Researchers extract precious metals from industrial wastewater using edible rice paper

Researchers have developed a technology that converts rice paper — an eco-friendly food material — into a high-performance, environmentally safe adsorbent capable of recovering gold from industrial wastewater.

The National Research Foundation of Korea announced Sunday that a research team led by Lee Jung-hyun, a professor at Korea University, developed the adsorbent by chemically modifying rice paper through a simple process, enabling the selective recovery of gold ions from wastewater.

Conventional gold adsorbents often involve complex manufacturing processes or rely on petroleum-based chemicals and organic solvents, imposing both economic and environmental burdens. Powder-form adsorbents are also difficult to retrieve after use, while biopolymer-based adsorbents require additional cross-linking processes to maintain stability in water. The findings address a longstanding need for an eco-friendly adsorbent that uses low-cost biomass materials, is simple to produce, and delivers both aquatic stability and effective gold recovery.

The research team focused on rice paper, which is already processed into film form and requires no additional shaping.

The starch-based rice paper was chemically modified under aqueous conditions — rather than with organic solvents — to give it the ability to adsorb gold ions. The resulting adsorbent maintains high mechanical stability in water and exhibits a porous structure, maximizing its applicability in real industrial processes.

In acidic electronic-waste wastewater, the developed adsorbent selectively captured gold ions while excluding other metals, operating through electrostatic attraction and chelation mechanisms.

The adsorbent also spontaneously reduced some of the captured gold ions into gold nanoparticles, boosting both recovery efficiency and selectivity. After adsorption, high-purity gold could be recovered through a simple calcination process.

The research is significant for converting a low-cost food material into a high-value resource-recycling material, contributing to a circular economy. The manufacturing process is simpler and more environmentally friendly than conventional petroleum-based adsorbents, and the technology is expected to be adopted quickly at industrial wastewater treatment and electronic-waste resource recovery sites.

"Not only rice paper, but other starch-based food materials such as glass noodles and tapioca pearls can also be converted into adsorbents," Lee said. "We are conducting research to recover metal resources that face serious supply challenges — such as lithium and rare earth elements — in addition to precious metals."

The study, supported by the Ministry of Science and ICT and the National Research Foundation of Korea through their Mid-Career Research and Engineering Research Center projects, was published in the Proceedings of the National Academy of Sciences on May 27.