The effect of sub-zero temperatures on the oxidative leaching of elements from high-sulfide tailings

The large-scale spread of man-made objects such as tailings dams in areas where there are significant temperature drops, as well as global warming processes that lead to the opening of weathering profiles in the Arctic regions, necessitate knowledge about the patterns of oxidative leaching of potentially toxic elements and precious metals from the sulfide-bearing cyanidation wastes. The leaching and the migration ability of elements (Na, Mg, K, Ca, Al, Fe, Cu, Zn, As, Cd, Hg, Pb, Au, Ag) from high-sulfide cyanidation wastes under the influence of cryoprocesses using sulfide and oxide tailings of the Ursk tailing dump (Ursk settlement, Kemerovo region, Western Siberia, Russia) were studied. The laboratory experiments consist of the phased freezethaw cycles (from -20 °С to +25 °С) of the wastes, followed by the sampling of pore waters by squeezing using hydraulic press. pH and Eh were measured, and the contents of elements were determined in the obtained experimental pore waters. It was found that pore waters are formed during the experiments, which correspond to acid mine drainage in terms of geochemical characteristics and contents of potentially toxic elements. The intensity of oxidative leaching in freeze-thaw cycles is most active in two cases. The first is that continuous long-term freezing of a substance leads to a significant increase in the mineralization and content of elements in pore waters, compared with the contents in pore waters of the original non-frozen substance. The second is that the first stages of freeze-thaw cycles lead to a more intense leaching process than the subsequent stages. The degree of leaching decreases with each new cycle. It is assumed that the process of oxidative leaching in the oxide tailings is easier and more smooth, in contrast to the sulfide tailings due to the different species of sulfur in the wastes (sulfide species prevail in the sulfide tailings; sulfate species - in the oxide tailings). It is assumed that the processes occurring in the spring period at Ursk tailing dump contribute to more intense environmental pollution. There are quite frequent temperature fluctuations even during the day in the spring period, which can cause a pulsating influx of potentially toxic elements into the environment. The results obtained can be used as the basis for the development of new, modern methods of ensuring environmental safety (for example, thermal insulation covers) in the territories adjacent to such man-made objects.

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