At Alcoa's Warrick smelting operation in Indiana, a carbon-dust recycling process is eliminating 1,633 metric tons (1,800 tons) of waste that previously headed to the landfill each year. The technology also saves Alcoa $154,000 annually in landfill costs and material acquisition.
Aluminum smelting currently depends on a continuous supply of carbon anodes. Most of each anode is consumed during the smelting process, but the remnants of a spent anode are crushed and recycled. Crushing anodes generates dust that is collected by an air pollution control device called a baghouse, so named because it is equipped with bag-shaped filters. This dust, which is predominantly carbon, previously could not be recycled for use in Warrick's anode-forming process because it contained high levels of cryolite bath material carried over from the smelting operation. The result was dust that had to be landfilled.
In late 2001, Warrick began using a new spent-anode cleaning machine to remove the cryolite from the spent anode before crushing. The system uses shot-blasting, which projects small steel pellets at the anode to clean its surface of all impurities. The cleaned spent anode is then crushed, and the impurity-free baghouse dust is recycled into the smelter's anode-forming process.
Not only does this process reduce the amount of material heading to the landfill, it also reduces the amount of additional coke Warrick must purchase to make its anodes. Similar carbon dust recycling processes are used at other Alcoa facilities around the world.
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