Characterization of Physico-Chemical Changes During the Alkali Roasting of Niobium and Tantalum Oxides

Niobium and tantalum are considered critical materials because the increasing demand in the energy sector which is reliant on limited abundance of these two metals in minerals. Traditionally, niobium and tantalum minerals are digested using hydrofluoric acid at moderate temperatures, producing oxy-fluorides which are separated by solvent extraction, involving the use of hazardous chemicals. The increasing demand for Nb2O5 and Ta2O5, for energy and environmental pressures are the main reasons forcing industry to search for alternative low carbon processing methods. In this paper alkali roasting based separation and beneficiation, which is not well understood in the literature, is proposed, for which the kinetics and thermodynamic equilibria for the formation of sodium tantalate and niobate with sodium hydroxide are analyzed at the temperature range of 400ºC to 700ºC. The apparent activation energy of formation, changes from 31.0±0.8 to 22.3±1.2 kJ mol-1 and from 23.8±1.2 to 110.2±12.8 kJ mol-1, for tantalate and niobate, respectively. The reaction mechanism is examined on the basis of the analysis of reaction products using X-ray powder diffraction (XRPD) and X-ray fluorescence (XRF).