Rheological properties of coal-based colloidal composite binder for iron ore pelletization

The rheological properties of an innovative coal-based colloidal composite binder (3Co-Binder) prepared via alkaline–oxygen excitation and mechanochemical synthesis are revealed. Derived from low-rank coal, 3Co–Binder is applied in iron ore pelletization as a replacement for traditional bentonite, with the aim of improving the iron grades of the pellets. Cryoscanning electron microscopy revealed that 3Co-Binder exhibits a densely populated, porous network structure. It was determined to be a pseudo-plastic fluid with yield stress and shear-thinning characteristics. The stability of 3Co-Binder was influenced by the humic acid extraction rate, temperature, and static placing time. An extraction rate of humic acids above 96% was found to prevent sedimentation of 3Co-Binder, while lower temperatures and prolonged static placing time increased its apparent viscosity. A storage duration of less than 2 weeks and a temperature range of 25–35 °C were found to be optimal for maintaining the stability of 3Co-Binder. The viscous flow activation energy of 3Co-Binder remained stable at approximately 60 kJ mol^–1 as the shear rate increased from 0.5 to 5 s^–1. However, at higher shear rates, up to 100 s^–1, the viscous flow activation energy decreased to 46.48 kJ mol^–1. To ensure stability and dispersibility during storage, the rheological parameters of 3Co-Binder must meet the following criteria: yield stress below 10 Pa, consistency coefficient below 1.5 Pa s, non-Newtonian index below 1, and apparent viscosity below 10,000 mPa s at a shear rate of 1 s^–1.