DEACTIVATION OF PYROPHORIC IRON SULFIDES

Rust formed by corrosion on the inner surfaces of oil tanks may react with hydrogen sulfide gas in the vapor above crude oil. This reaction produces mixtures of iron sulfides which are pyrophoric, and they caus e explosions when they are exposed to air during the unloading of the tankers. This paper shows that it is possible, by exposure to an atmos phere of nitrogen containing 2 or 4 vol % oxygen, to deactivate these sulfides with mackinawite, FeS, pyrite, FeS2, and greigite, Fe3S4. Mac kinawite undergoes slow oxidation to give goethite, FeO(OH), which has a lower reactivity. Pyrite and greigite are pyrophoric, present in th e mixture in a finely divided state and produce sparks on exposure to air. During deactivation they do not oxidize but transform to a frambo idal morphology which has a lower surface area and is less reactive.