SELECTIVITY OF TRACE ELEMENT UPTAKE BY THE SURFACE OF ORE PYRITE: ICP-MS DATA
S.V. Lipko, V.L.Tauson, R.G. Kravtsova, N.V. Smagunov, A.S. Makshakov, A.V. Nikolaev
Federal state budgetary institution of science Vinogradov Institute of Geochemistry SB RAS, Irkutsk, Russia
Keywords: Pyrite, trace elements, species, selectivity, surface, lanthanoids, ICP-MS, laser ablation
Abstract
Using a model sample of pyrite ore collected at the Degdekan gold deposit (North East Russia), we demonstrate the use of different variants of the IСP-MS method to determine the ratio of surficial-bound and structural-bound forms of trace elements (TE) in pyrite. Despite the difference in the physicochemical nature of the analysis methods involving the decomposition of crystals of different sizes (analytical data selections for single crystals - ADSSC) and direct determination by scanning the surface with a laser beam of different power (LA-IСP-MS), it has been shown that a number of elements tend to enrich the surface layer of pyrite crystals. The ratio of TE contents in the surface layer and in the volume (structure) of the crystal is defined as the selectivity (S) of surficial phases in the uptake of a given element. According to ICP MS – ADSSC data, the selectivity was 3.9 (Mn), 3.3 (Ag), 6.4 (Pd), 6.4 (La), 0.3 (Pr), 0.8 (Tb), 2.6 (Ho), 0.5 (Er), 1.0 (Lu), according to the results of LA-ICP-MS 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), 0.6 (Dy). A comparison with experimental data for S Mn, Pd, and Ag reveals comparable results. However, it is concluded that LA-IСP-MS should be more representative in order to enable criterion-based statistical sampling (CBSS) according to a principle similar to ADSSC for more accurate discrimination of the structural component of TE concentration. Otherwise, significant errors are possible due to the influence of microinclusions of autonomous phases, in this case galena, which concentrates As, Au and Sb due to heterovalent isomorphism, resulting in S<1 for these elements. Most of the studied TEs show a direct correlation between selectivity and the difference in the ionic radii of the element and Fe, which confirms the relationship between S and the level of incompatibility of the impurity element in FeS2. High correlation coefficients between light REEs in the surface and the absence or negative correlations between light and heavy REEs are noted. This may reflect differences in the species of heavy and light lanthanides and requires more detailed study using LA-ICP-MS surface analysis and the application of the CBSS procedure. Despite the preliminary nature of the results, they deserve attention in practical terms as a justification for the development of technology for the extraction of critically important REEs as by-products in the processing and enrichment of pyrite ores and concentrates. They also justify the importance of the surface accumulation effect of REEs and the need to take it into account in meta-analysis and statistical processing of the results of analytical determinations of element content.
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