Abandoned Copper Pyrite Mines: Migration of Chemical Elements from the Acid Mine Water Discharge Zone to the Hydrographic Network

Abstract

The paper presents a study of river water pollution by acid mine drainage (AMD) in the Middle Urals, Russia. We analyzed the macro- and microcomponent contents of waters and bottom sediments in the area of the abandoned Levikha copper pyrite deposit (Middle Urals, Russia) and variations in these contents throughout the following chain: mine water discharge (acidic environment) - neutralization (alkaline environment) - clarification (acidic environment) - small river (weakly acidic environment) – discharge into the hydrographic network (circumneutral environment). The degree to which the waters at this nature-manmade object are in equilibrium with respect to minerals was assessed, which enabled us to identify secondary mineral formation processes, forms of metal migration in the water bodies, and their impact on the environment. At sampling points, Ca, Mg, Na, K, Fe(2+), and Mn were found to migrate in all media mainly in free form. In acidic and weakly alkaline media, Cu and Zn tend to migrate both in free form and in the form of sulfate complexes, while in strongly alkaline media - only in the form of hydroxyl complexes. Al migrates in a sulfate and, less often, hydroxide form. Acidic water is supersaturated with respect to the minerals of the oxide and oxide hydroxide groups. Strongly alkaline and weakly alkaline waters are supersaturated in the group of oxides, oxide hydroxides, hydroxides, and sulfates. The waters of all environments are close to equilibrium or are undersaturated with respect to gypsum; and undersaturated with respect to carbonates. The most intense processes of metal precipitation and sorption by bottom sediments occur in a circumneutral medium: the concentration ratio (CR) exceeds n*105 (L/kg) for Al, Fe, Cu, and Pb.