Sulfuric acid leaching of low-grade refractory tantalum–niobium and associated rare earths minerals in Panxi area of China

By mineral liberation analyzer (MLA) automated quantitative system, the niobium–tantalum ore in this study was classified as refractory mineral of low-grade which was mainly composed of fergusonite, polycrase, ilmenorutile, and bastnasite. Most of niobium and rare earth metals were disseminated in these minerals (particle sizes of 95 % rare earth elements <40 μm), which cannot be concentrated through traditional floatation process and treated by the current hydrofluoric acid leaching in industry application. It is necessary to develop a new approach to recovery these valuable metals. In this study, an improved method is proposed to extract these metals, which includes acid roasting and sulfuric acid leaching. The influence of mineralogy, acid concentration, leaching temperature, leaching time, and liquid to solid ratio was experimentally studied. It is observed that after the ground ore (−74 μm) was roasted at 350 °C for 2 h with sulfuric acid (18.4 mol·L⁻¹) in the ore to acid mass ratio of 1:1, and then the roasting residue reacted with 25 % sulfuric acid at 90 °C for 2 h, the recovery rate of rare earth elements reaches >90 %, and the leaching extent of niobium can reach 84 %.