In this study, we investigated the removal of Fe, Pb, Cd, and Zn from synthetic mine waters by a natural zeolite. The emphasis was given to the zeolite's behavior toward a few cations in competition ...with each other. Pb was removed efficiently from neutral as well as from acidic solutions, whereas the uptake of Zn and Cd decreased with low pH and high iron concentrations. With increasing Ca concentrations in solution, elimination of Zn and Cd became poorer while removal of Pb remained virtually unchanged. The zeolite was stable in acidic solutions. Disintegration was only observed below pH 2.0. Forward- and back-titration of synthetic acidic mine water were carried out in the presence and absence of zeolite to simulate the effects of a pH increase by addition of neutralizing agents and a re-acidification which can be caused by subsequent mixing with acidic water. The pH increase during neutralization causes precipitation of hydrous ferric oxides and decreased dissolved metal concentrations. Zeolite addition further diminished Pb concentrations but did not have an effect on Zn and Cd concentrations in solution. During re-acidification of the solution, remobilization of Pb was weaker in the presence than in the absence of zeolite. No substantial differences were observed for Fe, Cd, and Zn immobilization. The immobilization of the metals during pH increase and the subsequent remobilization caused by re-acidification can be well described by a geochemical equilibrium speciation model that accounts for metal complexation at hydrous ferric oxides, for ion exchange on the zeolite surfaces, as well as for dissolution and precipitation processes.
Several bacterial strains isolated from granitic rock material in front of the Damma glacier (Central Swiss Alps) were shown (i) to grow in the presence of granite powder and a glucose-NH₄Cl minimal ...medium without additional macro- or micronutrients and (ii) to produce weathering-associated agents. In particular, four bacterial isolates (one isolate each of Arthrobacter sp., Janthinobacterium sp., Leifsonia sp., and Polaromonas sp.) were weathering associated. In comparison to what was observed in abiotic experiments, the presence of these strains caused a significant increase of granite dissolution (as measured by the release of Fe, Ca, K, Mg, and Mn). These most promising weathering-associated bacterial species exhibited four main features rendering them more efficient in mineral dissolution than the other investigated isolates: (i) a major part of their bacterial cells was attached to the granite surfaces and not suspended in solution, (ii) they secreted the largest amounts of oxalic acid, (iii) they lowered the pH of the solution, and (iv) they formed significant amounts of HCN. As far as we know, this is the first report showing that the combined action of oxalic acid and HCN appears to be associated with enhanced elemental release from granite, in particular of Fe. This suggests that extensive microbial colonization of the granite surfaces could play a crucial role in the initial soil formation in previously glaciated mountain areas.
The mobility, bioavailability, and environmental fate of heavy metals in soil are controlled by their adsorption onto soil minerals and solid organic matter. The adsorption is strongly affected by ...the presence of various low-molecular-weight organic acids. In this study, effect of hydroxamate siderophore desferrioxamine B (DFOB) on cadmium (Cd) and zinc (Zn) adsorption onto two micaceous clay minerals, muscovite and phlogopite, was evaluated in batch experiments. Results showed that the presence of DFOB diminished the adsorption of Cd and Zn onto both minerals, particularly under neutral to alkaline pH conditions. For instance, at pH 8.2, the presence of DFOB caused a decrease in the adsorption of Zn onto phlogopite by nearly 50%. The equilibrium adsorption of Cd and Zn was satisfactorily described using Freundlich isotherm. The adsorption isotherms showed that the affinity of Cd and Zn onto the minerals decreased in the presence of DFOB. For example, at pH 8.0, the presence of siderophore caused a decrease in the Freundlich adsorption isotherm coefficient KF for Zn adsorption onto muscovite and phlogopite from 4.60 to 0.07 L g−1 and from 3.56 to 0.36 L g−1, respectively. These findings confirm the potential influence of siderophore on the fate of Cd and Zn in arid soils containing substantial contributions of micaceous silicate minerals.
Natural zeolites, known for their excellent sorption properties towards metal cations, are widely used for the purification of wastewaters. The selectivity of clinoptilolite, a common zeolite ...mineral, for Pb is known to be particularly high, whereas its selectivity for Cd is often lower. Extraordinarily high sorption capacities for soft metal cations were observed in the case of thiol-functionalized silica gels and clays. In order to enhance the zeolites’ sorption capacity for Cd, we treated natural heteroionic and Na-clinoptilolite in aqueous suspensions with cysteamine and propylamine solutions and investigated the sorption of Cd and Pb to amine-modified zeolite by a series of batch experiments. Stability constants for amine sorption on all zeolite samples at room temperature and 50
°C were obtained. Partial dimerization of cysteamine explains the enhanced sorption of this compound.
In contrast, amine treatment did not enhance the adsorption capacity or selectivity of the clinoptilolite towards Cd and Pb. Instead, the amounts of adsorbed heavy metals decreased stoichometrically with increasing sorption of cysteamine and propylamine. This reduction can be explained by the blockage of channels by amine molecules and revealed that the modification of zeolites with mercaptoamines does not enhance the sorption capacity of zeolite for Cd and Pb.
Recently deglaciated areas are ideal environments to study soil formation and primary microbial succession where phototrophic microorganisms may play a role as primary producers. The aim of our study ...was to investigate the cyanobacterial and green algal community composition in three different successional stages of the Damma glacier forefield in the Swiss Alps using 16S rDNA and ITS rDNA clone libraries. Cyanobacterial target sequences varied along the glacier forefield, with the highest cyanobacterial 16S rRNA gene copies found in sparsely vegetated soils. Sequence analysis revealed that the phototrophic communities were distinct in each of the three soil environments. The majority of the cyanobacterial sequences retrieved from barren soils were related to the Oscillatoriales. The diversity in sparsely vegetated soils was low, and sequences closely related to Nostoc sp. dominated. The majority of the algal phylotypes are related to members of the Trebouxiophyceae known to live as symbiotic partners in lichens. We conclude that the community composition appears to shift markedly along the chronosequence, indicating that each soil environment selects for its phototrophic community. When cyanobacteria occur together with eukaryotic microalgae, they form a rich source of organic matter and may be important contributors of carbon in nutrient-deficient deglaciated soils.
Over 400
tons of Pb enters Swiss soils annually at some 2000 military shooting ranges (MSRs). We measured elements in the leaves of 10 plant species and associated rhizospheric soil on the stop butt ...of a disused MSR. The geometric mean concentrations of Pb, Sb, Cu, Ni in rhizospheric soils were 10,171
mg/kg, 5067
mg/kg, 4125
mg/kg and 917
mg/kg. Some species contained Pb, Cu and Ni, above concentrations (30
mg/kg, 25
mg/kg and 50
mg/kg) shown to be toxic to livestock. Most contaminants in leaves resulted from surface deposition. However, at soil Pb concentrations >60,000
mg/kg,
Equisetum arvense and
Tussilago farfara took up >1000
mg/kg Pb into the leaves. These plants are not hyperaccumulators, having <100
mg/kg Pb in leaves at lower soil concentrations. Removal of soil with more than 30,000 Pb, from which one could smelt this metal to offset remediation costs, followed by revegetation, would minimise dust and hence leaf-borne contaminants.
Establishment of a complete vegetation cover on shooting ranges would reduce the contamination of plant leaves by toxic trace elements.
Distinct layers of iron(
iii
) and manganese(
iv
) (Fe/Mn) oxides are found buried within the reducing part of the sediments in Lake Baikal and cause considerable complexity and steep vertical ...gradients with respect to the redox sequence. For the on-site investigation of the responsible biogeochemical processes, we applied filter tube samplers for the extraction of sediment porewater combined with a portable capillary electrophoresis instrument for the analyses of inorganic cations and anions. On the basis of the new results, the sequence of diagenetic processes leading to the formation, transformation, and dissolution of the Fe/Mn layers was investigated. With two exemplary cores we demonstrate that the dissolution of particulate Fe and Mn is coupled to the anaerobic oxidation of CH
4
(AOM) either
via
the reduction of sulphate (SO
4
2−
) and the subsequent generation of Fe(
ii
) by S(−
ii
) oxidation, or directly coupled to Fe reduction. Dissolved Fe(
ii
) diffuses upwards to reduce particulate Mn(
iv
) thus forming a sharp mineral boundary. An alternative dissolution pathway is indicated by the occurrence of anaerobic nitrification of NH
4
+
observed at locations with Mn(
iv
). Furthermore, the reasons and consequences of the non-steady-state sediment pattern and the resulting redox discontinuities are discussed and a suggestion for the burial of active Fe/Mn layers is presented.
Extraordinary buried iron- and manganese oxide layers were investigated in early diagenetic Lake Baikal sediments. Porewater analyses were performed on-site with a portable capillary electrophoresis instrument.
Background, aim, and scope Phosphorus loss from terrestrial to the aquatic ecosystems contributes to eutrophication of surface waters. To maintain the world's vital freshwater ecosystems, the ...reduction of eutrophication is crucial. This needs the prevention of overfertilization of agricultural soils with phosphorus. However, the methods of risk assessment for the P loss potential from soils lack uniformity and are difficult for routine analysis. Therefore, the efficient detection of areas with a high risk of P loss requires a simple and universal soil test method that is cost effective and applicable in both industrialized and developing countries. Materials and methods Soils from areas which varied highly in land use and soil type were investigated regarding the degree of P saturation (DPS) as well as the equilibrium P concentration (EPC₀) and water-soluble P (WSP) as indicators for the potential of P loss. The parameters DPS and EPC₀ were determined from P sorption isotherms. Results Our investigation of more than 400 soil samples revealed coherent relationships between DPS and EPC₀ as well as WSP. The complex parameter DPS, characterizing the actual P status of soil, is accessible from a simple standard measurement of WSP based on the equation graphic removed . Discussion The parameter WSP in this equation is a function of remaining phosphorous sorption capacity/total accumulated phosphorous (SP/TP). This quotient is independent of soil type due to the mutual compensation of the factors SP and TP. Thus, the relationship between DPS and WSP is also independent of soil type. Conclusions The degree of P saturation, which reflects the actual state of P fertilization of soil, can be calculated from the easily accessible parameter WSP. Due to the independence from soil type and land use, the relation is valid for all soils. Values of WSP, which exceed 5 mg P/kg soil, signalize a P saturation between 70% and 80% and thus a high risk of P loss from soil. Recommendations and perspectives These results reveal a new approach of risk assessment for P loss from soils to surface and ground waters. The consequent application of this method may globally help to save the vital resources of our terrestrial and aquatic ecosystems.
The Origin of Aluminum Flocs in Polluted Streams Furrer, Gerhard; Phillips, Brian L.; Ulrich, Kai-Uwe ...
Science (American Association for the Advancement of Science),
09/2002, Volume:
297, Issue:
5590
Journal Article
Peer reviewed
About 240,000 square kilometers of Earth's surface is disrupted by mining, which creates watersheds that are polluted by acidity, aluminum, and heavy metals. Mixing of acidic effluent from old mines ...and acidic soils into waters with a higher pH causes precipitation of amorphous aluminum oxyhydroxide flocs that move in streams as suspended solids and transport adsorbed contaminants. On the basis of samples from nine streams, we show that these flocs probably form from aggregation of the$\varepsilon-Keggin$polyoxocation$AlO_{4}Al_{12}(OH)_{24}(H_2O)_{12}^{7+}(aq) (Al_{13})$, because all of the flocs contain distinct$Al(O)_4$centers similar to that of the$Al_{13}$nanocluster.
There is growing interest in using layered double hydroxides (LDH) as controlled release systems of essential nutrients for plants. The Zn-Mg-Fe(III)-LDH intercalated with nitrate (LDH-NO3−), ...phosphate (LDH-HPO42−) and carbonate (LDH-CO32−) were synthesized with the aim of investigation the effect of oxalic acid (OX), tartaric acid (TAR) and citric acid (CIT) (three common low molecular organic acids (LMWOAs) available in soil solution) to release structural Zn. In this regard, effects of time, initial pH and background electrolyte on the release of structural Zn from LDH in the presence of LMWOAs were performed based on the batch technique. According to the results, although the Zn-complexing abilities of organic acids were pH-dependent, the overall extent of Zn release was sensitive to the concentration of organic acid as well as to the type of available cation in the electrolyte solution and intercalated anion. Among the LMWOAs, CIT was the most effective ligand in releasing Zn, followed by OX and TAR. Also, our observation suggested that the intercalation of carbonate strongly suppressed the release of Zn in the absence and presence of organic acids, especially in CaCl2 electrolyte. The effect of organic acids on the kinetics of Zn release (KCl solution; initial pH = 6.0) were investigated and several kinetic models were tested to describe the time-dependent Zn release. Results showed that Elovich and pseudo-second order equations were the best-fit equations among five kinetic models used. The presence of the LMWOAs generally increased initial release rate (h) and the extent of Zn released at equilibrium (qe) from LDH; however, the enhancement effect of CIT was pronounced in LDH-NO3− and LDH-HPO42−.
•LDH dissolution kinetics - a ligand-promoted phenomenon•Release of Zn from LDHs was high in the presence of citrate•The LDH-CO32– released lower Zn compared to the other compounds.
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