Caustic potash assisted roasting of the Nigerian ferro-columbite concentrate and guanidine carbonate-induced precipitation: A novel technique for extraction of Nb–Ta mixed-oxides

Abstract

The current study focuses on alkali-assisted roasting, dissolution, and recovery of mixed oxides of niobium (Nb) and tantalum (Ta) from a ferro-columbite concentrate collected from Jos Plateau in Nigeria. Alkali-assisted roasting and water-based leaching to extract Nb and Ta using guanidine carbonate salt were adopted for sustainable extraction. The concentrate was roasted with caustic potash (KOH) as flux at optimized conditions (250 °C, 100% mass flux-to-concentrate ratio, 1 h) and leached with water. This resulted in dissolution of 97-96% Nb, 80-96% Ta, 92-91% W and 64-65% Mn for −250 and + 250 μm size fractions respectively while leaving behind in the residue most of Sn (94-83%) and Fe (79-81%). The amount of Nb and Ta dissolved were selectively recovered with novel application of guanidine carbonate salt as precipitating agent. High extraction yield (∼100%) was achieved. The final recovery of approximately 96% Nb and 85% Ta contained in the +250 μm concentrate feed sample was obtained under optimum conditions of 50 mg/mL guanidine. The (Nb,Ta)-guanidine precipitate obtained was then calcined at 900 °C for 1 h and converted into mixed (Nb,Ta)2O5 (97%) and removed the guanidine. Based on material balance, it was found that approximately 734.5 kg of (Nb,Ta)-guanidine precipitate with purity higher than 84% could be obtained from one tonne of ferro-columbite feed concentrate. The current technique of alkali-assisted roasting, dissolution, and recovery of mixed oxides of Nb and Ta is a novel process and presents an environmentally benign, and it is an efficient technique to replace the traditional method which uses an environmentally harmful hydrofluoric acid to extract Nb and Ta.