I have melted aluminum in the past. It is not toxic, but you need to be careful not to burn yourself. I wouldn't start with aluminum foil, because it is so thin most of it tends to oxidize before it melts. I would start with a thicker piece of aluminum. How do you plan to melt it?
You could read the safety data sheet: Google aluminum safety data sheet to find a copy. While reading, keep in mind that aluminum is commonly used for cookware.
A safety hazard not mentioned in the SDS is that molten aluminum has a very low emissivity. Molten aluminum at, say 1500 deg F, does not look hot, while steel at that temperature will be glowing bright red. If you are near a hot piece of steel, you will feel the radiant heat because steel has high emissivity. Aluminum is different. A piece of aluminum, or pot of molten aluminum, at the same temperature as a hot piece of steel will not feel hot until you actually touch it. Then you will have an instant burn. Remember: hot aluminum has low emissivity so you will not feel the heat until it is too late.
I've done some sand casting and it can be dangerous. Water is used to dampen the sand. On one occasion someone squirted the water at their mate and some went in the furnace. The resulting "blast" burnt the ceiling.