Niobium and tantalum beneficiation from tantalite ore

[摘要] English: Tantalum and niobium occur in nature in the form of minerals such as tantalite andcolumbite. Recent advances in technology have increased the demand for theseelements and their chemical compounds. Tantalum is extensively used in theelectronics industry, especially in cell phones and laptops while niobium is usedmainly in the production of super metal alloys for the use in the construction industry.The presence of U and Th in these Nb/Ta containing minerals (NORMs) howevercomplicates the beneficiation process of the minerals immensely. Regulatoryconstraints on the quantity of material that can be handled at one time, processingequipment, transportation and waste disposal of these materials put more strain onthe processing of these minerals. This strain adds a financial burden on the totalbeneficiation value chain when U and Th are present.The overall aim of this study was to investigate the selective removal of U and Thfrom these minerals prior to their complete dissolution in order to increase the safetyof processing and/or transportation procedures. The methods included acid leaching(time and temperature variation), anion precipitation and ion exchangechromatography. The results obtained from these studies indicated varying degreesof success. The acid leaching study involved the use of sulphuric acid, phosphoricacid, hydrochloric acid, nitric acid, perchloric acid and aqua regia, of which the firstthree of these acids proved to be the most effective in the removal of the majority ofU and Th from the mineral.Analytical results obtained for while using concentrated sulphuric acid as reagentindicated that an increased amount of radioactive material was removed from themineral. The Th content removed from the mineral ore increased from 68.82% at 50°C to approximately 100% at 100°C after 3 hours of leaching in both cases.Additionally, the U content in the filtrate increased from 64.37% at 100°C to 81.27%at 150°C and finally to 90.08% at 200°C. Phosphoric acid was less effective in theremoval of uranium and thorium at 50°C while an increase in temperature to 150 °Cresulted in 85.10 and 98.77 % of U and Th respectively being removed after 3 hours.On the other hand, hydrochloric acid exhibited the same trend as sulphuric andphosphoric acid with an increasing amount of U and Th present in the filtrate as timeand temperature were increased. At 90°C and 3 hours of leaching, hydrochloric acidsucceeded in removing 51.53 and 91.09% of U and Th respectively. The maindisadvantage of the use of these concentrated acids as leaching reagents atelevated temperatures and extended times, is the simultaneous removal of Ta andNb from the mineral. Analytical results indicated that 9.70 and 29.11% of Ta and Nbrespectively were dissolved at 150°C after 3 hours using sulphuric acid. The use ofsulphuric acid as reagent, a temperature of 50°C and 2 hours leaching time wereselected as the most suitable conditions for the subsequent beneficiation process asa compromise between the maximum U and Th removal and the minimum amount ofTa and Nb removed from the NORMs.The selective removal of the radioactive elements using anion precipitation and ionexchange was also investigated. The selective precipitation using several differentanions indicated that sulphate (SO42-) was the most successful anion in the selectiveremoval of U and Th from the mineral solution compared with all of the acidsinvestigated. The sulphate resulted in the precipitation of 5.11 % of the total Uprecipitated along with 82.58 % of the Th, 80.13 % of the Nb and 99.21 % of the Ta.The ion exchange chromatography method, however, was unsuccessful in theseparation of uranium and thorium from the tantalum and niobium as there was noselectivity in retention and/or elution of these elements.The final step in this study was to investigate the possible beneficiation of thetantalite ore by combining the acid leaching with the magnetic removal andmicrowave dissolution of the mineral. The mineral sample which was investigatedpossessed minute magnetic properties and small amounts of Ta and Nb (1.79 and1.69 % respectively) together were removed together with Fe by magneticseparation. The acid leaching resulted in consistent but lower U and Th removal.Interestingly, the microwave digestion preferentially removed U, Th and Nb, asindicated by their presence in the filtrate, leaving the precipitate with significantlymore Ta. The ratio of niobium to tantalum changed from 1:1 in the initial mineralsample to 3:1 and 1:2 in the filtrate and the precipitate respectively. The finalinsoluble mineral contained 0.13 % Th (initially 0.50 %), 1.33 % U (initially 3.07 %),12.18 % Nb (initially 28.1 %) and 21.41 % Ta (initially 27.71 %). The filtrate, on theother hand, contained 0.14 % and 0.98 % of thorium and uranium as well as 13.00 %niobium and 3.99 % tantalum.

[发布机构] University of the Free State