XAS study of acid rock drainage samples from an abandoned Zn-Pb-Ag mine at Freiberg, Germany

Ore crystals in clay play a key role in the sulfide oxidation and water mineralization process in abandoned ore mines. Highly mineralized, red-colored solutions are formed by the weathering of the ore particles which causes acid rock drainage (ARD). Major cationic components (>1 g/l) of the ARD solution under study were Zn, Fe, Mg, Al, and Mn. Important minor components were toxic and heavy metals, e.g., As, Cu, Pb, and Cd. This XAS investigation deals with the in-situ characterization of the near-order surrounding of As in ARD solutions containing colloidal particles as well as with the determination of the particle mineralogy. The atomic surrounding of Fe and As in ARD samples is compared to those found in model compounds. The arsenate seems to be bound to the colloids (iron hydroxy sulfate) in a way similar to that of arsenate binding onto ferrihydrite. The presented study is an example for the broad application of XAS techniques to environmental research.