Studying the Formation of Ni3C from CO and Metallic Ni at T=265 degrees C in Situ Using Ni K-Edge X-ray Absorption Spectroscopy

Metallic Ni nanopowder (Ni-0) was monitored during 23 h of carburization (2CO + 3Ni(0) - Ni3C + CO2, T = 265 degrees C) using Ni K-edge X-ray absorption spectroscopy. X-ray diffraction analysis made afterward at room temperature revealed 28 +/- 3% Ni3C among 72% unreacted Ni-0. The chi(k) data recorded during carburization showed small changes at low k indicative of carbon backscattering. The identification of carbon was possible with wavelet transform analysis after eliminating the integral contribution from the unreacted Ni-0 phase using experimental chi(k) data collected during methanation (CO + 3H(2) -> CH4 + H2O) at T = 265 degrees C. The Fourier-transformed chi(k) data recorded during carburization revealed destructive interference between signals from Ni atoms in slightly different (Ni-0, Ni3C) environments. The interference effect mainly lowered the peak amplitude of the first two Ni-Ni coordination shells compared to metallic Ni at T = 265 degrees C and it propagated very slowly with increasing carburization run time. In simulation of the amplitude lowering of the first Ni-Ni peak by destructive interference as a function of the carburization run time, it followed that the carbon atoms migrate into the Ni-0 particle lattice according to the diffusion-induccd grain boundary motion advocated in the literature

Separation and Recycling Potential of Rare Earth Elements from Energy Systems: Feed and Economic Viability Review

This review explores the potential of separating and recycling rare earth elements (REEs) from different energy conversion systems, such as wind turbines, electric vehicles batteries, or lighting devices. The REEs include 17 elements (with global production of 242 kilometric tons in 2020) that can be found abundantly in nature. However, they are expensive and complicated to extract and separate with many environmental challenges. The overall demand for REEs is continuously growing (with a 10% yearly increase) and it is quite clear that recycling has to be developed as a supply strategy in addition to conventional mining. However, the success of both mining and recycling depends on appropriate separation and processing technologies. The overall REE recycling situation today is very weak (only 2% of REEs are recovered by recycling processes compared with 90% for iron and steel). The biggest recycling potentials rely on the sectors of lamp phosphors (17%), permanent magnets (7%), and NiMH batteries (10%) mainly at the end-of-life stage of the products. The profitability of rare earth recycling mostly depends on the prices of the elements to accommodate the processing costs. Therefore, end-of-life REE recycling should focus on the most valuable and critical REEs. Thus, the relevant processes, feed, and economic viability warrant the detailed review as reported here

Studying sulfur functional groups in Norway spruce year rings using S L-edge total electron yield spectroscopy

Profiles of the major sulfur functional groups in mature Norway spruce wood tissue have been established for the first time. The big challenge was the development of a method suitable for sulfur speciation in samples with very low sulfur content (<100 ppm). This became possible by synchrotron X-ray absorption spectroscopy at the sulfur L-edge in total electron yield (TEY) detection mode with thin gold-coated wood slices. Functional groups were identified using sulfur compound spectra as fingerprints. Latewood of single year rings revealed metabolic plausible sulfur forms, particularly inorganic sulfide, organic disulfide, methylthiol, and highly oxidized sulfur. Form-specific profiles with Norway spruces from three different Swiss forest sites revealed high, but hitherto little-noticed, sulfur intensities attributable to natural heartwood formation and a common, but physiologically unexpected maximum around year ring 1986 with trees from the industrialized Swiss Plateau. It is hypothesized whether it may have resulted from the huge reduction in sulfur emissions after 1980 due to Swiss policy. Comparison with total S content profiles from optical emission spectroscopy underlined the more accurate and temporally better resolved TEY data with single wood year rings and it opened novel insights into the wood cell chemistry (C) 2008 Elsevier B.V. All rights reserved

Sulphur poisoning of Ni catalysts in the SNG production from biomass: A TPO/XPS/XAS study

Ni-based catalysts are prone to deactivation (poisoning) of their active surface sites by sulphur and carbon species contained in the gas fed to the reactor. This study focuses on Ni/Al2O3-based catalyst samples which had allegedly been deactivated by sulphur poisoning. The samples had been collected from a 10 kW methanation reactor fed with producer gas from the industrial biomass gasifier in Gussing (Austria). The samples allowed intensive investigation using several analytical tools to identify the chemical nature (inorganic, organic) of the S-poisoning species. Temperature-programmed oxidation (TPO) allowed quantification of the sulphur content, but not the identification of the S species responsible. S 2p X-ray photoelectron spectroscopy (XPS) pointed at the presence of sulphide and sulphate, but the data were too noisy to reach more specific conclusions. Ni K-edge X-ray absorption spectroscopy (XAS) in the fine structure (EXAFS) region suggested the presence of elemental or thiophenic sulphur, but the contribution was masked heavily by other backscattering paths. Only S Kedge analysis in the near edge (XANES) region showed unambiguously that the catalyst could not have been deactivated by inorganic H2S only. This conclusion is supported by S K-edge XANES results with model catalysts which had either been poisoned by H2S or thiophene (C4H4S), representing a cyclic, aromatic S compound. Short-term H2S poisoning in the absence of air led to a white-line position characteristic for sulphide (2470 eV), whereas with thiophene the white-line position started at 3 eV higher energy. The XANES signatures changed with the catalyst samples after contacting air, but remained unique for each of the two S-poison types studied here. (C) 2009 Elsevier B.V. All rights reserved

Inertisation of heavy metals in municipal solid waste incineration fly ash by means of colloidal silica – a synchrotron X-ray diffraction and absorption study

Many efforts have been undertaken in past decades to minimize pollution from municipal solid waste incineration fly ash (MSWI FA). This residue is toxic, because of its high concentration of heavy metals, mainly Pb and Zn. A new method for heavy metals entrapment with MSWI FA was proposed recently. The method is based on the use of colloidal silica and it was applied to other FA typologies (flue gas desulfurization and coal fly ashes). The first results, in terms of material recovery, are very promising. The present paper is dedicated to the study of the mechanism of entrapment of heavy metals as promoted by the use of colloidal silica in the inertisation process by means of X-ray Absorption Spectroscopy (XAS) and by synchrotron-based XRD. Only XAS allowed focussing on the local environmental changes for Pb and Zn atoms on a molecular level. Chemical equilibrium calculations predict that, without silica, water-soluble Pb and Zn salts form stable phases, such as carbonates. XAS analysis showed that, despite carbonation of alkaline earth metals such as Ca, colloidal silica promotes the stabilisation of major heavy metals in phases other than carbonates and most likely in the more inert silicate form