57Fe Mössbauer Investigation of Naturally Pure α-FeOOH from the Sukinda Ochre

Fungal-induced modification of spontaneously precipitated ochreous sediments from drainage of abandoned antimony mine

Iron-containing spontaneously precipitated ochreous sediments serve as natural scavengers of various migrating elements and in this way contribute to removal and immobilization of potentially hazardous elements especially from mine drainage outflows. On the other hand, presence of filamentous fungi in their surroundings triggers biotransformation and contributes to the mobility of these elements. Three groups of samples of spontaneously precipitated ochreous sediments from an abandoned antimony mine in Poproč, Slovakia were studied: as-collected, sterilized at 95 °C for 30 min, and exposed to incubation with filamentous fungus Aspergillus niger which is frequently found in soils. Employing chemical analyses have determined the content of Fe, As, Sb, and Zn in the samples as well as their mobilization among the non-dissolved residue, culture medium of the fungus and/or its biomass. Significant degree of biovolatilization of antimony was unveiled. Speciation of iron was performed by ⁵⁷Fe Mössbauer spectroscopy performed in a wide temperature range 300-4.2 K and external magnetic field of 6 T. Hyperfine interactions between ⁵⁷Fe nuclei and their electronic shells have revealed superparamagnetic behavior characteristic for small particles. Their blocking temperatures of 46, 53, and 40 K, respectively, indicate a dependence of the size of the particles upon the sample treatment. While sterilization has supported their growth, incubation with fungus has changed their chemical environment and removed mainly bigger particles.