Microbially-mediated mineralization processes in acid mine drainage systems: Influence on metal removal

Abstract

This doctoral dissertation has addressed a detailed investigation of the precipitation of mineral phases by biomineralization and bio-induced mineralization processes in different acidic sub-environments affected by acidic mine drainage and the control exerted on the biogeochemical cycling of dissolved metals. This included acidic pit lakes and acidic stream from Huelva (Filón Centro, Guadiana, Cueva de la Mora, Tintillo) and Murcia (Brunita) provinces (Spain) and derived incubation column experiments. The results showed a direct link between the bacterial sulfate reduction and the amelioration of extreme conditions (e.g., low pH (1.9-4.5), high ionic strength and high dissolved sulfur and metals), mainly conditioned by the availability of organic carbon. The increase of pH triggered the precipitation of Fe and Al (oxy)hydroxysulfates and oxyhydroxides, (proto)phyllosilicates (gel-like allophane-like and well-developed aggregates) and transformation of the detrital clay minerals (enrichment of chlorite and illite with depth). The combination of biogenic H2S with dissolved metals lead to the precipitation of Zn (wurtzite), Cu (covellite, chalcocite), Cu-Fe (chalcopyrite), Fe (marcasite, pyrite, pyrrhotite), As (orpiment) and Pb (galena) sulfides. The highly reductive environment in Brunita simulated medium was linked to the precipitation of native Cu. The microscopic techniques showed that these mineral phases (most remarkably chalcopyrite and native sulfur) were closely associated to the cell membranes. Ferrous iron concentration was commonly detected intracellularly by cryo-TXM, in addition to Zn- and P-rich granules. It also showed the generalized formation of vacuole-like microcompartments and intracellular dense bodies in the microbial cells