MOBILIZACE CHEMICKÝCH SLOŽEK STRUSKOVÉ DEPONIE V NÁRODNÍ PŘÍRODNÍ REZERVACI RUDICKÉ PROPADÁNÍ

The Rudice swallow hole (Rudicke propadani) National Nature Monument is a locality affected by occasional mass movements and landslides. During exceptional rainfall events, the slag material from the slopes of a small valley called “Ve struskach” (“In the Slags”) slides into an episodic stream, which enters the local karst system near the swallow hole of the Jedovnice Creek (Jedovnický potok). The slag was dumped in the locality in consequence of the past processing of iron ore in blast furnaces, which had been built near Jedovnice by the princely Salm family in the 19th century. Even though the blast furnaces were closed down a hundred years ago, the slag components leaking into the Rudice stream sink cave system still demonstrably damage the speleothems. This was the major impulse for us to have a closer look at the geochemical properties of the slag. The chemical composition was determined by silicate analyses carried out in the Institute of Geological Sciences at the Faculty of Sciences of the Masaryk University in Brno and in the ACME laboratories in Canada. The ACME laboratories determined heavy metal contents by atomic absorption spectroscopy (AAS) and by inductively coupled plasma mass spectrometry (ICP-MS). The petrographic characterization of the slag and its enclosures was conducted based on point analyses by a wavelength dispersive X ray (WDX) electron microprobe. Predictions regarding the geochemical behavior of the slag components in an aqueous environment were made using the sequential extraction analysis (SEA) according to Tessier (1979). We have found the expected spatial variability of the basic chemical composition of the slag dumps, as well as the presence of heavy metals (cadmium and especially zinc are present at high concentrations). The slag material exhibits a glassy amorphous structure containing occasional mineral crystals, droplets of pure or oxidized iron and fragments of other materials (such as charcoal or blast furnace bricks). The ongoing weathering of the slag is accompanied by oxidation of crude iron and formation of limonite. Apart from that, the material is not subject to signifi cant secondary transformations. The results of the sequential extraction analyses of slag and soil samples suggest that Cd and Zn are chemically bound to the “carbonate fraction”, which, in general, tends to dissolve under acidic conditions. Even though the environment of the carbonate rock cave systems is typically alkaline, there is a persisting risk of mobilization of heavy metals by acid soil solutions. From the environmental point of view, the slag deposition primarily represents a source of clastic material, which contaminates the cave system and damages speleothems by mechanical abrasion.