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

Alidor Shikika,Julien L Colaux,Mohamed Aatach,Mac C Mugumaoderha,Stoyan Gaydardzhiev,Fabrice Muvundja,Francois Zabene

doi:10.3390/min11121392

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.

Highlights

Tantalum (Ta) and niobium (Nb) are two refractory metals with similar physical and chemical properties that are almost always found in nature as paired metals
ammonium bifluoride (ABF) with an analytical purity of 99% was obtained from VWR (Avantor) and was used as a fluorination agent, and sulfuric acid (98%, ρ = 1.84), supplied by Central Drug
The effects of key operational parameters of a two-stage process that involves fluorination followed by sulfuric-acid leaching on the degree of Ta and Nb extraction has been studied

Summary

Introduction

Tantalum (Ta) and niobium (Nb) are two refractory metals with similar physical and chemical properties that are almost always found in nature as paired metals. Niobium is characterized by an elevated melting point, relatively low density and quite marked magnetic and superconductive properties [2]. These unique properties determine their irreplaceable position and use in specific sectors of the electronics industry, in defense-equipment manufacturing, steel making, cuttingtools fabrication, etc. The leaching of Ta and Nb still remains quite a challenge, since the process requires highly aggressive conditions. The currently existing processes for leaching of Ta–Nb ores mainly use HF-H2 SO4 -based media and temperatures between 80–100 ◦ C. Under these conditions, the majority of the studies

Methods

Discussion

Conclusion