Towards sustainable rare earth elements recovery

Our contribution, made in joint research efforts of ICTM Institute, University of Belgrade with IME Institute, Aachen University, to the molten salt electrolysis within the field of recycling rare earth metals from end-of-life NdFeB magnets containing significant amounts of rare earth elements, was focused on the Nd-Pr alloy formation that could be fed directly back to the vacuum alloying step in the production of the new NdFeB magnets. In order to make extracting of individual rare earth metals for reuse in magnets or other materials economically viable, additional knowledge onto the electrodeposition of Nd and Pr from molten fluoride electrolyte had to be acquired. We started the investigation with the reaction mechanism of Nd electrodeposition and continued with simultaneous electrodeposition processes of neodymium and praseodymium.Plenary Lectur

Aluminium electrodeposition onto glassy carbon from deep eutectic system made of AlCl3+urea

Electrochemical deposition of aluminium onto glassy carbon from deep eutectic solvent (DES), made of the AlCl3+urea, at 25-50°C have been investigated. The deposition was performed in potentiostatic mode. The morphology of the obtained deposits were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Critical overpotential of aluminium deposition decreased from around – 0.150 V at 25°C to around – 0.100 V at 50°C. All recorded currents were small but would substantially increase with increasing working temperature (from 0.01 mA cm-2 up to 0.25 mA cm-2). The deposits obtained showed variety of morphological shapes depending on the working temperature and potential applied. All the deposits were made of very small crystallites grouped randomly into more or less separate agglomerates. Density of the crystallites distribution over the substrate and complicity of the crystal forms increased with the potential applied. Electrodeposition/dissolution of aluminium in used electrolyte onto used substrate obviously promises positive results if research aiming at reversible systems of such composition working at temperatures very close to room temperature.Ispitivano je elektrohemijsko taloženje aluminijuma na staklastom ugljeniku iz eutektičke smeše (DES), AlCl3+urea, na temperaturama od 25-50°C. Elektrotaloženje je izvođeno potenciostatski. Morfologija dobijenih taloga je analizirana skenirajućom elektronskom mikroskopijom (SEM) i energetsko disperzivnom spektroskopijom (EDS). Kritične prenapetosti elektrotaloženja aluminijuma kretale su se od oko – 0.150 V pri 25°C do oko – 0.100 V pri 50°C. Zabeležene gustine struje bile su male, ali su njihove vrednosti značajno rasle sa povećanjem radne temperature (od 0.01 mA cm-2 do 0.25 mA cm-2 uz povećanje temperature od 25°C do 50°C). Dobijeni talozi pokazali su raznovrsne morfološke oblike što je zavisilo od primenjene temperature i potencijala. Svi talozi sastojali su se od veoma malih kristala objedinjenih u aglomerate koji su bili nasumično raspoređeni po površini radne electrode. Gustina rasporeda kristalita po površini elektrode i njihova pojedinačna raznovrsnost po obliku rasle su sa povećanjem primenjenog potencijala. Elektrohemijsko taloženje/rastvaranje aluminijuma u upotrebljenom elektrolitu i na upotrebljenoj podlozi obećava pozitivne rezultate u istraživanjima usmerenim na reverzibilne sisteme istog ili sličnog sastava koji bi trebalo da rade na temperaturama veoma bliskim sobnoj

Aluminum/zirconium alloys obtained by Al underpotential deposition onto Zr from low temperature AlCl3+NaCl molten salts

Contrary to the widely accepted hypothesis that it is not possible, aluminum underpotential deposition (UPD) onto zirconium from a low temperature (200, 250 and 300 °C) equimolar chloroaluminate melt was recorded. Furthermore, it was shown that aluminum UPD facilitates alloy formation between the deposited aluminum monolayer and the zirconium substrate by interdiffusion. The aluminum/zirconium alloys formed at temperatures substantially lower than those needed for thermal preparation of the same alloys were Al3Zr2 and Al3Zr. The experimental techniques linear sweep voltammetry, potential step, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction were used for the characterization of the obtained electrode surfaces

Alloy formation by mg under-potential deposition on al from nitrate melts

Magnesium was underpotentially deposited on aluminium electrodes from magnesium nitrate-ammonium nitrate melts at temperatures ranging from 390 to 500 K. The electrochemical techniques used were linear sweep voltammetry and potential step. Electrodes were studied by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). It was found that reduction processes of nitrate, nitrite and water (when present), in the underpotential range studied, took part simultaneously with magnesium underpotential deposition. Consequently, magnesium UPD reduction and stripping voltammetry peaks were not pronounced and well defined. Nevertheless, EDS, EDX and XRD measurements showed evidence of Mg2Al3, MgAl2 and Al12Mg17 alloys formed by underpotential deposition of magnesium onto aluminium substrate

Formation of niobium oxides by electrolysis from acidic aqueous solutions on glassy carbon

In this study niobium oxide films were formed without peroxo-precursors from three different mixed acidic aqueous solutions on glassy carbon. Linear sweep voltammetry and potential step were techniques used for electrochemical experiments. The simultaneous and consecutive electrochemical reduction of water, nitrate and sulphate ions provided an alkaline environment with oxygen in the near vicinity of the working cathode, which in combination with the present niobium ions, produced niobium oxides and/or oxyhydroxides on the glassy carbon substrate. The formed deposits were analyzed using scanning electron microscopy and energy dispersive spectroscopy and appear to consist of NbO, NbO2 and Nb2O5. Both the niobium and acid concentration of the electrolytes used influenced the morphology and particle size of the deposits. The formation of niobium-fluoride and hydrogen-niobiumoxide complexes is addressed

Galvanostatsko elektrohemijsko taloženje aluminijuma na aluminijumu iz rastopa AlCl3+NaCl

The processes of galvanostatic electrochemical deposition of aluminium onto aluminium from chloroaluminate melt made of equimolar AlCl3+NaCl mixture at 200°C have been investigated. The obtained deposits were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Galvanostatic Al deposition from the used melt onto aluminium substrate with smaller current densities (2-5 mA cm-2) gave relatively close-packed and well adhering deposits. Aluminium deposits obtained galvanostatically with current densities larger than 5 mA cm-2 are less compact, more crystalline and less adhering to the aluminium substrate. Al deposits obtained with 10 and 12.5 mA cm-2 were voluminous, very crystalline and poorly adhering to the working electrode substrate. These deposits were made of very small crystallites grouped randomly into more or less separate agglomerates

Aluminium electrodeposition onto glassy carbon from deep eutectic system made of AlCl3+urea

Electrochemical deposition of aluminium onto glassy carbon from deep eutectic solvent (DES), made of the AlCl3+urea, at 25-50°C have been investigated. The deposition was performed in potentiostatic mode. The morphology of the obtained deposits were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Critical overpotential of aluminium deposition decreased from around – 0.150 V at 25°C to around – 0.100 V at 50°C. All recorded currents were small but would substantially increase with increasing working temperature (from 0.01 mA cm-2 up to 0.25 mA cm-2). The deposits obtained showed variety of morphological shapes depending on the working temperature and potential applied. All the deposits were made of very small crystallites grouped randomly into more or less separate agglomerates. Density of the crystallites distribution over the substrate and complicity of the crystal forms increased with the potential applied. Electrodeposition/dissolution of aluminium in used electrolyte onto used substrate obviously promises positive results if research aiming at reversible systems of such composition working at temperatures very close to room temperature.Ispitivano je elektrohemijsko taloženje aluminijuma na staklastom ugljeniku iz eutektičke smeše (DES), AlCl3+urea, na temperaturama od 25-50°C. Elektrotaloženje je izvođeno potenciostatski. Morfologija dobijenih taloga je analizirana skenirajućom elektronskom mikroskopijom (SEM) i energetsko disperzivnom spektroskopijom (EDS). Kritične prenapetosti elektrotaloženja aluminijuma kretale su se od oko – 0.150 V pri 25°C do oko – 0.100 V pri 50°C. Zabeležene gustine struje bile su male, ali su njihove vrednosti značajno rasle sa povećanjem radne temperature (od 0.01 mA cm-2 do 0.25 mA cm-2 uz povećanje temperature od 25°C do 50°C). Dobijeni talozi pokazali su raznovrsne morfološke oblike što je zavisilo od primenjene temperature i potencijala. Svi talozi sastojali su se od veoma malih kristala objedinjenih u aglomerate koji su bili nasumično raspoređeni po površini radne electrode. Gustina rasporeda kristalita po površini elektrode i njihova pojedinačna raznovrsnost po obliku rasle su sa povećanjem primenjenog potencijala. Elektrohemijsko taloženje/rastvaranje aluminijuma u upotrebljenom elektrolitu i na upotrebljenoj podlozi obećava pozitivne rezultate u istraživanjima usmerenim na reverzibilne sisteme istog ili sličnog sastava koji bi trebalo da rade na temperaturama veoma bliskim sobnoj

Alloy formation by al and nb electrodeposition from chloroaluminate low temperature melt

Electrodeposition of Nb and Al onto platinum from equimolar AlC13+NaCl melt enriched with niobium ions was studied at 200 °C. Nb was introduced into the melt by anodic dissolution of Nb anode. Experimental techniques used for deposition and dissolution processes were cyclic voltammetry and potential step, and for analysis of the deposits obtained, scanning electron microscopy-SEM, X-ray diffraction-XRD and energy dispersive spectrometry-EDS. Niobium was deposited at overpotential individually and co-deposited with aluminium at aluminium overpotentials. It was found that Nb/Al, Nb/Pt, Al/Pt alloys were formed and Al and Nb deposited, depending on the potential applied

Aluminium Underpotential Deposition from AlCl3+NaCl Melts and Alloy Formation with Vanadium Substrate

Aim of this work was to study underpotential deposition of aluminium onto polycrystalline vanadium electrode from equimolar AlCl3+NaCl melt at 473, 523 and 573 K. It was found that aluminium was deposited and incorporated into polycrystalline vanadium electrode at potentials more positive than the Al reverse potential. Applied electrochemical techniques: linear sweep voltammetry and potentiostatic deposition/ galvanostatic striping, showed clear evidence of formation of three intermetallic compounds whose presence depends on temperature and applied deposition time. Deposits were studied via scanning electron microscopy (SEM), energy dispersive spectrometry and X-ray spectroscopy (EDS and EDX), atomic force microscopy (AFM) and X-ray diffraction (XRD)

Morphology of aluminium electrodeposited on aluminium from AlCl3+urea solvate ionic liquid

The ionic liquid, made of urea and AlCl3, known as deep eutectic solvent (DESs) has already shown to be low‐cost electrolyte suitable for aluminum electrodeposition. By applying appropriate potentiostatic or galvanostatic electrolysis regime, aluminium is successfully electrodeposited from the deep eutectic solvent onto aluminium substrate at nearly room temperatures. Morphologies of the produced deposits were characterized by scanning electron microscopy (SEM) and chemical composition by energy-dispersive X-ray (EDX) analysis. The electrodeposited aluminium displayed different morphology depending on the deposition conditions applied