Materials Science Forum Vol. 959

Abstract: In the photovoltaic industry a total of 100,000 tons of silicon is lost as waste per year. This waste is originating from several cropping and sawing steps of the high purity silicon blocks and ingots during the solar cell wafer production, resulting in a silicon containing suspension. Among different approaches to recycle the silicon from this waste is the utilization of hydrocyclones, which can be used to separate or classify particles by weight and size. In this work the use of a hydrocyclone was evaluated to upgrade the silicon fraction from a typical sawing waste. A potential field of use for the recycled silicon particles might be as anode material for next generation lithium ion batteries.

Abstract: Interfaces between two fluid phases are a potential barrier for particles. Certain particles may not be able to pass such an interface, because they have to overcome a certain resistance. The latter depends on the strength of the interface, which is the surface tension. The second relevant property is the three phase wetting angle, which shows the fluid with the preferred wetting to the particle surface. It depends on the particle properties, like chemical composition, surface structure and surface modification. The third relevant parameter is the particle size. From these three main influence parameters it emerges that fluid-fluid interfaces can show a selectivity to special particle properties, which enables a separation of a particle mixture. Since there are possibilities to address the governing effects, the separation cut, size or composition cut respectively, can be engineered in a certain range. Separation at boundaries is feasible when the driving force is in the same order of magnitude as the retaining resistance force of the interface. The driving force is either the Brownian movement for very small particles or any field force like gravity or the centrifugal force. To describe the separation at interfaces it is necessary to understand the process of the phase transfer of particles through the interface, either the gas-liquid or the liquid-liquid interface between two immiscible liquids. In addition to the effects mentioned above, also dynamic phenomena such as surfactant depletion of the interface may have to be taken into account.

Abstract: Critical raw materials (CRMs) are of primary importance for energy storage systems as needed for electromobility. Many mineral deposits which contain CRMs are low-grade ores. To liberate the CRMs, a grinding of the mineral ores to very fine sizes below 20 µm particle size is necessary. However, the present class of industrial flotation plants fail to extract such fine and ultrafine particles. To improve the recovery in fine particle flotation, techniques have been developed which attempt to agglomerate the fine valuable particles into larger aggregates which subsequently can be separated by established technologies such as froth flotation. Carrier flotation is one of these techniques. The present work reviews the state of the art of this technique for the recovery of fines and ultrafines.

Abstract: In the year 2016 alone, more than 1.35 billion smartphones were manufactured globally. These smartphones contain up to 60 different chemical elements and the summarized metal weight of the 2016 production may have well exceeded 50,000 metric tons. At present, most elements contained in this very complex “mixture” represented by a smartphone have recycling rates well below 50%, and the recycling rates of rare earths, indium, tantalum or gallium are even below 1%. The major challenge of mobile phone recycling is the complex composition of the devices made of many individual components – and the lack of transparent information as to the composition of these components. This is aggravated by the fact that many elements occur in traces only and / or are located in highly complex material composites. To enable more effective recycling of mobile phones, it is thus imperative to characterize the constituent components, the presence of elements in it, as well as their behavior during comminution. In a pilot study, a Nokia mobile phone Model 5228 Type RM-625, crushed with a granulator UG300, was examined by Mineral Liberation Analysis. The analysis of three particle size fractions of the comminuted material was carried out in an automated measurement mode with a grid of energy-dispersive X-ray spectra. A total of 130 different phases were detected during this analysis. More than 100 of these phases occur at levels <1% by weight. This strongly illustrates the very complex composition of smartphones. A comparison of the modal content of the three particle size fractions showed good liberation of certain components and an enrichment of some components in specific fractions. These observations reveal the potential to successfully separate different technical components from one another with the goal to increase the resource efficiency of the recycling process.

Abstract: Copper is one of the most common tramp elements in steel scrap. It originates from recycling of copper-alloyed steels, such as weather-resistant construction steel (up to 0.3 mass% Cu) or austenitic stainless steels (up to 3 mass% Cu). In both cases, corrosion resistance is increased. Certainsteels, on the other hand, be alloyed with Cu to influence the M_s point, ductility and/or antiseptic properties. However, copper increases the risk of hot shortness and cold work hardening in low-alloyed steels, which is even more pronounced if Sn is also present in the alloy. Furthermore, Cu is frequentlyintroduced into the scrap melt unintentionally, when steel scrap contains undiscovered parts or components of Cu or its alloys. Because the oxygen affinity of copper is lower than that of iron, selective oxidization of Cu from steel melts is not possible. Therefore, various alternative decopperization methods have been proposed by researchers, starting from the mid-1950s, up to the present. Among those are, apart from scrap pre-treatment, sortation and physical separation, melt dilution, treatment with chemical elements, carrier-metal equilibration, distillation/volatilization, slag treatment, melt filtration and oxide powder blowing. In this paper, various methods for decopperization of steel scrap melts, as reported in available literature, are being reviewed. This is complemented by pretest results from the Institute of Iron and Steel Technology at TU Bergakademie Freiberg (IIST).

Abstract: This article reports on the development of a hardenable PHFP steel for energy-efficient and distortion-reduced production of cold-formed, high-strength structural components. Based on an alloying concept containing 0.8 wt.-% copper, a technology for the production of screws has been developed to exploit the precipitation-hardening effect of copper for increasing strength by tempering while avoiding final quenching.

Abstract: Impurities and resulting inclusions are an issue when processing higher amounts of scrap during steel making. To increase the recycling rate, the removal of impurities from the scrap in form of inclusions is of great interest. In previous studies was found that inclusions attach primarily on carbon containing refractories, especially if on their surface an interfacial layer (1–3 µm thickness) was formed in-situ. This study investigates the formation mechanism of this in-situ layer in detail by application of computer tomography (CT) measurements on two scales. The large scale CT scans visualized the general appearance whereas the small scale measurement regarded the in-situ formed layer and the attached inclusions in detail. Based on these measurements, previous results and a literature review it was concluded that the layer formed mainly due to carbothermally reduced impurities which moved to the decarburized surface of the refractory in gaseous form and enhanced sintering of the surface region to develop the layer.

Abstract: Since more than 100 years blast furnace slags are used as additive material or substitute material in cementitious systems like mortar and concrete. Due to their different syntheses the slag systems have binding properties which differ from conventional clinker. With the help of mechanical activation due to fine grinding the properties of blast furnace slags are shifted towards clinker systems. The application of stirred media mills allow for a production of a very fine reactive system.

Abstract: Transitioning from combustion engine-driven transportation to e-mobility demands a paradigm shift – from a system geared to maximize energy efficiency (i.e. fuel consumption) to a system that may be constrained by the availability of high technology (critical) metals required for electrical energy storage systems and drives. In the wake of these developments efforts in securing new resources of these metals from recycling of end-of-life products are increasing steadily.