Basic Research On The Process Of Separating Niobium And Tantalum By Extraction With MIBK In Low Concentration Hydrofluoric Acid System

Niobium and tantalum are important rare and precious metals, they and their alloys have been widely used in steel, electronics and other high-tech fields. Current treatment method for the niobium-tantalum ore is the process of decomposition in high concentration hydrofluoric acid and extraction in high acid. However, the process causes serious fluorine pollution and the resource utilization of the refractory ore is low. Therefore, the new technology of niobium-tantalum clean production with sub-molten salt method was developed by the institute of process engineering, Chinese Academy of Sciences. The decomposition rate of refractory niobium-tantalum ore with this new technology increased by 10% or more than that with current hydrofluoric acid method, and the middle product, niobium tantalum hydrated oxide, can be dissolved by the low concentration hydrofluoric acid of the theoretical amount. The new technology was expected to reduce significantly the amount of hydrofluoric acid and achieve the separation of niobium and tantalum by extraction in low concentration hydrofluoric acid system, and then reduce fluoride pollution to a large extent to achieve cleaner production.The process of separating niobium and tantalum by extraction in low concentration hydrofluoric acid system was the key technology which controled fluorine pollution and product quality in the niobium-tantalum clean production technology with sub-molten salt method. Based on previous research result of sub-molten salt clean production technology, the systematic research on separating niobium and tantalum by extraction in low concentrations hydrofluoric acid system was carried out in this thesis. The optimal process conditions of separating tantalum and niobium by extraction and impurities removing were obtained, and corresponding extraction mechanism was also studied. The main work and achievement were as following:(1) By the analysis of the differences of niobium, tantalum existing forms and properties in low concentration hydrofluoric acid system, extracting selectively tantalum with MIBK was determined and then the new process of separating tantalum and niobium was achieved.(2) By using the method of multi-spectral fitting (MSF), a reasonable MSF model was established in ICP-AES. The spectral interference of niobium from tantalum matrix of high concentration in extract liquid was effectively corrected. The accurate determination of niobium element method for this experimental system was established, which provided a guarantee for the accuracy of the analytical process of following experiments. (3) In the low concentration hydrofluoric acid system, tantalum and niobium was separated by extraction with MIBK. The effects of contact time, O/A ratio, concentration of hydrofluoric acid, tantalum and niobium concentration, tantalum and niobium mass ratio, concentration of sulfuric acid and temperature on extraction rate of tantalum and niobium and separation factor of tantalum and niobium(βTa/Nb) were investigated. The results indicated: In the conditions of contact time 5 min, O/A ratio 5, concentration of hydrofluoric acid 0.5 mol·L-1, tantalum and niobium concentration 60 g-L-1, tantalum and niobium mass ratio 2, the extraction rate of tantalum and niobium were 96.01% and 0.048% respectively, and separation factor of tantalum and niobium(βTa/Nb) nearly reached 50,000. So with MIBK as extractant, efficient separation of tantalum and niobium by extraction can be achieved. Through pickling organic phase containing tantalum twice with 3 mol·L-1 H2SO4 and O/A ratio 1:1, the trace niobium was all removed. In addition, the extraction behavior of Fe, Si, Al, Ti impurities was investigated. The results indicated all Fe, Si, Al, Ti were not extracted into the organic phase containing tantalum which provided the technology foundation to prepare high-purity tantalum.(4) The method of niobium oxalate crystallization was used to purify niobium in extract liquid.effective separation of impurities and niobium can be achieved. The contents of Fe, Si, Ti, Al impurities can meet the industry requirements. (5) The mechanism of extracting tantalum with MIBK was studied.The slope method and the method of saturation capacity were used to determine the molar ratio of MIBK and tantalum, and the means of infrared spectroscopy and nuclear magnetic resonance spectroscopy were also used to analyse MIBK before and after extraction. The results indicated:In the condition of hydrofluoric acid 0.5 mol·L-1, tantalum mainly existed in the form of HTaF6, with only a small part as HTaF7. The mechanism of extracting tantalum with MIBK was solvent extraction, the extraction equation can be abbreviated as: 3 MIBK+HTaF6=HTaFe·3MIBK.