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- Bioleaching (2)
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Institute
Within the next few years major changes in mobility are expected. Increasing numbers of electric powered cars, electrobikes and E-Scooters define the transport sector. Recently lithium based traction batteries as storage medium have led into matrurity of series production combining high electrical efficiencies with low weights and compact dimensions. Due to the relatively young development with lithium batteries utilization, only few investigation were conducted regarding their recycling. Conventional battery recycling processes can not be applied due to differences in design and chemistry.
So an automated disassembly and processing procedure for lithium traction batteries has been developed in the R/D-project "Li-WERT". Instead of complete smelting of the batteries without pretreatment, an automated disassembly and specific treatment of the material streams was realised, adjusted to the needs of the subsequent recovery technologies. A higher quality, with reduced expenses for the separation of fine-grained or fused material mixes, can be obtained for the individual components. The automated disassembly using an industrial robot significantly reduces dangers for the operating crew.
The selective disassembly and beneficiation allows full recovery of the fractions. The batteries will be disassembled to cell level by the industrial robot. Anodes, cathodes, and separation layers are isolated and processed. The technology is designed, that no waste is generated for disposal. The pelletised cathode coating and the other separated metals (stainless steel, copper, aluminum) can be used in respective metallurgical plants. Circuit boards and plug contacts are also coveted secondary raw materials for reuse.
The process is modular and offers high flexibility, e. g. for new battery types/ sizes by quick adjustment of the robot and tool change. Adaptation to other cathode materials (e. g. Li[FePO]) is possible. After finishing the R/D-project, a pilot plant for demontage was realised in 2013.
Die automobile Antriebstechnik steht in den nächsten Jahrzehnten vor tief greifenden Verän-derungen. Nachdem über 125 Jahre der Verbrennungsmotor die vorherrschende Antriebsart darstellte, basieren neue Entwicklungen auf Elektroantrieben oder auf der Kombination ver-schiedener Antriebsformen. Fahrzeuge mit elektrischen Antrieben haben mittlerweile den Status der Serienreife erreicht und werden perspektivisch zunehmend das Straßenbild be-stimmen.
Mit der so genannten Lithium-Ionen-Traktionsbatterie wurde in den letzten Jahren ein Spei-chermedium zur Serienreife geführt, welches einen hohen elektrischen Wirkungsgrad mit kompakten Maßen und geringem Eigengewicht vereinigt. Mit den auf der Nutzung von Li-thium-Akkumulatoren basierenden Antriebskonzepten kann ein entscheidender Schritt zur Umsetzung einer umfassenden Verbreitung der elektrischen Antriebstechnik im Bereich der individuellen Mobilität erfolgen.
Waste electrical and electronic equipment is a complex waste stream and treatment options that work for one waste category or product may not be appropriate for others. A comprehensive case study has been performed for plastic-rich fractions that are treated in German dismantling centres. Plastics from TVs, monitors and printers and small household appliances have been characterised extensively. Based on the characterisation results, state-of-the-art treatment technologies have been combined to design an optimised recycling and upgrade process for each input fraction. High-impact polystyrene from TV casings that complies with the European directive on the restriction of hazardous substances (RoHS) was produced by applying continuous density separation with yields of about 60%. Valuable acrylonitrile butadiene styrene/ polycarbonate can be extracted from monitor and printer casings by near-
infrared-based sorting. Polyolefins and/or a halogen-free fraction of mixed styrenics can be sorted out by density separation from monitors and printers and small household appliances. Emerging separation technologies are discussed to improve recycling results.
Rückgewinnung und Aufbereitung der Kathodenbeschichtungen von Lithium-Ionen-Traktionsakkumulatoren
(2019)
Die energie- und ressourcenschonende Aufbereitung von End-of-life-Lithium-Ionenakkus ist ein gesellschaftliches und wirtschaftliches Erfordernis, da mit dem zunehmenden Einsatz von Elektrofahrzeugen die Zahl von ausgedienten oder defekten Li-Traktionsbatterien zunehmen wird. Die klassische Aufbereitung dieser Akkus, insbesondere mit Hochtemperaturverfahren, ist energetisch aufwändig und führt zudem nur zur partiellen Rückgewinnung der Wertelemente, die dann auch erst durch weitere mechanische und chemische Prozesse wieder zu verwendbaren Materialien werden.
Die vom Fachgebiet Aufbereitungstechnik der BTU mit verschiedenen Industriepartnern seit 2010 entwickelte Technologie verfolgt einen grundlegend anderen Ansatz. Ausgehend von einer hoch mechanisierten und teilweise automatisierten Demontage der Akkus können dabei die Einzelkomponenten weitgehend unzerstört und ohne thermische Schädigung oder Verlust brennbarer und leicht flüchtiger Anteile zurück gewonnen werden.
Für die Abtrennung der Kathodenbeschichtung von der Trägerfolie kommt nach der Zellendemontage eine hoch mechanisierte Nassaufbereitung zum Einsatz, bei der mittlerweile vollständig auf den Einsatz von Chemikalien verzichtet werden kann. Das separierte NMC-Schwarzmaterial soll so aufbereitet werden, dass es zukünftig in Recyclat-Zellen für verschiedene Anwendungen genutzt werden kann. Dazu werden verschiedene Zerkleinerungs- und Sortiertechnologien getestet.
Automotive technology is increasingly determined by electric vehicles driven by high-performance lithium ion batteries (LIB). Li-ion batteries equipped with layered oxide cathodes, which are constituted by oxides of nickel, manganese and cobalt, are proven as storage devices that combine high electrical power, high cycling stability and compact dimensions. These batteries contain large amount of valuable elements, such as the cathodes consisting of cobalt and nickel, the electrode carrier foils consisting of copper and aluminium. Therefore, spent LIB’s are valuable secondary resources.
Thermal processing as the classical recycling-technology for LIB’s is energy-intensive and allow only a partial recovery of some value elements.
Scientists of the Brandenburg University of Technology (Germany) developed in collaboration with industrial partners (SME) a process, in which the complex system LIB is partly automated dismounted into its basic components. The core of this process is the separation of anodes and cathodes from each other and an almost complete recovery of the cathode material from the foil.
The recovered cathode material has an enormous potential for a re-use in new LIB’s. By a proper combination of separation and post-treatment the material has a quality that is close to virgin cathode material. Preliminary studies made on LIB’s containing a fraction of recycled cathode material up to 50% show an electrical performance comparable to LIB’s made from virgin material.
Production waste from the manufacture of printed circuit boards often has gold-containing contact strips and dots whose gold content is very low. Recycling of these gold coatings by means of conventional melting processes is technically hardly possible, since the carrier materials often contain mechanical reinforcements and flame retardants in addition to thermosetting plastics. Furthermore, there would be significant gold losses in the smelting process. Together with two industrial partners, at BTU in the last years a technology was developed, which can be used to decoat gold-bearing waste from PCB-production and contact stripes using biotechnological methods. As a result, a complete and separate recovery of the gold tinsel and the carrier material copper with high purity is possible. The bioleaching process is realized with iron and sulfur oxidizing bacteria, especially Leptospirilum ferrooxidans and Acidithiobacillus ferrooxidans. The first pilot plant with a planned throughput of nearly 2000 kg per year is currently in realization. The biotechnological apparatus consists of a closed leaching reactor (with a capacity of approx. 300 liters of fluid) as the core element and the peripheral equipment (fermenter, cementation reactor, filter systems etc.).
Compared to processes using inorganic acids, shorter leaching times can be achieved, partial regeneration and multiple use of the bioleaching solution is possible. After optimizing the conditions, a process time of only 60 hours per leaching-charge is possible. Over a period of 2-3 days, the microorganisms dissolve the copper layers present as gold carriers on the polymer. The dissolved gold flakes are filtered off and the leaching liquid containing copper is fed to the next process stage. There, during approx. 3-4 days, the dissolved copper is recovered by feeding metallic iron (with a sacrificial anode). The microorganisms present in the solution accelerate this process.
All process steps take place at moderate temperatures (< 40°C) and in a slightly acidic environment.
The separated gold tinsel as main product with a content of over 900 mg/g Au is a suitable input for the precious metal smelter. The copper precipitates in metallic form and can be recovered in high purity (>90%) as a by-product.
Due to the biological leaching and the resulting concentration of the gold components, only < 1 wt.% of the waste containing precious metals has to be thermally treated. This can significantly reduce the CO 2 -emissions from the gold recycling process compared with thermal processes and with conventional gold mining.
Metal-coated thermoplastic parts find more and more functional and aesthetic applications in the interior and exterior of cars. The vapor-deposited or electroplated coatings are usually composed of a plurality of nickel- and chromium-containing layers, which are applied to copper-containing carrier layers on the polymers. Previously, recycling processes are mainly focussed at the recovery or thermal utilization of the plastics. Targeted and selective recycling of the metallic coatings is usually not carried out.
Together with several SME, BTU developed a process, in which a complete and separate recovery of all components in high purity is possible with biotechnological methods. The bioleaching is carried out with iron and sulfur-oxidizing bacteria, esp. Acidithiobacillus ferrooxidans. The copper-containing layers are dissolved in the solution; chromium- and nickel-containing particles are precipitated as solids. After the bioleaching, a mechanical separation of the individual metal-containing components and their separate workup are carried out. End-products are metallic copper, a nickel- and chromium-containing solid and the cleaned plastics. The bioleaching ensures a high purity of the end products. Through the use of bacteria, which are also found in nature, the process is environmentally friendly. Compared to chemical leaching using inorganic acids, considerably shorter leaching times can be achieved. In addition to the optimization of the leaching process, the R/D-project also includes the development and testing of the apparatus technology.
Due to the European Directive 2000/53/EC on end-of-life-vehicles, from 2015 on more than 95% of car materials have to be recycled. In order to recycle the materials back into the economic cycle, it is necessary to produce products with high quality and purity.
Plastic components in cars, which are coated with metals by vapour deposition or electroplating, have a wide circulation (e.g., as cladding panel or trim strip for interiors and exteriors). In the end-of-life-vehicle recycling process, these plastic-metal composites are not considered in usual technologies (car shredder) and are not separated from Automotive Shredder Residue. These parts can be separated by optical or HF-detection sorting and then introduced to a specific treatment.
Experiments with a specially developed bioleaching configuration showed that the thin coatings, which consist mainly of copper, nickel and chromium, can be removed efficiently from the polymer base materials by a bioleaching solution with Acidothiobacillus ferrooxidans as a leaching agent. The solution used was produced in special fermenters with a 9K-nutrient salt media. During the bioleaching process at 35°C maximum temperature, most of the copper is dissolved and the other metals accumulate as metal sludge. The bacterial cultures based on A. ferrooxidans are robust and resilient.
After a 48-hour bioleaching period while the composites were stirred regularly with ventilation, the plastic particles were completely free from metallic coatings. The metal components are separated for further use: undissolved components (mainly Ni and Cr) are separated by decantation of the solution; dissolved copper recovey is carried out by cementation of copper. The cementated solid contains ~98% Cu, along with small amounts of other metals.
With the bioleaching process, good separation and re-utilization of the metallic coatings is possible. The cleaned plastic parts were prepared by compounding for new applications with injection-moulding.