Extraction of Ta and Nb from a Coltan Bearing Ore by Means of Ammonium Bifluoride Fluorination and Sulfuric Acid Leaching

Abstract

A novel approach for Ta and Nb extraction consisting of the pre-treatment of a coltan-bearing ore with an ammonium bifluoride sub-molten salt and subsequent acid leaching has been studied. The effects from ore granulometry, ammonium bifluoride (ABF) to ore mass ratio, temperature and duration of fluorination on the degree of Ta and Nb extraction were examined. The ABF to ore ratio and process temperature were found to have the most pronounced impact on extraction efficiency. The following optimal process conditions were determined: ore granulometric fraction (−75 + 45 µm), ABF-ore (5/1), fluorination temperature (200 °C) and fluorination time (2.5 h). Maintaining these parameters enabled about 94% of Ta and 95% of Nb to be brought into solution during the sulfuric-acid-leaching stage. A comparison of the proposed method with previously reported studies suggests that due to the effects of mechanical agitation and the recirculation of the HF-containing gaseous phase back into the process, the dosage rate of ABF at the fluorination stage could be reduced significantly without sacrificing the overall recovery of Ta and Nb. In such a way, the approach could offer added environmental benefits since release of fluoride-containing effluents into the environment could be limited.

Niobium and tantalum recovery from the primary source and from tin slag, an industrial challenge: A review

“…Shikika et al [ 10 ] demonstrated that Nb is easier to dissolve than Ta, which may be because it is less refractory. It was proven that particles under 75 μm presented better recovery due to a larger surface area.…”

“…The chemical interactions of Nb and Ta with NH 4 HF 2 are presented in Reaction (), where ‘M’ is Fe or Mn. [ 10 ] …”

“…Shikika et al [ 10 ] studied Nb and Ta extraction from coltan. The initial coltan ore had 41% Nb, 8.43% Ta, and the Si amount was 1.5%.…”

“…Nb and Ta recovery was 95% and 94% after a 2.5 h fluorination process at 200°C with a mass ratio of 5, considering a HCl 1 M leaching as solubilization process. [ 10 ]…”

“…[ 3 ] Besides, Ta has high electrical conductivity, so it is used in the electronics industry for the production of capacitors. [ 10 ] Thus, very specific characteristics make these rare metals difficult to replace.…”