Determination of tungsten in niobium-tantalum, vanadium and molybdenum bearing geological samples using derivative spectrophotometry and ICP-AES

Two different procedures, one using derivative spectrophotometry and anothe r using inductively coupled plasma atomic emission spectrometry (ICP-AES) h ave been developed for the determination of tungsten in niobate-tantalates, tin slag samples, ores, concentrates and vanadium and molybdenum bearing g eological materials. In the first method involving derivative spectrophotom etry, 0.05-0.5 g of the sample is fused with sodium hydroxide, the tungsten is extracted by leaching the melt with distilled water and estimated as th iocyanate using a second derivative spectrophotometric method in the presen ce of interferents, i.e. Nb, Mo and V, without separating them. Mixtures of tungsten with V, Nb and Mo are used for standardizing the various paramete rs like zero-crossing wavelength, wavelength range, etc. Tolerance limits f or V, Nb and Mo have also been evaluated. In the second method involving IC P-AES, 0.05-0.5 g of sample is fused with KHSO4 to a clear melt and dissolv ed in ammonium oxalate solution. Ammonium hydroxide precipitation is then c arried out to separate Nb and Ta as hydroxides and the filtrate is boiled w ith nitric acid to destroy the oxalates before aspiration into the plasma f or measurement of tungsten values by ICP-AES using the 207.911 nm emission line. Both methods have been applied to niobate-tantalate and tin slag samp les and the results obtained are reported in this paper. The values obtaine d by both methods are in good agreement with each other. The proposed metho ds have also been applied to the determination of tungsten in two Canadian Certified Reference Standards (CT-1 and MP-2) and the values obtained are i n good agreement with the certified values and the R.S.D.% in case of the I CP-AES method varied from 1-2% at > 1000 mu g g(-1) level to 9.4% at the 20 mu g g(-1) level whereas the R.S.D.% in case of the derivative method vari ed from 1 to 7.8%. (C) 1999 Elsevier Science B.V. All rights reserved.