Hanno Vogel

An Estimation of PFC Emission by Rare Earth Electrolysis

Currently there is no inventory of the emission and no documentation of the smelting capacity, technology level and location of rare earth smelters. So far, the emission from rare earth smelting is not taken into account in climate change research and policy makers. This work creates an estimate of the PFC emission by rare earth electrolysis. First, the annual rare earth metal production by electrolysis is estimated in the range of up to 35,000 t per year. The process technology review and theory of PFC formation suggest a high amount of PFC emission. Laboratory measurements of CF4 and C2F6 in the off-gas of a neodymium electrolysis confirm the possibility of continuous PFC emission with about 74 g CF4 and 12 g C2F6 per kilogram RE metal. Combined with the production estimate, an annual PFC emission by RE electrolysis of about 25,000,000 t CO2-eq is calculated. Based on the consumption of raw material, a medium-emission scenario with up to 10,000,000 t CO2-eq is attained, with a mass of 30 g CF4 and 3 g C2F6 per kilogram RE metal. This range of PFC emission highlights the importance of conducting industrial measurements and improving the electrolysis process to lower emissions. The regional distribution of PFC emission is derived by analyzing the light metal production quota of Chinese companies. In Baotou the majority of PFC is emitted, followed by the mining region in Sichuan. Southern China and the border region of Laos and Vietnam emit much less PFC.

A Comparison between Two Cell Designs for Electrochemical Neodymium Reduction Using Numerical Simulation

Nowadays, neodymium is almost solely produced by the electrochemical reduction of Neodymium oxide in fused fluoride salts. Thereby, the fluid flow distribution within the electrolysis cell is important for the productivity and efficiency of the process. In this work, the flow field within a conventional cell with vertical electrodes is compared to that of an innovative cell concept with horizontal electrodes by computational fluid dynamics. The numerical model uses the Eulerian volume of fluid approach to track phase boundaries between the continuous phases, while the Lagrangian discrete phase model is applied to compute the rising trajectories of emitted off-gas bubbles. The calculated results indicate that the new cell type is more suitable for the efficient, large-scale production of neodymium, since there is potential to decrease the cell voltage and enhance the current efficiency. By that, the specific energy consumption can be lowered significantly. However, an advanced level of automation is necessary to operate the new cell.