MATERIALS


which also have minimum environmental footprint.’ Over the past four years,


the partners have concentrated their efforts in one of several ‘bottleneck’ areas: pre- treatment of the ore; bioleaching methods for extracting copper; recovery of the metal from solution, including selective metal precipitation; and characterisation of the ores before and after pre-treatments to help identify the optimum composition for the subsequent leaching steps. Research groups at Geological and Mining Research Institute (BRGM) in Orléans, France, and the German Federal Institute for Geosciences and Natural Resources (BGR), for example, focused their efforts on optimising the classical bioleaching method for use on copper concentrates of the ore. The ore is first put through several pre-treatments, such as froth flotation, to provide a material with a higher concentration of the metal than is in the primary source. The scientists developed a bi-


oreactor that uses a combination of different bacteria to extract copper from the concentrate. The team optimised the growth conditions for its ‘consortium’ of bacteria – temperature, aera- tion etc – as well as identifying the optimum grain size that the


bacteria could work on. But although technically pos- sible, the pre-treatments to pro- duce the concentrate currently render the process too expensive for commercialisation. Scientists at the Helmholtz


Institute Freiberg (HIF) in Germany and independently at BRAIN took a different approach to the problem, focusing instead on the troublesome ore itself. Katrin Pollmann, lead scientist at HIF on the EcoMetals project, explains: ‘We focused on bioleaching the ore at neutral conditions with heterotrophic bacteria. The idea was to use the resulting organic acids both to dissolve carbonates in the ore and act as complexing agents for metal extraction.’ Using just heterotrophic


bacteria from strain collections, the HIF scientists could recover around 45% of the dissolved metal, which Pollmann says is on a par with classical bioleaching. However, the method is still too inefficient for it to be economically viable, she says. The BRAIN scientists have


taken a slightly different approach to extracting the copper from its ore, with encouraging results. The company has been


working in the field of urban and


green mining for


the past 10 years, focusing in the main on the extraction of precious and rare metals. During this time, it has characterised over 50,000 microorganisms. Out of this extensive BioArchive, the company has identified several microbes that are capable of being used to extract metals from a variety of waste streams and ores and under extreme conditions of pH, and in the presence of inorganic and organic components. Esther Gabor, programme


manager green and urban mining at BRAIN, comments: ‘For the EcoMetals project, we have developed a process to reduce the alkalinity of the copper ore first by using microorganisms to dissolve the carbonate in the ore. We selected bacteria that produce organic acids from our BioArchive. The bacteria convert the carbonate to carbon dioxide, which leaves the solution and in doing thus lowers the pH of the solution. We then use the classical acid-producing bacteria in a second step, to deal with the copper and bring it into solution.’ In this way, Gabor says the


project partners can recover 97% of the dissolved copper. According to Gabor, the


process is ready to be taken to pilot plant scale, the first step towards commercialisation of the process.


In the meantime, also as part


of the EcoMetals project, the HIF scientists have developed a new technology for recovering the metal from the leachate. They have identified specific bacterial viruses (bacteriophages) from commercial libraries, which express peptides on their surfaces that are capable of binding with metal ions. ‘The idea is to use these biomolecules as part of a filter material to remove specific metals, not just copper but also cobalt and nickel, from what is a very complex solution. Our next step, for a future project, is to design a filter material,’ explains Pollmann. Later in 2018, in collaboration


with project partner GEOS, a German mining company, the HIF scientists will complete the construction of a pilot plant for metal recovery from bioleaching processes, and in the future, Pollmann expects the biosorption technology could be integrated into this plant.


A full report of the EcoMetals Project is expected later in 2018.


02 | 2018 33


SCIENCE SOURCE/SCIENCE PHOTO LIBRARY


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