When the lining of an electrolysis furnace has reached the end of its life, the furnace is taken out of operation and the contents are removed. The furnace is ready for use again after the lining has been replaced. This process is called relining the electrolysis furnace.

The resulting waste is the so-called furnace outbreak (SPL), which is also classified as dangerous due to its fluoride content. Hydro's aluminum smelters in Norway have been supplying this waste to the NOAH hazardous waste landfill on Langøya, an island in the southern Oslofjord near the town of Holmestrand for years.

Use in the manufacture of insulation materials

With a contract recently signed between Hydro and Rockwool, however, the recovery of the furnace breakout could now be regulated: Carbon-rich material is recovered from the furnace breakout and transported to Rockwool's processing plant in Germany. The carbon is crushed there and then used in the production of rock wool, an important component of refractory insulation materials.

“In the Rockwool production plant, the process temperatures are so high that all pollutants from the cathode linings are destroyed. This contract is therefore a very positive alternative in terms of environmental protection, "says Kristin Mørkved, head of the so-called SPL project at Hydro.

Less landfill waste

Hydro's management decided some time ago that the amount of waste to be landfilled should be reduced by 60 percent by 2020 compared to 2010. In addition, the Primary Metal business unit has set itself the goal of increasing the recycling rate for the annual waste to 70 percent by 2020.

"This contract is an important contribution to achieving these goals, because it ensures that around 45 percent of our used cathode linings are recycled," explains Kristin Mørkved.

Last summer, the SPL project also entered into an agreement with the Norcems cement factory in Brevik in Telemark, Norway, for the disposal of anode waste.

savings in the millions

In addition to the positive environmental impact, Hydro expects the Rockwool contract to save approximately five million Norwegian kroner annually.

"The contract initially only runs until the end of 2013, but includes an option for both partners to extend and renew contract negotiations," explains Ms. Mørkved. She adds that a formal export permit from the Norwegian Agency for Climate Protection and Pollution (Klif) is required before the contract can enter into force.

"We have already applied for the export permit and are in good dialogue with Klif," says Kristin Mørkved.

OVEN REPLAY: The cathode bottom must be provided with new lining at regular intervals. According to a new agreement with Rockwool, 45 percent of the used cathode linings from Hydro's electrolysis furnaces will be recycled.