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Direct and indirect effects (DIERec) of the recovery of secondary resources are in the range of 500 million tons per year in Germany; energy savings are 1.4 million TJ. These savings are between 10 and 20% of the total. The effects of materials recovery exceed those of energy recovery by far except for secondary plastic material, where DIERec from energy recovery is higher by factor of 2.7. Untapped potential for the recovery of secondary resources exists in the fine fraction of bottom ash from municipal solid waste incineration, mainly Cu and precious metals, and in urban mining.
In Germany, the direct material input (DMI) was 1727 million tons in the year 2014. This figure would be even higher by more than 14 % if no secondary materials were already used in industrial production. For example, production of secondary Cu is advantageous due to lower energy consumption and conservation of scarce natural resources. The presentation will discuss pathways to increase the use of secondary raw materials to foster a circular economy with a focus on waste treatment processes.
Raw material supply is essential for all industrial activities. The use of secondary raw material gains more importance since ore grade in primary production is decreasing. Meanwhile urban stock contains considerable amounts of various elements. Photovoltaic (PV) generating systems are part of the urban stock and recycling technologies for PV thin film modules with CdTe as semiconductor are needed because cadmium could cause hazardous environmental impact and tellurium is a scarce element where future supply might be constrained. The paper describes a sequence of mechanical processing techniques for end-of-life PV thin film modules consisting of sandblasting and flotation. Separation of the semiconductor material from the glass surface was possible, however, enrichment and yield of valuables in the flotation step were non-satisfying. Nevertheless, recovery of valuable metals from urban stock is a viable method for the extension of the availability of limited natural resources.
Waste-to-energy (WtE) is one of the leading technologies for municipal solid waste (MSW) treatment in Europe. According to Eurostat data, in 2015, 27 % of MSW was utilized in WtE plants, which represents more than 80 million tons per year. Therefore, the European annual production of incineration bottom ash (IBA) is about 20 million tons, as it is about 25 wt% of input MSW. In the European List of Waste, IBA is listed as mirror entry (i.e. waste materials which should be classified as either non-hazardous or hazardous, depending on its hazardous properties and/or content of hazardous substances) under codes 19 01 11 and 19 01 12.
Recent trends indicate that WtE allows, apart from utilization of the energy content of waste, also the recovery of various valuable components. Hence, WtE can be included in the key technologies that can put the circular economy concept into practice. Secondary raw materials in the case of WtE are solid residues, especially IBA, as it is a secondary source, particularly of ferrous metals (Fe) and non-ferrous metals (NF) and glass. Moreover, the residual mineral fraction can be used for various applications in the construction industry, i.e. as aggregates substitute for bound or unbound applications, in cement manufacturing or, as indicated by recent research, also in more sophisticated applications, e.g. for ceramics production. Recovery of these metals can also cause huge greenhouse gas savings. Alone in Europe, metal recovery from IBA reduces greenhouse gas emissions by approximately 3.2 million tonnes of CO2 equivalent.
Resource consumption is always accompanied by environmental impacts. In most cases, it is not possible to quantify the extent of such negative impacts. However, the external cost of uranium mining in Germany can be estimated at 30 Euro/kg U. The environmental impact can be reduced when waste materials are processed, so that their use as a secondary raw material, substituting for natural resources, is possible. The recyclability of waste materials depends on the price of a resource and the concentration of the component in the waste.
The use of renewable energy technologies, such as photovoltaics (PV) should be sustainable and environmentally compatible and therefore protect the environment from risks and damaging impacts. Regarding the growing number of installed photovoltaic systems, the end-of-life management of the pv-modules will become increasingly important. Thin film panels contain hazardous substances that may harm the environment if they are not recycled or disposed properly after reaching the end of their service life. Heavy metals, for example, can be toxic as well as carcinogenic or teratogenic. Processing methods for the recycling of PV thin film modules have to take these facts into account. Currently the available recycling techniques usually utilise chemicals such as acids for a wet-chemical treatment of end-of-life modules. The aim of RESOLVED was to identify and test alternative methods for a wet-mechanical treatment in order to reduce the consumption of chemicals in the recycling of thin film modules. Furthermore, the recovered Cadmium-Telluride (CdTe) and Copper-Indium-Diselenide/Disulfide (CIS) should be helping to save scare resources especially for limited elements such as tellurium and indium. The project RESOLVED investigated the recovery of semiconductors material as secondary raw material and the decontamination of the residues of the PV thin film modules. These goals were achieved by testing and optimising existing technologies for the recycling process as well as for the enrichment of the semiconductor materials. The target is to re-use the enriched recovered material in the production of new PV modules. Special efforts were made to look into life cycle analysis, process sustainability, economical aspects, and resource availability.
The recycling of refractory materials in the chemical, metallurgical and glass industry has only had minor relevance until now because of the high performance required from these materials (stability against corrosion, inert when coming into contact with the glass melt, etc.). Refractory lifetimes are limited because of corrosion at higher temperatures. The best furnace lifetimes has been achieved with chromium oxide and chromium oxide corund refractories. Waste from the production and use of refractory material is generated in three main forms: as residues from cutting and grinding, as refractories which have limited or no contact with glass melts, and as refractories with infiltration of sublimation residues or condensates. The waste material is classified as hazardous waste due to its chromium content. In this study, arc furnace technology was used for thermal treatment of the waste materials to enable recycling of refractory materials. (author abst.)
Over the past two decades, per- and polyfluoroalkyl substances (PFASs) have emerged as worldwide environmental contaminants, calling out for sophisticated treatment, decomposition and remediation strategies. In order to mineralize PFAS pollutants, the incineration of contaminated material is a state-of-the-art process, but more cost-effective and sustainable technologies are inevitable for the future. Within this review, various methods for the reductive defluorination of PFASs were inspected. In addition to this, the role of mechanochemistry is highlighted with regard to its major potential in reductive defluorination reactions and degradation of pollutants. In order to get a comprehensive understanding of the involved reactions, their mechanistic pathways are pointed out. Comparisons between existing PFAS decomposition reactions and reductive approaches are discussed in detail, regarding their applicability in possible remediation processes. This article provides a solid overview of the most recent research methods and offers guidelines for future research directions.