Wettability Modification of Lignite by Adsorption of Dodecyl Based Surfactants for Inhibition of Moisture Re‐adsorption

Abstract

In order to restrain moisture re-adsorption of dried lignite, a series of dodecyl based surfactants with various hydrophilic heads including dodecyltrimethylammonium bromide (DTAB), sodium dodecyl sulfonate (SDS), dodecyl nonaethoxyl ether (C 12 EO 9 ) and a gemini surfactant (G12-2-12) were used to adsorb on lignite surface for wettability modification. The adsorption isotherms and zeta potential were determined to study the adsorption process. Lagergren-first-order and pseudo-second-order kinetics models were used to simulate the adsorption kinetics. The modified lignite was characterized by FTIR spectroscopy, and the wettability of it was evaluated by the wetting heat and moisture re-adsorption ratio. The results indicate that hydrophilic heads of surfactants play an important role in adsorption mechanisms and structures of their adsorption layers on lignite surface, which are responsible for wettability alteration. Four surfactants produce different effects on restraining moisture re-adsorption of lignite: the effect of cationic surfactants is better and worse for anionic surfactant SDS, while the nonionic surfactant C 12 EO 9 shows intermediate behavior. But with the formation of double-layer adsorption, hydrophilic headgroups of surfactant face outward, which causes hydrophilicity of lignite to rise again. Combining adsorption situations and wettability modification effects, the relationship between molecular orientation of four surfactants on a lignite surface and wettability reversal of lignite are discussed.

Improvement of Low‐Rank Coal Flotation Based on the Enhancement of Wettability Difference between Organic Matter and Gangue

“…Adsorption isotherms combined with the corresponding zeta potential measurements were often used for adsorption mechanism analysis (Liu and Liu, 2017; Markiewicz et al, 2013; Rosen and Kunjappu, 2012). Figures 4 and 5 display the results of adsorption capacity and the zeta potential, respectively.…”

“…On the one hand, Ca2+ promotes the surfactant adsorption layer more compact on the gangue surface. It has been reported that the adsorption of non‐ionic surfactant had less influence on surface charge of coal (Liu and Liu, 2017). In this study, the Ca 2+ was added to the liquid system after surfactant adsorption equilibrium to reach the new adsorption equilibrium.…”

“…The separated supernatant solution was used for quantitative analysis of the C 12 EO 15 adsorption, and the separated solid particles were collected for follow‐up experiments. The concentration of purified supernatant was measured by UV–Vis spectrophotometer (Persee TU‐1901 Model UV, China) at the wavelength of 500 nm (Liu and Liu, 2017). The standard curve of C 12 EO 15 is shown in Fig.…”

“…At the same time, the high concentration of cationic surfactant was not conducive to adsorption between the coal and collector as well as the adhesion between the coal particles and bubbles (Xia et al, 2019). The anionic surfactants had poor adsorption on the surface of low rank coal due to the electrostatic repulsion of surfactant and coal surface (Liu and Liu, 2017). In response to the low adsorption capacity and selectivity, researchers found that the surfactant mixtures could reduce the total amount of surfactants used, and it could achieve relatively high selectivity and catchability (Ejtemaei et al, 2011; Geng et al, 2019; Parekh et al, 2011).…”

Enhancement of Flotation Performance of Oxidized Coal by the Mixture of Laurylamine Dipropylene Diamine and Kerosene

“…Lin Li et al [6] prepared an emulsified collector with NP-10/n-pentanol/diesel/water, reduce the particle size of diesel, reduce the required quality of diesel by 70%, reduce the amount of foaming agent, however, the emulsified collector has a slightly poorer selectivity, and the ash content of the clean coal has increased. For cationic and anionic surfactants, Liu and Liu [13] studied the effect of surfactants with different structures on the surface hydrophobicity of low-rank coals, as a result, the polar groups of the cationic surfactant are adsorbed on the surface of the low-rank coal with negative electricity through the action of strong electrostatic force. Make the hydrophobic alkyl chain facing outward, effectively improving the hydrophobicity of low-rank coal, the polar groups of anionic surfactants have an electrostatic repulsion effect on the surface of low-rank coals, making it impossible to effectively improve the hydrophobicity.…”