Determination of Sc in Geological Samples by Inductively Coupled Plasma-Atomic Emission Spectrometry with Four-Acid Digestion

The national standard method for the analysis of scandium in geological samples uses sodium peroxide to fuse samples. After the filtration and separation of the sample solution, Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) is applied to determine scandium. This process is complex, moreover, large amounts of salts are brought in during the pretreatment and the accuracy of the result is not satisfactory, and the procedure is lengthy, making it unsuitable for current mineral exploration. A mixture of four-acid system, which includes nitric acid, hydrochloric acid, perchloric acid and hydrofluoric acid, to decompose geological samples has been used and is reported in this paper. The Sc was measured by ICP-AES. Hydrochloric acid of 5% is used as the solution medium. When the interference element content is lower than 2%, the interference factor correction (IEC) is applied to optimize the intensity of the spectral line and the solution is diluted appropriately to reduce the matrix effects. Through these steps, the accuracy and precision of the measurement results of scandium were improved. The detection limit of this new method is 0.0016 μg/mL, which is better than the detection limit (0.004 μg/mL) of the national standard method, and the recovery rate of this method is 97.0%-99.3% with measurement range of 0.00003%-10%. The relative standard deviation (RSD, n=6) is in the range of 0.4%-2.3%. National standard reference materials were analysed by this method, and the test results of scandium agree well with the recommended values. Unlike the alkali fusion method, the acid leaching method can avoid bringing in interfering substances. Hereby, the stability has been improved greatly by using ICP-AES to determine Sc. This method is less demanding on the regional and environmental conditions, is simple and fast and can be applied to a large number of geological samples in laboratories.