What led you into the research you are doing now?

When I was at university, I studied clay and clay minerals, which are used as raw materials for pottery. As soon as I finished university, I began work as a researcher at the Japan Atomic Energy Research Institute in Tokai Village, Ibaraki Prefecture. Can you imagine what the connection is between clay and atomic energy? The fact is that atomic power stations, hospitals, research institutions and other places that handle radioactive material all produce radioactive waste. Radioactive waste is extremely dangerous, and is scheduled for disposal, either in the ground or between geological strata.

Photo 1 The water is being held in place!?

Clay (Photo 1) is used as a barrier material to ensure that water does not pass through it, and that radioactivity does not escape from it. In my work at the Japan Atomic Energy Research Institute, in order to evaluate the barrier effectiveness of clay, I visited uranium mines and clay mines throughout the world, and investigated the barrier effectiveness of clay in an environment similar to a disposal site. This sort of research is known as natural analogue (similar phenomena in nature) research. As I built up a body of natural analogue research, I found many examples in which groundwater was naturally purified by nature, without spending any money or effort, and where hazardous substances were prevented from leaking. In order for a company that comes face-to-face with a wide range of hazardous substances every day to maintain sustainable growth, I realized there was a great need to develop an “environmental cleanup material that learns from nature”. Since then, I have visited not only areas of Japan, but also Australia, Oman, Cambodia, Bangladesh, the Philippines, etc., with my students, and learned more and more about natural analogues.

 

Please explain what research procedure is involved in the development of environmental cleanup materials.

Photo 2 We will go anywhere if an interesting field awaits


Fig 1 The purification of arsenic by Schwertmannite is a natural nanotechnology


Fig. 2 The project that saved residents’ lives in Bangladesh. Students also took part in this project.

First, you need to look at what sort of hazardous elements and chemical environments (pH, redox environment, etc.) are causing problems in terms of water/soil purification and waste disposal. Next, we look for an area in which these hazardous elements are concentrated, or a field with a similar chemical environment. With uranium, for example, you would look in the environs of a uranium mine; with arsenic, an arsenic mine, or for an acidic or alkaline hot spring, for example. Once you have selected the field, you would bring maps and equipment to survey the water and rocks, and head to it. Photo 2 shows a survey of an alkaline spring in Oman (a pH12 hot spring!) As it was in the desert, we had to use off-road vehicles. In addition to measuring the pH of the water and soil around the area, we collect samples and bring them back to the laboratory. We analyze water flowing downstream from locations where hazardous elements are present in concentration, and if we find their concentration has decreased, we determine that a “natural cleanup is being achieved”, and investigate how and where the hazardous element is being removed. Once the purification mechanism has been determined, we check to see if the same purification can be achieved in the laboratory. Figure 1 shows a mineral called Schwertmannite, which has been shown to naturally purify arsenic that has leaked from mines into river water. Our team turned Schwertmannite into a commercial product for use as an environmental cleanup material. We now know that Schwertmannite selectively adheres to arsenic in river water, and stores the arsenic in a tunnel structure (Fig. 1). Schwertmannite is a unique mineral, which is itself stabilized by this process. Since it is stabilized by the arsenic that has entered its structure, it is also possible to dispose of safely. Furthermore, it has also been established that Schwertmannite can be synthesized from wastewater. Since it functions extremely well as an arsenic adsorbent, and is extremely cheap to produce, we were able to apply its use to the purification of well water in Bangladesh, where countless people die each year from arsenic pollution of groundwater (Fig. 2), with the result that the arsenic levels in well water were successfully reduced below the WHO standard.

Radioactive waste disposal sites use large volumes of concrete, and it is therefore anticipated that the areas around these sites will be subject to significant alkalization. For this reason, it is extremely important to evaluate the behavior of hazardous elements in highly alkaline environments when assessing the safety of radioactive waste sites. Our study of the highly alkaline spring in Oman is part of a project begun in order to learn from nature about techniques to enclose hazardous elements even within a highly alkaline environment. We developed multiple commercial products for use as environmental cleanup materials as a result of this project, too. We apply for and obtain patents prior to developing these products, and the students who have been part of the surveys and research projects are listed among the inventors.

 

What would you like to do next?

It turned out that the alkaline spring in Oman was also found to be spouting hydrogen and methane gas. The rocks in Oman react with water and carbon dioxide to generate these gases. My next objective is to clarify the mineral that is responsible for this generation, and explain its function. It should be possible to achieve quite cheaply. Nature teaches us so many things like this. I look forward to talking to my students about their dreams, as we experience nature together.