Effect of mineral impurities on the charge and surface potential of coal: Application to obtaining concentrated suspensions of coal in water

Abstract

The surface charge of pulverized coal particles in water at different pH values was studied and the surface potential was shown to reach —50 mV at 20°C. The surface charge essentially originates from the presence of mineral impurities. The effect of these mineral impurities on the surface potential of the coals was then studied: the point of zero charge was a direct function of the SiO 2/ Al 2O 3 molar ratio of the mineral impurities contained in the coal (linear dependency). These mineral impurities have a majority effect in creating an electric double-layer shell around the coal particles. Having found this, we were able to prepare stable, fluid concentrated suspensions (up to 72% coal by weight) in water in the presence of sodium tripolyphosphate and sodium lignosulfonate, which are also stabilizers and thinners of concentrated suspensions of clay (drilling muds, for example).