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Investigation of the carbochlorination process for the conversion of rare earth oxides into chlorides and measurement of their solubility in inert molten salts
Anderson, Alexandra
Anderson, Alexandra
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2015
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The current experimental investigation focuses on generating data and understanding about the feasibility of developing an improved, continuous electrolytic process for the reduction of rare earth oxides to rare earth metals in a molten salt media. The rare earth oxides are the typical starting material for conversion into their metals because they are the most common products of ore processing and separation operations. The extreme chemical stability of the rare earth oxides is responsible for the rather complex and energy intensive methods used for rare earth metal production. In the proposed electrolysis scheme, a mixture of rare earth oxide and carbon would be used as a consumable anode in the electrolysis cell. The electrolyte in the cell would contain dissolved rare earth halides of the metal to be extracted as the seed. Once the electrowinning of metals from halides begins, the halogen would report to the anode and convert the rare earth oxide to a rare earth halide via a process called carbohalogenation. Halogen gas would also be introduced into the system to help promote the rare earth oxide to halide conversion. The produced rare earth halide would then dissolve in the electrolyte and be available for reduction to metal. The chlorine based route rather than the fluoride based route was chosen for evaluation in this study. In order to fully develop a continuous chloride electrolysis process, the individual steps in the scheme need to be understood and optimized. The three steps in the proposed continuous chloride electrolysis scheme are: 1. Carbochlorination of the rare earth oxide 2. Dissolution of the rare earth chloride in the molten electrolyte 3. Electrowinning of the rare earth metals This project focused on proving the carbochlorination reaction for cerium oxide and neodymium oxide as well as optimizing the process parameters involved. A preliminary kinetic study was performed for both carbochlorination reactions to determine the optimal time for the reaction and the rate controlling mechanism. The experimental work also focused on evaluating different electrolytes for use in the electrolysis process based on the degree of rare earth chloride solubility and electrolyte stability at various operating temperatures. The information gathered from these two process steps was used to perform two scoping tests to evaluate the feasibility of executing the carbochlorination reaction within the molten electrolyte. The present work does not focus on evaluating the electrolysis step of the proposed metal reduction scheme.
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