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SURFACE PHENOMENA IN THE DEWATERING OF COAL
Citation:
Keller, Jr., D., G. Stelma, AND Y. Chi. SURFACE PHENOMENA IN THE DEWATERING OF COAL. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/7-79/008 (NTIS FE90011).
Description:
The influence of certain surfactants on the dewatering of fine coal has been investigated. The surfactants investigated were found to have a two-fold effect. They were found to effect the pressure differentials required for dewatering in addition to the residual water contents of the coal beds attainable by this dewatering. Both effects were attributed to surfactant adsorption. Adsorption at the liquid-air interface resulted in a decrease in the interfacial tension between the two phases. The effect this decrease had on the pressure differentials required for dewatering was found to be in agreement with that predicted by the capillary theory applied to the system. Adsorption at the solid-liquid interface was correlated with the complex behavior of the residual water contents as a function of surfactant addition. A comprehensive model for the adsorption of the surfactants onto the coal was presented, based on the Stern--Grahame theory of adsorption at an electrical double layer. The model allowed for the mode of physisorption to change as the amount of surfactant adsorbed increased, and also for a phenomenon known as hemi-micellation. Using the model, consistent and reasonable results were found for the specific surface area of the coal and for the standard free energies of adsorption. The model was also found to be appropriate when the heterogeneous nature of the coal was considered. Furthermore, the hydrophobicity of the molecular groups of the molecules, expected from the model to be controlling the hydrophobicity of the interface, was found to be in agreement with that predicted by other means. (ERA citation 04:052524)