Electrolytic production of metallic neodymium is carried out in fused neodymium fluoride salts containing neodymium oxide. Two major challenges pertaining to neodymium production in fluoride salts are a) low solubility of neodymium oxide in fluoride melt, b) possibility of anodic gas evolution (CO, CO ₂ , CF ₄ , C ₂ F ₆ ). In this study, iron is used as a reactive anode in the electrolysis process, promoting electrochemical dissolution of iron into the melt, preventing PFC (perfluorocarbon) gas evolution at the anode. Further, the rare earth oxide is converted to rare earth fluoride by the use of iron fluoride formed as the result of iron dissolution. Thus, the fluoridizing agent is constantly regenerated in-situ which enables the continuous conversion of neodymium oxide feed. The cathodic product is Nd–Fe alloy which can be used as a master alloy for the production of NdFeB magnets.

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Electrolysis of molten fluorides is one of the promising methods for the recovery and recycling of rare earth metals from used magnets. Due to the dearth of phase equilibria data for molten fluoride systems, thermodynamic modelling of LiF-DyF₃-NdF₃ system using the CALPHAD approach was carried out. Gibbs energy modelling for LiF-NdF₃ and LiF-DyF₃ systems was performed using the constitutional data from literature. Ab initio calculations were used to obtain enthalpy of reaction of LiDyF₄, an intermediate phase that is found to exist in the LiF-DyF₃ system. Differential thermal analysis was carried out for selected compositions in the NdF₃-DyF₃ system, in order to determine liquidus and solidus temperatures. The Gibbs energy parameters for the limiting binaries determined in this work is used for modelling the Gibbs energy functions of equilibrium phases in the ternary system. Selected compositions of LiF-NdF₃-DyF₃ were subjected to DTA in order to validate the calculated phase temperatures involving melt.

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Electrochemical metal extraction in molten salts is the dominant industrial method for production of Rare Earth (RE) metals from their oxides. Two major challenges pertaining to RE metals extraction using this technology are a) low solubility of RE oxides in molten salts and b) carbon monoxide or carbon dioxide generation and possibility of fluorocarbon gas generation. The primary objective of this thesis is to find new methods to overcome the problem of low solubility of RE oxides in molten fluorides in order to increase the RE metal extraction yield from RE oxides. Another objective is to study novel routes in order to prevent CO, CO2 and halogen gas generation in the RE metal production from RE oxide and RE magnet scrap in molten salt electrolysis process. In view of this, a treatment route is suggested for the conversion of RE oxide to RE chloride/fluoride using strong chemical agents. Chapters 2, 3 and 4 investigate the conversion routes for RE oxides as well as RE magnet scrap in both chlorides and fluorides molten salts. Chapter 5 investigates the electrolysis step in which iron as a reactive anode is used, preventing generation of fluorocarbon, CO and CO2 gas in the extraction process. In Chapter 6 a thermodynamic modelling of the fluoride salt using CALPHAD approach is carried out. The phase equilibria and thermodynamics of molten fluorides system can be used for optimal design of RE extraction processes. @en

A new recycling process for the extraction of rare earths from neodymium–iron–boron (NdFeB) magnet scrap is being developed, based on the direct extraction of rare earths from end-of-life magnet material in a molten fluoride electrolysis bath. Rare earths are required in their metallic form for the production of new NdFeB magnets, and the suggested process achieves this through a single step. The process is being developed on a laboratory scale and has been proven to work in principle. It is expected to be environmentally beneficial when compared to longer processing routes. Conducting life cycle assessment at R&D stage can provide valuable information to help steer process development into an environmentally favorable direction. We conducted a life cycle assessment study to provide a quantitative estimate of the impacts associated with the process being developed and to compare the prospective impacts against those of the current state-of-the-art technology. The comparison of this recycling route with primary production shows that the recycling process has the potential for much lower process-specific impacts when compared against the current rare earth primary production route. The study also highlights that perfluorocarbon emissions, which occur during primary rare earth production, warrant further investigation.@en

In the present research on rare earth extraction from rare earth oxides (REOs), conversion of rare earth oxides into rare earth fluorides with fluoride fluxes is investigated in order to overcome the problem of low solubility of the rare earth oxides in molten fluoride salts as well as the formation of oxyfluorides in the fluorination process. Based on thermodynamic calculations, a series of experiments were performed for converting the rare earth oxides into rare earth fluorides using AlF3, ZnF2, FeF3, and Na3AlF6 as fluorinating agents in a LiF–Nd2O3 system. The formation of neodymium fluoride as a result of the reactions between these fluxes and neodymium oxide is confirmed. The rare earth fluoride thus formed can subsequently be processed through the electrolysis route in the same reactor, and rare earth metal can be produced as the cathodic deposit. In this concept, the REO dissolution in molten fluorides would become unnecessary due to the complete conversion of the oxide into the fluoride, REF3. The results of XRD and EPMA analysis of the reacted samples indicate that AlF3, ZnF2, and FeF3 can act as strong fluorinating agents for the neodymium oxide giving rise to a complete conversion of neodymium oxide into neodymium fluoride.@en

In the present work, selective extraction of rare earth (RE) metals from NdFeB magnets is investigated by studying the effects of various fluxes, viz. AlF₃, ZnF₂, FeF₃ and Na₃AlF₆ in the LiF-NdFeB system. The aim is to convert RE from RE magnet into the fluoride salt melt. The results show the complete selective separation of neodymium (also dysprosium) from the magnet and formation of rare earth fluoride, leaving iron and boron unreacted. The formed rare earth fluoride can subsequently be processed in the same reactor through an electrolysis route so that RE can be deposited as a cathode product. The results of XRD and EPMA analysis of the reacted samples indicate that AlF3, ZnF2 and FeF3 can act as strong fluorinating agents for extraction of rare earth from NdFeB magnet, converting the RE to REF3. The results confirm the feasibility of the rare earth metals recovery from scrap NdFeB magnet as raw material. The fluoride conversion-electrolysis route suggested in the present work enables the extraction of rare earth metals in a single step using the above-mentioned fluxes.

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Electrolytic production of metallic neodymium is carried out in fused fluoride salts containing neodymium oxide. Two major challenges pertaining to neodymium production are (a) low oxide solubility, (b) possibility of anodic fluorine gas evolution if the electrolysis rate exceeds feeding rate of neodymium oxide. In this study, a novel method is proposed in which iron fluoride (FeF3) is used as a fluorinating agent to convert neodymium oxide into neodymium fluoride. Electron Probe Micro Analysis (EPMA) results of as-converted salt show a complete conversion of neodymium oxide into neodymium fluoride. In the electrolysis process, iron is used as a reactive anode with electrochemical dissolution of iron into the melt, thus preventing fluorine gas evolution at the anode. Therefore, the fluorinating agent is constantly regenerated in situ which enables the continuous conversion of neodymium oxide feed. The cathodic product is a Nd–Fe alloy which can be directly used as a master alloy for the production of NdFeB permanent magnets.@en