Pyrite is an ore used as a raw material for the production of sulfuric acid and iron. By oxidizing 1.2 kg of pyrite, according to the chemical reaction equation,

4FeS₂ + 11O₂ → 2Fe₂O₃ + 8SO₂

A mass of 640 g Fe₂O₃ is obtained. Calculate the purity of the pyrite used, considering chemically inert impurities. Determine the amount of sulfur dioxide released.