FG Aufbereitungstechnik und Sekundärrohstofftechnologie (ehemals)
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Together with industrial partners, a complex apparatus was developed at the Brandenburg Technical University Cottbus-Senftenberg, which can be used to decoat gold-bearing waste from PCB- produc-tion waste and contact stripes using biotechnological methods. As a result, a complete and separate recovery of the gold flakes and the carrier material copper with high purity is possible. The bioleaching process is done with iron and sulfur oxidizing bacteria, especially Acidithiobacillus ferrooxidans, Leptospirilum ferrooxidans and Acidithiobacillus thiooxidans. Compared to processes using inorganic acids, shorter leaching times can be achieved, partial regenera-tion and multiple use of the bioleaching solution is possible (more than 10 times with the same leach-ing solution). After optimizing the conditions a process time of only 60 hours was reached. The sepa-rated gold tinsel with a content of over 900 mg/g Au is then fed into a precious metal smelter. 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.
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.
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.
The treatment of iron-hydroxide-containing water from ground water and surface water is achieved by a combination of the process steps of flocculation and subsequent mechanical dewatering. The aim is to create solid pellet structures by extending the structure forming flocculation process with a build-up pelletizing process which can be transferred directly into a drying unit. A Taylor-Couette-reactor (diameter of the inner cylinder – 40 mm, gap width – 5 mm) was used for these experimental studies. To produce the necessary flow profile the inner cylinder was rotated at a speed of 230 rpm. The iron hydroxide-containing suspension (dry matter content: 2 mass %) was added simultaneously with the addition of a cationic high-molecular flocculant in various flocculant dosages and residence times of 5 to 15 min. The pellets were examined for parameters such as geometric dimensions, dry substance content and dewatering behaviour. As the results show, there is a direct relationship between the residence time and the geometric dimensions of the pellets. After a residence time of 5 min, round pellets with an average diameter of 6 mm were formed. With an increase in the residence time up to 15 min, a compaction of the pellets could be observed, which resulted in an increase in the dry substance content of 8.0 to 11.2 mass % on average. After completion of the pelletizing process, the pellets were mechanically dewatered by filtration. By applying this innovative wet pelletizing of iron-hydroxide containing suspensions in a Taylor-Couette-reactor, it is possible to carry out the process of flocculation combined with the pellet formation with simultaneous pellet compaction in a single process step. The resulting pellet structures are distinguished from conventional floc structures by an improved water discharge capacity. After classification the pellets can be marked directly as easy-to-handle bulk material, suitable as feedstock in percolation columns for the purification of contaminated fluid streams
A mathematical model for the prediction of phase change temperatures and crystallization paths for mixtures consisting of palmitic (P), stearic (S), oleic (O), linoleic (L) and linolenic acid (Ll) in any distribution is presented in this paper. This model is based on the information gathered from modeled ternary phase diagrams, namely PSO, PSL, PSLl and OLLl, that were based on experimental binary phase diagrams of all possible combinations of these fatty acids. These experimental binary phase diagrams were obtained by means of differential scanning calorimetry and mathematical function fitting, within which the eutectic region of binary palmitic/stearic with oleic/linoleic/linolenic acid was investigated in detail. The basic mathematical model used was previously shown in literature which delivered good results for such systems. The importance of the developed model was then justified by investigations on real and composed synthetic fatty acid mixtures, where a high accuracy of the predicted temperatures could be shown for the technically relevant liquidus and solidus temperatures. A satisfying prediction for thermal events below the first solidus line could be reached as well. This work directly contributes to an enhanced understanding of the thermodynamic and kinetic background of such important mixtures applied in diverse products and industries, thereby showing a large optimization potential for crystallization technologies.
Vegetable oils and their derivatives are increasingly replacing mineral oils in their applications.[1,2] Among other constituents in vegetable oil, both saturated and unsaturated fractions are important raw materials. The latter possesses double bonds which can provide as substrates or raw materials for various chemical industries.[3] Fractionation of these oils or as in our case the Poly-Unsaturated Fatty Acid (PUFA) mixture is required so as to generate favorable compositions according to applications. Generation of Solid Liquid Equilibrium (SLE) phase diagrams for real mixtures is extremely important to enable a thorough understanding of the thermodynamics of the fractionation process of crystallization. The PUFA mixture was fractionated in a multistage scrubbing layer crystallizer. The product was put into a decanter centrifuge so as to fractionate them into mother liqor and crystal fraction. The temperature in the jacket was maintained such that △T< 5K from the liquidus point obtained from the Differential Scanning Calorimeter (DSC) thermal analyses. Each crystallizer was also maintained at a temperature 5K below the previous one. This way a slow and successive cooling of the PUFA was achieved such that probes from different fraction could be obtained. They were analyzed thermally and chemically in the DSC and Gas Chromatography – Flame Ionization Detector (GC-FID) setup respectively.[4] Similar to previous literature as in [5], technically relevant partial SLE diagrams for high oleic palm oil was created by fractionating the mixture in a scrubbed layer crystallizer along with their metastable range were determined.[6]
The range of application of fatty acids is as broad and varied as the diverse kinds of fatty acids themselves, stretching from bulk scale productions as in the case of biodiesel or lubricant manufacturing over consumer or end products like cosmetics, medicinal or nutritional additives to relatively smaller scale specialty chemicals like epoxy resins, insect repellents and so on. The crystallization temperatures of the unsaturated fatty acids are much lower than those of the saturated ones, which is an important and desirable property for raw materials such as in the production of epoxy resins. Separation and purification of these enriched unsaturated fatty acid fractions depending on their applications is mainly performed by two thermal fractionation processes, namely, distillation and crystallization. The potential behind the success of purification of these multi-component organic fatty acid mixtures with the help of melt crystallization, apart from the fact that it is cost effective owing to the obvious reduction of solvent removal and regeneration steps, is that of the relatively large differences in the melting points of the individual fatty acids.
A detailed and fundamental understanding of the crystallization especially nucleation kinetics of a variety of vegetable oil based fatty acid mixtures has been provided in this work. It also describes the solid-liquid phase diagrams of these poly-unsaturated mixtures including their metastable zone widths of nucleation and solidification. This theoretical part of this thesis is a detailed resource on the global production and application of vegetable oils and their derivatives. A clear mathematical and physical road map for the application of the Fisher Turnbull model to calculate the enthalpy values starting from the very basic supersaturation equation has been established and extensively explained as well. Nucleation studies have been carried out on various reactor setups in micro-, milli- and liter-scale. It successfully models the induction times of nucleation as a function of supercooling at different cooling rates both in micro and macro scale. 3D modeling of this parameter to see the combined effects of temperature and in turn viscosity have also been successfully implemented on the milliliter scale results, as more of the bulk nucleation phenomenon was observed in the latter. Fisher Turnbull plot and the Gibbs Thompsons model were adjusted and applied to correlate the Gibbs free energy, involved with the rate of nucleation captured by the FBRM™ (Focused Beam Reflectance Measurement) technology. The scope of this measurement technology was also tested in liter scale. The results showed that FBRM technology is applicable when the solution is relatively dilute and does not have too many overlapping crystals.
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.