As part of the Research Spotlight series, SIM² highlights the people behind the research and the ideas that drive them. This time, we talked with Christian Steuwe, Lukas Brijs and Zhou Fang about their project Recyclear that tackles a step in recycling that is often overlooked but absolutely crucial: sorting.
Who are you and what is Recyclear?
We are part of the research group of Rob Ameloot at KU Leuven. Recyclear started as a separate R&D effort to address sorting challenges. We began with plastics and are now expanding to critical raw materials, metals, scrap, and minerals. The long-term goal is to develop this into a spin-off.
Why was Recylear started?
Most research in recycling focuses on processing technologies, such as how to depolymerize polymers or how to extract, purify and smelt metals. Much less attention is given to what happens before that step. For recycling to be economically viable, the input stream should be as pure and clean as possible. Sorting is therefore essential. Without proper sorting, even the best processing technologies cannot perform well.
What is your research about?
In simple terms, we make specific polymers, ores or additives within plastics visible so waste, scrap or minerals of interest can be separated from other materials under UV light on the blink of an eye. For example, plastics that contain antimony will light up brightly yellow under UV light after our treatment. This in return allows sorting machines to detect and separate them efficiently.
Why is this important?
Antimony for example is often used as a synergist for flame retardant in electronic waste. You find it in cables, power supply housings, screens, keyboards, and car components – in general, everything that can heat up during operation. In shredded electronic waste streams, antimony concentrations inside the polymer matrix can reach up to 5%, which can be significantly higher than in naturally occurring ore. However, right now antimony is not recovered from waste electronics because antimony-containing pieces are mixed with other plastic pieces and without sorting, the recovery is not profitable. Hence, most of this waste is incinerated or landfilled without recovering the metals. Yet antimony has a high value, up to around 50 euro per kilogram. To make recycling viable, you need to concentrate the material first! This is where our sorting technology becomes critical.
We developed a spray containing chemicals that bind selectively to antimony available in plastic. Once the complex is formed material becomes fluorescent under UV light. It effectively works like a biomarker by It creating a clear on-off signal, making it easy to distinguish between materials that contain antimony and those that do not. Only a very small amount of spray is needed to achieve a strong contrast.
Why is the spray necessary, why not use an online detection method such as XRF?
In industrial sorting, materials move very quickly, often several tons per hour. Techniques such as XRF require more time per measurement than is available in such fast-moving systems.
Our approach allows for rapid detection at high throughput, which is essential for industrial applications.
Can Recyclear spray-tagging technology be applied beyond sorting antimony containing plastics?
Absolutely! While our current focus is on antimony-containing plastics, the concept can be widely extended. We can apply similar strategies to distinguish between metal-containing and gangue mineral in ore pieces: in the meanwhile, we developed a solution to distinguish copper containing ores from gangue (see photo). Obviously polymer sorting is one of our areas closest to industrialization: our most advanced application is separating PVC that contains lead from PVC that does not. Lead was widely used as a stabilizer until 2015, especially in construction materials such as pipes and window frames. Since these materials have long lifetimes, we will continue to face this sorting challenge for decades when the market wants to offer lead-free, recycled PVC.
So, you are working on sorting minerals and scrap as well?
Yes, we made a first step with the copper ores and we have a bunch of ideas on how to expand this to other ores or scrap metals. In general, we developed know-how on how to make metals detectable through fluorescence, and this can be extended further. So if you are interested in detecting a specific metal, come to us! 😊
What was an unexpected moment in your research?
We initially worked with a tagging bath approach. In theory it worked fine, but in practice it quickly became complicated. The bath was not stable, it needed heating and generated wastewater. Obviously, all materials came out wet and had to be dried. Not exactly ideal if you think about industrial scale material processing.
Switching to a spray system was a turning point. Suddenly everything became simpler. You use a tiny amount of material, there is no need for drying, and it fits much better with how real sorting lines operate.
What keeps you motivated when things do not work as planned?
We have developed a certain level of frustration tolerance. Research rarely works on the first attempt, so you keep trying, adjusting, and learning. Working in a strong interdisciplinary team helps a lot, as different perspectives often lead to better solutions. Another thing that helps is a beer with your colleagues!
More info on Recyclear activities with antimony and chalcopyrite is in this presentation: click here
To learn more about Recyclear, visit the website
