Reductive processes within lignite dumps—chance of a long-term natural attenuation process

At the lignite dump site Espenhain (East Germany) weathering zones with the typical phenomena of acid mine drainage (high salt content, increase of acidity and metal mobility) are obvious. Considerable amounts of Fe2+, SO42−, Ni, Zn and Al are dissolved there. To understand the distribution of the acidity potential and the dump water composition a geochemical fore field balance is essential. Therefore a thickness weighted balance of the important geochemical parameters was carried out. At the 50 year old southern part of the covering dump, beneath the weathering zone, anaerobic conditions are established and a sequence of microbial reductive processes occurs. This sequence reaches up to the sulphate reduction stage. Together with the subsequent iron sulphide precipitation this represents a natural attenuation process. For the East German lignite dumps further investigations should be carried out to determine process rates, to characterise boundary conditions and to develop technical methods to enhance the process.