During several past decades, plenty of technologies for platinum group metals (PGM) and rhenium (Re) recovery from electronic wastes and spent catalysts have been developed and published. The reasons for the rising interest in this area are: □ The abundance of these elements in the earth's crust is less than 10 -3 ppm (~6.6 10 4 t all over the world); □ global demand for PGMs is over 590 t; □ electronics and catalysts industry consumes over 90% of precious metals (about 65% of Pd, 45% of Pt and 84% of Rh are consumed in catalytic converters); □ properties of PGMs and Re (resistance towards corrosion and oxidation, high melting temperatures, electrical conductivity, and catalytic activity) are of great commercial interest.Even though several comprehensive reviews on the recovery of precious metals from spent catalysts have been recently published, several developments were out of the attention of the scientific community. The reviews divide the technologies into hydro-and pyrometallurgical ones. However, the variety of different approaches requires a more detailed classification. This article is an overview of the recently reported works and the comparison of different technologies in terms of extraction efficiency, environmental friendliness, and capital and operational expenditures. The new electrochemical method, which is now under development, is also presented.

Regularities of the cathodic and the anodic behaviour of aluminium on tungsten in halide melts are investigated. The study of such systems is relevant in connection with the prospects for their use as bipolar electrodes for efficient extraction of noble metals from spent petrochemical Al 2 O 3 -based catalysts by the electrometallurgical method with associated production of highpurity aluminium and oxygen. Stationary and non-stationary polarization curves were obtained for the reduction and the oxidation of aluminium in molten NaCl-KCl+5wt.%AlF 3 and 1.3KF-AlF 3 systems at 700 -850 °C (973 -1123 K) in the range of current densities from 0.01 to 1.5 A•cm -2 and in the range of potential sweep rates from 0.01 to 5 V•s -1 . Electrochemical characterization of the electrode showed that electroactive particles in chloride-based melts have higher diffusion coefficients (in comparison with fluoride melt) due to the high concentration of Na(I) and K(I) cations, low density and viscosity of the melt. Electrochemical dissolution and reduction of aluminium in both chloride-based and fluoride melts are quasi-reversible diffusioncontrolled processes complicated by several parallel phenomena. Cathodic reduction of Al(III) in both studied melts occurs at high overvoltages (more than 200 mV at 0.1 A•cm -2 ) with the limiting current densities of 0.3-0.4 A•cm -2 at 800 °C. The cathodic reduction of Na(I) starts in chloride-based melts at the potential of -0.5 -(-0.7) V relative to Al reference electrode; the reduction of K(I) in both studied melts starts at -1.0 -(-1.2) V. In general, the kinetic parameters of the processes show that the extraction in two-sectioned cell can be beneficially performed at 800 °C with high current densities, and the liquid aluminium bipolar electrode seems to be the promising solution.

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Electrochemical decomposition of spent catalyst dissolved in molten salts is a promising approach for the extraction of precious metals from them. This article reports the results of the study of aluminum electrowinning from the xLiF–(1-x)AlF3 melt (x = 0.64; 0.85) containing 0–5 wt.% of spent petroleum Pt/γ-Al2O3 catalyst on a tungsten electrode at 740–800 °C through cyclic voltammetry and chronoamperometry. The results evidence that the aluminum reduction in the LiF–AlF3 melts is a diffusion-controlled two-step process. Both one-electron and two-electron steps occur simultaneously at close (or same) potentials, which affect the cyclic voltammograms. The diffusion coefficients of electroactive species for the one-electron process were (2.20–6.50)∙10−6 cm2·s–1, and for the two-electron process, they were (0.15–2.20)−6 cm2·s−1. The numbers of electrons found from the chronoamperometry data were in the range from 1.06 to 1.90, indicating the variations of the partial current densities of the one- and two-electron processes. The 64LiF–36AlF3 melt with about 2.5 wt.% of the spent catalysts seems a better electrolyte for the catalyst treatment in terms of cathodic process and alumina solubility, and the range of temperatures from 780 to 800 °C is applicable. The mechanism of aluminum reduction from the studied melts seems complicated and deserves further study to find the optimal process parameters for aluminum reduction during the spent catalyst treatment and the primary metal production as well.