An overview on recent separation and purification strategies for recovery of Nb and Ta from primary and secondary ore sources

This paper focuses on processing technologies for the exploitation and purification of Nb and Ta from primary and secondary ore sources that have been used for extraction of these critical metals. Fusion and leaching processes are widely used in hydrometallurgical strategies along with solvent extraction and ion exchange technology aiming to obtain mixed Nb and Ta products or separated compounds with a demanded industrial purity degree. Although solvent extraction is a well-established and industrially applied strategy, it mostly requires the presence of fluoride to enable the formation of complexes in combination with organic phase. Methyl iso-butyl ketone (MIBK), tri-butyl phosphate (TBP), octanol (OCL) and cyclohexanone (CHN) are the most employed extractants in industrial operations. The use of organic or different mineral acids rather than the fluoride-based, allows the use of tertiary amines as organic extractant, and constitutes a worthy strategy in the seeking for innovative, environmentally cleaner and less harmful strategies of separation and purification of Nb and Ta. Likewise, ion exchange technology paves the way for the obtaining of highly pure Nb and Ta compounds from low-grade sources. Herein is presented an overview of the recent literature regarding hydrometallurgical processes involving Nb and Ta ore sources, and the use of solvent extraction and ion exchange as strategies for separation and purification of these metals.