Abstract
The grouping and segregation error, one of the seven sampling errors defined by Pierre Gy, is related to the combined effects of gravity and characteristics of the target analyte such as particle size, density, shape, and moisture content of the particulate materials being sampled. Kinetic energy acting on particulate materials that are moved, flow, transported, or stockpiled causes the spatial distribution of fragments relative to one another to change. The grouping and segregation error is identified, quantified, and measured in relative sampling variance terms by comparing the sampling variability due to fractional shovelling (scooping) with that using a Jones riffle splitter. The relative sampling variance of low concentrations, approximately 0.01%, of steel balls, lead balls, and flakes of tungsten carbide in the host substrate indicates that, in this specific sampling space, the grouping and segregation error is primarily a function of particle density. Conclusions from the experiments are that components of the grouping and segregation error, namely the grouping factor and segregation factor, can be identified, measured, and mitigated. Whereas the grouping and segregation error has historically been considered to be less than the fundamental sampling error, these experiments suggest that it can be up to four times the fundamental sampling error depending on the density of the segregated materials.
Highlights
Introduction and Segregation Error in theRiceSampling experiments in a teaching environment provide simple and meaningful examples for understanding concepts of particulate sample behaviour
Recent work on the inducement of segregation as a result of using riffle splitters [7] indicates that where the particle size distribution is narrow, as is the case in all of these experiments, riffle splitting is not responsible for segregation; for wider particle size distributions, it may be
Scoop sampling reveals that high-density target analytes are strongly segregated in the lot, while incremental sampling using a standard 20 vane riffle splitter, results in the almost complete removal of segregation
Summary
Sampling experiments in a teaching environment provide simple and meaningful examples for understanding concepts of particulate sample behaviour. The so-called rice experiment is a simple classroom exercise for teaching sampling concepts and modelling the behaviour of non-cohesive particulate materials using scooping (fractional shovelling) and riffle splitting as mass reduction sampling methods. This would represent a rare and extreme case in practice but is an effective teaching tool to demonstrate the characteristics and behaviour of sampling errors as a result of differing modes of sample selection and extraction [1–5]. Mark suggested that Dominique use the experiment in his sampling course entitled “The Theory and Practice of Particulate Sampling”. The “rice experiment” was based on principles found in Gy’s [2] Theory of Sampling, but “ . . . there is a body of knowledge, that can be organized such that it forms—albeit imperfectly—the beginnings of an expandable and coherent framework to describe mixing and segregation of granular materials?” [6]
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