A specialised sponge could harvest uranium from seawater for use as fuel in nuclear power plants, and could also be used to help clean waste from those plants.
The easiest way to get uranium is to mine it from ores in Earth鈥檚 crust. There are about 7.6 million tonnes of uranium that should be relatively simple to mine, which is projected to be enough to cover global needs for about a century. Seawater holds more than 4.5 billion tonnes of uranium, making it potentially an excellent backup source.
Natural sponges are often used to monitor heavy metals in the ocean because they accumulate the substances as huge amounts of water flow through them. Dong Wang at Hainan University in China and his colleagues have created a special sponge that sucks up uranium through the same process.
Advertisement
The sponge is made of melamine foam, which is also used in certain household cleaning sponges. The foam is dipped in a solution of chemicals that easily bond to uranium and then dried, leaving a chemical film over the sponge鈥檚 internal structure.
After eight weeks submerged in a five-tonne tank of seawater, the sponge had absorbed about 1.9 milligrams of uranium per gram of sponge. This is a similar yield to other methods of harvesting uranium from the ocean, says Sheng Dai at Oak Ridge National Laboratory in Tennessee. But the melamine sponge is more biodegradable than the plastics used in many of those other methods, making it more environmentally friendly, he says.
When the sponge has absorbed uranium, it takes on the element鈥檚 yellowish hue. It can then be rinsed out, the uranium extracted for use in a nuclear power plant, and the sponge placed back in the ocean. It loses some efficacy with every recycling because it also picks up other elements that can be harder to rinse off.
This method is more expensive than mining uranium from the ground for now, but when ores eventually run low, relatively little sponge material could be used to harvest lots of nuclear fuel from the seas. 鈥淵ou don鈥檛 need to put acres of sponges in the ocean,鈥� says Dai. 鈥淭hat鈥檚 the beauty of the nuclear industry 鈥� you don鈥檛 need much.鈥�
Advanced Functional Materials
