Wavelength-Dispersive X-Ray Fluorescence Spectrometric Determination of Tantalum in Columbite-Tantalite Using Takα and an Lif 420 Analysing Crystal

The paper proposes a simple, accurate, precise, and rapid method for determining the high atomic number (Z) major-element, tantalum (Z = 73), in the rare mineral, columbite [(Fe,Mn) (Nb,Ta)₂O₆] - tantalite [(Fe,Mn) (Ta,Nb)₂O₆], by wavelength-dispersive x-ray fluorescence spectrometry (WDXRFS). The other major-element in columbite-tantalite is the lower atomic number niobium (Z = 41). The method uses the characteristic radiation, TaKα, and an LiF 420 analysing crystal, to overcome the problems associated with the serious x-ray spectral-line interference of the secondorder NbKα and NbKβ with the first-order TaLα₁ and TaLβ₁ respectively.

Samples of columbite-tantalite ground to minus 300 mesh are blended with cellulose in the proportion of 1:1, and pressed powder-pellets are made from 1-g aliquots, with boric acid as a backing. The analytical standards consist of chemically analysed columbite-tantalite containing 5 to 80% by weight of Ta₂O₅. The instrumental parameters include a rhodium x-ray tube (operating voltage = 100 kV; current = 10 mA), air path, fine collimator (150 μm), and scintillation counter. The counting involves fixed time with three readings of 20s each on the peak and three readings of 20s each on one background.

The accuracy achieved is excellent (within 1.6 to 2.2%), as is the precision (within 0.4 to 2.4%). The time taken for determining Ta₂O₅ in a batch of twentyfour samples of columbite-tantalite, for a replication of four analyses per sample, by one operator using a manual WDXRF spectrometer, is only five hours.