Adsorption of Surfactants on Coal Surfaces in the Coking Wastewater Environment: Kinetics and Effects on the Slurrying Properties of Coking Wastewater–Coal Slurry

Coking wastewater, instead of clean water, is used to prepare coking wastewater–coal slurry (CWCS), which can be used as liquid fuel for combustion and gasification. Surfactant adsorption on coal surfaces affects the preparation and industrial application of coal slurry because it is essential for improving the surface wettability of coal. The study of the adsorption kinetics of surfactants on coal surfaces contributes to mastering the adsorption behavior of surfactants on coal surfaces. In this work, we focused on the influence of the internal components (phenol, quinoline, indole, NH₄⁺–N, and metal ions) of coking wastewater on the adsorption kinetics of surfactants on coal. Adsorption kinetics was determined by fitting the adsorption capacity of surfactants at different adsorption times with the pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. Then, the effects of the internal components of coking wastewater on the slurrying characteristics of CWCS were analyzed. Results showed that adsorption closely followed the pseudo-second-order model and was controlled by the mechanisms of liquid membrane diffusion, surface adsorption, and intraparticle diffusion. The influences of various internal components of coking wastewater on the secondary adsorption rate k₂ likely remained unclear because the models cannot effectively address the competition and promotion effects between wastewater components and the surfactant. Organic and inorganic components increased surfactant adsorption on coal surfaces but exerted different influences on the slurryability and stability of the coal slurry. Specifically, organic components increased slurryability but slightly decreased stability, whereas inorganic components decreased slurryability but increased stability.