OXIDATION-KINETICS OF SEDIMENTARY PYRITE IN SEAWATER

Long-term (weeks to months) experiments were conducted on the oxidation kinetics of sedimentary pyrite in which initially anoxic sediments containing pyrite were suspended in seawater that was kept in equilibrium with the atmosphere. During an initial reaction period the oxidation of pyrite is relatively rapid, with 3% to 18% oxidation occurring in one day. Calculations indicate that this initial rapid rate of oxidation is the result of the oxidation of very fine (< 0.3-mu-m) pyrite. Following this initial period of rapid oxidation, the oxidation rate slows, with about 20% oxidation typically occurring during the first week. Only a few percent more of the pyrite is oxidized over months of reaction time. Framboidal pyrite is likely to dominate in this period of oxidation and iron oxide or other coatings may significantly inhibit oxidation kinetics. These results indicate that suspended pyrite can persist in oxic seawater for long periods of time and, consequently, be transported substantial distances.