with statistical F-tests is used to investigate the local atomic structures of Ni(II) adsorbed on Na-rectorite. The EXAFS analysis results of Ni(II) sorption samples indicate that the first coordination shell consists of ∼6 O at the Ni–O interatomic distance (R) of ∼2.04Å. The presence of Ni backscattering at RNi–Ni=∼3.06Å in the second coordination shell suggests the formation of Ni(II) precipitate. The results of F-tests show that the Ni(II) precipitate is Ni–Al layered double hydroxide (LDH). Our results demonstrate that Ni(II) ions are retained via different mechanisms depending on solution conditions. At low pH, Ni retention is controlled mainly by the outer-sphere surface complexation. With increasing pH, outer-sphere and inner-sphere surface complexation dominate Ni uptake. Furthermore, Ni surface loading increases with temperature increasing at pH 6.5 due to the formation of inner-sphere surface complexes and Ni–Al LDH. The formation of Ni–Al LDH becomes the dominate mechanism at the elevated pH and temperature. In the presence of humic substances, the sorption of Ni(II) on Na-rectorite is dominated by the formation of ternary surface complexes. These results are important to understand the physicochemical behavior of Ni(II) in the natural environment.

Interfacial sorption/desorption studies of Pu(IV) on Silica and alumina surfaces

AbstractCombination of sorption, desorption and kinetic experiments for Pu(IV) in silica and alumina suspensions over the pH range (2–9) have been employed to study the factors controlling Pu mobility from the near field of the repositories. These studies have been carried out using shorter lived isotope of Pu (238Pu) thereby achieving Pu concentration (∼10-9M) near the solubility limit. Kinetic experiments were carried out to investigate the mechanism of the sorption process. In order to conclude about the surface speciation, desorption and leaching studies have been carried out on short as well as long time equilibrated sorption samples. Oxidation state transformation in the kinetic experiment was determined using parallelly carried out solvent extraction procedures. Silica was found governing the sorption at pH values≲ 5.5while both the surfaces quantitatively sorb the metal ion at higher pH values. The leaching and desorption experiments, in light of kinetic experiments, concluded the formation of small polynuclear Pu(IV) oxide/hydroxide species on both the surfaces. These experiments did not show any evidence for PuO2(am.) as the surface speciation. Oxidation state determination in silica supernatants revealed V as the oxidation state of Pu, while alumina suspensions favour higher oxidations state,i.e., (VI) over (V) in the supernantant. Disproportionation of Pu(V) in the interfacial region, caused by the higher sorption affinity of alumina, produces Pu(VI) in the alumina supernatant. These findings provide new insight for defining the source term of Pu migration in geosphere.

Interaction of radionickel with diatomite as a function of pH, ionic strength and temperature

Sequestration of Ni(II) on diatomite as a function of reaction time, pH, ionic strength, foreign ions and temperature were investigated by batch sorption technique. The results indicated that the sorption of Ni(II) on diatomite was quickly in the first contact time of 2 h and then slowly with increasing contact time. The interaction of Ni(II) with diatomite was strongly pH- and ionic strength-dependent at low pH values (i.e., which was dominated by ion exchange or outer-sphere surface complexation), while the pH-dependent and ionic strength-independent sorption at high pH suggested that inner-sphere or multinuclear surface complexation was the main sorption mechanism. With increasing temperature, the sorption of Ni(II) on diatomite increased and the experimental data were well fitted by Langmuir model. The sorption samples at pH 6.8 and 10.0 were also characterized by XPS spectroscopy, and the results suggested that Si atoms also participated in Ni(II) sorption on diatomite. The results are important to evaluate the physicochemical behavior of Ni(II) and other similar radionuclides and heavy metal ions in the environment.

Speciation of Np(V) uptake by Opalinus Clay using synchrotron microbeam techniques

Synchrotron-based X-ray absorption spectroscopy has been used to determine the chemical speciation of Np sorbed on Opalinus Clay (OPA, Mont Terri, Switzerland), a natural argillaceous rock revealing a micro-scale heterogeneity. Different sorption and diffusion samples with Np(V) were prepared for spatially resolved molecular-level investigations. Thin sections of OPA contacted with Np(V) solution under aerobic and anaerobic conditions as well as a diffusion sample were analysed spatially resolved. Micro-X-ray fluorescence (μ-XRF) mapping has been used to determine the elemental distributions of Np, Fe and Ca. Regions of high Np concentration were subsequently investigated by micro-X-ray absorption fine structure spectroscopy to determine the oxidation state of Np. Further, micro-X-ray diffraction (μ-XRD) was employed to gain knowledge about reactive crystalline mineral phases in the vicinity of Np enrichments. One thin section was also analysed by electron microprobe to determine the elemental distributions of the lighter elements (especially Si and Al), which represent the main elements of OPA. The results show that in most samples, Np spots with considerable amounts of Np(IV) could be found even when the experiments were carried out in air. In some cases, almost pure Np(IV) L(III)-edge X-ray absorption near-edge structure spectra were recorded. In the case of the anaerobic sample, the μ-XRF mapping showed a clear correlation between Np and Fe, indicating that the reduction of Np(V) is caused by an iron(II)-containing mineral which could be identified by μ-XRD as pyrite. These spatially resolved investigations were complemented by extended X-ray absorption fine structure measurements of powder samples from batch experiments under aerobic and anaerobic conditions to determine the structural parameters of the near-neighbour environment of sorbed Np.

Immobilization of Hg(II) by Coprecipitation in Sulfate-Cement Systems

Uptake and molecular speciation of dissolved Hg during formation of Al- or Fe-ettringite-type and high-pH phases were investigated in coprecipitation and sorption experiments of sulfate-cement treatments used for soil and sediment remediation. Ettringite and minor gypsum were identified by XRD as primary phases in Al systems, whereas gypsum and ferrihydrite were the main products in Hg–Fe precipitates. Characterization of Hg–Al solids by bulk Hg EXAFS, electron microprobe, and microfocused-XRF mapping indicated coordination of Hg by Cl ligands, multiple Hg and Cl backscattering atoms, and concentration of Hg as small particles. Thermodynamic predictions agreed with experimental observations for bulk phases, but Hg speciation indicated lack of equilibration with the final solution. Results suggest physical encapsulation of Hg as a polynuclear chloromercury(II) salt in ettringite as the primary immobilization mechanism. In Hg–Fe solids, structural characterization indicated Hg coordination by O atoms only and Fe backscattering atoms that is consistent with inner-sphere complexation of Hg(OH)20 coprecipitated with ferrihydrite. Precipitation of ferrihydrite removed Hg from solution, but the resulting solid was sufficiently hydrated to allow equilibration of sorbed Hg species with the aqueous solution. Electron microprobe XRF characterization of sorption samples with low Hg concentration reacted with cement and FeSO4 amendment indicated correlation of Hg and Fe, supporting the interpretation of Hg removal by precipitation of an Fe(III) oxide phase.

Probing the Surface Structure of Divalent Transition Metals Using Surface Specific Solid-State NMR Spectroscopy

Environmental and geochemical systems containing paramagnetic species could benefit by using nuclear magnetic resonance (NMR) spectroscopy due to the sensitivity of the spectral response to small amounts paramagnetic interactions. In this study, we apply commonly used solid-state NMR spectroscopic methods combined with chemometrics analysis to probe sorption behavior of the paramagnetic cations Cu(2+) and Ni(2+)at the amorphous silica surface. We exploit the unique properties of paramagnets to derive meaningful structural information in these systems at low, environmentally relevant cation surface loadings by comparing the NMR response of sorption samples to paramagnetic free samples. These data suggest that a simple sorption model where the cation sorbs as inner sphere complexes at negatively charged, deprotonated silanol sites is appropriate. These results help constrain sorption models that are used to describe metal fate and transport.

Some Experiments on Sorption Behavior of Iodide ions into CSH Gel under the Condition Saturated with Saline Groundwater

ABSTRACTThe main hydrate of cement is calcium silicate hydrate (CSH). Such a cement-based material is essential for constructing the geological disposal system of TRU radioactive wastes including I-129 in Japan. So far, the sorption behavior of iodine on CSH gel has been examined by using the CSH samples dried once. However, the Japan’s repository would be constructed under water table. Therefore, we must focus on also the interaction of altered cementitious material and iodine under the condition saturated with saline groundwater.In this study, the sorption behavior of iodide ions into CSH gel, formed without dried processes, was examined in imitated saline groundwater. Ca/Si ratio was set to 0.4, 0.8, 1.2 and 1.6, and NaCl concentration of each sample also was set to 0.6 M, 0.06 M or 0.006 M. These samples were synthesized with CaO, SiO2 (fumed silica), and distilled water in a given combination of 20 ml/g in liquid/solid ratio. A NaI solution was added after curing the CSH gel (hereinafter referred to as the “Surface sorption sample”) for 7 days, setting the initial concentration of NaI to 0.5 mM in sample tube. The values of Eh and pH of each sample showed iodide ions as the chemical species of iodine in the sample tube. Furthermore, this study prepared the “Co-precipitation sample” of CSH gel with iodide ions. Here, the NaI solution was added before curing the CSH gel. For all samples, the contact time-period of the CSH gel with iodide ions was set to 7 days. After each contact time-period, each sample for analyses was separated into the solid and the liquid phases by 0.20 µm membrane filter. In the liquid phase, the concentrations of Ca, I, Si and Na ions in the liquid phase were measured by ICP-AES. Besides, the Raman spectra were obtained from the solid phases of the surface sorption sample and the co-precipitation sample without dried process.The results showed that the sorption of iodide ions into CSH gel strongly depends on the amount of water included in the CSH gel. Such a sorption behavior was confirmed in both co-precipitation samples and the surface sorption samples, even if the Ca/Si ratio is low. This means that iodide ions can be easily immobilized through the water-molecular of CSH gel. Besides, Na concentration did not so much affect the sorption behavior of iodide ions into CSH gel. In addition, the Raman spectra showed that the degree of polymerization of SiO4 tetrahedrons in CSH gel was unaffected with increasing Na ions concentration. These results suggest that the CSH gel saturated with groundwater would retard the migration of iodide ions, even if the groundwater includes salinity.