A novel technique for evaluating cleaned fine and ultrafine coal. [Quarterly] technical report, 1 March 1992--31 May 1992

Abstract

As a standard industrial practice all commercially cleaned coals are evaluated by washability analysis to predict their cleaning potential. The results of this analysis are so important that coal washability is a major factor in deciding to purchase and develop coal holdings. However, washability analysis are at present limited to coal particle sizes of greater than -28 mesh (0--6 mm)- Coal particles smaller than this limit 0 separate well in the standard sink-float process used in the washability tests. The increasing demand for cleaner coals requires that coals be crushed to fine (-100 mesh - 0.15 mm) and ultrafine (-325 mesh- 0.045 mm) sizes to liberate more of the fine-grained mineral matter including pyrite. However, such small coal particles can not be analyzed in the standard washability analysis. The purpose of this study is to develop a washability analysis system for fine and ultrafine coal particles using Density Gradient Centrifugation (DGC) and Thermal Gravimetric Analysis (TGA) techniques. The unique advantages of this proposed technique is that it provides a means to obtain usable washability curves on fine and ultrafine coal samples. The DGC technique will produce a large number of density fractions in a single run and, thus, is much faster and more efficient that normal washability analysis. The results to date indicate that only a single DGC run is needed to produce all twelve density fractions for a washability analysis. The recoveries of the fractions are sufficient for sulfur and ash analysis and washability analyses have been successfully completed using the DGC technique. For the Herrin No. 6 sample (IBCSP 101-SIU 2181) there appears to be little difference in recovery for the four size fractions, however, the smaller size fractions do have slightly more liberated ash and pyrite.