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.

This paper presents a preliminary study on the thermal decomposition process of aluminium chloride hexahydrate (AlCl₃·6H₂O) crystal with non-isothermal thermal kinetic analysis and static calcination experiments. The ‘kinetic triplets’ including activation energy, pre-exponential factor and mechanism function for the decomposition reaction were determined through thermal analysis from Differential Scanning Calorimetry–Thermos Gravimetric Analysis results. It is found that the average activation energy and pre-exponential factor were 59.668 kJ mol⁻¹ and 6.67 × 10⁵ min⁻¹, respectively, and the most suitable conversion function was . The emission rates of the gaseous products, water (H₂O) and hydrogen chloride (HCl), were calculated from the chlorine content evolution obtained from the static calcination tests, respectively. The phase transformation and the change of particle morphology during the decomposition process were also investigated through X-ray diffraction and scanning electron microscope technologies.

Smelter grade alumina (SGA) plays multiple roles in the Hall–Héroult process for primary aluminum production. Given its very porous nature, one major role of SGA is to adsorb toxic hydrogen fluoride (HF) in the dry scrubber. However, also because of its porous nature, SGA inevitably adsorbs ambient moisture. This paper discusses the influence of alumina properties, including pore size distribution and specific surface area, on the physical adsorption of water vapor on SGA, as well as the adsorption kinetics. The result shows that the adsorption enthalpy of moisture on SGA is in the range of 4–13 kJ/mol. The adsorption capacity increases significantly with the particle specific surface area and total pore volume. A higher adsorption temperature indicates a much faster adsorption rate but corresponds to a lower equilibrium adsorption capacity.

This paper proposes a technical viewpoint for the recovery of waste heat in aluminum electrolysis. The idea of combining heat‐generating electrolysis process and the heat‐consuming alumina tube digestion process is discussed in detail. The structural design of the heat‐exchanging system as well as the matching problems between the heat exchanger and cell design are also mentioned. Several major concerns including the automatic temperature regulation of the cell sidewall and the preferred selection principles for the heat medium are introduced. A 2 kA heat exchangeable cell is developed and a series of tests are carried out in the laboratory. It is found that approximate 80% of the sidewall waste heat can be recovered while the cell behaves steadily. It is also proved possible to control the thickness of the frozen ledge through adjusting the heat convection rate of the heat exchanger. The heat‐exchanging system is also suitable for aluminum cells when the fluctuating wind power is applied as a major energy supply.