The onset of pyrite is observed at about 40 min, followed by the formation of magnetite at about 60 min. Goethite is present
throughout almost the entire run. In the figure, the large increase in background scatter as compared to Fig. 4. between 10 and 35 2 is due to the decrease in sample density after treatment with compressed air. The slurry was disturbed in the process and, due to time constraints, not allowed to settle