Historical ferrous slag induces modern environmental problems in the Moravian Karst (Czech Republic)
Ferrous slag produced by a historic smelter is washed from the heap and transported by a creek through the cave system. There is concern that the slag fills cave spaces, abrades cave walls / calcite speleothems, and contaminates the aquatic environment with heavy metals and other toxic components. The study objectives were to better characterize the slag in its deposition site, map its transport through the cave system, characterize the effect of slag transport, and to judge the risks to both cave and aqueous environments. The study was based on methods of chemical and phase analysis supported laboratory experiments and geochemical modeling. The slag in the heap was dominated by amorphous glass phase (66 to 99 wt%) with mean composition of 49.8±2.8 wt% SiO2, 29.9±1.6 wt% CaO, 13.4±1.2 wt% Al2O3., 2.7±0.3 wt% K2O and 1.2±0.1 wt% MgO. Minerals such as melilite, plagioclase, anorthite, and wollastonite / pseudowollastonite with smaller amounts of quartz, cristobalite, and calcite were detected. Slag trace elements formally enrich the cave environment with Se, As, W, Y, U, Be, Cs, Sc, Cd, Hf, Ba, Th, Cr, Zr, Zn, and V. However, only Zr, V, Co, and As exceed specified limits for soils (US EPA and EU limits). The life of a 1 mm3 volume of slag was estimated to be 27,000 years. The mean residence time of the slag in the cave defined by the flood frequency was 47 years. The main conclusion was that the extent of slag weathering is small and that the slag does not contaminate the cave aqueous environment under given conditions. However, the slag enriched in U / Th can increase radon production as a result of alpha decay. The slag has an abrasive effect on surrounding rocks and disintegrated slag can contaminate calcite speleothems.
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