Spent Potlining (SPL) is a waste material generated in the primary aluminium smelting industry. Spent Potlining is also known as Spent Potliner and Spent Cell Liner.
Primary aluminium smelting is the process of extracting aluminium metal from aluminium oxide (also known as alumina). The process takes place in electrolytic cells that are known as pots. The pots are made up of steel shells with two linings, an outer insulating or refractory lining and an inner carbon lining that acts as the cathode of the electrolytic cell. During the operation of the cell, substances, including aluminium and fluorides, are absorbed into the cell lining. After some years of operation, the pot lining fails and is removed. The removed material is spent potlining (SPL). SPL was listed by the United States Environmental Protection Agency in 1988 as a hazardous waste.[1] Hazardous properties of SPL are:
- Toxic fluoride and cyanide compounds that are leachable in water
- Corrosive - exhibiting high pH due to alkali metals and oxides
- Reactive with water - producing inflammable, toxic and explosive gases.[2]
The toxic, corrosive and reactive nature of SPL means that particular care must be taken in its handling, transportation and storage.[2]SPL from aluminium reduction cell cathodes is becoming one of the aluminium industry's major environmental concerns. On the other hand, it also represents a major recovery potential because of its fluoride and energy content.[3]
Most SPL is currently stored at the aluminium smelter sites or placed in landfills. Dissolved fluorides and cyanides from SPL that are placed in landfills, along with other leachates may have environmental impacts. Environmentally safe storage methods include secure landfills or permanent storage buildings. However, many of the environmentally safe solutions are expensive and may develop unforeseen problems in the future.[4]