Towards Understanding the Cathode Process Mechanism and Kinetics in Molten LiF-AlF3 during the Treatment of Spent Pt/Al2O3 Catalysts

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/gamma-Al2O3 catalyst on a tungsten electrode at 740-800 degrees 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)center dot 10(-6) cm(2)center dot s(-1), and for the two-electron process, they were (0.15-2.20)(-6) cm(2)center dot 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-36AlF(3) 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 degrees 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.

Automated summary

The study investigated the electrochemical decomposition of spent catalyst in molten salts for the extraction of precious metals, focusing on aluminum electrowinning from xLiF-(1-x)AlF3 melts. The results revealed a diffusion-controlled two-step process with both one-electron and two-electron reductions occurring simultaneously at close potentials. Further research is needed to optimize the process parameters for aluminum reduction during catalyst treatment and primary metal production.