Determination of platinum group elements in catalysts recycling products by SEM with energy dispersive spectrometer 13 D O I: 1 0. 15 82 6/ ch im te ch .2 02 0. 7. 1. 02 Chebykin N. S., Sandalov I. P., Zamyatin D. A., Votyakov S. L. Chimica Techno Acta. 2020. Vol. 7, no. 1. P. 13–16. ISSN 2409–5613 Nikolai S. Chebykina,*, Ivan P. Sandalovb, Dmitry A. Zamyatina, Sergey L. Votyakova a Zavaritsky Institute of Geology and Geochemistry UB RAS, 15 Vonsovskogo st., 620016, Ekaterinburg, Russia b Plaurum АО “Ekaterinburg non-ferrous metals processing plant”, 131 Uspensky Ave., Verhnyaya Pyshma, 624088, Sverdlovsk region, Russia *email: tchebykinnikolai@yandex.ru Determination of platinum group elements in catalysts recycling products by SEM with energy dispersive spectrometer Analysis of platinum group elements (PGE) extracted from various catalysts used in the car, petroleum and chemical industries requires use of microanalyti- cal methods. PGE content in the platinum powder concentrates K176 and K177 was studied by SEM-EDS. The content of main elements was determined using analytical lines Fe Kα1, Si Kα1, Sn Lα1, Pt Lα1, Re Lα1. The obtained data for the chemical composition are in good agreement with the result obtained by X-ray fluorescence analysis and ICP-MS method. Powdered platinum concentrates are considered to be ferrosilicide (FeSi), where PGE are localized at the phase boundaries and in separate patches of the K176 sample, or distributed over the volume of particles in the K177 sample. Keywords: PGE; platinum powder concentrate; SEM-EDS; microanalysis; X-ray lines Received: 24.12.2019. Accepted: 06.03.2020. Published: 31.03.2020. © Chebykin N. S., Sandalov I. P., Zamyatin D. A., Votyakov S. L., 2020 Introduction High cost of  platinum group elements (PGE) dictates the  economic feasibility of their recovery from various catalysts which had been used in car, pe- troleum and chemical industries. In order to extract PGE, Plaurum АО “Ekaterinburg non-ferrous metals processing plant” (JSC EZOCM) applied a smelting technology on an iron collector using a Tetronics plasma furnace with the  subsequent processing of  the  collector in  acids [1]. The  quan- titative electron probe microanalysis of the processed powdered platinum con- centrate, in order to determine its compo- sition is difficult due to the rough surface of  the  particles and the  significant over- laps of  the  X-ray emission lines of  PGE. Therefore development of a microanalysis method for the determination of PGE con- tent in the products of catalyst recycling allow to optimize the technology and assess the efficiency of metal extraction. The aim of the work is to develop a mi- croanalysis technique for the determina- tion of PGE content in platinum powder concentrate and in the products of its recy- cling using scanning electron microscopy (SEM) equipped with an  energy disper- 14 sive spectrometer (EDS), as well as to test the modified technique for the examina- tion of  chemical composition and mor- phological characteristics of the samples. Samples and Methods The  powder concentrate samples, denoted as  K176–177 (see Fig.  1) were obtained by  melting of  catalysts with lime, quartz sand, magnetite and coke. The samples differ in melting parameters and charge composition. The samples were placed on a conductive adhesive tape and studied using a scanning electron micro- scope JEOL JSM-6390LV equipped with EDS Oxford INCA X–Max80. The  used working distance was equal to 10 mm, ac- celerating voltage of 30 kV and accumula- tion time of  60 s. The  refinement of  ob- tained X-ray spectra was performed using the Aztec v.3.1 software (including mod- eling of background by integral line and X-ray peaks by Voigt profile) [2]. Results and Discussion Semi-quantitative analysis of the PGE content was performed using a standard sample of metallic cobalt with consequent normalization of  total elements content to 100%. We used both reference materials (minerals hematite and diopside for analysis of Fe and Si content, respectively) and pure metal standards (such as, Sn, Pt, and Re) for X-ray peak intensity calibration. The con- tent of the main elements (Fe, Si, Sn, Pt, Re) was determined using the following analyti- cal lines of the X-ray spectrum: Fe Kα1, Si Kα1, Sn Lα1, Pt Lα1, Re Lα1 (see Fig. 2b). The lines for the two last of the listed PGEs do not overlapped with X-ray lines for Al, Cr, Ti, V, Ca, Cl, the  presence of  which is typical for studied samples (Fig. 3); their content was measured by the corresponding X-ray lines Al Kα1, Cr Kα1, Ti Kα1, V Kα1, Ca Kα1, Cl Kα1. In order to determine qualitatively (or semi-quantitatively) the  average chemi- cal composition of the samples, we have studied a region with the area of 1.5 mm2 which contained about 300–400 particles of powder in scanning mode. The surface of  the  particles in  the  samples exhibited either complex branched structure (K176) or rounded shape with developed edges (K177). The size of particles in the sam- Fig. 1. BSE images of platinum concentrate particles (a, b — samples K176 and K177). The rectangle area separated in image (a) — corresponded to the plot for the sample K176, shown in Fig. 3a 15 ples varied from 50 to  300 microns. The content of main elements in the K176 sample can be represented as: Fe = 81.7, Si = 12.1, Pt = 2.4, Sn = 1.3 wt.%; whereas the detected impurities are: Al, Cr, Ti, V, Cl. The  sample K177 contains Fe = 77.7, Si = 16.2, Pt = 1.5, Re = 2.3  wt.% as  main elements and the detected impurities are: Al, Ti, V, Ca, Cl. The  relative standard deviation (Δ) for the  elements’ content in  the  samples determined in  the  scan- ning mode is 1.3 (1.1 wt.%), 5.0 (0.8 wt.%), 4.3 (0.1 wt.%), and 4.9 (0.1 wt.%) %, for Fe, Si, Pt, and Re respectively. The chemi- cal composition of Fe, Si, Pt, Re obtained by  SEM-EDS within these standard de- viations completely coincides with the val- ues obtained in  the  EZOCM laboratory using X-ray fluorescence analysis (XRF) (Fe = 77.1 wt.%, Si = 15.9 wt.%) and induc- tively coupled plasma mass spectrometry (ICP-MS) (Pt = 1.6  wt.%, Re = 2.5  wt.%) Fig. 2. X-ray spectra for the K176 (a) and K177 (b) samples. Scanning mode, the scanning region area of 1.5 mm2 Fig. 3. The BSE image for the K176 (a) sample, X-ray spectra reflects the presence of three phases (b). 1 — dark-grey phase on BSE image (the main phase in the volume); 2 — middle- grey (intermediate); 3 — bright-grey (blotches) 16 for sample K177 and is  close for sam- ple K176 (Fe = 77.3 wt.%, Si = 15.6 wt.%, Pt = 1.9 wt.%). The main reason for the dis- crepancy of the K176 sample is heteroge- neity. In  order to  identify the  nature and chemical composition of phases that con- tained in different particles of the inhomo- geneous K176 sample we used the mode of individual point analysis. The spatial res- olution in this mode is 1–3 microns. Three different phases inside the  K176 sample (see Figs. 1, 3) with different BSE bright- ness were clearly distinguished: dark-grey (main phase inside the volume), middle- grey (intermediate) and bright-grey (sepa- rate blotches). It was found that the chemi- cal composition of  these phases varied significantly (see Table 1). The main ele- ments are: Fe and Si in a dark-grey phase, Fe and Pt in a middle-grey phase, Pt and Sn in a bright-grey phase. Conclusions The results of the elaborated microa- nalysis technique by means of a scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS) ap- plied to measure the PGE content in powder catalysts recycling products were in good agreement with the result obtained by other methods and allow to demonstrate the re- distribution of PGE after processing in plas- ma furnace and acids. Based on the obtained data one can conclude that powdered plati- num concentrates in the K176 and K177 samples are mainly ferrosilicide (FeSi) [3], and the platinum group elements are local- ized at the phase boundaries and in separate patches of the K176 sample, or distributed over the volume of particles in the K177 sample. Acknowledgements This work was supported by the theme of state agreement of IGG UB RAS (theme No. АААА-А19-119071090011-6). References 1. Borbat VF, Maslenitskij IN, Nikitin MV, Strizhko LS, Chugaev LV. Metallurgiya blagorodnyh metallov. Moscow: Metallurgiya; 1987. 432 p. Russian. 2. Briggs D, Seah MP. Practical surface analysis: By auger and x-ray photoelectron spectroscopy. New York: John Wiley & Sons; 1983. 533 p. 3. Bannykh OA, Budberg PB, Alisova SP et al. Diagrammy sostoyaniya dvojnykh i mnogokomponentnykh sistem na osnove zheleza. Moscow: Metallurgiya; 1986. 440 p. Russian. Table 1 The chemical composition of the phases detected in the K176 sample by SEM-EDS Phase Brightness on BSE Concentration *, wt. % Fe Si Sn Pt 1 Dark-grey 80.2–85.7 12.5–17.6 <1 0.7–1.3 2 Middle-grey 60.0–85.7 3.0–9.2 1.1–13.7 6.9–16.0 3 Bright-grey 8.5–16.0 <1 39.9–49.5 38.6–39.3 * the variation in the data obtained as a result of three measurements in each phase.