How microrecycling is growing a green aluminium revolution

Research by the UNSW Sustainable Materials Research and Technology (SMaRT) Centre has found a way that could start a new ‘green aluminium’ manufacturing revolution.

The new technique to recover aluminium from complex, multilayered packaging is based on the microrecycling science pioneered by the SMaRT Centre under the leadership of its director, Professor Veena Sahajwalla, and builds on their waste materials innovations including Green Steel and Microfactorie® technologies.

 Green aluminium

The research, published across two international scientific journals, demonstrates there is now a way to sustainably recycle polymer-laminated aluminium packaging (PLAP) materials, such as post-consumer food and coffee packaging, into high-quality aluminium and be a potential source of high-energy hydrocarbon products.’

“We developed Green Steel technology where we extract hydrogen and carbon from old rubber tyres and plastic as an innovative and green pathway in steel making , and we now can develop new ‘Green Aluminium’ with our novel technique called Thermal Disengagement Technology (TDT),”  Sahajwalla said whose SMaRT Centre is part of the UNSW Science Faculty.

“Recycling using new technologies can be a foundation for the manufacturing of high-quality materials from our waste resources, as we seek to develop greater sovereign capability along with economic prosperity.”

Thermal Disengagement Technology

The new Thermal Disengagement Technology, described in scientific publications Springer Nature and the Journal of Cleaner Production, offers an innovative, efficient, and sustainable microrecycling technique to separate the materials in complex polymer-laminated metal packaging waste. TDT can transform the aluminium into a clean and green metal, allowing it to be extracted in a way that means it can be used as a high-quality material for manufacturing, while minimising residual waste.

According to Sahajwalla, “Green Steel and green manufacturing are capabilities we have been pioneering for over a decade. The jobs and sustainability revolution our government wants to create as announced in its 2020 Budget can get a boost from some of these sort of existing innovations where industry and researchers are already successfully partnering.

“Using waste-reforming technology can create new supply chains and jobs, especially in regional locations, because it doesn’t have to be large scale nor expensive. That is why I see a future where recycling and manufacturing are aligned, where waste and recycling become part of the manufacturing supply chain, and that is important in this new COVID era where we now highly value ‘sovereign capability’.

In one demonstration of how SMaRT is helping to create these new supply chains and aligning these sectors, it has connected an e-waste recycler directly with a steel maker enabling undervalued metals and plastics destined for overseas, landfill or incineration, can be used as feedstock.

Key research findings

Waste polymer laminated aluminium packaging (PLAP) material were analysed by Thermal Disengagement Technology (TDT) to explore the prospect of recycling the metal-polymer multilayer materials with minimum contamination and zero waste of metal (aluminium). Laminated polymers on the metallic surface essentially demand some extra effort and energy to recycle the metal in its original form. In these studies, the effect of the laminated polymers of the aluminium surface to protect the surface contamination by means of oxidation was explored. The rate of the transformation of the polymers in the air atmosphere is higher than the rate can be achieved in an inert atmosphere.

TDT to recycle the polymer laminated Aluminium packaging with and without an inert gas supply has been developed to produce specifically high-quality aluminium. The oxidation of the aluminium surface in air media was higher and non-uniform compared to the inert media. At 550 degrees centigrade, the complete degradation of the polymers was observed within 20 min and the recovery of the aluminium was achieved without any metal loss with a very high purity. The surface analysis of the laminated and non-laminated TD aluminium confirms that the rate of oxidation in oxygen-rich atmosphere for disengaged aluminium from PLAP is 80-90% lower and the polymers can act as the protection against the oxidation of the aluminium surfaces even after the complete degradation of the polymers by leaving the carbonaceous residues behind onto the surfaces.

The level of purity of recovered Aluminium is achieved ~96-99% with minor impurity/alloying elements of C, Si, Fe, etc. Oxidation of the recovered aluminium was controlled and detected less than 1% by our new and innovative TDT. The cleaner aluminium produced by this process has the desired scalability which is required for taking laboratory batch reactions towards industrial production.

The recycling of PLAP materials demands a process where whole materials can be processed and recycled with a minimum waste of energy and materials. TDT overcomes these constraints. Several recycling techniques including traditional smelting have been practiced by the researchers and professionals. But the major problems associated with the traditional smelting of PLAP materials are excessive material loss and lack of controlling aids during the smelting.

In many countries, waste polymer laminated metal packaging materials along with other municipal solid waste going to landfills or incineration and some of the materials are recycled in metallic forms from the bottom ash components by industrial separation. The low value packaging materials containing polymers and aluminium found in the MSW draw no interest from recyclers.

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