A Review of Niobium-Tantalum Separation in Hydrometallurgy
Niobium and tantalum are chemically similar and are associated with each other in nature which makes it very difficult to separate. For many years, the separation of tantalum from niobium involved the fractional crystallization of potassium heptafluorotantalate away from potassium oxypentafluoroniobate monohydrate, this method has been supplanted by solvent extraction from fluoride-containing solutions by the use of solvent extractants such as Octanol, bis(2-ethylhexyl)phosphoric acid (DEHPA), Alamine 336, methyl isobutyl ketone (MIBK), tri-nbutyl phosphate (TBP) or cyclohexanone. A detailed review of the various processes involved in the breakdown treatment of niobium and tantalum primary sources, extraction and separation and newer processes of extraction as well as the various technique involved were discussed. Keyword: Niobium, Tantalum, Columbite, Tantalite, Solvent extractant and Solvent extraction.
Kinetic study of niobium and tantalum hexameric forms and their substituted ions by capillary electrophoresis in alkaline medium.
In this work a capillary electrophoretic (CE) method is used for the kinetic study of the intermetallic substitutions in hexameric ions of two strategic metals, tantalum and niobium in an alkaline medium. Recently proposed processes for the production and analytical separation of tantalum and niobium that are faster, more economical and environmental friendly are based on the use of highly alkaline media. It was previously established that in these media, tantalum and niobium exist as hexameric species, HxTa6O19X-8 (Ta6) and HxNb6019x-8 (Nb6), which can be analysed with a CE method using an alkaline electrolyte and UV detection. However, when using the above method on an industrial sample a minor species that should correspond to the substituted Ta1Nb5 form was observed. The purpose of the present study is to probe, by means of CE, the kinetic of the formation of substituted niobate-tantalate ions, Ta6-xNbx (1 ≤ x ≤ 5), starting from mixtures of pure hexaniobate and hexatantalate ions. This study required the development of a new CE method allowing the separation of all the five substituted ions and their two non-substituted hexameric parent ions in less than seven minutes. In details, a previously developed separation method was transferred to a Beckman instrument and the separation improved by adjusting the total length, the applied voltage, the injection volume, the rinsing steps and the internal standard. The kinetic study shows that samples initially containing non-substituted hexameric forms of tantalum and niobium in a 1:1M ratio naturally form the five possible substituted species Ta6-xNbx (1 ≤ x ≤ 5) after only a few hours which may represent an issue for future Nb-Ta separation processes operated in alkaline media. The developed method was also transferred to an Agilent instrument and the kinetic study repeated. Results obtained with the Agilent instrument corroborate those obtained with the Beckman instrument. The proposed electrophoretic separation method lays the ground for new analytical techniques that could help assessing the presence of substituted species that can be deleterious for Nb-Ta purification processes.
Melanocins A, B and C, new melanin synthesis inhibitors produced by Eupenicillium shearii. I. Taxonomy, fermentation, isolation and biological properties.
New melanin synthesis inhibitors, melanocins A, B and C, were isolated from the fermentation broth and mycelium extract of Eupenicillium shearii F80695. Melanocin A, an isocyanide compound, inhibited mushroom tyrosinase and melanin biosynthesis of B16 melanoma cells with IC50 value of 9.0 nM and MIC value of 0.9 microM, respectively. Melanocin A also inhibited growth of Streptomyces bikiniensis. While, the structurally very related but non-isocyanide compounds melanocins B and C did not show inhibitory activity in these assays. Melanocins A, B and C showed potent antioxidant activity with scavenging activity of DPPH radical and superoxide anion radical.