Researchers at the Idaho National Laboratory in the United States used a water treatment technology to selectively separate rare earth elements and transition metals.
A recent article published by Nature Communications describes this chemical process, which reduces the energy and product consumption involved in recycling rare earth elements.
This new method involves the use of dimethyl ether, which is a gaseous compound and one of the earliest commercial refrigerants. This compound drives fractional crystallization - a process of dividing chemicals according to their solubility - to separate rare earth elements and transition metals from waste magnets.
Caleb Stetson, the experimental director of the project, said in a media statement: "The process starts with a magnet that is no longer useful. It is cut and ground into shavings."
Then, the magnetic chips are put into a solution with a leachant, which is used to selectively extract metals from the material. Once the required metal is leached from the material into the liquid, we can apply the treatment process. "
The process driven by dimethyl ether consumes much less energy and pressure than traditional methods, and is usually carried out at very high temperatures. On the other hand, fractional crystallization can be carried out at ambient temperature, requiring only a slight increase of about 5 atmospheres of pressure. In contrast, an unopened 12 ounce can of soda is 3.5 atmospheres. These lower energy and stress requirements also save money.
Less waste
According to scientists involved in the project, the competitive technology also uses added chemical reagents to drive sedimentation and other separations, which inevitably becomes additional waste and brings economic and environmental consequences. This is not the case of fractional crystallization of dimethyl ether.
In their paper, the researchers pointed out that they chose dimethyl ether because it was easy to recover, overcoming the shortcomings of previous attempts to use solvents to drive the separation of key substances. By reducing the pressure and then recompressing the gas at the end of the experiment, the team was able to recover the solvent and reuse it in future cycles.
There are other advantages to this process. Stetson said: "The temperature of evaporation crystallization is difficult to adjust, but this fractional crystallization process eliminates all these challenges." "For the process of separating different components from the metal containing solution, we only need to adjust the temperature by 10 degrees."
When developing this solvent based zero waste metal recovery process, the team worked closely with some electrochemical rare earth metal recovery processes that already existed in the laboratory. This includes the E-RECOV project, which uses electrochemical batteries to effectively recover metals from discarded electronic products.
In the view of scientists, reducing the energy intensity and waste proportion of key materials recycling is expected to not only bring environmental benefits, but also encourage developed countries to carry out these processes locally rather than at sea.