2012|13 Annual Report Fraunhofer IGB

99 applicable. Furthermore, the precision of separation is not suf- ﬁcient to achieve a quality equal to that of the primary mate- rial. To close the material cycles within production processes and in recycling there is therefore a great need to develop new technologies that are efﬁcient, easy to integrate and can be applied ﬂexibly to various groups of metals. Process steps and an integrated concept In the project “Molecular Sorting”, funded as part of the Fraunhofer-Gesellschaft’s “Markets Beyond Tomorrow” re- search program, the Fraunhofer IGB is developing new metal- recovery technologies based on the microbiological, separa- tion [1, 2] and electrophysical technology know-how available at the IGB. For this purpose the technologies bioleaching (to dissolve the metals), adsorption and membrane ﬁltration (to concentrate the dissolved metal ions), electrophoretic separa- tion and the use of ionic liquids for electrolytic processes (for fractionation and galvanic deposition of metals) are being studied, further developed and incorporated in an integrated process. Selected reference substances For the development work, the following substances were chosen as reference substances: Precious metals: gold, silver, copper, palladium Rare earths: neodymium Toxic metals: lead, mercury. Here, both economic criteria (economic signiﬁcance, range) and ecological reasons (toxicity, prevalence) were decisive. Bioleaching Interactions of metallic surfaces with microorganisms are gen- erally not noticed until they cause damage as a result of bio- corrosion. The same processes can be used to dissolve metal ions from materials and to make them recyclable. Without knowing the scientiﬁc background, people used microbiologi- cal processes centuries ago to obtain metals such as copper from natural deposits. The ﬁeld of bioleaching includes enrich- ing microbial populations with the aim of recovering metals from industrial waste materials, consumer goods or various types of process water by using technical processes. Two procedures for bioleaching were established at the Fraun- hofer IGB: An anaerobic process An aerobic process The bioleaching processes were tested on metallic recycla- ble materials as well as on waste wood and rail sleepers and were initially set up on the laboratory scale. In the ﬁrst process step suitable microbial mixed populations were enriched and then metal ions were successfully solubilized from particulate source material. Fig. 1A shows an example of a micropopula- tion of various types of bacteria that had colonized the source material (metal shavings). The process of metal solubilization was evaluated analytically by means of ICP spectroscopy. Con- siderable quantities of manganese, nickel, iron, copper, zinc and titanium were solubilized especially from waste wood and rail sleepers. There was also evidence of a precipitation of the metals in the suspension (Fig. 1B). The conception for a technical process was developed on the basis of these results. For the bioleaching process the design includes a ﬁxed-bed reactor that ensures a sufﬁciently high catalyst density by means of biomass retention. 1 A: A microbial mixed population on recyclable material particles. B: Precipitation of metals. 2 Process chain for an efﬁcient recov- ery of metals. 3 Bioleaching. 3 »

2012|13 Annual Report Fraunhofer IGB

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