Determination of Rare Earth Elements in Fluorite Samples by Open Boric Acid Dissolution and Inductively Coupled Plasma-Mass Spectrometry

The research of rare earth elements (REEs) in fluorite has very important significance for determining the source of ore-forming materials, the nature of ore-forming fluid and genesis. The determination of REEs in fluorite can be solved by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) with sodium peroxide fusion, but the sample handling process is complex; sodium peroxide is difficult to purify and matrix interferences derive from high salinity solution, making it unsuitable for processing large numbers of samples. Nitric acid and hydrofluoric acid, which are used for the conventional method, do not react with calcium fluoride, which can be dissolved in sulfuric acid and boric acid. To this end, a method for the determination of 15 rare earth elements in fluorite by ICP-MS has been developed. The fluorite samples were decomposed with boric acid solution (media with 10% H₂SO₄ and 25% HCl) and hydrofluoric acid in PTFE beakers, and then dissolved with nitric acid. Two internal standards of 103Rh and 185Re were selected to compensate the drift of analytical signals and correct matrix effects by ICP-MS. Compared with the traditional sodium peroxide alkali fusion method, this method adopted the reagents of high purity which can reduce the background effectively. The detection limits were 0.002-0.016 μg/g, which is lower than that by sodium peroxide fusion (0.006-0.058 μg/g), and the precisions were 0.7%-2.7%. The results of this method were consistent with the results by sodium peroxide fusion. The new established method was is simple and had has a low detection limit for processing large numbers of fluorite samples.