Environmental aspects of the low-sulphide post-flotation tailings transformation into antrophogenic soil (Smolník, Slovakia)
An anthropogenic soil developed on the mine tailing impoundment in Smolník was studied to document a transformation of post flotation mud (tailings) to the soil. The tailing can be characterised as fine sand to silt grain size milled wall rock mineral matter composed by quartz, mica, chlorite, and siderite with low pyrite content. Surface of the tailing impoundment have been covered by a 10-15 cm thick layer of wood-waste material and forested by pine-plants. Two soil horizons A-topsoil (humus)
... and B-subsoil horizons have been recognised above the post flotation mud (tailings). Oxidation of pyrite and "acid" generation, leach and dissolution of the minerals and precipitation of iron oxy-hydroxides have been main processes beginning the tailings alteration. The processes were indicated by yellowish colours and raised homogeneity of the subsoil tailings. Variegated and relative high content of organic matter (TOC ≈ 3-15 wt. %), neutral to low acid pH (6.01-7.25), decreased amount of carbonates but a saturation with the bases (CEC: 20-80 mmol.100 g-1), especially with Ca 2+ characterised A horizon. Contents of 0.5 M HCl extractable fractions of Cu, Pb, Zn and As were locally higher as in the sub-soils, respective as in the tailings/substrate. There were favourable conditions to Fe oxide precipitation as indicated contents of oxalate extractable Fe oxide (Fe OX in range 1.3-6.1 wt. %) in the soil profile. Besides the iron oxide precipitation the remobilization of metals has been limited by other factors, mainly by organic matter accumulation and by humus formation which actively "aggregated" mineral particles in A horizon. Indicated mixed-layered vermiculite-chlorite or vermiculite-illite minerals formation also suggested a role of organic matter in the soil-pH decrease and primary phyllosilicates transformation. Soil-forming process was positively "accelerated" by fine-milled character and primary mineralogy (pyrite < 5 wt. %) of the tailings but also by horizontal morphology and favourable (wet and cold) climate, which have supported bio-production and organic matter accumulation. Nevertheless the ongoing migration of the potentially toxic elements from the waste/ substrate into the soil horizons must be evaluated as long term risk factor of the following soil development and suggested anthropogenic pollution and environmental instability of the mine tailings impoundment in the area.