I noticed you mentioned the acid consumption rate for the pH 3 test at 6 kg/t stil seemed high. It is important to remember that ionic clay projects don't run a neutral pH, they run slightly acid pH 3-4 and use sulphuric acid to keep the pH in that range.
The ionic clay projects are very tight lipped on acid usage as they appear to prefer the idea that they don't use it at all. Ausenco, completing the scoping study for Aclara Resources Penco project in South America, were transparent enough to share detailed acid consumption data for Penco's pH 4 30-minute AMMSUL washing process (the same as VMM and MEI), copied below. It is evident they still use 2-3 kg/t H2SO4 depending on the source clay, not far off Sybella at 6 kg/t at pH 3.
Now, a further point to drive home when thinking about the Sybella leaching process, it is
acid driven not salt driven. So the acid is doing the leaching, not the salt. Sybella does not require the addition of expensive ammonium sulphate up to 60 g/L (high concentration) to do the REE leaching, but rather uses a very dilute acid which is purchased at a significantly lower unit cost and importantly readily available locally.
It can be cheaper to leach REE with acid than it is with salt if you can do it selectively. To iterate this point, annoted from the Penco scoping study:
What I have annotated above is using the reagent costs, converted their consumption rates from AMMSUL washing into a cost per tonne, then converted that back into what acid consumption rate would that equate to for the Sybella acid driven leaching. The highlighted yellow reagents are the "leaching" reagents that are used for AMMSUL washing and replaced by just sulphuric acid in the case of Sybella heap processing. The non-highlighted reagents are associated with downstream impurity removal and MREC production. As can be seen, the equivalent acid consumption rate on a leaching reagent cost basis is 5.2 kg/t, pretty much the same as the 6 kg/t pH 3 leaching on fresh ore for Sybella.
To summarise the
pH 3 leach test on coarse fresh ore achieved an equivalent reagent cost of leaching as AMMSUL washing per tonne ore. The reagent cost will be Sybella's main disadvantage against the Brazilian clays, the processing cost (heap stacking vs tank leach and filtration) and CAPEX will both be significantly lower based on studies in the public domain. So this pH 3 result really is a breakthrough for Sybella and I can't wait to see what they can do with pH 3.5 in column tests.
(20min delay)