Synthesis of Zeolites from Fine-Grained Perlite and Their Application as Sorbents.

The hydrothermal alteration of perlite into zeolites was studied using a two-step approach. Firstly, perlite powder was transformed into Na-P1 (GIS) or hydro(xy)sodalite (SOD) zeolites at 100 °C and 24 h using 2 or 5 M NaOH solutions. Secondly, the Si:Al molar ratio of the reacted Si-rich solution was adjusted to 1 by Na-aluminate addition to produce zeolite A (LTA) at 65 or 95 °C and 6 or 24 h at an efficiency of 90 ± 9% for Al and 93 ± 6% for Si conversion. The performance of these zeolites for metal ion removal and water softening applications was assessed by sorption experiments using an artificial waste solution containing 4 mmol/L of metal ions (Me2+: Ca2+, Mg2+, Ba2+ and Zn2+) and local tap water (2.1 mmol/L Ca2+ and 0.6 mmol/L Mg2+) at 25 °C. The removal capacity of the LTA-zeolite ranged from 2.69 to 2.86 mmol/g for Me2+ (=240-275 mg/g), which is similar to commercial zeolite A (2.73 mmol/g) and GIS-zeolite (2.69 mmol/g), and significantly higher compared to the perlite powder (0.56 mmol/g) and SOD-zeolite (0.88 mmol/g). The best-performing LTA-zeolite removed 99.8% Ca2+ and 93.4% Mg2+ from tap water. Our results demonstrate the applicability of the LTA-zeolites from perlite for water treatment and softening applications.

A novel nZVI-bentonite nanocomposite to remove trichloroethene (TCE) from solution.

Nanoscale zero-valent iron (nZVI) based (nano)composites supported by clay mineral substrates are a promising technology for the in-situ remediation of groundwater and (sub)soils contaminated with chlorinated hydrocarbons, such as trichloroethene (TCE). However, the physicochemical processes and interaction mechanisms between nZVI particles, clay minerals and TCE are poorly understood, yet. We immobilized nZVI particles on a commercial bentonite substrate to prepare a novel nZVI-B nanocomposite and tested its performance for TCE removal from solution against pure nZVI in batch reactors. The nZVI-B exhibited a higher reactivity (2.2·10-3 L h-1·m-2) and efficiency (94%) for TCE removal than nZVI (2.2·10-4 L h-1·m-2; 45%). Sorption of TCE onto the clay surfaces and reductive de-chlorination in "micro-reactors" developing within the nZVI-B controlled the kinetics and the magnitude of TCE loss from solution. Contrary to pure nZVI, no signs of nZVI particle agglomeration or inactivation due to oxide shell formation were found in nZVI-B. We attribute this to the uptake of dissolved Fe species that are liberated via progressing nZVI particle corrosion by the bentonite substrate to form Fe-smectite (nontronite domains), which prevented from a deterioration of the properties and reactivity of the nZVI-B. The use of nZVI-B in permeable reactive barriers at contaminated field sites could be feasible, where a system-inherent reduction of the soil-bearing capacity has to be minimized.

Investigation of hydrated smectite microstructure through wet environmental transmission electron microscopy.

Water is an essential constituent of all biological materials as well as many non-biological materials. Not only the removal of water may result in undesirable morphological and structure change, the inability to sustain the hydrated conditions in the microscope also prevents the study of reactions which take place in aqueous environment. In order to overcome these problems we used wet environmental-cell transmission electron microscopy TEM (WETEM). Conventional TEM of dry smectite showed well-defined particle outlines (but without a specific shape) and typical smectite aggregates. Selected area electron diffraction (SAD) of dry particles showed stacking of smectite particles (i.e., aggregate) in very clear dot and ring patterns. In contrast, WETEM depicted well-dispersed clay particles showing a variety of different particle shapes. Analysis of SAD patterns obtained from dry and hydrated states illustrated a lattice change in different environments. The small lattice expansion in (h k 0) resulted from the expansion of the (0 0 l) plane resulting from the addition of water molecules in the crystal along the c-axis.

Traffic-related distribution of antimony in roadside soils.

Vehicular emissions have become one of the main source of pollution of urban soils; this highlights the need for more detailed research on various traffic-related emissions and related distribution patterns. Since the banning of asbestos in the European Union, its substitution with antimony (Sb) in brake linings has led to increased inputs of this toxic metalloid to environmental compartments. The objective of this study was to provide detailed information about the spatial distribution patterns of Sb and to assess its mobility and bioavailability. Roadside soils along an arterial road (approx. 9000 vehicles per day) in Cologne (Germany) were studied along five transects, at four soil depths and at seven sampling points set at varying distances from the road (n = 140). For all samples, comprehensive soil characterization was performed and inverse aqua regia-extractable trace metal content was determined being pseudo-total contents. Furthermore, for one transect, also total Sb and a chemical sequential extraction procedure was applied (n = 28). Pseudo-total Sb for all transects decreased significantly with soil depth and distance from the road, reflecting a distribution pattern similar to that of other trace metals associated with brake lining emissions. Conversely, metals associated with exhaust emissions showed a convex distribution. The geochemical fractionation of Sb revealed the following trends: i) non-specifically sorbed Sb was <5%; ii) specifically sorbed Sb was only detected within 1 m distance from the road and decreased with depth; iii) Sb associated with poorly-crystalline Fe oxides decreased with distance from the road; and iv) content of Sb bounded to well-crystalline Fe oxides, and Sb present in the residual fraction remained relatively constant at each depth. Consequently, roadside soils appear to inhibit brake lining-related Sb contamination, with significant but rather low ecotoxicological potential for input into surface and groundwater.

Microbial Community Dynamics in Soil Depth Profiles Over 120,000 Years of Ecosystem Development.

Along a long-term ecosystem development gradient, soil nutrient contents and mineralogical properties change, therefore probably altering soil microbial communities. However, knowledge about the dynamics of soil microbial communities during long-term ecosystem development including progressive and retrogressive stages is limited, especially in mineral soils. Therefore, microbial abundances (quantitative PCR) and community composition (pyrosequencing) as well as their controlling soil properties were investigated in soil depth profiles along the 120,000 years old Franz Josef chronosequence (New Zealand). Additionally, in a microcosm incubation experiment the effects of particular soil properties, i.e., soil age, soil organic matter fraction (mineral-associated vs. particulate), O2 status, and carbon and phosphorus additions, on microbial abundances (quantitative PCR) and community patterns (T-RFLP) were analyzed. The archaeal to bacterial abundance ratio not only increased with soil depth but also with soil age along the chronosequence, coinciding with mineralogical changes and increasing phosphorus limitation. Results of the incubation experiment indicated that archaeal abundances were less impacted by the tested soil parameters compared to Bacteria suggesting that Archaea may better cope with mineral-induced substrate restrictions in subsoils and older soils. Instead, archaeal communities showed a soil age-related compositional shift with the Bathyarchaeota, that were frequently detected in nutrient-poor, low-energy environments, being dominant at the oldest site. However, bacterial communities remained stable with ongoing soil development. In contrast to the abundances, the archaeal compositional shift was associated with the mineralogical gradient. Our study revealed, that archaeal and bacterial communities in whole soil profiles are differently affected by long-term soil development with archaeal communities probably being better adapted to subsoil conditions, especially in nutrient-depleted old soils.

Volatilization of elemental mercury from fresh blast furnace sludge mixed with basic oxygen furnace sludge under different temperatures.

Blast furnace sludge (BFS) is a waste with elevated mercury (Hg) content due to enrichment during the production process of pig iron. To investigate the volatilization potential of Hg, fresh samples of BFS mixed with basic oxygen furnace sludge (BOFS; a residue of gas purification from steel making, processed simultaneously in the cleaning devices of BFS and hence mixed with BFS) were studied in sealed column experiments at different temperatures (15, 25, and 35 °C) for four weeks (total Hg: 0.178 mg kg(-1)). The systems were regularly flushed with ambient air (every 24 h for the first 100 h, followed by every 72 h) for 20 min at a flow rate of 0.25 ± 0.03 L min(-1) and elemental Hg vapor was trapped on gold coated sand. Volatilization was 0.276 ± 0.065 ng (x m: 0.284 ng) at 15 °C, 5.55 ± 2.83 ng (x m: 5.09 ng) at 25 °C, and 2.37 ± 0.514 ng (x m: 2.34 ng) at 35 °C. Surprisingly, Hg fluxes were lower at 35 than 25 °C. For all temperature variants, an elevated Hg flux was observed within the first 100 h followed by a decrease of volatilization thereafter. However, the background level of ambient air was not achieved at the end of the experiments indicating that BFS mixed with BOFS still possessed Hg volatilization potential.

Corrosion of high-level radioactive waste iron-canisters in contact with bentonite.

Several countries favor the encapsulation of high-level radioactive waste (HLRW) in iron or steel canisters surrounded by highly compacted bentonite. In the present study the corrosion of iron in contact with different bentonites was investigated. The corrosion product was a 1:1 Fe layer silicate already described in literature (sometimes referred to as berthierine). Seven exposition test series (60 °C, 5 months) showed slightly less corrosion for the Na-bentonites compared to the Ca-bentonites. Two independent exposition tests with iron pellets and 38 different bentonites clearly proved the role of the layer charge density of the swelling clay minerals (smectites). Bentonites with high charged smectites are less corrosive than bentonites dominated by low charged ones. The type of counterion is additionally important because it determines the density of the gel and hence the solid/liquid ratio at the contact to the canister. The present study proves that the integrity of the multibarrier-system is seriously affected by the choice of the bentonite buffer encasing the metal canisters in most of the concepts. In some tests the formation of a patina was observed consisting of Fe-silicate. Up to now it is not clear why and how the patina formed. It, however, may be relevant as a corrosion inhibitor.

Porosity and distribution of water in perlite from the island of Milos, Greece.

A perlite sample representative of an operating mine in Milos was investigated with respect to the type and spatial distribution of water. A set of different methods was used which finally provided a consistent view on the water at least in this perlite. Infrared spectroscopy showed the presence of different water species (molecular water and hydroxyl groups / strongly bound water). The presence of more than 0.5 mass% smectite, however, could be excluded considering the cation exchange capacity results. The dehydration measured by thermal analysis occurred over a wide range of temperatures hence confirming the infrared spectroscopical results. Both methods point to the existence of a continuous spectrum of water binding energies. The spatial distribution of water and/or pores was investigated using different methods (CT: computer tomography, FIB: scanning electron microscopy including focused ion beam technology, IRM: infrared microscopy). Computer tomography (CT) showed large macropores (20 - 100 µm) and additionally revealed a mottled microstructure of the silicate matrix with low density areas up to a few µm in diameter. Scanning electron microscopy (FIB) confirmed the presence of µm sized pores and IRM showed the filling of these pores with water. In summary, two types of pores were found. Airfilled 20 - 100 µm pores and µm-sized pores disseminated in the glass matrix containing at least some water. Porosity measurements indicate a total porosity of 26 Vol%, 11 Vol% corresponding to the µm-sized pores. It remains unsolved wether the water in the µm-sized pores entered after or throughout perlite formation. However, the pores are sealed and no indications of cracks were found which indicated a primary source of the water, i.e. water was probably entrapped by quenching of the lava. The water in these pores may be the main reason for the thermal expandability which results in the extraordinarily porous expanded perlite building materials.

Mercury in dumped blast furnace sludge.

Blast furnace sludge (BFS) is a waste generated in the production of pig iron and was dumped in sedimentation ponds. Sixty-five samples from seven BFS locations in Europe were investigated regarding the toxic element mercury (Hg) for the first time. The charge material of the blast furnace operations revealed Hg contents from 0.015 to 0.097mgkg(-1). In comparison, the Hg content of BFS varied between 0.006 and 20.8mgkg(-1) with a median of 1.63mgkg(-1), which indicates enrichment with Hg. For one site with a larger sample set (n=31), Hg showed a stronger correlation with the total non-calcareous carbon (C) including coke and graphite (r=0.695; n=31; p<0.001). It can be assumed that these C-rich compounds are hosting phases for Hg. The solubility of Hg was rather low and did not exceed 0.43% of total Hg. The correlation between the total Hg concentration and total amount of NH4NO3-soluble Hg was relatively poor (r=0.496; n=27; p=0.008) indicating varying hazard potentials of the different BFS. Finally, BFS is a mercury-containing waste and dumped BFS should be regarded as potentially mercury-contaminated sites.

Dioxins in primary kaolin and secondary kaolinitic clays.

Since 1996 dioxins have been repeatedly detected worldwide in Tertiary ball clays used as anticaking agent in the production of animal feed and a variety of other applications. The dioxins of these natural clays are very unlikely of anthropogenic source, but no model of dioxin enrichment has been established. A hypothetical model is presented which explains the highly variable dioxin loadings of the Tertiary kaolinitic clays by natural addition during clay-sedimentation. To prove this hypothesis, Tertiary primary nonsedimentary kaolin and sedimentary kaolinitic clays were collected at three profiles in Europe and analyzed for mineralogy, chemistry, organic carbon, and polychlorinated dibenzo-p-dioxins/-furans (PCDD/F). Primary kaolin, kaolinitic, and lignitic clays contained almost no PCDFs. PCDD concentration differed markedly between primary kaolin (3-91 pg/g) and secondary kaolinitic clay (711-45935 pg/g), respectively, lignitic clays (13513-1191120 pg/g). The dioxin loading of secondary kaolinitic and lignitic clays is approximately 10 to a few thousand times higher than in the primary kaolin or recent environmental settings. The dioxin concentrations decrease from octachlorodibenzo-p-dioxin to the tetrachlorodibenzo-p-dioxins and exhibit the "natural formation pattern". No correlation between PCDD/F concentration and bulk composition of clays was found. These findings support the hypothesis of the enrichment of dioxin in clays during sedimentation.

Chemical and mineralogical characterization of blast-furnace sludge from an abandoned landfill.

Blast-furnace sludge is generated during the production of pig iron and is disposed of in the environment in large surface landfills. We investigated blast-furnace sludge samples of an abandoned landfill in order to determine its chemical and mineralogical nature and to evaluate some environmental hazards that may arise from this industrial waste. The mineralogical inventory, which was quantified by Rietveld refinement of XRD analyses using the fundamental-parameter approach, revealed that blast-furnace sludge is dominated by X-ray amorphous substances (with a mean of 590 g kg(-1)) including coke and (hydr)oxides of Fe, Si, Al, Zn, and Pb. Calcite (CaCO3) (136 g kg(-1)), dolomite (Ca,Mg[CO3]2) (14 g kg(-1)), quartz (SiO2) (55 g kg(-1)), kaolinite (Al2[OH]4Si2O5) (40 g kg(-1)), graphite (C) (27 g kg(-1)), and chemically not specified layered double hydroxides (28 g kg(-1)) were identified in almost all samples. Iron is present as magnetite (Fe3O4) (34 g kg(-1)), hematite (Fe2O3) (38 g kg(-1)), wuestite (FeO) (20 g kg(-1)) and alpha-iron (Fe0) (6 g kg(-1)). Chemically, blast-furnace sludge is dominated by C (190 g kg(-1)) and Fe (158 g kg(-1)) reflecting the process of pig-iron production. On the basis of total contents, environmentally problematic metals (including As) are Zn (32.6 g kg(-1)), Pb (10.3 g kg(-1)), Cd (81 mg kg(-1)), and As (129 mg kg(-1)). As the forested landfill is used by residents for leisure activities, the exposure assessment by pathway oral uptake of blast-furnace sludge particles by humans has to be critically evaluated, particularly as significant proportions of metals are acid-soluble. However, under the prevailing slightly alkaline pH values of the sludge (pH 7.6-9.2), the solubility of the metals is very low as indicated by low pore water concentrations. Currently, groundwater monitoring should be focused mainly on F- since the F- concentrations in the pore water of blast-furnace sludge are at high level (2.65-24.1 mg of F- L(-1)).