An estimated 700 million m3 of mature fine tailings (MFT) have accumulated, and continue to accumulate, in a growing number of containment ponds. Various combinations of mechanical and chemical treatments have been proposed for reclaiming tailings ponds, but a common theme is that they involve a critical amount of mixing. If too little mixing energy is introduced, the chemical additives are not adequately dispersed into the tailings, resulting in poor performance. If too much mixing energy is added, the shear tears flocs apart, regardless of the chemistries used. The “Goldilocks zone” of proper mixing can be small and elusive, and missing it can severely hamper dewaterability. However, the chemistries employed can affect the size of this window.
In this research, MFT samples were treated with different chemical additives. A rheometer equipped with a helical stirring shaft was used to record mixing speed and torque as a function of time, allowing mixing energy inputs to be carefully measured. It was observed that when high molecular weight ionic polymers were dosed into MFT, torque sharply rose, making it easier to overmix. Lower-molecular weight and nonionic additives, conversely, resulted in a gradual increase in torque, allowing for better mixing control. Blending additives selected from both groups can result in mature fine tailings that not only dewater, but also are tolerant of a broader range of mixing energies.