Title Promoter Affiliations Abstract "Extraction of Rare Earths." "Koen Binnemans" "Sustainable Chemistry for Metals and Molecules, Process Engineering for Sustainable Systems Section, Sustainable Metals Processing and Recycling" "The rare earths are a group of 17 elements in the periodic system, including neodymium (Nd), europium (Eu), terbium (Tb), dysprosium (Dy) and yttrium (Y). These elements are becoming more and more important, because of their essential role in permanent magnets, lamp phosphors, catalysts and rechargeable batteries. The rare earths occur in Nature as mixtures and these mixtures are difficult to separate due to the similar chemical properties of the rare earths. This project is about new approaches for the concentration and separation of rare-earth elements, and their transformation into metallic form, starting from rare-earth slags or recycled rare- earth concentrates. These processes can be described under the general name of extraction of rare earths.The problem of dispersion of the rare earths in oxide slags will be solved by concentrating the rare earths in rare-earth-rich phases formed by addition of fluorine or phosphorus compounds to molten slags. New separation methods will be developed. These include photochemical oxidation or reduction of rare earths, and separation of rare-earth ions in strong magnetic fields." "Separation of rare earths by non-aqueous solvent extraction" "Koen Binnemans" "Sustainable Chemistry for Metals and Molecules" "Solvent extraction is widely used for the separation of mixtures of rare earths on an industrial scale. However, these separation processes are not very efficient so that many extraction stages are required to produce pure rare earths. In this project, we develop a new approach to separation of rare earths: non-aqueous solvent extraction with two immiscible organic phases. Non-aqueous solvent extraction offers some advantages compared to conventional solvent extraction with an aqueous feed phase. The speciation of rare-earth ions in non-aqueous solutions often differs greatly, hence influencing the extraction. Making use of these differences, novel and very selective separation processes can be developed. Research efforts were directed towards the development of a continuous non-aqueous solvent extraction process for separation of a rare-earth concentrate by means of mixer-settler cascades." "Research Platform for the Advanced Recycling and Reuse of Rare Earths (RARE³)." "Koen Binnemans" "Sustainable Chemistry for Metals and Molecules, Process Engineering for Sustainable Systems Section, Department of Materials Engineering, Research Centre for Economics and Corporate Sustainability, Brussels Campus, Surface and Interface Engineered Materials, Sustainable Metals Processing and Recycling" "To contribute to the transition towards low-carbon, closed-loop economies the recycling of rare earths (REEs) will be crucial. Currently, End-of-Life recycling rates for REEs are less than 1%. RARE³ targets to develop recycling flow sheets to recover the five critical rare-earth elements (Nd, Eu, Tb, Dy, Y) from phosphors and magnets, being the two economically most important REE containing postconsumer streams. More efficient, direct and environmentally benign separation methods are targeted as well. Consequential LCA and economic modelling will be used to gain insights in the different scenarios for the global rare earth material flows and their environmental impact, which will lead to recommendations for decision makers (within companies) which technologies to implement and stimulate and how to secure REE availability in the EU. RARE³ is structurally embedded in the flagship SIM² research line at KU Leuven and features a User Committee consisting of all major REE players in the EU and the US." "Recycling of rare earths from fluorescent lamps" "Koen Binnemans" "Sustainable Chemistry for Metals and Molecules" "Ionic liquids (ILs) are of high interest as alternative solvents in solvent extraction applications and metal processing. Their negligible vapor pressure and low flammability make them safer and more convenient to handle than volatile organic solvents. Furthermore, their structure can be modified and functionalized to incorporate metal extracting groups and to tune their physical properties. In this thesis we used smart IL design to provide new innovative solutions to the recycling of critical metals from end-of-life products. Recycling of critical metals is important to guarantee a sustainable long-term supply, diminish the impact on the environment and to diminish the geopolitical dependence on certain countries. An important advantage of recycling is the fact that these metals are already present in the correct ratios in consumer products, but innovative recycling technologies must be developed to recover these metals efficiently without the creation of additional waste. The development of greener and more selective metal processing techniques is therefore at the core of this thesis.New IL-based recycling processes were developed for lamp phosphor waste and NdFeB permanent magnets. These consumer products have the highest recycling potential when it comes to the recovery of rare earths. Using the unique properties of ionic liquids, we developed processes which are more efficient, use less chemicals and produce less waste than classic hydrometallurgical processes. We also worked on the synthesis of new classes of ionic liquids, with strongly acidic extractants incorporated in their structure, designed to dissolve and/or extract metal ions. We have demonstrated that ionic liquid technology can overcome many problems encountered in classic solvent extraction and hydrometallurgy. The ionic liquids and processes that were developed in this thesis can be used as a toolbox to tackle future issues, because we took care to understand the underlying fundamentals which explain the often unexpected behavior of metals in ionic liquids. We therefore also worked on developing a general theory to explain and predict the effect of metal salts and acids on the (thermomorphic) behavior and mutual solubility of biphasic IL/water systems. This general theory, based on the principles of the Hofmeister series, can be used for the rational synthesis of ionic liquids as well as for the design of IL-based solvent extraction systems." "Ionic Liquid Technology for the Separation of Rare Earths" "Koen Binnemans" "Sustainable Chemistry for Metals and Molecules" "Ionic liquids possess some interesting properties for solvent extraction experiments such as a negligible volatility, a low flammability and high structure tuneability. Moreover, their ionic structure and metal complex solvation power is totally different from apolar aliphatic or aromatic solvents. Even though ionic liquids are considered as safer and more environmentally friendly alternatives for traditional organic diluents, they have one main disadvantage which is their slower extraction kinetics due to the higher viscosity and mass transport of this kind of solvents. In the last years, the supply of rare earths and NdFeB magnets has been under a constant pressure due to a cheaper production process of China resulting in a quasi-monopoly and its strong export. Therefore, the recovery of rare-earths from end-of-life materials such as NdFeB magnets becomes strategically very interesting as it reduces the rare-earth supply dependency on China. In the first results part of this PhD dissertation, the basic extractant trihexyl(tetradecyl)phosphonium in combination with chloride and nitrate anions is used to separate some main transition metals from the rare earths present in NdFeB or SmCo magnets. The process is based on a salting-out procedure by using high concentrations of salt or acid in the aqueous phase. The most promising process was tested on a real NdFeB magnet, which was first roasted and leached selectivily to remove the iron. Than, the remaining transition metals were removed by solvent extraction with trihexyl(tetradecyl)phosphonium chloride in the presence of 3.5 M of NH4Cl in the aqueous phase. Afterwards, the rare earths were precipitated by the addition of oxalic acid and calcinated. In this way, a highly pure mixture of the rare-earth oxides was produced which can be used directly as starting material for the production of NdFeB magnets. The processes are operated in that way that they minimize the amount of waste streams and the amount of chemicals consumption. Moreover, the ionic liquid or even aqueous phases are reused to obtain a closed and environmentally friendly process. The second part of this PhD dissertation focuses on the use of the ionic liquid betainium bis(trifluoromethylsulfonyl)imide for the extraction of metals. An innovative process, increasing the reaction and extraction rate by reducing the ionic liquid phase viscosity during the extraction process, is worked out. In this method, called homogeneous liquid-liquid extraction, the aqueous/ionic liquid mixture is heated above its critical temperature, at which one homogeneous phase is formed. Afterwards, the mixture is cooled and two phases are reformed. In this way, mixing and reaction between the metal and the extractants occurs at molecular scale in the homogeneous state, whereas phase and metal separation can be achieved by cooling down and obtaining two phases. The ionic liquid betainium bis(trifluoromethylsulfonyl)imide, in combination with trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide and water was used as well for a triphasic extraction system. In this triphasic system, three different metals (Sc(III), Y(III) and Sn(II)) can be separated in one single step, a separation that cannot be achieved when working with the conventional two phases." "Separation of rare earths by homogeneous liquid-liquid extraction with functionalized ionic liquids." "Koen Binnemans" "Sustainable Chemistry for Metals and Molecules" "The rare earths are a group of 17 elements in the periodic system, including neodymium (Nd), europium (Eu), terbium (Tb), dysprosium (Dy) and yttrium (Y). These elements are becoming more and more important, because of their essential role in permanent magnets,lamp phosphors, catalysts and rechargeable batteries. The rare earths occur in Nature as mixtures and these mixtures are difficult to separate due to the similar properties of the rare earths. Solvent extraction is the most important technique for the separation of rare earths. The separation depends upon a preferential distribution of rare earth complexes between two immiscible phases, typically an aqueous and an organic phase, in contact with each other. Because a good contact between the two phases is required, the solvents have to be vigorously stirred during the extraction process. Sometimes the two phases are not easily separated after agitation and an emulsion is formed. This project introduces a new approach for the separation of rare earths. A system of two immiscible solvents is heated. Above a certain critical temperature, only one phase is formed. Upon cooling, the two phases reappear, but with part of the dissolved metals transferred to the other phase. Ionic liquids are selected as the organic phase. These solvents are low-melting organic salts. They offer the advantage of being non-volatile and non-flammable, so that an inherently safe extraction system can be obtained." "Extraction of rare earths with functionalised hydrophobic ionic liquids." "Koen Binnemans" "Sustainable Chemistry for Metals and Molecules" "The rare earths are a group of 17 elements in the periodic system, including neodymium (Nd), europium (Eu), terbium (Tb), dysprosium (Dy) and yttrium (Y). These elements are becoming more and more important, because of their essential role in permanent magnets, lamp phosphors, catalysts and rechargeable batteries. The rare earths occur in Nature as mixtures and these mixtures are difficult to separate due to the similar properties of the rare earths. Solvent extraction is the most important technique for the separation of rare earths. The separation depends upon a preferential distribution of rare earth complexes between two immiscible phases, typically an aqueous and an organic phase, in contact with each other. The replacement of organic diluents in liquid-liquid extractions by ionic liquids could lead to more sustainable extraction processes, because of their low volatility and low flammability. Ionic liquids are solvents that consist entirely of ions. The transfer of hydrated metal ions from an aqueous phase to a hydrophobic ionic liquid phase is unfavorable, so that the use of extractants is necessary. The advantage of using ionic liquids for solvent extractions is lost when neutral molecules are selected as extractants. However, functionalized ionic liquids combine the properties of ionic liquid and extractant into one compound. This project is about the development of solvent extraction systems for rare earths based on such functionalized ionic liquids." "Separation of rare earths by ionic liquid technology" "Koen Binnemans" "Sustainable Chemistry for Metals and Molecules" "The first part of this PhD thesis shows how ionic liquids can be employed as a green alternative to replace the conventional organic phase in solvent extraction processes of rare-earth elements. In a first approach, the selective leaching of rare earths from NdFeB magnets and their solvent extraction from a nitrate media is presented. More specifically, neodymium and dysprosium were separated from cobalt by extracting them to the ionic liquid trihexyl(tetradecyl)phosphonium nitrate (Cyphos® IL 101 nitrate). Afterwards neodymium and dysprosium were separated using ethylenediaminetetraacetic acid (EDTA) as a selective stripping agent. The purified metals were recovered as oxalates and then transformed into the corresponding oxides by calcination. In a second approach, the recovery and separation of rare earths from chloride media is presented. Neodymium and dysprosium were separated by using Cyphos® IL 101 in its thiocyanate form combined with the molecular extractant CyanexÒ 923. The addition of a molecular extractant provided a beneficial lower viscosity of the organic phase and a higher loading capacity in comparison with the pure ionic liquid. Stripping of the metals from the loaded organic phase was carried out with water and the rare earths were also recovered as oxalates.In the second part of this PhD dissertation, the deep-eutectic solvent choline chloride:lactic acid (molar ratio 1:2) was employed to dissolve the magnets. The solvent extraction process was carried out by contacting the deep-eutectic solvent (more polar phase) with ionic liquids and conventional extractants diluted in toluene (less polar phase).  Iron, boron and cobalt were separated from neodymium and dysprosium using the ionic liquid tricaprylmethylammonium thiocyanate (Aliquat® 336 SCN) diluted in toluene. The separation of neodymium and dysprosium was assessed by using two different types of extractants, a mixture of trialkylphosphine oxides (Cyanex® 923) and bis(2-ethylhexyl)phosphoric acid (D2EHPA). Based on the distribution ratios, separation factors and the easiness of the subsequent stripping, Cyanex® 923 was chosen as the most adequate extractant. This new methodology offers higher selectivities and efficiencies than the corresponding aqueous system.  Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to elucidate the mechanisms for extraction of cobalt and iron from the deep-eutectic solvent. Furthermore, the feasibility of scaling up this separation process was tested in a mixer settler setup.Finally, considering that the correct quantification of metal ions in aqueous solutions is essential for the evaluation of a solvent extraction system and also for the follow up of continuous systems, practical and easy guidelines for the correct preparation of aqueous samples and posterior quantification by total-reflection X-ray fluorescence (TXRF) were developed. The most important parameters that play a role in the calibration of a TXRF apparatus such as the choice of the standard element and the concentration ratio between the analyte and the standard were discussed." "Efficient design of continuous countercurrent solvent extraction processes for separation of rare earths (ELECTRA)" "Koen Binnemans" "Sustainable Chemistry for Metals and Molecules" "Solvent extraction is an important separation technique for purification of rare-earth elements that are essential for the permanent magnets used in motors of electric vehicles, wind turbines, .... However, the design of solvent extraction processes is a labour-intensive and time-consuming process, with many laboratory experiments. The objective of the ELECTRA project is to simplify the design of solvent extraction processes in the metallurgy of rare-earth elements so that the number of required experiments can be minimised. This will be achieved by predictive thermodynamic modelling based on the mixed-solvent electrolyte model. Rather than measuring distribution isotherms under many different experimental circumstances, the distribution of metals between the aqueous and organic phases is predicted by using standard and excess thermodynamic data, in combination with Gibbs energy minimisation (GEM) methods. The thermodynamic modelling software is coupled to a flowsheet simulator to determine the number of mixer-settlers, flow rates and other process variables for the extraction, scrubbing and stripping sections of an extraction battery. The design principles will be applied to the two most important approaches to rare-earth separation: the nitrate and chloride routes. The optimised flowsheet designs will be validated in a setup of 3D-printed mixer-settlers, with real time online analysis by UV-VIS absorption spectroscopy and X-ray fluorescence (XRF)." "Mechanistic study of solvent extraction of rare earths with sterically hindered alkyl phosphonic acids." "Koen Binnemans" "Sustainable Chemistry for Metals and Molecules" "The rare-earth elements (REEs) are a group of 17 chemically similar metallic elements (15 lanthanides, plus Sc and Y). Although REE minerals contain most of these elements simultaneously, high-tech and cleantech applications such as permanent magnets and lamp phosphors typically require only one specific, high-purity REE. To provide the individual REEs on an industrial scale, REE separation is performed by solvent extraction. Solvent extraction involves two immiscible liquid phases: an aqueous and an organic phase containing organic molecules (extractant). The REE with the highest affinity for the extractant preferentially moves to the organic phase, whereas the REE with the lowest affinity tends to remain in the aqueous phase. Due to the very similar chemical properties of REEs, the separation needs to be performed in 30-100 steps until the desired purity is obtained. Therefore, state-of-the art rare-earth separation is a costly, energy and resource intensive process. In this project, the structure of typical extractants used in industry for REE separations are modified. The reaction between the REEs and the extractants is studied on a molecular scale by various techniques. These techniques allow to modify the structure of the extractants and to drastically improve the REE separation efficiency. Hence, the number of separation steps and the environmental footprint of the process significantly decrease."