Geochemical behavior of potentially toxic elements in riverbank-deposited weathered tailings and their environmental effects: Weathering of pyrite and manganese pyroxene

Uncontrolled management of mine tailings can cause serious environmental problems. Red and black deposits of weathered mine tailings are observed in the upstream of the Nakdong River in Korea, washed away from abandoned mines during floods. Herein, the geochemical and mineralogical changes that occur during weathering of these deposited mine tailings and the mobility of resulting potentially toxic elements were investigated. Primarily, johansennite (manganese pyroxene) was identified in the deposits. Goethite and jarosite were identified as secondary minerals in the red or brown layers. Manganese oxide (MnO) formed by the weathering of johansennite in the black layers and schwertmannite in the red and brown layers were also identified via energy-dispersive X-ray spectroscopy. The three most abundant potentially toxic elements in the residual and iron and manganese oxide fractions were Zn, Pb and As. The high percentage of potentially toxic elements in these oxide fractions indicated that the weathering products of pyrite and manganese pyroxene were crucial in fixing these elements, and MnO likely played an important role in controlling the behavior of heavy metals. In addition, metals were detected in significant concentrations in the exchangeable and carbonate-bound fractions, which can be toxic to the river’s ecological system.