Selective Extraction Process of Niobium and Tantalum from Tin Slag Derived from the Thermal Processing of Cassiterite

The metallurgical industry for niobium and tantalum extraction from secondary resources typically relies on conventional hydrometallurgical processes, based on acid leaching with hydrofluoric acid. However, these methods pose significant challenges due to the generation of nonselective solutions containing large amounts of codissolved impurities, as well as handling and safety risks in operational practices. In this context, the development of economically viable and environmentally friendly alternatives is essential. This study proposes an innovative and fluoride-free methodology for recovering Nb and Ta from tin slag. The material was subjected to thermal treatment with KHSO₄, with operational parameters defined through thermodynamic simulations. The optimal conditions identified were a temperature of 600 °C, a slag-to-KHSO₄ ratio of 1:3 (w/w), a particle size of -74 μm, and a calcination time of 3 h. Then, the material was leached with oxalic acid under the following conditions: a solid-to-liquid ratio of 33 g/L, a concentration of 0.5 M, a temperature of 60 °C, and a leaching time of 60 min. This approach achieved recovery efficiencies of 82% for Nb and 80% for Ta. Under optimal leaching conditions, the dissolution of impurities remained low, with approximately 4% U, 2% Th, and less than 1% Zr, while these elements predominantly remained in the solid residue. These results demonstrate the effectiveness and selectivity of the method, enabling the production of solutions suitable for subsequent purification stages.