Flame-retardant plastics recycling: flash heating recovers antimony from electronic waste

Flame-retardant plastics recycling is one of the most stubborn problems in e-waste management: the antimony locked inside power-supply housings, circuit boards and connectors is almost entirely lost, while the bromine-based additives form toxic compounds when heated. In a study published in Nature Chemical Engineering on 16 October 2026, a team at Rice University in Houston led by James Tour presents a flash-heating process that, within seconds, recovers around 90 percent of the antimony as metal at over 97 percent purity, while converting 83 percent of the bromine into usable hydrogen bromide.

In short: Flame-retardant plastics recycling can be carried out in a single step – without solvents, acids or catalysts and at ambient pressure – using Rice University’s new isothermal-clamped flash Joule heating (IC-FJH), so far at laboratory, gram scale. The process recovers antimony, a critical raw material, and removes bromine at the same time, while cutting toxic brominated organic by-products by 34–51 percent compared with slow heating.

Why is antimony in e-waste both valuable and a problem?

For fire safety, brominated flame retardants (BFRs) are mixed into the plastic housings and components of electronic devices, and their effect is boosted by antimony trioxide (Sb₂O₃) acting as a synergist. According to the study, roughly 39 percent of the world’s antimony ends up in such flame-retardant plastics, making this one of the metal’s main markets alongside lead-acid batteries and ammunition. Electronic waste is the fastest-growing waste stream: the authors estimate that 82 million tonnes a year could be generated worldwide by 2030.

Antimony is a critical metal. Based on US Geological Survey data, the ratio of reserves to annual production is only 23:1, leaving a very thin buffer against demand growth or supply disruption. The European Union also lists it among its critical raw materials, and China introduced export restrictions on it in 2024. Yet less than 15 percent of antimony is recovered, and almost all of that comes from lead-bearing waste – the antimony in flame-retardant plastics is effectively lost.

The problem is not only economic. Brominated flame retardants and their breakdown products build up in the environment and in the food chain, and many of them are linked to hormone disruption and impaired child development, as we explained in our analysis of chemicals in plastics and their health effects.

Where does conventional treatment fall short?

When treating plastics that contain brominated flame retardants and antimony, the bromine has to be dealt with first. In conventional thermal processes, the released bromine reacts with antimony trioxide to form volatile antimony tribromide (SbBr₃), which boils at just 288 °C. This compound leaves with the off-gas and mixes with fly ash, making it very difficult to condense and recover the antimony. Poorly controlled combustion also produces polycyclic aromatic hydrocarbons (PAHs) and brominated dioxins and furans (PBDD/PBDF).

Under the rules on waste electrical and electronic equipment and on persistent organic pollutants, plastic fractions must undergo complex testing of their bromine content and flame-retardant composition before anyone can decide whether they are recyclable. Fractions above the limits are conventionally debrominated with organic solvents and strong acids, generating hazardous wastewater and sludge, while the fractions with the highest flame-retardant content are classed as non-recyclable and sent to specialised incineration.

Newer supercritical processes – supercritical carbon dioxide at around 50 MPa, supercritical water above 22 MPa – can achieve more than 89 percent debromination, but they require high-pressure batch reactors and do not recover antimony as high-purity metal. What was missing was a single-step, ambient-pressure process delivering both pure metallic antimony and deep debromination. Additives also complicate recycling more broadly: UN experts have warned that recycled plastics used for food packaging can carry flame retardants and other contaminants.

How does isothermal-clamped flash Joule heating work?

James Tour’s laboratory has been developing flash Joule heating (FJH) since 2020: an electric current is passed through the material or an adjacent resistor, reaching temperatures above 3,000 °C within milliseconds, at heating rates of more than ten thousand degrees per second. The method has previously been used to make graphene, recover metals from e-waste and recycle batteries.

Ultrafast heating has an often-overlooked pitfall: the temperature of the carbon heater is not the same as that of the material being processed. In the new isothermal-clamped variant (IC-FJH), the ground plastic is therefore clamped between two electrically heated sheets of carbon paper, creating a uniform temperature across the whole sample.

The temperature programme has two stages:

• Pulsed stage: five consecutive capacitor discharges heat the sample to about 900 °C within 50 milliseconds. This stage controls the chemistry: debromination and the reduction of antimony trioxide to metal.
• Hold stage: a direct-current power supply then keeps the material at around 1,750 °C for 30 seconds. Since antimony boils at 1,635 °C, the metal evaporates and then condenses as a metallic deposit on the cooler wall of the quartz tube.

For the experiments, the plastic was ground in a hammer mill under liquid nitrogen cooling and melted between the electrodes, and the reactor was purged with argon. The released halogens were captured in scrubbers.

Ninety percent antimony at over 97 percent purity

The test material was the housing of a discarded uninterruptible power supply (UPS). Its acrylonitrile-butadiene-styrene (ABS) plastic contained 3.08 percent antimony and 6.04 percent bromine by weight; the antimony was present as crystalline antimony trioxide and made up 53 percent of the metal content.

Results depended on the heating rate. At 10 and 100 °C per second – comparable to conventional furnaces – 69–74 percent of the antimony was recovered; at 1,000 °C per second, 85 percent; and at 10,000 °C per second, 89 ± 2 percent. Purity stayed above 97 percent throughout. In control experiments, skipping the pulsed stage and heating directly to 1,750 °C gave only 71 percent recovery, while replacing the pulsed stage with a conventional tube furnace gave only about 50 percent.

Fast pyrolysis helps because it produces less dense char, which would otherwise physically trap the antimony. After IC-FJH, only 3.5 percent of the antimony remained in the solid residue. The other inorganic components of the plastic – compounds of magnesium, aluminium, silicon, titanium and calcium – do not react with hydrogen bromide below 1,950 °C, so they do not evaporate with the antimony, which explains the high purity.

The researchers also used machine learning to map the optimal operating window: purity above 97 percent and recovery above 89 percent can be achieved together at heating rates between 12,506 and 59,091 °C per second and temperatures between 600 and 1,206 °C. At device level, this translates into an input voltage of 184–232 volts and a pulse duration of 0.05–0.14 seconds. High-resolution electron microscopy confirmed that the recovered material is metallic antimony with a rhombohedral crystal structure.

From bromine to hydrogen bromide – with far fewer toxic by-products

More than 99.7 percent of the bromine left the solid residue regardless of heating rate. The difference lay in where the bromine went. With slow heating, 28–30 percent of the bromine stayed in the volatile condensate, typically as toxic brominated organic compounds; at heating rates above 1,000 °C per second, this fell to 4–7 percent.

In the gas phase, IC-FJH converted 83 ± 1 percent of the bromine into hydrogen bromide (HBr), compared with 62 ± 2 percent for slow heating; elemental bromine stayed below 3 percent in both cases. According to the authors, conventional furnace processes typically achieve HBr yields of only 30–69 percent. In the condensate, mono-brominated organics fell by 34 percent and multi-brominated ones by 51 percent, and no brominated organic volatiles were detected in the gas. Slow heating also produced PAHs such as phenanthrene; IC-FJH did not.

The explanation lies in a “danger window” of temperatures. Toxic brominated organics form mainly between 200 and 500 °C. In IC-FJH, the sample spent just 9.4 milliseconds in this range, compared with 386 milliseconds under slow heating. The resulting hydrogen bromide is corrosive but a valuable industrial feedstock: with sodium hydroxide it can be turned into a stable salt, sodium bromide, which the authors’ cost analysis treats as a sellable co-product.

What happens inside the reactor? The key role of hydrogen

The researchers broke the process down into three interacting parts: pyrolysis of the ABS plastic, partitioning of bromine and transformation of antimony. Under fast heating, the ABS released 1.42 millimoles of hydrogen per gram, versus only 0.96 millimoles under slow heating, while the share of solid carbon residue was 8.1 percent compared with 20.6 percent.

This hydrogen does two jobs. First, it strips bromine from brominated aromatic intermediates as hydrogen bromide. Density functional theory calculations show that this reaction is thermodynamically favourable but, with an activation barrier of 3.70 electronvolts, proceeds efficiently only at high temperatures reached quickly. Under slow heating, the brominated intermediates evaporate before they can react with hydrogen. With tetrabromobisphenol A (TBBPA) as a model compound in argon, IC-FJH gave an HBr yield of 59 percent versus 39 percent for slow heating; adding 2 percent hydrogen to the gas raised these to 85 and 71 percent.

Second, hydrogen reduces antimony trioxide and any antimony tribromide already formed to metallic antimony before they can escape. In model experiments, 83 percent of pure antimony trioxide stayed in the solid residue, but with TBBPA added only 58 percent did – the HBr carried the metal away as volatile antimony bromide. Adding carbon improved this only to 63 percent, whereas 2 percent hydrogen raised it to 77 percent. No carbon monoxide appeared in the gas phase either, further indicating that carbon plays only a minor role in the reduction and hydrogen is the decisive factor.

Does it work on other plastics and at larger scale?

To test generality, the team examined two more flame-retardant plastics: the polyamide 66 (PA66) plastic of a printed circuit board (3.79 percent antimony, 8.64 percent bromine) and the polycarbonate (PC) housing of an electrical connector (4.05 percent antimony, 9.70 percent bromine). Antimony recovery reached 89.3 and 87.2 percent, at purities of 98.6 and 96.3 percent. In both cases more than 92 percent of the bromine was removed from the condensate, with recovery above 82 percent.

For scale-up, the entire sealed reactor, the carbon heater and the scrubber train were enlarged, with the hold stage powered by an arc welder. Treating 2 grams of ABS gave 83.6 percent antimony recovery at 97.1 percent purity, with similar results over three consecutive runs. Using a carbon felt heater, a 5-gram sample was also processed, with 80.2 percent recovery.

The authors also sketch a concept for continuous operation: ground e-waste is carried on a conveyor between two carbon heaters, antimony vapour condenses on a cold grid, hydrogen bromide is captured in a separate unit, and the entire line runs under inert gas. As a reality check, they note that flash Joule heating is already used in a 1-tonne-per-day pilot facility for graphene production at Universal Matter, and for reclaiming metals from printed circuit boards at 1 tonne per day in a 10-kilogram pilot reactor at Flash Metals USA. At industrial scale, dedicated emission-control and bromine-destruction units would also be needed after recovery to deal with the residual brominated condensate.

Environmental footprint and costs

The authors also carried out a preliminary screening life-cycle assessment (LCA) and techno-economic analysis. The functional unit was 1 kilogram of antimony recovered as antimony trioxide; the comparison was against a solvent-based route and a conventional pyrolysis route, with impacts calculated using the European Commission’s Environmental Footprint 3.1 method.

Compared with the solvent route, IC-FJH would cut energy resource use by 72 percent, water use by 80 percent and land use by 90 percent, since it uses no organic solvents. Compared with pyrolysis, it would reduce climate impact by 65 percent and ecotoxicity by 90 percent. Greenhouse gas emissions were estimated at 164.8 kilograms of CO₂ equivalent, around 92 percent of which comes from electricity use – meaning low-carbon power and heat recovery could push this down further. Conventional pyrolysis produces roughly 28,000 ppm of PAHs, whereas none were detected with IC-FJH.

According to the cost estimate, recovering one kilogram of antimony would cost US$397 via the solvent route, US$60 via pyrolysis and US$22 via IC-FJH; crediting the sodium bromide co-product brings the latter down to US$18. The authors stress that these are scenario-based estimates, not design data for a final industrial plant.

What does flame-retardant plastics recycling mean for Europe’s waste industry?

The brominated plastic fraction generated during e-waste processing is one of the waste industry’s dead ends today: it cannot be recycled, incinerating it is expensive, and its antimony is lost with the fly ash. If IC-FJH confirms its results at industrial scale, this fraction could turn from a cost item into a source of antimony, with the bromine returning to the chemical industry as sodium bromide.

The timing is no coincidence. In October, the European Parliament adopted its position on the Critical Raw Materials Act amendments, which treat recycling as a pillar of supply security; the regulation expects 25 percent of EU consumption to come from recycling by 2030. In its latest selection round, the Commission named 46 new EU Strategic Projects, more than half of them recovering raw materials from waste. And according to the FutuRaM project’s assessment, European waste could cover more than half of critical raw material demand by 2050, yet today only a fraction of the material reaching waste streams is actually recovered.

Technology alone is not enough, however. Flame-retardant plastics recycling can only work if e-waste actually reaches processors and the brominated plastic fraction is cleanly separated there. That cannot be taken for granted: a University of Surrey study showed how much repairable and recoverable electronics still end up in the bin, and flame-retardant plastics that leave the formal system often end up where metals are extracted by open burning.

Limitations and open questions

The results are promising, but they should be viewed realistically:

• Scale: the experiments used gram quantities, and the continuous system is still only a concept. During scale-up, antimony recovery dropped from 89 to 80–84 percent.
• Samples: the e-waste tested came from the researchers’ own laboratory and covered three well-defined plastic types. The process has not yet been tested on real-world mixed fractions containing several flame retardants and contaminants.
• Environmental analysis: the LCA and cost estimates are screening-level and scenario-based, not built on plant operating data.
• Safety: hydrogen bromide is a corrosive gas; at industrial scale the fully sealed system, gas handling and disposal of the residual condensate could add significant costs.
• Interests: Rice University has filed a patent application on the antimony and bromine recovery process; an earlier patent on selective metal recovery from e-waste has been licensed to Flash Metals USA/Metallium Ltd, in which James Tour is a shareholder. The research was funded by the US Air Force Office of Scientific Research, the US Army Corps of Engineers and the US Department of Energy.

Even so, the study delivers an important insight: when treating flame-retardant plastics, what matters most is not how hot the process gets but how the temperature changes over time. If processing crosses the window in which toxic compounds form within milliseconds, both bromine and antimony can be steered – and today’s “problem fraction” could become a valuable secondary raw material.

FAQ – flame-retardant plastics recycling

Why is flame-retardant plastics recycling so difficult?

Because brominated flame retardants and antimony trioxide react with each other when heated. The resulting antimony tribromide boils at just 288 °C and leaves with the off-gas, so the antimony is lost, while poor combustion produces PAHs and brominated dioxins. Debromination conventionally needs solvents and strong acids, and fractions with the highest flame-retardant content are sent to incineration.

How does isothermal-clamped flash Joule heating work?

Ground plastic is clamped between two electrically heated sheets of carbon paper. Five capacitor discharges heat it to about 900 °C within 50 milliseconds, driving debromination and antimony reduction. The material is then held at about 1,750 °C for 30 seconds, so the antimony evaporates and condenses as metal on the wall of a quartz tube.

How much antimony does the new process recover?

Under laboratory conditions, around 89 percent of the antimony at over 97 percent purity. With plastics from a printed circuit board and an electrical connector, recovery reached 89.3 and 87.2 percent. A scaled-up 2-gram trial achieved 83.6 percent at 97.1 percent purity, and a 5-gram sample reached 80.2 percent.

What happens to the bromine during flash heating?

Some 83 percent of the bromine is converted into hydrogen bromide, versus 62 percent with slow heating. Hydrogen bromide can be captured with sodium hydroxide as stable sodium bromide, a sellable co-product. Toxic brominated organics fell by 34–51 percent because the sample spent only 9.4 milliseconds in the critical 200–500 °C range.

How much could antimony recovery cost with this method?

According to the preliminary cost estimate, US$22 per kilogram, or US$18 when the sodium bromide co-product is sold. The same would cost US$397 via a solvent-based route and US$60 via conventional pyrolysis. The authors stress that these are scenario-based estimates, not design data for a final industrial plant.

When could the process reach industrial use?

There is no date yet: the experiments were carried out at gram scale, and the continuous system is still a concept. The process has not been tested on real-world mixed e-waste fractions. However, flash Joule heating is already used in 1-tonne-per-day pilot plants for graphene production and for recovering metals from printed circuit boards.

🔗 Official sources and references: 👉

• Original study (Nature Chemical Engineering, 16 October 2026): Ye, L. H. et al.: Simultaneous antimony recovery from and debromination of flame-retardant electronic-waste plastics – DOI: 10.1038/s44286-026-00455-3
• Free-to-read version of the study (sharing link): Nature Chemical Engineering – full text
• Rice University news release (16 October 2026): Rice researchers develop new way to quickly recycle electronic waste
• Source code for the simulations, machine learning analysis and cost model (GitHub): ABS-supporting-code

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