Impact of chemical and physical treatments on freeze-thaw dewatering of fluid fine tailings

Abstract

Fluid fine tailings (FFT) are a by-product of the oil sands bitumen extraction process and are composed of sand, fines (silts and clays), water, and residual bitumen. FFT can take decades to settle without intervention due to the small size of particles suspended in the water, resulting in a large footprint of environmental disturbance. Therefore, FFT are required to be managed to create a sustainable terrain for mine closure. In this study, a simple, rapid, and one-cycle directional desiccation-freeze-thaw method was developed on a small laboratory scale under a three-dimensional closed freezing condition. Two types of chemically and physically treated fluid fine tailings were prepared by two approaches: 1) two types of fluid fine tailings were flocculated with an anionic polyacrylamide and dried to four different desiccation points; 2) two types of fluid fine tailings were coagulated with alum, followed by flocculation with the anionic polyacrylamide. The chemically amended FFT samples were then subjected to shear energy to simulate pipeline transportation. The sheared-FFT were dried to four different desiccation points. All the dried materials prepared by the two approaches were frozen at −15 °C for 24 h and then completely thawed at room temperature. Four factors were discussed to assess the impact on the freeze-thaw dewatering effect: coagulant addition, flocculent dosage, shear energy input, and desiccation point. In addition, a term of water layer index was introduced to evaluate the tailings management performance.