NaCl Background Electrolyte Research Articles

Impact of microporous structures of esterified cellulose filter papers on Co (II) rejection in cross-flow microfiltration

• Ion rejection by a low-pressure filtration is possible by Donnan exclusion effect. • A microporous structure is important for establishing Donnan exclusion effect. • This phenomenon could be explained by the Gouy-Chapman-Stern (GCS) model. • Highly overlapped EDLs are responsible for developing Donnan exclusion effect. The Donnan exclusion effect is a unique phenomenon in which ions are electrostatically repelled by a surface bearing an identical charge. In this study, cellulose filter papers were esterified by ten different organic acids to systematically evaluate how surface properties regulate the development of the Donnan exclusion effect and subsequent Co(II) rejection. Among the esterified cellulose filter papers, those exhibiting high Co(II) rejection (>80% in 1.0 mg/L Co(II) in 1.0 mM NaCl background electrolyte solution) were noted to simultaneously possess positive zeta potential when in contact with Co(II), low adsorption affinity, and a relatively high microporous environment. This behavior could be explained by the Gouy–Chapman–Stern (GCS) model, in which the ion retention in the overlapped electrical double layers (EDLs) regulates the zeta potential development and consequently the Co(II) rejection. In addition to introducing reactive carbonyl and carboxyl groups, we suggest that the creation of a relatively microporous environment is essential for high Co(II) rejection. Our results are valuable for developing low-energy filtration systems for environmentally friendly water and wastewater treatment.

Tuning microscopic structure of Al-based metal-organic frameworks by changing organic linkers for efficient phosphorus removal

In this study, five aluminum-based metal-organic frameworks ( i.e. Al-BDC, Al-BDC-NH 2 , Al-BHTA, Al-PMA and Al-BPDC) were synthesized by changing the organic linker. Among the five Al-MOFs, Al-BDC, which used 1,4-benzenedicarboxylate as a linker, showed the highest phosphorus adsorption capacity (97.50 mg P/g), while Al-PMA, which used 1,2,4,5-benzenetetracarboxylic acid as a linker, exhibited the lowest phosphorous adsorption capacity (42.25 mg P/g). The adsorption capacity was higher than most adsorbents reported in the literature. In addition, Al-PMA and Al-BPDC are more cost-effective for removing low concentrations of phosphorous from water. When the aqueous phosphorus concentration was less than 1.0 mg P/L, and the dosage of the five Al-MOFs was only 0.10 g/L, more than 90% of phosphorus was removed. The Al-MOFs are suitable for phosphorus removal from water over a wide pH range (5.0–9.0). In this pH range, almost no Al was detected in water after phosphorus removal, indicating that the Al-MOFs can remove phosphorus from water without causing secondary pollution. Moreover, in a NaCl (0.01 mol/L) background electrolyte solution, the Al-MOFs showed high phosphorus removal stability. The Al-MOFs have the potential to remove phosphorus from natural water. Furthermore, the mechanism study shows that electrostatic interaction and ligand exchange were defined as the main phosphorus removal pathways using the prepared Al-MOFs. These findings demonstrate that the synthesized Al-MOFs are promising candidates for removal of phosphorus from eutrophic water. • The microscopic structures of Al-MOFs were tuned with different organic linkers. • Surface area and pore structure of MOFs significantly affect the phosphorus adsorption performance. • Al-BDC shows high adsorption capacity of 97.50 mg P/g for phosphorus. • Excellent phosphorus removal efficiency was obtained in real water. • Electrostatic interaction and ligand exchange are responsible for the adsorption mechanism.

Bentonite Nanoparticle Stability and the Effect of Fulvic Acids: Experiments and Modelling

In this study, the critical coagulation concentration (CCC) for FEBEX bentonite colloids is determined by colloid coagulation studies under variation of pH, electrolyte concentration, and fulvic acid (GoHy-573FA) content. For CaCl2 electrolyte solution, a pH-independent Ca-CCC of 1 mmol L−1 is found. In the case of NaCl background electrolyte, a pH-dependent Na-CCC can be determined with 15 ± 5 mmol L−1 at pH 6, 20 ± 5 mmol L−1 at pH 7, 200 ± 50 mmol L−1 at pH 8, 250 ± 50 mmol L−1 at pH 9, and 350 ± 100 mmol L−1 at pH 10, respectively. The addition of 1 mg L−1 dissolved organic carbon in the form of fulvic acid (FA) increases the Ca-CCC to 2 mmol L−1. An association of FA with FEBEX bentonite colloids as surface coating can clearly be identified by scanning transmission X-ray microscopy (STXM). The experimental bentonite stability results are described by means of an extended DLVO (Derjaguin–Landau–Verwey–Overbeek) approach summing up hydration forces, short-range Born repulsion, van der Waals attraction, and electrical double layer repulsion. The measured zeta (ζ)-potential of the bentonite colloids is applied as platelet face electrokinetic potential and the edge electrokinetic potential is estimated by the combination of silica and alumina ζ-potential data in the ratio given by the FEBEX bentonite structural formula. Adjusting the montmorillonite face electrokinetic potential by a maximum of ±15.9 mV is sufficient to successfully reproduce the measured stability ratios. Due to the uncertainty in the ζ-potential measurement, only semiquantitative calculations of the stability ratio can be given.

Control of the colloidal depletion force in nonionic polymer solutions by complexation with anionic surfactants

HypothesisCharge, size and concentration of depletants control the magnitude and range of depletion and structural forces. Noncovalent association of nonionic polymers with ionic surfactants may therefore synergistically enhance these forces to an extent that depends on the structure and composition of the resulting complexes. ExperimentsForces were measured between a silica sphere and a silica plate in solutions of Pluronic F108 nonionic poly(ethylene oxide – block – propylene oxide – block – ethylene oxide) triblock copolymers and anionic sodium dodecylsulfate (SDS) surfactants using colloidal probe atomic force microscopy as a function of polymer, surfactant and NaCl background electrolyte concentrations. Trends in the magnitudes of the depletion attraction minimum and the first repulsive maximum in the oscillatory structural force were interpreted with the aid of pyrene solubilization assays, sodium ion-selective electrode analysis, and dynamic light scattering measurements that characterized the formation, charge, and hydrodynamic radius of F108/SDS complexes respectively. FindingsSynergistic enhancement of the depletion force and first repulsive maximum occurred within a finite range of SDS concentrations, to an extent that depended on F108 and NaCl concentrations. This was due mainly to charging of F108/SDS complexes. Size effects were important at low NaCl concentration. Forces measured above the synergistic SDS concentration range were indistinguishable from those in polymer-free SDS solutions due to the appearance of excess unbound SDS micelles.

Compositional and Temperature Effects on the Rheological Properties of Polyelectrolyte-Surfactant Hydrogels.

The rheological properties of hydrogels prepared by physical interactions between oppositely charged polyelectrolyte and surfactant in micellar form were studied. Specifically, hyaluronan was employed as a negatively charged polyelectrolyte and Septonex (carbethopendecinium bromide) as a cationic surfactant. Amino-modified dextran was used as a positively charged polyelectrolyte interacting with sodium dodecylsulphate as an anionic surfactant. The effects of the preparation method, surfactant concentration, ionic strength (the concentration of NaCl background electrolyte), pH (buffers), multivalent cations, and elevated temperature on the properties were investigated. The formation of gels required an optimum ionic strength (set by the NaCl solution), ranging from 0.15–0.3 M regardless of the type of hydrogel system and surfactant concentration. The other compositional effects and the effect of temperature were dependent on the polyelectrolyte type or its molecular weight. General differences between the behaviour of hyaluronan-based and cationized dextran-based materials were attributed to differences in the chain conformations of the two biopolymers and in the accessibility of their charged groups.

Complexation of Cu(II) with cefotaxime in NaCl solution

Complexation of Cu2+ cations with anions of cefotaxime antibiotic (Cxm–) was studied by pH-metric titration at 37°C in 0.15 mol/L NaCl background electrolyte. The formation of complex of composition CuCxm was revealed, the value of logβ(CuCxm) = 2.3 ± 0.2 was calculated. A computer model of the complex was calculated by DFT using B3LYP hybrid functional and LACV3P**++ basis set. According to calculation results, Cu(II) in the complex has CN = 4, close to square planar structure of coordination sphere, and coordinates Cxm– through the oxygen atoms of the carboxylate, β-lactame, and amide groups, as well as through the nitrogen atom of the thiazole ring.

Highly sensitive potentiometric sensor for detection of mercury in Cl−-rich samples

Potentiometric sensors have been exploited for the determination of Hg2+ ions. However, applications of such sensors are limited to mercury detection in the absence of a Cl−-rich background since Hg2+ can readily form coordination complexes with Cl−. This paper describes a potentiometric sensor for the determination of anionic mercury species using tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide) as anion-selective ionophore and tridodecylmethylammonium chloride as ion exchanger. An asymmetric membrane rotating ion-selective electrode configuration is used to improve the detection sensitivity. By using HgCl3− as a model of anionic mercury species, the proposed method allows potentiometric detection of mercury down to nanomolar levels in samples containing 0.05M NaCl background electrolyte. The practical application of the proposed sensor has been performed for the determination of total mercury concentrations in diluted seawater samples.

Thermodynamic characteristics of the heparin-leucine-CaCl2 system in a diluted physiological solution

Chemical equilibria in aqueous solutions of high-molecular weight heparin (Na4hep) and leucine (HLeu) are calculated through the mathematical modeling of chemical equilibria based on representative experimental pH titration data. In addition, chemical equilibria in the CaCl2-Na4hep-HLeu-H2O-NaCl system in the presence of 0.154M NaCl background electrolyte at a temperature of 37°C in the range of 2.30 ≤ pH ≤ 10.50 and initial concentrations of basic components n × 10−3 M (n ≤ 4).

Adsorption of Plutonium Oxide Nanoparticles

Adsorption of monodisperse cubic plutonium oxide nanoparticles ("Pu-NP", [Pu(38)O(56)Cl(x)(H(2)O)(y)]((40-x)+), with a fluorite-related lattice, approximately 1 nm in edge size) to the muscovite (001) basal plane from aqueous solutions was observed in situ (in 100 mM NaCl background electrolyte at pH 2.6). Uptake capacity of the surface quantified by α-spectrometry was 0.92 μg Pu/cm(2), corresponding to 10.8 Pu per unit cell area (A(UC)). This amount is significantly larger than that of Pu(4+) needed for satisfying the negative surface charge (0.25 Pu(4+) for 1 e(-)/A(UC)). The adsorbed Pu-NPs cover 17% of the surface area, determined by X-ray reflectivity (XR). This correlates to one Pu-NP for every 14 unit cells of muscovite, suggesting that each particle compensates the charge of the unit cells onto which it adsorbs as well as those in its direct proximity. Structural investigation by resonant anomalous X-ray reflectivity distinguished two different sorption states of Pu-NPs on the surface at two different regimes of distance from the surface. A fraction of Pu is distributed within 11 Å from the surface. The distribution width matches the Pu-NP size, indicating that this species represents Pu-NPs adsorbed directly on the surface. Beyond the first layer, an additional fraction of sorbed Pu was observed to extend more broadly up to more than 100 Å from the surface. This distribution is interpreted as resulting from "stacking" or aggregation of the nanoparticles driven by sorption and accumulation of Pu-NPs at the interface although these Pu-NPs do not aggregate in the solution. These results are the first in situ observation of the interaction of nanoparticles with a charged mineral-water interface yielding information important to understanding the environmental transport of Pu and other nanophase inorganic species.

A new x-ray interface and surface scattering environmental cell design for in situ studies of radioactive and atmosphere-sensitive samples

We present a novel design of a purpose-built, portable sample cell for in situ x-ray scattering experiments of radioactive or atmosphere sensitive samples. The cell has a modular design that includes two independent layers of containment that are used simultaneously to isolate the sensitive samples. Both layers of containment can be flushed with an inert gas, thus serving a double purpose as containment of radiological material (either as a solid sample or as a liquid phase) and in separating reactive samples from the ambient atmosphere. A remote controlled solution flow system is integrated into the containment system that allows sorption experiments to be performed on the diffractometer. The cell's design is discussed in detail and we demonstrate the cell's performance by presenting first results of crystal truncation rod measurements. The results were obtained from muscovite mica single crystals reacted with 1 mM solutions of Th(IV) with 0.1 M NaCl background electrolyte. Data were obtained in specular as well as off-specular geometry.

Fibrinogen Adsorption on Mica Studied by AFM and in Situ Streaming Potential Measurements

Adsorption of fibrinogen from aqueous solutions on mica was studied using AFM and in situ streaming potential measurements. In the first stage, bulk physicochemical properties of fibrinogen and the mica substrate were characterized for various ionic strength and pH. The zeta potential and number of uncompensated (electrokinetic) charges on the protein surfaces were determined from microelectrophoretic measurements. Analogously, using streaming potential measurements, the electrokinetic charge density of mica was determined for pH range 3-10 and the NaCl background electrolyte concentration of 10(-3) and 10(-2) M. Next, the kinetics of fibrinogen adsorption at pH 3.5 and 7.4 in the diffusion cell was studied using a direct AFM determination of the number of molecules per unit area of the mica substrate. Then, streaming potential measurements were performed to determine the apparent zeta potential of fibrinogen-covered mica for different pH and ionic strength in terms of its surface concentration. A quantitative interpretation of these streaming potential measurements was achieved in terms of the theoretical model postulating a side-on adsorption of fibrinogen molecules as discrete particles. On the basis of these results, the maximum coverage of fibrinogen Θ close to 0.29 was predicted, in accordance with previous theoretical predictions. It was also suggested that anomalous adsorption for pH 7.4, where fibrinogen and the mica substrate were both negatively charged, can be explained in terms of a heterogeneous charge distribution on fibrinogen molecules. It was estimated that the positive charge was 12 e (for NaCl concentration of 10(-2) M and pH 7.4) compared with the net charge of fibrinogen at this pH, equal to -21 e. Results obtained in this work proved that the coverage of fibrinogen can be quantitatively determined using the streaming potential method, especially for Θ < 0.2, where other experimental methods become less accurate.

Complex formation in Nb6O 19 8− -WO 4 2− -H+-H2O system where c Nb: c W = 4 : 2

Processes occurring in Nb6O198−-WO42−-H+-H2O system where cNb: cW = 4: 2, cNb+W0 = 5 × 10−3, 2.5 × 10−3, or 10−3 mol/L, and ionic strengths I = 0.01–0.14 are created by NaCl background electrolyte were studied by pH titration and mathematical modeling. Solute ion species distribution diagrams were obtained for \( Z = \frac{{c_{H^ + }^0 }} {{c_{Nb + W}^0 }} = 0 - 1.5 \). The concentration constants and thermodynamic constants of formation were calculated for isopolyniobotungstate anions (IPNTAs). HxNb4W2O19(6−x)−, (x = 1–5), ions were shown to appear in solution only after Nb6O198− was protonated and aquapolytungstate anions were formed. The results of modeling were supported by the synthesis of Tl3H3Nb4W2O19 · 16.5H2O, Tl2H4Nb4W2O19 · 11H2O, and NaTl3(H4Nb4W2O19)2 · 22H2O salts, which were identified by chemical analysis and IR spectroscopy.

Electrochemical Sample Matrix Elimination for Trace-Level Potentiometric Detection with Polymeric Membrane Ion-Selective Electrodes

Potentiometric sensors are today sufficiently well understood and optimized to reach ultratrace level (subnanomolar) detection limits for numerous ions. In many cases of practical relevance, however, a high electrolyte background hampers the attainable detection limits. A particularly difficult sample matrix for potentiometric detection is seawater, where the high saline concentration forms a major interfering background and reduces the activity of most trace metals by complexation. This paper describes for the first time a hyphenated system for the online electrochemically modulated preconcentration and matrix elimination of trace metals, combined with a downstream potentiometric detection with solid contact polymeric membrane ion-selective microelectrodes. Following the preconcentration at the bismuth-coated electrode, the deposited metals are oxidized and released to a medium favorable to potentiometric detection, in this case calcium nitrate. Matrix interferences arising from the saline sample medium are thus circumvented. This concept is successfully evaluated with cadmium as a model trace element and offers potentiometric detection down to low parts per billion levels in samples containing 0.5 M NaCl background electrolyte.

XPS study of the hematite–aqueous solution interface

AbstractThe interaction between the surface of hematite colloidal platelets and Na+ and Cl− ions was investigated by XPS using the cryogenic technique. Pastes in ionic strengths of 0 and 10 mM NaCl contained about 10 at. % water and water/NaCl atomic ratios of 3 to 6. These results fall within the range of values obtained for a variety of minerals studied with this technique. Pastes in 100 mM NaCl background electrolyte, however, contained an unusually larger water content of 25 at. %, yielding a Na+: Cl−: H2O ratio of 1:1:2. This result is in strong contrast with other minerals at the same ionic strength, which typically reveal about 10 at. % water. Substituting Na+ for Cs+ in the hematite paste with 100 mM CsCl yielded, on the other hand, the same amount of water as in the pastes with 0 and 10 mM NaCl, and underpinned the role of Na+ ions in the large water content of the hematite paste. As surface concentrations of Na+ and Cl− exceeded those of hematite surface structural hydroxyl groups and Na 1s and Cl 2p spectra exhibited energy loss features, the electrolyte ions are proposed to be distributed in a three‐dimensional array in the fast‐frozen paste, possibly in a hydrohalite‐like (NaCl·2H2O) phase. In addition, because the fast‐frozen solution of 100 mM NaCl yields a water/NaCl ratio of about 70, hematite is proposed to play an important role in the stabilization of this three‐dimensional distribution of Na+ and Cl− ions. The role of the neutrally charged {001} plane, a predominant feature in the hematite particles of this study, is notably discussed in the light of recent molecular models showing that this plane can stabilize several layers of hydrated ions up to 15 Å from the surface. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Equilibria of aqueous solutions of isopolyniobotungstates-6 with c Nb : c W = 1 : 5

Complex formation in the Nb6O198−-WO42−-H+-H2O system with cNb : cW = 1 : 5 and varied cNb + W0 = 10−2, 5 × 10−3, 2.5 × 10−3, and 10−3 mol/L) has been studied. Distribution diagrams were simulated for individual niobium(V) and tungsten(VI) isopolyanions and mixed isopolyniobotungstates for \(Z = \frac{{c_{H^ + }^0 }}{{c_{Nb + W}^0 }} = 0 - 3.0\) in an NaCl background electrolyte. We have shown that isopolyniobotungstates-6 of composition HxNbW5O19(3 − x)− are formed via HxNbnW6−nO19(2 + n − x)− (n=2, 3, 5) ions. The concentration formation constants and thermodynamic formation constants of isopolyniobotungstate anions (IPNTAs) in aqueous solution have been calculated. Salt Tl3NbW5O19·9H2O has been synthesized and identified by chemical analysis and IR spectroscopy.

Adsorption to goethite of extracellular polymeric substances from Bacillus subtilis

Extracellular polymeric substances (EPS) are heterogeneous biopolymers produced by Gram-negative and Gram-positive bacterial cells. Adsorption of EPS to minerals can alter the substrata physico-chemistry and influence initial bacterial adhesion processes via conditioning film formation, but the effects of solution chemistry on uptake of EPS remain poorly understood. In this study, the adsorption to goethite (α-FeOOH) of EPS isolated from the early stationary growth-phase culture of Bacillus subtilis was investigated as a function of pH and ionic strength ( I) in NaCl background electrolyte using batch studies coupled with Fourier transform infrared spectroscopy and size-exclusion high-performance liquid chromatography. Proteins, particularly those of higher molar mass, and phosphorylated macromolecules were adsorbed preferentially. Increasing solution I (1–100 mM NaCl) or pH (3.0–9.0) resulted in a decrease in the mass of EPS adsorbed. Batch studies and diffuse reflectance infrared Fourier transform spectra are consistent with ligand exchange of EPS phosphate groups for surface hydroxyls at Fe metal centers. The data indicate that both electrostatic and chemical bonding interactions contribute to selective fractionation of the EPS solution. Proteins and phosphate groups in phosphodiester bridges of nucleic acids likely play an important role in conditioning film formation at Fe oxide surfaces.

Trace Metal Ion Partitioning at Polymer Film−Metal Oxide Interfaces: Long-Period X-ray Standing Wave Study

The distributions of Pb(II) and As(V)O4(3-) ions in the interfacial region between thin poly(acrylic acid) (PAA) coatings and aalpha-A12O3(0001), alpha-Al2O3(1-102), and alpha-Fe2O3(0001) single-crystal substrates were studied using long-period X-ray standing wave fluorescent yield (XSW-FY) and X-ray reflectivity techniques. The PAA film serves as a simplified analogue of natural organic matter (NOM) coatings on mineral surfaces. Such coatings are often assumed to play an important role in the partitioning and speciation of trace heavy metals in soils and aquatic systems. On the alpha-Al2O3(1-102) surface, Pb(II) ions were found to preferentially bind to the PAA coating, even at sub-micromolar Pb(II) concentrations, and to partition increasingly onto the metal oxide surface as the Pb(II) concentration was increased ([Pb(II)] = 5 x 10(-8) to 2 x 10(-5) M, pH = 4.5; 0.01 M NaCl background electrolyte). This observation suggests that the binding sites in the PAA coating outcompete those on the alpha-Al2O3(1-102) surface for Pb(II) under these conditions. The As(V)O4(3-) oxoanion partitions preferentially to the L-Al2O3(1-102) surface for the As(V)O4(3-) concentrations examined (1 x 10(-7) to 5 x 10(-7) M, pH = 4.5; 0.01 M NaCl background electrolyte). Partitioning of Pb(II) (at 1 x 10(-7) M and pH 4.5) was also examined at PAA/alpha-Al2O3(0001), and PAA/alpha-Fe2O3(0001) interfaces using XSW-FY measurements. Our results show that the PAA coating was the dominant sink for Pb(II) in all three samples; however, the relative order of reactivity of these metal oxide surfaces with respect to Pb(II) sorption is alpha-Fe2O3(0001) > alpha-Al2O3(1-102) > alpha-Al2O3(0001). This order is consistent with that found in previous studies of the PAA-free surfaces. These XSW results strongly suggest that the characteristics of the organic film (i.e., binding affinity, type, and density of binding sites) as well as metal oxide substrate reactivity are key factors determining the distribution and speciation of Pb(II) and As(V)O4(3-) at organic film/metal oxide interfaces.

Surface complexation of neodymium at the rutile-water interface: A potentiometric and modeling study in NaCl media to 250°C

The adsorption of Nd 3+ onto rutile surfaces was examined by potentiometric titration from 25 to 250°C, in 0.03 and 0.30 m NaCl background electrolyte. Experimental results show that Nd 3+ sorbs strongly, even at low temperature, with adsorption commencing below the pH znpc of rutile. In addition, there is a systematic increase in Nd 3+ adsorption with increasing temperature. The experimental results were rationalized and described using surface oxygen proton affinities computed from the MUlti SIte Complexation or MUSIC model, coupled with a Stern-based three-layer description of the oxide/water interface. Moreover, molecular-scale information was incorporated successfully into the surface complexation model, providing a unique geometry for the adsorption of Nd 3+ on rutile. The primary mode of Nd 3+ adsorption was assumed to be the tetradentate configuration found for Y 3+ adsorption on the rutile (110) surface from previously described in situ X-ray standing wave experiments, wherein the sorbing cations bond directly with two adjacent “terminal” and two adjacent “bridging” surface oxygen atoms. Similarly, the adsorption of Na + counterions was also assumed to be tetradentate, as supported by MD simulations of Na + interactions with the rutile (110) surface, and by analogous X-ray standing wave results for Rb + adsorption on rutile. Fitting parameters for Nd 3+ adsorption included binding constants for the tetradentate adsorption complex and capacitance values for the inner-sphere binding plane. In addition, hydrolysis of the tetradentate adsorption complex was permitted and resulted in significantly improved model fits at higher temperature and pH values. The modeling results indicate that the Stern-based MUSIC surface-complexation model adequately accommodates molecular-scale information to uniquely rationalize and describe multivalent ion adsorption systematically into the hydrothermal regime.

Modeling the surface complexation of calcium at the rutile-water interface to 250°C

The adsorption behavior of metal-(hydr)oxide surfaces can be described and rationalized using a variety of surface complexation models. However, these models do not uniquely describe experimental data unless some additional insight into actual binding mechanisms for a given system is available. This paper presents the results of applying the MUlti SIte Complexation or MUSIC model, coupled with a Stern-based three layer description of the electric double layer, to Ca 2+ adsorption data on rutile surfaces from 25 to 250°C in 0.03 and 0.30 m NaCl background electrolyte. Model results reveal that the tetradentate adsorption configuration found for Sr 2+ adsorbed on the rutile (110) surface in the in situ X-ray standing wave experiments of Fenter et al. (2000) provides a good fit to all Ca 2+ adsorption data. Furthermore, it is also shown that equally good fits result from other plausible adsorption complexes, including various monodentate and bidentate adsorption configurations. These results amply demonstrate the utility of in situ spectroscopic data to constrain surface complexation modeling, and the ability of the MUSIC model approach to accommodate this spectroscopic information. Moreover, this is the first use of any surface complexation model to describe multivalent ion adsorption systematically into the hydrothermal regime.

Adsorption of cadmium, copper, nickel, and zinc to a poly(tetrafluorethene) porous soil solution sampler.

Suction cups made of poly(tetrafluorethene) (PTFE) are widely used for sampling of soil solution. A brand (Prenart) of PTFE cups was tested for adsorption of Cd, Cu, Ni, and Zn at low concentrations under different conditions. In a laboratory experiment adsorption from a 10 microg L(-1) heavy metal solution with a 0.01 M NaCl background electrolyte was investigated at pH 3.6, 4.5, and 5.8 by pumping the solutions through the cups. The effect of three different ionic compositions was also investigated using 0.01 M CaCl2, 0.01 M NaCl, and no background electrolyte at pH 4.5. In 0.01 M NaCl electrolyte at pH 5.8 the cups acted as effective filters. At pH 3.6 after 300 mL of solution had passed through the cup, equivalence between the Cd and Ni concentrations in influent and effluent was found. No equivalence between effluent and influent concentrations was found for Zn and Cu at pH 4.5 and 5.8. With Ca as the electrolyte, no adsorption of Cd, Ni, or Zn was found. In Na electrolyte, equivalence between influent and effluent concentrations for Cd, Ni, and Zn was reached. The difference between effluent and influent concentrations of Zn, Ni, and Cd remained significant in the absence of electrolyte. For all pH values and electrolytes the difference between effluent and influent concentrations of Cu was significant. It is concluded that PTFE cups affect the concentrations of heavy metals sampled at low soil solution concentrations. Cadmium, Cu, Ni, and Zn adsorb to the cup at pH > 4.5 and low ionic strength.