Determination of Rare Earth Elements in Wolframite by Inductively Coupled Plasma-Mass Spectrometry with Nitric Acid-Hydrofluoric Acid Discomposition

Wolframite is the rare earth elements (REEs) bearing mineral and was mixed with Cr, Ca, Mg, Co, Sc and REEs. The accurate measurement of REEs in wolframite is very important to study ore forming in wolframite deposits. A method has been developed for the determination of REEs in wolframite by Inductively Coupled Plasma-Mass Spectrometry. Samples were dissolved by nitric acid-hydrofluoric acid in a sealed bomb under high pressure. The hydrofluoric acid was then evaporated. REEs were dissolved using nitric acid. Tungsten was precipitated from the solution in the form of tungstic acid and the matrix interference of the tungsten substrate was eliminated. By dissolving precipitation it was shown that the relative residual rare earth amount was less than 10%. The results of this method were consistent with the results by sodium peroxide melting. The double internal standards of Rh and Re were applied to reduce the effect by the drift of analytical signals. ¹⁵³Eu and ¹⁵⁷Gd had interferences from Eu, and the polyatomic ion interferences from Gd were calibrated using Ba, Pr and Ce oxides and hydroxides. The interferences from Eu and Gd were calibrated by using pure standard solutions of Ba, Pr and Ce with on-line analysis software. Recoveries ranged from 94.2%-104.0%, detection limits were less than 0.026 μg/g, and the relative standard deviations were better than 10% (n=10). The established method was simple and had a low detection limit with high accuracy.