Yes the question about Hydrochloric acid is valid and if you...

Yes the question about Hydrochloric acid is valid and if you look at the Hydromet process it is not a high risk.
...........from LMG web site:
Our hydromet extraction process uses acid to treat fly ash. Our process can be summarized as:
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• Dissolving Magnesium (Mg), iron and calcium minerals with Hydrochloric Acid (HCl), & leaching out magnesium as MgCl2

• Removing Iron Oxide (Fe2O3) & calcium as Calcium Carbonate CaCO3
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• Converting MgCl2 into Magnesium Oxide (MgO) & recovering the HCl for reuse in the process
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• Processing MgO into Mg and SCM using the thermal reduction process.
............

So, the only hazardous substance is HCl and to a lesser extent Mg metal. Transportation and storage of HCl is common-place and less hazardous than oxidizing acids like Nitric or the highly corrosive Sulphuric. In any case, little needs to be transported because it's recovered and re-used. If there is a HCl spill, it's easily treatable by either dilution or soda ash. I don't see any other "toxic substances" but happy to be enlightened - yes, I am a retired chemist and materials scientist.

It sounds like you are down-ramping to try and buy-in cheaper.