Posted: May 22nd, 2023
The production of Aluminum is through the Hall-Heroult process that Hall and Heroult invented in 1886. This method entails the dissolution of alumina (Al2O3) into molten cryolite (Na3AlF6) at 1223K or 950 degrees C. The resulting product is oxygen ions and aluminum metal. Given that the density of molten aluminum is higher than that of molten cryolite, the former goes to the bottom of the bath. Oxygen reacts with a carbon anode to produce CO2. The equation for this reaction is: 2Al2O3 (solution)Â + 3C(s)Â = 4AlÂ (l)Â + 3CO2 (g).
While the Hall-Heroult process has been around for about 120 years, the chemistry and physics behind the process started unfolding in recent years with the arrival of numerical methods and computing techniques. Initially, one could carry out mathematical modeling by carrying out some calculations on the sidewall ledge. Later on, things changed and there was a need for one to know the magnetohydrodynamic effects properly.
In addition to the MHD forces, the other force that acts on the bubbles is in the form of buoyancy and it originates from an anode. Further, the bubbles induce certain uniformity between bathâ€™s temperature field and the distribution of the solid alumina. Besides, they increase the energy consumption or ohmic overvoltage of the cell. Moreover, they enhance a stable operation as they perturb the bath-metalâ€™s interface and also by provoking the anode effects. A balance between the inputs and outputs should be in place. The inputs are energy, charge, carbon, or alumina, whilst the possible outputs may include gases evolved, heat generated, and aluminum in its liquid form. The solid alumina is vertical, introduced in the electrolyte (bath) either between the anodes or in the sidewallâ€™s channels. The alumina should be moved and distributed horizontally within the inter-electrode space. Gravity does not only separate the aluminium metal but also expels any gas generated from the process of electrolysis.
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