Kaolin clay is a complex of silica and alumina created in some (unknown to me) geochemical process.
I am pretty sure it possible to refine silica from clay, the left over being mostly alumina and iron oxide. This is based on wispers I’ve heard, mostly relating to geopolymer chemistry. This would not be any sort of break through, as aluminum is cheap and the refining process involves many steps. Here is how i think it would go (based on “Extraction of silicon dioxide from waste colored glasses by alkali fusion using potassium hydroxide” by Hidetsugu Mori):
First, the clay is mixed with an excess of sodium or potassium hydroxide and fired at a moderate temperature (~400C for potassium, ~600C for sodium). This forms water soluable alkali-silicate and leaves other metal oxides insoluble.
second, the alkali silicate solution is neutralized to percipitate out the silicic acid (SiO4H4), and silica is just the calcinated (dried) silicic acid. The literature reports this being 99.9% pure.
it is not as easy as this (for instance, what acid and how to reclaim it), but I’ll keep you posted on my ideas.
edit: I may be wrong about alkali not fusing with alumina, though iron would not.
(from Hidetsugu Mori in a personal correspondence)
Si(OH)4 is not dissolved in strong acid.
But Al and Al hydroxide are just dissolved in the acid.
From this difference, Si(OH)4 can be collected from the
sample solutoin, and SiO2 can be prepared by heating
the collected Si(OH)4. So, Si(OH)4 can be separated
from the solution containing Al ion.
If Alumina does fuse, then only iron and other trace metals would be left from the original wash, silica percipitates in the neutralization and then the solution is made acidic to get the alumina out. more complicated. only experiments will show.