Figure 12

Arrhenius plot for the rate of oxidation of pyrite determined in the dark and under illumination. Because the surface temperature of the pyrite particles under illumination is higher than the measured temperature in the slurry, the activation energy should be higher than the value derived from the slope of the Arrhenius plot. However, even if the temperatures are increased by 3°C at each of the reported temperatures to take into account the effect of light-induced heating of the surface (see text), the activation energy from the temperature-adjusted plot is essentially the same as the activation energy based on the recorded temperatures in the experiment under illumination. This suggests that illumination induces a change in reaction mechanism; the difference in activation energy cannot be accounted for by a simple temperature correction.