# Is there any way to refine Feldspar?

Feldspars are mostly composed of three compounds:

• KAlSi$_3$O$_8$

• NaAlSi$_3$O$_8$

• CaAl$_2$Si$_2$O$_8$

I notice they each have Aluminum. Feldspar is far more common than Bauxite (the only Aluminum ore commercially mined). As it stands now, Feldspar is used in glass-making, but I'm wondering if there's some chemical refining process that can extract the Aluminum somehow?---especially that third one, since it has two Al's.

Note: I'm not looking for an economical method. That's proly asking too much. I'm not worried about aluminum reserves, because bauxite is still very plentiful. I'm simply interested in a chemical method to extract Aluminum, or at least Alumina (Al$_2$O$_3$), from Feldspar, purely for reasons of chemical curiosity.

The only thing I've researched is the Bayer Process, but I have no idea if it can be applied or modified for Feldspar.

## 1 Answer

Aluminium oxide can be isolated from feldspar by first acid digestion with a mixture of hydrofluoric acid and sulfuric acid (get rid of silicon by formation of silicon tetrafluoride), then digesting the residue with sodium-potassium carbonate, dissolving the obtained mass in dilute hydrochloric acid and then precipitating $\ce{Al(OH)3}$ by adding ammonia. The $\ce{Al(OH)3}$ can be calcined to aluminium oxide by heating to over 1100°C.

Note that the described procedure requires a suitably equipped laboratory .

• Thank you. To be honest it doesn't sound very expensive compared to the Bayer Process for refining Bauxite. It does, however, seem a bit more complicated since it involves more chemicals. I don't think those acids or ammonia will make it much more expensive. – DrZ214 May 5 '16 at 16:18
• The price of hydrofluoric acid alone is probably at least ten times higher than the price of sodium hydroxide. Additionally, the handling of hydrofluoric acid is quite difficult since it is volatile, corrosive and highly toxic. – aventurin May 5 '16 at 20:13
• I see. I imagine it's expensive largely because of safety precautions slowing down the workforce. I suppose a large fully automated plant could be set up to make it, but such a plant would be very expensive in its own right. One more thing, though: does your process work on all three species of feldspar that I listed? – DrZ214 May 5 '16 at 22:50
• I think the procedure would work with all three species of feldspar you have listed. – aventurin May 6 '16 at 13:30