Authored by Guven O*
Abstract
Characterization of inter-particle forces between fine particles is very important on their processing behavior either via flotation, coagulation or dewatering separation. Besides particle size and solid wt. %, these interactions are mainly influenced by surface chemistry which in turn dependent on pH, electrolyte concentration and reagent concentration. In this study, the particle interactions were modelled with classical DLVO theory and correlated with rheological properties of different coal samples (Soma, Agacli, Siberia) which were reported in previous studies [1].The results indicated that in contrary to particle-bubble interaction during flotation, the higher the energy barrier height between particles will increase the viscosity and quality of coal-water slurries. Therefore, these findings highlighted the importance of modelling the particle-particle interactions and their relationship with rheological indices prior to experiments.
Keywords: DLVO; Coal; Rheology
Opinion
Based on the depletion of present fuel reserves in the world, many investigations are carried out for finding alternatives. Thus, coal-water slurries (hereafter CWS) is one of these alternatives that consists of finely dispersed coal particles suspended in water. A commercial CWS includes 55-70% fine coal, 25-40% water and 1% chemical additive [2] while these values are effective on the basic characteristics like viscosity, density and fluidity of mixtures that constitute their quality and selling conditions. As well known, the flow and the stability characteristics vary upon physical and physicochemical properties of coal suspensions, regarding volume fraction of solids, particle size, size distribution, temperature, concentration of salt and thus particle-particle interactions in mixture. Therefore, modeling of these interactions is significant for determining the relevant characteristics of suspensions by means of the movement of very fine particles dominated by surface forces [3]. In this manner, DLVO theory (Derjaguin-Landau-Vier-Overbeek theory) is the most commonly used assumption consisting of attractive London van der Waals and repulsive electrostatic double layer forces for modeling the colloidal dispersion stability. Figure 1 shows a typical potential energy vs. separation distance (h) for particle-particle interaction.
VTOT shows the energy barrier which is used to define the maximum repulsion between particles. When the height of this energy barrier is high, particles will be in the dispersed form while they will coalesce at lower heights [3,5].
In consequence, the aim of this study is to model the coal particle interactions by classical DLVO theory and suggest a correlation between their rheological indices and theoretical energy barrier.
Materials and Methods
As mentioned in “Introduction” section, only the modelling of reported values and accordingly their responses as barrier heights were examined in this study. Therefore, both the characteristics of samples and other experimental measurements were prepublished, and the methods were extensively explained in aforementioned papers [2]. However, in order to give introduction about the materials characteristics and methods, both the methods and the outputs from these tests were briefly explained and reevaluated with relation to their calculated energy barrier heights.
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