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Comparison of Hydrometer Analysis and Laser Diffraction Method for Measuring Particle and Floc Size Distribution Applied to Fine Coal Refuse

Traditional grain size distribution measurement techniques assume that the measured particle diameters are of individual grains. However, for suspended particulate materials, particles may be dispersed or associated in flocs. Further, particle-level associations depend on the surrounding fluid chemistry, which may change over time. The purpose of this study is to compare two different methods of grain size analysis for detecting particle and floc sizes in suspensions of fine coal refuse (FCR): hydrometer analysis, the well-known traditional method, and laser diffraction, a lesser known method. The influence of background solution—flocculant, dispersant, or distilled water—on the apparent grain size of FCR was also investigated. Analogous slurry suspensions made from a well-characterized kaolin were analyzed for comparison. Results from the grain/floc size analysis indicate that there are several advantages of laser diffraction over hydrometer analysis including a short measurement period, small sample size requirement, and the ability to measure a wide range of particle sizes in the same analysis. Moreover, this study highlights the ability of the particle size analyzer (PSA) to accurately measure changes in apparent particle size over time for the same suspension and thereby indicate the presence of flocs. Finally, the PSA has the capability of capturing dynamic particle interactions—flocculation and deflocculation—in real time.