Rapid tailings dewatering by flocculation-sedimentation-filtration-microwave sequential treatment

Abstract

Achieving low-water-content oil sands fluid fine tailings (FFT) for reclamation is a significant challenge, even with the otherwise effective dewatering methods such as pressure filtration. FFT from mineable oil sands processing comprises high concentrations of clays,which impede its dewatering. This study established a classification of the dominant forms of water in oil sands tailings, namely free water (FW), interstitial pore water (IPW), vicinal pore water (VPW), and surface-bound water (SBW), based on the ease of their removal in dewatering. Most FW and IPW could be removed by sedimentation and filtration following chemical treatment with polymeric flocculants and coagulants. However, removing the VPW and SBW by mechanical dewatering methods was very challenging. Microwave heating was found to be an effective alternative to remove part of the VPW and SBW from filtered FFT or to facilitate subsequent water removal treatment by other less energy-intensive methods, such as air drying. Based on these findings, we propose a concept of an oil sands tailings dewatering process for targeted removal of different forms of water by specific methods. It consists of a sequential chemical treatment of FFT with a flocculant and coagulant, followed by gravity sedimentation and vacuum filtration to remove FW and IPW, generating 50–55 wt% solids filter cakes. This is followed by a microwave treatment with or without subsequent air drying to partially remove the VPW and SBW, achieving ≥65 wt% solids in filter cakes that would be ready for preliminary reclamation activities.