Summary if don't want to read past 1 paragrpah
I am sure others have a perspective, but this is my perspective at this stage. In summary it is a difficult to answer but 1.69% is ok but you need to look at the whole product sold instead of just one element, but 1% would be far better mica IMO, but it also depends on what actually the elements are in the mica itself as wellin the spodumene sold.
The below is essentially on research/trying to put down m understanding of deleterious elements which I was going to put in the Understanding Lithium Demand thread (wjich I will do at some point) but given your question I thought well I just give you an answer as best explained I can.
General:
I will build on some comments I made in this post - when talking about the AVZ resource compared to other plays - Post #:
43092083.
Some relevant comments in that post I will expand on below:
"
In summary, DMS can be an effective means to pre-concentrate spodumene from hard rock operations with the benefit of less feed to the grinding and flotation circuits and subsequent capital, energy and operating cost savings. However, the effectiveness of DMS is highly dependent on the degree of spodumene liberation at coarse particle sizes. Poor spodumene liberation will result in significant lithium losses to the float product and negate economic justification for its use."
"
In liberating spodumene note that mica and Fe203 really cannot be removed from the spodumene itself at the DMS stage, so liberation at that stage is also where they are unattached (and that is how DMS is viable at that stage been large crystals and low deleterious elements in the spodumene itself). Certainly at floatation you can remove impurities but IMO you don't want to be significantly reliant on floatation to achieve 80% recovery rates IMO (note: AVZ will retrofit floatation and based on previous DMS Ann, IMO over half the more than 80 percentage point recovery rate because of the high DMS rate likely with floatation will come from DMS btw)."
Now, when talking deleterious elements there are three main types you don't want - phosphorous (P), fluorine (F) and Fe (iron) especially. these are essentially your penalty elements, including some of the ones below in pricing spodumene - the spodumene needs to keep these in check or you have the clinkers effect.
When they talk mica, the key thing you are really focussing on is fluorine and iron, because fluorine and iron is an element of mica. The other is magnesium (Mg), potassium (K) and calcium (Ca). I should say here, feldspar and quartz may also contain impurities you don't want as well, so the key is around liberation as well in crush sizes etc.
Understanding formulas and specific gravity
Spodumene formula is: LiAlSi₂O₆
You can get the Mica formula here:
https://en.wikipedia.org/wiki/Mica
Quartz formula here: SiO2
Feldspar formula here:
https://www.britannica.com/science/feldspar/Chemical-composition
Feldspar = specific gravity - 2.6, spodumene SG = 2.8 - 3.0, quartz specific gravity = 2.65 and mica specific gravity 2.76.
The point of the above, is when you look at the formulas you can certainly see which rock some of the impurities come from, but others can come from a couple sources and then you have to think of likely source. Given the SG of micas are close to spodumene there removal is the hardest so some of the key impurities discussed below may originate from micas (and that is why micas are particularly looked at in my opinion). There removal by and large at the DMS stage is really based on large coarse crystal sizes
that ineffect allow for spodumene liberationas per the quote above in order to minimize lithium losses to the float product.
When they talk DMS what they are saying is you can effectively liberate the deleterious elements from the spodumene. If you cannot do that then you must rely on floatation and specifically the units before floataton. A key issue with mica is you also don't want it to be "
mica schist, if it is in the ore especially, especially IMO given it is flakey and could clog the SAG/Ball Mill efficient operation if not adequately addresses before the ball milling stage for example IMO" This comment is relevant if you intend to produce the bulk of your spodumene concentrate product at floatation.
This patent -
https://patents.google.com/patent/US2748938 - gives an idea as to mica removal etc in floatation, but my point is the more you rely on floatation for achieving an 80% recovery rate the more probability of cost overruns and issues - again see embedded post above for explanation. As does this explanation of mica removal in preparation and floatation -
https://www.911metallurgist.com/blog/froth-flotation-spodumene-processing-lithium-extraction
Scematic roasting process
What you want to prevent is the clinkers effect in the 1080 roasting process below. Most converters operate on a 85% -90% recovery of the spodumene so the clinkers effect means a lower recovery than that which can impact the purity of the LCE and would result in lower prices been paid for the spodumene IMO.
https://www.linkedin.com/pulse/all-chemical-grade-spodumene-concentrates-same-harman-grant
Given the difference in grain sizes of 6% grade spodumene after floatation, compared to DMS 6% grade spodumene I am also mindful that in calcination process that it is likely to be easier to deal with large grains than smaller grains as well (so that is also something to keep in mind).
DMS AVZ
Going to AVZ there DMS process is going to have a recovery rate of 55% - 60%, and you can't have DMS product if it doesn't meet specs. Having a high DMS recovery rate gives a little confidence that the spodumene recovered in floatation will also be low in deleterious elements, given that it suggests the different zones in the pegmatites are visible and can be worked with (again refer opening post), but that is IMO - see concluding paragraph below
Relevant Anns
This Ann from August 2018 provides commentary that is a key to understanding the deleterious elements issues - in effect what is been said is that the main deleterious elements are not significantly in the spodumene zone but in the
"in apatite, lithium micas and black tourmaline which are accessory minerals within the pegmatite. Trace amounts of iron can also be included in spodumene crystals."
https://www.asx.com.au/asxpdf/20180802/pdf/43x0zdmdjsrn7g.pdf (page 7)
That suggests mica, or the key deleterious elements in the mica to meet product specs, can be removed in the product stream, orelse DMS would not be an option.
Now this Ann is also relevant -
https://www.asx.com.au/asxpdf/20191022/pdf/449qx4q9rkwxlc.pdf
Page 4: "
Mica Removal Process. Mica is not desirable in spodumene concentrates due to its ability to dilute the lithium grade and its possible contamination by elements such as species of iron and fluorine forming part of the mica structure. Iron and fluorine are highly deleterious to the downstream processing of chemical grade spodumene concentrates."
To your question - page 5:
"A typically acceptable mica level is sub 2% but is preferred at 1%. AVZ is on track to produce a very marketable product in this respect. Table 2 below compares AVZ’s results to date with various other lithium producers globally.AVZ intends to further improve on these numbers for final production figures."
This statement above on mica is vague IMO because it is what is in the mica that counts and whether it is attached to the spodumene or not and that determines the extent of its removal.
Page 11 comment of the above Ann:
Ultimately it is what is in the mica that counts as well.
Latest Mets to complement above:
AVZ have played around with grain sizes since that October 2019 Ann btw, The 1.69% in the latest Ann for a DMS option is ok, but I wouldn't say exceptional btw for the following reasons below when compared to technical grade applications. Just a question of what deleterious elements present in that 1.69% is also important.
But based on previous Mets and comments, the main deleterious elements that are key concerns, i.e fluorine, are low, and iron is shown to be below 0.8%. It is a balance, but I would prefer mica be closer to 1% personally but as I said the level is acceptable provided iron, fluorine and phosphorous is low to compensate for the fact the mica level is between 1% - 2% IMO. Obviously with floatation, mica levels will be well below 1% IMO, and Fe203 levels will be even lower than 0.8%.
Using published Albermale data
In terms of Greenbushes sales, SC6.0 is your chemical grade spodumene that is what goes into your batteries, the others products it produces are technical grade (TG) applications. The key difference what makes something CG or TG is in effect Fe203, because TG with low Fe203 content is found in higher end markets (glass/ceramics) and TG can be used for CG applications but not the other way round btw.
I can find data on Albermale's TG sales and they are interesting, but not CG sales as I suspect they are used for its own chemical converters in China. In effect, for TG applications your getting mica content of about 1% where shown.
https://www.albemarle.com/businesses/lithium/products/product-finder
So taking an example, from the above link, scroll down to "Spodumene Concentrate 7.2 standard" and open it up, working through it you come to about 1% mica.
Take "Spodumene Concentrate 6.5" not reported like 7.2, but if add spodumene, quartz (Si20 - https://www.britannica.com/science/quartz) and feldspar (https://digitalfire.com/4sight/material/feldspar_310.html) and look at what is left over I get to 1% mica (could be slightly higher or lower depending on rounding). (6.5%/8.03% theoretical Li20 = 81%, which is the spodumene number btw).
When you do the calcs across those TG products you get to about 1% mica (again could be slightly higher or lower depending on rounding).
CG does not have the stringent applications of TG, so in a nutshell can have a slightly higher mica level, so that can support what AVZ is saying, but I would prefer 1% or less (and certainly floatation gets you less than that btw). Obviously though, without floatation AVZ will not be able to supply the TG market (glass/ceramics) IMO despite Fe203 been below 0.8% and in any event Fe203 would probably need to be lower than that reported in DMS for TG, but can on current specs supply the chemical grade market.
But working through the Albermale specifications, certainly on the TG front, as I said without floatation won't be able to supply that market without floatation. And the key too me is what is in the mica, but moreso for converters if you think about it when you say 6% grade spodumene, what you are saying is 75% of the concentrate is spodumene, so the key is ensuring the other 25% that is removed in the chemical conversion process doesn't form clinkers (explained above).
Nonetheless,given what AVZ can do with DMS, which appears to be good enough for the chemical grade market - see conclusion, I suspect that when they install floatation the difference in the recovery rate - say 80% with floatation - to the DMS recovery rate - say 58% - is going to target the higher end markets IMO (including higher end EV battery requirements market such as possibly the emerging solid state batteries etc"
AJM Ann
This Ann was before AJM had its problems but after floatation it was saying that Fe203 would be 1.04% and mica 0.63%. The Ann below says in effect these represent low impurity levels. The AVZ DMS outcomes has a lower Fe203 count but a higher mica count so only thing conclude is mica is ok for DMS, but 1% would be preferable IMO (but in totality deleterious elements produced in the current METs are in specks for the downstream market).
https://alturamining.com/wp-content/uploads/2019/03/1912571.pdf (slide 10)
GXY
You might recall, GXY CG (battery grade 6% spodumene) pricing in 2017 was around the US$900 mark - https://www.asx.com.au/asxpdf/20161214/pdf/43dpy354rjhp49.pdf - for 6% grade spodumene. I found this Ann interesting. What they say on page 14 is mica content is well below contractual obligations, i.e. not sure what those contractural obligations are, but when you look at the table on that page they were reporting mica content of 1.77% in that year (so would appear what is in the mica is the key, and AVZ's DMS mica result is ok).
Conclusion
At the end of the day, would like to see more commentary from AVZ around its views on mica and impurities btw. The lower the better btw as well IMO, but on balance when looked at in the context holistically they are ok IMO for battery applications but that is based on limited information (but ultimately the key test is what happens in the converters).
Getting Offtake Agreements will put the issue to bed, but the fact AVZ is reporting these results overall suggests it is comfortable that the results are fine and within specs. Time will tell how the others report, but looking at the main MET anns AVZ has continuall stated that the main deleterious elements of phosophorous, fluorine and Fe203 are low, and based on my own searches I haven't found industry and/or 'industry specialist' commentary questioning those statements.
Time will tell.
Obviously otheres may have a different view, but my view to date is teh resource is good and amenable to DMS. Obviously a premium product, and by that I mean one also supplying the Technical Grade market, will certainly happen IMO, based on comparisons to Greenbushes, with floatation. But current specs for DMS product are certainly good for the Chemical Grade market (given commentary from AVZ, no opposing views from industry commentators, and looking at the specs against published Alebrmale TG applications (which are higher end to battery grade specifications).
All IMO
(20min delay)