It’s time to scrape that salmon semen off your plate, because it’s got a much better use than tickling your taste buds (yes, fish sperm is actually a delicacy in Japan). This unusual magical ingredient could help us extract and recycle rare earth elements from ore and a variety of other materials, such as magnets or old electronics. Not only would this process be significantly cheaper than traditional chemical extraction methods, but it’s also much better for the environment.
Rare earth elements (REEs) are a group of chemically similar elements that have been used in the manufacture of various advanced materials and hi-tech products for more than a decade, including catalysts, magnets and lasers. Neodymium, for example, is used in a variety of green technologies, such as wind turbines and hybrid cars, as well as high-performance permanent magnetic materials.
Although REEs have become essential for many innovative products and applications, extracting them is a dirty process. Vast amounts of environmentally damaging chemicals are used in the refining process, such as hydrofluoric acid and mercury, which can change water and soil chemistry. It’s estimated that in refining one ton of REEs, 75 cubic meters of acidic waste water and around one ton of radioactive waste are produced. This, combined with the fact that the supply of REEs from the Earth’s crust is often limited due to geopolitical reasons, is why it is important to recover REEs from their wastes so that they can be reused.
Unfortunately, the traditional chemical extraction process used in REE recycling also uses expensive, harmful reagents, which is why there has been a growing interest in developing greener, inexpensive alternatives. University of Tokyo researchers, for example, have been investigating the possibility of using bacteria to recover REEs. They found that the phosphate site on bacterial cell surfaces served as a crucial binding site of REEs, which is why they began to wonder whether DNA could be used to extract REEs in solution, since DNA has phosphate as part of its backbone.
As pointed out by Chemistry World, the problem they faced was that DNA is soluble in water, so they needed to find a source where it is attached to something solid to prevent it from breaking down. This is where milt, or salmon sperm, came in. Milt is insoluble, cheap, and thousands of tonnes of the stuff is discarded each year by the Japanese fishing industry, making it an ideal candidate.
As described in PLOS ONE, scientists tested it out by adding powdered milt to a solution containing the main REEs using in neodymium magnets, and found that the metals bound strongly to the phosphate. The REEs were then subsequently extracted using an acid bath and centrifugation (spinning). Although the process still requires the use of strong acids, some experts think the technique is promising. It might be difficult to scale up, but it could at least be useful in extracting REEs from waste electronics, such as mobile phones and computers, saving them from landfill.