Tantalum and niobium are the most important materials for various sectors of the national economy. They are used for structural steel, superconducting, electron tubes, cemented carbide, steel modifiers, scientific lens additives, dental prosthetic materials, etc.
Tantalum and niobium are found in over 130 kinds of minerals, composed of tantalate and niobate or complex oxide of titanium-niobium-tantalate. The widely used minerals in the production of metallic tantalum and niobium are tantalum-columbite, pyrochlore, rare-earth perovskite, etc. Among them, pyrochlore is a very valuable mineral due to its high content of rare earth elements as well as tantalum and niobium.
The separation methods of tantalum and niobium include fractional crystallization of fluoride complexes, solvent extraction, ion exchange, distillation of chlorides, and selective reduction of NbCl5. Among them, those that have been commercialized for many years are fractional crystallization and solvent extraction.
Recently, the development of inexpensive and efficient solvent extractants by many researchers has led to the separation of tantalum and niobium by solvent extraction methods. Although the use of neutral extractants such as MIBK and TBP in hydrofluoric or hydrofluoric-sulfuric acid media is common for the separation of tantalum and niobium, the separation of tantalum and niobium from sulfuric acid decomposition has been rarely studied so far.
Kang Chung Su, a section head at the Faculty of Chemical Engineering, conducted a study to separate the impurities from the aqueous leachate of pyrochlore sulfate decomposition product and to separate tantalum and niobium with octanol as the extractant.
After keeping the pH of the sulfate leaching solution at 2 and mixing 100% octanol to an aqueous phase/organic phase ratio (A/O) of 1:1, the extraction at room temperature for 15min resulted in more than 99% tantalum extraction, but no niobium extraction. After stripping of the tantalum-loaded octanol with distilled water at room temperature for 20min at a phase ratio of 1:1, more than 99% tantalum was stripped. When ammonia solution is added to the tantalum pregnant strip solution to pH 4.5-5.5, tantalum hydroxide is precipitated and when ammonia solution is added to the raffinate to pH 6-7, niobium hydroxide is precipitated.