This text is part of the special Research section
Do you know where the rare earths are found in the periodic table? Professor at the Institute for Research in Mines and Environment (IRME) of the University of Quebec in Abitibi-Témiscamingue (UQAT), Jean-François Boulanger can point them without problem. Above all, he knows how to extract them from the ground so that their properties can be used in the batteries of electric cars or the magnets of wind turbines.
Jean-François Boulanger recently set himself the task of improving the process for separating these metals. Launched in December 2022, his research project could have a major impact on the costs generated by this energy-intensive process. For, side by side at the bottom of the periodic table, these metals resist attempts to isolate them. “When they are extracted from the mines, the rare earths are all grouped together, explains the researcher. It helps to find them, but it’s hard to separate them later. »
The separation step currently represents 15% to 25% of the cost of producing rare earths. It also harms the environmental balance of these metals intended precisely for green technologies.
periodic chocolate
For the moment, the separation of rare earths is done through a process called “liquid-liquid extraction”. Metals are brought into contact with solvents which will retain some elements, but not all. Like a chocolate bar that you break in half to share with a friend, each step in the process divides the rare earths into increasingly pure sets. By repeating these steps almost a thousand times, we finally manage to isolate each element from its neighbors – the chocolate bar is separated into small squares.
“I have a colleague who has developed a simulator that reproduces these stages on a computer,” says Jean-François Boulanger. This is essential for our research, otherwise it would take a thousand students to reproduce each step in the laboratory. In short, the separation of rare earths is a particularly complex task.
This step can also produce a lot of waste. The method used in China, the country where most of these elements come from, is done using caustic soda and hydrochloric acid, a base and an acid that combine following a process to become salt. “Brine poses a significant environmental management challenge,” notes the researcher. Before being discharged into the environment, this salty water must be treated, which increases production costs.
Reduce steps
Are things about to get easier? The researcher believes he has found a solution that could reduce the costs of this step by 25% to 50%. It was while rummaging through expired patents that he came across a method that would make it possible to “pre-separate” certain rare earths. “The method creates two more subsets,” he explains. But instead of cutting the chain in two, we extract disparate elements. A bit like removing squares of chocolate from various places on our shelf rather than breaking off the ends. Separating the neighboring elements greatly facilitates the subsequent steps.
“There was little work surrounding this patent, recalls Jean-François Boulanger. It didn’t appear to have been used by anyone else. With colleagues, we did laboratory tests and everything seemed to check out. It was almost too good to be true. The researcher moderates expectations, however: “It’s not an easy process. We still have to see if it really works. »
This new process uses techniques already commonly used by the industry. First, the rare earths are mixed with water in a reactor where CO is injected2. Some elements will react with carbon dioxide, a process called carbonation.
We then move on to leaching, where an acid solution is added to the mixture in order to make the carbonates soluble. It then becomes easy to separate the liquid, containing the elements transformed at the carbonation stage, and the solid, which contains the other elements. These two substances are then processed as usual, using the liquid-liquid extraction process, but since the elements have been pre-separated, the number of steps is significantly reduced.
If all goes well, Jean-François Boulanger estimates that a quarter, or even half, of the stages could be eliminated. “We would reduce the quantity of reagent required, therefore the quantity of effluent to be treated, the quantity of salt generated…” explains the researcher. Enough to make the extraction of these coveted metals even greener.
This research is conducted in partnership with Laval University, Commerce Resources Corp. and SGS Canada Inc. as well as the Metal Processing Research and Innovation Consortium (CRITM).
This special content was produced by the Special Publications team of the Duty, pertaining to marketing. The drafting of Duty did not take part.
The current stage of the separation of rare earths harms the environmental balance of these metals intended precisely for green technologies