Leaching of niobium and tantalum from a low-grade ore using a KOH roast–water leach system

A new process is proposed for the leaching and recovery of niobium and tantalum from a low-grade refractory niobium–tantalum ore after adding pure Nb2O5 to adjust the niobium to tantalum ratio. The ore was roasted and decomposed with KOH then leached with water. Experiments were carried out to study the effect of the Nb2O5-to-Ta2O5 mass ratio, decomposition temperature, alkali-to-ore mass ratio and decomposition time on the leaching of niobium and tantalum, as well as the associated impurity elements, such as titanium, iron, manganese, silicon and tin. The optimal conditions were determined to be: Nb2O5-to-Ta2O5 mass ratio 2.33:1; KOH-to-ore mass ratio 2:1; reacting for 60 min at 400 °C. Leaching with water extracted ~ 95% Nb and 94% Ta together with about 80% Si and Sn, 50% Ti and < 20% Fe and Mn. The niobium and tantalum was recovered as high purity (Nb,Ta)2O5 (99.3%) through evaporation, crystallization and phase transformation processes.