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Historical disposal sites of red mud can be found all around Europe, most notably at Sardinia, in Hungary, or at many locations in East-Southeast Europe. Red mud contains dominantly iron, aluminum, and silicon oxides, with races of various metals and compounds that can still be reprocessed if appropriate methods are applied. Some of the promising methods include microorganisms, and in particular bacteria.The main objective of the study was to determine whether prolonged bacterial activity changes the geochemistry of the red mud. The bacteria for the experiment were isolated through several selective steps from activated sludge of wastewater treatment plant and red mud from three different locations: Dobro Selo and Zvornik (Bosnia and Herzegovina), and Almásfüzitő (Hungary).After successful isolation, the bacteria were applied to the homogenized red mud samples, with nutrient media and water added in different combinations and ratios. The experiment lasted for 6 months after the bacteria were first applied to the red mud samples. During this period, geochemical analyses of the red mud were carried out twice, after 4 weeks and after 24 weeks, while the analysis of bacterial survival and quantity in the red mud samples were carried after 4, 8, and 24 weeks. The goal of geochemical analyses was to determine whether the bacteria caused changes in the concentrations of the elements of interest in the red mud when used as cultivating substrate and whether the elements of interest became more available to the bacteria due to their growth and adaptation to the red mud.Prior to geochemical analysis, subsamples were heated at 100°C for 60 minutes to induce bacteriolysis and filtered twice with MiliQ water (red band filter paper). The eluates were stored in plastic cuvettes and kept in a dark place at 4°C until analysis (HR-ICP-MS). The filter papers containing the treated red mud were dried, sealed, and stored for further geochemical analysis of total major and trace element concentrations by ICP-MS and mineralogical (XRPD) analyses. Detailed results of the geochemical and mineralogical analyses are pending.This work has been supported by EIT Raw Materials project RIS-RESTORE, project number 19269. |
