Acid Generation and Heavy Metal Leachability from Lignite Spoil Heaps: Impact to the Topsoils of Oropos Basin, North Attica, Greece

The disposal of lignite spoil and tailings poses a major environmental problem in lignite mining sites which is associated with the oxidation of sulfide minerals contained in the primary ore. This process renders acidic effluents. Lignite mining in the Oropos Neogene basin, North Attica, Greece operated since the last century and ceased in the late 1960s. Piles of complex waste material are dispersed close to the mining sites. The high sulfur content and low Net Neutralization Potential, i.e. values < - 20 CaCO3 kg/t in most analyzed waste samples, indicate that the waste is prone to acid generation. The leachates (EN12457) from the lignite spoils showed high concentrations in Ni and Zn exceeding the EU regulatory limits for the non-hazardous wastes. GIS-based geochemical maps of the topsoil showed enrichment in Ni (Cr, V) associated with the regional geogenic enrichment but also local accumulation around the hot spot sites of lignite spoil heaps.

Automated summary

Disposal of lignite waste in mining sites results in environmental issues due to the oxidation of sulfide minerals, leading to acidic effluents. The lignite mining activities in Oropos Neogene basin, North Attica, Greece, have ceased, but the problem of dispersed waste material remains. High sulfur content and low net neutralization potential in the waste samples indicate a risk of acid generation, with leachates showing elevated Ni and Zn concentrations exceeding EU regulatory limits. Geochemical maps demonstrate enrichment in Ni (Cr, V) in topsoil, linked to both regional geogenic factors and local accumulation around lignite spoil heaps.