CTAB Adsorption On Lignite And The Oxidized Coal And Surface Wettability Modification

With porosity and amount of oxygen-functional groups, lignite holds character of highly hydrophilic. When putting in air, it dried by ordinary technology at105～110℃could re-absorb moisture, so it has important industrial value that changing the wettability and hydrophilic ity of lignite. Absorbing cetyl-trimethyl ammonium bromide (CTAB) surfactant in solution is always used to achieve this goal. The adsorption behavior of CTAB on coal samples was systematically studied in this thesis, which contains characters of lignite and solution.Lignite and oxidized coal, as adsorbents, have significant influence on the adsorption process. The results showed that oxygen-containing function groups contained in lignite increased with the increase of oxidation time, as well as adsorption in CTAB solution, which due to the obviously decrease of heat of wetting of oxidized coal adsorbed CTAB. The heat of wetting of lignite decreased by27.12%and3#oxidized coal decreased about42.47%by dealing with CTAB solution with initial concentration at100mg/L and tempeture at25℃, which showed that the modification of lower rank coal is more effective. On the other hand, demineralized coal had more adsorption for CTAB than lignite because former has larger specific surface area with pickling treatment, which removed hydrophilic minerals, such as quartz, kaolinite, ettringite, biotite, etc. What’s more, the adsorption process was also influenced by different size ranges and specific surface area of lignite:the adsorption increased with decreasing particles and enlarging specific surface area of lignite.For the study of adsorption characteristics of surfactants on the surfaces of oxidized coal and its influence on coal surface wettability, the effects of solution temperature, initial concentration, pH value, and adsorption time on the cationic surfactant CTAB adsorbing capacity on the oxidized coal surface were investigated. The influence of adsorbing CTAB on the oxidized coal surface wettability modification has been studied. The obtained results showed that enhancement of CTAB solution temperature and initial concentration can increase the adsorption quantity of CTAB on the oxidized coal surfaces. It was observed that the optimum pH value for the adsorption process of CTAB on coal surfaces was range from pH6to pH8. It was proved that the adsorption capacity of CTAB on coal surfaces increased with a rise in the amount of oxygen containing functional groups for all the studied samples. The adsorption of CTAB on the oxidized coal surfaces leads to a very significant change of the contact angle change with time from the sharp decrease into decreased slightly, as well as equilibrium contact angle changed from0°to70°, both of moisture re-absorption and heat of wetting decline. These changes are attributed to the wettability alteration from hydrophilicity to hydrophobicity of CTAB adsorption on the coal surfaces.