Impact of acid mine drainage from Tinoca Mine on the Abrilongo Dam (southeast Portugal)

This work presents a geochemical study conducted on the abandoned Tinoca Copper mine (southeast Portugal) to evaluate the potential hazard in surrounding areas particularly the effect on the Abrilongo River Dam which receives the acid waters from the mine watershed. The characterization of the area was performed over a period of 3 y and involved the study of waters, sediments and mine wastes. A sequential extraction methodology was conducted on the sediments and mine wastes and five elements were selected (Cu, Fe, Zn, Cd and Pb). The statistical and spatial analysis allowed the inference of the affinities between the chemical elements and specific mineralogical phases and to characterize chemical behaviour such as mobility and bioavailability. The results show that the distance to the source (mine-waste deposit), the point of zero charge, and the dynamics of the system are factors that control the behaviour of the elements studied. The acid drainage is characterized by an average pH of 2.5 and concentrations of copper 20 times greater than the legal limit for irrigation waters.