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Recycling Rice Husks

Silica in rice’s protective outer layer can be reduced to silicon for high-capacity lithium battery anodes

by Bethany Halford
July 15, 2013 | A version of this story appeared in Volume 91, Issue 28

Credit: Shutterstock
A photograph of rice husks.
Credit: Shutterstock

Delicate grains of rice grow with tough husks that keep insects and bacteria out yet still circulate air and moisture. The husks accomplish this feat thanks to nanoporous layers of silica that are strong yet breathable. Now, researchers in South Korea have come up with a way to convert this silica into silicon so that the hundreds of millions of tons of rice husks produced each year might find new life as high-value materials (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1305025110). Currently, the husks wind up in low-value applications, such as fertilizer additives. A team led by Jang Wook Choi of Korea Advanced Institute of Science & Technology treated rice husks with hydrochloric acid and heat to remove the husks’ organic and metal components from the silica while maintaining its nanoporous structure. They then reduced the silica to silicon with magnesium at 850 °C and used the resulting nanostructured silicon to make high-capacity lithium battery anodes. “Waste from one of the most popular crops, rice husks, can be a resource that helps meet the ever-increasing demand for Si in advanced batteries,” the researchers note.


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