Efficient Extraction of Ta and Nb from a Coltan Ore Through Alkaline Roasting, Water Leaching, Precipitation, and Oxalic Acid Leaching

Current industrial processes of tantalum (Ta) and niobium (Nb) extraction from primary resources rely in majority on hydrofluoric (HF) acid leaching, which is raising material handling and safety issues. In this work, a novel HF-free treatment route for a coltan ore, based on alkaline roasting, water-leaching, precipitation, and oxalic leaching is presented. A raw ore from Lulingu deposit (the Democratic Republic of the Congo) was subjected to alkaline roasting followed by water leaching to bring Ta and Nb into solution. The most influential operating parameters of the roasting were outlined using Taguchi orthogonal array L-16 (4(4)) method. The optimal roasting conditions determined as temperature (450 degrees C), roasting time (2 h), molar ratio KOH/(Ta,Nb)(2)O-5 of 13.2 (e.g., mass ratio KOH to ore of about 2/1) and granulometric fraction (- 105 + 75 mu m), enabled about 87% of Ta and 92% of Nb to be subsequently water leached. The resulting alkaline pregnant leach solution (PLS) was subjected to precipitation, followed by oxalic acid leaching of the formed precipitates. This step brought about 86% of Ta and 92% of Nb in solution confirming the efficiency of the method. Globally, an extraction efficiency of ca. 75% for Ta and 84% for Nb could be expected from the entire process. In addition, the obtained Ta-Nb leachate was deemed suitable to downstream solvent extraction in view yielding high-purity Ta2O5 and Nb2O5 compounds. [GRAPHICS] .