Electrochemical Study of Nd and Pr Co-Deposition onto Mo and W from Molten Oxyfluorides

Abstract

Electrodeposition processes of neodymium and praseodymium in molten NdF3 + PrF3 + LiF + 1 wt.%Pr6O11 + 1 wt.%Nd2O3 and NdF3 + PrF3 + LiF + 2 wt.%Pr6O11 + 2 wt.%Nd2O3 electrolytes at 1323 K were investigated. Cyclic voltammetry, square wave voltammetry, and open circuit potentiometry were applied to study the electrochemical reduction of Nd(III) and Pr(III) ions on Mo and W cathodes. It was established that a critical condition for Nd and Pr co-deposition in oxyfluoride electrolytes was a constant praseodymium deposition overpotential of ≈−0.100 V, which was shown to result in co-deposition current densities approaching 6 mAcm−2. Analysis of the results obtained by applied electrochemical techniques showed that praseodymium deposition proceeds as a one-step process involving exchange of three electrons (Pr(III)→Pr(0)) and that neodymium deposition is a two-step process: the first involves one electron exchange (Nd(III)→Nd(II)), and the second involves an exchange of two electrons (Nd(II)→Nd(0)). X-ray diffraction analyses confirmed the formation of metallic Nd and Pr on the working substrate. Keeping the anodic potential to the glassy carbon working anode low results in very low levels of carbon oxides, fluorine and fluorocarbon gas emissions, which should qualify the studied system as an environmentally friendly option for rare earth metal deposition. The newly reported data for Nd and Pr metals co-deposition provide valuable information for the recycling of neodymium-iron-boron magnets.

Influence of Rare Earth Oxide Concentration on Electrochemical Co-Deposition of Nd and Pr from NdF3-PrF3-LiF Based Melts

“…Development and implementation of such technologies are expected to assume a very important role in supplementing virgin REE production in supply chains. Electrochemical deposition has proven to be a capable alternative in selective recovery of a desired element from an electrolyte containing mixed rare earth ions [3,[6][7][8][9]. The ability to monitor and control the deposition process, composition, morphology and especially the purity of the final products are some of the advantages attributed to the electrolytic production method.…”

“…Selective electrolytic production of RE elements (RE = Nd, Pr or Dy) alone or RE alloys using an appropriate working substrate by electrolysis from fluoride or chloride molten salts system have been studied to some extent [2,5,[11][12][13][14][15][16]. Significant work has been done concerning the electrochemistry of each element separately or as part of a group in the corresponding molten salt mixture using molten salt electrochemistry [6,7,11,[17][18][19][20]. However, there has been little related research conducted on selective neodymium/praseodymium electrochemical deposition from oxidefluoride electrolytes [6][7][8][21][22][23].…”

“…Significant work has been done concerning the electrochemistry of each element separately or as part of a group in the corresponding molten salt mixture using molten salt electrochemistry [6,7,11,[17][18][19][20]. However, there has been little related research conducted on selective neodymium/praseodymium electrochemical deposition from oxidefluoride electrolytes [6][7][8][21][22][23]. Currently, industrial production of Nd-Pr alloys is mostly based on the electrochemical processes of oxide-fluoride electrolytes, using PrF 3 -NdF 3 -LiF as the base electrolyte and Nd and Pr oxides as a feedstock.…”

“…Recently, we successfully employed a fluoride based molten PrF 3 -NdF 3 -LiF bath as a solvent for neodymium and praseodymium oxides and as an electrolyte for the electrodeposition of Nd and Pr metals on an inert working substrate [6,7,17]. Our study was focused on the fundamentals underlying the electrochemical reduction of both Nd(III)/Nd(0) and Pr(III)/Pr(0) cations that occurs in the oxide-fluoride melt using a glassy carbon counter electrode (anode), W reference electrode and W (or Mo) working electrode.…”

“…Our study was focused on the fundamentals underlying the electrochemical reduction of both Nd(III)/Nd(0) and Pr(III)/Pr(0) cations that occurs in the oxide-fluoride melt using a glassy carbon counter electrode (anode), W reference electrode and W (or Mo) working electrode. The anode gas composition during electrolysis in the NdF 3 + PrF 3 + LiF + Nd 2 O 3 + Pr 6 O 11 electrolyte at 1050 • C was also analysed [6,7,17]. By applying different electrochemical techniques, we succeeded in obtaining solid Nd metal and Nd-Pr metal composition on the cathodes used from the oxide-fluoride electrolyte at 1050 • C [6,7,17].…”