Developmental history of ionic adsorption clays as a source of...

Developmental history of ionic adsorption clays as a source of REE.

Minerals | Free Full-Text | Review on the Development and Utilization of Ionic Rare Earth Ore (mdpi.com)

"As a unique rare earth resource, ionic rare earth ore (IREO) has the outstanding advantages of complete composition, rich resource reserves, low radioactivity, and high comprehensive utilization value. IREO is the main source of medium and heavy rare earth raw materials, which are in great demand all over the world."

Not just HREE but MREE are also mainly being supplied by IACs.


I reproduced this diagram from a previous post of mine on this thread. On the x-axis is the pH. At the far left, when the pH is very low (<<1, strong acid conditions), all the metal ions are in solution (aka soluble). As the pH is raised (moving L-to-R on the horizontal axis), one by one the metals become insoluble and fall out of solution (lines drop from high to low on vertical axis).

FOR EXAMPLE: If you follow the dotted "Al III" black line upwards, it hits the top almost exactly at pH=3; if you follow the same line to the bottom, it hits the bottom line just below pH=4. So as pH is raised from 1 to 3, all the Al III (aka Al+3 ions) remains dissolved in the water and nothing happens; as the pH is raised further, the solution turns cloudy as the aluminum becomes a solid that falls out of the solution like rain. By pH=4, "all" the aluminum has "precipitated".

The REEs are not shown in this diagram, but they also fall out of solution as pH is raised forming a group of "solubility" curves are similar to those above. Their curves are all slightly different from one another, starting at a pH of about 2.5. As the pH of a leachate mixture is raised from 1, the IRON (aka Fe III, solid red line) begins to fall out at pH ~1.4 and it has "all" precipitated by pH~2.3 (where the RED line seems to reach the lower line). All the other metal ions remain in solution until their curve indicates otherwise.

Raise the pH just a bit more (to ~2.5) and your first rare earth metal ions start precipitating. There might still be a wee bit of iron contaminating them. Raise the pH a bit more and several LREEs start precipitating, but the process is not completed, and pH must be raised further to do so. Unfortunately, at pH ~3 the aluminum starts to precipitate with the REEs as discussed above. Clay is 21% aluminum, so this is the biggest impurity challenge for ionic clay deposits, but just another of many for those trying to refine hard rock leachates.

NOTE: The curves aren't always as nicely shaped when they are in a mixture. The presence of other metals and of multiple counter-ions (sulfate, phosphate, mainly) also has a large impact.

Obtaining higher purity metals from complex precipitation schemes is often a function of recovery. If you aim for higher purity, you will lower recovery. The more processes you include, the lower the recovery will be. Huge ramifications for product suite and sales not to mention margins and profitability. Mischmetal uses are much more sustainable.

Rare earth sulfates in aqueous systems: Thermodynamic modeling of binary and multicomponent systems over wide concentration and temperature ranges (sciencedirectassets.com)

Just for fun for ftm.