Japanese scientists have discovered that salmon semen from industrial fish farms could help to recycle rare earth metals.
Researchers led by Yoshio Takahashi from the University of Tokyo, found that salmon semen, known as milt, can be used in a process to extract certain rare earth elements that are used in products such as catalysts, alloys, magnets, optics, lasers and notably mobile phones.
The findings have been published in a paper in the scientific journal PLOS ONE.
Although techniques exist to recycle rare earth elements, “the solvent extraction method has some shortcomings, including the use of harmful reagents such as strong acids and organic solvents and the high cost of chemicals such as extractants”.
Once used to fertilise female salmon, the milt is discarded as a waste product.
Scientists used milt purchased from an industrial farm in Hokkaido and discovered that the milt was a widely available material.
The paper said: “More than 10,000 tonnes per year of milt from salmon, trout and others have been discarded as industrial wastes from fishery industries in Hokkaido, Japan. Thus the cost of using milt is low, which enables is to use milt as a cost-effective material for the recovery of rare earth elements or even other metal ions.
“In addition, milt is an environmentally friendly biomaterial that has no hazardous effects on the environment after use.”
The scientists suggested that the material could be used with other materials that have a positive charge including other metals, as well as in waste water treatment.
This is because the milt has the capacity to bind to positively charged ion material.