Using bacteria to mine precious metals
The high content of organic matter and carbonates in black shale ore deposits makes recovery of precious metals technically difficult. Furthermore, conventional techniques have come under scrutiny due to environmental considerations. Biohydrometallurgy is a branch of biotechnology involving the use of microbes (‘bio’) in an aqueous environment (‘hydro’) to recover or treat metals (‘metallurgy’). Microbes are introduced to the shale, speeding chemical transformations that result in dissolution of metals and subsequent selective recovery (bioleaching). The rest of the material is transformed into inert waste. Although commercial application of biohydrometallurgy for copper extraction began in the 1950s and was extended to gold in the 1980s, the true potential for biotechnology in metallurgy has remained untapped. European scientists thus initiated the ‘Search for a sustainable way of exploiting black shale ores using biotechnologies’ (Bioshale) project. The goal was to define innovative biotechnological processes for the effective and eco-friendly recovery of numerous precious metals from black shale deposits. Three extensive metal-rich European black shale deposits were selected for case study: an unexploited site in Finland, a site currently being mined in Poland and an old site in Germany no longer mined. Researchers first evaluated the nature of the geological resources at the sites in order to select appropriate bacteria and processing methods.Simultaneously they developed bioleaching technologies and investigated novel microorganisms of interest. Given the project umbrella goal of sustainable mining, scientists developed a software tool used to conduct a global environmental impact study of conditions before, during and after mining activities. The Bioshale consortium successfully demonstrated the ability to use biohydrometallurgy to bioleach precious metals from black shale ore deposits rich in organic matter. Bioshale project results should enable Europe to tap into the wealth of valuable metals present in its black shale ore deposits without damaging the environment.
