Mechanism analysis of DTAB on the change in surface wettability of low-rank coal and its relationship to flotability

The mechanism of dodecyltrimethyl bromide (DTAB) on the change in surface wettability of low-rank coal and its relationship to flotability were investigated in this study. Experimental tests of contact angle, water re-adsorption, fourier transform infrared spectroscopy, van Oss-Chaudhury-Good theory, induction time, and flotation were conducted to analyze the surface hydrophilicity/hydrophobicity, group composition, free energy composition, and flotability. The results indicated that the adsorption capacity of water on low-rank coal first increased and then decreased with increasing DTAB concentration. DTAB can significantly improve the surface hydrophobicity because the oxygen-containing sites on the coal surface were covered by the DTAB head group. The calculation of surface free energy predicted the trends in the change of water-adsorbing ability. Furthermore, the calculation of interfacial interaction free energy proved that the appropriate DTAB concentration is indeed beneficial to prevent the water adsorption. With respect to flotability, it is shown that the addition of DTAB enhanced the flotation yield when DTAB concentration is less than 1.75 mM. The change in flotation yield is closely related to induction time. A lower induction time indicates stronger interaction between the coal particles and bubbles, and will result in high flotation yield.