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

Abstract

The production of high purity niobium (Nb) or tantalum (Ta) compounds still relies on processes that require highly acidic conditions and concentrated HF or NH 4 F solutions. Recent progress in the chemistry of group V elements, along with the evolution of the environmental concerns, call for the development of more sustainable industrial processes for these strategic elements. In sharp contrast with the historical fluoride approach chosen by the Nb and Ta refining industry, there has been a recent surge in the literature concerning the chemistry of these elements in diluted alkaline or oxalate media. We here propose an innovative liquid-liquid extraction process that is amenable to separate Nb and Ta from alkaline feed solutions, can be operated at low acidity and that does not require any fluoridebased chemical. The developed strategy is as follows: first, Nb and Ta are co-extracted from their alkaline solution (pH 12) using a quaternary ammonium salt (Aliquat® 336) dissolved in an organic diluent; then, Nb is selectively back-extracted in a mixture of diluted nitric and Page 2/31 oxalic acids; and finally, Ta is stripped in a diluted nitric media. The process also affords purifying Nb from Ti, Fe and Na. Following an optimization at laboratory scale, the full process has been validated during continuous running tests (160 h at 1.4 L.h-1) using industrial Nb-Ta caustic solutions coming from the development of the so-called Maboumine process. The developed process works at room temperature, low acidity ([H + ] < 1 M), exhibits high recovery yields, and allows producing Nb 2 O 5 •nH 2 O with purity higher than 99.5 %. The process also yields a tantalum product (Ta 2 O 5 •nH 2 O with >20 wt% Ta) even when starting from a diluted feed (39 ppm Ta). The proposed strategy paves the way for new Nb and Ta hydrometallurgical processes operating under mild chemical environments and represents a concrete alternative to the current fluoride-intensive industrial methods. Highlights A new process for separating Nb and Ta in fluoride-free media is proposed High-purity Nb oxide (99.5 %) can be produced Nb and Ta can be recovered and separated starting from an alkaline feed solution The process works at room temperature and under mild chemical conditions

Speciation and Fractionation of Less-Studied Technology-Critical Elements (Nb, Ta, Ga, In, Ge, Tl, Te): A Review

“…Group speciation is difficult due to the similar chemical properties of these two elements and methods are currently being developed to separate Nb and Ta, including a capillary zone electrophoresis (CE), a method which is able to separate and quantify Nb and Ta directly in alkaline media [39].…”

Extraction of polyoxotantalate by Mg–Fe layered double hydroxides: elucidation of sorption mechanisms

“…The recovered materials were washed by Milli-Q water. The aqueous phases were ltered with 0.45 mm syringe lter followed by the addition of H 2 O 2 3% and HNO 3 5% to avoid precipitation 14,15 and then the concentrations of Ta were determined by ICP-OES using an iCAP 6000 series spectrometer (Thermo Scientic).…”

“…Therefore, these processes represent a serious health hazard for the humans and the environment and recent efforts were focused on alkaline matrices to generate polyoxotantalates (POTas), which have a high solubility in alkaline medium. 14,15 Tantalum, whether in metallic or oxidized form (Ta 2 O 5 ), is insoluble in solution but its alkaline fusion produces a POTa that is soluble in a basic medium. It is present as highly charged polyoxometallates (POM) such as H 2 Ta 6 O 19 6À , HTa 6 O 19 7À or Ta 6 O 19 8À .…”

Tantalum Recycling by Solvent Extraction: Chloride Is Better than Fluoride

“…Recent efforts towards fluoride-free tantalum recovery processes have focused on alkaline matrices to generate polyoxotantalates that are recovered at elevated temperatures by solvent extraction [16][17][18]. Ionic liquids (ILs) have also been investigated as potential extractants for tantalum recovery.…”

“…As such, it is evident that there is a need to develop more sustainable processes which can not only efficiently recycle tantalum from secondary sources but do so using milder reagents [12][13][14][15]. Recent efforts towards fluoride-free tantalum recovery processes have focused on alkaline matrices to generate polyoxotantalates that are recovered at elevated temperatures by solvent extraction [16][17][18]. Ionic liquids (ILs) have also been investigated as potential extractants for tantalum recovery.…”