Leaching of Columbite Using an Organic Acid to Obtain Nb and Ta: Effects of Sulfate Thermal Treatment on Hydrometallurgical Processing

Global energy transition is driving the search for alternative, sustainable methods for producing critical minerals. This study evaluates thermal treatments of columbite, followed by organic acid leaching to recover Nb and Ta. Hydrometallurgical processes currently use HF combined with other inorganic acids for columbite leaching, and here, the use of oxalic acid after sulfation. Our analysis considers KHSO4 a better technical alternative than H2SO4, achieving 90% leaching efficiency. Leaching of Nb and Ta by oxalic acid (H2C2O4) after thermal treatment is possible due to the formation of stable metal-oxalate complexes, avoiding risks (operational and occupational health) of handling HF leaching. Leaching efficiencies reached 92.8% for Nb (3.48g/L) and 88.4% for Ta (0.45g/L) at a L/S ratio of 3 (columbite/KHSO4) at 650 °C for 3 h, followed by leaching with 1.0 mol/L H2C2O4 at a L/S ratio of 10 at 90 °C for 8 h. However, a preliminary economic analysis indicated that the proposed process is currently not economically feasible, mostly due to the cost of organic acid.