Cr(VI) removal from aqueous solution by activated carbon coated with quaternized poly(4-vinylpyridine)

A composite sorbent (GAC-QPVP) was prepared by coating poly(4-vinylpyridine) onto a granular activated carbon, followed by cross-linking and quaternization processes. The sorbent was characterized by scanning electron microscopy, point of zero charge measurement, and BET analysis. Batch experiments with variable pH, ionic strength, and concentrations of Cr(VI), sorbent, and competing anions were conducted to evaluate the selective sorption of Cr(VI) from aqueous solutions. The results showed that Cr(VI) sorption rates could be described by a reversible second-order kinetics, and equilibrium uptake of Cr(VI) increased with decreasing pH, decreasing ionic strength, and increasing sorbent concentration. The estimated maximum equilibrium uptake of chromium was 53.7 mg/g at pH = 2.25, 30.7 mg/g at pH = 3.65, and 18.9 mg/g at pH = 6.03, much higher than the maximum capacity of PVP-coated silica gel, an adsorbent for Cr examined previously. When compared with the untreated granular activated carbon, sorption onto GAC-QPVP resulted in much less Cr(VI) reduction and subsequent release of Cr(III). The effect of phosphate, sulfate, and nitrate was minor on the selective sorption of Cr(VI). An ion exchange model that was linked with aqueous speciation chemistry described Cr(VI) sorption reasonably well as a function of pH, ionic strength, and Cr(VI) concentration. Model simulations suggested that sorbed Cr(VI) was partially reduced to Cr(III) on the sorbent when pH was less than 4. The presence of Cr(III) on the sorbent was confirmed by the X-ray photoelectron spectroscopic analysis. Overall, the study has demonstrated that GAC-QPVP can effectively remove Cr(VI) from aqueous solutions under a wide range of experimental conditions, without significant Cr(III) release associated with the virgin GAC treatment.     

Effects of Fe(III) chemical speciation on dissimilatory Fe(III) reduction by Shewanella putrefaciens

Shewanella putrefaciens, a heterotrophic member of the gamma-proteobacteria is capable of respiring anaerobically on Fe(III) as the sole terminal electron acceptor (TEA). Recent genetic and biochemical studies have indicated that anaerobic Fe(III) respiration by S. putrefaciens requires outer-membrane targeted secretion of respiration-linked Fe(III) reductases. Thus, the availability of Fe(III) to S. putrefaciens may be governed by equilibrium chemical speciation both in the solution phase and at the bacterial cell-aqueous or cell-mineral interface. In the present study, effects of Fe(III) speciation on rates of bacterial Fe(III) reduction have been systematically examined by cultivating S. putrefaciens anaerobically on a suite of Fe(III)-organic complexes as the sole TEA. The suite of Fe(III)-organic complexes spans the range of stability constants normally encountered in natural water systems and includes Fe(III) complexed to citrate, 5-sulfosalicylate, NTA, salicylate, tiron, and EDTA. Rates of bacterial Fe(III) reduction in the presence of dissolved chelating agents correlate with the thermodynamic stability constants of the Fe(III)-organic complexes, implying that chemical speciation governs Fe(III) bioavailability. Equilibrium Fe(III) sorption experiments measured the reversible coordination of Fe(III) with S. putrefaciens as a function of cell/Fe(III) concentration, time, and activity of competing chelating agents. Results show that S. putrefaciens readily sorbs dissolved Fe(III) but that adsorption is restricted by the presence of strong Fe(III)-chelating agents. Our results indicate that dissimilatory Fe(III) reduction by S. putrefaciens is controlled by equilibrium competition for Fe(III) between dissolved organic ligands and strongly sorbing functional groups on the cell surface.     

Bioreduction of selenate using a hydrogen-based membrane biofilm reactor

A H2-based, denitrifying and sulfate-reducing membrane-biofilm reactor (MBfR) was shown to be effective for removing selenate (Se(VI)) from water or wastewater by reducing it to insoluble Se(0). When Se(VI) was first added to the MBfR, Se(VI) reduction--first to selenite (Se(IV)) and then mostly to Se(0)--took place immediately and then increased over three weeks, suggesting enrichment for dissimilatory selenium-reducing bacteria. Increasing the H2 pressure improved the Se(VI) reduction rate and total-Se removal, and lowering the influent Se(VI) concentration from 1000 to 260 microg Se/L increased the average Se removal to 94%, which corresponded to an effluent Se concentration of less than 12 microg Se/L, a value well below the standard of 50 microg Se/L. The fact that the effluent suspended solids contained reduced Se suggests that Se(0) was retained in the biofilm, which detached to form the effluent suspended solids. A series of short-term experiments elaborated on how decreased influent selenate loading and increased H2 pressure could systematically improve the reduction of Se(VI) and removal of total Se. Short-term experiments also demonstrated that selenate reduction improved with lower influent nitrate concentration, suggesting that H2 was more available for selenate reduction when the H2 demand for denitrification was smaller. Complete sulfate reduction, which occurred in parallel to nitrate reduction, dominated the electron-equivalent flux. Like selenate reduction, but unlike nitrate reduction, sulfate reduction was sensitive to H2 pressure and appeared to be inhibited by selenate. Finally, selenate reduction was relatively insensitive to pH in the range of 7.0 to 9.0. This research shows that the MBfR can be effective for removing Se(VI) in water or wastewater to below the 50 microg Se/L standard.     

Combined speciation analysis by X-ray absorption near-edge structure spectroscopy, ion chromatography, and solid-phase microextraction gas chromatography-mass spectrometry to evaluate biotreatment of concentrated selenium wastewaters

In this study we evaluate the potential of anaerobic granular sludge as an inoculum for the bioremediation of selenium-contaminated waters using species-specific analytical methods. Solid species formed by microbial reduction were investigated using X-ray absorption near-edge structure (XANES) spectroscopy at the selenium K-edge. Furthermore, dissolved selenium species were specifically determined by ion chromatography (IC) and solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS). Least-squares linear combination of the XANES spectra for samples incubated with the highest selenate/selenite concentrations (10(-3) M) show the predominance of elemental selenium and a Se(-I) selenide, such as ferroselite, the thermodynamically most stable iron selenide. In contrast, elemental selenium and Se(-II) selenides are the main species detected at the lower selenate/selenite concentrations. In each repeated fed batch incubation, most aqueous selenite anions were converted into solid selenium species, regardless of the type of electron donor used (acetate or H(2)/CO(2)) and the selenium concentration applied. On the other hand, at higher concentrations of selenate (10(-4) and 10(-3) M), significant amounts of the oxyanion remained unconverted after consecutive incubations. SPME-GC-MS demonstrated selenium alkylation with both electron donors investigated, as dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe). Selenite was even more alkylated in the presence of H(2)/CO(2) (maximum 2156 μg of Se/L of DMSe + DMDSe) as compared to acetate (maximum 50 μg of Se/L). In contrast, selenate was less alkylated using both electron donors (maximum 166 and 3 μg of Se/L, respectively). The high alkylation potential for selenite limits its bioremediation in selenium laden waters involving H(2)/CO(2) as the electron donor despite the fact that nontoxic elemental selenium and thermodynamically stable metal selenide species are formed.     

Lead sorption onto ferrihydrite. 1. A macroscopic and spectroscopic assessment

In this research, traditional macroscopic studies were complemented with XAS analyses to elucidate the mechanisms controlling Pb(II) sorption onto ferrihydrite as a function of pH, ionic strength, and adsorbate concentrations. Analyses of XANES and XAFS studies demonstrate that Pb(II) ions predominantly sorb onto ferrihydrite via inner-sphere complexation, not retaining their primary hydration shell upon sorption. At higher pH values (pH > or = 5.0), edge-sharing bidentate complexes are mainly formed on the oxide surface with two Fe atoms located at approximately 3.34 A. In contrast, XAS studies on Pb(II) sorption onto ferrihydrite, at pH 4.5, reveal two distinct Pb-Fe bond average radial distances of 3.34 and 3.89 A, suggestive of a mixture of monodentate and bidentate sorption complexes present at the oxide surface. Interestingly, at constant pH, the configuration of the sorption complex is independent of the adsorbate concentration. Hence, Pb(II) sorption to a highly disordered adsorbent such as ferrihydrite can be described by one average type of mechanism. Overall, this information will aid scientists and engineers in improving the current models that predict and manage the fate of toxic metals, such as Pb(II), in the aquatic and soil environments.     

Immobilization of selenite on Fe3O4 and Fe/Fe3C ultrasmall particles

The sorption of selenite ions onto Fe3O4 and Fe/Fe3C nanoparticles (NPs) was studied in aqueous solutions under anoxic conditions using gamma spectrometry and X-ray absorption spectrometry (XAS) techniques. This is the first study related to the remedial applications of Fe/Fe3C NPs. FesO4 NPs have been prepared by conventional coprecipitation of Fe(II) and Fe(III) in basic solutions. Stable Fe/Fe3C NPs have been prepared by Fe(CO)5 sonicating in diphenylmethane solutions and subsequently annealing the as-prepared product. Kinetic study demonstrated that Se(IV) sorption is extremely rapid: the equilibrium is reached in approximately 10 and 30 min for Fe3O4 and Fe/Fe3C NPs, respectively, at pH = 4.9-5.1 in solutions of 0.1 M NaCl. The distribution coefficients are also very high for both kinds of NPs (Kd > 3000). Increasing the pH to 10.3 or adsorption of organic ligands, like L-lysine or dodecanoate, at the surface of NPs causes the decrease in Kd values. However, even in these cases Kd values exceed 150. Magnetic NPs loaded with selenium can be easily and completely removed from solution with a 0.4 T permanent magnet. XAS study revealed the absence of Se(IV) reduction during the sorption onto Fe3O4 NPs in the pH range of 4.8-8.0. By contrast, the removal of Se(IV) with Fe/Fe3C NPs in anaerobic conditions occurs via Se(IV) reduction to Se(-II) and subsequent formation of iron selenide at the particle surface. Thus, the Fe/Fe3C NPs are superior to Fe3O4 NPs due to their ability to immobilize rapidly and irreversibly Se(IV) via reductive mechanism. Presumably these particles could be also effective for the removal of other contaminants such as hexavalent chromium, actinides, technetium, and toxic organic compounds.     

Np(V) and Pu(v) ion exchange and surface-mediated reduction mechanisms on montmorillonite

Due to their ubiquity and chemical reactivity, aluminosilicate clays play an important role in actinide retardation and colloid-facilitated transport in the environment. In this work, Pu(V) and Np(V) sorption to Na-montmorillonite was examined as a function of ionic strength, pH, and time. Np(V) sorption equilibrium was reached within 2 h. Sorption was relatively weak and showed a pH and ionic strength dependence. An approximate NpO(2)(+) → Na(+) Vanselow ion exchange coefficient (Kv) was determined on the basis of Np(V) sorption in 0.01 and 1.0 M NaCl solutions at pH < 5 (Kv ~ 0.3). In contrast to Np(V), Pu(V) sorption equilibrium was not achieved on the time-scale of weeks. Pu(V) sorption was much stronger than Np(V), and sorption rates exhibited both a pH and ionic strength dependence. Differences in Np(V) and Pu(V) sorption behavior are indicative of surface-mediated transformation of Pu(V) to Pu(IV) which has been reported for a number of redox-active and redox-inactive minerals. A model of the pH and ionic strength dependence of Pu(V) sorption rates suggests that H(+) exchangeable cations facilitate Pu(V) reduction. While surface complexation may play a dominant role in Pu sorption and colloid-facilitated transport under alkaline conditions, results from this study suggest that Pu(V) ion exchange and surface-mediated reduction to Pu(IV) can immobilize Pu or enhance its colloid-facilitated transport in the environment at neutral to mildly acidic pHs.     

Adsorption of alkylimidazolium and alkylpyridinium ionic liquids onto natural soils

The mechanism of ionic liquid sorption onto selected natural soils differing in their organic content, cation exchange capacity, and particle size distribution was investigated in detail. Isotherms were employed to describe sorption. In most cases,the maximum achievable surface concentrations were well above CEC values. This observation may indicate that initially sorbed solutes modify the sorbent, a process favoring further sorption. The experimental data suggest that if a multilayer process occurs, such a mechanism will be applicable to all ionic liquids; but saturation of the second layer occurred only with the longest alkyl chain compound. The shorter alkyl chain cations did not reach saturation in the concentration range investigated here. The influence of the varying pH and ionic strength of an aquifer on sorption strength was also determined.     

X-ray absorption spectroscopy study of the effects of pH and ionic strength on Pb(II) sorption to amorphous silica

Pb(III) sorption to hydrous amorphous SiO2 was studied as a function of pH and ionic strength using XAS to characterize the sorption products formed. Pb sorption increased with increasing pH and decreasing ionic strength. The XAS data indicated that the mechanism of Pb(II) sorption to the SiO2 surface was pH-dependent. At pH < 4.5, a mononuclear inner-sphere Pb sorption complex with ionic character dominated the Pb surface speciation. Between pH 4.5 and pH 5.6, sorption increasingly occurred via the formation of surface-attached covalent polynuclear Pb species, possibly Pb-Pb dimers, and these were the dominant Pb complexes at pH > or = 6.3. Decreasing ionic strength from I = 0.1 to I = 0.005 M NaClO4 significantly increased Pb sorption but did not strongly influence the average local coordination environment of sorbed Pb at given pH, suggesting that the formation of mononuclear and polynuclear Pb complexes at the surface were coupled; possibly, Pb monomers control the formation of Pb polynuclear species by diffusion along the surface, or they act as nucleation centers for additional Pb uptake from solution. This study shows that the effectiveness of SiO2 in retaining Pb(II) is strongly dependent on solution conditions. At low pH, Pb(II) may be effectively remobilized by competition with other cations, whereas sorbed Pb is expected to become less susceptible to desorption with increasing pH. However, unlike for Ni(II) and Co(II), no lead phyllosilicates are formed at these higher pH values; therefore, SiO2 is expected to be a less effective sink for Pb immobilization than for these other metals.     

Lead sorpion onto ferrihydrite. 2. Surface complexation modeling

Few studies have combined molecular- and macroscopic-scale investigations with surface complexation model (SCM) development to predict trace metal speciation and partitioning in aqueous systems over a broad range of conditions. In this work, an extensive collection of new macroscopic and spectroscopic data was used to assess the ability of the modified triple-layer model (TLM) to predict single-solute lead(II [Pb(II)] sorption onto 2-line ferrihydrite in NaNO3 solutions as a function of pH, ionic strength, and concentration. Regression of constant-pH isotherm data together with potentiometric titration and pH edge data was a much more rigorous test of the TLM than fitting pH edge data alone. When combined with spectroscopic data, the choices of feasible surface species/site types were limited to a few. In agreement with the spectroscopic data, very good fits of the isotherm data were obtained with a two-species, one-site model using the bidentate-mononuclear/monodentate-mononuclear species pairs, ((is equivalent)FeO)2Pb/(is equivalent)FeOHPb2+ and ((is equivalent)FeO)2Pb/ (is equivalent)FeOPb+-NO3-. Regressing edge data in the absence of isotherm and spectroscopic data resulted in a fair number of surface-species/site-type combinations that provided acceptable fits of the edge data but unacceptable fits of the isotherm data. Surprisingly, best-fit equilibrium "constants" for the Pb(II) surface complexes required adjustment outside the pH range of 4.5-5.5 in order to fit the isotherm data. In addition, a surface activity term was needed to reduce the ionic strength dependence of sorption forthe species pair, ((is equivalent)FeO)2Pb/(is equivalent)FeOHPb2+. In light of this, the ability of existing SCMs to predict Pb(II) sorption onto 2-line ferrihydrite over a wide range of conditions seems questionable. While many advances have been made over the past decade, much work still needs to be done in fine-tuning the thermodynamic framework and databases for the SCMs.     

疏水淀粉皮克林乳液凝胶的稳定机理及影响因素

研究不同因素（温度、pH值和离子强度）对淀粉-脂质复合物（starch-fatty acid complex,SFAC）稳定的皮克林乳液凝胶的影响规律并揭示其稳定机理。激光共聚焦扫描显微镜和扫描电子显微镜结果显示,SFAC颗粒通过吸附于油水界面,形成一层紧密的屏障包裹油滴,形成呈圆状的乳滴,乳滴之间紧密堆积形成稳定的乳液凝胶网络结构。光学显微镜、粒径分布及Zeta电位等结果显示该疏水淀粉皮克林乳液凝胶在pH 3～9范围内以及离子浓度0.1～0.9 mol/L条件下都能维持乳液凝胶结构并具有良好的贮藏稳定性。此外,该皮克林乳液凝胶具有热可逆性,在高温下粒径增大、黏度下降,出现流动性,冷却后可重新呈现凝胶状。研究结果表明疏水淀粉皮克林乳液凝胶在较宽的温度、pH值和离子强度范围内均有较高稳定性,适用于多种植物油的稳定。     

Experimental study of the adsorption of an ionic liquid onto bacterial and mineral surfaces

Ionic liquids are being developed as a replacement for volatile organic solvents in a range of industrial applications. These liquids have a vanishingly small vapor pressure, making them an attractive alternative to the volatile organic solvents. However, a thorough assessment of the environmental impact of the use of ionic liquids requires a more complete understanding of their fate and transport in environmental systems. Toward this end, we measured the adsorption of the ionic liquid 1-butyl, 3-methylimidazolium chloride (Bmim CI) onto a range of surfaces meant to represent those commonly found in the near-surface environment. We measured adsorption onto the Gram-positive soil bacterial species Bacillus subtilis, onto gibbsite, onto quartz, and onto Na-montmorillonite. We conducted experiments as a function of pH, solid:solute ratio, time, and ionic strength. The experimental results reveal that Bmim CI is unstable in water below pH 6 and above pH 10 and that it exhibits pH independent and ionic strength dependent adsorption onto Na-montmorillonite with 0.4, 0.8, 1.0, 1.2, and 2.0 g/L of clay. We observed no adsorption of the Bmim CI onto B. subtilis (3.95 or 7.91 g (dry weight) bacteria/L) at pH 5.5-8.5 or onto gibbsite (500 or 1285 g/L) or quartz (1000 and 2000 g/L) over the pH range 6-10. Calculated distribution coefficient (KD) values for Bmim CI onto the Na-montmorillonite change as a function of ionic strength; the 10(-4) M ionic strength KD value is 1735 +/- 269 L/Kg, and the 10(-1) M ionic strength KD is 1133 +/- 291 L/Kg. Our results suggest that the geologic retardation of this class of ionic liquid, if present as a dissolved contaminant in the subsurface, would be significant when a significant fraction of interlayer clays are present. However, adsorption onto other common geologic and biological surfaces is likely to be minimal, and the ionic liquids may travel unimpeded in groundwater systems in which these types of surfaces dominate.     

Surface complexation modeling of U(VI) sorption to Hanford sediment with varying geochemical conditions

A series of U(VI) sorption experiments with varying pH, ionic strength, concentrations of dissolved U(VI), and alkalinity was conducted to provide a more realistic database for U(VI) sorption onto near-field vadose zone sediments at the proposed Integrated Disposal Facility (IDF) on the Hanford Site, Washington. The distribution coefficient (Kd) for U(VI) in a leachate that is predicted to result from the weathering of vitrified wastes disposed in the IDF is 0 mL/g due to the high sodium and carbonate concentrations and high pH of the glass leachate. However, when the pH and alkalinity of the IDF sediment native pore water increases during mixing with the glass leachate, U(VI) uptake is observed and the value of the U(VI) Kd increases 4.3 mL/g, because of U(VI) coprecipitation with newly formed calcite. A nonelectrostatic, generalized composite approach for surface complexation modeling was applied and a combination of two U(VI) surface species, monodentate (SOUO2+), and bidentate (SO2UO2(CO3)2-), simulated the measured U(VI) sorption data very well. The generalized composite surface complexation model, when compared to the constant or single-valued Kd model, more accurately predicted U(VI) sorption under the varying geochemical conditions expected at the IDF.     

Sorption of selenite and selenate to cement minerals

The sorption of selenite and selenate to ettringite (3CaO x Al2O3 x 3CaSO4 x 32H2O), "monosulfate" (3CaO x Al2O3 x CaSO4 x 12H2O), and calcium silicate hydrate (C-S-H) was investigated in order to understand Se immobilization by cement in hazardous wastes. Sorption kinetics were fast with equilibrium between the minerals and Se species reached within 1 d. Selenite is suggested to sorb by surface reactions, and for ettringite, a sorption maximum of 0.03 mol kg(-1) was determined. Distribution ratios (Rd) for selenite were 0.18, 0.38, and 0.21 m3 kg(-1) for ettringite, monosulfate, and C-S-H, respectively. At high selenite additions, CaSeO3 was precipitated with a solubility product of Kso = 10(-7.27) (I = 0, 25 degrees C). Selenate sorbed only weakly to ettringite (Rd = 0.03), and no significant sorption to C-S-H was found. In contrast, sorption to monosulfate was strong (Rd = 2.06). With increasing selenate addition, XRD analyses revealed changes in the interlayer distance of monosulfate, in parallel with an increase of the ettringite fraction. Substitution of sulfate is suggested to be the relevant process. This indicates that selenate is sorbed more efficiently by monosulfate-rich cement, while the cement composition is of minor importance for selenite sorption.     

The effect of heat treatment on intrinsic and fortified selenium levels in cow's milk

The effects of two heat processing methods (pasteurisation and spray drying) routinely used in the processing of cow's milk and the production of infant formula powder on the selenium (Se) content of liquid milk, milk fortified with sodium selenite and sodium selenate were studied. Pasteurisation reduced intrinsic Se and selenate levels by 7.9% and 6.2% at p < 0.05 level and selenite levels by 7.0% at p > 0.05 level. Se losses following spray drying were 44.8% (p < 0.001), 11.4% (p < 0.01) and 10.0% (p < 0.01) for intrinsic selenium, selenite and selenate fortified milk, respectively. Total Se losses from unprocessed milk following processing (pasteurisation and spray drying) were 49.2% (p < 0.001), 17.6% (p < 0.001) and 15.6% (p < 0.001) for intrinsic selenium, selenite and selenate fortified milk, respectively.     

Modeling of single and competitive metal adsorption onto a natural polysaccharide

Sugar beet pulp, a common agricultural waste, was studied in the removal of metal ions from aqueous solutions. Potentiometric titrations were used to characterize the surface acidity of the polysaccharide. The acid properties of the material can be described by invoking three distinct types of surface functional groups with the intrinsic acidity constants (pKa(int)) values 3.43+/-0.1, 6.05+/-0.05, and 7.89+/-0.1, respectively. The contents of each functional group (i.e., the carboxyl and phenol moieties) were also determined. Then, a simple surface complexation model with the diffuse layer model successfully described the sorption of several metal ions (Cu2+, Zn2+, Cd2+, and Ni2+) onto the polysaccharide under various experimental conditions: pH ranging from 2 to 5.5, ionic strength from 0.01 to 0.1 M, metal concentration between 10(-4) and 10(-3) M, for a constant sorbent concentration equal to 2.5 g x L(-1). It was observed experimentally that the affinity of the polysaccharide was in the sequence of Cu2+ > Zn2+ > Cd2+ > Ni2+. Predictions of sorption in binary-metal systems based on single-metal data fits represented competitive sorption data reasonably well.     

Modeling tetracycline antibiotic sorption to clays

Sorption interactions of three high-use tetracycline antibiotics (oxytetracycline, chlortetracycline, tetracycline) with montmorillonite and kaolinite clays were investigated undervaried pH and ionic strength conditions. Sorption edges were best described with a model that included cation exchange plus surface complexation of zwitterion forms of these compounds. Zwitterion sorption was accompanied by proton uptake, was more favorable on acidic clay, and was relatively insensitive to ionic strength effects. Calcium salts promoted oxytetracycline sorption at alkaline pHs likely by a surface-bridging mechanism. Substituent effects among the compounds in the tetracycline class had only minor effects on sorption edges and isotherms under the same solution pH and ionic strength conditions. At low ionic strength, greater sorption to montmorillonite than kaolinite was observed at all pHs tested, even after normalizing for cation exchange capacity. These results indicate that soil and sediment sorption models for tetracyclines, and other pharmaceuticals with similar chemistry, must account for solution speciation and the presence of other competitor ions in soil or sediment pore waters.     

Effect of selenium source on selenium status, neutrophil function, and response to intramammary endotoxin challenge of dairy cows

The effects of feeding dry and early lactation dairy cows diets with selenate or selenized yeast (Se-yeast) on concentrations of Se in serum, milk, and newborn calves, neutrophil function, and inflammatory response were determined. At 60 d before anticipated calving until approximately 30 d in milk (DIM), cows were fed diets that contained 0.3 mg of supplemental Se/kg of DM from sodium selenate or Se-yeast. Diets also contained 0.2% supplemental S (as sulfate) because it has been shown to reduce absorption of Se by dairy cows. The concentration of Se in serum at calving and 28 DIM was about 1.4 times greater for cows fed Se-yeast than for those fed selenate. Serum concentrations decreased 45 and 23% from dry-off to calving for cows fed selenate or Se-yeast, respectively. Selenium concentrations in serum from newborn calves were also about 1.4 times greater when the dams were fed Se-yeast. Concentrations of Se in colostrum and milk were about 1.8 times greater when cows were fed Se-yeast. Blood neutrophils were isolated from cows at 28 DIM and were used in an in vitro kill assay. Selenium treatment did not affect bacterial kill or the percentage of neutrophils that phagocytized bacteria. At approximately 28 DIM, one quarter from each cow was infused with a solution containing endotoxin. Peak body temperature (40.7°C) occurred 6 h postinfusion, and peak somatic cell count (6.5 log₁₀/mL) occurred at 12 h postinfusion. Neither measure was influenced by Se treatment.     

Sorption of basic dyes onto iron humate

Iron humate (IH) was examined as a new low-cost sorbent for removing basic dyes (Methylene Blue, Methyl Violet, Crystal Violet, Malachite Green, and Rhodamine B) from waters. The sorption of the dyes from aqueous solutions was described by a multisite Langmuir isotherm; the sorption capacities ranging from ca. 0.01 to 0.09 mmol/g were calculated from the parameters of the isotherm for individual dyes. A more detailed study was carried out with Methylene Blue to examine an influence of the composition of aqueous phase on the sorption. pH and the presence of inorganic salts have only minor effects on the sorption. The presence of anionic surfactant (sodium dodecyl sulfate, SDS) increases dramatically the sorption of Methylene Blue. A model describing the sorption of basic (cationic) dyes in the presence of anionic surfactants was proposed; two main mechanisms are considered in this model: the sorption of cationic dyes onto the polar (or cation-exchange) active sites and the sorption of relatively small dye-surfactant aggregates onto the nonpolar part of the sorbent. Experimental dependencies comply well with those predicted from the model. Both in the presence as well as in the absence of SDS, the dye sorption proceeds relatively quickly--most of the dye is sorbed within the first several hours. Leachability of the dye from the loaded sorbent was found to be very low, especially with water as leachant.     

Effect of solid surface composition on the migration of tributyltin in groundwater

Tributyltin (TBT) is the most important organotin compound that has been introduced into aquatic ecosystems. A better understanding of its interactions with solid surfaces is essential to estimate the possibilities of TBT migration through subsurface environments. For this purpose, TBT sorption onto a porous matrix of natural origin, a quartz sand as an aquifer material, was studied at low concentration levels with a monodirectional model of column type allowing sequential investigation of sorption and desorption processes. Different treatments of the solid phase were performed by injecting alkaline solutions, NaOH at pH 10.8 or NaClO-NaCl at pH 11.5, by decreasing the ionic strength or by adding kaolinite to change the surface composition and properties. The removal of iron and aluminum (hydr)oxides from the sand surface did not affect so much the sorption (decrease in 14% as compared to sorption on the raw sand). The original use of X-ray photoelectron spectroscopy to control treatment efficiency and to characterize sand surface modifications permitted to relate TBT sorption onto the aquifer material to quartz, the main component of the sand, and clay minerals (mainly kaolinite) present at trace levels at the sand surface. A first attempt of transport modeling with these two surface sites showed the consistency of our assumption. Moreover, estimation of Langmuir-type constants showed that TBT sorption affinity for the quartz surface (KL = 26.7 L micromol(-1)) was much greater than for kaolinite (KL = 6.3 L micromol(-1)).