4.4 Thermochemische Reststoffbehandlung und Wertstoffrückgewinnung
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- Diffusive gradients in thin films (DGT) (3)
- Electric arc furnace dust (3)
- Landwirtschaft (3)
- Phosphorus recovery (3)
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Conventional fertilisers have their disadvantages as nutrient release is not synchronised with the demand of plants. Several approaches of "next generation fertilisers" are aiming at controlled nutrient release. Recycling fertilisers are often not soluble in water but fully plant available. They are suitable raw materials for the production of new types of controlled release fertilisers.
Carbonfasern sind äußerst stabil und werden auch in Anlagen zur Verbrennung von Sondermüll kaum zerstört. Beim Handling carbonfaserhaltiger Abfälle können Gesundheitsrisken auftreten (Abgabe von WHO-Fasern). Es werden Methoden der Verwertung carbonfaserhaltiger Reststoffe in der Pyrometallurgie diskutiert.
Die P-Rückgewinnung aus Teilströmen mit erhöhten P-Gehalten kann direkt in den Kläranlagenbetrieb integriert werden und führt dort in vielen Fällen zu betrieblichen und ökonomischen Vorteilen. Sie ist in der Regel auf Bio-P-Kläranlagen beschränkt, da hier die anaerobe P-Rücklösung initiiert und genutzt werden kann. Durch die reine P-Rücklösung durch Schaffung anaerober Bedingungen ist allerdings das Potential der Rückgewinnung auf 5 bis 15 Prozent der Zulauffracht limitiert.
Die meisten Kläranlagen in Deutschland werden mit einer chemischen Phosphor-Fällung betrieben. Diese Anlagen können aus dem Klärschlamm Phosphat in ausreichend hoher Konzentration nur zurückgewinnen, indem zusätzlich anorganische Säuren wie Schwefelsäure zugeführt werden oder ein Aufschluss mit flüssigem Kohlendioxid stattfindet. Es wird angenommen, dass sich mit diesen Verfahren mehr als 50 Prozent der Zulauffracht einer Kläranlage zurückgewinnen lassen. Der Aufschluss von Klärschlamm mit Schwefelsäure geht aber mit vergleichsweise hohen Umweltwirkungen sowie mit höheren Kosten im Vergleich zu anderen Phosphor-Rückgewinnungsverfahren einher. Ein sehr hohes Potential der Rückgewinnung von Phosphor (P) ist bei allen Verfahren gegeben, die als Rohstoff die Asche aus der Monoverbrennung verwerten. Der Aufschluss mit anorganischen Säuren ermöglicht die sichere Phosphor-Rückgewinnung von mehr als 80% Prozent des Kläranlagenzulaufs. Die Verfahren sind zum Teil großtechnisch umgesetzt oder es befinden sich großtechnische Anlagen im Bau. Auch thermochemische Verfahren wurden entwickelt und deren Einsatzbereitschaft im großtechnischen Maßstab erfolgreich demonstriert. In dem nachfolgenden Beitrag werden unterschiedliche praxiserprobte Verfahren zur Phosphor-Rückgewinnung unter technischen und wirtschaftlichen Aspekten vorgestellt.
Treatment and reusing of hazardous wastes have become significant issues of modern societies. Blast furnace sludge (BFS) and electric arc furnace dust (EAFD) are such typical wastes, because they usually contain high amounts of undesirable elements such as zinc (Zn) and lead (Pb).
These elements can cause operational problems in reusing of BFS and EAFD. In this study, the Ferro Duo GmbH and the Federal Institute for Materials Research and Testing have investigated a novel approach for eliminating and/or recovering Zn and Pb from both wastes. Applied was a selective chlorination and volatilization of Zn and Pb as chlorides at temperatures between 500 °C and 1100 °C. Both product obtained, Zn and Pb in the form of ZnCl2 and PbCl2 and the purified solid mineral compound are attractive materials for further use. Hydrochloric acid and iron(II) chloride were used as chlorination agents. Exceptionally high Zn and Pb removal efficiencies of >99.5 % could be achieved with both chlorination agents, whereby iron(II) chloride exhibited better performance.
Brazilian farming industry consumed around 2.2 million tons of phosphorus (P) fertilizers in 2016. The agricultural industry depends on imported P fertilizers and over 98% of P fertilizers were used for sugarcane, soybean and maize production.
An alternative is to use P from sugarcane bagasse. Bagasse is the fibrous plant material remaining after extraction of sugarcane juice, and it is combusted for energy production. Remaining ash con-tains up to 0.6 wt% P. The use of bagasse ash (BA) as P fertilizer could decrease the annual import of P fertilizers by 6% of the imported P fertilizer based on 2016 values. Since the bioavailability of P from BA to plants is poorly investigated, this study addresses the effects of (i) gasification tempera-ture (710-849°C), (ii) processing method (gasification vs. combustion), (iii) biomass modifications by co-processing bagasse with chicken manure (BA+CM), and (iv) the soil (Brazilian Oxisol soil vs. nutri-ent poor substrate) on the bioavailability of P from BA to soybeans (Glycine max).
Gasification of BA at 806 °C resulted in significantly highest uptake of P by soybeans and was around 0.33 mmol after 51 days growing. The bioavailability of P significantly increased due to co-gasification of bagasse and chicken manure (BA+CM) and the soybeans took up around 16% more P. Compared to the nutrient-poor substrate, the bioavailability of P in BA+CM ash treated Oxisol soil was signifi-cantly lower by 46% and there was no significant effect of processing method on the bioavailability of P from the BA+CM ash to soybeans. Contrary to the Oxisol soil, the bioavailability of P from co-combusted BA+CM ash was significantly higher compared to co-gasified BA+CM ash. In conclusion, co-processing of bagasse with nutrient rich residues can increase the value of BA as P fertilizer. The bioavailability of P from ash to plants depends on the P forms. Mineralogical analyses of ash P forms by NMR and X-ray diffraction are in progress and will be presented at the conference.
Dieser Vortrag beschreibt die Entwicklung eines neuen chemischen Verfahrens, das in einem Kooperationsprojekt zwischen der Bundesanstalt für Materialforschung und -prüfung (BAM) und der Ferro Duo GmbH entwickelt wird. Mit dem entwickelten Verfahren soll es ermöglicht werden, schwermetallhaltige Filterstäube und -schlämme, die als Abfälle während der Produktion von Roheisen und Rohstahl anfallen und die derzeit größtenteils deponiert werden, zu recyceln und die darin enthaltenen Wertstoffe (v.a. Eisen, Kohlenstoff und Zink) wieder in den Rohstoffkreislauf zurückzugeben. Dies wird durch eine Chlorierung der in den Filterstäuben und -schlämmen enthaltenen Schwermetalloxiden erreicht, die bei Temperaturen zwischen 650 und 1100 °C in Form von Schwermetallchloriden verdampft und so selektiv separiert werden. Erste experimentelle Ergebnisse zeigen, dass die Gehalte an Schwermetallen wie Zink, Blei und Cadmium um bis zu 99,7% reduziert werden können und die thermochemisch behandelten Filterstäube und -schlämme durch das Verfahren in sekundäre Rohstoffe für die Roheisenproduktion umgewandelt werden können.
Blast furnace (BF) sludge and electric arc furnace (EAF) dust are typical wastes that incur from iron and steel production. In addition to iron, calcium, carbon, and silicon they usually contain high concentrations of heavy metals such as zinc, lead, and cadmium that are potentially hazardous to the environment, rendering disposal in landfills ecologically problematic and costly. Consequently, pyrometallurgical, hydrometallurgical, and hybrid methods for selective elimination of non-ferrous heavy metals from BF sludge and EAF dust have been conceived, of which only the carbothermic reduction route taken in the so-called Waelz rotary kiln process has been proven to be economically successful. However, this process has several drawbacks regarding efficiency of heavy-metal removal and recovery of iron, and it does not allow processing of BF sludge. In this study, we investigated the efficiency and feasibility of selective chlorination and evaporation of non-ferrous heavy metals, particularly zinc and lead, in both BF sludge and EAF dust as an alternative, thermochemical processing route. To this end, hydrochloric acid and iron(II) chloride solution have been used as chlorinating agents, and the process of heavy-metal chlorination and evaporation has been investigated under inert operating conditions, at variable chlorine concentrations, and at temperatures between 500 and 1200 °C.
High zinc and lead removal efficiencies of > 99.5 % were achieved with both chlorinating agents, but iron(II) chloride turned out to be overall more efficient for removal of zinc and lead from BF sludge and EAF dust. Interestingly, and in contrast to previous studies, the iron was completely retained in the processed solid residue, therefore rendering the processed residues virtually zinc- and lead-free raw materials that may either be used internally (e.g., feeding processed BF sludge and EAF dust back into the respective furnaces) or externally (e.g., for cement production).
Dieser Beitrag beschreibt die Entwicklung eines neuen chemischen Verfahrens, das in einem Kooperationsprojekt zwischen der Bundesanstalt für Materialforschung und -prüfung (BAM) und der Ferro Duo GmbH entwickelt wird. Mit dem entwickelten Verfahren soll es ermöglicht werden, schwermetallhaltige Filterstäube und -schlämme wie Gichtgasschlämme oder Elektroofenstäube, die als Abfälle während der Produktion von Roheisen und Rohstahl anfallen und die derzeit größtenteils deponiert werden, zu recyceln und die darin enthaltenen Wertstoffe (v.a. Eisen, Kohlenstoff und Zink) wieder in den Rohstoffkreislauf zurückzugeben. Das Verfahren basiert auf dem Prinzip der Chlorierung der in den Filterstäuben und -schlämmen enthaltenen Schwermetalloxide nach Zugabe eines flüssigen Chlordonators wie Eisen(II)-chlorid-Lösung oder Salzsäure. Die so chlorierten Schwermetalloxide werden bei Temperaturen zwischen 650 und 1100 °C in Form von Schwermetallchloriden verdampft und so selektiv vom behandelten Feststoff separiert. Erste experimentelle Ergebnisse zeigen, dass die Gehalte an Schwermetallen wie Zink, Blei und Cadmium um bis zu 99,7% reduziert werden können und die thermochemisch behandelten Filterstäube und -schlämme durch das Verfahren in sekundäre, im Wesentlichen aus Eisenoxiden bestehenden Rohstoffe für die Roheisenproduktion umgewandelt werden können. Da die chlorhaltigen Lösungen selbst Abfallstoffe aus anderen Industriezweigen sind (z.B. aus der Titandioxidproduktion oder der Stahlbeize), vereint das hier entwickelte Verfahren auf elegante Weise zwei Abfallstoffströme und wandelt diese in sekundäre Rohstoffe – einem mineralischen Rohstoff für die Roheisenproduktion sowie Zinkchlorid – um.
In a rapidly evolving world, the demand on raw materials is increasing steadily and many technologies are dependent on a secure supply of hi-tech metals. Recently, scandium (Sc) has attracted attention since its use in high strength Al-alloys and solid-oxide-fuel-cells strongly improves the performance of those materials.
The element Sc is not exceptionally rare but quite resistant to geochemical enrichment processes, it is scarcely found enriched to high concentrations and is recovered as a by-product. Since Sc enrichment in Greek bauxite residues was shown by Ochsenkühn-Petropoulou et. al (1994), intensive research on this material and development of efficient Sc-recovery methods is ongoing.
This study investigates Sc-bearing species in bauxite residues from alumina production. It aims to provide direct evidence about the Sc-speciation’s in those secondary resources and tries to find the link to speciation’s in primary resources, e.g. bauxites and laterites.
Therefore, Sc K edge XANES (X-ray absorption near edge structure) spectroscopy is performed using synchrotron radiation to determine the presence of certain Sc-components and distinguish between adsorbed and chemically bonded Sc as was shown for lateritic deposits in Australia by Chassé et al. 2016. For comparison, reference standards of Sc-bearing and Sc-adsorbed species are synthesized. Indirect inferences from leaching behavior of bauxites, in cases supported by analyses with LA-ICP-MS, suggest Sc to be associated with either iron- or aluminum phases (Vind et al. 2017); (Suss et al.). It remains unclear how different primary materials influence Sc-speciation in the bauxite residue. Therefore, a comparison between different European bauxite residues is made in this study. The investigations should help to understand Sc chemistry and
behavior in different primary and secondary materials and provide fundamentals for metallurgical processing. The research is incorporated in the SCALE project (GA No. 730105) funded by EU Horizon 2020 research and innovation program.
Small-scale variations in mineral chemistry, textures, and platinum group element (PGE) mineralization were investigated in the Lower and Middle Group chromitite layers LG6, LG6a, MG1, MG2, and MG2 II from vertical drill core profiles at the Thaba mine in the northwestern limb of the Bushveld Complex. We present detailed geochemical profiles of chromite composition and chromite crystal size distribution curves to shed light on the processes of chromite accumulation and textural modification as well as mineralization. Multiple samples within each layer were assayed for PGE concentrations, and the respective platinum group mineral association was determined by mineral liberation analysis (MLA).
There is strong evidence for postcumulus changes in the chromitites. The crystal size distribution curves suggest that the primary chromite texture was coarsened by a combination of adcumulus growth and textural equilibration, while compaction of the crystal mush played only a minor role. Mineral compositions were also modified by postcumulus processes, but because of the very high modal amount of chromite and its local preservation in orthopyroxene oikocrysts, that phase retained much primary information. Vertical variations of chromite composition within chromitite layers and from one layer to another do not support the idea of chromite accumulation from crystal-rich slurries or crystal settling from a large magma chamber. Instead, we favor a successive buildup of chromitite layers by repeated injections of relatively thin layers of chromite-saturated magmas, with in situ crystallization occurring at the crystal mush-magma interface. The adcumulus growth of chromite grains to form massive chromitite required addition of Cr to the layers, which we attribute to downward percolation from the overlying magma.
The PGE concentrations are elevated in all chromitite layers compared to adjacent silicate rocks and show a systematic increase upward from LG6 (avg 807 ppb Ir + Ru + Rh + Pt + Pd + Au) to MG2 II (avg 2,062 ppb).
There are also significant internal variations in all layers, with enrichments at hanging and/or footwalls. The enriched nature of chromitites in PGEs compared to host pyroxenites is a General feature, independent of the layer thickness. The MLA results distinguish two principal groups of PGE mineral associations: the LG6, LG6, and MG1 are dominated by the malanite series, laurite, and PGE sulfarsenides, while the MG2 and MG2 II layers are characterized by laurite and PGE sulfides as well as Pt-Fe-Sn and PGE-Sb-Bi-Pb alloys. Differences in the PGE associations are attributed to postcumulus alteration of the MG2 and MG2 II layer, while the chromitites below, particularly LG6 and LG6a, contain a more pristine association.
P recycling fertilizers are gaining increasing importance in our efforts to close nutrient cycles. An unsatisfactory performance of standard chemical extraction methods to assess the fertilizing effects of such products was reported. They demonstrated that DGT extractions of incubated soil/fertilizer mixtures were able to predict the fertilizing effects of the respective products more accurately. Since DGT works with soil/fertilizer mixtures, its interpretation is soil-dependent. Therefore, in order to facilitate its use as a tool to predict fertilizer performance, it needs to be standardized based on a standard substrate. This research aims to develop a standard substrate based on which evaluation categories for the DGT fertilizer extraction can be derived. The substrate composition should allow to vary the most important soil properties determining the plant availability of fertilizer P. It must also be reproducible at any time and any place. Substrate variants with varying proportions of quartz sand, a clay mineral and sphagnum peat were prepared and set to pH-levels 5.5 and 7 by addition of CaCO3. 7 variants were incubated with a set of test fertilizers (2 recycling fertilizers based on sewage sludge ash and 2 conventional mineral fertilizers) for 2 weeks. Substrate/fertilizer mixtures were then extracted with DGT and an ANOVA was performed to test if the DGT extraction was able to depict significant differences between fertilizers and substrate variants. An 8-week pot trial with ryegrass (3 cuts) was set up with the same substrate variants and test fertilizers. P uptake was determined to assess the fertilizing effect and correlated with the results of the DGT extractions. Statistically significant differences were found between DGT results for the various test fertilizers and substrate variants, indicating that DGT is able to differentiate between P solubility of fertilizers in relation to substrate quality. DGT results showed a strong relationship with P uptake, confirming that this method is suitable to predict the fertilizing effect of P fertilizers. Further optimization of substrate composition and tests with a wider variety of crops and fertilizer types are needed, before evaluation categories for DGT values can be derived.
Die agronomische Effizienz von Düngemitteln wird üblicherweise in Vegetationsversuchen geprüft. Diese erlauben die es, unterschiedliche Kulturpflanzen und deren Strategien der Nährstoffmobilisierung und -aneignung zu betrachten und verschiedene Substrattypen und deren Eigenschaften im Hinblick auf Nährstofffixierung und -freisetzung zu berücksichtigen. Solche Versuche, selbst wenn sie nicht im Feld, sondern nur im Gefäß durchgeführt werden, sind jedoch sowohl zeit- als auch kostenintensiv. In erster Näherung wird die Pflanzenverfügbarkeit insbesondere von Phosphor (P)-Düngemitteln daher in der Regel mit Hilfe standardisierter chemischer Extraktionsmethoden abgeschätzt, deren Durchführung in der deutschen ebenso wie in der europäischen Düngemittelverordnung normiert ist. Diese Methoden werden auch bei der staatlichen Düngemittelverkehrskontrolle genutzt, um zu überprüfen, ob die düngemittelrechtlichen Vorgaben eingehalten werden. Wie jüngere Arbeiten gezeigt haben, ist es jedoch schwierig, herkömmliche Standardextraktionsmethoden auf neue Dünger aus Recyclingmaterialien wie Klärschlamm zu übertragen. Korrelationen zwischen P-Aufnahme im Vegetationsversuch und chemischer Löslichkeit im Standardextrakt sind oft nur mäßig bis schwach oder überhaupt nicht signifikant. Die vorliegende Literaturübersicht gibt einen Überblick zum aktuellen Stand des Wissens über die chemische Löslichkeit von klärschlammbasierten P-Recyclingdüngern, deren Effizienz im Vegetationsversuch und statistische Relationen zwischen beiden Parametern. Anschließend werden alternative Methoden zur Abschätzung der P-Verfügbarkeit von Recyclingdüngern vorgestellt, die derzeit Gegenstand der wissenschaftlichen Diskussion sind.
Phosphorus (P) is an essential element for all life forms, and P-availability thus an important driver of a functioning agriculture. However, phosphate rock resources for P-fertilizer production are only available in a few countries. Therefore, P-recovery from waste materials has become of increasing interest during the last decade and has been investigated worldwide. In order to characterize potential novel P-fertilizers made from recycled materials, a large array of P-compound characterizations, chemical extractions and growth experiments were performed. This review bundles the work carried out in that field over the last years. Overall, P-fertilizers from recycled materials show a broad range of P-compounds with very different chemical structure and solubility. Growth experiments performed to assess their fertilizing effects display high variations for most of the products. While these experiments have demonstrated that some fertilizers made of recycled materials may reach P effects in the same order of magnitude as water-soluble phosphate rock-based fertilizers, an important limitation in their interpretation is the fact that they often vary considerably in their experimental design. The existing data show clearly that standardization of growth experiments is urgently needed to achieve comparable results. Standard chemical extractants used to assess the chemical solubility of P-fertilizers were found to be of limited reliability for predicting plant P uptake. Therefore, alternative methods such as sequential fractionation, or the extraction of incubated soil/fertilizer mixtures with standard soil extractants or with P sink methods should be tested more intensively in the future to provide alternative options to predict the P-availability of fertilizers from recycled materials.
In Denmark, increasing amounts of woody biomass are being used for the production of renewable energy, resulting in more wood ashes being generated. While these materials have been mainly landfilled, wood ashes may also be utilised for fertilizing and liming purposes on top of soils. Pre-treatments involving hardening or granulation may be carried out prior to soil application. In this study, two Danish wood ash samples were hardened and/or granulated. Lab-hardening induced rapid changes in the shape of the acid neutralisation capacity curve of the ashes. Up-flow column tests, assuming local equilibrium conditions, were employed to investigate the leaching from pre-treated ashes. Granules and loose ashes demonstrated similar leaching behaviours, indicating that similar geochemical processes were governing their leaching. In comparison with untreated fresh ashes, the hardened ashes demonstrated reduced leaching of Ca, Ba, Pb and Zn with concentration levels generally below or close to the analytical limits of quantification; to the contrary, the leaching of As, P, Sb, Si, V and Mg was enhanced in the hardened ashes. The release of alkalinity was reduced by hardening. In general, all granules were barely breakable by finger-pinching and they could withstand one month of continuous leaching, preserving their overall shape. The solubility of phosphorous in neutral ammonium citrate indicated that about 30–51% of the total P content in the ash samples was released, suggesting that the ashes could be potentially valuable as P-fertiliser if applied onto soil.
CFK-Abfälle werden trotz der bestehenden Verfahren zur Rückgewinnung der Carbonfasern zukünftig vermehrt anfallen. Für diese Abfälle wird nach technischen Lösungen der energetischen oder stofflichen Verwertung gesucht. Eine Möglichkeit ist die Nutzung der CFK-Abfälle als Primärkohleersatz im Lichtbogenofen bei der Stahlherstellung.
Tricalcium-silicate (C3S) or Alite is the most important mineral in Portland cement. Since pure tricalcium-silicate is only stable above temperatures of 1250 °C, its decomposition has to be prevented technically by fast cooling after the sintering process. At room temperature, the decomposition velocity is very slow so that metastable tricalcium-silicate is obtained.
Although the mechanisms of clinker phase formation during burning process of Portland cement in a rotary kiln were solved and improved over the years, in view of possible economic and ecological benefits current projects aim to produce clinker phases from metallurgical slags. Recent studies discovered that the mineral phase which remained after a reducing treatment and separation of formed metallic iron from molten Linz-Donawitz (LD-) slags contained about 60 wt.% Alite despite it was cooled slowly. Because the results could be verified using slags from different origins and varying cooling velocities a chemical stabilisation of the Alite can be assumed. First tests in mortars indicate that workability, hardening and solid state properties are comparable with an ordinary Portland cement. An application of the observed phenomenon in cement production requires enhanced knowledge about formation and stabilisation conditions of Alite during crystallisation from melts in contrast to the sintering reactions in conventional Portland cement production. Therefore, this study focuses on the stabilisation mechanisms of Alite in consolidating melts. Samples from different melting experiments are analysed to determine stabilising factors.
Die landwirtschaftliche Klärschlammverwertung ist in der Bundesrepublik Deutschland seit Jahren rückläufig. Neben den Risiken durch Schadstoffeinträge gibt es in Deutschland Regionen mit einem stark erhöhten Nährstoffüberschuss. Um die Grundwasserbelastung zu verhindern wurde u.a. das Düngerecht verschärft, was die Flächenkonkurrenz zwischen Klärschlamm und Wirtschaftsdünger vergrößern wird.
Es ist davon auszugehen, dass sich die neuen Regelungen im Düngerecht und der Klärschlammverordnung massiv auf die landwirtschaftliche Verwertung von Klärschlamm und damit auf die Kreislaufwirtschaft verschiedener Nährstoffe auswirken werden. In diesem Beitrag werden erste Ergebnisse des Projekts extraWERT vorgestellt.