Acoustic and electrophoretic mobilities of coal dispersions

Abstract

The electrokinetic characterization of coal dispersions with ultrasonics is demonstrated. Ultrasonics offer several advantages over conventional electrokinetic techniques such as microelectrophoresis, mass transport, or streaming potential, which require extreme dilution, a narrow concentration range, or packed beds. Some of the more important advantages of ultrasonics are (i) a wide range of particle sizes can be utilized, from ions to aggregates, (ii) coal concentrations can range from a few tenths of a percent to volume-filling systems, (iii) samples can be optically opaque or photosensitive, and (iv) measurements can be made on flowing streams applicable to on-line applications. It is demonstrated that colloid vibration potentials or acoustic mobility measurements can be successfully utilized to characterize the electrokinetic properties of concentrated coal dispersions. Experimental results for dilute coal dispersions are compared to the theory of Enderby and Booth and an independent technique, namely, microelectrophoresis. It is also demonstrated that colloid vibration potential measurements in concentrated coal dispersions can be explained by using the Levine, Neale, and Epstein cell model approach proposed by Marlow, Fairhurst, and Pendse. Evidence suggests that measurements in dilute coal dispersions cannot be extrapolated with reasonable confidence to particle concentrations typical of process conditions, an effect observed by others. The focus of this work, however, is to describe a technique that can be used to explore the reasons for this discrepancy because of its versatility with coal concentration. At coal concentrations comparable to process conditions significant deviations from ppm studies result. Deviations include the shifting of isoelectric points as well as the appearance of maxima in the mobility versus pH dependence. The deviations are proposed to result from the dissolution of the coal matrix with subsequent deposition onto the coal surface, although this work is not definitive in this regard.The coal-water interfacial chemistry is controlled by coal rank, mineral content, surface functional groups, pore structure, adsorption, pH, ionic strength, etc. These interactions can be probed by using electrokinetic techniques.1-12 Electrokinetic techniques presently used to study the coal-water interface include microelectrophoresis, mass transport, and streaming potential.13 Although these techniques are invaluable to the study of coal-water interactions, they cannot be used for the wide range of conditions that occur in processing coal water dispersions.+Presented at the Symposium on the Surface Chemistry of Coals, 193rd National Meeting of the American Chemical Society, Denver, CO, April 5-10 1987.These techniques require extreme dilution (microelectrophoresis), a narrow concentration range (mass transport), or packed beds (streaming potential). As a result, questionable extrapolations (see below) to process conditions must be performed.Below we describe a relatively new electrokinetic tech...

Dispersion of H−Magadiite and H−Kenyaite Particles by Ion Exchange of H+ with Alkali Ions

“…The colloid vibration potential (CVP), pH, and solution specific conductivity were measured using a Pen Kem System 7000. The relative acoustophoretic mobility (RAM) was calculated from the CVP which is related to the ζ potential through RAM = C ζ ( C is a positive constant) …”

Kinetics of colloidal deposition, assembly, and crystallization in steady electric fields

“…Other values reported in Table 1, and which are needed for the modeling are: (i) the free particle electrophoretic mobility (U 0 /E); (ii) K 2 , the estimated O(f) correction to the particle velocity, U(f) = U 0 (1 + K 2 (f)) for the deposition and for the relaxation portions of the experiments. [29][30][31] K 2 accounts for the effects of hydrodynamic interactions on field-induced particle convection, including the effects of backflow. We experimentally measure U 0 for all deposition conditions from data collected at short times when the particle concentration is low; details of these measurements are included in the ESI.…”

“…Note that K 2 varies between deposition (field on) and relaxation (field off) experiments because of the effect of the steady electric field on the concentration dependent mobility. [29][30][31] The concentration-dependent mobility for the relaxation experiments is taken as that of amorphous hard spheres. Crystallinity and charge is known to affect the concentration-dependent mobility, and these effects have been studied by both experiment and theory.…”

Colloid Vibration Potential and Ion Vibration Potential in a Dilute Suspension of Spherical Colloidal Particles

“…Dukhin et al. − and Shilov et al further developed a general theory of CVP for concentrated suspensions. The readers are also referred to Zana and Eager, Marlow and Rowell, Hunter, and Dukhin and Goets…”