A research group led by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has succeeded in recovering a high concentration of gold from the hydrothermal waters of the deep sea off the coast of Aogashima, Tokyo, by adsorbing it on a special sheet.
Why Aogashima? How to collect? And the possibility of commercialization?
I will explain in detail.
In the deep sea at a depth of 700 meters ...
In the deep sea off the coast of Aogashima, Tokyo, hydrothermal vents with hot water as high as 700 degrees Celsius have been found, and it is known that the surrounding rocks contain a high concentration of gold.
A research group of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and IHI, a major machinery manufacturer, has developed a sheet made from special algae that adsorbs gold in order to recover gold from this hot water.
Processed "algae" into sheets
In August 2021, the research group installed this sheet around a hydrothermal vent off the coast of Aotoshima, and after nearly two years, it was withdrawn in June.
Gold Rush Falls: Gold Veins Sleeping in the Deep Sea
The history of seat installation is in this article
The highest concentration of gold in the world! It also adsorbs silver.
The analysis showed that the sheet contains up to about 20 ppm = 1 grams of gold per ton, which is about five times the concentration of gold contained in the ores of the world's major gold mines.
Furthermore, it was revealed that not only gold but also silver could be adsorbed at a maximum concentration of about 20,5 ppm, more than 7000 times that of gold.
According to the research group, this is the first time in the world that gold contained in deep-sea hydrothermal water has been successfully recovered by adsorbing it on algae sheets.
Tatsuo Nozaki, Senior Researcher of the Japan Agency for Marine-Earth Science and Technology, says:
Tatsuo Nozaki, Senior Researcher: "While we were relieved that we succeeded in adsorbing more gold than expected,
it is surprising that silver adsorbed so much.
Why in Aogashima?
In 2015, a research team at the University of Tokyo discovered a hydrothermal vent in which high-temperature hot water spews out from the seabed at a depth of 400 meters off the coast of Aogashima, 700 kilometers south of central Tokyo.
Many other hydrothermal vents have been confirmed in the deep sea around the Izu Islands and Okinawa, but the rocks collected around the hydrothermal vents off the coast of Aogashima Island contain an average of 17 ppm = equivalent to 1 grams per ton, which is one of the highest concentrations in the world.
As for the reason for the high concentration of gold, Tatsuo Nozaki, Senior Researcher of the Japan Agency for Marine-Earth Science and Technology, speculates that "the temperature of the hydrothermal water on Aogashima Island is about 17 degrees Celsius, which is slightly lower than the hot water in other regions, and this temperature may be the role of the hot water collecting gold under the seafloor just as gold is easily dissolved. The exact reason is not yet known.
In addition to the high concentration of gold in the hydrothermal water, the research group decided to conduct a gold recovery experiment in the deep sea off the coast of Aogashima Island because it is relatively accessible at 270 kilometers from the city center.
How to recover? The key was the algae in the hot spring area
In order to recover the gold, the research group focused on a type of primitive algae called "orchid algae" that has been found only in a limited number of hot spring areas in the Tohoku region.
According to Yasuyuki Fukushima, Senior Researcher at IHI, who was involved in the development, "gold" dissolved in hot water exists mainly in the form of a compound called "gold chloride" by combining with chloride ions, but by using this "orchid algae", the bond between "gold" and "chloride ion" is first removed.
"Algae" that adsorb gold cultivated in Yokohama City
"Gold" carries positive electricity, and "algae" carry negative electricity, so they strongly attract each other.
This means that when heated at a high temperature of 1000 degrees Celsius in this state, the "algae" will burn out and only "gold" can be extracted.
Gold adsorbed by "algae" in experiments
Furthermore, it has been clarified that the adsorption efficiency of gold is improved by chemically treating algae into sheets and exposing them to light.
According to Mr. Fukushima, silver is also adsorbed at a high concentration this time, but the mechanism is basically the same as gold.
Development of a special method for extracting gold from hot springs Research Team
How to use "algae" from hot springs, details can be found in past articles
What is the potential for commercialization?
The retail price of gold in Japan has continued to soar, exceeding 8,1 yen per gram in August, reaching a new high.
According to the research group, it costs about 1 million yen per dive to recover gold from the deep sea at a depth of more than 700 meters using this method, so it is not profitable at present.
Image of the moment when algae were collected for the first time in about two years
Sheets of collected "algae"
On the other hand, the research group has already succeeded in recovering "gold" from onshore hot springs using the same method, and in the future, they plan to test whether gold can be recovered in sewage in urban areas and wastewater from abandoned mines, and in the future, the method using algae sheets may become an effective method of recovering gold.
In addition, there are areas overseas where toxic chemicals such as mercury are used for gold mining, and environmental pollution and effects on the human body in the surrounding area are serious problems, but the research group believes that the method using algae sheets may lead to a solution to these problems.