Laboratory Study of the Impact of the Cathode Grade on the Formation of Deposits on the Cathode Surface in Hall-Héroult Cells

Abstract

This experimental study investigates the effect of the cathode grade on the formation of deposits at the carbon aluminium interface in Hall-Héroult electrolysis cells. Five different industrial cathode grades are tested in a bench scale aluminum electrolysis setup with the following operational parameters: cathodic current density of 0.9 A/cm2, under a nitrogen atmosphere at 960 °C for 8 h with initial bath composition of 9% alumina, cryolite ratio of 2.18 and 5% CaF2. Post mortem analyses include X-Ray diffraction on the ledge toe, side ledge, sludge and bath samples as well as scanning electron microscopy-energy dispersive spectroscopy and optical microscopy of the carbon aluminum interface. Early results suggest that the thickness of the aluminium carbide layer increases with the porosity of the carbon material. Secondly, the amount of sludge seems to be more related to the cathode grade than to the other operational parameters such as the temperature.