Although no significant major-element contamination is introduced by grinding coal in a steel pulverizer, abraded steel particles can conceivably affect the magnetic properties of pulverized coal. Magnetic and scanning-electron-microscope analyses of pulverized coal and coal fragments from the Herrin No. 6 seam in Illinois showed ferromagnetic and superparamagnetic contamination from the grinder. Significant changes in the magnetic properties of the coal were noted, indicating a total steel contamination of approximately 0.02 wt%. When coal samples were vibrated in the magnetic field of the vibrating-sample magnetometer, the superparamagnetic steel particles moved through the pulverized coal, and participated in the formation of multidomain clusters that in turn substantially affected the magnetization of the coal. ?? 1982.
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Ferromagnetic and superparamagnetic contamination in pulverized coal