Solid Oxide Membrane (SOM) technology for environmentally sound production of tantalum metal and alloys from their oxide sources

Abstract

The Solid‐Oxide‐Oxygen‐Ion conducting membrane (SOM) technology offers great potential for environment friendly and energy‐efficient extraction of high‐energy‐content metals. This work was performed to demonstrate the technical viability of the SOM technology to produce tantalum metal and tantalum–niobium alloy directly from tantalum oxide and ore concentrates. An electric potential is applied to dissociate the tantalum oxide source, reduce the Ta metal at the cathode, pump the oxygen ions through the membrane (SOM), and oxidize them at the anode. The process can be used to efficiently produce tantalum metal without the expensive pre‐processing of raw materials and generation of harmful byproducts. The work reported in this paper demonstrates that the SOM process can produce high‐purity tantalum metal. The electrochemical behavior of the cell and the method to increase membrane stability are also discussed.

Clean Metals Production by Solid Oxide Membrane Electrolysis Process

“…c SEM image of the reduced Ta metal surrounded by the unreduced tantalum oxide in the pellet. Reproduced with permission from Krishnan et al [20]. Copyright 2005, Wiley order for it to compete with the state-of-the-art metal production processes.…”

“…Krishnan et al first demonstrated the technical viability of the SOM technology with carbon anode current collector to produce Ta metal directly from sintered Ta 2 O 5 pellets [20]. 5 hydrogen storage alloys from a sintered NiO-CeO 2 pellet and a sintered NiO-CeO 2 -La 2 O 3 pellet, respectively, immersed in molten CaCl 2 at 1273 K by SOM process [35].…”

“…• another metal if an alloy with that metal is desired (e.g., Si or Nd is produced on an iron cathode to form Fe-Si or Fe-Nd alloy, respectively), • another metal from which the desired metal can be crystallized out in a pure form (e.g., Si crystallized from a liquid Sn cathode) [34,52], or • the oxide of the desired metal in the form of a compressed pellet (e.g., Ta, CeNi 5 , Ti-Si, Ti-Fe) [20,31,35,36,39].…”

“…• an inert metal if the desired metal is produced in the form of a gas and subsequently condensed in a separate chamber (e.g., Mg (g) produced on a steel cathode) [19,21,50], • an inert electronic conductor such as TiB 2 (e.g., for Al production) [27,51], • the desired metal itself (e.g., Ta) [20,31],…”

“…Since the late 1960s, researchers have recognized and investigated the use of zirconia solid electrolyte for metals production and refining [14][15][16][17][18]; however, limited progress was achieved due to the poor stability of the zirconia membrane, low current density, and lack of an appropriate current collector assembly. A decade ago, Pal's pioneering work on new molten salt compositions increased solubility of many oxides, e.g., CaF 2 -MgF 2 eutectic molten salt dissolves *10 wt% MgO, decreased zirconia corrosion rate, and has generated new interest in commercialization of the process for metals production [19,20]. The SOM process has been applied to reduce various metal oxides or oxide compounds to the respective metals or alloys, including Mg [19,[21][22][23][24][25][26], Al [27], Ti [28], Ca [29,30], Fe [22], Cu [31], Ta [20], Cr [20], Nb [20,32], Yb [33], Nd, Pr, Dy, Si [34], CeNi 5 , and La x Ce 1-x Ni 5 [35], Ti-Fe alloy [36,37], Ti-Si intermetallics [38,39].…”