Simulationsbasierte Bewertung des Einsatzes von Röntgenfluoreszenzsortiersystemen am Beispiel der metallischen Grobfraktion von kupferhaltigen Produktionsrückständen der Gießerei- und Halbzeugindustrie

During the production of copper alloys such as brass (copper-zinc alloys), red brass (copper-tin-zinc-lead alloys) or aluminium bronze (copper-aluminium-nickel-iron alloys) various metal-containing residues such as dross are generated. To recover the metals contained in these residues they are usually subjected to mechanical processing consisting of crushing and screening. The process results in a coarse metal fraction that contains a variety of different alloys and is therefore complex in composition. This is due to insufficient source separation (e.g. in foundries) or mixed collection of the residues. There are two different metallurgical recycling processes for copper-bearing materials: direct recycling by simple remelting to produce new alloys, and multi-stage pyrometallurgical processing to produce copper cathodes. While the alloying elements (e.g. zinc in brass) are retained in direct recycling, they are removed as impurities in pyrometallurgical processing and often cannot be recovered or can only be recovered inefficiently. In addition, pyrometallurgical processing is much more energy intensive and therefore causes higher greenhouse gas emissions. Given the increasing scarcity of resources and Germany's growing dependence on raw material imports, as well as the political and social objective of limiting global warming as quickly as possible by reducing greenhouse gas emissions, direct recycling of copper alloy scrap is clearly the preferred option. Direct recycling requires high quality and accurately sorted input materials. As this is not the case for the coarse fraction, which contains a mixture of different alloys, and remelters lack refining capacity, an additional sorting stage is required. Against this background, the use of an X-ray fluorescence sorting system for the separation of the alloys in the coarse fraction has been examined and assessed in the present work. The assessment considers the contribution to climate and resource protection as well as economic aspects. First, a material flow model was developed to simulate two different sorting scenarios with three differently composed fractions (20 - 40 mm) based on large-scale trials and material characterisations. Both scenarios simulate the stepwise recovery of a brass, red bronze and aluminium bronze fraction and the enrichment of a high copper fraction. While scenario A focuses on six-stage sorting with the highest possible purity, scenario B simulates sorting with the highest possible yield by implementing three additional stages. A second model was developed to quantify the contribution of sorting to climate and resource protection, based on the results of the material flow model. A comparative assessment with the status quo (pyrometallurgical processing of unsorted material) was performed based on the indicators cumulative energy demand (CED) and global warming potential (GWP). The entire recycling process chain was considered, from sorting to the final product (copper alloy, copper cathode). Depending on the quality of the sorted products, the additional virgin material required to meet the alloy specifications was included in the assessment. The results show that X-ray fluorescence sorting allows an optimised metallurgical recycling with a reduction in CED of about 23 - 38 % and a reduction in GWP of about 19 - 33 % compared to the status quo. This is mainly due to the direct recycling of the recovered brass, red brass and aluminium bronze fractions. This not only recycles the alloying elements but also saves large amounts of energy in the remelting process, in contrast to the status quo. In addition to the alloyed products, a high copper fraction is produced, which is pyrometallurgically processed with significantly less energy input than the original material. The scenario comparison shows that the greatest savings are achieved in scenario B. The additional sorting stages result in a higher yield of copper and brass fractions, further reducing the amount of material requiring complex pyrometallurgical processing. In addition, an economic evaluation was carried out to determine the benefits of investing in an appropriate sorting system using the net present value method and a dynamic amortisation calculation. The results show that in scenario A the sorting plant can be operated economically from an annual throughput of approximately 1,000 - 1,130 Mg. In scenario B, due to the higher yield, this is already the case with an annual throughput of approx. 740 - 800 Mg. Scenario B is therefore more advantageous from both an environmental and an economic point of view. The use of X-ray fluorescence sorting systems for further processing of the coarse fraction can therefore significantly contribute to climate and resource protection and, under certain conditions, also offer economic advantages for recycling companies. Likewise, there is great application potential for other copper-bearing mixed fractions which are not of sufficient quality for direct recycling due to their complex composition.