I dissolved household aluminium foil in hydrochloric acid until the reaction stopped. The result was a dark greyish solution, which I tried to filter but failed due to the high viscosity. I eventually pressed it through the filter though.
I then heated the solution, leaving behing a grey/white powder. I dissolved this in hot water and froze it. The remaining liquid was filtered again and heated, leaving behing a greenish/yellowish powder.
Here's what I think happened: HCl + Al = AlCl (+ some side products like lubricants, since it is commercial aluminium foil). Then AlCl + H2O = Al(Oh)3.
(I only had one year of chemistry back in high school, so excuse any mistakes.)