Possibilities of Mine Wastes Bioleaching from Old Mining Burdens

Low-grade sulfidic mining wastes, in the form of heaps and tailings, are a negative impact of the active but mainly finished mining activity on ore deposits. They are subject to different natural chemical and biological transformation processes that result in the leaching of various toxic elements, primarily metals and metalloids into the soils and waters. However, these mining wastes also have a positive side. Although they contain low concentrations of elements, by applying appropriate methods they can be used as alternative raw materials sources of metals and metalloids, including critical metals. Several technologies are known for processing mining dumps and heaps. These include also the bioleaching by acidophilic iron- and sulfur-oxidizing bacteria and archaea. The focus of the paper was to conduct and evaluate preliminary bioleaching tests on solid mine wastes collected from the mine heap of an abandoned mining area, Zlatá Baňa, in the Slovak Republic. In the experiment, non-autochthonous and autochthonous bacterial cultures of Acidithiobacillus sp. were used. Bioleaching experiments were carried out under laboratory aerobic conditions at 30 °C. The acid sulfate media 9KA (without iron, tests at Conditions - 1) and 9K (complete medium, tests at Conditions - 2) were used. Pulp density was 4 %. Mine wastes were characterized by X-ray fluorescence analysis, FT-IR spectrometry, and XRD diffractometry. Concentrations of elements in leachates were analyzed using atomic absorption spectrometry and sulfate was analyzed using ion chromatography during bioleaching. The obtained results show that higher leaching of Fe, Al, Zn, and Ca was achieved with the application of the complete nutrient medium, and no difference in metal leaching was observed between the use of autochthonous and non-autochthonous bacterial cultures.