ИСТИНА

Laser-Induced Breakdown Spectrometry (LIBS) is a valuable tool for rapid multielement analysis without chemical digestion. It can be especially helpful for in-line control and decision making. One example of this task is ore analysis during mining process, which is usually carried out in laboratory through ICP-MS or in some cases WDXRF. On the conveyor line, however, it is best to use laser-based technique capable of remote analysis. In this way one can see in real time if the ore layer is enriched with enough REE to continue mining. Thus, the aim of this work is to provide an assessment of LIBS coupled with Chemometrics as a tool for direct analysis of lanthanides in RЕE-rich ores. In this work, we used partial least squares regression (PLS-R) to circumvent spectral interferences in LIBS emission spectra so that we would have robust calibrations for all rare-earths from La to Sm. To provide a uniform distribution of lanthanide concentrations in a training set we implemented specialized design of experiment (DoE) based on Latin hypercube sampling (LHS) [1]. We obtained the matrix of 5 factors (elements), 20 levels (concentrations as well as samples) and 0.03 maximum pairwise correlation. The samples were prepared by mixing reagent grade REE oxides according to the DoE, and Fe2O3, TiO2 to roughly simulate the ore matrix. Powders were pressed into pellets. We used thermodynamic modeling of a wide spectral range to find REE lines free from self-absorption and intensive enough to be used for the determination of Ce (0.046–3.95 %), La (0.026–2.41 %), Nd (0.015–1.18 %), Pr (47–3800 ppm) and Sm (24–1500 ppm) in 6 niobium (OREAS 460–465) and 4 uranium (OREAS 100a–102a) ore samples [2]. Preprocessing of all experimental spectra included baseline substruction and variable selection. The latter means narrowing down the raw spectral ranges to minimize the influence of false correlations with Fe and Ti very strong emission. Calibration was performed by choosing the lowest RMSECV and at the same time simplest models in terms of PC number as follows: Element Ce La Nd Pr Sm RMSECV (leave one out), % 8 11 18 23 26 PC number 2 2 3 2 2 Thereafter, our models were validated by direct analysis of lanthanides in RЕE-rich ore standard reference materials. Chemometrics provided quantitative determination of Ce, La and semiquantitative results for Nd, Pr and Sm with 5, 9, 20, 18, 24 % RMSEP respectively. This level of accuracy shows that LIBS coupled with Chemometrics is a powerful tool for direct analysis of lanthanides in RЕE-rich ores. 1. Akhmetzhanov T.F., Pashkova G.V., Chubarov V. M., Labutin T.A., Popov A.M. J. Anal. At. Spectrom. 2021. 36. 224–232. 2. Zaytsev S.M., Popov A.M., Labutin T.A. Spectrochim Acta - Part B. 2019. 158. 105632. The reported study was funded by RFBR according to the research project № 19-33-90242.