Chemistry and chemical technology / 7. Inorganic chemistry

PhD-doctoral Troeglazova A.V., associate professor Zlobina E.V.
Kazakh National University named after al-Farabi
Atomic-emission determination of rhenium and platinum in exhaust catalysts

Increased demand for rhenium, along with its low prevalence in the crust [1] necessitates the extraction of metals from secondary raw materials, such as exhaust platinum-rhenium catalysts. According to OST 153-39.2-034-2003 [2], determination of rhenium and platinum in exhaust catalysts and in the waste of their production is carried out by photo colorimetric method after acid dissolution of the catalyst in an open system.

The aim of this study is to optimize conditions for sample preparation of exhaust catalysts and determination of platinum and rhenium by ICP-MS. 

Microwave mineralizer "Minotaur-1" (Lumex, Russia) was used for the decomposition of the catalyst samples in a closed system. The content of rhenium and platinum in the solutions obtained after the expansion was determined using Agilent-7500 mass-spectrometer with inductively coupled plasma (Agilent Technologies, Japan). Standard solution of rhenium with concentration of 1 mg/mL was prepared by dissolving accurately weighed ammonium perrhenate [3]. Preliminary semi-quantitative analysis of catalyst samples was carried out using a diffraction spectrograph DFS-8 with arc source.

The chemical composition of the exhaust aluminum-platinum-rhenium catalyst is shown in Table 1. 

Table 1 – Composition of the exhaust aluminum-platinum-rhenium catalyst (%)

Cu	Pb	Mn	Zn	Cr	Co	Re	Be	Pt	MgO	Al2O3
0,003	0,002	<0,005	0,003	0,005	0,0015	>0,1	0,00015	0,4	<0,1	>10

Certified methods of decomposition of the catalyst in open and closed systems are presented in Table 2.

Table 2 – Methods of decomposition of exhaust catalysts

№	Method	Reagents
1	Acid dissolution in the open system	H2SO4 (1:1)+ Н2О2+ HCl
2	Acid dissolution in the closed system	HNO3+ Н2О2
3	Alloying	NaOH + Na2O2
4	Sintering	MgO
5	Sintering	CaO

Three measurements of rhenium analytical line intensity and then calculation of the average value by which the mass concentration of metal in the sample solution (µg/mL) was found using the calibration characteristic were performed for each solution obtained after decomposition of the catalyst samples. Average arithmetical mean of n-parallel determinations each of which is made from a single sample was taken as the test result ().

Completeness of the transfer of rhenium and platinum to solution for autoclave decomposition was controlled by comparing the results with the results of the analysis of metals after decomposition of the samples in the open system. It was established that the acid dissolution in open and closed systems can completely dissolve the sample of exhaust catalyst (Table 3). When autoclave acid dissolution with a mixture of (HNO₃ + H₂O₂) (method #2), time spent for the decomposition, is reduced from 2 h to 20-30 min; the influence of the blank experiment is also reduced by reducing the amount of reagents used almost to stoichiometric compared to the mass of the samples. The relative standard deviation () was used to estimate the random component of the error of analysis (Table 3).

Table 3 – Methods of decomposition of rhenium-containing samples in the open system (n – number of results, n = 8, – average arithmetic mean of the results of analysis, – the relative standard deviation analysis)

№	Rhenium		Platinum
	, %		, %
1	0,18±0,02	0,078	0,27±0,03	0,093
2	0,26±0,01	0,054	0,22±0,02	0,050
3	0,08±0,01	0,163	3·10^-3 ± 2,1·10^-4	0,133
4	0,17±0,01	0,076	6,5·10^-3 ± 1,3·10^-4	0,015
5	0,12±0,01	0,150	2,7·10^-5 ± 3,2·10^-6	0,036

Thus, the decomposition of samples of exhaust platinum-rhenium catalyst was carried out using many methods described in the literature. It was established that the performing the decomposition of samples in the analytical autoclaves with microwave heating allows not only reduce the duration of the decomposition process, but also to eliminate losses of volatile components, as well as to reduce the amendment to the blank-experiment by reducing the amount of reagents used. Obtained results can be used to develop ICP-AES technique of simultaneous determination of rhenium and platinum in exhaust catalysts.

References

1. Borisova L.V., Ermakov A.N. Analytical chemistry of rhenium. – Moscow: Nauka, 1974. – 319 p.

2. OST 153-39.2-034-2003. "Exhaust aluminum-platinum-rhenium polymetallic catalysts and wastes of the catalyst production. – Moscow: The Ministry of Energy of the Russian Federation, 2003.

3. Korostylev P.P. Preparation of solutions for chemical-analytical works. – Moscow: Publishing house of AS USSR, 1962. – 222 p.