Magnetic Components and Particle-Size Distribution of Coal Fly Ash

摘要

Coal fly ash samples are known to contain magnetic components. In this work we report the results of a first detailed study in which the nature and concentrations of the magnetic components have been measured as a function of particle size. Five bituminous coal fly ash samples were size-fractioned with sieves and a sieve shaker into 10 fractions each. Using temperature-dependent magnetic measurements and powder x-ray diffraction studies, it is established that the samples contain magnetite (Fe sub 3 O sub 4 ) and haematite ( alpha -Fe sub 2 O sub 3 ). About half the mass and magnetic components are contained in the fraction with the smallest particles (diameter < 38 mu m). Since the magnetization M for alpha -Fe sub 2 O sub 3 (at 7 kOe) approx. = 1/250 (the saturation magnetization M/sub s/ for Fe sub 3 O sub 4 ), it follows that the measured M/sub s/ is mainly due to Fe sub 3 O sub 4 . The variation of M/sub s/ with particle size then simply reflects the relative abundance of Fe sub 3 O sub 4 in various fractions. A correlation between all the observations is established, thus, providing useful information about the combustion conditions of fly ash. Possible applications of these results are outlined. (ERA citation 08:001565)