Adsorption of hydrophobically modified polyacrylamide P(AM-NaAA-C16DMAAC) on model coal and clay surfaces and the effect on selective flocculation of fine coal

Abstract

Selective flocculation separation has been widely used in fine coal flocculation. In order to promote the adsorption selectivity of flocculants onto coal surface, hydrophobically modified polyacrylamide P(AM-NaAA-C16DMAAC) was synthesized. The adsorption of P(AM-NaAA-C16DMAAC) on model clay and coal surfaces (i.e., silica, alumina and asphaltene surfaces) was investigated using quartz crystal microbalance with dissipation (QCM-D) monitoring technique. Floc size distribution, Fourier transform infrared spectrum, zeta potential measurement and selective flocculation flotation test were also conducted to study the performance of P(AM-NaAA-C16DMAAC) in the separation of fine coal. QCM-D measurements showed that a thin and rigid adsorption layer was formed on silica and alumina surfaces after injecting 1 mM sodium hexapolyphosphate (Calgon). This pre-formed layer inhibited the further adsorption of P(AM-NaAA-C16DMAAC) on silica and alumina. Meanwhile, the asphaltene surface could not be passivated by calgon due to the weak and reversible adsorption. Thus, a significant amount of P(AM-NaAA-C16DMAAC) (20 mg/L) absorbed on the calgon-treated asphaltene surface in 100 mM KCl solution was detected. With 20 mg/L P(AM-NaAA-C16DMAAC) in 100 mM KCl and 1 mM calgon solution, the maximum diameters of 10%, 50% and 90% of the cumulative volume distributions of the floc, i.e., d10 (20.29 μm), d50 (45.55 μm) and d90 (89.99 μm) of the coal floc were 7.42, 3.20 and 2.19 times of those of kaolinite floc, respectively. Clean coal with a combustible recovery of 80.87% and ash content of 9.78% was obtained at a dosage of 5 g/t of P(AM-NaAA-C16DMAAC) and 900 g/t kerosene. Experimental results demonstrated that selective flocculation flotation with P(AM-NaAA-C16DMAAC) could enhance the recovery of fine coal particles with a lower dosage of collector. Our work sheds lights on the fundamental and practical understanding of the hydrophobic interactions in the selective flocculation of coal in the industries, and rational development of flocculants with better selectivity and flocculation efficiency.