Beyond the minimum dimension for particle size control

Abstract

Particle size control is important in efficient mineral processing, but today many milling operations are controlled using techniques which only consider the minimum particle dimension and assume that shapes of the particles remain constant. Many process operations suffer from variation in efficiency which cannot be explained by conventional techniques such as screening. This can be as a result of process changes such as ore source causing a change in particle morphology which is simply not detected when only the minimum particle dimension is considered.Image analysis data will be used to demonstrate the key principles behind particle size measurement and the reality of mineral slurry shape distributions. Unfortunately the application of image analysis techniques to on-line analysis of mineral slurries is not a practical proposition for reasons of sampling, statistics and cleanliness, therefore alternative techniques must be used on-line to obtain reliable and process sensitive data.Ultrasonic extinction fulfils many of the requirements for on-line particle size analysis, being able to monitor vast numbers of particles at high concentration and since the technique responds to the area of the particles, a more process sensitive measure may be obtained. The OPUS ultrasonic extinction system uses 31 frequencies to measure a full particle size distribution from approx. 1um to 3mm and for the first time allows for parameters such as distribution width, fine particle levels and solids concentration to be measured reliably on-line in a single unit. Data will be presented to show the potential for better process understanding through utilisation of the full particle size distribution information.