Waste
When a pot has reached the end of its useful life, normally 6-7 years, it is rebuilt with a new carbon lining (the cathode). At this time it is necessary to dispose of the old lining, which consists of old refractory bricks and carbon - normally containing material from the electrolytic bath)plus a small amount of cyanide.
Disposal techniques vary according to local conditions, environment laws and operating licenses.
Where landfill is used, precautions are taken to ensure that the waste material cannot leach out of the site as a result of rainfall. This preventive measure is normally done by lining the landfill site and covering it with an impermeable liner. Groundwater and soil in the area around the landfill are then continually monitored for contamination.
In some plants the cathode waste is securely stored above ground in dry conditions to await recycling or final disposal.
Other aluminium companies have studied processes to re-use or treat cathode waste prior to disposal. On a worldwide basis, processes to either recycle or treat cathode waste prior to landfilling are beginning to emerge.
The aluminium industry is currently researching other methods of cathode waste use – including:
- Extracting and recycling some of its useful components; Using the waste material as a combustion source for power generation;,
- Using the waste material as raw material in other industrial processes (for example, cement and steel).