Effect of elevated pressure on ferric iron reduction coupled to sulfur oxidation by biomining microorganisms

Abstract

Acidophiles, including a mixed mesophilic, iron-oxidizing culture (FIGB) and a thermophilic enrichment culture (TK65) from a black shale and sandstone copper ore (Kupferschiefer), were used to evaluate microbial ferric iron reduction coupled to oxidation of reduced inorganic sulfur compounds (RISCs) at elevated pressure to simulate potential biogeochemical processes in deep in situ leaching operations. Experiments were performed from atmospheric pressure (0.1 MPa) up to 36 MPa in different incubation chambers and high-pressure reactors. Microbial abundance and activity were determined by quantifying iron and sulfur species concentrations, by direct cell counting, terminal restriction fragment length polymorphism (T-RFLP) analysis and quantitative PCR (qPCR). The data indicate that the tested acidophilic cultures were able to reduce soluble ferric iron coupled to oxidation of sulfur compounds under anaerobic conditions. Even at high pressure (up to 36 MPa) these acidophiles were capable of growing, and microbial ferric iron reduction was only partially inhibited. These results show that the tested acidophiles are barotolerant and their activities may contribute to sulfur and iron cycling in anaerobic environments including deep ore deposits, which is relevant for in situ leaching operations.