Automated microscopical method for the characterization of pyrite in coal

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Abstract
The Rapid Scan system of automated reflectance microscopy is a line scanning device capable of characterizing the pyrite content of a coal. The system combines a sophisticated software base with standard hardware components to provide flexibility in analytical format. As a prepared coal sample is moved automatically beneath the microscope objective, reflectance values from adjacent 2 ..mu..m squares are sampled by the photomultiplier tube. These values are stored in computer memory for subsequent calculation of the volumetric proportion of pyrite in the sample. Simultaneously, the Rapid Scan also accumulates a distribution of pyrite chord lengths. In a modification of the Rosiwal linear scanning technique, the number of consecutive readings on a pyrite particle are recorded and stored independently in computer memory. In order to determine the precision of pyrite volume estimates, a suite of coals with varying pyrite content was analyzed at several sample-point densities. The level of precision achieved was found to be a function of sample density and was always superior to the precision of the conventional, visual point counting technique. From these data, sampling plans to achieve a desired level of analytical precision were designed. The ability of the Rapid Scan system to quickly characterize many samplesmore » of a feed coal in this manner, makes it a potentially effective tool in helping to optimize preparation facility operation for the removal of pyrite.« less

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