Cation Concentration In Solution Research Articles

On‐Demand Plasmon Nanoparticle‐Embedded Laser‐Induced Periodic Surface Structures (LIPSSs) on Silicon for Optical Nanosensing

AbstractUltrashort laser pulses deliver electromagnetic energy to matter causing its localized heating that can be used for both material removal via ablation/evaporation and driving interface chemical reactions. Here, it is shown that both mentioned processes can be simultaneously combined within straightforward laser nanotexturing of Si wafer in a functionalizing solution to produce a practically relevant metal–semiconductor surface nano‐morphology. Such unique hybrid morphology represents deep‐subwavelength Si laser‐induced periodic surface structures (LIPSSs) with an extremely short period down to 70 nm and high‐aspect‐ratio nano‐trenches loaded with controllable amount of plasmonic nanoparticles formed via laser‐induced decomposition of the precursor noble‐metal salts. Moreover, heat localization driving reduction process is utilized to produce surface morphology locally decorated with dissimilar plasmon‐active nanoparticles. Light‐absorbing deep‐subwavelength Si LIPSSs loaded with controllable amount of noble‐metal nanoparticles represent an attractive architecture for plasmon‐related applications such as optical nanosensing where efficient coupling of the propagating optical waves to highly localized electromagnetic “hot spots” is a mandatory requirement. To support this statement, applicability of such hybrid morphology for fluorescence‐based detection of nanomolar concentrations of mercury cations in solution is demonstrated.

UV-Induced Photocatalytic Reduction of Methylene Blue Dye in the Presence of Photochromic Tungsten Oxide Sols

In spite of the wide application of nanodisperse tungsten oxide (from photo- and electrochromic devices to biomedical materials), its physicochemical properties were studied insufficiently. In this work, we have performed a comparative analysis of photochromic and photocatalytic properties of polyvinylpyrrolidone-stabilized tungsten oxide nanoparticles prepared by ion exchange and precipitation from sodium tungstate solution. Reversible UV-induced reduction of Methylene Blue dye in the presence of photochromic tungsten oxide sol has been shown, the dependence of photochromic properties of tungsten oxide sols on sodium cation concentration in solution has been revealed.

Cation-Activated Avidity for Rapid Reconfiguration of DNA Nanodevices.

The ability to design and control DNA nanodevices with programmed conformational changes has established a foundation for molecular-scale robotics with applications in nanomanufacturing, drug delivery, and controlling enzymatic reactions. The most commonly used approach for actuating these devices, DNA binding and strand displacement, allows devices to respond to molecules in solution, but this approach is limited to response times of minutes or greater. Recent advances have enabled electrical and magnetic control of DNA structures with sub-second response times, but these methods utilize external components with additional fabrication requirements. Here, we present a simple and broadly applicable actuation method based on the avidity of many weak base-pairing interactions that respond to changes in local ionic conditions to drive large-scale conformational transitions in devices on sub-second time scales. To demonstrate such ion-mediated actuation, we modified a DNA origami hinge with short, weakly complementary single-stranded DNA overhangs, whose hybridization is sensitive to cation concentrations in solution. We triggered conformational changes with several different types of ions including mono-, di-, and trivalent ions and also illustrated the ability to engineer the actuation response with design parameters such as number and length of DNA overhangs and hinge torsional stiffness. We developed a statistical mechanical model that agrees with experimental data, enabling effective interpretation and future design of ion-induced actuation. Single-molecule Förster resonance energy-transfer measurements revealed that closing and opening transitions occur on the millisecond time scale, and these transitions can be repeated with time resolution on the scale of one second. Our results advance capabilities for rapid control of DNA nanodevices, expand the range of triggering mechanisms, and demonstrate DNA nanomachines with tunable analog responses to the local environment.

Partitioning behavior of Br and Cl during jarosite precipitation and its implications for sedimentary rock on Mars

National Aeronautics and Space Administration (NASA)′s Opportunity rover landed at Meridiani Planum on Mars in 2004, and discovered the first sedimentary record on Mars called Burns formation. The detection of magnesium- and iron- sulfates, jarosite (KFe3(SO4)2(OH)6), and hematite (Fe2O3) in the outcrop of Burns formation indicates that aqueous activities have been once present in this region. The Alpha Particle X-ray Spectrometer (APXS) onboard the rover detected enrichment of elemental Br in rock and soil samples which varied by three orders of magnitude, and primarily controlled the variations of Br/Cl ratios in these samples. Although aqueous related processes have been suggested to explain the enrichment of Br, the speciation of Br and the mechanisms for Br variations are poorly constrained. Jarosite has been reported to be able to preferentially incorporate Br− over Cl− during precipitation, and result in Br enrichment and Br/Cl fractionation. However, the partitioning behavior of Br− and Cl− during jarosite formation and how the incorporation of halogens would influence properties of jarosite are not well known. In this work, we synthesized a series of halogen bearing jarosite with Br− and Cl− concentration gradients by oxidation of ferrous sulfate at room temperature. After synthesis, we used X-ray diffraction (XRD), Raman spectrometer, infrared spectrometer (IR), scanning electron microscope (SEM) to analyze structure information and surface morphology of jarosite solids. Anion and cation concentrations in solution and solid were analyzed by ion chromatography (IC), atomic absorption spectrophotometer (AAS) and X-ray fluorescence (XRF). Our work shows that Br and Cl contents in the synthesized jarosite are positively correlating with its initial concentrations in solutions. Starting at the same concentrations in solution, incorporation of Br− in jarosite is about two orders of magnitude higher than that of Cl−. Coexisting Br− can significantly interfere with Cl− partitioning into jarosite. The distribution coefficients of Br− and Cl− are negatively correlated with their initial concentrations in solutions, and in the Br− and Cl− coexisting setting, the distribution coefficients of Cl− decrease as the initial Br− concentration increase in the solution. Therefore, during precipitation of jarosite, Br− prefers to participate into jarosite while Cl− prefers to remain in solution. Incorporation of halide anions into jarosite directly affected the range of hydroxyl and water in Raman spectra, indicating that Br− and Cl− substitute for OH position in jarosite without changing its fundamental structure. We calculated that in our experiment settings, Br/Cl ratios in jarosite are about two orders of magnitude higher than that of initial solutions. Therefore, if jarosite precipitates from a brine containing Br− and Cl−, it can enrich Br over Cl and bearing significant higher Br/Cl ratio signature comparing to the initial brine. For sedimentary outcrop composed of substantial amount of jarosite, Br/Cl ratios may not be controlled solely by evaporation and precipitation of halide evaporites, but might also be influenced by precipitation and dissolution of halogen bearing jarosite. The aqueous stability of halogen bearing jarosite and the possible release of halide anions during jarosite dissolution require further evaluation.

Interfacial interactions between Skeletonema costatum extracellular organic matter and metal oxides: Implications for ceramic membrane filtration

In the current study, the interfacial interactions between the high molecular weight (HMW) compounds of Skeletonema costatum (SKC) extracellular organic matter (EOM) and ZrO2 or Al2O3, were investigated by atomic force microscopy (AFM). HMW SKC-EOM was rigorously characterized and described as a hydrophilic organic compound mainly comprised of polysaccharide-like structures. Lipids and proteins were also observed, although in lower abundance. HMW SKC-EOM displayed attractive forces during approaching (i.e., leading to jump-to-contact events) and adhesion forces during retracting regime to both metal oxides at all solution conditions tested, where electrostatics and hydrogen bonding were suggested as dominant interacting mechanisms. However, the magnitude of these forces was significantly higher on ZrO2 surfaces, irrespective of cation type (Na+ or Ca2+) or concentration. Interestingly, while HMW SKC-EOM interacting forces to Al2O3 were practically insensitive to solution chemistry, the interactions between ZrO2 and HMW SKC-EOM increased with increasing cation concentration in solution. The structure, and lower charge, hydrophilicity, and density of hydroxyl groups on ZrO2 surface would play a key role on favoring zirconia associations with HMW SKC-EOM. The current results contribute to advance our fundamental understanding of Algogenic Organic Matter (AOM) interfacial interactions with metal oxides (i.e., AOM membrane fouling), and would highly assist in the proper selection of membrane material during episodic algal blooms.

Beachrock formation via microbial dissolution and re-precipitation of carbonate minerals

Cementation of beach sand in the intertidal zone produces beachrock, such as that found on Heron Island (Heron Reef, Great Barrier Reef, Australia). Although common to coastlines in many low-latitude beach environments, the cause of cementation is not fully understood. In this investigation, electron and X-ray fluorescence microscopy were used to characterize previously undocumented features of beachrock. Two generations of beachrock were examined as a means of understanding the progression of cementation. Meniscus-shaped attachments at point contacts appear to be the first cements to form in biofilms near the beachrock surface. This is followed by isopachous fringe cements within the now ‘enclosed’ beachrock, composed of aragonite needles that are enriched in strontium and contain extracellular polymeric substances (EPS). Cement precipitation is driven by locally high concentrations of cations in solution, undoubtedly generated via microbial dissolution of the detrital carbonate grains. Binding to negatively charged bacterial EPS retains these cations within beachrock microenvironments. The metabolism of cyanobacteria and associated heterotrophs induce the supersaturating conditions needed for cement precipitation. Deeper within beachrock (mm to cm-below the surface), abundant microbialites are found on the edges of grains and contain trapped and bound detrital material. These structures are laminated, enriched in strontium in some layers, and contain microfossils. The results of this investigation clearly demonstrate a biological influence in the precipitation of aragonite cement involving internal recycling of cations through microbial dissolution and precipitation of carbonate minerals.

Swelling clays and salt-affected soils : demixing of Na / Ca clays as the rationale for discouraging the use of sodium adsorption ratio (SAR)

Sodium adsorption ratio SAR defined as SAR = (Na) / V w(Ca+Mg)/2 here concentrations of cations in solution are expressed in meq/L has long been considered as correlated to exchangeable sodium percentage (ESP) on clay minerals or soil exchange complex, and as the key concept to explain swelling of clay minerals and the difficulties of reclaiming salt-affected soils. Though its basis is empirical, it was alleged to be theoretically justified on the basis of ion exchange, derived from the Gapon convention. However, it has long been challenged on the basis of both field observations and experimental evidence : it fails to account for the fact that calcium and magnesium do not play the same role, while potassium is absent from the formula ; calcium concentration must be “corrected “when calcite is present etc. There exist specific ion effects. Experimental measurements of the decrease of permeability when solutions are diluted led Quirk and Schofield (1955) to define the concept of critical threshold, and to show that potassium and magnesium play an intermediate role between sodium and calcium. This threshold is simply determined by the concentration of calcium, irrespective of the value of SAR or ESP. Indeed, demixing of Ca-Na clay minerals during ion exchange, a phenomenon well known since Glaeser and Mering (1954), implies that there exists an interaction between adjacent sites. This undermines the theoretical basis of SAR : the derivation of SAR from ion exchange equilibria implies to use an equilibrium constant. This parameter is no more constant if demixing occurs. The results obtained are positive : demixing leads to expulsion of sodium from inner exchange surfaces and its replacement by calcium, according to the “three crystals pore”proposed by Quirk (2003b). Sodium can then be more easily leached, as permeability is maintained by clusters of Ca-sites. Calcium concentration in solution appears thus as the simpler parameter to guide saltaffected soils reclamation when swelling clays are present.

SO2 impurity impacts on experimental and simulated CO2–water–reservoir rock reactions at carbon storage conditions

Some industrial CO2 streams stored geologically may contain impurities including SO2, O2, and NOX. The impacts of these reactive gases in CO2–water–rock interactions have received limited attention relative to pure CO2 studies. An experimental and geochemical modelling study of reservoir and cap-rock core samples from a potential CO2 storage site in the Surat Basin, Queensland, Australia is described. Reservoir and cap-rock samples were reacted with low salinity fluid saturated with an impure CO2 stream containing 0.16% SO2 at reservoir simulated in situ conditions. This study is relevant to the storage of impure CO2 streams from industrial sources in sandstone reservoirs.Experimentally, dissolution of SO2 from the supercritical gas phase into the aqueous phase showed a kinetic control. The acidification from sulphuric acid generation, and the resulting silicate and carbonate dissolution were generally observed in all experiments. Significant dissolved cation concentrations in solution (up to ~843mg/kg) indicated a higher potential for CO2 trapping, especially from mineralogically reactive core samples. The extent of mineral dissolution was dependent on the rock mineralogy. Precipice Sandstone samples showed the lowest reactivity indicating its suitability as a reservoir unit. However this study indicates the potential for localised changes to water quality in the near wellbore region that necessitate further investigation. Corrosion of the carbonates calcite, siderite and ankerite, and silicates including iron-rich chlorite, plagioclase, and K-feldspar was observed on rock surfaces in potential seal rocks. Calcite cement partially dissolved and acicular gypsum precipitated on the surface of a sandstone formation that could act as a potential secondary sealing unit. The formation of dense sulphates may self-seal some cap-rock. Simulations showed a good history match with the experiments, with the main predicted reactive phases including calcite, ankerite, siderite and chlorite +/− Fe oxides on the time scale of the experiments. Redox potential of the system was important; where oxidised iron was present SO2 oxidation to sulphuric acid was predicted to dominate in the simulations; otherwise pyrite and elemental S formation were also predicted (as observed experimentally). The findings of this study are generally applicable to understanding likely impacts to water quality from impure CO2 injection in CCS sites in Australia and internationally. Data has been provided which may be used to improve longer term modelling predictions.

Sorption/Desorption of Lincomycin from Three Arid-Region Soils

The antibiotic lincomycin is commonly found in treated municipal waste water and in waste from swine and poultry production. Environmental disposal of these wastes has the potential to introduce a significant mass of lincomycin into the ecosystem. In the present study, a series of sorption and desorption experiments were conducted to determine the potential mobility of lincomycin in soils from arid environments. Sorption and desorption isotherms were obtained for lincomycin using three different soils. Isotherms were fit to the Freundlich equation. Adsorption of lincomycin was found to have a of 11.98 for a biosolid-treated soil (1.58% OC) and a of 210.15 for a similar unamended soil (1.42% OC). It was also found that for a low-organic-content soil the was 5.09. The differences in adsorption can be related to the soil pH and the pKa of lincomycin (7.5-7.8). When the soil solution pH is below the pKa, the cationic species of lincomycin dominates, resulting in increased water solubility. Interaction with the cation exchange complex is minimal due to a high solution cation concentration (Ca and Na). Desorption isotherms also indicate that when the solution pH is lower than the pKa, retention of lincomycin is reduced. Our results indicate that the mobility of lincomycin in these arid region soils is dependent on soil pH.

Biosynthesis of natrojarosite by immobilized iron-oxidizing bacteria

Natrojarosite is a very important material. In this paper biosynthesis of pure natrojarosite by immobilized Acidithiobacillus ferrooxidans was described. Scanning electron microscopy (SEM), ICP-AES and XRD analysis revealed the character of natrojarosite. The process is principally influenced by extracellular substances. H+ reduction and the oxidation of Fe2+ can accelerate production of the precipitation. Monovalent cation of the precipitation depends on pH value, especially the type and concentration of monovalent cation in solution. This research thus shows a novel application of A. ferrooxidans.

Evaluation of the effects of cation combinations on soil hydraulic conductivity

Effects of soil solution cation concentrations and ratios on hydraulic properties must be understood in order to model soil water flow in reactive soils or develop guidelines for sustainable land application of wastewater. We examined effects of different ratios and concentrations of the cations Ca2+, Mg2+, Na+, and K+, using hydraulic conductivity measurements in repacked soil cores, as an indicator of soil structural stability. We examined widely used indices—sodium, potassium, and monovalent cation absorption ratios (SAR, PAR, MCAR)—which assume that the flocculating effects of Ca2+ and Mg2+ are the same, and the dispersive effects of Na+ and K+ are the same. Our laboratory measurements indicate that at any given values of MCAR, the reductions in soil hydraulic conductivity with decrease in electrolyte concentration are not identical for different cation combinations in solution. The hydraulic conductivity curves showed a marked lateral shifting for both the surface and subsurface soils from a winery wastewater application site. This indicates that MCAR is inadequate as a soil stability parameter in soil solutions containing a mixture of Na+, K+, Ca2+, and Mg2+. We employed an unpublished equation that was proposed by P. Rengasamy as a modified index of soil stability for mixed cation combinations, using calculated relative flocculating powers of different cations (‘CROSS’, cation ratio of structural stability). Our observation of lateral shift in hydraulic conductivity measurements at any value of MCAR appears to relate to changes in CROSS values for all cation combinations tested, except for K–Mg solutions, for which a more generalised CROSS equation with modified parameters seems more suitable for calculating the CROSS value. Appropriate modified parameters for use in this generalised CROSS equation were determined empirically, using the experimental data. We derived a combination of threshold electrolyte concentration and CROSS values required to maintain high hydraulic conductivity for the soils at a winery wastewater application site. The potential use of this relationship in developing management practices for sustainable wastewater management at the site is discussed. Further research on the applicability of CROSS and generalised CROSS equations for other soils in the presence of different mixed cation combinations is needed.

Solvatochromism and Halochromism of N-(4-Oxyphenyl) 5-nitro-2-thiophenecarboxaldimine

ABSTRACT The solvatochromic behavior of the title phenolate 1 was described and interpreted by means of theoretical calculations employing the PCM model and a TD-DFT method. The cationic halochromism of 1 was studied in DMSO and in ethanol solutions of LiClO4 and interpreted by a simple model that reproduced the variation of the charge-transfer transition energy of 1 with the cation concentration in solution.

Impedance analysis of gramicidin D in pore-suspending membranes

Porous alumina substrates with a pore diameter of 60 nm were functionalized with cholesterylpolyethylenoxy thiol (CPEO3) chemisorbed on gold, which is a prerequisite for the formation of pore-suspending membranes obtained from spreading of large unilamellar vesicles with a mean diameter of 730 nm. By means of vesicle fusion, a large number of gramicidin D ion channels, selective for monovalent cations, was successfully reconstituted into these pore-suspending membranes as probed by impedance spectroscopy. An electrical equivalent circuit was developed to fully describe the electrical properties of the gramicidin D-doped membrane system, which allowed us not only to extract the membrane resistance but also the mass transport in bulk solution as a function of the monovalent cation concentration in solution. Blocking of channel activity was demonstrated by the addition of Ca2+ ions verifying the reconstitution of fully functional peptides.

Aqueous polymer–nitrate solution deposition of YBCO films

High critical current density YBa 2Cu 3O 7− x (YBCO) films were prepared by solution deposition of aqueous non-fluorine precursors. Non-fluorine polymer-assisted deposition (PAD) processes utilizing rheology modifiers and chelating agents were used to produce 50 nm films with a critical current density ( J c) over 3 MA/cm 2 and 400 nm films with J c > 1 MA/cm 2 . T c measurements indicated that films have T c values near 90 K. The total heat treatment time to produce these high performance films was less than 4 h. Rheology modifiers such as polyvinyl alcohol (PVA) and hydroxyethyl cellulose (HEC) were used to increase the thickness of deposited films independent of the solution cation concentration. Chelating agents such as polyethylene glycol (PEG) and sucrose increased the barium ion solubility. Nitrate crystallization during deposition was controlled through rapid drying with vacuum and coating with hot solutions.

Modelling exchange kinetics of copper at the water-aquatic moss ( Fontinalis antipyretica) interface: Influence of water cationic composition (Ca, Mg, Na and pH)

The present study investigated the effect of water cationic composition (Ca, Mg, Na, pH) on the bioaccumulation and elimination rates of copper by an aquatic moss ( Fontinalis antipyretica), under laboratory conditions. For this purpose, mosses were exposed to copper at an environmentally relevant and usually non-toxic concentration (5 μg L −1) in natural waters where cationic composition and concentrations were varied. To describe copper bioaccumulation by aquatic mosses, a two-compartment model was the first-order kinetics, was developed and calibrated under a wide range of water cationic composition. Bioaccumulation rates of Cu in mosses were significantly reduced as the concentrations of competitive cations in solution increased. Hence, in hard-water, Ca and Mg cations play a protective role as they compete with Cu 2+ ions for the absorption on transport sites at the organism–water interface. Based on the relationships between each major cation concentration and the exchange kinetics on mosses, the binding constants ( K C i BL ) of each competing cations to the biological surfaces were derived. Using the present cationic-dependant kinetic model, it is now feasible to incorporate water cationic composition in the (re)interpretation of bryophytes contamination levels and in the (re)definition of Water Quality Criteria (WQC) as illustrated through two selected examples of biomonitoring programmes. In the framework of future national water quality guidelines revisions, a such flexible and mechanistic biomonitoring tool (integrating the protective effects of competing cations) may greatly improve the ability of regulators to derive site-specific Cu (metal) guidelines for protecting aquatic biota, while limiting the use of conservative assumptions.

Cartilage stress–relaxation is affected by both the charge concentration and valence of solution cations

Understanding the mechanical functions of specific cartilage molecules such as aggrecan is important for understanding both healthy cartilage and disease progression. Cartilage is primarily composed of chondrocytes and an extracellular matrix consisting of multiple biopolymers, ions, and water. Aggrecan is one matrix biopolymer which consists of a core protein and multiple anionic glycosaminoglycans. Previous research has demonstrated that the stiffness of extracted aggrecan decreases under increased solution cation concentration, and the purpose of this study was to determine whether changes in solution ion concentration resulted in changes in tissue-level viscoelastic properties. Middle-zone explants of bovine calf patellofemoral cartilage were harvested and cultured overnight before mechanical testing. Repeated stress-relaxation and cyclical loading tests were performed after equilibration in solutions of 0.15 M and 1 M NaCl and 0.075 M and 0.5 M CaCl(2). A stretched exponential model was fit to the stress-relaxation data. Storage and loss moduli were determined from the cyclical loading data. Changes in ionic strength and species affected both stress-relaxation and cyclical loading of cartilage. Stress-relaxation was faster under higher ionic strength. CaCl(2) concentration increases resulted in decreased peak stress, while NaCl increases resulted in decreased equilibrium stress. Storage and loss moduli were affected differently by NaCl and CaCl(2). These results show that cartilage stress-relaxation proceeds faster under higher concentrations of solution cations, consistent with the theory of polymer dynamics. These data demonstrate the complexity of cartilage mechanical properties and suggest that aggrecan stiffness may be important in tissue-level cartilage viscoelastic properties.

Soil amendments modify phosphate sorption in an acid soil: the importance of P source (KH2PO4, TSP, DAP)

Soil acidity is a widespread problem in Victoria, Australia, affecting at least 4 million ha of agricultural land. Soil amendments such as lime and organic materials may ameliorate acid soils, resulting in raised soil pH and increased availability of plant nutrients such as phosphorus (P). The addition of lime, lignite, and compost significantly modified P sorption in an acid soil, with the degree of change highly dependent upon the source of P applied. The application of 2.5 t/ha of lime increased P sorption for all P sources, while P sorption was decreased in the lignite and compost treatments when di-ammonium phosphate (DAP) was applied. Lime and compost addition increased the solution pH, with no change in pH in the lignite treatment. Addition of TSP decreased the pH in all treatments, while DAP addition only increased solution pH in the untreated soil and the lignite treatment. The addition of soil amendments had a significant effect on solution cation concentrations, due to both the influx of cations, and the resultant changes in solution pH. The source of P applied (KH2PO4, TSP (triple superphosphate), DAP) also had a significant effect due to both the counter-ions present and the pH of each P source (e.g. TSP pH 2.7; DAP pH 7.4). The lignite treatment decreased total P sorption relative to the other amendments. The combination of lignite and DAP resulted in both the greatest decrease in P sorption, and the formation of soluble Al–organic complexes. Therefore, a combination of lignite and DAP may be of use in decreasing P sorption in acid soils.

Evaluating the removal of Cd(II), Pb(II) and Cu(II) from a wastewater sample of a coating industry by adsorption onto vermiculite

This work presents an evaluation of vermiculite as a low cost adsorbent for treatment of wastewater from a coatings industry containing Cd(II), Pb(II) and Cu(II). Determination of metal cation concentrations in solution was made by continuous flow anodic stripping voltammetry. Adsorption data was fitted by Freundlich isotherms, as well as by partition constants at pH 4, 5 and 6. In this pH range, a 180 min interaction time was long enough to allow the system to reach apparent equilibrium. It is possible to state that non-expanded vermiculite presents the following affinity orders by the studied ions: pH 4: Cu(II) < Cd(II) < Pb(II); pH 5: Cu(II) ≅ Cd(II) < Pb(II); pH 6: Cd(II) < Cu(II) < Pb(II). For Pb(II) and Cd(II), the adsorption percentages determined in real wastewaters were around 20% lower than the removal percentage previewed by the Freundlich parameters, a fact that may be explained by competition of the studied cations among themselves, and with Fe(III) species, which were present in the water at concentration levels similar to Cd(II), Cu(II) and Pb(II). Additionally, the high content of organic compounds in the wastewater may have decreased the adsorption of Cu(II) and Pb(II) because of possible formation of soluble complexes between the heavy metal cations and the organic compounds. On the other hand, adsorption of Cd(II) from the real wastewater was about 20% higher than previewed by the Freundlich parameters, denoting the complexity of interactions that ions are liable in matrices of wastewaters.

Estudio cinético de la eliminación de Cu (II) de soluciones acuosas mediante cascarilla de laminación

The removal of Cu (II) from aqueous solutions by rolling mill scale occurs through a process of oxidation-reduction or cementation of Cu 2+ ions in aqueous solution onto metallic iron (Fe 0 ) contained in the mill scale. The kinectics of cementation of copper onto iron was evaluated over different temperatures, initial copper concentrations and solid/liquid relations. Process of copper removal by rolling mill scale obeys a first-order kinetic law. The rate constant value (k) varies with temperature and initial cation concentration in solution at low temperatures. At high temperatures the value of k remains practically constant. The solid/liquid relation value affects the rate constant value too.

Heterogeneous reduction of uranyl by micas: Crystal chemical and solution controls 1

This contribution primarily uses X-ray photoelectron spectroscopy (XPS) to better understand mechanisms for coupled sorption-reduction of aqueous U VI by ferrous micas. Additional information was obtained with X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM). The research is important because homogeneous reduction of aqueous U VI is sluggish compared to heterogeneous reduction pathways, and micas are important sorbents for uranium in granitic terrains, which have been proposed as potential radionuclide waste disposal sites. Three micas (high, medium and low Fe/Mg biotites), prepared as thin centimeter-sized books, were reacted with U VI solutions that contained 0–25 mM Na + or K + , at pH = 4.5, 5.0, 6.0, and 9.5. All the experiments were performed under argon at one bar. Solid samples were retrieved at timed intervals for up to 20 h. Both mica edge and basal plane orientations were analyzed by XPS. Analyses of peak positions, core satellites, and the 5f valence band indicate that U VI can be reduced by biotite and that heterogeneous reduction depends on the type and concentration of alkali cation in solution, crystallography, and mica composition. We conclude that ferrous micas can reduce U VI on edge sites, but not on exposed basal plane surfaces, and that Na + and K + facilitate and hinder the reaction, respectively. These observations pertain over a broad range of pH. X-Ray absorption near edge spectroscopy (XANES) of annite sections indicates that the interlayer region, as opposed to external basal surfaces, also offers possible sites for heterogeneous reduction of U VI . TEM of annites with high uranium coverage confirmed the presence of interlayer uranium; interestingly, this uranium is concentrated in U-rich nano-scale zones.