Potential of bioleaching for metal recovery
from different waste fractions
W. Schnitzhofer, S. Thallner, C. Hemmelmair, S. Martinek, M. Haberbauer, G.M. Gübitz
Introduction
Bioleaching is a well-established process in mining of low-grade ores, being responsible for a significant part of world copper production. Additionally bioleaching is
applied for production of cobalt, nickel, zinc and uranium as well as at the biooxidation of sulfidic refractory gold concentrates. New substrates for bioleaching are
metal containing waste fractions. In times of diminishing resources (critical raw materials) recycling of these fractions is of increasing importance avoiding landfilling
of waste material and minimizing dependence from imports.
Methods
Waste fractions with significant metal content were identified on basis of literature data. Selected fractions were subjected to bioleaching batch tests using shaking
flasks, varying solid feed concentration and Acidithiobacillus sp. as reference microorganisms. Incubation time was 4 weeks, flasks were shaken at a fixed speed at an
orbital shaker for oxygen supply.
Results
Fractions selected for bioleaching potential tests:
1. Waste electro and electronic equipment (WEEE): In Austria more than 80000 t of WEEE were collected
in total in 2015, of which 92% were processed and 79% reused or recycled respectively [1]. The efficiency
of recycling is not specified. Typical composition of printed circuit boards is copper 16%, solder 4%, iron
3%, nickel 2% and non-metals. Testing an e-scrap fraction, cobalt and copper could be leached to high
extents and good rates were found for aluminum, nickel and zinc (Fig. 1). However, the medium mediated
Fig.1: Leaching efficiency of an e-scrap fraction for
different metals at a solid feed concentration of 10 g/l
effect was dominant in this setup due to rather high acid content of the microbial medium. This finding
could be observed at every batch experiment performed in this study.
2. Ashes and slags from waste incineration plants and others, incurred to an amount of 356000 t in Austria in
2008 [2], containing variable amounts of different metals. Due to the oxidic character and its solubilization
behavior yielding high pH values, these fractions are most challenging for bioleaching applications. This
fact was confirmed when testing a municipal solid waste incineration (MSWI) ash sample for its bioleaching
potential (Fig. 2). Even if high efficiencies were found for aluminum, chromium and copper, a biological
mediated effect was only visible for zinc.
3. Shredder light fractions: are heterogeneous fractions deriving from the shredder process after separation
of iron/non-iron metals (estimated amount 10000 - 20000 t/a in Austria). Used cars are the typical input
Fig.2: Leaching efficiency of a MSWI bottom ash sample
for different metals at a solid feed concentration of 1 g/l
material. In Austria 250000 t cars are annually decommissioned, from which 100000 cars undergo further
treatment. The composition of the fractions strongly depends on the material inserted, usually containing 510% metals [3]. In Fig. 3 the bioleaching efficiency of a shredder light fractions is displayed depending of
increasing solid feed concentrations. In general the efficiency was above 90% for copper and zinc, and 65%
for nickel, but efficiency was decreasing with increasing input concentration, showing a partly negative
biological effect. Reason for this effect was the increasing pH on the one hand, and possible inhibition on
the other hand. For industrial applications a high solid feed concentration is essential. Adaption of
microorganisms could be the key to solve this problem.
Fig.3: Leaching efficiency of a shredder light fraction for
Cu, Ni and Zn at different solid feed concentrations
Conclusion
- Waste materials as electronic scrap, ashes, slags or shredder light fractions could serve as future sources for valuable metals
- Bioleaching is a promising method for separation of metals from complex waste fractions
- Further studies are necessary for optimization of bioleaching processes for selected waste fractions
References
[1] Elektroaltgeräte Koordinierungsstelle Austria GmbH (EAK): Tätigkeitsbericht 2015
[2] Bundesrepublik Österreich: Bundes-Abfallwirtschaftsplan - BAND 1. Bundesministerium für Land- und Forstwirtschaft, Umwelt und Wasserwirtschaft, Wien (2011)
[3] LUA NRW: Abfalldatenblatt Shredderabfälle: Leichtfraktion und Filterstaub aus Abluftreinigung (2003)
Acknowledgements: This work has been supported by the Austrian BMWFW, BMVIT, SFG, Standortagentur Tirol, Government of Lower Austria and Business Agency Vienna through the Austrian FFG-COMET- Funding
Program and partly by FFG Bridge project “Shlaubi2” as well as by the ‘Produktion der Zukunft’ project “GRecoMet”, funded by BMVIT.
Kontaktperson zum Poster:
DI Dr. Wolfgang Schnitzhofer
Acib GmbH
Stahlstr. 14/2, 4020 Linz, Austria
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E-Mail: [email protected]
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