Kurt Barmettler

Experimental determination of colloid deposition rates and collision efficiencies in natural porous media

Mobile colloids in groundwater aquifers and soils can serve as carriers for strongly sorbing contaminants and thereby facilitate contaminant transport. Therefore mobile colloids may have to be considered in modeling the fate of strongly sorbing contaminants in subsurface environments. In this study we present a Chromatographic short-pulse technique for measuring colloid deposition rate coefficients and experimental collision efficiencies in natural porous media. The method was evaluated using four different experimental systems of increasing complexity. Short pulses (equivalent to 0.002 to 0.03 pore volumes) of latex or humic-coated hematite suspensions were injected under saturated flow conditions into laboratory columns packed with glass beads, soil, or aquifer materials. Colloid breakthrough curves were measured on-line using fluorescence and UVVIS spectrophotometers. Deposition rate coefficients determined with the short-pulse method were in excellent agreement with results from step-input experiments. Experiments with different flow rates and column dimensions showed that colloid deposition generally followed a first-order kinetic rate law. On the basis of experimental fast deposition rates, collision efficiencies for colloid deposition can be calculated. The results demonstrate that the short-pulse method can be used very efficiently for studying the effects of solution chemistry and flow velocity on the kinetics of colloid deposition in natural porous media. The short-pulse method has several advantages over the more traditionally used step-input experiment and allows running several experiments on a single column without significant blocking or filter ripening effects.

Release and transport of colloidal particles in natural porous media: 2. Experimental results and effects of ligands

We present an extensive experimental data set of particle release from natural porous media saturated with monovalent cations. The generation process of mobile colloidal particles is studied by means of leaching of saturated laboratory columns packed with a noncalcareous soil material with various monovalent electrolytes and by analyzing the colloids in the effluent over typically 1000 pore volumes. The concentration of released particles cannot be modeled with simple first-order kinetics but can be rationalized in terms of a distribution of release rate coefficients k. The experimentally observed effluent concentration often decays with time as a power law c ∝ t−(α+l) for long times, suggesting a distribution of release rate coefficients p(k) ∝ kα−1 for small k. The observed values of exponent α range between 0.01 and 0.8. The composition of the pore water is found to have a profound influence on the particle release characteristics. With decreasing salt concentration the rate for particle release increases. Anionic organic and inorganic ligands have a major effect on the release process. For the ligands studied, the amount of released particles decreases in the sequence malonate, chloride, phtalate, and azide.

Zinc Fractionation in Contaminated Soils by Sequential and Single Extractions : Influence of Soil Properties and Zinc Content

We studied the fractionation of zinc (Zn) in 49 contaminated soils as influenced by Zn content and soil properties using a seven-step sequential extraction procedure (F1: NH4NO3; F2: NH4-acetate, pH 6; F3: NH3OHCl, pH 6; F4: NH4-EDTA, pH 4.6; F5: NH4-oxalate, pH 3; F6: NH4-oxalate/ascorbic acid, pH 3; F7: residual). The soils had developed from different geologic materials and covered a wide range in soil pH (4.0-7.3), organic C content (9.3-102 g kg(-1)), and clay content (38-451 g kg(-1)). Input of aqueous Zn with runoff water from electricity towers during 26 to 74 yr resulted in total soil Zn contents of 3.8 to 460 mmol kg(-1). In acidic soils (n = 24; pH <6.0), Zn was mainly found in the mobile fraction (F1) and the last two fractions (F6 and F7). In neutral soils (n = 25; pH > or =6.0), most Zn was extracted in the mobilizable fraction (F2) and the intermediate fractions (F4 and F5). The extractability of Zn increased with increasing Zn contamination of the soils. The sum of mobile (F1) and mobilizable (F2) Zn was independent of soil pH, the ratio of Zn in F1 over F1+F2 plotted against soil pH, exhibited the typical shape of a pH sorption edge and markedly increased from pH 6 to pH 5, reflecting the increasing lability of mobilizable Zn with decreasing soil pH. In conclusion, the extractability of Zn from soils contaminated with aqueous Zn after decades of aging under field conditions systematically varied with soil pH and Zn content. The same trends are expected to apply to aqueous Zn released from decomposing Zn-bearing contaminants, such as sewage sludge or smelter slag. The systematic trends in Zn fractionation with varying soil pH and Zn content indicate the paramount effect of these two factors on molecular scale Zn speciation. Further research is required to characterize the link between the fractionation and speciation of Zn and to determine how Zn loading and soil physicochemical properties affect Zn speciation in soils.

Time-dependent changes of zinc speciation in four soils contaminated with zincite or sphalerite.

The long-term speciation of Zn in contaminated soils is strongly influenced by soil pH, clay, and organic matter content as well as Zn loading. In addition, the type of Zn-bearing contaminant entering the soil may influence the subsequent formation of pedogenic Zn species, but systematic studies on such effects are currently lacking. We therefore conducted a soil incubation study in which four soils, ranging from strongly acidic to calcareous, were spiked with 2000 mg/kg Zn using either ZnO (zincite) or ZnS (sphalerite) as the contamination source. The soils were incubated under aerated conditions in moist state for up to four years. The extractability and speciation of Zn were assessed after one, two, and four years using extractions with 0.01 M CaCl(2) and Zn K-edge X-ray absorption fine structure (XAFS) spectroscopy, respectively. After four years, more than 90% of the added ZnO were dissolved in all soils, with the fastest dissolution occurring in the acidic soils. Contamination with ZnO favored the formation of Zn-bearing layered double hydroxides (LDH), even in acidic soils, and to a lesser degree Zn-phyllosilicates and adsorbed Zn species. This was explained by locally elevated pH and high Zn concentrations around dissolving ZnO particles. Except for the calcareous soil, ZnS dissolved more slowly than ZnO, reaching only 26 to 75% of the added ZnS after four years. ZnS dissolved more slowly in the two acidic soils than in the near-neutral and the calcareous soil. Also, the resulting Zn speciation was markedly different between these two pairs of soils: Whereas Zn bound to hydroxy-interlayered clay minerals (HIM) and octahedrally coordinated Zn sorption complexes prevailed in the two acidic soils, Zn speciation in the neutral and the calcareous soil was dominated by Zn-LDH and tetrahedrally coordinated inner-sphere Zn complexes. Our results show that the type of Zn-bearing contaminant phase can have a significant influence on the formation of pedogenic Zn species in soils. Important factors include the rate of Zn release from the contaminant phases and effects of the contaminant phase on bulk soil properties and on local chemical conditions around weathering contaminant particles.

Cation transport in natural porous media on laboratory scale: multicomponent effects

Abstract Multicomponent transport experiments were performed with four major cations, Na + , K + , Ca 2+ and Mg 2+ , in laboratory columns packed with a non-calcereous soil. The breakthrough curves are explained quantitatively with a box model including cation exchange. We use a single set of selectivity coefficients, an independently verified value of the cation-exchange capacity (CEC), and an adjusted value of the Peclet number. This Peclet number is smaller than the value determined from independent tracer experiments. The model is able to predict all experimentally observed breakthrough curves quite well. The selectivity coefficients determined from binary exchange experiments prove unreliable for the prediction of multicomponent experiments. We propose to estimate the selectivity coefficients by directly fitting the multicomponent breakthrough curves. Their shape is a very sensitive function of the values of these coefficients. Concepts from non-linear chromatography can be used in order to interpret several qualitative features of the breakthrough curves.

Speciation of Zn in blast furnace sludge from former sedimentation ponds using synchrotron X-ray diffraction, fluorescence, and absorption spectroscopy.

Blast furnace sludge (BFS), an industrial waste generated in pig iron production, typically contains high contents of iron and various trace metals of environmental concern, including Zn, Pb, and Cd. The chemical speciation of these metals in BFS is largely unknown. Here, we used a combination of synchrotron X-ray diffraction, micro-X-ray fluorescence, and X-ray absorption spectroscopy at the Zn K-edge for solid-phase Zn speciation in 12 BFS samples collected on a former BFS sedimentation pond site. Additionally, one fresh BFS was analyzed for comparison. We identified five major types of Zn species in the BFS, which occurred in variable amounts: (1) Zn in the octahedral sheets of phyllosilicates, (2) Zn sulfide minerals (ZnS, sphalerite, or wurtzite), (3) Zn in a KZn-ferrocyanide phase (K(2)Zn(3)[Fe(CN)(6)](2)·9H(2)O), (4) hydrozincite (Zn(5)(OH)(6)(CO(3))(2)), and (5) tetrahedrally coordinated adsorbed Zn. The minerals franklinite (ZnFe(2)O(4)) and smithsonite (ZnCO(3)) were not detected, and zincite (ZnO) was detected only in traces. The contents of ZnS were positively correlated with the total S contents of the BFS. Similarly, the abundance of the KZn-ferrocyanide phase was closely correlated with the total CN contents, with the stoichiometry suggesting this as the main cyanide phase. This study provides the first quantitative Zn speciation in BFS deposits, which is of great relevance for environmental risk assessment, the development of new methods for recovering Zn and Fe from BFS, and potential applications of BFS as sorbent materials in wastewater treatment.

Isolation and purification of Cu-free methanobactin from Methylosinus trichosporium OB3b

BackgroundThe isolation of highly pure copper-free methanobactin is a prerequisite for the investigation of the biogeochemical functions of this chalkophore molecule produced by methane oxidizing bacteria. Here, we report a purification method for methanobactin from Methylosinus trichosporium OB3b cultures based on reversed-phase HPLC fractionation used in combination with a previously reported resin extraction. HPLC eluent fractions of the resin extracted product were collected and characterized with UV-vis, FT-IR, and C-1s NEXAFS spectroscopy, as well as with elemental analysis and ESI-MS.ResultsThe results showed that numerous compounds other than methanobactin were present in the isolate obtained with resin extraction. Molar C/N ratios, mass spectrometry measurements, and UV-vis spectra indicated that methanobactin was only present in one of the HPLC fractions. On a mass basis, methanobactin carbon contributed only 32% to the total organic carbon isolated with resin extraction. Our spectroscopic results implied that besides methanobactin, the organic compounds in the resin extract comprised breakdown products of methanobactin as well as polysaccharide-like substances.ConclusionOur results demonstrate that a purification step is indispensable in addition to resin extraction in order to obtain pure methanobactin. The proposed HPLC purification procedure is suitable for semi-preparative work and provides copper-free methanobactin.

Colloid Facilitated Transport in Natural Porous Media: Fundamental Phenomena and Modelling

Reactive transport phenomena, in particular, the transport of contaminants, are of fundamental interest in environmental sciences. The presence of hazardous chemicals in the subsurface environment has become an important driving force to develop reactive transport models capable to predict their fate (Dagan 1989; Jury and Roth 1990; Sardin et al. 1991; Knox et al. 1993; Appelo and Postma 1996; Lichtner et al. 1996). These models represent the natural porous medium as two types of phases: (i) immobile solid phases and (ii) mobile liquid (and/or gaseous) phases. Depending on the affinity to the respective phases, chemical species distribute between the different phases and the corresponding phase boundaries. Accordingly, the transport of chemicals is dictated by partitioning of the mobile dissolved species and the stationary species adsorbed to the solid phase. Distribution into the solid phases and interfacial reactions result in a reduction of the dissolved contaminant concentrations in the liquid phase, and accordingly in a slow-down of the contaminant spreading.

Organomineralization processes in freshwater stromatolites: a living example from eastern Patagonia

Living stromatolites have been mostly described within shallow marine and (hyper)saline lacustrine environments. Southernmost South America lacks detailed investigations of these (organo)sedimentary buildups, particularly in regions experiencing extreme and variable environmental conditions. Here, we report and describe living freshwater stromatolites in the Maquinchao region, north‐western Patagonia, Argentina. Fossil stromatolites characterized by globular and cauliflower shapes are also present in a continuous palaeoshoreline of a former lake at an altitude of 830 m, whereas their living counterparts only occur in the calm waters of sheltered or meandering sections of the Maquinchao River. The living stromatolites and their host waters have been sampled and studied using various chemical and microscopic techniques to better constrain the environmental versus biological factors controlling their development. Our results indicate that today stromatolites only proliferate in freshwater when Ca2+ levels are high. A microscopic inspection of the living stromatolite mat indicates stronger photosynthetic activity in the upper green layer associated with crypto/microcrystalline calcite (nanoglobules) compared to the lower beige‐white biofilm. This biofilm contains more low‐Mg calcite (rhombohedra) precipitates, which can form millimetre‐sized aggregates in the underlying anoxic layer. Although sulphate‐reducing bacteria are living in the entire mat, they appear more abundant and widely distributed in the lower beige‐white layer and are always associated with Mg calcite. Low salinity and low‐turbidity water along with microbial (photosynthetic and heterotrophic) activity are the most important factors promoting low‐Mg calcite precipitation in the Maquinchao Basin. These conditions are very different from those proposed for recently described lacustrine stromatolites at high altitude in the subtropical and tropical Andes as well as in Chilean Patagonia. Hence, all these observations in modern freshwater stromatolites show the importance of geomicrobiological studies in identifying proxies of the hydrological conditions prevailing during their formation.

Speciation and Mobility of Mercury in Soils Contaminated by Legacy Emissions from a Chemical Factory in the Rhône Valley in Canton of Valais, Switzerland

Legacy contamination of soils and sediments with mercury (Hg) can pose serious threats to the environment and to human health. Assessing risks and possible remediation strategies must consider the chemical forms of Hg, as different Hg species exhibit vastly different environmental behaviors and toxicities. Here, we present a study on Hg speciation and potential mobility in sediments from a chemical factory site, and soils from nearby settlement areas in the canton of Valais, Switzerland. Total Hg ranged from 0.5 to 28.4 mg/kg in the soils, and 3.5 to 174.7 mg/kg in the sediments, respectively. Elemental Hg(0) was not detectable in the soils by thermal desorption analysis. Methylmercury, the most toxic form of Hg, was present at low levels in all soils (<0.010 mg/kg; <0.8% of total Hg). Sequential extractions and thermal desorption analyses suggested that most of the Hg in the soils was present as “matrix-bound Hg(II)”, most likely associated with soil organic matter. For factory sediments, which contained less organic matter, the results suggested a higher fraction of sulfide-bound Hg. Batch extractions in different CaCl2 solutions revealed that Hg solubility was low overall, and there was no Hg-mobilizing effects of Ca2+ or Cl− in solution. Only in some of the factory sediments did high CaCl2 concentrations result in increased extractability of Hg, due to the formation of Hg-chloride complexes. Additional experiments with soil redox reactors showed that even mildly reducing conditions led to a sharp release of Hg into solution, which may be highly relevant in soils that are prone to periodic water saturation of flooding.