Abstract
The study attempted to map and predict the remobilization of metals in a floodplain which had been heavily affected by long-term Zn–Pb mining. This research, based on Zn, Cd, Pb, Ca and Fe speciation, mineralogy and the stratigraphy of sediments which had accumulated over the distance of a dozen or so km from the mine, revealed variable potential for metal mobilization. The results suggest that a drop in the water table, something to be expected after the closure of a mine, would be accompanied by a decrease in the pH of the river water and can induce the remobilization of metals associated with carbonates and exchangeable cations over the short-reach downstream of the mine. However, the mobilization of contaminants may be impeded by the alkaline, impermeable stratum of loams, which play a pivotal role in maintaining anaerobic conditions and buffering the acidity resulting from the partial degradation of sulfides. Based on the findings of the study, it can be expected that the intrinsic attenuation will limit the need for remediation works, although monitoring river water quality is recommended to determine the need for any intervention in cases where permissible quality values have been exceeded over a longer period. Results of this research can be useful as a reference for remediation works planned in other contaminated river systems experiencing water table lowering, where the mobilization of contaminants as a consequence of sediment oxidization can be expected.
Highlights
Metal mining generates contamination at both mine sites, where waste materials are stored in tailings and spoil heaps, as well as over longer distances from mines, when leachates or processing waters reach river systems [1,2]
The differences in the floodplain morphology of the Biała and the Biała Przemsza rivers result from the distinct deposition rate of waterborne sediment during the mining period in the second half of the 20th century
This research–based on Zn, Cd, Pb, Ca and Fe speciation, mineralogy and the stratigraphy of sediments which accumulated over the distance of a dozen or so km from the mine–revealed variable potential for metal mobilization
Summary
Metal mining generates contamination at both mine sites, where waste materials are stored in tailings and spoil heaps, as well as over longer distances from mines, when leachates or processing waters reach river systems [1,2]. Sulfide ore minerals, which are among the most commonly mined throughout the world, oxidize in contact with aerated waters, resulting in pH lowering and raising the content of sulfates and dissolved metals in the draining waters [4]. In such circumstances, pyrite weathering, resulting in acid mine drainage (AMD), is mainly responsible for the high mineralization of the receiving waters [5,6], but, in regions where carbonate lithology prevails, discharged neutral or alkaline waters can contain a high content of dissolved substances [7]. The fresh in-channel precipitates in alluvia and sediment-associated trace metals are relatively unstable and, during floods, they are eroded and mixed with parent rock material, eventually accumulating on river floodplains [3]
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