Potentiometric determination of Tantalum content in ores using an ion selective membrane electrode

Abstract

In this paper, a method for determination of tantalum in ores by direct potentiometry using an ion selective membrane electrode sensitive to the ion TaF₆̅  has been proposed. After checking the Nernstian behavior of the electrode in the presence of TaF₆̅ , the influence of NbF₆̅  concentration on the determination of tantalum was also investigated. Potentiometric measurements on synthetic solutions of TaF₆̅ in the concentration range from 10^-3 to 10^-5 mol.l^-1 were performed in the presence of 10^-3 mol.l^-1 of NbF₆̅  as interferering ions. From the results recorded, it appeared that the response of the electrode deviate to the Nernstian behavior when TaF₆̅ concentration is less or equal to 5×10^-5 mol.l^-1 corresponding to a concentration of NbF₆̅ at least twenty times greater than that of TaF₆̅. Using the standard addition method, it was observed that the ion NbF₆̅ is no longer interferering with TaF₆̅  on the entire range of concentration of TaF₆̅  investigated. The accuracy of the method conducted on a series of potentiometric measurements was about 1%. The technique developed has then been applied to the determination of tantalum in samples of Colombo-tantalite from various region of Rwanda.