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

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.

KEYWORDS:

• Coal
• density
• RhoVol
• 3D image processing
• float–sink
• washability
• pycnometry

Acknowledgments

We gratefully acknowledge that this study was supported by North West University. We also express our appreciation to De Beers Group for financial support and laboratory facilities. We are thankful to Dr. Garry Morrison for his support and valuable suggestions during this research work.

Disclosure statement

No potential conflict of interest was reported by the author(s).