Greenhouse Gas Emissions from Molten Fluoride Electrolysis Composed of Raw and Magnet Recycling Derived Oxides: A...

In situ measurements of the chemical identity and quantity of anode gases during electrochemical measurements and rare earth (RE) electrolysis from fluoride-based molten salts composed of different kinds of rare earth oxides (REOs) were performed using FTIR spectrometry. Linear sweep voltammetry (LSV) was carried out to characterize oxidation processes and determine the anodic effect from NdF₃ + PrF₃ + LiF + REO melt. RE complex formation and subsequent reactions on the GC anode surface were discussed to understand the formation pathways of CO/CO₂ and perfluorocarbon gases (PFC), mainly CF₄ and C₂F₆. The LSV shows that increasing the REO content from 1 wt.% up to 4 wt.% in the system, leads to a positive shift in the critical potential for a full anode effect, recorded around 4.50 V vs. W with 4 wt.% REO. The FTIR results from on-line off-gas analysis during LSV measurements indicate that the anode gas products were composed mainly of CO and CO₂, whereas CF₄ can be detected before the full anode effect and C₂F₆ at and after this phenomenon. Compositions of off-gases from electrolysis performed using different kinds of REOs were compared. The main off-gas component was found to be CO in RE electrolysis with REOs as raw materials, while in electrolysis with magnet recycling derived oxides (MRDOs), CO₂ content was slightly higher compared to CO. PFC emissions during RE electrolysis were generally similar: CF₄ was detected periodically, but in negligible concentrations, while C₂F₆ was not detected.