A Japanese research team developed a technology to selectively separate and collect rare earth materials such as neodymium (Nd) and dysprosium (Dy) from used neodymium-iron-boron (NdFeB) magnets.
The research team is led by Toru Okabe, professor at the Institute of Industrial Science, the University of Tokyo. Because the technology uses a dry process that uses halide salts such as chlorides and iodides, it does not generate a harmful waste liquid.
This time, the research team conducted experiments by using magnesium chloride (MgCl2) and zinc iodide (ZnI2). The processes of separation and collection are as follows.
First, magnet alloy bars and a chloride are put in a crucible and heated so that the magnet alloy soaks into the molten salt. Then, rare earth materials contained in the magnet alloy such as Nd and Dy are salified or iodized and seep out in the molten salt while Fe and B stay solid.
Second, the mixed salt including Nd and Dy is distilled in vacuum. The mixed salt is placed at the end of a long and thin quartz tube. After the tube is sealed up, the air pressure is reduced to 2 x 10-4. Then, it is placed in a heating device that can generate a temperature gradient in the length direction and heated so that the temperature at the end opposite to the end having the mixed salt becomes lower.
The vaporized mixed salt clumps together on the inner surface of the quartz tube. And MgCl2and ZnI2 gather near the end whose temperature is low while NdCl3 becomes massed together near the center, where the temperature is higher, making it possible to separate and collect rare earth materials.