Eco-friendly utilization of waste oil for preparing coal water slurry: Additive suitability and dispersion mechanism

• Industrial waste oil was recycled for eco-friendly utilization. • The optimal additive and composition of waste-oil-coal-water slurry were determined. • Viscosity reduction effect of Tween 80 in the waste oil-coal-water slurry was best. • The interface properties of coal particles, oil, and water were studied. • Dispersion and stabilization mechanism for waste oil-coal-water slurry was proposed. Industrial waste oil is a type of hazardous waste with a high calorific value. Mixing it with coal for combustion or gasification is an environmentally friendly and efficient way of recycling. Here, the suitability of additives for waste oil-coal slurry and waste oil-coal-water slurry was investigated experimentally, and their dispersion and stabilization mechanisms were also explored. The results show that water-soluble additives such as Tween 80, MF and xanthan gum form reverse micelles in the oil phase of the waste oil-coal slurry, which results in agglomeration and failure to function as intended. Of the different additives, the viscosity reduction effect of Tween 80 in the waste oil-coal-water slurry was best. Further, the comprehensive performance of the waste oil-coal-water slurry, including slurry ability, stability and fluidity, was found to be best at a water content of 10% and a Tween 80 content of 5%. Under these conditions, a solid concentration of 45.75% results in a continuously flowing slurry with good dispersion and stability. The interface properties of coal particles, oil, and water were studied by means of Fourier transform infrared spectroscopy (FTIR) and contact angle measurements, and a dispersion and stabilization mechanism for the waste oil-coal-water slurry was proposed. In this mechanism, some of the coal particles enter the reverse micelle, causing the water core to become a hydration film on the surface of the particles, which blocks hydrophobic particle aggregation. In addition, the surfaces of some coal particles are rapidly coated with an oily film, which also inhibits particle aggregation.