I am planning to melt and cast aluminium from soda cans. I went to quora page that deals with "burning" aluminium can, which can release toxic gases as the cans are coated with plastic inner lining. So my question is if melting aluminium has the same effect? If so can the affects be mitigated by melting aluminium in the open and wearing respiratory masks (not sure if they are rated for plastic related fumes)?
There will be some organic coatings that will burn ,producing -who knows what? You will have little success melting aluminum cans in air , they will basically oxidize. Aluminum cans were not worth anything as scrap until years ago commercial melting began in inert ( non-oxidizing) atmospheres. I have seen the remains aluminum tank trucks ( gasoline) that burned , only steel is left , no melted puddles of aluminum. Apparently, the burning gasses carry away most of the alumium oxides produced.
In addition to the problems listed in the other answer (typically you get very low yield because most of the aluminum oxidizes, and you have to burn off a toxic plastic coating), aluminum cans are made out of aluminum sheet, which is rolled (hot/cold rolled) and not cast. The alloys used are not especially suited for casting, (the obviously named) cast aluminum alloys are way better. You find cast aluminum often in car parts such as pistons, other engine parts, and some wheels. Since these are in big chunks instead of sheets, they won't oxidize nearly as badly, either.