Predictions of triboelectrostatic separation of minerals in low-rank coal based on surface charging characteristics in relation to their structures

Abstract

Clay minerals are the inorganic components in low-rank coal, which are particularly hard to remove as they commonly stick to the organic carbonaceous parts. Surface tribocharging characteristics including charge-to-mass ratio and specific resistivity of three typical minerals (kaolinite, montmorillonite and quartz) and clean coal under different relative humidity and temperature conditions were investigated in the present study for the prediction and evaluation of their effect on triboelectrostatic separation. X-ray diffraction (XRD) and X-ray fluorescence (XRF) were applied to minerals for phase and element identification, their microstructures features were also provided for supplementary analyses. Four candidate materials (stainless steel, copper, polyvinyl chloride and polyamide) for tribo-charger were arranged in charge-to-mass ratio measurements. Stainless steel would be the best choice for tribocharging three minerals and clean coal, which could be gathered in opposite plates with a considerable charge gap. Copper could also be a good choice in dry ambient atmosphere. In both comparison of charge-to-mass ratio and specific resistivity, separation efficiency order of three minerals were same in predictions as kaolinite ＞ quartz ＞ montmorillonite. Montmorillonite is weak in charging and holding charges, and the most likely factors should be its interlayer swelling with water molecules and greater isomorphous substitution, which makes it the hardest to separate from coal among three minerals. A basic separating could be achieved if the relative humidity is kept in low range but better results need to be reached under higher environmental temperature.