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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 protection of natural ressources as well as the conservation of landfill sites. Regarding the predicted decrease of gypsum supply in Germany, particularly the recycling of gypsum (calcium sulfate) is of growing importance. Currently, the gypsum demand is fulfilled (at least 60%) by gypsum as side product from coal-fired power plants (FGD Gypsum). Germany’s natural gypsum deposits fulfil the remaining gypsum demand. Due to national climate protection goals the gypsum supply from coal power plants will decrease significantly in the future.
In addition, the content of sulfates in other secondary building materials, in particular in recycled concrete aggregates, should be minimized for quality reasons. Separated gypsum can be used in gypsum production if the high quality requirements for recycled gypsum are met. Accordingly, there have been significant advancements in the processing of gypsum residues in the last years. Since almost all processing steps in the recycling process are associated with environmental impacts, an evironmental evaluation of the use of recycled gypsum as a substitute in gypsum production has to be carefully conducted.
The presentation focusses on the techniques for generating recycled gypsum from gypsum plaster boards, the related quality requirements and a comprehensive environmental evaluation of the complete process.
A wide range of methods are used to estimate the plant-availability of soil phosphorus (P). Published research has shown that the diffusive gradients in thin films (DGT) technique has a superior correlation to plant-available P in soils compared to standard chemical extraction tests. In order to identify the plantavailable soil P species, we combined DGT with infrared and P K- and L2,3-edge X-ray adsorption near edge structure (XANES) spectroscopy. This was achieved by spectroscopically investigating the dried binding layer of DGT devices after soil deployment. All three spectroscopic methods were able to distinguish between different kinds of phosphates (poly-, trimeta-, pyro- and orthophosphate) on the DGT binding layer. However, infrared spectroscopy was most sensitive to distinguish between different types of adsorbed inorganic and organic phosphates. Furthermore, intermediates of the time-resolved hydrolysis of trimetaphosphate in soil could be analyzed.
Specific co-fertilization of nutrients can enhance their plant-availability and thus the yield of plants. To investigate this effect, we performed a pot experiment with three different P-fertilizers and ammonium nitrate sulfate as a co-fertilizer, without and with a nitrification inhibitor (NI), and analyzed the form of nitrogen (N) in the soil via novel X-ray spectroscopic method. The application of NI with the N fertilizer led to a higher dry matter yield of maize. Novel N K-edge micro-X-ray absorption near-edge structure (micro-XANES) spectroscopy identified that the application of a NI promotes the temporary formation of a non-exchangeable N in detectable hot-spots in the soil. The subsequent slow release and prolonged availability of N during plant growth leads to higher yield. It can be concluded that NIs lead to a temporary fixation of ammonium-N in a pool that can be accessed by plant roots. Those types of available nutrient pools meet the idea of so-called “next generation fertilizers” as plants have access to nutrients according to their current demand.
Previous research shows that analytical methods based on Diffusive Gradients in Thin films (DGT) provide very good correlations to the amount of bioavailable nutrients and pollutants in the environmental samples. However, these DGT results do not identify which compound of the specific element has the high bioavailability. Using various spectroscopic techniques (infrared, XANES and NMR spectroscopy) to analyze the dried DGT binding layers after deployment could allow us to determine the specific elements or compounds. Nutrients such as phosphorus and nitrogen are often, together with other elements, present as molecules in the environment. These ions are detectable and distinguishable by infrared and NMR spectroscopy, respectively. In addition, XANES spectroscopy allows for the specification of nutrients and pollutants (e.g. chromium) on the DGT binding layer. Furthermore, microspectroscopic techniques make it also possible to analyze compounds on the DGT binding layer with a lateral resolution down to 5 µm2. Therefore, species of elements and compounds of e.g. a spatial soil segment can be mapped and analyzed, providing valuable insight to understand the dynamics of nutrients and pollutants in the environment. Here we will present the advantages and limitations of this novel combination of techniques.
Phosphorus (P) fertilizers from secondary resources became increasingly important in the last years. However, these novel P-fertilizer can also contain toxic pollutants e.g. chromium (Cr) in the hexavalent state (Cr(VI)), which is regulated with low limit values in agricultural products (German fertilizer ordinance limit: 2 mg/kg Cr(VI)). The determination of Cr(VI) in these novel fertilizer matrices can be hampered by redox processes that lead to false results with the standard wet chemical extraction method (German norm DIN EN 15192). Therefore, we analyzed Cr(VI) in various P-fertilizers with the DGT technique. DGT devices equipped with a APA (polyacrylamide) diffusion layer and Cr(VI) selective N-methyl-D-glucamine (NMDG) binding layer were used for the study. After a 24 h conditioning period of the fertilizer at 60% of the water holding capacity (WHC), the fertilizers were brought to 100% WHC, transferred onto the DGT devices and deployed for 24 h at 25°C. The extraction of Cr from the DGT binding layer was carried out with 1 M HNO3 for 24 h. The Cr-concentrations of the extract were determined by means of ICP-MS. We found a good correlation between the standard wet chemical extraction and the DGT method for the whole range of P-fertilizers. However, partly soluble Cr(VI) compounds cannot be detected in full extent by the DGT method that is best suited for mobile Cr(VI). Furthermore, Cr K-edge XANES spectroscopy showed that the Cr(VI)-selective DGT binding layer also adsorbs mobile Cr(III) compounds from acid treatment of phosphates which can therefore cause an overestimation of Cr(VI). The DGT method was very sensitive and in most cases selective for the analysis of Cr(VI) in P-fertilizers made from recycled materials. However, the results of certain types of P-fertilizers containing mobile Cr(III) or partly immobile Cr(VI) show that still some optimization of the method is required to avoid over- or underestimation of Cr(VI).
Phosphorus (P) resource availability is declining and the efficiency of applied nutrients in agricultural soils is becoming increasingly important. This is especially true for P-fertilizers from recycled materials which often have a lower plant-availability compared to commercial P-fertilizers but are expected to play an increasingly important role into the future (Kratz et al. 2019). One promising way to increase the plant-availability of the fertilizer P is a co-fertilization with specific nitrogen (N) forms which can enhance the P uptake and make P-fertilizers from recycled material more competitive to commercial phosphate rock-based P-fertilizers (Rahmatullah et al. 2006; Vogel et al. 2018). To investigate this effect, we performed a pot experiment with three different P-fertilizers (sewage sludge-based, phosphate rock and triple superphosphate) and ammonium nitrate sulfate as a co-fertilizer, without and with a nitrification inhibitor (NI), and analyzed the form of N and P in soil via a suite of chemical and novel X-ray spectroscopic methods. The application of NI with the P and N fertilizers led to a higher dry matter yield and a higher P uptake of maize. Novel N K-edge micro-X-ray absorption near-edge structure (micro-XANES) spectroscopy identified that the application of a NI promotes the temporary formation of a non-exchangeable N in detectable hot-spots in the soil. The subsequent slow release and prolonged availability of N during plant growth leads to higher yield and nutrient uptake. It can be concluded that NIs lead to a temporary fixation of ammonium-N in a pool that can be accessed by plant roots. Those types of available nutrient pools meet the idea of so-called “next generation fertilizers” as plants have access to nutrients according to their current demand.
An existing pyrometallurgical process for tantalum and niobium recovery, mainly from low grade pyrometallurgical residues, was investigated. Series of melting experiments were carried out in a pilot-scale electric arc furnace to study how the amount, the grain size and the way of feeding affect the activity of carbon as a reducing agent. During the pyrometallurgical treatment refractory metals such as tantalum and niobium are reduced to their carbide form and enriched in the molten iron-based metal phase. The cooled down slag and metal phase were analysed to investigate thermodynamic and kinetic conditions of the carbide formation. FACT Sage simulations were also used to investigate the material system in state of thermodynamic equilibrium. Results show that mass transfer and kinetics may play an important role if compared to equilibrium analyses using FACT Sage.
An existing pyrometallurgical process for tantalum and niobium recovery, mainly from low grade pyrometallurgical residues, was investigated. Series of melting experiments were carried out in a pilot-scale electric arc furnace to study how the amount, the grain size and the way of feeding affect the activity of carbon as a reducing agent. During the pyrometallurgical treatment refractory metals such as tantalum and niobium are reduced to their carbide form and enriched in the molten iron-based metal phase. The cooled down slag and metal phase were analysed to investigate thermodynamic and kinetic conditions of the carbide formation. FACT Sage simulations were also used to investigate the material system in state of thermodynamic equilibrium. Results show that mass transfer and kinetics may play an important role if compared to equilibrium analyses using FACT Sage.
Phosphorus (P) recycling from sewage sludge for agricultural needs has to meet requirements for agricultural implementation, such as short and long-term P-plant-availability under field conditions. Field experiments often bring no evaluable results, because agricultural soils got a high potential of P-supply even if they are classified as low in P-supply according to the CAL extraction method. The present study presents a possible way to investigate the P-plant-availability of P-recycling-fertilizers under field-like conditions. The plant experiments are firstly performed in small Mitscherlich pots in growth chambers and subsequently in containers with a high soil volume of 170 kg under greenhouse conditions, in which plants can grow until ripening. The tested P-recycling fertilizers were produced from sewage sludge in a large-scale thermal process. It was a two-step treatment process performed with a pyrolysis of sewage sludge at 550°C (SSC-550) and a subsequent thermochemical post-treatment at 950°C with Na2SO4 (SSA-Na) and HCl + Na2SO4 (SSA-HCl/Na) as additives. The results show, that the P-recycling-products from pyrolysis got an adequate long-term but a 65% lower short-term P-plant-availability compared to triple superphosphate. SSA-Na and SSA-HCl/Na show both a high short and longterm P-plant-availability comparable to triple-superphosphate. This can be explained by their highly plant-available P-compound CaNaPO4.
In the transition to the Circular Economy (CE) model, where the added value of products is kept as long as possible and waste is eliminated, the sustainable management of raw materials plays a key role. In above CE model, especial attention is paid to CRMs which are economically and strategically important for the European economy, but have a high-risk associated with their supply.
One of the most important element which can not be replaced and is an essential element for human nutrition, yet limited resource is phosphorus (P). An importance of issues related to sustainable P management results from EU legislation, which indicated P as a Critical Raw Material (CRM).
The sustainable management of P-resources is especially important for the Baltic region. A consequence of waterborne loads passing into the sea, mainly as wastewater with a high P content is the eutrophication of the Baltic Sea environment. Due to the largest inputs of P (37%) into the Baltic Sea originate from Poland, the development of sustainable solutions aimed at more rational P management for this country is externally important.