The criticality of raw materials has become an important issue in recent years. As the supply of certain raw materials is essential for technologically-advanced economies, the European Commission and ...other international counterparts have started several initiatives to secure reliable and unhindered access to raw materials. Such efforts include the EU Raw Materials Initiative, European Innovation Partnership on Raw Materials, US Critical Materials Institute, and others. In this paper, the authors present a multi-faceted and multi-national review of the essentials for the critical raw materials (CRMs) Co, Nb, W, and rare earth elements (REEs). The selected CRMs are of specific interest as they are considered relevant for emerging technologies and will thus continue to be of increasing major economic importance. This paper presents a 'sustainability evaluation' for each element, including essential data about markets, applications and recycling, and possibilities for substitution have been summarized and analysed. All the presented elements are vital for the advanced materials and processes upon which modern societies rely. These elements exhibit superior importance in 'green' applications and products subject to severe conditions. The annual production quantities are quite low compared to common industrial metals. Of the considered CRMs, only Co and REE gross production exceed 100 000 t. At the same time, the prices are quite high, with W and Nb being in the range of 60 USD kg−1 and some rare earth compounds costing almost 4000 USD kg−1. Despite valiant effort, in practice some of the considered elements are de facto irreplaceable for many specialized applications, at today's technological level. Often, substitution causes a significant loss of quality and performance. Furthermore, possible candidates for substitution may be critical themselves or available in considerably low quantities. It can be concluded that one preferred approach for the investigated elements could be the use of secondary resources derived from recycling. W exhibits the highest recycling rate (37%), whereas Co (16%), Nb (11%) and rare earths (~0%) lag behind. In order to promote recycling of these essential elements, financial incentives as well as an improvement of recycling technologies would be required.
This paper addresses the sustainability of vanadium, taking into account the current state-of-the-art related to primary and secondary sources, substitution, production, and market developments. ...Vanadium plays a critical role in several strategic industrial applications including steel production and probable widespread utilization in next-generation batteries. Confirming the importance of vanadium, the European Commission identified and formally registered this metal on the 2017 list of Critical Raw Materials for the European Union. The United States and Canada have also addressed the importance of this metal. Like the European economy, the American and Canadian economies rely on vanadium and are not globally independent. This recognized importance of vanadium is driving many efforts in academia and industry to develop technologies for the utilization of secondary vanadium resources using hydrometallurgical and pyrometallurgical techniques. In this paper, current efforts and their outcomes are summarized along with the most recent patents for vanadium recovery.
•Behavior of natural radionuclides (238U, 232Th and their decay products, 40K) in the Bayer process was analyzed.•Thorium and its decay product 228Ra were found only in bauxites and bauxite ...residue.•Minor portion of uranium was found to dissolve in the process liquors and 3% of the input content ended up in alumina.•40K dissolved and moderately accumulated in the process liquors, however it did not end up in the alumina.•From the radiation protection perspective, all the materials analyzed in the current study pose no radiological hazard.
Naturally occurring radionuclides were studied through the Bayer process by calculating their mass flows. Aluminium of Greece (AoG) provided sample materials and plant data from several process stages. Measurements of radionuclide concentrations were carried out by gamma-ray spectroscopy.
The performed measurements show that in the specific case of the AoG plant, the majority of the natural radionuclides were introduced with karst bauxites, which showed higher activity concentrations for nuclides compared to lateritic bauxites. Most of these nuclides accumulated in the bauxite residue, while only a minor portion of uranium isotope 238U was found in alumina, corresponding to 3% of its input value. Uranium was observed to partially dissolve in the process liquors similarly to 40K, whereas the latter was not associated with aluminium hydroxide.
All the materials studied in the current research work had radionuclide concentrations well below the exemption limits set by EURATOM Basic Safety Standard, indicating that these naturally occurring radionuclides do not pose a radiological hazard for workers of the AoG plant or the public.
This paper describes the characterization of commercially available plastic scintillation detectors to be used as an active shield or veto system to reduce the neutron background resulting from ...atmospheric muon interactions in low-level nuclear waste assay systems. The shield consists of an array of scintillation detectors surrounding a neutron detection system. Scintillation detectors with different thicknesses are characterized for their response to gamma rays, neutrons, and muons. Response functions to gamma rays were determined and measured in the energy range from 0.6 MeV to 6.0 MeV using radionuclide sources. Neutron response functions were derived from results of time-of-flight measurements at the Van de Graaff accelerator of the INFN Legnaro and from measurements with quasi mono-energetic neutron beams produced at the Van de Graaff accelerator of the JRC Geel. From these data, the light output and resolution functions for protons and electrons were derived. The response to muons was verified by background measurements, i.e. without the presence of any neutron or gamma source. It was found that the muon peak is more pronounced when the detectors are placed horizontally. The results indicate that a scintillator with a minimum thickness of 20 mm is needed to separate events due to atmospheric muons from natural gamma ray background, and contributions due to neutron production in nuclear waste based on only the total energy deposition in the detector. In addition, it was shown that muons can be identified with a coincidence pattern when the detectors are stacked. The effectiveness of the proposed system was demonstrated based on muon induced spallation reactions in a lead sample.
Electrowetting of Ionic Liquids Millefiorini, Stefano; Tkaczyk, Alan H; Sedev, Rossen ...
Journal of the American Chemical Society,
03/2006, Volume:
128, Issue:
9
Journal Article
Peer reviewed
We have successfully demonstrated that imidazolium- and pyrrolidinium-based commercial room-temperature ionic liquids can electrowet (with a dc voltage) a smooth fluoropolymer (Teflon AF1600) ...surface. Qualitatively, the process is analogous to the electrowetting of aqueous electrolyte solutions: the contact angle versus voltage curve has a parabolic shape which saturates at larger voltages (positive or negative). On the other hand we observed several peculiarities: (i) the efficiency is significantly lower (by about an order of magnitude); (ii) the influence of the bulky cation is larger and the importance of the smaller anion is lesser, especially with respect to electrowetting saturation; (iii) there is an asymmetry in the saturation contact angles found for positive and negative voltages. The asymmetry may be correlated with the cation−anion asymmetry of the ionic liquids. The low efficiency may be caused by the presence of water and other impurities in these commercial materials.
A ray-tracing approach is used to demonstrate efficient application of the vectorial laws of reflection and refraction to computational optics problems. Both the full width at half-maximum (fwhm) and ...offset of Gaussian beams resulting from off-center reflection and refraction are calculated for spherical and paraboloidal surfaces of revolution. It is found that the magnification and displacement depend nonlinearly on the miscentering. For these geometries, the limits of accuracy of the lens approximation are examined quantitatively. In contrast to the ray-tracing solution, this paraxial approximation would predict a magnification of a beam's fwhm that is independent of miscentering, and an offset linearly proportional to the miscentering. The focusing property of paraboloidal surfaces of revolution is also derived in setting up the calculation.
This study employs thermal and epithermal neutron activation analysis (NAA) to quantitatively and specifically determine absorption dose rates to various body parts from uranium, thorium and ...potassium. Specifically, a case study of bauxite residue (red mud) from an industrial facility was used to demonstrate the feasibility of the NAA approach for radiological safety assessment, using small sample sizes to ascertain the activities of
U,
U,
Th and
K. This proof-of-concept was shown to produce reliable results and a similar approach could be used for quantitative assessment of other samples with possible radiological significance.
U and
Th were determined by epithermal and thermal neutron activation analysis, respectively.
U was determined based on the known isotopic ratio of
U/
U.
K was also determined using epithermal neutron activation analysis to measure total potassium content and then subtracting its isotopic contribution. Furthermore, the work demonstrates the application of Monte Carlo Neutral-Particle (MCNP) simulations to estimate the radiation dose from large quantities of red mud, to assure the safety of humans and the surrounding environment. Phantoms were employed to observe the dose distribution throughout the human body demonstrating radiation effects on each individual organ.
Measurements of UV-laser stimulated piezo-optical effects were conducted on nanocrystals (NC) of several double tungstate materials such as Ln
3+:KYb(WO
4)
2 (Ln
=
Eu and Er) and KGd(WO
4)
2 immersed ...in poly(methyl methacrylate) (PMMA) matrices. At the same time, similar measurements were performed on KNd(PO
3)
4 and KTiOPO
4 NC for comparison. The NC were synthesized by a modified Pechini method with maximum calcination temperatures of 973–1173
K. It was established that the incorporation of NC with a large dispersion of sizes and substantial aggregation favors UV-induced piezo-optical effects which are dependent only on the content of the NC being optimal at 10–12% in weighting units. The measured piezo-optical dependences are related to the chemical content of the compounds that form the NC studied.
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