A spectacular transformation of Vietnamese spring roll: The birth of alchemy that catches ‘gold’ from waste water > News

Conventional precious metal recovery processes are very harsh from an environmental perspective. Existing adsorbents used to filter gold from waste at industrial sites contain large amounts of chemicals or organic solvents mainly extracted from petroleum, and it has been pointed out that the process itself creates another source of environmental pollution. In addition, powder-type adsorbents are very cumbersome to separate from liquid after use, and even biopolymer-based natural adsorbents had to go through a complex cross-linking process to maintain their shape in water, making them extremely economically unfeasible. In this situation, the research team focused on the structural advantages of rice paper, which already had a certain shape. By using a film-type material that does not require a separate molding process, a breakthrough has been made that simultaneously solves economic efficiency and manufacturing simplicity, which were the biggest challenges of the existing process.

The key strategy adopted by the research team was to chemically modify rice paper in an environmentally friendly aquatic environment. In this process, rice paper is transformed from a simple starch lump into a high-performance adsorbent with a porous structure with numerous micropores. In particular, this adsorbent boasts excellent mechanical stability, preventing tearing or loosening even in e-waste wastewater in an acidic environment. The secret to selectively capturing only gold ions lies in electrostatic attraction and chelation mechanisms. By allowing metal ions to combine with atoms in rice paper to form a stable ring structure, excellent selectivity is achieved to precisely select only gold ions even among numerous impurities. This resulted in maximizing gold recovery efficiency while suppressing the adsorption rate of other metals such as copper to less than 0.5%.

Another reason why this study is highly regarded in academia is because of the ‘self-reduction’ characteristic that occurs during the adsorption process. Rice paper adsorbents not only absorb gold ions, but also exhibit a unique chemical reaction that reduces some of them into gold nanoparticles. These characteristics dramatically increase the gold recovery efficiency, while at the same time making it possible to separate high-purity gold with a simple calcination process (heat treatment) after adsorption is completed. In fact, the researchers suggested that not only rice paper, but also all starch-based food materials such as glass noodles and tapioca pearls can be used in this adsorbent conversion process. This supports the strong possibility that a high-value resource circulation model using discarded food materials can be expanded throughout the industry as long as the stability of supply and demand of raw materials is secured.

Although some practical challenges remain to commercialize this technology, its potential is great. Researchers, including Dr. Seung-su Shin, emphasize that in order to commercialize the technology, standardization of the quality of adsorbent raw materials as well as process optimization and scale-up research for application to actual large-scale industrial sites are essential. Nevertheless, it is significant that the existing complex and expensive chemical process was replaced by a simple and environmentally friendly biomass process. This technology has the versatility to expand the scope of research in the future to the field of recovering not only electronic waste but also various rare resources such as rare earths. The process of transforming low-cost food ingredients into ‘guardians’ that protect key resources of high-tech industries can be said to be an excellent example of how science and technology can contribute to a sustainable future.