Wettability study of mineral wastewater treatment filter media

Filtration is a typical tertiary treatment method for oily water. The wettability of oil-in-water emulsions to filter media probably has a significant effect on oil removal efficiency during oil-bearing wastewater treatment using filtration process. Based on Washburn's equation, a lipophilic hydrophilic ratio (LHR) concept was defined and used to compare quantitatively the wettabilities of five filter media. The selected mineral filter media were magnetite, zeolite, manganese sand, quartz sand and ceramsite sand particles with a size range of +0.45–0.9 mm and the wetting liquids were apolar cyclohexane and polar deionized water. At the same time, the surface morphologies and chemical compositions of these five filters were also characterized using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The desirable reproducibility and high precision are achieved by strict control of experimental parameters. The calculated LHR values of magnetite, zeolite, manganese sand, quartz sand and ceramsite sand are 1.057, 0.640, 0.736, 0.652 and 0.877, respectively. Magnetite seems slightly lipophilic, while others are comparatively hydrophilic because of the presence of polar hydrophilic Si–O bonds on surfaces. Probably owing to smoother surface, wetting rates of both cyclohexane and water for ceramsite sand are the lowest consistently. These different results of wetting behaviors and LHR values could be attributed to the differences of not only surface morphology but also chemical composition.