Coal washability determination using RhoVol technology

Abstract

Density is one of the key properties of coal and provides information about its physical and chemical composition. Washability analyses (or densimetric information) are used to specify the yield and quality of clean coal produced in coal processing plants. Traditional coal washability analysis is determined by conducting a sink-float test. However, this method involves environmentally hazardous chemicals, is expensive, time-consuming, and is highly dependent on the expertise and experience of the operator. Therefore, the research to develop an alternative technique for determining coal washability would be highly applicable, especially in a coal-rich country like South Africa. In this study, an alternative method based on a 3D imaging system, the RhoVol Density Measurement System (De Beers Group IgniteTM), where the densities of individual particles are determined using mass and volume measurements, was introduced. This technology can instantly, repeatably, and efficiently produce the density distribution of a batch of particles. Additional data, like shape and particle size, are also calculated and recorded per particle. The RhoVol is equipped with a sorting functionality that enables the operator to sort the sample into bins according to any captured particle parameters such as density, compactness, flatness or elongation. This study aimed to determine whether RhoVol can be used as an alternative method for coal washability determination. Four different coal samples were taken from the three coal fields (Highveld, Witbank, and Molteno-Indwe) in South Africa. The coal samples (-8 mm +3 mm) were analysed using the traditional zinc chloride float-sink method and RhoVol. Helium pycnometry (true density) was used for the calibration of the RhoVol results. It was found that the correlation coefficients (R2) between pycnometry data and the Rhovol were higher than 0.97 after the application of a correction factor. Based on this correlation, a linear correction was applied to the RhoVol output data to estimate the true density distribution. The washability curves generated using RhoVol were in agreement with the washability information produced by the float-sink test. Our findings showed that RhoVol can be used in the determination of coal washability data in a non-destructive and non-toxic way.