Niobium and tantalum processing in oxalic-nitric media: Nb2O5·nH2O and Ta2O5·nH2O precipitation with oxalates and nitrates recycling

Abstract

Oxalate-based aqueous media represent one of the rare options for solubilizing macroscopic amount of niobium (Nb) and tantalum (Ta) without using toxic fluoride-based mixtures. Recent progress in the hydrometallurgy of Nb and Ta also highlighted the potential of oxalate-nitrate media for the separation of Nb and Ta. Nonetheless, the resulting purified aqueous solutions, containing Nb or Ta in HNO3-H2C2O4 mixtures, need to be further processed in order to yield Nb and Ta solid products that can be commercialized. Furthermore, oxalic acid is relatively expensive in the frame of the hydrometallurgy of Nb and its recycling is necessary. In this study, the precipitation of Nb and Ta, as well as their usual minor impurities (Ti and Fe), from oxalic-nitric acid solutions has been investigated for the first time. Neutralization of Nb-HNO3-H2C2O4 mixtures to pH 7-8 by concentrated NaOH or NH4OH was found to be effective at decomposing the oxalate complexes ([NbO(C2O4)3] 3and [NbO(C2O4)2(H2O)]-) and precipitating Nb in the form of Nb2O5•nH2O while leaving the Page 2/27 oxalate ions in solution. Taking advantage of the solubility difference between nitrate and oxalate salts, the subsequent concentration of the filtrates yields to the recovery of the oxalates as Na2C2O4 or (NH4)2C2O4•H2O and a concentrated solution of sodium or ammonium nitrate. The developed method exhibits high precipitation yields (>99.9%) for Nb and Ta and high recovery yields (>99%) for the nitrates and oxalates. The process was optimized at the laboratory scale (~50 mL) and then validated on industrial Nb and Ta solutions (~225 L) with successful production of purified Nb2O5•nH2O and Ta2O5•nH2O, recovery of the oxalates in the form of Na2C2O4 or (NH4)2C2O4•H2O and a concentration solution of nitrates. Taking together, the proposed precipitation method and the fluoride-free liquid-liquid Nb-Ta separation recently reported pave the way for more suitable hydrometallurgical processes for Nb and Ta. [19] K[NbO(C2O4)2(H2O)2]•3H2O A[NbO(C2O4)2(H2O)2]•2H2O (A = Rb, Cs) Mg[NbO(C2O4)2(H2O)2]2•8H2O

Solvent-Impregnated Sorbents for Tantalum from Niobium Separation Using a Fixed-Bed Column

“…As mentioned in the introduction, recently published papers mainly concern the separation of the elements from their ores and their subsequent separation, and the level of purification is not very deep. The highest reported purity of niobium is about 99.5% [43], 99% [18], 98.88% [40], or 87% [39]. In our studies, such material is only a starting material for the obtaining ultrapure niobium, so it is difficult to compare the cited results with ours.…”

A fluoride-free liquid-liquid extraction process for the recovery and separation of niobium and tantalum from alkaline leach solutions

“…The back-extraction yield of Ti was around 10 % throughtout the campaign indicating that the process also exhibits a good selectivity Nb/Ti. In the case of Fe, this impurity was totally co-stripped with Nb but this impurity is removed during downstream treatment of the Nb stripped solution [47]. The purity of the final Nb product was higher than 99.5 wt% (Table 4) which is enough to use it as starting material in the HSLA steels manufacture or for the high-end applications described in the introduction.…”

“…The Nb stripped solution was quantitatively converted to niobium oxide by a neutralizationprecipitation procedure which also affords recovering the oxalates and nitrates. This procedure is detailed in a follow-up paper [47]. The final stripping of the organic phase was performed with different solutions during the campaign.…”

“…The process also affords purifying niobium from titanium, iron and sodium. The treatment of the Nb and Ta stripped solutions and subsequent recycling of the oxalate are detailed in a follow-up publication [47]. The Nb-Ta separation detailed in the present study has been optimized at laboratory scale and then validated by pilot scale testing.…”

Dismantling of Printed Circuit Boards Enabling Electronic Components Sorting and Their Subsequent Treatment Open Improved Elemental Sustainability Opportunities

“…Overall, the recycling efficiency into pure tantalum metal form was above 50% [146]. Alternative solutions to solubilize significant amounts of tantalum and niobium, such as oxalate-based aqueous media [147] have also been proposed and investigated. The authors further indicate that recycling of the relatively expensive oxalic acid is needed to make the process economically viable.…”