TITLE:
Reducing Greenhouse Gas Emission from the Neodymium Oxide Electrolysis. Part II: Basics of a Process Control Avoiding PFC Emission
AUTHORS:
Hanno Vogel, Bernd Friedrich
KEYWORDS:
Rare Earth, Neodymium, Electrolysis, Greenhouse Gas Emission, Process Control
JOURNAL NAME:
International Journal of Nonferrous Metallurgy,
Vol.6 No.3,
July
7,
2017
ABSTRACT: The neodymium
electrolysis produces unnecessary high emission of CF4 and C2F6.
These perfluorocarbons (PFCs) are potent greenhouse gases and are not filtered or
destroyed in the off-gas. A process control in analogy to the aluminum electrolysis
can reduce the PFC emission to a great extend and keep the process in a green process
window. Therefore, a theoretical analysis is done of the cell voltage of the industrial
neodymium electrolysis in dependence on the neodymium oxide concentration in the
electrolyte. The analysis shows the different contributions to the cell voltage
focusing on the impact of the anodic overvoltage on the cell voltage, by which the
electrolysis process can be controlled. The model of the cell voltage is evaluated
by laboratory neodymium electrolysis with
a similar setup as the industrial cell. The relation of the oxide concentration,
the anodic current density and the cell voltage with the cell resistance are measured. The continuous off-gas measurements show the
gas concentration and PFC emissions. The effect of Nd2O3 feeding on the galvanostatic electrolysis is analyzed
as well. Based on the results a process control strategy is proposed similar to
the aluminum electrolysis strategy. The green process window is in a narrow oxide
concentration range, making a continuous and precise oxide feeding essential.