Simple Sorption Research Articles

Reactions of radium and barium with the surfaces of carbonate minerals

Abstract Radium-226 is a naturally-occurring radioisotope with potentially significant radiological impact and whose environmental behaviour is of concern. The reactions of tracer (0.1–1 nM) dissolved Ra and its chemical analogue Ba with the surfaces of a range of carbonate minerals have been studied. All of the minerals react with Ra but, whereas calcite, dolomite, strontianite, rhodocrosite, ankerite and witherite all show increased uptake with increasing Ra concentration, suggesting a coprecipitation reaction (hence with phase formation limiting uptake), siderite, magnesite and ankerite show behaviour suggesting simple sorption (with decreasing uptake as Ra concentration increases, or with no dependence on [Ra]). Magnesite, in particular, has a low sorption capacity. Barium has been used at higher (0.1–1 mM) concentrations to enable the use of surface analytical and imaging techniques in addition to bulk uptake measurements. Although the same eight carbonates were studied, measurable uptake occurs only on dolomite, magnesite and siderite. For siderite and magnesite, there is an approximately linear relationship between the increasing solid and solution phase Ba concentrations, suggesting a simple sorption process. Dolomite shows more complex behaviour suggesting simple sorption at the lowest concentrations and phase formation at higher concentrations (>0.4 mmol L−1). The latter observation is consistent with spectroscopic evidence for the formation of witherite. Surface analysis and imaging of the three carbonate substrates that react with Ba show a diversity of behaviour, partly as a result of using natural minerals in these experiments. Witherite is commonly formed as a surface precipitate although the presence of even trace SO 4 2 - leads to barite formation. The surface phases display a range of characteristic morphologies, and the surface structure has the effect of templating growth. The presence of even minor amounts of Fe (hydr)oxide phases as alteration products or precipitates on the carbonates is also important, since Ba has a strong affinity for these phases.

Pb(II) and Cd(II) biosorption on Chondracanthus chamissoi (a red alga)

Chondracanthus chamissoi is an efficient biosorbent for Pb(II) and Cd(II). The sorption efficiency increases with pH and reaches an optimum around pH 4. Maximum sorption capacity reaches 1.37 mmol Pb g −1 and 0.76 mmol Cd g −1. The biosorbent has a marked preference for Pb(II) over Cd(II), though insufficient for separating these metals by a simple sorption step. The uptake kinetics is controlled by the resistance to intraparticle diffusion with a limited impact of particle size, metal concentration and sorbent dosage. In the present case, grinding the biomass does not improve sorption capacity and uptake kinetics. The sorption of metal ions is probably due to their interaction with carrageenan (one of the main constituents of the biosorbent): sulfonic groups (on the sulfated polysaccharide) have a higher affinity for Pb(II) than for Cd(II) according to HSAB rules.

Sorption performance of cysteine-modified bentonite in heavy metals uptake

A local clay, bentonite (N-Ben), was modified by the biologically-based ligand, cysteine (Cys), through a simple sorption technique. The modified sorbent (Cys-Ben) demonstrated affinity for soft and moderately soft heavy metal ions (HMI), such as Cd(II) and Pb(II), probably as a result of the soft basic character of the thiol ligand side chains. The resulting modified system was effective for metal binding with capacities of 0.503 and 0.525 mmol g-1, for Pb(II) and Cd(II), respectively. Comparative batch experiments were performed for removing lead and cadmium from aqueous solutions. The sorption parameters were derived from a Langmuir fit to the sorption isotherms of the studied ions. The study showed that the sorption capacity of Cys-Ben was higher than that of N-Ben for these ions. The effect of pH was examined over the range 2.0-6.0. The sorption capacities of Cys-Ben showed that this modified clay is a good sorbent for the examined heavy metal ions.

Quantifying Conservatism of Performance Assessment Calculations by Sorption Model Reduction: Case Study on Near Field Cs Migration in Callovo-Oxfordian Clay

AbstractImplementation of full thermodynamic models in performance assessment (PA) calculations (large domain and very large timescales) is practically unfeasible due to excessive computational times. The complex competitive sorption processes of radionuclides are often simplified.In this paper, such simple sorption models (i.e. linear Kd and Langmuir isotherms) were compared with more complex thermodynamic models for a reduced geometry and relatively short timescales (compared to traditional PA calculations).Within the context of a safety case the value of this study is twofold. Primarily, it provides support information on how to choose adequate parameter values in a consistent simplified analysis for compliance with safety criteria. For the cases studied in this paper it became clear that a linear model is sufficient to represent sorption, but a proper choice of the Kd values is critical. Secondly, the comparison of results from these compliance calculations with more realistic analyses demonstrates quantitatively the safety margin implicitly present in PA calculations through model abstraction.

Performance study of a consolidated manganese chloride–expanded graphite compound for sorption deep-freezing processes

A consolidated composite sorbent made from manganese chloride and expanded graphite was produced for sorption deep-freezing processes and used for cold production at a temperature as low as −35 °C. Experimental results showed that the addition of a porous graphite matrix can prevent the agglomeration and the attenuation of sorption capacity of reactive salt. The composite sorbent could incorporate 0.537 kg of ammonia per kg of reactive salt and the average specific cooling power (SCP) obtained varied between 200 W kg −1 and 700 W kg −1 when the evaporation temperature ranged from −35 °C to 0 °C. The analysis of the data suggested that the heat transfer characteristic in the composite sorbent was strongly influenced by chemical reaction and the conversion rate was very sensitive to the constraint temperatures. The SCP and coefficient of performance (COP) of a simple sorption deep-freezing system were 350 W kg −1 and 0.34, respectively, at the generation temperature of 180 °C, the heat sink temperature of 25 °C and the evaporation temperature of −30 °C.

Moisture Stability of Maltodextrin-Based Delivery Systems

The water sorption isotherms are exploited here for maltodextrin-based perfume-delivery systems with the aim of predicting water vapor stability of the samples at a given temperature. A combination of Couchman (glass-transition temperature) and Guggenheim-Anderson-deBoer (GAB) (fraction of water condensed) models is shown demonstrating important information hidden in a simple sorption experiment (rate of loss of perfume by diffusion and capacity to retain volatiles under humid air conditions). Pure maltodextrin and maltodextrin loaded with apolar and polar perfume components are treated using the same developed methodology. It is shown that apolar molecule release from classical carbohydrate spray dry particles follows a zero-order kinetic.

Morphology and transport characteristics of poly(ethylene- co-vinyl acetate)/clay nanocomposites

Poly(ethylene- co-vinyl acetate)/clay nanocomposite membranes were prepared with different clay loadings. The morphology of the nanocomposites was investigated using X-ray diffraction technique and transmission electron microscopy. The dispersion of layered silicates decreased with increasing filler loading. Samples with low filler content showed excellent dispersion of layered silicates resulting in a partially exfoliated structure. The transport characteristics of aromatic hydrocarbons through the nanocomposite membranes were studied by the simple sorption gravimetric analysis in the temperature range 28–70 °C and the results were compared with unfilled membranes. The solvent uptake nature of the nanoclay filled polymer samples was found to be much reduced. The solvent uptake was minimum for composites with 3 wt% of filler and increased with increasing filler content, which is presumably due to aggregation of clay filler at higher loading. The influence of free volume on the transport properties of the membranes was studied using positron annihilation lifetime spectroscopy. The transport phenomenon was found to follow an anomalous mode. Activation parameters were estimated and the molar mass between crosslinks was calculated using Flory–Rehner Theory. The experimental data were compared with theoretical predictions.

Synthesis and utilization of Mg/Al hydrotalcite for removing dissolved humic acid

It has been synthesized Mg/Al layered double hydroxide anionic clay (Mg/Al hydrotalcite) through direct precipitation by adding 0.5 M NaOH solution into a mixed solution containing Mg(NO 3) 2 and Al(NO 3) 3 with molar ratio of 0.1:0.05 until the medium acidity reached pH 10.1. The synthesized Mg/Al hydrotalcite was then utilized to remove dissolved humic acid in aqueous medium. The humic acid was isolated from peat soil taken in Gambut District, South Kalimantan, Indonesia using the recommended procedure of IHSS (International Humic Substances Society). The removal of humic acid was mostly occurred through simple sorption process without accompanied by significant intercalation. The sorption was optimum at pH 9.0, with the first order rate constant, capacity and energy of sorption were 5.50 × 10 −3 min −1, 0.12 mmol g −1 (69 mg g −1), and 28.32 kJ mol −1, respectively.

SORPTION AND LEACHING OF SHORT-TERM-AGED PAHS IN EIGHT EUROPEAN SOILS

Polycyclic aromatic hydrocarbons (PAH) are among the major contaminants in the terrestrial environment. In tools for ranking contaminated soils according to risks and cleanup measures, simple predictions of contaminant leaching rates and actual leaching concentrations need to be established preferably using simple sorption and leaching estimates based on easily measured soil characteristics. In this study, 24 hrs PAH sorption experiments were performed with the PAH pyrene and phenanthrene onto eight European soils, and sorption characteristics were compared with and related to soil characteristics. Also, the leaching of pyrene and dissolved organic carbon from the soils was investigated using a short multicolumn setup and a 30 mm h−1 of water application rate. The soils were spiked with pyrene and aged between 7 and 180 days before leaching. Freundlich sorption coefficients, Kf, correlated well with the soil organic carbon contents, but the variability of Koc values among soils indicated that sorption could not be predicted from soil organic carbon contents alone. However, sorption predictions based on organic matter content and one additional simple soil parameter (e.g., clay content, cation exchange capacity, or pH) would yield accurate predictions of Kf. The leaching of both pyrene and dissolved organic carbon (DOC) was characterized by a two-stage release behavior with high concentrations in the initial samples followed by sharp decrease to lower baseline concentrations. In all experiments, only 1.2% of the spiked pyrene mass had been leached after 200 mm of water had leached, pointing to a low release of PAHs with water. The similar release behavior of pyrene and DOC along with pyrene concentrations in the leachate above the maximum solubility suggests that pyrene was mobilized along with DOC. Relating the leached amounts of pyrene to the amounts of leached DOC and subtracting the initial flush of pyrene and DOC yields fairly identical curves for accumulated pyrene leaching as a function of accumulated DOC leaching. These findings seem useful for estimating DOC-facilitated PAH leaching at contaminated sites.

Molecular Transport Characteristics of Poly(ethylene-co-vinyl Acetate) in Presence of Aliphatic Chlorinated Hydrocarbons

The molecular transport characteristics of poly(ethylene-co-vinyl acetate) (EVA) with aliphatic chlorinated hydrocarbons as probe molecules have been investigated by simple sorption gravimetric analysis. Uncrosslinked and crosslinked EVA membranes were prepared. The cross links were introduced by peroxide technique using dicumyl peroxide (DCP). Samples with different crosslinking densities were also prepared. The influence of crosslinking, different crosslinking density, temperature, size and polarity of penetrants on transport were analyzed. It has been observed that a critical concentration of crosslinker is necessary for maximum sorption. D1 sample showed a higher solvent uptake than the uncrosslinked sample. But when the extent of crosslinking increases, the equilibrium uptake decreases. The influence of temperature on the sorption and the activation energies of sorption have been calculated. Thermodynamic parameters were also estimated. The mechanism of transport showed anomalous behavior in all solvents. Sorption (S), desorpion (D), resorption (RS), redesorption (RD) experiments have been performed for studying the transport phenomenon. After attaining equilibrium, EVA sample was allowed to desorbe fully. The desorbed sample is then exposed to solvents for resorption followed by redesorption. Transport parameters namely diffusion coefficient, sorption coefficient and permeation coefficient have been calculated. The values of polymer-solvent interaction parameter and molar mass between crosslinks were calculated using Flory-Rehner theory. First order kinetics model was used to investigate the transport kinetics.

Sorptive stabilization of organic matter in soils by hydrous iron oxides

Strong correlations between iron oxides (FeOx) and organic matter (OM) in soils have implied the importance of the former in stabilizing the latter. One mechanism thought to be important in this stabilization is sorption. We tested this possibility by reductively dissolving FeOx in a wide variety of soils and measuring the organic carbon (OC) that was solubilized. The OC dissolved from non-FeOx phases via anion exchange was corrected for by parallel control extractions. The resultant pool, reductively soluble OC, made up a minor amount of total soil OC in all but one of these soils, indicating that simple sorption reactions do not stabilize the bulk of soil OC in most mineral soils. OC:Fe ratios in the extracts from 2/3 of these soils were less than 0.22 (wt/wt), consistent with a sorbed state for this OC and showing that OC sorption by FeOx in these soils is limited by the amount of FeOx. The remaining soils had low pH and high OM concentrations; their higher OC:Fe ratios indicate inclusion of precipitated organo-Fe complexes in the extracts, which are likely only partially extracted by our method. The high volumetric ratios of OM to FeOx found in correlations between them from the literature are inconsistent with a dominant sorption control and point instead to stabilization to other mechanisms such as organo-Fe complexes or ternary associations among FeOx, OM and other minerals.

Topographical properties of polymer films deposited in capillaries for electrophoretic separations of large organic molecules

Topography and thickness of hydrophilic polymer coatings of fused-silica capillaries for capillary electrophoresis (CE) were investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM), and profilometry. Three hydrogels, poly(2-hydroxyethyl methacrylate) [poly(HEMA)], poly(diethylene glycol monomethacrylate) [poly(DEGMA)], and poly(triethylene glycol monomethacrylate) [poly(TEGMA)], were deposited using two procedures, either by simple physical sorption of the polymers, or by derivatization of the capillary wall surface with glycidyl methacrylate (EPMA) followed by polymerization of the appropriate monomers. The performance of the modified capillaries was tested under CE conditions (decrease in the electroosmotic flow, EOF dependence on pH, separation of milk and standard proteins). It has been found that the most important property of the polymer coating is its thickness, whereas its topography and the degree of its hydrophobicity are less significant. Film deposition by physical adsorption is preferable to polymerization on the derivatized surface.

Preparation of porous polysulfone beads for selective removal of endocrine disruptors

Porous polysulfone (PSf) beads are prepared using a liquid–liquid phase separation technique. The porous PSf beads are then used for the removal of endocrine disruptors, such as Biphenyl (BP), dibenzofuran (DBF), dibenzo- p-dioxin (DBD), biphenol A (BPA), and diethylstylbestrol (DES) from their aqueous solutions. The endocrine disruptors could be removed efficiently by a simple sorption method with hydrophobic porous PSf beads. The removal ratio was high for endocrine disruptors having high octanol–water distribution coefficients. The effect of sorption time, weight of PSf beads, ethanol amount in the solution, and the porosity of the beads on the removal of endocrine disruptors was investigated. The adsorbed endocrine disruptors in the PSf beads could be effectively removed by 2-propanol or ethanol, which indicated that the beads could be reused. The study suggested that the porous PSf beads have a potential ability to be used for the removal of endocrine disruptors in environmental application.

Feasibility of L/ILW fission waste repository concepts for fusion waste

This paper discusses the feasibility of a low and intermediate level fission waste (L/ILW) repository, similar to those operating in Finland, for final disposal of fusion waste. Radiotoxicity concentrations in a postulated drinking water well are calculated. The near-field model is a simple sorption model with an anticipated water-backfilling ratio—the real waste package and layout configuration in a future repository is not addressed. In the far-field model the dilution of groundwater, as well as sorption and matrix diffusion in the bedrock fractures are considered. The study implies the repository concept is feasible for a major part of the fusion waste, once a few uncertainties are resolved.

Uptake of elements from seawater by ferromanganese crusts: solid-phase associations and seawater speciation

Marine Fe–Mn oxyhydroxide crusts form by precipitation of dissolved components from seawater. Three hydrogenetic crust samples (one phosphatized) and two hydrothermal Mn-oxide samples were subjected to a sequential-leaching procedure in order to determine the host phases of 40 elements. Those host-phase associations are discussed with respect to element speciation in seawater. The partitioning of elements between the two major phases, Mn oxide and Fe oxyhydroxide, can in a first-order approximation be explained by a simple sorption model related to the inorganic speciation of the elements in seawater, as has been proposed in earlier models. Free and weakly complexed cations, such as alkali and alkaline earth metals, Mn, Co, Ni, Zn, Tl(I), and partly Y, are sorbed preferentially on the negatively charged surface of the MnO 2 in hydrogenetic crusts. The driving force is a strong coulombic interaction. All neutral or negatively charged chloro (Cd, Hg, Tl), carbonate (Cu, Y, Pb, and U), and hydroxide (Be, Sc, Ti, Fe, Zr, Nb, In, Sn, Sb, Te, Hf, Ta, Bi, Th, and Tl(III)) complexes and oxyanions (V, Cr, As, Se, Mo, and W) bind to the slightly positively charged surface of the amorphous FeOOH phase. While coulombic interaction can explain the sorption of the negatively charged species, the binding of neutral species is based on specific chemical interaction. Organic complexation of elements in deep-ocean water seems to be at most of minor importance. Surface oxidation can explain some strong metal associations, e.g. of Co and Tl with the MnO 2 and Te with the FeOOH. Sorption reactions initially driven by coulombic forces are often followed by the formation of specific bonds between the adsorbate and the atoms of the oxide surface. Differences in the associations of some metals between the non-phosphatized and phosphatized hydrogenetic crusts and between the hydrogenetic and the hydrothermal samples reflect the different physico-chemical environments of formation and speciations in oxic seawater vs. less-oxic fluids, especially for the redox-sensitive metals such as Mo and V. These environmental-related differences indicate that the methodology of chemical speciation used here in combination with spectroscopic methods may allow for the detection of changes in paleoceanographic conditions recorded during the several tens of millions of years of crust growth.

Travel time moments for sorbing solutes in heterogeneous domains under nonuniform flow conditions

A methodology for evaluating the unconditional and conditional moments of travel time for a sorbing solute is presented. The approach is applicable for any flow configuration and for a wide range of mass transfer rate‐limited linear processes. The methodology is applicable to the general case of spatially variable hydrological and chemical parameters. The sorption model used to derive the temporal moments is that of a continuous distribution of mass rate coefficients [Haggerty and Gorelick, 1998]. Models such as instantaneous equilibrium, first‐order and two‐site sorption kinetics, among others, can be considered as particular cases of this general model. Using a deterministic approach, the low‐order moments of the breakthrough curves for reactive solutes can be obtained as a function of those for conservative tracers. Using a stochastic approach, the unconditional low‐order statistics of the travel time moments can be obtained. These moments depend on the statistics of two Lagrangian functions, the travel time for a conservative solute, and an integral of the variations of the chemical parameters weighted by the inverse local velocity along the trajectory. Finally, conditional temporal moments are derived. Moments can be conditioned to any type of information, hard or soft, hydraulic or geochemical. Conditioning is found to reduce uncertainty, characterized by a reduction in the variance of the travel time. The general results are particularized for both uniform in the mean and convergent flow conditions and for simple sorption models such as linear instantaneous equilibrium and first‐order kinetics. In all such cases, close‐form results, based on small perturbations expansions, are presented for the travel time moments.

Pyrene bioavailability; effect of sediment-chemical contact time on routes of uptake in an oligochaete worm.

Bioavailability of sediment-sorbed compounds may vary with increasing contact time. This may result in the dietary uptake route becoming more significant as conditions in the gut flora aid the extraction of contaminants, which have migrated into sites within the sediment particle. Such mechanisms may have important implications on risk assessments performed on substances released into the environment. A series of experiments were carried out using sediment spiked with 14C-labelled pyrene, a polycyclic aromatic hydrocarbon. The sediment was left at room temperature over a period of 220 days. Periodically (at 0, 1, 14, 28, 70, 220 days) the sediment was used to perform a bioaccumulation study using the freshwater oligochaete Lumbriculus variegatus. A novel methodology using feeding and (decapitated) non-feeding worms, allowed differentiation between uptake via ingestion and simple sorption. Results showed that there was a decline in bioavailability with time and that this was a 3 stage process. A rapid initial decline was observed over the first day when a 40% decrease was measured, an intermediate period were levels remained stable (day 14 to day 70) and an ultimate decrease in pyrene activity in worm tissue of 70% after 220 days. Over this period the chemical extractability of pyrene also decreased by 50%, as the chemical migrated deeper into unavailable sites within the sediment matrix. Normalising bioavailability to the chemically extractable fraction of pyrene within the sediment provided an overall decrease in bioavailability of 58%. The importance of the dietary route of uptake for pyrene varied during the sediment aging process, reflecting the changes in the physico-chemical interactions between the pyrene, sediment and pore water.

Organic–mineral interactions in marine sediments studied using density fractionation and X-ray photoelectron spectroscopy

Interactions between organic matter (OM) and minerals are important for the preservation of organic material in marine sediments. Recent evidence suggests that these interactions may not be due to protection of the organic matter via simple sorption to minerals, but rather that the organic matter is acting as a glue between mineral particles resulting in aggregate formation. Density fractionation into multiple density intervals is a powerful approach for looking at the patchy nature of organic matter distribution (Bock, M.J., Mayer, L.M., 2000. Mesodensity organo-clay associations in a near-shore sediment. Marine Geology 163, 65–75), because isolates with varying organic matter loadings can be obtained. The aggregate surfaces can be examined using X-ray photoelectron spectroscopy (XPS), because this technique is restricted to the top 10 nm of the sample surface. XPS gives quantitative information on all the elements on the surface (except H and He) and, in addition, gives information on the chemical bonding of carbon and nitrogen. We used these techniques, along with more standard geochemical tools (CHN, surface area and amino acid analyses), to study a sediment sample of high organic matter content from the oxygen deficient zone off the western coast of Mexico. We found that amino acid composition indicates that the fractions get progressively more degraded as density increases, while the fraction of carbon bonded to oxygen suggests that the oxidation state of the organic matter is similar for all fractions. In addition, the comparison of surface carbon concentrations from XPS and OC:SA suggests that the OM is located in discrete spots on the surface and that as density increases (OC:SA decreases) the organic matter decreases in thickness while retaining the same proportional areal extent.

A Variable Reactivity Model for Ion Binding to Environmental Sorbents

The conceptual and mathematical basis for a new general-composite modeling approach for ion binding to environmental sorbents is presented. The work extends the Simple Metal Sorption (SiMS) model previously presented for metal and proton binding to humic substances (Ganguly et al., 1999). A surface complexation modeling approach is presented, where metal ion binding is conceptualized as occurring at a single (diprotic) binding site with variable reactivity. The overall sorption constant (Kads) is represented as the product of three terms: Kads = Kchem Kcoul Khet. The chemical contribution to metal binding is included in Kchem, while Kcoul and Khet define coulombic and/or heterogeneity effects, and are approximated by empirical power functions of H+ and metal to site concentration ratio (MT/ST), respectively. Because of the difficulty in separating electrostatic and heterogeneity effects for field sorbents, the model is applied first to synthetic data where these effects can be examined separately and cumu...

Specialty polymeric membranes 10

Poly(hexyl methacrylate), which is expected to show affinity toward benzene rather than cyclohexane, was introduced onto nylon 6 by radical graft polymerization of hexyl methacrylate. The membranes from modified nylon 6, having poly(hexyl methacrylate) as a side chain, permeated benzene in preference to cyclohexane from benzene/cyclohexane mixtures by pervaporation. From the pervaporation and the sorption experiments, it was made clear that the introduction of poly(hexyl methacrylate) onto nylon 6 membrane led to the enhancement of permselectivity toward benzene. The solubility data for benzene were described by a combination of simple and specific sorptions, while those for cyclohexane were described by simple sorption.