Abstract
In the Hall-Héroult process for extracting aluminum, the evolution and dynamics of anodic bubbles have a significant influence on the efficiency of the overall electrolysis process. In this study, the behavior of the bubbles beneath the carbon anode in cryolite-alumina molten salt was studied for the first time using a laboratory-scale transparent electrolysis cell to view the anode from the bottom. The bubble dynamics and the relevant characteristic parameters of bubbles were obtained using video cameras and image processing. It was found that the bubbles were observed to preferentially generate at several areas on the underside of the anode and the morphologies of coalesced bubbles show excellent similarity. Moreover, the behavior of gas on carbon and graphite anodes was significantly different, where the carbon anode favored the forming of larger bubbles. These observations confirmed different types of carbon anodes cause different bubble behavior. These findings are expected to be useful in optimizing the aluminum electrolysis process on an industrial scale.
Highlights
The Hall-Héroult electrolytic process has been the most common method for primary aluminum production since its invention in 1886 [1]
This study presents detailed observations of bubble dynamics under the carbon anode using a transparent electrolysis cell
It was found beneath that larger bubbles werewas formed onfor thethe carbon anode with a release
Summary
The Hall-Héroult electrolytic process has been the most common method for primary aluminum production since its invention in 1886 [1]. It is widely accepted that the air−water system is able to represent the CO2 −cryolite system because of the similar kinematic viscosity of water to cryolite In these studies, the “anode gas” is produced by injecting air underneath the anode surface, which is different from the actual occurrence in the real cell. Zhao et al [19] investigated the effects of anode slots on bubble behavior and cell voltage They found that anode slots with a width of 4 mm were able to prevent smaller bubbles from coalescing into larger ones, decreasing bubble size and gas coverage on the anode. In those studies, the anodes were made of graphite, different from the carbon material used in industrial reduction cells. A comparison of the surface properties of the anodes was carried out to explain the very different gas behavior observed
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