Problem 1 -- Fuel delivery
So refuelling my car will take 350 lbs of SOLID material? And then removing an even greater weight (the Al will be oxidized) of solid waste product and transporting all that back to the refinery?!?!
Just imagine a distribution system set up to handle 7 times the weight of todays gasoline distribution, storage, and delivery system. And all as solid material, not an easily pumpable liquid. You won't even save anything on the volume -- Al has a density of about 3.5 or so, so you actually need twice the volume of current storage faciliites for the same amount of stored energy. That hardly sounds like an attractive approach