August 2008

Recycling the pots

Alcan's new pilot plant first to offer a way to recycle spent pot linings

By D. Zlotnikov

Aluminium is a modern-day staple. Despite being in use for just over 150 years, total annual production of aluminium (approximately 50 million tonnes) is second only to steel. Even though aluminium is very abundant, it is found in nature in very stable forms, which require great expenditures of energy to break down. This is the reason the final metal is sometimes referred to as “stored energy” — energy costs account for a full third of the total cost of production.

Beyond energy, there is also an issue surrounding byproducts — spent pot linings, in particular. “Aluminium is smelted in what are called pot lines,” explained Stefano Bertolli, Rio Tinto Alcan’s director of communications. “These lines are usually composed of around 300 pots.” Each of the pots is lined with a thick layer of graphite or carbon, which serves as the cathode in the electrical smelting process. “These linings have a useful lifespan of five to seven years,” continued Bertolli.

At the end of that period, the linings must be discarded and replaced with new ones. The environmental problem has always been the disposal of the spent linings, which can release sulphur dioxide and fluoride when exposed to the elements.

Alcan’s new pilot plant in Saguenay-Lac-Saint-Jean, Quebec, is set to change that. It is the first plant to offer a way of recycling the spent pot linings.

“We are prepared to process 80,000 tonnes of linings at the pilot plant,” said Bertolli. The process is expected to recover a portion of the original lining for reuse and render the remaining byproduct inert, ready for safe (and much less costly) disposal.

The primary goal of the $180 million facility is to take care of Alcan’s own pot linings, but if the plant proves to be a success, there is the potential to offer the recycling option to other aluminium smelters as well.

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