Suizenji nori is a well-known ingredient in Japanese cuisine, a blue-green algae peculiar to Japan. Recently the Kaneko Laboratory, School of Materials Science, Japan Advanced Institute of Science & Technology (JAIST) developed a way to use an extract from nori to recover rare metals. The group hopes to commercialize the technology to recover indium (In) from the liquid crystal display (LCD) panels used in flat-panel televisions, mobile phones, etc.
Assuring a stable supply of rare metals such as indium is an urgent need for industry, faced with problems such as surging costs and import restrictions from producing nations. One possible solution attracting increasing interest is the lode of rare metal accumulated in electronic equipment: so-called "urban mines".
It has been
estimated (see Fig) that the tonnage of indium used in LCD panel
transparent electrodes and other applications is very large in
comparison to natural global reserves. No technology has existed to
recover indium from used LCD panels or other sources, though, and
recycling has been at a standstill. The new technology is one possible
solution to the problem. According to one engineer involved in
recycling at a domestic television manufacturer, "Recovering indium
from LCD panels is something that will be absolutely necessary in the
future.
Any technologies that might make it possible are going to be watched very closely."
The key to the technology is a polysaccharide named Sakuran, extracted from Suizenji nori. The Kaneko Laboratory discovered in 2006 that the substance has a molecular weight of 1.6 million, the heaviest naturally-derived material known, and a molecular chain length of over 10um, and a host of intriguing characteristics. Of these, researchers were especially interested in its adsorption of trivalent metal ions, such as In3+. The phenomenon is said to be due to the fact that Sakuran itself is negatively charged.
According to Kaneko Laboratory researcher Maiko Okajima, who developed the technology, "Algin acid is well-known as a substance with high metal adsorption, but Sakuran is significantly more effective in adsorbing trivalent metals. Rare metal recovery is infeasible with algin acid and there have been very few reports of research into such applications, but I believe Sakuran offers commercial-level performance."
The probable flow for indium recovery from an LCD panel would begin with breaking the glass substrates coated with indium, and melting them in sulfuric acid. This would ionize the indium and dissolve it out. Sakuran is then added to adsorb the indium, which gels the Sakuran by acting as a cross-linking agent. The gel is then removed, and Sakuran and indium separated out for recovery using electrolytic refining. Okajima has already demonstrated that indium recovery is possible with this process flow, at the demonstration level.
There are a number of problems to be resolved before the technology can enter practical use. The principle of operation has only been demonstrated, and researchers still have to determine a number of quantitative details, such as how much sacrum is needed to recover a given amount of indium. Investigation is also needed to improve recovery efficiency in the electrolytic refining process.
In addition to these technical issues, the biggest problem is assuring the needed supply of nori. JAIST has already established a tech start-up named Green Science Material Inc of Japan to handle nori procurement, Sakuran production (extraction) and sale, and plans to begin sample-shipping Sakuran in fall 2008. At present, though, it is said to be difficult to secure the quantities needed for industrial use. "Sacrum can only be extracted from Suizenji nori, but that type of nori has always been used only as a food, and the supply is limited. We have explained to the producing regions - Kumamoto Prefecture, Fukuoka Prefecture and elsewhere - that it is extremely effective in recovering indium, and we are trying to convince them to expand cultivation," explained Okajima.
It is also possible that other polysaccharides extracted from similar blue-green algae would have the same characteristics as Sakuran, and Okajima is investigating those possibilities in parallel.
by Takuya Otani
Nikkei Electronics |
Nikkei Monozukuri |
Nikkei Automotive Technology |
|---|---|---|
 |
 |
 |
| The magazine for electronics designers and managers. | Design You Won't Regret - How to Reduce the Risk of Accidents | The comprehensive automotive technology magazine. |
Copyright © 1995-2010 Nikkei Business Publications, Inc. All rights reserved.
All editorial content and graphics on this Web site may not be reproduced in whole or in part without the express permission of the copyright owner.
