Addition of X-ray fluorescent tracers into polymers, new technology for automatic sorting of plastics : proposal for selecting some relevant tracers

A description of a new technology for automatic sorting of plastics, based on X-ray fluorescence detection of tracers, added in such materials is presented. This study describes the criteria for the selection of tracers, and concluded that the most adapted for XRF are some rare earth oxides. The plastics chosen for tracing and identification are the ones contained in ELV and WEEE from which discrimination is difficult for the existing sorting techniques due to their black colour.A description of a new technology for automatic sorting of plastics, based on X-ray fluorescence detection of tracers, added in such materials is presented. This study describes the criteria for the selection of tracers, and concluded that the most adapted for XRF are some rare earth oxides. The plastics chosen for tracing and identification are the ones contained in ELV and WEEE from which discrimination is difficult for the existing sorting techniques due to their black colour

Addition of X-ray fluorescent tracers into polymers, new technology for automatic sorting of plastics : proposal for selecting some relevant tracers

A description of a new technology for automatic sorting of plastics, based on X-ray fluorescence detection of tracers, added in such materials is presented. This study describes the criteria for the selection of tracers, and concluded that the most adapted for XRF are some rare earth oxides. The plastics chosen for tracing and identification are the ones contained in ELV and WEEE from which discrimination is difficult for the existing sorting techniques due to their black colour.A description of a new technology for automatic sorting of plastics, based on X-ray fluorescence detection of tracers, added in such materials is presented. This study describes the criteria for the selection of tracers, and concluded that the most adapted for XRF are some rare earth oxides. The plastics chosen for tracing and identification are the ones contained in ELV and WEEE from which discrimination is difficult for the existing sorting techniques due to their black colour

NASA SBIR abstracts of 1991 phase 1 projects

The objectives of 301 projects placed under contract by the Small Business Innovation Research (SBIR) program of the National Aeronautics and Space Administration (NASA) are described. These projects were selected competitively from among proposals submitted to NASA in response to the 1991 SBIR Program Solicitation. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 301, in order of its appearance in the body of the report. Appendixes to provide additional information about the SBIR program and permit cross-reference of the 1991 Phase 1 projects by company name, location by state, principal investigator, NASA Field Center responsible for management of each project, and NASA contract number are included

Membrane electrolysis for separation of cobalt from terephthalic acid in industrial wastewater

Recovery of valuable metals from wastewaters containing both metals and organics is challenging with current technologies, in part due to their interactions. Typical approaches are chemical intensive. Here, we developed a membrane electrolysis system coupled to an acidic and alkaline crystallizer to enable separate precipitation of the organics and metals without additional chemicals. The target industrial wastewater contained mainly purified terephthalic acid (PTA), benzoic acid (BA), p-Toluic acid (PA), cobalt (Co), and manganese (Mn). We examined the removal and recovery efficiency of PTA and cobalt from two types of synthetic stream and the real process stream using several configurations. The acidic crystallizer reached a removal efficiency of PTA of 98.7 +/- 0.2% (Coulombic efficiency 99.71 +/- 0.2%, pH 3.03 +/- 0.18) in batch tests of the simple synthetic stream. The alkaline crystallizer achieved a cobalt recovery efficiency of 94.51 +/- 0.21% (Coulombic efficiency 87.67 +/- 0.31%, pH 11.37 +/- 0.21) in batch tests of the simple synthetic stream (TPA and Co). Then, the system was operated continuously with complex synthetic stream (TPA, BA, PA, Co and Mn). The alkaline crystallizer achieved a cobalt recovery efficiency of 97.78 +/- 0.02% (Coulombic efficiency 90.45 +/- 0.17%)at pH 11.68 +/- 0.02. The acidic crystallizer obtained a PTA removal efficiency of 61.2 +/- 0.1% (Coulombic efficiency 62.3 +/- 0.2%) over 144 h (pH 3.71 +/- 0.03). A real stream was tested over 5 h runs in batch showing 31.1 +/- 1.0% PTA (Coulombic efficiency 26.5 +/- 0.2%) and 82.92 +/- 0.22% cobalt removal (Coulombic efficiency 75.27 +/- 0.31%) at pH 2.71 +/- 0.12 and 8.07 +/- 0.02, respectively. However, micron-scale precipitates were generated from real stream tests. To conclude, the membrane electrolysis cell coupled with acidic and alkaline crystallizers enabled simultaneous separation of PTA and cobalt as solid precipitates from a complex stream with no chemical addition. The efficiencies were lower with the real stream than the synthetic streams, showing the impact of matrix effects and the need to optimize the performance of the crystallizers

Functionalized metal-organic frameworks as selective metal adsorbents

A sustainable future for our world, with the help of renewable energy and green technologies... For a long time, this sounded like an idealism, a concept at best. But now, a little over 250 years since the first industrial revolution, it has become clear that all those decades of mindless resource consumption have left their mark on our planet. Sustainability is no longer a prestigious school project, but a dire necessity, at least if we want to keep our species alive for a few more centuries. However, as the Greek tragedian Euripides once said: “Nothing has more strength than dire necessity”, and thankfully the world is gradually shifting its views. We have developed and optimized technologies to help us achieve such a sustainable future. Electric cars, wind energy, solar and hydropower… The world is ready for its gradual shift towards clean energy, leaving fossil fuels behind. Sadly, the problems do no end there. While our intentions are noble this time, we have come to the realization that, in order to keep using these clean technologies, a sufficient supply of several important resources is required. Resources such as metals and other elements that are indispensable in the design and operation of ‘clean’ devices and machinery. As it turns out, some of these elements have become increasingly scarce over the past decades, up to a point where complete exhaustion is expected if we do not act in time. In this context, a group of metals, called the rare earths elements (REEs), play a central role. They are amongst the most critical elements in several sustainable technologies, whilst also being critical with respect to their (future) availability. It is shown throughout this work that it is difficult to mine them in a cost-effective way, and that a lot of geopolitics come into play to acquire them. Moreover, their recycling rate is disappointingly low, mainly because they are present in small quantities in their respective devices, and the current recycling technologies, in most cases, do not allow a cost-effective recovery. It is nonetheless of extreme importance that a steady REE supply is ensured, because in most cases these elements have no worthy replacements. In the domain of recycling, more and more interest is shown in the concept of urban mining, where the technosphere (i.e., electronic waste) serves as an actual mine, full of valuable resources. This ‘e-waste’ has the potential to supply a significant amount of rare earths to help satisfy an increasing demand. On the other hand, next to urban mining, improved (sustainable) primary mining should also be able to increase our REE supply. It is in this context that the core of this work resides. Both in primary REE mining and recycling processes, aqueous streams are often generated, containing varying fractions of these metals. It is shown that in the treatment of these solutions, a lot of improvement can be made in terms of applied technologies. While industrial techniques like solvent extraction will remain an obvious choice for highly concentrated solution processing (e.g., g/L scale), they prove to be cost-ineffective for more dilute streams (e.g., mg/L scale). In addition, when dealing with REE recycling or the processing of secondary deposits (e.g., resources with a typically lower REE content than primary ores), these techniques would face the similar issues. Therefore, adsorption technology is proposed in this work, as a worthy alternative. The advantages of this technique are discussed, and it is shown that adsorbents are ideal materials for low concentration recovery or removal or certain species of interest. With respect to REE mining and recovery, different domains are proposed where selective adsorption could earn its place as the prevailing technology, and the requirements for such adsorbents are discussed. Whether it is to recover rare earths from process or waste streams, or to purify REE-containing solutions from toxic elements (uranium, thorium…), adsorbents can be tailored readily towards a certain application. Further on, an introduction is given into the world of metal-organic frameworks (MOFs). The concept of using these versatile coordination polymers in aqueous environment as adsorbents is explored and documented with existing literature. The stability of MOFs will play a major role in their possible application as aqueous adsorbents. It was therefore investigated which structural parameters have a significant influence on this stability. In short words; What makes a MOF suitable for water-based applications? In addition, a study was performed on the long-term stability of several popular MOFs, regarding their behavior in different aqueous conditions, i.e., acidic, alkaline, oxidative... With this information a rational choice can be made in the selection of suitable MOFs for aqueous adsorption applications. This work then describes the application of a specific cage-type MOF, namely MIL-101(Cr), as a potential ideal support for aqueous adsorption. It was chosen based on its incredible stability, high porosity, and ready functionalizability. The MIL-101(Cr) was functionalized via two different routes with a specific ligand and its affinity for certain critical metals (REEs, uranium…) was investigated. In one approach, a carbamoylmethylphosphine oxide-type ligand (CMPO) was covalently anchored onto the surface of MIL-101 via a three-step method. Another approach encapsulates another CPMO-type ligand in-situ in the cages of MIL-101, where it is confined and cannot leach out. Both materials have been subjected to a comprehensive adsorption study, in which their performance in terms of selectivity, stability, uptake, kinetics, recyclability… is investigated. In conclusion, it is shown that several MOFs do possess the required characteristics to serve as aqueous-phase adsorbents. They can be tailored towards a specific application, via different functionalization methods. This was proven for the ultra-stable MIL-101(Cr), which could be functionalized with selective ligands for critical metals recovery. As there are several stable MOFs to explore, and various strategies to tailor them, it is safe to say that MOF-based adsorption opens up exciting avenues in the field of aqueous-phase metal recovery