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During the last decades the material composition of buildings has become increasingly diverse. However, largely sorted material flows are needed for generating high quality secondary building materials. The use of secondary building materials can meet the requirements of sustainability in several ways: the extended time availability of primary raw materials and, thereby, the preservation of natural resources as well as the conservation of landfill sites.
Recycling of gypsum (calcium sulfate) can be a good example for the environmental benefits of closed-loop recycling. The content of sulfates in other secondary building materials, in particular in recycled concrete aggregates, should be minimized for quality reasons. In contrast, separated gypsum can also be used in gypsum production if the high quality requirements for the recycled gypsum are met. Since almost all processing steps in the recycling process are associated with environmental impacts, an environmental evaluation of the use of recycled gypsum as a substitute in gypsum production has to be carefully conducted.
This paper focusses on the techniques for generating recycled gypsum from gypsum plasterboards, the related quality requirements and a comprehensive environmental evaluation of the complete process.
The aim of this study was to investigate the passive sampler method Diffusive Gradients in Thin-films (DGT) for ammonium and nitrate in amended soils. Therefore, we used soils from a pot experiment with maize where nitrogen (N) was supplied as ammonium sulfate nitrate (ASN), without and with a nitrification inhibitor (NI). The additional use of a NI can delay the nitrification in the soil and making the ammonium available for a longer period in the soil solution after its application. Homogenized soil samples were collected directly from each pot after one week of incubation before sowing and after harvesting the maize. Nitrate and ammonium in these soil samples were extracted using DGT devices equipped with a Putolite A520E (for nitrate) and Microlite PrCH (for ammonium) binding layer. Ammonium DGT which determined the mobile and labile ammonium forms based on diffusion and the resupplies from the solid soil phase, only showed a significantly higher amount of extractable ammonium with NI compared to that without NI for some samples. However, significantly lower values were found for nitrate of treatments with NI compared to without NI after harvest. Thus, the lower nitrate amounts for treatments with NI compared to the treatments without NI after harvest indicated the delay of the nitrification process by the NI. Furthermore, we compared also the ammonium and nitrate
DGT results to chemical extraction with KCl solutions. The results demonstrated that the trends of DGT results and chemical extraction were complimentary through all the treatments.
The challenge of the project ASHES is focused on the recycling of nutrients from residues of thermochemical processing of by-products of sugar cane industry (bagasse/straw) in Brazil to increase the energy efficiency of thermal conversion and to enable the recycling of process ashes as fertilisers. Dry lignocellulosic biomass (straw, bagasse) are combusted, gasified and subsequently combined with post-thermochemical treatment in the AshDec process to increase the plant availability of phosphorus. Different fertilizer formulations are granulated/pelletized and tested regarding their storage/handling characteristics.
Phosphorus (P) fertilizers from secondary resources became increasingly important in the last years. However, these novel P-fertilizers can also contain toxic pollutants. Chromium in its hexavalent state (Cr(VI)) is regulated with low limit values for agricultural products due to its high toxicity, but the determination of Cr(VI) in these novel fertilizer matrices can be hampered by redox processes that lead to false results. Thus, we applied the passive sampler technique Diffusive Gradients in Thin-films (DGT) for the determination of Cr(VI) in fertilizers and compared the results with the standard wet chemical extraction method (German norm DIN EN 15192) and Cr K-edge X-ray absorption near-edge structure (XANES) spectroscopy. We determined an overall good correlation between the wet chemical extraction and the DGT method. DGT was very sensitive and in most cases selective for the analysis of Cr(VI) in P-fertilizers. However, hardly soluble Cr(VI) compounds cannot be detected with the DGT method since only mobile Cr(VI) is analyzed. Furthermore, Cr K-edge XANES spectroscopy showed that the DGT binding layer also adsorbs small amounts of mobile Cr(III) compounds which leads to overestimated Cr(VI) values. The results of certain types of P-fertilizers containing mobile Cr(III) or partly immobile Cr(VI), showed that optimization of the DGT method is required to avoid over- or underestimation of Cr(VI).
Lightweighting as a cross-cutting technology contributes significantly to achieve the European Green Deal goals. Based on, but not limited to, advanced materials and production technologies, the demand for natural resources and CO2 emmissions are reduced by lightweighting during production, as well as use phase. Therefore, lightweighting is a crucial transformation technology assisting in decoupling economic growth from resource consumption. In this manner, lightweighting contributes significantly as a key technology of relevance for many industrial sectors such as energy, mobility, and infrastructure, towards resource efficiency, climate action and economic strength, as well as a resilient Europe. To strengthen international partnerships, addressing global issues of today at the edge of science with high performance lightweight material based on carbon fibers, an overview about the BAM expertise in carbon fiber reinforced materials is given.
The increasing use of carbon fiber reinforced polymers (CFRP), as lightweight materials essential for the transformation, demands for a safe treatment option of carbon fiber (CF) containing waste streams. Because of their low reactivity towards oxidation processes, CF can neither be treated in a conventional nor hazardous waste incineration plant. Even the extremely high temperature in a cement rotary kiln does not lead to full conversion. To increase the sustainability of CF, other processes need to be investigated. Opening other reaction pathways, using CF waste streams as secondary resource in pyrometallurgy to replace fossil carbon, can be a solution for a safe and sustainable treatment. After first small scale experiments, CF containing waste streams were used as reductant in a semi-industrial scale electric arc furnace (EAF). First results and impressions are presented.
The increasing use of carbon fiber reinforced polymers (CFRP), as lightweight materials essential for the transformation, demands for a safe treatment option of carbon fiber (CF) containing waste streams. Because of their low reactivity towards oxidation processes, CF can neither be treated in a conventional nor hazardous waste incineration plant. Even the extremely high temperature in a cement rotary kiln does not lead to full conversion. To increase the sustainability of CF, other processes need to be investigated. Opening other reaction pathways, using CF waste streams as secondary resource in pyrometallurgy to replace fossil carbon, can be a solution for a safe and sustainable treatment. To support the industrial application, experiments on different scales were conducted. Here, results of thermochemical investigations, reactivity studies, crucible experiments and pilot plat trials are reported.
Recycled fertilizers produced using processes for the recovery of phosphate from residual materials such as wastewater, sewage sludge and sewage sludge ashes show very good bioavailability, but it is still a product largely unknown to the market. The aim of CLOOP is therefore to document the properties and effects of such fertilizers through chemical, mineralogical and ecological analyses as well as analytical method development and pot and field plant growth trials.
Outotec focused on 3 points in CLOOP: Experimental campaigns, process simulations as well as economic analyses with focus on the AshDec process, respectively the design of a large-scale AshDec plant for phosphorus recovery. The laboratory scale trials as well as the semi-industrial scale campaign provided valuable insights into the operating parameters of the process and the plant. As a result, for example, the temperature range could be significantly lowered, and the additive addition reduced by approx. 20 %. They have further shown that the AshDec process is not susceptible to operating fluctuations and that the product can be consistently produced at high quality. With the selection of suitable operating parameters, heavy metals (As, Pb, Cd, (Zn)) can be removed. Within the campaign, about 1.5 t of fertilizer for the plant trials in CLOOP could be produced. An AshDec plant process was digitally created in simulation software, allowing valuable process parameters to be simulated at various operating parameters. On this basis, a full-scale plant was designed. The data obtained in the project were used for a detailed economic analysis including a sensitivity analysis. It was possible to show under which conditions this plant can be operated economically.
At BAM, the AshDec fertilizer was synthesized with different additives and then applied to plant experiments at Uni Bonn. The goal hereby was to check differences in plant uptake. Because of the promising results of AshDec synthesized with sodium-carbonate and because this AshDec version does not require special off gas treatment for sulfur recovery (compared to AshDec synthesized with sodium-sulfate), all project partners agreed on continuing working with this AshDec variation. It was then used as a raw P-source for formulating it into NPK-fertilizers, by granulation with ammonium-sulfate and straw ash as potassium source. These recycling fertilizers were applied to plant- and field experiments by project partners in Brazil (University of Sao Paulo) and Australia (University of Queensland). Furthermore, in leaching experiments, the solubility of phosphorus in AshDec was compared to triple super phosphate. The experiments were carried out on soils with a varying phosphorus buffering index. Results show, that the phosphorus form in AshDec is way less soluble in water. This indicates that AshDec has the potential for a so-called next generation fertilizer – a fertilizer which’s nutrients remain in the soil and supply the plant according to its needs. At the moment, this behavior gets examined more in depth in lysimeter experiments in cooperation with University of Technology Berlin.
The focus of KWB is the Life Cycle Assessment (LCA) of different NextGen fertilizers to evaluate the entire process chain from recovery to fertilizer application. The NextGen fertilizer is credited by the amount of plant available nutrients in the product, which replace nutrients from conventional fertilizer. The LCA covers N-struvite precipitation from municipal wastewater, K-struvite precipitation from industrial wastewater and the AshDec-product from sewage sludge. The LCA task is almost complete. It could be shown that struvite precipitation has comprehensive environmental benefits, mainly since positive side effects occur in sewage sludge treatment (e.g. reduced sludge volume). In principle, the energetic and ecological profile of the AshDec process compared to direct use of sewage sludge ash cannot be assessed as being generally beneficial or negative. Regarding the global warming potential, the Ashdec process shows that the expenses (e.g. energy, chemicals) cannot be covered by the P fertilizer credit. In contrast, the impact categories “terrestrial acidification potential”, and “freshwater eutrophication potential” show positive results as the credits for conventional fertilizer are higher than the burdens for the process.
At University Bonn, the standardized pot experiments were conducted with several AshDec variations, using ryegrass, soybean, and spinach on a slightly acidic sandy soil and an organic-free standard substrate. P-uptake and biomass production of different AshDec variations were generally like those of triple super phosphate and struvite, and clearly outperformed untreated sewage sludge ash and rock phosphate. Field trials in Australia and Brazil with sugarcane on acidic soils are still ongoing and results are expected by the end of 2021.
As one of the most energy and carbon consuming industries, steelmakers have an intrinsic interest in the development of technologies, reducing their carbon footprint as well as their carbon input. Besides generating new feedstocks from biomass or waste polymers, the valorization of carbon fiber reinforced polymer (CFRP) waste streams seems to be extremely promising based on the high carbon content of carbon fibers (CF), chars from CFRP and even unprocessed CFRP waste of >92%, 98% and 79%, respectively. Although, reduction of environmental impact from those high-performance materials was achieved by the development of smart recycling solutions, the continuous truncation by mechanical treatment of CF over multiple cycles, analogous to paper fibers, and the large global CFRP waste stream of 62 kt/a demand for a sustainable management of end-of-life (EOL) CFRP. Recently it was demonstrated that CF can be used safely as reductant in pyrometallurgical processes in a downhole electric furnace without significant WHO fiber emission. Therefore we anticipate a huge potential of CF based materials as sustainable reductant for steelmaking in an electric arc furnace (EAF). To facilitate the applicability of EOL CFRP in steelmaking, we investigated the interaction between CF based materials and liquid metal phases, appearing during the process, on different scales. Particularly, we examined the reactivity, wettability and dissolution behavior of CF and CFRP concerning liquid slag and steel. The presented results indicate that understanding the impact of the microstructure of CF on their behavior is crucial for their application in EAF steelmaking without risking potential hazards by WHO fiber emission. Besides the detailed elucidation of structure reactivity relationships of CF, the broader impact on circular economy will be presented.
Despite its contribution to tackling climate change by lightweight design, growing CFRP production also results in a global waste generation of 62 kt/a. Accordingly, the energy-intensive production process of carbon fibers (CF) necessitates sustainable recycling solutions.
Herein we will give an overview of current recycling processes, discuss their limitations and present a novel approach for safe treatment of CF unsuitable for material recovery . Our project CF Pyro examines feedstock recycling in pyrometallurgical processes, focusing on reactivity of CF, process stability and prevention of hazardous WHO fiber release. Besides fundamental experimental breakthroughs, their broader impact on circular economy will be presented.