Enhancement of the wettability of coal powders using surfactants

The wettability of coal powders in the presence of a series of ethoxylated alkylphenols and other commercial surfactants has been studied in this thesis with an objective to enhance the effectiveness of water sprays in dust suppression.;The Walker sink time method for measuring wettability of coal particles was modified to obtain more reliable data. In addition, a new technique (Imbibition Time Measurements) was developed to determine the engulfment time of coal particles. Kinetic adsorption studies were carried out to determine the mechanism of adsorption of an ethoxylated nonylphenol on coals of different rank. In addition, selected contact angle measurements were made to explain wetting phenomena.;From the wetting tests a minimum concentration of the surfactant necessary to wet the coals was determined and it was found to be independent of the coal rank but was dependant upon the number of ethoxy groups in the surfactant molecule. An HLB number of 13.4 was found to be optimum for wetting a hvA bituminous coal reflecting the importance of the adsorption phenomena at the various interfaces in the three-phase system. The higher rank coals were found to be more easily wetted than were the lower rank coals.;The short time contact angle measurements suggest that spreading might control the engulfment of particles. From the imbibition time measurements of a large number of individual particles, the homogeneity/heterogeneity of particles with regard to their wetting behavior was determined. The imbibition times of hydrophilic particles were less than a second, while that for coal particles in surfactant solutions ranged from one to a hundred seconds. Short time adsorption studies indicate that the uptake of the surfactant involved both a rapid adsorption process at the external surface and a slow diffusion process.;It is proposed that at low surfactant concentrations, the nonionic surfactant adsorbs through both hydrophobic and hydrophilic interactions with the molecule lying parallel to the surface. Under such conditions coal becomes more hydrophobic and wetting is not possible. At higher concentrations 'surface micelles' form at the hydrophobic sites through hydrophobic chain interaction and wetting is spontaneous under such conditions.