Abstract
Through electron spin resonance (e.s.r.) studies, three different kinds of free radicals have been identified in pyrite samples containing coal impurities. Changes in the e.s.r. parameters ( g-value, linewidths, and concentration n) of free radicals have been monitored as the coal-derived pyrites are heated in different atmospheres (vacuum, N 2 and H 2) from room temperature to 500°C in 50°C steps for a residence time of 30 min at each temperature. Changes in n (concentration/g) and other parameters begin to occur at 300°C in vacuum, at 200°C in N 2, and at 100°C in H 2 amtospheres. At these temperatures conversion of pyrite to pyrrhotite is also observed to occur. It is argued that the enhancement of n in these samples is related to the conversion mechanism of pyrite to pyrrhotites. The maximum relative increase in n follows the sequence n (vacuum)> n(N 2)> n(H 2). At high temperature n decreases due to recombination of free radicals formed so that at 500°C, all three types of radicals have small but equal concentrations.
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