Product

Anode butts (also called anode stubs or spent anodes) are the residual carbon blocks remaining after a prebaked carbon anode has been consumed during aluminium electrolysis in the Hall-Héroult process. When an anode block has been reduced to approximately 15–25% of its original mass — typically after 24–33 days of service — it is removed from the cell and replaced with a fresh anode to prevent the steel stub assembly from contacting the molten bath.

Composition & Characteristics

Anode butts retain essentially the same physical and chemical properties as the original prebaked anode — high carbon content, low porosity, and good electrical conductivity — but are contaminated on their lower surface with bath crust (solidified cryolite) and electrolyte impregnation that must be removed before recycling.

Recycling & Disposal

Anode butts are a valuable carbon resource and are handled by two routes:

• Recycling into new anode production — the primary route; butts are stripped of bath crust, crushed, and reintroduced as aggregate into the anode paste mix at typically 15–25% substitution of virgin CPC; reduces raw material costs and improves paste consistency​

• External sale as carbon additive — butts not suitable for anode recycling (excessive bath contamination or high sulphur) are sold as carbon raisers for steelmaking, foundry, or ferroalloy applications

References

1. Wikipedia. Prebaked consumable carbon anode (Page version: Nov 7, 2025)​
2. ​Patra, B. (2021). Studies on influence of recycled anode butts on properties of prebaked anodes used in aluminium electrolysis. TRAVAUX 50, Proceedings of the 39^th International ICSOBA Conference (pp. 605–613). November 22–24, 2021.
3. Andrews A., Gikunoo E., Kyei-Fram B.K., & Sarfo, R. (2012). Characterization of spent prebaked aluminium carbon anode as a source of fuel for foundrymen. Journal of Minerals & Materials Characterization & Engineering, 11(1), 31–41. DOI: 10.4236/jmmce.2012.111004
4. SMF Metall (Nov 4, 2025). Carbon Anode Scrap
5. TechSolutions (Oct 23, 2021). Pre-baked Anode Carbon Block