Rapid Coal Analysis. Part I: Particle Size Effects in Slurry Methods Based on Flame AA and Swing-Mill Grinding

Abstract

Laser diffraction particle size measurements are used to study aerodynamic mass transport losses of a finely ground aqueous coal slurry aerosol in the spray chamber of a conventional atomic absorption spectrometer. A swing mill used to grind the coal produces many particles small enough to transport efficiently in the aerosol stream, but some are too large and can settle out in the spray chamber. This effect is reduced but not eliminated if one passes the grindings through a 325-mesh sieve prior to weighing and direct analysis. In spite of the partial “leveling effect” produced by the sieve, the residual mass transport loss in the spray chamber for direct coal slurry analysis by flame AA is about 51% (relative to aqueous standard transport). This accounts for part of the five-fold decrease in absorbance previously reported for finely ground coal slurries as compared with aqueous solutions. The remainder of the decrease is due to incomplete combustion and vaporization of coal particles in the nitrous-oxide/acetylene flame.