Electrochemical characterization of the liquid aluminium bipolar electrode for extraction of noble metals from spent catalysts

Abstract

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.

The Cathodic Behavior of Aluminum from Pt/Al2O3 Catalysts in Molten LiF-AlF3-CaF2 and Implications for Metal Recovery from Spent Catalysts

“…2 Hydrometallurgical and pyrometallurgical methods are extensively used at industrial scale for the recovery of PGM's from the spent catalysts while electrochemical techniques are infrequently used. [3][4][5][6] The one-step electrochemical method was developed for the recovery of PGMs from the spent catalyst, where the process can be performed with an operating temperature between 973 and 1123 K. 7 A liquid bipolar electrode (LBE) divides the cell into two sections. The first section acts as an electrolysis cell with 1.3 KF-AlF 3 + (2-3 wt.% SC) electrolyte, where the catalyst carriers decompose into aluminium and oxygen while the PGMs accumulate in the LBE.…”

Electrolysis of Low-temperature Suspensions: An Update

“…The using KF-AlF3 systems widens the electrochemical window for the aluminium electrodeposition without an alkali metal reduction. In (1.3NaF-AlF3)-Al2O3 melts at 860 °С sodium is reduced at a potential 0.2...0.25 V more negative than the aluminium reduction potential [46,47]. This can be a significant obstacle to the sustainable electrolysis of the suspension since the recirculation of the cathode layer in suspensions is extremely difficult.…”