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

Abstract

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.

Advances in Understanding Metal Electrolysis Process

“…This innovative research provides a solid foundation for the development of a controllable electrochemical synthesis of vanadium trialuminide (Al 3 V) and A15 alloy (AlV 3 ) intermetallics [5]. Contributing to the fundamental understanding of primary aluminum production, the electrochemical behavior of aluminum in the LiF-AlF 3 melt and the presence of the spent catalyst at 740-800 • C was presented in [6]. Experimental data obtained the optimal process parameters for aluminum reduction during the spent catalyst treatment and primary production, as well as key parameters; the effect of the catalyst content, temperature, and electrolyte composition was outlined.…”

“…Both one-electron and two-electron steps occur simultaneously at close (or the same) potentials, which affect the cyclic voltammograms. The diffusion coefficients of electroactive species for the one-electron and two-electron processes were presented in [6].…”

Pt and Al Recovery from a Spent Pt/Al2O3 Catalyst via an Integrated Soda Roasting–Alkaline Leaching–Carbonization Process

“…Platinum (Pt) is an important precious metal, and it has strong catalytic activity [1][2][3]. Al 2 O 3 is usually used as the carrier where Pt is loaded to enhance its catalytic performance [4,5].…”