No worries. At this point we are just guessing since they have...

No worries. At this point we are just guessing since they have impurity removal trials underway so we will know an answer this quarter, but my thoughts:

Impurity removal (selective precipitation) is done by all REE clay projects, even pH 4 ionic clays. I recommend reading the Aclara Penco scoping study, they cover the impurity removal circuit for pH 4 AMMSUL leach which involves adding ammonium bicarbonate in tanks to bring the pH up to 5.5-6 to remove, you guessed it, aluminium and iron! So CAPEX is largely the same either way, still need stirred tanks and an alkali dosing system to remove Al/Fe as well as a filter to seperate the impurity solids, size of the tanks doesn't change as residence time is typically constant at 1-2 hours. Also worth reading IXR DFS as they use pH 2 leaching so have a fair bit of Al/Fe to remove (but they never stated how much).

From Penco PEA:


OPEX is a direct function of the impurity load, more impurities = more alkali to remove them. You can try estimate this yourself, 2Al³⁺ + 3MgO = Al₂O_3. MgO cost could assume 500-700 AUD/t delivered. Could also use a cheaper alkali such as Ca(OH)₂ (around $270 AUD/t delivered) if it can work.

Some reagent cost references you may find useful in this exercise from Penco PEA. Note ammonium bicarbonate is an insanely expensive alkali per tonne of OH^- contained, but all the ionic clay projects are proposing to use it, so their impurity removal OPEX would be much higher for the same units of Al/Fe removed vs using MgO or lime.


Could the project be unviable due to the MREC product not meeting spec? Yes, and this is a real technical risk for any REE clay project operating on low head grades and/or low pH. MREC spec into China is approx 50% TREO, 0.1% Al (noting MEI achieved 57% TREO, 0.3% Al). But IXR (pH 2) say they have saleable MREC. I think IXR having around 1/4 the TREO leached per tonne ore probably have a higher impurity load:TREO compared to RDM's test work to date, but unfortunately IXR data is very sparse on the impurities. We will just have to wait for RDM to share results from their impurity trials and making MREC to see if they can do it.