Identification of geochemical processes controlling the neutralization of abandoned coal mine drainage using integration of geochemical modelling, geochemical analysis, and batch test: an example from the south of Bochum, Germany

Geochemical modelling, geochemical analysis, and batch extraction test were used to determine the geochemical processes controlling neutralization of the abandoned coal mine drainage of a Ruhr hard coal coalfield, presented in the south of Bochum. The geochemical modelling was performed on the surface water and the groundwater samples collected from the vicinity of the abandoned coal mines, while the geochemical analysis and the batch extraction test were performed on man-made materials, untreated soil samples, treated fertilized soil samples, and rock samples collected from the study area. The geochemical analysis, represented by pH and carbonate test, and the batch test aimed to classify the buffering systems existing in the study area, to identify the buffering level of each system, and to determine the potential sources and reactions controlling the buffering levels. Conversely, the geochemical modelling aimed to determine the source of the carbonate alkalinity. The results of experiments and methods used in this study showed that the neutralization of the abandoned coal mine drainage in this area is controlled by dissolution of carbonate minerals (calcite, aragonite, and dolomite), weathering of silicate and clay minerals, and redissolution of secondary minerals (hydroxides). Furthermore, the buffering systems in this area were divided into geogenic and anthropogenic. The anthropogenic buffering system includes the man-made materials and the treated fertilized soil covers, while the geogenic buffering system consists of the untreated soil cover, the hydroxides and the rock formations. The anthropogenic system has a buffering level of 5.6-11.71 identifying a highly effective short-lived buffer system, while the geogenic system has a buffer level of 4.01-7.17 identifying a moderately effective long-lived buffer system. The importance of this research is related to being a foundation that must be taken into account when making plans for the management of water in the coal mines that will be closed in the near future all over Germany.