PARTICLE SIZE MEASUREMENT AND INTERPRETATION

At Queensland Alumina, three different techniques are used to measure particle size distribution of hydrate. These are dry sieving, Fraunhofer diffraction using a Malvern Laser Particle Sizer, and electrical conductivity sensing zone principle using a Particle Data Electrozone Celloscope.

As each method measures a different physical parameter, absolute agreement is neither expected nor achieved. For selected sizes of interest relative agreement is very good with coefficients of correlation in the order of 0.99. While each method has definite advantages, it also has limitations. The significance of method limitations, particularly for sieving, have not always been given due attention.

This paper explores what they measure and how they compare. Performances in terms of precision, accuracy and speed are listed. Data on particle size measurements from different laboratories on identical samples show that analytical differences need to be reduced.