SELECTIVITY OF TRACE ELEMENT UPTAKE BY THE SURFACE OF ORE PYRITE CRYSTALS: ICP-MS DATA
S.V. Lipko, V.L. Tauson, R.G. Kravtsova, N.V. Smagunov, A.S. Makshakov, A.V. Nikolaev
Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
Keywords: Pyrite, impurity element, speciation, selectivity, surface, lanthanide, ICP-MS, laser ablation
Abstract
A model sample of ore pyrite from the Degdekan gold deposit (Northeastern Russia) is used to demonstrate the application of different variants of inductively coupled plasma mass spectrometry for the purpose of determining the ratio of surface-bound and structurally bound trace elements in pyrite. Despite the differing physicochemical principles of the analytical methods, namely, the decomposition of crystals of varying sizes and data processing using the statistical sample of analytical data for single crystals (SSADSC) and direct surface scanning with a laser beam of varying power using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), a number of elements show a tendency to be enriched in the surface layer of pyrite crystals. The ratio of the trace element content in the surface layer to that in the volume (structure) of the crystal is defined as the selectivity of surface phases for a given element. The selectivity (S) values obtained by the first method are as follows: 3.9 (Mn), 3.3 (Ag), 6.4 (Pd), 6.4 (La), 0.3 (Pr), 0.8 (Tb), 2.6 (Ho), 0.5 (Er), and 1.0 (Lu). The LA-ICP-MS results yield the following values: 3.9 (Mn), 1.4 (Co), 6.2 (Ni), 1.6 (Cu), 0.9 (Sb), 0.2 (Au), 0.3 (As), 6.8 (Ag), 18 (La), 46 (Ce), 5.2 (Pr), 11 (Nd), 1 (Eu), and 0.6 (Dy). A comparison with experimental selectivity values for Mn, Pd, and Ag shows a reasonable agreement. Most of the studied trace elements show a direct correlation between selectivity and the difference in the ionic radii of the element and Fe, confirming the relationship between selectivity and the incompatibility of the impurity element in the FeS2 structure. High correlation coefficients are observed among light rare earth elements on the surface, whereas correlations between light and heavy rare earth elements are either absent or negative. Despite the preliminary nature of these results, they warrant practical consideration as a foundation for developing technologies to extract critically important rare earth elements as byproducts during the processing and beneficiation of pyrite ore and concentrate.
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