Robert Möckel

Leaching of rare earth elements from fluorescent powder using the tea fungus Kombucha

In most modern technologies such as flat screens, highly effective magnets and lasers, as well as luminescence phosphors, Rare Earth Elements (REE) are used. Unfortunately no environmentally friendly recycling process exists so far. In comparison to other elements the interaction of microorganisms with REE has been studied to a less extent. However, as REE are ubiquitously present in nature it can be assumed that microorganisms play an important role in the biogeochemistry of REE. This study investigates the potential of organic acid-producing microbes for extracting REE from industrial waste. In Germany, 175 tons of fluorescent phosphor (FP) are collected per year as a distinct fraction from the recycling of compact fluorescent lamps. Because the FP contains about 10% of REE-oxides bound in the so-called triband dyes it is a readily accessible secondary resource of REE. Using the symbiotic mixed culture Kombucha, consisting of yeasts and acetic acid bacteria, REE were leached at a significant rate. The highest leaching-rates were observed in shake cultures using the entire Kombucha-consortium or its supernatant as leaching agent compared to experiments using the isolates Zygosaccharomyces lentus and Komagataeibacter hansenii as leaching organisms. During the cultivation, the pH decreased as a result of organic acid production (mainly acetic and gluconic acid). Thus, the underlying mechanism of the triband dye solubilisation is probably linked to the carboxyl-functionality or a proton excess. In accordance with the higher solubility of REE-oxides compared to REE-phosphates and -aluminates, the red dye Y2O3:Eu2+ containing relatively expensive REE was shown to be preferentially solubilized. These results show that it is possible to dissolve the REE-compounds of FP with the help of microbial processes. Moreover, they provide the basis for the development of an eco-friendly alternative to the currently applied methods that use strong inorganic acids or toxic chemicals.

Uranium and uranyl luminescence in agate/chalcedony

Abstract A systematic investigation of agates from different occurrences in Europe, Northern and Southern America reveals that macrocrystalline quartz and chalcedony within them have an unusually high uranium content. Whereas agates may contain >70 ppm of U, quartz from magmatic and metamorphic rocks as well as pegmatite quartz commonly exhibit U concentrations at sub-ppm levels. Spatially resolved trace-element analyses by laser ablation inductively coupled plasma mass spectrometry show that the distribution of U within the agate samples is heterogeneous and coincides with the structural banding. The results indicate that U is incorporated into agate as uranyl ions. These ions, which are bound to the silica surface, are interpreted to originate from the parallel accumulation of Si and U by alteration processes of surrounding host rocks during agate formation. The uranyl ion is the cause of greenish photoluminescence (PL) in agate, which can only be excited by short wavelengths (<300 nm). The green PL is due to the electron transition from an excited to a ground state of the uranyl ion and is shown by a typical emission line at ~500 nm accompanied by several equidistant lines. These are due to the harmonic vibration of oxygen atoms along the uranyl axis. Luminescence can be detected in samples with a U content down to the 1 ppm level.

Electron Probe Microanalysis of REE in Eudialyte Group Minerals: Challenges and Solutions

Accurate quantification of the chemical composition of eudialyte group minerals (EGM) with the electron probe microanalyzer is complicated by both mineralogical and X-ray-specific challenges. These include structural and chemical variability, mutual interferences of X-ray lines, in particular of the rare earth elements, diffusive volatility of light anions and cations, and instability of EGM under the electron beam. A novel analytical approach has been developed to overcome these analytical challenges. The effect of diffusive volatility and beam damage is shown to be minimal when a square of 20×20 µm is scanned with a beam diameter of 6 µm at the fastest possible speed, while measuring elements critical to electron beam exposure early in the measurement sequence. Appropriate reference materials are selected for calibration considering their volatile content and composition, and supplementary offline overlap correction is performed using individual calibration factors. Preliminary results indicate good agreement with data from laser ablation inductively coupled plasma mass spectrometry demonstrating that a quantitative mineral chemical analysis of EGM by electron probe microanalysis is possible once all the parameters mentioned above are accounted for.

Drone-Borne Hyperspectral Monitoring of Acid Mine Drainage: An Example from the Sokolov Lignite District

This contribution explores the potential of unmanned aerial systems (UAS) to monitor areas affected by acid mine drainage (AMD). AMD is an environmental phenomenon that usually develops in the vicinity of mining operations or in post-mining landscapes. The investigated area covers a re-cultivated tailing in the Sokolov lignite district of the Czech Republic. A high abundance of AMD minerals occurs in a confined space of the selected test site and illustrates potential environmental issues. The mine waste material contains pyrite and its consecutive weathering products, mainly iron hydroxides and oxides. These affect the natural pH values of the Earth’s surface. Prior research done in this area relies on satellite and airborne data, and our approach focuses on lightweight drone systems that enables rapid deployment for field campaigns and consequently-repeated surveys. High spatial image resolutions and precise target determination are additional advantages. Four field and flight campaigns were conducted from April to September 2016. For validation, the waste heap was probed in situ for pH, X-ray fluorescence (XRF), and reflectance spectrometry. Ground truth was achieved by collecting samples that were characterized for pH, X-ray diffraction, and XRF in laboratory conditions. Hyperspectral data were processed and corrected for atmospheric, topographic, and illumination effects using accurate digital elevation models (DEMs). High-resolution point clouds and DEMs were built from drone-borne RGB data using structure-from-motion multi-view-stereo photogrammetry. The supervised classification of hyperspectral image (HSI) data suggests the presence of jarosite and goethite minerals associated with the acidic environmental conditions (pH range 2.3–2.8 in situ). We identified specific iron absorption bands in the UAS-HSI data. These features were confirmed by ground-truth spectroscopy. The distribution of in situ pH data validates the UAS-based mineral classification results. Evaluation of the applied methods demonstrates that drone surveying is a fast, non-invasive, inexpensive technique for multi-temporal environmental monitoring of post-mining landscapes.

Feldspar flotation as a quartz-purification method in cosmogenic nuclide dating: A case study of fluvial sediments from the Pamir

Graphical abstract

Major and trace element geochemistry of the European Kupferschiefer – an evaluation of analytical techniques

Simple and rapid techniques are needed for routine quantitative chemical bulk-rock analyses of Kupferschiefer, a black shale containing variable amounts of silicates, base metal sulphides, carbonates and an organic content of up to 30 weight percent. In this study, WD-XRF, TXRF, and ICP-OES of acid- as well as peroxide-digested samples were tested as potential techniques based on their availability and adaptability to analyse major (Si, Ti, Al, Mg, Ca, Fe, K, but also Cu, Zn, Pb) and selected trace (Ag, As, Ba, Co, Mo, Ni, V) element concentrations. Because of the absence of a suitable reference material, a comparative study was undertaken using instrumental neutron activation analysis to ascertain the accuracy of different approaches. Our results suggest that data from ICP-OES were much higher in accuracy compared to INAA than those from WD-XRF and TXRF, independent of the digestion procedure. The choice of digestion procedure is reflected in low detection limits but an underestimation of Cu, Ag, Co, and V concentrations reported by ICP-OES relative to those obtained by INAA in the case of acid digestion and increased detection limits coupled with a loss of over 25% Ag relative to INAA for peroxide digestion. Supplementary material: Geochemical data, list of irradiation times and measured isotopes can be found at https://doi.org/10.6084/m9.figshare.c.4015507