@Okeido I have ZERO experience in mining. My background is in Biomedical Engineering and Chemistry and I have spent a few years working in R&D for specialty chemical produciton working at lab and pilot plant scale. I am familiar with a lot of the chemical processes proposed and some of the physical processes described in LAC's feasibility studies for Thacker Pass and C-O. This allows me some competence, but not expertise, in looking at the purification process proposed and the ability to go into more depth to fill in some of the blanks. What I do not possess as background, I source from reading and watching videos on mining for other chemicals as well reading feasibility studies written by other lithium developers. 

For Thacker Pass, there has always been the big question mark hanging in the air as to whether battery-grade lithium can be purified economically from a sedimentary or clay-like deposit. This was my motivation for researching the proposed physical and chemical processes. In my previous post, I brought up two concerns. The first was the physical processess of working with clay as an input to the process. I take for granted that most people are familiar with the propsed process of using sulfuric acid to dissolve lithium minerals out of the clay into the liquid acid solution. The concern would be removing the liquid from the clay. The particle size is very small and my sense is clay likes to hold onto water. Therefore, it could be perceived as difficult to remove the liquid phase containing acid and dissolved lithium (aka leachate or brine). Low efficiency would be a concern because that would mean high acid consumption, low lithium recovery, and hazardous sulfuric acid filled tailings. I looked into this process and there seem to be well-established technologies for processing clays such that I do not share these concerns. The second concern I brought up was the concentration of lithium in the liquid phase. I am not sure we have a value for what the percentage of lithium in the leachate is. For context, I tried to put this in the context of hard rock and brine operations. We know that spodumene is enriched from ~1.2 up to ~7% lithium oxide prior to roasting and acid leaching. By comparison, brine pumped out of the ground at Cauchari-Olaroz contains 600 mg/L (0.06%)% which is then concentrated through evaporation to 10.5 g/L = (~1%) prior to chemical processing.  I do not know what the concentration of lithium in the leachate from spodumene is as a point of comparison, but presuming it is proportional to the starting material, it likely falls somewhere above that of concentrated brine. The clay at Thacker Pass that will be processed is around 3500 ppm Li (~0.3%). The PFS indicates that the concentration of lithium in the leachate is ~0.3% (pg 80 of the PFS).This would put the concentration of lithium in leachate from Thacker pass ~ 3-fold lower than that of brine. This suggests to me that there might be more capital expenses associated with handling the larger volume of solution and energy required to concentrate and crystallize lithium. 

Since the PFS, the planned process for Thacker pass now includes ore upgrading which will increase the concentration of lithium in the clay prior to acid leaching, but we do not know what the extent of upgrading will be or the final concentration of lithium in the new leachate. Taking the worst case, I am assuming no appreciable increase in concentration of leachate from clay above the 0.3% reportered in the PFS. The concerns for the downstream purification of lithium from the acid solution are whether lithium can be recovered from what I assume will be a relatively dilute lithium solution relative to other processes as well as expense of removing impurities relative to the leachate from spodumene or concentrated brine like that at Cauchari-Olaroz. Ultimately, we will have to wait and see how economical these processes are at scale.

As a potential positive, I see the improvements brought by ore upgrading as coming in ways that might not be expected at a quick glance. Reduced sulfuric acid consumption will reduce cost, but the senstivity analysis for suggests the process is not very senstivite to the price of sulfur, so I would not expect an appreciable reduction in costs associated with sulfur. What is unclear from the Thacker Pass PFS are other savings associated with reduced acid consumption including reduced Capital Expenses (either a smaller sulfuric acid plant or same sized plant that has a higher capacitity for LCE produced), perhaps reduced chemical costs for acid neutralization, and maybe reduced costs for dealing with the tailings. 

Another positive I have mentioned before is that the lithium in the clay at Thacker Pass does not require high temperature roasting prior to acid leaching. Roasting converts the lithium mineral from a form that can't be leached into acid to one that can. This in contrast to spodumene deposits and shale at Bacanora in Mexico. Not only is roasting energy intensive, expensive, and arguably not consistent with ESG. 

Another concern brought up by I believe the CEO of Cypress Development is the sulfuric acid chemistry. Apparently this can cause build-up of mineral precipitates on equipment. I think he is proposing a hydrochloric acid baced chemistry for their process and stated this mineral build-up is not a concern. However, sulfuric acid leaching is used in the purification of metals, so I imagine there are plenty of solutions to this potential problem. 

AXP