Abstract:
BACKGROUNDDue to its high digestion efficiency, low equipment cost and low detection limit, atmospheric acid dissolution is widely used in the geological laboratory. However, the commonly used four acid methods (hydrofluoric acid-nitric acid-hydrochloric acid-perchloric acid) is insufficient to dissolve niobium and tantalum. At the same time, niobium and tantalum would be partially adsorbed or would settle on the vessel caused by hydrolysis and polymerization reactions leading to the test results are lower than the real values.
OBJECTIVESTo determine accurately the concentrations of Nb and Ta in geochemical samples, and to solve the two key problems of the dissolution rate and hydrolysis of Nb and Ta in the solution.
METHODSFor the insufficiency of dissolution, sulphuric acid was introduced into the acid solution system. The acid solution system of hydrofluoric acid-nitric acid-hydrochloric acid-perchloric acid-sulphuric acid is used to completely dissolve niobium-tantalum in the sample. In view of the hydrolysis, extracting agent of 5% hydrofluoric acid-5% sulphuric acid-5% hydrogen peroxide was used. At the same time, the standard material curves were made using the same analytical process as the sample. The combination of these two methods effectively inhibited the hydrolysis of niobium-tantalum in sample solution. The method of standard material curves reduced the error caused by the matrix inconsistency between the sample solution and the standard solution in ICP-MS analysis.
RESULTSThe relative deviation was less than ±7% and the relative standard deviation was 3.11%-6.27% (n=11). The detection limits of niobium and tantalum were 0.04 μg/g and 0.03 μg/g, respectively. Compared with the detection limit of 0.33 μg/g by alkali fusion method, it has obvious advantages.
CONCLUSIONSBy changing the acid solution system, the extracting agent, and the method of standard material curves, the proposed method can be applied to measure niobium and tantalum in geochemical exploration samples.
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