2020-08-22, Viacava, Karen, Ammann, Erik, Lenz, Markus

Selenium nanoparticles (SeNPs) have been suggested for various applications such as food, animal feed, and biomedicine. However, thus far, wet chemical synthesis cannot produce sufficient quantities of SeNPs at the required quality. In this study, reactive aerosol processing is employed to produce SeNPs as powder concentrates of 2.2 to 4.0% (dry weight basis) on the scale of hundreds of kilograms. Citric acid is the most efficient organic precursor (92.5% SeNPs), but polydisperse particles are obtained, and some unknown dissolved Se species are present in the final product. Glycine is less efficient (82.2% SeNPs); however, monodisperse nanoparticles (153 nm; D90 = 215 nm) are obtained, with selenite being the only residue in the final product. The obtained particles consisted of X-ray amorphous (i.e., not diffracting) Se, since no elemental Se allotrope or other solid Se phases were indicated in X-ray diffraction. Reactive aerosol processing involves a limited number of preparation steps (i.e., dissolution and atomization), uses only food-/feed-approved ingredients (selenite, citric acid, glycine) and allows continuous operation and zero waste generation. This makes reactive aerosol processing ideal for the large-scale production of SeNPs.

2016, Rajpert, Liwia, Kolvenbach, Boris, Ammann, Erik, Hockmann, Kerstin, Nachtegaal, Maarten, Eiche, Elisabeth, Schäffer, Andreas, Corvini, Philippe, Sklodowska, Aleksandra, Lenz, Markus

Concentrations of soil arsenic (As) in the vicinity of the former Złoty Stok gold mine (Lower Silesia, southwest Poland) exceed 1000 μg g–1 in the area, posing an inherent threat to neighboring bodies of water. This study investigated continuous As mobilization under reducing conditions for more than 3 months. In particular, the capacity of autochthonic microflora that live on natural organic matter as the sole carbon/electron source for mobilizing As was assessed. A biphasic mobilization of As was observed. In the first two months, As mobilization was mainly conferred by Mn dissolution despite the prevalence of Fe (0.1 wt % vs 5.4 for Mn and Fe, respectively) as indicated by multiple regression analysis. Thereafter, the sudden increase in aqueous As[III] (up to 2400 μg L–1) was attributed to an almost quintupling of the autochthonic dissimilatory As-reducing community (quantitative polymerase chain reaction). The aqueous speciation influenced by microbial activity led to a reduction of solid phase As species (X-ray absorption fine structure spectroscopy) and a change in the elemental composition of As hotspots (micro X-ray fluorescence mapping). The depletion of most natural dissolved organic matter and the fact that an extensive mobilization of As[III] occurred after two months raises concerns about the long-term stability of historically As-contaminated sites.