Analysis of Tantalum Products by Inductively Coupled Plasma Atomic Emission Spectrometry

Abstract

Inductively coupled plasma atomic emission spectrometry was applied to the analysis of different products during the various steps of Ta processing. The products were the ore tantalite, three solutions coming from the liquid–liquid extraction plant,i.e., liquor, Ta-rich and Nb-rich solutions, aluminothermic Ta (Ta containing about 15% m/m Al), pure Ta pentoxide (Ta₂O₅) and Ta metal. Dissolution was used for the solid materials without separation of the matrix. Dissolution of the tantalite ore sample was achieved by using a mixture of HBF₄+H₂SO₄+HClO₄ on a PTFE Vigreux-type column heated in an atmospheric pressure microwave oven. Decomposition of the aluminothermic Ta, Ta₂O₅ and Ta metal was achieved using a mixture of HF+HNO₃ in a PTFE-lined pressure vessel. Because Ta and Nb are line-rich elements, a high-resolution sequential dispersive system was used as well as a careful selection of the wavelengths to avoid spectral interferences. Major, minor and trace elements were determined in each matrix leading to a precision <3% RSD. The recoveries for the analyte spiked samples were >95%. The limits of detection for the trace elements in a 10 g dm^–3 Ta matrix were suitable to qualify Ta products for major applications, except for those for the microelectronics industry, which requires 5N or 6N grade materials.