Presence Of Other Metals Research Articles

Competitive adsorption of copper(II), cadmium(II), lead(II) and zinc(II) onto basic oxygen furnace slag

Polluted and contaminated water can often contain more than one heavy metal species. It is possible that the behavior of a particular metal species in a solution system will be affected by the presence of other metals. In this study, we have investigated the adsorption of Cd(II), Cu(II), Pb(II), and Zn(II) onto basic oxygen furnace slag (BOF slag) in single- and multi-element solution systems as a function of pH and concentration, in a background solution of 0.01 M NaNO 3. In adsorption edge experiments, the pH was varied from 2.0 to 13.0 with total metal concentration 0.84 mM in the single element system and 0.21 mM each of Cd(II), Cu(II), Pb(II), and Zn(II) in the multi-element system. The value of pH 50 (the pH at which 50% adsorption occurs) was found to follow the sequence Zn > Cu > Pb > Cd in single-element systems, but Pb > Cu > Zn > Cd in the multi-element system. Adsorption isotherms at pH 6.0 in the multi-element systems showed that there is competition among various metals for adsorption sites on BOF slag. The adsorption and potentiometric titrations data for various slag–metal systems were modeled using an extended constant-capacitance surface complexation model that assumed an ion-exchange process below pH 6.5 and the formation of inner-sphere surface complexes at higher pH. Inner-sphere complexation was more dominant for the Cu(II), Pb(II) and Zn(II) systems.

Arsenate-induced expression of a class III chitinase in the dwarf sunflower Helianthus annuus

Dwarf sunflower cultivars of Helianthus annuus were exposed to 30 mg/L As alone and in combination with other toxic metals (30 mg/L each of Cd, Cr, and Ni). Total uptake of metals at the end of a 17-day exposure cycle showed variable sequestration of the metals in roots, leaves, and stems with metal concentrations highest in roots and lowest in leaves. The presence of other metals appeared to have little effect on the uptake of As. Proteins were extracted from leaves of plants exposed to arsenic alone or in combination with other metals and size-fractionated by one-dimensional SDS-polyacrylamide gel electrophoresis. Several polypeptides, with molecular masses ranging from less than 10 to over 45 kDa appeared to be unique in extracts obtained from leaves of plants in response to arsenic stress. One polypeptide was induced strongly. It had an approximate molecular mass of 32 kDa and was recovered from gels and analyzed using LC–MS/MS. It was identified as a class III chitinase, whose gene appeared to be induced at the transcription level when As was present.

Competitive adsorption of Cd, Cu, Hg and Pb by agricultural soils of the Changjiang and Zhujiang deltas in China

Soils can often be contaminated simultaneously by more than one heavy metal. The sorption-desorption behavior of a metal in a soil will be affected by the presence of other metals. Therefore, selective retention and competitive adsorption of the soils to heavy metals can affect their availability and movement through the soils. In this study, the simultaneous competitive adsorption of four heavy metals (Cd, Cu, Hg, and Pb) on ten agricultural soils collected from the Changjiang and Zhujiang deltas, China was assessed. The results showed that the competition affected the behavior of heavy metal cations in such a way that the soils adsorbed less Cd and Hg, and more Pb and Cu with increasing total metal concentrations, regardless of the molar concentration applied. As the applied concentrations increased, Pb and Cu adsorption increased, while Cd and Hg adsorption decreased. The adsorption sequence most found was Pb>Cu>Hg>Cd. The maximum adsorption capacity for the heavy metal cations was calculated, and affected markedly by soil properties. The results suggest that Hg and Cd have higher mobility associated to the lower adsorption and that Pb and Cu present the opposite behavior. Significant correlations were found between the maximum adsorption capacity of the metals and pH value and exchangeable acid, suggesting that soil pH and exchangeable acid were key factors controlling the solubility and mobility of the metals in the agricultural soils.

Exploring multi-metal biosorption by indigenous metal-hyperresistant Enterobacter sp. J1 using experimental design methodologies

A novel experimental design, combining mixture design and response surface methodology (RSM), was developed to investigate the competitive adsorption behavior of lead, copper and cadmium by an indigenous isolate Enterobacter sp. J1 able to tolerate high concentrations of a variety of heavy metals. Using the proposed combinative experimental design, two different experiment designs in a ternary metal biosorption system can be integrated to a succinct experiment and the number of experimental trials was markedly reduced from 38 to 26 by reusing the mutual experimental data. Triangular contour diagrams and triangular three-dimensional surface plots were generated to describe the ternary metal biosorption equilibrium data in mixture design systems. The results show that the preference of metal sorption of Enterobacter sp. J1 decreased in the order of Pb 2+ > Cu 2+ > Cd 2+. The presence of other metals resulted in a competitive effect. The influence of the other two metals in ternary metal biosorption system can be easily determined by comparing the stray distance from the single metal biosorption. The behavior of competitive biosorption was successfully described and predicted using a combined Langmuir–Freundlich model along with new three-dimensional contour-surface plots.

Divalent metal adsorption by the thermophile Anoxybacillus flavithermus in single and multi-metal systems

Recent studies have applied surface complexation models (SCMs) to describe metal adsorption by mesophilic bacteria. However, only one SCM has been developed for metal biosorption by a thermophile and the study was limited to adsorption of Cd. In this study, we quantify adsorption of a variety of metals onto the thermophile Anoxybacillus flavithermus with surface complexation modeling. We conduct both single and multi-metal sorption studies using Cd, Cu, Mn, Ni, Pb, and/or Zn, in order to compare the relative affinities of the metals for the cell surface and investigate if these individual affinities change in the presence of other metals. We also use linear free energy relationships (LFERs) to compare the stability constants for the metal-bacteria surface complexes with a variety of aqueous metal–ligand stability constants, and we compare the metal binding capacity of Cd, Cu, Mn, Pb, Ni, and Zn of A. flavithermus to that of the commonly studied mesophile Bacillus subtilis. We find that the metals exhibit different preferences for the bacterial surface in the order Mn ≈ Ni < Zn < Cd < Pb ≈ Cu. Metal binding is described best by formation of a M–carboxyl complex and either a MOH–carboxyl, M–phosphoryl, or MOH–phosphoryl complex (where M is the metal cation). Stability constants determined from the single metal and multi-metal systems are comparable. It is therefore possible to obtain reasonable stability constants in multi-metal systems. This has the potential to greatly simplify the acquisition of metal-bacteria thermodynamic data. However, stability constants obtained from the single metal systems remain more accurate because the experimental conditions are more ideal. Under our experimental conditions, competition effects are observed for the low affinity metals in the presence of higher affinity metals. The LFER plot using the formation of M–carboxyl and MOH–carboxyl with M–acetate complexes yields linear correlation coefficients (r) of 0.82 and 0.73, respectively. We also observe that A. flavithermus generally adsorbs less metal than B. subtilis at similar metal-to-biomass concentration ratio over the pH range studied.

Functionalized HMS mesoporous silica as solid phase extractant for Pb(II) prior to its determination by flame atomic absorption spectrometry

In this work, a mesoporous silica has been chemically modified with 5-mercapto-1-methyl-1-H-tetrazol using the homogeneous route (MTTZ-HMS). This synthetic route involved the reaction of 5-mercapto-1-methyl-1-H-tetrazol with 3-chloropropyltriethoxysilane, prior to immobilization on the support. The resulting material has been characterized and employed as solid phase extractant for Pb(II). The effect of several variables (stirring time, pH, temperature, metal concentration, presence of other metals) has been studied using batch and column techniques. In batch experiments, 15 min stirring time, 55 degrees C and pH 8 were the optimal conditions for Pb(II) adsorption. In column experiments, sorption was quantitative for 1000 mL of 2.41 x 10(-4 )mM of Pb(II) solution and adsorbed ions were eluted out by 5 mL of 1 M HCl (preconcentration factor of 200). Spiked tap water was used for the preconcentration and determination of Pb(II) by flame atomic absorption spectrometry, and a 100% recovery was obtained. The LOD and LOQ values of the proposed method were found to be 3.52 x 10(-3) and 4.20 x 10(-3 )mM, respectively. The RSD for three preconcentration experiments was found to be <or= 2%. The linear working range for measurements was between 2 x 10(-3 )and 0.14 mM (y = 0.0136x + 0.0007, R(2 )= 0.9999).

Preparation, characterization, and Zn 2+ adsorption behavior of chemically modified MCM-41 with 5-mercapto-1-methyltetrazole

A mesoporous silica (MCM-41) has been chemically modified with 5-mercapto-1-methyltetrazole using the homogeneous route. This synthetic route involved the reaction of 5-mercapto-1-methyltetrazole with 3-chloropropyltriethoxysilane prior to immobilization on the support. The resulting material (MTTZ-MCM-41) has been characterized by powder X-ray diffraction, nitrogen gas sorption, FT-IR and MAS NMR spectroscopy, thermogravimetry, and elemental analysis. The solid was employed as a Zn(II) adsorbent from aqueous solutions at room temperature. The effect of several variables (stirring time, pH, metal concentration, addition of ethanol, presence of other metals in the medium) has been studied using batch and column techniques. Flame atomic absorption spectrometry was used to determine the Zn(II) concentration in the filtrate or in the eluted solution after the adsorption process. Results obtained indicate that under the optimum conditions (pH 8 and 2 h stirring time), the maximum adsorption value for Zn(II) was 1.59 ± 0.01 mmol / g , whereas the adsorption capacity of the unmodified mesoporous silica was about 0.010 ± 0.001 mmol / g . On the other hand, the Zn(II) adsorption on the MTTZ-MCM-41 was independent of the presence of ethanol and other metals (Cu(II), Mn(II), Ca(II), and Mg(II)) in the medium. Finally, experiments carried out in order to study the regeneration capacity of the MTTZ-MCM-41 revealed that the adsorption capacity of this material was maintained after 3 cycles of the adsorption/desorption process.

Uptake and Translocation of Heavy Metals in Salt Marsh Sediments by Spartina patens

The Hackensack Meadowlands is a coastal marsh system in northeastern New Jersey, located approximately 10 km west of New York City. Within the Meadowlands, twelve destructed or degraded estuarine wetland sites are currently part of ecological restoration projects that are in various phases of development from planning to completion (http:// www.meadowlands.state.nj.us/naturalresources/wetlands/ Wetlands.cfm). A completed restoration site is Harrier Meadow (North Arlington, NJ) where mitigation work included the creation of channels, impoundments, low marsh habitat and upland habitat islands. Important salt marsh plant species such as salt-meadow grass (Spartina patens), and spike grass (Distichlis spicata) dominate portions of the marsh. The sediments of Harrier Meadow contain heavy metals at concentrations that are below regulatory action limits (e.g., cadmium (Cd) 0–1 ppm; chromium (Cr) 10–18 ppm; copper (Cu) 13–60 ppm; nickel (Ni) 7–15 ppm; lead (Pb) 0–87 ppm; zinc (Zn) 28–94 ppm) (http:// www.meri.njmeadowlands.gov/ecorisk/), but above those typically found in uncontaminated environments (van Driel et al. 1995; Swaileh et al. 2004). Since Spartina species have been shown to take up heavy metals into roots and translocate them into aboveground parts (see Weis and Weis (2004) for review), we had investigated the fate and the effects of selected heavy metals (i.e., Cd, Cr, Cu, Ni, Pb, and Zn) in sediment cores that were densely covered with Spartina patens in a recent short-term study (Suntornvongsagul et al. 2007). Since levels of metals taken up and translocated had been shown to vary depending on the metal concentration in the substrate (Vogel-Mikus et al. 2005), and to be affected by the presence of other metals (McKenna et al. 1993; Podar et al. 2004), half of these cores were artificially amended with Ni in order to increase its availability, and to assess potential effects on uptake of other metals. Ni was chosen since it was the most accumulated metal in shoots from a mixture containing Cd(II), Cu(II), Ni(II) and Zn(II) in identical concentrations (Peralta-Videa et al. 2002), and was assumed to persist in hydrated form in pore water. We demonstrated that Ni-amendment had no significant effect on the fate of other metals in sediments, however, observed increased root-uptake of certain metals. Although translocation of Ni into shoots reflected the 10-fold higher concentrations in sediments and roots in Ni-amended cores, metal translocation into shoots was generally small for all metals (Suntornvongsagul et al. 2007). The goal of the current study was to extend the observations beyond the first growing season, and to assess whether Ni-amendment had effects on metal uptake and translocation after three growing seasons.

Permeable Reactive Barriers for the Removal of Heavy Metals: Lab‐Scale Experiments with Low‐Grade Magnesium Oxide

AbstractThe attenuation of heavy metals in ground water depends on factors such as solid‐solution equilibrium or the solubility product (Ksp) of the solid phase. Metals are pH dependent, and the solubility of heavy metal hydroxides such as lead, cadmium, zinc, and nickel is minimal within pH range 9 to 11. MgO as material in a passive remediation system for removing heavy metals from contaminated ground water is very useful because of its minimal environmental impact and low solubility reaches a maximum pH of 10. Low‐grade MgO (LG‐MgO) was found to be suitable and economically feasible for use as permeable reactive barrier filler for remediation of ground water contaminated by heavy metals. The results of this study suggest that the coprecipitation of heavy metal hydroxides and magnesium hydroxide on the LG‐MgO particle surface and sorption in the neoformed precipitates are the main mechanisms of heavy metal release from contaminated ground water. Remediation is not affected by the presence of other metals, which ensures that the range of application is very broad in both subterranean and surface water. LG‐MgO used as a reactive medium for the treatment of contaminated water significantly diminishes the amount of heavy metals in ground water.

Metal-triggered Nanofiber Formation of His-containing β-Sheet Peptide

Metal-responsive nanofiber formation was achieved using a designed β-sheet peptide with His residues at the both N- and C-termini. The designed peptide, whose sequence was HPKFKIIEFEPH, was in a random coil in a neutral buffer, and did not show any structural change. However, the peptide underwent the structural transition to a β-sheet conformation in response to metal ions such as Cu2+, Zn2+, Ni2+, or Co2+, and Cu2+ was the most effective. The 1-anilinonaphthalene-8-sulfonate (ANS) binding assay suggested that the peptide assemblages in the presence of Cu2+ had a well-packed structure. The transmission electron microscopy study revealed that the peptide formed tape-like fibers in the presence of Cu2+, but amorphous flocculates in the presence of other metals. The peptide assemblages were rapidly broken by addition of EDTA. The metal responsiveness was acquired in the peptide assembly and nanofiber formation by attachment of His residues on the both termini of the β-sheet peptide.

Zn in the soil solution of unpolluted and polluted soils as affected by soil characteristics

Current legislative frameworks for soil pollution focus predominantly on total metal content. However, environmental risks posed by heavy metals are not only function of their overall presence in the soil, but also of their chemical speciation. Soil solution levels of Zn are indicative of its availability to plants and soil (micro)biota. In addition, levels present in the soil solution can tell us something of the potential risks for leaching and subsequently elevating ground water levels. In this research, a total of 29 polluted and unpolluted soils were characterised and assessed for the presence of Zn in the soil solution using Rhizon soil moisture samplers. Interactions between the soil properties and observed solubility of Zn was described and put into empirical multivariate formulations. All obtained equations without exception contained pH as a key factor in determining Zn solubility. Finally, soil solution speciation of Zn was assessed using 2 independent software packages (Visual Minteq 2.23 and WHAM VI), based on pH and the presence of other metals, exchangeable bases, anions, and dissolved organic matter. Both models were largely in disagreement in the fractionation between organically bound and inorganic Zn in the solution. Further investigation into the parametric background of both models will therefore be required to ascertain the cause and nature of the observed discrepancy.

Characterization of an Ochrobactrum intermedium strain STCr-5 manifesting high level Cr(VI) resistance and reduction potential

The investigation was conducted to evaluate the Cr(VI) resistance and reduction by a bacterial strain STCr-5 under different conditions. Strain STCr-5 tolerated very high concentration of Cr(VI) i.e., >10 mg ml −1 in nutrient broth and up to 8 mg ml −1 in M9 minimal medium. Based on 16S rRNA gene sequence homology, the isolate was identified as Ochrobactrum intermedium. It showed up to 90% reduction with different forms of Cr(VI) (CrO 4 2−, Cr 2O 7 2−). O. intermedium STCr-5 exhibited a broad range of Cr(VI) reduction efficiencies at temperatures from 28 to 50 °C and pH levels from 6 to 8. Cr(VI) reduction capability was related to initial cell concentration and Cr(VI) concentration. O. intermedium STCr-5 demonstrated highly efficient Cr(VI) reduction over the Cr(VI) concentration range 100–1000 μg ml −1. Strain STCr-5 reduced 200 μg Cr(VI) ml −1 within 72 h and displayed 50% reduction at the highest Cr(VI) concentration of 1000 μg ml −1 within 96 h. Cr(VI) reduction ability of strain STCr-5 was not influenced by sulphate and nitrate up to 1000 μg ml −1. The presence of other metals (Cu 2+, Co 2+, Mn 2+, Ni 2+, Zn 2+) significantly stimulated Cr(VI) reduction by this isolate. O. intermedium STCr-5, thus, holds great promise for detoxification of Cr(VI) under a wide range of environmental conditions.

Removal of lead(II) and cadmium(II) from aqueous solutions using grape stalk waste

The sorption of lead and cadmium from aqueous solutions by grape stalk waste (a by-product of wine production) was investigated. The effects of the contact time, pH of the solution, ionic medium, initial metal concentration, other metal ions present and ligands were studied in batch experiments at 20 °C. Maximum sorption for both metals was found to occur at an initial pH of around 5.5. The equilibrium process was described well by the Langmuir isotherm model, with maximum grape stalk sorption capacities of 0.241 and 0.248 mmol g −1 for Pb(II) and Cd(II), respectively, at pH around 5.5. Kinetic studies showed good correlation coefficients for a pseudo-second-order kinetic model. The presence of NaCl and NaClO 4 in the solution caused a reduction in Pb and Cd sorption, the latter being more strongly suppressed. The presence of other metals in the uptake process did not affect the removal of Pb, while the Cd uptake was much reduced. HCl or EDTA solutions were able to desorb lead from the grape stalks completely, while an approximately 65% desorption yield was obtained for cadmium. From the results obtained it seems that other mechanisms, such as surface complexation and electrostatic interactions, must be involved in the metal sorption in addition to ion exchange.

Extraction of chromium(VI) by salting-out with a homogeneous, mixed solvent of water and 2-propanol: A laboratory study

Chromium enters into the aquatic environment as a result of effluent discharge from steel works, electroplating, leather tanning industries and chemical industries. As the Cr(VI) is very harmful to living organisms, it should be quickly removed from the environment when it happens to be contaminated. Therefore, the aim of this laboratory research was to develop a rapid, simple and adaptable solvent extraction system to quantitatively remove Cr(VI) from polluted waters. Aqueous salt-solutions containing Cr(VI) as CrO4(2-) at ppm level (4-6 ppm) were prepared. Equal volumes (5 ml) of aqueous and organic (2-PrOH) phases were mixed in a 10 ml centrifuge tube for 15 min, centrifuged and separated. Concentrations of Cr(VI), in both the aqueous and organic phases, were determined by atomic absorption spectrometry. The effects of salt and acid concentrations, and phase-contact time on the extraction of Cr(VI) were investigated. In addition, the extraction of Cr(VI) was assessed in the presence of tetramethylammonium chloride (TMAC) in 2-PrOH phase. Effects of some other metals, (Cd(II), Co(II), Cu(II), Ni(II) and Zn(II)), on the extraction of Cr(VI) were also investigated. The Cr(VI) at ppm level was extracted quantitatively by salting-out the homogeneous system of water and 2-propanol(2-PrOH) using chloride salts, namely CaCl2 or NaCl, under acidic chloride media. The extracted chemical species of Cr(VI) was confirmed to be the CrO3Cl-. The ion-pair complex extracted into the organic phase was rationalized as the solvated ion-pair complex of [2-PrOH2+, CrO3Cl-]. The complex was no longer stable. It implied the reaction between extracted species. Studies revealed that salts and acid directly participated in the formation of the above complex. Use of extracting agents (TMAC) didn't show any significant effect on the extraction of Cr(VI) under high salting-out conditions. There is no significant interference effect on the extraction of Cr(VI) by the presence of other metals. The Cr(VI) in the organic phase was back-extracted using an aqueous ammonia solution (1.6 mol dm(-3)) containing 3 mol dm(-3) NaCl. The extraction mechanism of Cr(VI) is also discussed. Salting-out of homogeneous mixed solvent of 2-propanol can be employed to extract Cr(VI) quantitatively, as an ion-pair of [2-PrOH2+ * CrO3Cl-] solvated by 2-PrOH molecules. Then, the complex becomes 'solvent-like' and is readily separated into the organic phase. The increase of Cl- ion concentration in the aqueous phase favors the extraction. The 2-PrOH, salts and acid play important roles in the extraction process. There is no need to use an extracting agent at a high salting-out condition. Chromium(VI) must be quickly removed before it enters into the natural cycle. As the 2-PrOH is water-miscible in any proportion, ion-pairing between 2-PrOH2+ and CrO3Cl- becomes very fast. As a result, Cr(VI) can easily be extracted. Therefore, the method is recommended as a simple, rapid and adaptable method to quickly separate Cr(VI) from aqueous samples.

Percutaneous absorption of arsenic from environmental media

Current knowledge of percutaneous absorption of arsenic is based on studies of rhesus monkeys using soluble arsenic in aqueous solution, and soluble arsenic mixed with soil (Wester et al., 1993). These studies produced mean dermal absorption rates in the range of 2.0-6.4% of the applied dose. Subsequently, questions arose as to whether these results represent arsenic absorption from environmental media. Factors such as chemical interactions, the presence of other metals, and the effects of weathering on environmental media all can affect the nature of arsenic and its potential for percutaneous absorption. Therefore, research specific to more relevant matrices is important. The focus of this effort is to outline study design considerations, including particle size, application rates, means of ensuring skin contact and appropriate statistical evaluation of the data. Appropriate reference groups are also important. The potential for background exposure to arsenic in the diet possibly obscuring a signal from a dermally applied dose of arsenic will also be addressed. We conclude that there are likely to be many site- or sample-specific factors that will control the absorption of arsenic, and matrix-specific analyses may be required to understand the degree of percutaneous absorption.

Competitive adsorption of Zn (II), Cd (II) AND Pb (II) ions from aqueous and non- aqueous solution by maize cob and husk

Heavy metals rank as major environmental pollutants. Industrial wastewater effluents carry admixtures of these heavy metals. The competitive adsorption of Zn2+, Cd2+ and Pb2+ metal ions from aqueous and non-aqueous solutions by unmodified and modified maize cob and husk was investigated. The results showed that maximum adsorption occurred at 495.9 mg/g for Zn2+ ion, 456.7 mg/g for Pb2+ ion and 493.7mg/g for Cd2+ ion without modification. The adsorption in a mixture of the metal ions caused a leveling effect on the adsorption capacity of the maize cob and husk. The adsorption efficiency of each metal ion was influenced by the presence of other metal ions, presence of non-aqueous solvent and modification by carboxymethylation. The study significantly reveals the presence of other heavy metals and chemicals as design parameter in the treatment and management of heavy metal pollutants using cellulosic materials. Key words: Competitive adsorption, mixed metal ions, aqueous and non-aqueous solution, maize cob and husk.

Biosorption of cobalt by fungi from serpentine soil of Andaman

Fungi belonging to Aspergillus, Mortierella, Paecilomyces, Penicillium, Pythium, Rhizopus and Trichoderma, isolated from serpentine soil of Andaman (India) were screened for cobalt-resistance. Eleven out of total 38 isolated fungi which tolerated >6.0 mM Co(II) were evaluated for cobalt biosorption using dried mycelial biomass. Maximum Co(II)-loading (1036.5 μM/g, 60 min) was achieved with Mortierella SPS 403 biomass, which removed almost 50% of 4.0 mM cobalt from the aqueous solution. Co(II)-sorption kinetics of Mortierella SPS 403 biomass was fast and appreciable quantities of metal [562.5 μM/g] was adsorbed during first 10 min of incubation. The metal biosorption capacity of the isolate was accelerated with increasing cobalt concentration, while it was reverse with increase of initial biomass. The optimum pH and temperature for Co(II) removal were 7.0 and 30 °C, respectively. However, Co(II)-uptake was inhibited in presence of other metals (Pb, Cd, Cu, Ni, Cr and Zn). Freundlich adsorption isotherm appropriately describes Mortierella SPS 403 biomass as an efficient Co(II)-biosorbent.

Competitive adsorption behavior of heavy metals on kaolinite

Polluted and contaminated soils can often contain more than one heavy metal species. It is possible that the behavior of a particular metal species in a soil system will be affected by the presence of other metals. In this study we have investigated the adsorption of Cd(II), Cu(II), Pb(II), and Zn(II) onto kaolinite in single- and multi-element systems as a function of pH and concentration, in a background solution of 0.01 M NaNO 3. In adsorption edge experiments, the pH was varied from 3.5 to 10.0 with total metal concentration 133.3 μM in the single-element system and 33.3 μM each of Cd(II), Cu(II), Pb(II), and Zn(II) in the multi-element system. The value of pH 50 (the pH at which 50% adsorption occurs) was found to follow the sequence Cu < Zn < Pb < Cd in single-element systems, but Pb < Cu < Zn < Cd in the multi-element system. Adsorption isotherms at pH 6.0 in the multi-element systems showed that there is competition among various metals for adsorption sites on kaolinite. The adsorption and potentiometric titrations data for various kaolinite–metal systems were modeled using an extended constant-capacitance surface complexation model that assumed an ion-exchange process below pH 7.0 and the formation of inner-sphere surface complexes at higher pH. Inner-sphere complexation was more dominant for the Cu(II) and Pb(II) systems.

The influence of a cerium additive on ultrafine diesel particle emissions and kinetics of oxidation

The influence of a cerium additive on the kinetics of oxidation and size distribution of ultrafine diesel particles was studied using a high-temperature oxidation-tandem differential mobility analysis method over the temperature range 300–700 °C. The addition of cerium to the diesel fuel was observed to cause significant changes in number-weighted size distributions, light-off temperature, and kinetics of oxidation. The peak number concentration in the accumulation mode decreased 50 and 65%, respectively, for 25 and 100 ppm dosing levels under 1400 rpm and 75% engine load. The light-off temperature was reduced by 250 and 300 °C, respectively, for 25 and 100 ppm dosing levels. The oxidation rate increased significantly (×20) with the addition of cerium to the fuel; however, the rate was relatively insensitive to dosing level. The activation energy for cerium-dosed oxidation was, within experimental error, equivalent to that for undosed fuel ( E a = 100 – 110 kJ mol −1 ). From a phenomenological kinetic rate perspective, the increase in oxidation rate was attributed solely to an increase in the preexponential factor. These results suggested that diesel particles using regular, undosed diesel fuels were already metal-catalyzed to some extent, most likely from metals in the lube oil. The addition of cerium likely increased the number of catalytic sites but had no effect on the overall activation energy due to the presence of other metals in the diesel particulate matter coming from lube oil. The characteristics of cerium-laden diesel particles were also investigated. Two principal types of aggregates were found using transmission electron microscopy and energy-dispersive spectrometry analysis. The first was composed mainly of agglomerates of carbonaceous spherules and a few, considerably smaller cerium oxide nanoparticles. The second consisted of metallic aggregates composed mainly of cerium oxide nanoparticles and some carbon.

Interactions of metals affect their distribution in tissues of Phragmites australis

Culms of Phragmites australis were grown in vermiculite in a greenhouse. Some plants were exposed to 1000 μg/g Cu or Pb or Zn, or combinations of two or three of those metals. When plants reached senescence, they were harvested and analyzed for metal concentrations in upper leaves, lower leaves, stems and roots. While all metals accumulated in highest concentrations in the roots, Zn accumulated in aboveground tissues far more than the other metals. Furthermore, the concentration of any one metal in the different tissues was affected by the presence of other metals. The amount of copper in upper leaves increased when Zn was also present with the Cu. The amount of Cu in roots was increased in the presence of Pb and/or Zn. The amount of Zn in lower leaves was reduced when Cu was also present along with Zn. Thus, when combinations of metals were present, the distribution of metals was altered. The most important interactions appeared to be of Cu and Zn, which may reflect competition for binding sites on metal-binding proteins.