Aluminium Recycling in Single- and Multiple-Capillary Laboratory Electrolysis Cells

This work is a contribution to the approach for Al purification and extraction from scrap using the thin-layer multiple-capillary molten salt electrochemical system. The single- and multiple-capillary cells were designed and used to study the kinetics of aluminium reduction in LiF-AlF3 and equimolar NaCl-KCl with 10 wt.% AlF3 addition at 720-850 degrees C. The cathodic process on the vertical liquid aluminium electrode in NaCl-KCl (+10 wt.% AlF3) in the 2.5 mm length capillary had mixed kinetics with signs of both diffusion and chemical reaction control. The apparent mass transport coefficient changed from 5.6 center dot 10(-3) cm.s(-1) to 13.1 center dot 10(-3) cm.s(-1) in the mentioned temperature range. The dependence between the mass transport coefficient and temperature follows an Arrhenius-type behaviour with an activation energy equal to 60.5 kJ.mol(-1). In the multiple-capillary laboratory electrolysis cell, galvanostatic electrolysis in a 64LiF-36AlF(3) melt showed that the electrochemical refinery can be performed at a current density of 1 A.cm(-2) or higher with a total voltage drop of around 2.0 V and specific energy consumption of about 6-7 kWh.kg(-1). The resistance fluctuated between 0.9 and 1.4 omega during the electrolysis depending on the current density. Thin-layer aluminium recycling and refinery seems to be a promising approach capable of producing high-purity aluminium with low specific energy consumption.