Washability Analysis of Coal Using RhoVol: A Novel 3D Image-based Method

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Abstract
Density is one of the key factors of coal that provides useful information about its physical and chemical composition. Traditional coal washability analysis is determined by conducting float–sink test, which is time consuming, destructive, and uses environmentally hazardous chemicals. The motivation for this work is to develop a new technique as a rapid, safe, and viable alternative to the current laboratory of float–sink method in order to avoid harmful chemicals and save time. In this study, an alternative technique based on 3D imaging technology called RhoVol in which the density of individual particles is measured by separate mass and volume measurements to determine coal washability curves is introduced. Four different coal samples were taken from the three coal mines (Highveld, Witbank, and Molteno-Indwe) in South Africa. The coal samples (8 + 2.8 mm) were sorted based on density using zinc chloride float–sink procedures (1.2–1.8 g/cm3) and RhoVol. The true densities of each fraction were determined using helium gas pycnometer for calibration of the RhoVol results. After comparing the results of experiments, it was found that the washability curve and ash analysis obtained from the RhoVol technique was in line with the washability produced by the float–sink test. The successful application of RhoVol as a new nondestructive and nontoxic approach to determine coal washability curves and density of separation for coal sorting would allow selecting the most suitable separation method.

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