An investigation on hydrofluoric (HF) acid-free extraction for niobium oxide (Nb2O5) and tantalum oxide (Ta2O5) from columbite/tantalite concentrates using alkali reductive roasting

•We demonstrate a novel alkali roasting process for the treatment of niobium (Nb) and tantalum (Ta)-bearing minerals without the use of hydrofluoric acid.•Reductive alkali roasting above 800 °C produces metallic iron which can be separated magnetically for alloy making.•The remaining non-magnetic fraction contains a mixture of NaNbO3 and NaTaO3, which is then refined for producing niobium and tantalum oxides.•Sodium bisulphate roasting of the non-magnetic fraction yields a mixture of high-purity Nb2O5-Ta2O5 oxides.