[Bill.D.Katt. (OP)]

I'm trying to get relatively pure SiO2 from diatomaceous earth, which according to Wikipedia (http://en.wikipedia.org/wiki/Diatomaceous_earth) is primarily SiO2, Al2O3 and FexOy. H2SO4 would remove the FexOy, but I'm wondering if it would pull the Al2O3 into solution. I suppose I could use HNO3, but I would rather not use it on something like this. Are there any other methods for purifying the silica?

[Bored chemist]

HCl is likely to do a slightly better job because the chloride ion acts as a complexing agent. What do you want the silica for?

[Bill.D.Katt. (OP)]

Thanks, I've seen a reaction done where silica and aluminum powder react in a redox reaction akin to thermite (except energetic). I haven't done any calculations yet, which I suppose I should before actually trying the reaction.

[Bored chemist]

A little iron or aluminium wouldn't stop the reaction.
I'd try it with relatively crude (but carefully dried) silica first.
In any event, if your Al isn't pure there's not much point worrying about the SiO2.