Interfacial effects in the electro(co)deposition of Nd, Fe, and Nd-Fe from an ionic liquid with controlled amount of water

Neodymium is one of the most important rare earth elements due to its various applications, above all, in permanent magnets in consumer electronics and renewable power sources. Production of primary Nd is a rather complex and expensive process characterized by significant import dependency, which brings to the forefront Nd recovery from secondary sources. Electrowinning as one of the cheapest and processible solutions is not applicable for electropositive rare earths in aqueous systems but is a good option in the case of solutions based on ionic organic solvents. Nd electrodeposition and its induced codeposition with Fe are studied at room temperature in a fluorine-free dicyanamide ionic liquid (IL) using a complex set of electrochemical and physical (spectroscopic and microscopic) methods in dry solutions and in the presence of water. We show that the addition of water significantly promotes electrodeposition of individual metals in the respective single-component solutions but produces a hindering effect on the induced codeposition of Nd with Fe. We suggest an explanation for the acceleration of individual Nd and Fe in the presence of water based on the effects at the IL/electrode interface and for the inhibition of Nd-Fe deposition in the presence of water owing to the decelerating effect of formation of Nd oxide/hydroxide film. This is the first systematic study of the effect of water on the rare earth-transition metal codeposition in ILs providing information that can be essential for production of secondary rare earths and fabrication of novel lanthanide-based materials. (c) 2021 Elsevier Ltd. All rights reserved.