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- Sewage sludge ash (9)
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Eingeladener Vortrag
- nein (14)
Die Herstellung hydrothermal erhärteter Granulate ist eine Möglichkeit zur Wiederverwertung von ziegelhaltigem Mauerwerkbruch, der derzeit aufgrund der heterogenen Zusammensetzung und hoher Feinanteile ein besonders hohes Verwertungsdefizit aufweist. Dabei ist die hydrothermale Erhärtung in einem Autoklav bei 200 °C und 1.6 MPa in gesättigter Wasserdampfatmosphäre eine Alternative mit geringerem Energieverbrauch im Vergleich zur thermischen Herstellung von Leichtgranulaten aus mineralischen Abfällen (Blähgranulate) oder Tonen und Schiefer (kommerzieller Blähton bzw. Blähschiefer), die bei Temperaturen von 1200-1300 °C im Drehrohrofen erfolgt.
Die Festigkeit der Hydrothermalgranulate entwickelt sich bei diesem Prozess durch die Ausbildung von Calciumsilicathydrat-Phasen (CSH), die durch die Reaktion zwischen Quarzpartikeln und hydratisiertem Kalk entstehen. Die so erzeugten Hydrothermalgranulate haben Rohdichten zwischen 1500 kg/m3 und 2000 kg/m3. Damit und auch durch andere Eigenschaften unterscheiden sie sich von den thermisch erhärteten Blähgranulaten bzw. Blähtonen. Ursache dafür ist letztendlich eine sehr unterschiedliche Gefüge- und Porenstruktur. Im vorliegenden Beitrag wird hauptsächlich über die Ergebnisse der Mikrostrukturuntersuchungen an Hydrothermalgranulaten zusammen mit ihren technologischen Eigenschaften, wie Kornfestigkeit, Rohdichte und Wasseraufnahme, berichtet.
Synthese hydraulischer Phasen in Papierasche und Braunkohlenflugasche durch hydrothermale Behandlung
(2015)
Reststoffe aus industriellen Filter- und Verbrennungsprozessen, die in ihren Hauptbestandteilen aus Si02- und CaO-reichen Mineralphasen bestehen, besitzen das Potential hydraulische Eigenschaften auszubilden. Das bedeutet, dass sie in Anwesenheit von Wasser oder alkalischen Lösungen festigkeitsbildende Phasen entwickeln. Oft bedarf es zunächst einer Aufbereitung um die hydraulischen Mineralphasen zu aktivieren. Hydraulische Phasen sind z.B. die Calciumsilikate Alit (C3S) und Belit (C2S). Sie unterscheiden sich vorrangig durch ihr Ca/Si-Verhältnis. Im Allgemeinen hydratisiert Belit langsamer als Alit und das Hydratationsprodukt weist nach 28 Tagen eine geringere Festigkeit auf. Zur Herstellung von Belit wird weniger Calciumoxid benötigt als zur Herstellung von Alit. Daher muss weniger CaC03 kalziniert werden und der C02-Ausstoß bei der Produktion verringert sich. Zur Synthese von hydraulisch aktivem Belit kann eine hydrothermale Aufbereitung dienen. Verschiedene Autoren nutzten diese Behandlung zur Aktivierung verschiedener Reststoffe, wobei sich CaO-reiche Asche aus der Energieerzeugung (z.B. Braunkohlenflugasche) als sehr geeignet erwies, Papierasche (PA) aus dem Papierrecyling besitzt ebenfalls einen hohen CaO-Gehalt und ist Bestandteil der aktuellen Bindemittelforschung auf Reststoffbasis. Die Untersuchung einer hydrothermalen Aktivierung fehlt bisher. Dieser Artikel soll einen Beitrag zur Klärung der folgenden Fragen leisten: Eignet sich Papierasche zur Belitsynthese durch hydrothermale Behandlung? Wie entwickeln sich die Mineralphasen im Vergleich zur Braunkohlenflugasche?
Mikrostrukturelle und mineralogische Eigenschaften leichter Gesteinskörnungen aus Mauerwerkbruch
(2015)
Poröse RC-Leichtgranulate mit Rohdichten zwischen 600 kg/m³ und 1400 kg/m³ können nach einem mehrstufigen mechanischen Prozess durch thermische Erhärtung bei 1180 °C aus ziegelhaitigern Mauerwerkbruch hergestellt werden. Diese Granulate erfüllen die Anforderungen an leichte Gesteinskörnungen nach DIN EN 13055 und es lassen sich damit Leichtbetone nach DIN EN 206-1/DIN 1045-2 herstellen. Ihre Festigkeits- und Dauerhaftigkeitseigenschatten sind mit denen herkömmlicher Leichtbetone mit Blähtonkörnungen sehr gut vergleichbar. Das ist das Fazit aus dem in den letzten Jahren durchgeführten Verbundforschungsvorhaben "Aufbaukörnungen". Um jedoch die Granulatentstehung bzw. den Vorgang der Porosierung besser verstehen, den Herstellungsprozess optimieren und die Eigenschaften der Granulate maßschneidern zu können, wurden zusätzlich zu den makroskopischen Charakteristika, wie beispielsweise Porosität und Wasseraufnahme, die chemisch-mineralogischen und mikrostrukturellen Eigenschaften der Leichtgranulate untersucht. Dazu dienten Analysen mittels ICP-Emissionsspektrometrie, Röntgenpulverdiffraktometrie, Quecksilberporosimetrie und mikroskopischen Verfahren. Im Beitrag wird über die Ergebnisse der Gefüge- und Porenstrukturuntersuchungen an Leichtgranulaten im Vergleich zu herkömmlichem Blähton berichtet.
For the first time evidence is provided that a nanocrystalline and stacking-disordered, chemically stabilized β-cristobalite form of AlPO4 occurs in a sewage sludge ash (SSA). This proof is based on a combined X-ray powder diffraction and X-ray fluorescence investigation of an SSA produced at a large-scale fluidized bed incineration facility serving a catching area with a population of 2 million. The structural and chemical characterization was carried out on 'as received' SSA samples as well as on solid residues remaining after leaching this SSA in sodium hydroxide solution. Thus, it was ascertained that the observed nanocrystalline and stacking-disordered cristobalite-like component belongs to the aluminum phosphate component of this SSA, rather than to its silicon dioxide component. In addition, a direct proof is presented that the chemically stabilized β-cristobalite form of AlPO4 does crystallize from X-ray amorphous precursors under conditions that mimic the huge heating rate and short retention time (just seconds at T ≈ 850°C), typical for fluidized bed incinerators.
A model system was used to simulate the properties of tribofilms which form during automotive braking. The model system was prepared by ball milling of a blend of 70 vol.% iron oxides, 15 vol.% molybdenum disulfide and 15 vol.% graphite. The resulting mixture was characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and various transmission electron microscopic (TEM) methods, including energy dispersive X-ray spectroscopy (EDXS), high resolution investigations (HRTEM) with corresponding simulation of the HRTEM images, diffraction methods such as scanning nano-beam electron diffraction (SNBED) and selected area electron diffraction (SAED). It could be shown that the ball milling caused a reduction of the grain size of the initial components to the nanometer range. Sometimes even amorphization or partial break-down of the crystal structure was observed for MoS2 and graphite. Moreover, chemical reactions lead to a formation of surface coverings of the nanoparticles by amorphous material, molybdenum oxides, and iron sulfates as derived from XPS.
This paper reports the first successful synthesis and the structural characterization of nanocrystalline and stacking-disordered β-cristobalite AlPO4 that is chemically stabilized down to room temperature and free of crystalline impurity phases. Several batches of the title compound were synthesized and thoroughly characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectroscopy mapping in SEM, solid-state 31P nuclear magnetic resonance (31P-NMR) spectroscopy including the TRAPDOR method, differential thermal analysis (DTA), gas-sorption methods, optical Emission spectroscopy, X-ray fluorescence spectroscopy, and ion chromatography. Parameters that are critical for the synthesis were identified and optimized. The synthesis procedure yields reproducible results and is well documented. A high-quality XRD pattern of the title compound is presented, which was collected with monochromatic copper radiation at room temperature in a wide 2θ range of 5°–100°.
A set of 59 ancient magical artefacts, mainly made of lead, was selected from the collections of the Staatliche Museen zu Berlin in order to unravel their origins. All the selected artefacts have been studied for their Pb isotope compositions, which covered the whole range of the Mediterranean ore deposits. However, the majority (≈86%) were made of lead matching the small compositional range of the Laurion ore deposits. Only eight out of the 59 artefacts were made of recycled lead or lead from other ore deposits.
Additionally, all but two were approximately dated based on their inscriptions. The lead isotopic composition together with information obtained from the inscriptions, the resulting dating, the context of the find and the known history of each item allowed us to gain more detailed information about the origins of these magical artefacts. The Attic provenance of 36 curse tablets was confirmed, whereas for 11 curse tablets previously classified as non-Attic, the provenance was either confirmed and specified (six artefacts) or changed to Attic (five artefacts). Surprisingly, the majority (six out of eight) of the analysed curse tablets from the Egyptian collection showed a lead isotopic composition closely matching that of Laurion.
A Laurion-like lead isotopic composition was also observed for three of the four analysed oracular tablets from Dodona. Together with the dating information, this points to Laurion as the major and dominant lead source in the Aegean, at least during the fourth–third century B.C. The few curse tablets from earlier than the fourth–third century B.C. point to the use of multiple and thus isotopically more variable lead sources compared with the Roman times.
Morphology and structure of TixOy nanoparticles generated by femtosecond laser ablation in water
(2018)
In this work femto-second pulsed laser ablation in liquid (PLAL) procedure for the generation of titanium oxide nanoparticles (NP) is reported with the purpose of understanding morphology and structure of the newly generated NPs. Ablation duration was varied for optimization of NP generation processes between 10 and 90 min. Surface morphology of NPs as well as their size and shape (distribution) were analysed by various complementary electron microscopy techniques, i.e. SEM, TSEM and TEM. The crystalline structure of titanium oxide particles was investigated byXRD(two instruments operated in different geometries) and HR-TEM. Concentration of generated titanium oxide NPs in liquid was analysed by ICP-MS. A mix of crystalline (mainly anatase), partly crystalline and amorphous spherical titanium oxide NPs can be reported having a mean size between 10 and 20 nm, which is rather independent of the laser ablation (LA) duration. A second component consisting of irregularly shaped, but crystalline titanium oxide nanostructures is co-generated in the LA water, with more pronounced occurrence at longer LA times. The provenance of this component is assigned to those spherical particles generated in suspension and passing through the converging laser beam, being hence subject to secondary irradiation effects, e. g. fragmentation.
A femto-second pulsed laser ablation in liquid (PLAL) procedure for the generation of titanium oxide nanoparticles (NP) is reported with the purpose of understanding morphology and structure of the newly generated NPs. Ablation duration was varied for optimization of NP generation processes between 10 and 90 min. Surface morphology of NPs as well as their size and shape (distribution) were analysed by various complementary electron microscopy techniques, i.e. SEM, TSEM and TEM. The crystalline structure of titanium oxide particles was investigated by XRD(two instruments operated in different geometries) and HR-TEM. Concentration of generated titanium oxide NPs in liquid was analysed by ICP-MS. A mix of crystalline (mainly anatase), partly crystalline and amorphous spherical titanium oxide NPs can be reported having a mean size between 10 and 20 nm, which is rather independent of the laser ablation (LA) duration. A second component consisting of irregularly shaped, but crystalline titanium oxide nanostructures is co-generated in the LA water, with more pronounced occurrence at longer LA times. The provenance of this component is assigned to those spherical particles generated in suspension and passing through the converging laser beam, being hence subject to secondary irradiation effects, e. g. fragmentation.
Sewage sludge and sewage sludge ashes (SSA) are produced in huge amounts at municipal waste water treatment plants (WWTP) all around the world and have become an issue for many urbanized areas. To deal with this unceasing mass flow in an ecologically and economically responsible way a comprehensive chemical and structural characterization of all types of SSA is needed. X-ray powder diffraction (XRD) is one of the most promising analytical methods for this task. Although, there has been ample chemical evidence showing that many SSA contain aluminium phosphate as a major component up to now no aluminium phosphate or aluminium-rich mixed phosphate phase has been reported to be identified by XRD in a SSA produced at a mono-incineration facility. The outcome of the present com-bined XRD and Mossbauer spectroscopy investigation provides comprehensive evidence closing this gap for the first time.
The sequence of reactions accompanying the thermochemical treatment of an iron- and aluminium-bearing sewage sludge ash was ascertained by investigating two systematic series of samples. The ash was thermochemically treated in a lab-scale rotary furnace after mixing it with a chlorine-donor, either CaCl2 or MgCl2. Within each of these two sample series only a single process parameter, the reaction temperature, was varied, namely between 350 and 1050°C. It was found, that among the numerous crystalline phases present in the raw ash only quartz and hematite continue to exist after thermochemical treatments carried out at 1050°C, whereas all other components undergo at least one decomposition-recrystallization cycle. Some of the components re-crystallize even several times. It was proved that the restructuring of the calcium- and phosphorus-bearing mineral phases proceeds via the formation of chlorspodioside, Ca2PO4Cl. The influence of the type of chlorine-donor on the final product was elucidated in detail and - to the best of our knowledge - for the first time crystalline AlPO4 was found in a sewage sludge ash and its decomposition was investigated, too.
New horizons of the structural characterization of stainless steel slags by X-ray powder diffraction
(2007)
Phosphorus (P) is an essential element for all living organisms and cannot be replaced. Municipal sewage sludge is a carrier of phosphorus, but also contains organic pollutants and heavy metals. A two-step thermal treatment is suggested, including mono-incineration of sewage sludge and subsequent thermochemical treatment of the ashes. Organic pollutants are completely destroyed by mono-incineration. The resulting sewage sludge ashes contain P, but also heavy metals. P in the ashes exhibits low bioavailability, a disadvantage in farming. Therefore, in a second thermochemical step, P is transferred into mineral phases available for plants, and heavy metals are removed as well. The thermochemical treatment was investigated in a laboratory-scale rotary furnace by treating seven different sewage sludge ashes under systematic variation of operational parameters. Heavy metal removal and the increase of the P-bioavailability were the focus of the investigation. The present experimental study shows that these objectives have been achieved with the proposed process. The P-bioavailability was significantly increased due to the formation of new mineral phases such as chlorapatite, farringtonite and stanfieldite during thermochemical treatment.
The present work shows that U can be effectively removed from groundwater using permeable reactive barriers with hydroxyapatite (HAP) as reactive material. The main factor influencing the removal processes is the composition of the groundwater, namely the concentration of Ca and carbonate. Sorption of U onto the HAP surface seems to be the dominant removal process with the possibility of remobilisation. Newly formed U-phosphate minerals were detected by ESEM/EDX and XRD in samples with high U content indicating either a dissolution-precipitation mechanism or sorption onto the apatite surface followed by alteration of the structure. The formed U-phosphate minerals are stable under common groundwater conditions and can be remobilised only at high pH-values and high carbonate concentrations.