Supported ionic liquids – an innovative way to recover rare earths

By Dženita Kasapović

When someone mentions the periodic table of elements, I am sure you can easily remember the image of the two rows of elements which are located separately below all of the other elements. The first line of these "special" elements are called rare earth elements, or simply, rare earths. Scandium and yttrium also belong to this family, which are located in the same columns within the neighborhood. However, their position in the periodic table is not the only reason that makes rare earths special, these elements also have a number of applications in many exotic technologies.

Rare earths play vital role in limiting green house gas emissions, through their unique application in green energy technologies.  This includes hybrid and electric vehicles as well as wind power generators [1]. They are also extensively used in aerospace applications, healthcare, chemical, oil refining and manufacturing and many other technologies [2].

Figure 1: Rare earths applications [3][4][5]

You can imagine by now with such a wide range of opportunities for applications, the demand for rare earths is also ever-increasing; especially in the recent years when the rare earths are becoming a geopolitical tool [6]. Taking that into an account, one of the great opportunities we can use to tackle this challenge in fulfilling demands for rare earths, especially scandium, is seen in the usage of a secondary resource like bauxite residue.

For the recovery of rare earths and other valuable metals from the bauxite residue within the REDMUD project, there is a carefully designed process which involves a number of stages for the different elements and each project has a young researcher in charge of its development. This also requires a strong collaborative effort between the researchers.

At a certain point of the valorization process of the bauxite residue, the rare earths should be taken from a diluted acidic solution in order to further process them into their final products. One of the ways to do this is by the use of ionic liquids. Because they are composed entirely of ions, ionic liquids do not evaporate even under a vacuum. They are also called designer solvents. Thanks to their many wonder properties, ionic liquids are considered as a green solvents which then can be used for the recovery of rare earths from the bauxite residue. However, ionic liquids are very viscous "honey-like" materials and this gives a certain disadvantage for handling and for their use in this specific part of the project. It can be argued that right here lies a better opportunity in introducing another kind of material such as supported ionic liquids, better known as SILPs.

They combine the unique properties of ionic liquids with the properties of a solid "carrier", circumventing the problem of high viscosity without the usage of high temperatures and providing us a product which is easier to handle and work with. With these advantages, ionic liquids become a more interesting and relevant material to use in industrial application, especially for selective recovery of rare earths from diluted solutions.

Figure 2: Ionic liquids [7][8]