Production of low magnesium twitch from zorba

Tomra Sorting Recycling has further developed its X-TRACT units to separate magnesium from aluminum in products such as Zorba and Twitch.
Photo: Tomra Sorting Recycling

The US generates an estimated 4 million tons of Zorba annually which typically contains between 2% and 4% magnesium. Historically, scrap metal processors exported the bulk of this material to China, but changes to China’s scrap import policies regarding purity and trade tariffs have created significant barriers to exporting over the past couple of years.

These limited export opportunities have resulted in a surplus of Zorba scrap in the US and a growing market need to produce recovered material in a furnace-ready form and purity that enables it to be traded and used in domestic markets. The challenge scrap metal processors face, however, is that secondary aluminum smelters in the US domestic markets require the aluminum from Zorba to contain very low magnesium, well below 0.5% by weight.

Until now the only way of treating Zorba for the removal of contaminants such as magnesium has been a two-stage sink-float operation whereby the majority of the heavy metals are separated from the shredder scrap, while the hollow aluminum scrap, magnesium and high-density plastics are floated out in an additional media stage. Sink-float processes have historically been difficult to manage, require a large footprint, can be relatively unstable and can be expensive because the operational cost per ton is relatively high.

Now, Tomra’s upgraded X-Tract for magnesium removal offers an alternative to sink-float separation. The system uses existing Tomra XRT technology but in a new configuration so that it is capable of sorting material of different density levels and separates magnesium from aluminum to create furnace ready products, including low magnesium Twitch, across the Zorba size spectrum from 5-120mm.

This degree of separation of fines simply could not be achieved using dense media plant technology/ sink-float separation process. And, until now, it wouldn’t even have been possible using Tomra’s sensor-based sorting technology because magnesium is very similar in density to aluminum so the technology couldn’t recognize the difference between the materials.


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