U.S. Researchers Develop Rapid Heating Technology to Recover 90% of Tin from Plastic Waste in Old Electronics

Researchers from Rice University have developed a novel rapid heating method capable of recovering approximately 90% of antimony from plastic electronic waste. Antimony is a key element in the flame-retardant properties of plastic casings used in electronic devices to mitigate the risk of electrical fires. In this new approach, the team briefly subjected laboratory-generated plastic waste to electronic heating at high temperatures, allowing the antimony to evaporate and condense in a collection area. Additionally, the plastic was exposed to temperatures between 392 and 932 degrees Fahrenheit for only 9.4 milliseconds, leaving minimal time for organic bromides to form toxic compounds.

Globally, nearly 39% of antimony supply is used in the production of flame-retardant plastics, most of which ultimately end up in landfills. By 2030, global production of flame retardants is expected to reach 82 million tons, accompanied by tens of millions of tons of electronic waste each year. This rising demand poses a serious threat to future mineral resources.

Problems with Traditional Recycling Methods

U.S. researchers have explored how to recapture this important raw material, which accumulates in electronic waste after the lifespan of electronic devices ends. Traditional recycling methods use slow heating to release metals, which presents significant environmental and health risks, as this processing releases toxic organic bromides, another key component of flame-retardant plastics that exist in forms that are difficult to capture. Hao-Hsin Yeh, a graduate student at Rice University and the first author of the paper, stated, "Traditionally, heating plastics releases antimony in a volatile and hard-to-collect form while generating and releasing hazardous organic bromides."

He also pointed out that other options, such as using strong acids, organic solvents, or multi-step processing, carry risks or are impractical.

Advantages of the New Technology

According to the team, slow heating of materials can alter the form of elements and create new compounds, which may be harmful. Realizing that slow heating was the culprit, the team turned to Tour's flash heating method. This method rapidly heats materials to hundreds of degrees Celsius in just a few milliseconds. The improved method is called isothermal holding flash Joule heating, which has been adjusted for efficient antimony recovery while capturing hazardous organic bromides. "We found that the flame-retardant plastic waste generated in the lab, after being ground, was placed between two pieces of electrically heated carbon paper. We used ultra-fast heating to pulse heat it multiple times," Yeh said.

Yeh stated.

This method exposes the plastic to high temperatures for only 9.4 milliseconds, preventing the formation of toxic organic bromides. The researchers converted 83% of the bromides into hydrogen bromide, a valuable industrial chemical. Treating the resulting inorganic byproducts with sodium hydroxide can capture and convert it into stable salts. "Isothermal holding flash Joule heating can enhance the speed, safety, and practicality of recovering antimony from discarded flame-retardant plastics," Tour said. After testing on power supply casings, printed circuit boards, and electrical connectors, the method proved successful across various flame-retardant plastics.

This process not only protects important antimony resources but also regenerates reusable bromide salts. The related research findings have been published in the journal Nature Chemical Engineering.