Determination of tungsten in ores and concentrates by atomic absorption spectrometry: suppression of atomisation interferences from calcium

Abstract

A simple and rapid method for the determination of tungsten in ores and concentrates by atomic absorption spectrometry is described. A dinitrogen oxide-acetylene flame was used and the absorbance was measured at 400.9 nm. The samples were decomposed using fused potassium hydrogen sulphate, which was found to be a suitable flux for opening tungsten minerals. The potassium hydrogen sulphate also proved to be a powerful enhancing agent for the tungsten absorbance signal while eliminating many reported interferences. Eighteen elements were examined for interferences and only calcium was found to interfere seriously when present in concentrations greater than 0.1 mg per 100 ml. The depressive effect of calcium could be easily suppressed and the absorbance signal wholly restored to the original level by the addition of a sodium silicate solution such that the minimum ratio of the concentration of Si : Ca was 1.5 : 1. The method has been applied to the determination of tungsten in wolframite, scheelite, wolframite-cassiterite and heavy mineral stream concentrate samples.