An initiative to feed waste tyres into One Steel’s electric arc furnaces is a good example of circular economy in action, so far diverting more than two million tyres from landfill.

Article from resourceful: Issue 8, November 2015

Professor Veema Sahajwalla and the high temperature furnance

Leading the charge on the innovative re-use of tyres as a carbon source for electric arc furnaces (EAF) is Laureate Professor Veena Sahajwalla and her team at the Centre for Sustainable Material Research and Technology (SMaRT) at the University of New South Wales.

The contents of an EAF resemble a cappuccino—with a molten iron bath at the bottom and a foam of iron oxides and contaminants, the slag, on top.

Carbon, usually in the form of coke, is fed in to react with those oxides, producing gas and more molten iron.

The electrodes which feed in the electricity to heat the system extend down from the lid.

What Professor Sahajwalla found in her research was that at the furnace temperature of about 1550°C, the addition of plastics and rubber led to a couple of useful things happening:

  • it increased and stabilised the foam, which led to a more efficient transfer of energy into the system.
  • depending on the type of plastic or rubber, different solid and gaseous forms of carbon were generated.
  • importantly it was the blending of materials that produced the benefits.

"The blends were transformed. We are not recycling the materials, but re-forming them," says Professor Sahajwalla.

That philosophy has now been applied to other waste problems. For instance, laboratory work at the SMaRT Centre utilising cars (which include ferrous materials, plastics, rubber, and laminated glass) is generating useful silicon carbide and ferrosilicon alloys.

Mixtures of building materials and furniture from demolition and refurbishment (including metals, plastics, timber and glass often bonded together and hard to separate) are showing promise for re-forming into new products.

Professor Sahajwalla is confident that the same approach may be the answer to the difficult problem of e-waste.

"Lets see the mixture as a positive—that the interaction between the materials at micro-levels can underpin positive transformations."

Professor Sahajwalla says that many of these ideas have been stimulated by collaboration with industry. Even as a PhD student she spent time on the production floor of an automobile factory in Michigan, and she has taken sabbaticals in industry since.

"You get a sense of the buzz and excitement from the people you get to talk to—the challenges and constraints and reactions taking place. To ensure such research is useful, you've got to put yourself in industry's shoes."

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