Peter Morgenstern

Sorption of aqueous antimony and arsenic species onto akaganeite.

Two akaganeite materials were tested for the removal of antimonate, trimethyl antimonate, arsenate, arsenite, and dimethyl arsenate from water: a commercial product (GEH) and a synthesized akaganeite. The two materials show similar q(max) values, but differ in their K(L) values. This could be a result of their different crystal sizes indicated by sharper XRD reflections of the synthesized akaganeite compared with GEH. Batch experiments were carried out using all species to investigate the influence of the pH on their sorption onto the commercial material. The best results for the removal of antimonate and arsenate were achieved under acidic conditions, while the sorption of arsenite has an optimum at pH 7. The maximum loadings vary from 450 mg g(-1) (antimonate at pH 2.2.) to 2 mg g(-1) (trimethyl antimonate at pH 7). Competition reactions (up to a 10-fold excess of the competitor ion) were studied with antimonate, arsenate, and phosphate. The sorption capacity of arsenate decreases up to 12.5% by adding phosphate (ratio 1:10), but the addition of antimonate did not influence the sorption of arsenate. Conversely, the sorption of antimonate decreases due to the addition of 10-fold concentration of arsenate (31%) or phosphate (27%).

Uptake of arsenite and arsenate by clinoptilolite-rich tuffs

Abstract Clinoptilolite-containing rocks were used to study the possible uptake of arsenite (H 3 AsO 3 ) and arsenate (H 2 AsO 4 − ) species from aqueous solution. Two samples also exhibited mordenite and erionite zeolitic phases. Batch and isotherm studies at pH 4 in the concentration range 0.1 −1 were performed. The experimental data were used to model Freundlich, Langmuir and Langmuir–Freundlich adsorption isotherms. Solutions were analyzed by means of ion chromatography coupled with inductively coupled plasma mass spectrometric detection (IC-ICP-MS). All zeolitic samples investigated removed more H 2 AsO 4 − than H 3 AsO 3 at equivalent arsenic concentrations. Although the saturation capacity of the tuffs studied was inversely related to the silicium dioxide content and directly to the iron content in the acid-washed zeolite, the addition of iron did not significantly improve the removal efficiency. Up to 98% of H 3 AsO 3 were removed from a 500 μg As l −1 solution by three of the samples studied after a contact time of 70 days.

In situ and ex situ study of the enhanced modification with iron of clinoptilolite-rich zeolitic tuff for arsenic sorption from aqueous solutions

Adsorption methods have been developed for the removal of arsenic from solution motivated by the adverse health effects of this naturally occurring element. Iron exchanged natural zeolites are promising materials for this application. In this study we introduced iron species into a clinoptilolite-rich zeolitic tuff by the liquid exchange method using different organic and inorganic iron salts after pretreatment with NaCl and quantified the iron content in all trials by XRF spectroscopy. The materials were characterized by XRD, FTIR, FTIR-DR, UV-vis, cyclic voltammetry, ESR and Mössbauer spectroscopies before and after adsorption of arsenite and arsenate. The reached iron load in the sample T+Fe was %Fe(2)O(3)-2.462, n(Fe)/n(Al)=0.19, n(Si)/n(Fe)=30.9 using FeCl(3), whereby the iron leachability was 0.1-0.2%. The introduced iron corresponded to four coordinated species with tetrahedral geometry, primarily low spin ferric iron adsorbing almost 12 mug g(-1) arsenite (99% removal) from a 360 mug(As(III)) L(-1) and 6 mug g(-1) arsenate from a 230 mug(As(V)) L(-1). Adsorption of arsenite and arsenate reached practically a plateau at n(Fe)/n(Si)=0.1 in the series of exchanged tuffs. The oxidation of arsenite to arsenate in the solution in contact with iron modified tuff during adsorption was observed by speciation. The reduction of ferric iron to ferrous iron could be detected in the electrochemical system comprising an iron-clinoptilolite impregnated electrode and was not observed in the dried tuff after adsorption.

Physical and chemical characterization of a complexly contaminated scrubber dust — a by-product of copper smelting in Sachsen-Anhalt, Germany

Abstract A physical and chemical description of a scrubber dust slurry, known as Theisenschlamm, is presented. This material is generated as a by-product during extraction of copper from a mineralized Permian black shale (Kupferschiefer) in Sachsen-Anhalt, Germany. The Theisenschlamm consists of sulphide grains which are a complex solid solution of Pb, Zn, Cu and Fe. The crystal structures are modified forms of galena and sphalerite/wurtzite. Variations in the X-ray diffraction peak positions of these minerals reflect the poorly developed lattice structures of these phases. Anglesite is a secondary phase. The Theisenschlamm contains 18% Zn and 14% Pb as well as significant concentrations of PAH, PCDD and other organic compounds, rare metals and radionuclides (e.g. 210 Po and 210 Pb). The original particles have a median diameter of 1.25 μm, however, these particles are themselves aggregates of still smaller particles, typically of submicron size.

Comparison of 24 h and long-term pHstat leaching tests for heavy metal mobilization from solid matrices

The dynamic leaching behaviour of environmentally relevant heavy metals makes it difficult to fix a suitable elution time of leaching tests. With ten different solid materials which were characterized by wavelength-dispersive X-ray fluorescence analysis and by the determination of aqua regia soluble amounts of heavy metals we performed 24 h and long-term leaching tests using the pHstat procedure at pH 4 to be able to compare the resulting acid neutralization capacities (ANC) and heavy metal mobilization. This comparison demonstrates firstly the limitations in predicting the extent of heavy metal release after a longer (geological) time period only from the leached amounts after 24 hours and the ratio of the ANC values measured in the 24 h test and in a long-term experiment, respectively. Secondly, the effect of elution time on the leachability is not uniform but element specific and matrix dependent. Hence, the pHstat leaching test performed in the usual manner does not seem to be suitable particularly for assessing long-term mobilization of heavy metals under acidic conditions. Additional experiments under variation of shaking frequency and time clearly demonstrate the dominant influence of the first parameter on the resulting ANC and support the necessity of further studies to optimize the pHstat leaching procedure before the test can be recommended in regulations for environmental protection. Vergleich von 24-h- und Langzeit-pHstat-Schutteltests zur Schwermetall-Mobilisierung aus festen Matrices Das dynamische Auslaugverhalten umweltrelevanter Schwermetalle macht es schwierig, eine geeignete Zeitdauer von Auslaugtests festzulegen. Mit zehn verschiedenen Feststoffen, die mittels wellenlangendispersiver Rontgenfluoreszenzanalyse und durch Bestimmung der konigswasserloslichen Schwermetallanteile charakterisiert wurden, haben wir 24-h- und Langzeit-Auslaugtests mit der pHstat-Prozedur bei pH = 4 durchgefuhrt, um die resultierenden Saureneutralisationskapazitaten (ANC) und die Mobilisierung der Schwermetalle vergleichen zu konnen. Dieser Vergleich zeigt erstens, das es nicht moglich ist, das Ausmas der Schwermetallfreisetzung nach langerer Kontaktzeit nur aus den ausgelaugten Mengen nach 24 Stunden und dem Verhaltnis der im 24-h- und Langzeit-Test gemessenen ANC-Werte vorherzusagen. Zweitens ist der Effekt der Elutionszeit auf die Auslaugbarkeit nicht einheitlich, sondern sehr elementspezifisch und matrixabhangig. Somit scheint der pHstat-Auslaugtest, in der ublichen Weise durchgefuhrt, wenig geeignet fur die Abschatzung der Langzeit-Mobilisierung von Schwermetallen unter sauren Bedingungen. Zusatzliche Experimente unter Variation der Schuttelfrequenz und Zeit zeigen klar den dominanten Einflus der ersteren auf die ermittelten ANC-Werte und unterstreichen die Notwendigkeit weiterer Untersuchungen zur Optimierung der pHstat-Auslaugprozedur, bevor diese fur das Regularium empfohlen werden kann.

Spatial variability of metal pollution in groyne fields of the Middle Elbe--implications for sediment monitoring.

High spatial heterogeneity of physical and chemical sediment properties was observed in both horizontal and vertical directions of deposits in a groyne field of the Middle Elbe. The respective sediment cores were less polluted on the top compared to consolidated deeper layers, indicating a decreasing trend of contamination in the river basin. In contrast to water quality monitoring, the impact of the large Elbe flood in 2002 was still visible in the deeper layers (5-30 cm) of the groyne field sediments six years after the event. Due to the fact that the environmental risk increases with erosion potential of discharge and contamination level of sediments, monitoring for environmental risk must capture not only surface sediments but also deeper layers up to an anticipated erosion depth.

Mobilization of Arsenic and Heavy Metals from Contaminated Sediments by Changing the Environmental Conditions

The solubility of arsenic (As) and heavy metals (Me) from two sediments with differing chemical characteristics and degrees of contamination was quantified by suspension leaching under both aerobic and anoxic conditions. Elemental sulphur (S°) was added as a substrate for the indigenous Thiobacillus spp. The objective of this study was to examine the effects of measures, which attempted to stimulate or to prevent the mobilization of the pollutants in the source material. By stimulating aerobic bioleaching with S°, up to 80% (660 mg/kg) of the As became soluble in a highly polluted lake sediment (Suesser See) in the form of arsenite and arsenate. Without the addition of S°, the As solubility ranged between 0.6 and 3.5 mg/kg. No toxic effects of As (III) on bacterial growth and microbial activity of the indigenous Thiobacillus spp. were observed. By comparison, the As solubility in an oxic sediment from the river Weisse Elster was low (max. 0.5 mg/kg), while the total Me solubility reached 60% (3.7 g/kg). The anaerobic leaching tests were performed under the conditions of a nitrogen atmosphere in a special vessel allowing the redox potential and the pH of the solution to be continuously recorded. In the lake sediment without adding S°, the As solubility increased temporarily; up to 9% of the total As became soluble, and As (III) was the dominant As soluble species (20 mg/kg). In the late leaching phase (-300 mV), the total soluble As decreased, and As (V) became the major soluble species (3.9 mg/kg). In the presence of S°, soluble As and Me were immobilized. The inhibition of As and Me release can be explained by fixation as insoluble sulphides, suggesting that immobilization was driven by dissimilatory sulphur reduction. The data indicate that the availability of oxidizable sulphur and the oxidation state of the polluted material play an important role in assessing the release of arsenic and heavy metals, including anaerobic conditions. Attention has to be paid to the maintaining of strong anaerobic conditions in sulphur-rich materials in order to prevent the mobilization of pollutants.

Toxic oxide deposits from the combustion of landfill gas and biogas

Oxide deposits found in combustion systems of landfill gas fired power stations contain relatively high concentrations of elements which form volatile species such as P, As, Sb and Sn. These deposits should be handled with care because of their potential toxicity. By contrast, deposits in biogas system engines were found to contain much lower levels of such elements. The enrichment of these elements can be attributed to a hypothetical multistage process. The elements form volatile species in the landfill body. They are selectively transported as part of the landfill gas into the gas-burning devices. Inside the burners, they are immobilized as nonvolatile oxides.

Behaviour of metalloids and metals from highly polluted soil samples when mobilized by water – Evaluation of static versus dynamic leaching

The mobilization behaviour of metalloids and metals when leached by water from highly polluted soil/sediment samples was studied using static and dynamic approaches employing batch methodology and rotating coiled columns (RCC), respectively. Increasing the solution-to-solid ratios during batch leaching resulted in different enhanced mobilization rates, which are element-specific and matrix-specific. When dynamic leaching is employed with continuous replacement of the eluent, a higher portion is mobilized than when using batch elution with an identical solid-to-water ratio. Using RCC the time-resolved leaching of the elements was monitored to demonstrate the leaching patterns. For the majority of elements a significant decrease could be shown in the mobilized portion of the elements with ongoing leaching process. The data were discussed targeted at solid liquid partitioning coefficients of the metal(loid)s. The capabilities in application of K(d) values was demonstrated for dynamic leaching which is relevant for environmental processes.

Oxidation treatment of a sulphide-bearing scrubber dust from the Mansfeld Region, Germany: Organic and inorganic phase changes and multi-element partition coefficients between liquid and solid phases

Abstract A low temperature oxidation process has been developed to separate Pb from Zn in a complexly contaminated scrubber dust. The material consists of approx. 50% galena (PbS) and sphalerite/wurtzite (ZnS), and also an amorphous component, a variety of different silicate and carbonate phases as well as naturally-occurring radionuclides and oil and grease. The two-stage process consists of a grinding stage followed by placing this material into a hydrogen peroxide solution. The resultant oxidation reaction is violently exothermic — the temperature rises spontaneously to approx. 96°C. The amount of solid phases remaining after completion of the reaction was reduced by approx. 40% and consisted largely of insoluble lead sulphate which retained the bulk of the radionuclides. Almost all of the zinc was placed into solution by this process as was the Cd, Re and Cu. The total PAH content of the original Theisenschlamm (468 ppm) was reduced to 11.25 ppm in the residual sediment and the PCDD/PCDF concentrations were reduced by approx. 40%. The radionuclides are almost totally concentrated in the solid phase. The method shows considerable promise as a separation technique for very fine-grained sulphide-bearing residues.