The kinetics of pyrite oxidation in aqueous suspension by nitric acid has been investigated. The effects of pyrite particle size (75-90, 106-125, 180-250, 250-425, 425-850 mu m), reaction time (0-12600s), nitric acid concentration (5-30% by weight), temperature (13-80 degrees C), and speed of stirring (5-20 s(-1)), were studied. The sulfur in the FeS2 was oxidized to sulfate and elemental sulfur during the leaching. Most of the oxidized pyritic sulfur was found in the solution as sulfate. All of the elemental sulfur was oxidized to sulfate as the reaction progressed to completion. The leaching rate was independent of stirring speed. The kinetic parameters were determined based on the shrinking core model. The apparent activation energies for the leaching of pyrite were found to be 52 kJ mol(-1) in the 25% HNO3 and 25 kJ mol(-1) for the temperature range 13-40 degrees C and 28 kJ mol(-1) for temperature range 50-80 degrees C in the 10% HNO3.