Adsorption Characteristic Of Surfactant Onto Lignite Surface And Its Influence On Coal Wettability

The pore structure and oxygen-containing groups of lignite are remarkably abundant. Association with water molecules is the reason of strong polar, for which lignite is vulnerable to modification and could not be made the most efficient use of. The means of lignite upgrading and dewatering were restricted because of heavy energy consumption and serious pollution, such as hydrothermal and thermal treatments. Surfactants have closer and closer relationship with surface wettability changes on account of the special molecular structure, which is composed of hydrophilic group and hydrophobic group. The hydrophobicity of lignite can be enhanced in theory by the reason of the hydrophilic ends of Surfactants being connected to the hydrophilic oxygen-containing groups on the surface of lignite and hydrophobic ends orienting solution. The type of hydrophilic groups of surfactant, the adsorption characteristics and mechanism of surfactants on lignite, the oxygen-containing groups of which are inevitably considered to be significant factors of lignite surface wettability changes owing to surfactants.This paper conducted a series of adsorption experiments of CTAB, gemini cationic surfactants and SDBS, SDS anionic surfactants systematically and investigated the impact of which on the wettability changes of lignite. The impact of oxygen-containing groups on the adsorption quantity of CTAB, gemini and wettability changes of lignite was studied with the preparation of oxidized coal by hydrogen peroxide oxidation. The adsorption mechanism of gemini cationic surfactant on lignite was deliberated. And the main results of this paper are shown below:1. The adsorption quantity on lignite rise with the increase of the concentration and temperature of surfactants. And cationic surfactants have higher adsorption capability, which play a prominent part in the improvement of the hydrophobicity of lignite. And the modification effect of gemini is more remarkable than CTAB.2. The quantity of oxygen-containing groups on the surface of lignite can be added by oxidation of hydrogen peroxide, which increase with the extension of time and the augment is not obvious when oxidation time exceeds 12 h. The adsorption quantity of CTAB and gemini surfactants on oxidized coal rise with the content of oxygen-containing groups. Hydrophobicity of oxidized coal and lignite can be enhanced by the adsorption of CTAB and gemini cationic surfactants and the change of surface wettability of oxidized coal is more conspicuous. The hydrophily would increase as a result of multimolecular layer adsorption on the condition of high CTAB surfactant concentration and high content of oxygen-containing groups on the surface of oxidized coal.3. Electrostatic force is the driving force of gemini surfactant adsorption on lignite. Hydrophobic interaction would be the main driving force rather than electrostatic force on the condition of certain ionic strength. And it can be demonstrated that hydrogen bonding plays a slight role in the adsorption of gemini surfactant on lignite. It can be concluded that the adsorption force could not be damaged by mechanical agitation at room temperature, which suggests adsorption is irreversible. The adsorption can be enhanced if gemini surfactant being put into alkaline environment or inorganic salt KCl being added to, especially on the condition of low concentration of gemini surfactant. The phenomenon of multimolecular layer adsorption is not likely to occur and the hydrophobicity of lignite could be reinforced effectively.