Environmental impact of the historical Cu smelting in the Rudawy Janowickie Mountains (south-western Poland)

Mining and smelting of Cu ores in the Rudawy Janowickie Mountains (southwestern Poland) from the 14th to the 16th century produced pyrometallurgical slags which currently form unconfined slag heaps in forests or are distributed within soils and streambeds. At present, the slag affected area has approximately 10 km2. Chemical and mineralogical analyses of the slags, slag-contaminated and slag-free soils and stream sediments are coupled with leaching experiments and speciation modeling to determine the environmental impact of historical smelting activities.Three subtypes of pyrometallurgical slags occur in the studied area: porous slag and two massive slags (equilibrated slag and undercooled slag) having different phase compositions. All of the studied slags still contain considerable amounts of metal(loid)s (up to 1.4 wt.% Cu, 1 wt.% Zn, 750 ppm Pb and 300 ppm As). A simple 24-hour laboratory slag-leaching experiment, using three different solutions (distilled water, stream water, citric acid solution), indicate the release of metal(loid)s under simulated natural conditions. Leachates from a stream water solution and distilled water contain lower concentrations of metal(loid)s (< 0.1% of total contaminant concentration in the solid) compared to leachates from a citric acid solution. Furthermore, leaching tests indicate that the release of the metal(loid)s is higher for porous slags than for those having a massive texture.Chemical analyses of soils, stream sediments and surface water indicate that some elements reach concentrations exceeding environmentally permissible standards (especially in soils: Cu up to 4000 ppm, Zn up to 1500 ppm, As up to 300 ppm, Pb up to 200 ppm). The impact of various sources of pollution including modern ones and those related to historical slag disposal was traced using Pb isotopes and indicate that the contamination by slag fragments and slag-derived metals is currently concentrated in soil B horizons and in river sediments. On the other hand, Pb isotopes and metal concentrations in soil O horizons are additionally affected by airborne contamination not related to the slag disposal.The most important factors controlling slag weathering and metal(loid) release include the following: (i) the textural characteristics and porosity of the slag material, (ii) the slag phase composition derived from the cooling rates of the slag melt and (iii) the environmental conditions (e.g., pH, organic matter content, etc.).

► Historical smelting-impacted areas may pose severe environmental risk.
► Long-term disposal of slags causes release of metal(loid)s.
► Factors controlling weathering and release of metal(loid)s from slags were determined.
► Texture and phase composition of slags control their weathering and element mobility.
► Low pH and high organic matter content increase slag weathering and element release.