Abstract
Wood charcoal is an attractive alternative to petroleum coke in production of carbon anodes for the aluminum smelting process. Calcined petroleum coke is the major component in the anode recipe and its consumption results in a direct greenhouse gas (GHG) footprint for the industry. Charcoal, on the other hand, is considered as a green and abundant source of sulfur-free carbon. However, its amorphous carbon structure and high contents of alkali and alkaline earth metals (e.g., Na and Ca) make charcoal highly reactive to air and CO2. Acid washing and heat treatment were employed in order to reduce the reactivity of charcoal. The pre-treated charcoal was used to substitute up to 10% of coke in the anode recipe in an attempt to investigate the effect of this substitution on final anode properties. The results showed deterioration in the anode properties by increasing the charcoal content. However, by adjusting the anode recipe, this negative effect can be considerably mitigated. Increasing the pitch content was found to be helpful to improve the physical properties of the anodes containing charcoal.
Highlights
All modern smelters use the Hall–Héroult process to electrolytically reduce the alumina dissolved in molten cryolite
Both green and baked apparent density decreased as the percentage of charcoal increased
Increasing the charcoal in the anode recipe resulted in remarkable deterioration in both electrical and mechanical properties of the baked anodes
Summary
All modern smelters use the Hall–Héroult process to electrolytically reduce the alumina dissolved in molten cryolite. In this process, carbon anodes are used to conduct the high amperage direct electrical current necessary for smelting from the busbar to the electrolyte. A typical prebaked anode consists of approximately 65% calcined petroleum coke, 20% recycled anode butts, and 15% coal tar pitch [2]. Petroleum coke is produced from the heavy residual fractions of crude oil by delayed coking. Due to changes in the oil refining industry (Edwards, 2015), most coke supplies do not comply with anode specifications, which are essentially based on the upper limit of sulfur and heavy metal content, the density, the molecular structure, as well as the mechanical properties [3]
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