Using acrylamide/propylene oxide copolymers to dewater and densify mature fine tailings

• Novel PAM-gPPO flocculate and dewater MFTs effectively.
• Shorter PPO grafts perform better than those with longer PPO grafts.
• PAM-PPO 300(86:14) performed best for flocculation, dewatering and densification.
• PAM-PPO have much lower molecular weights than commercial PAM flocculants.

Adding hydrophobic groups to polyacrylamide (PAM) flocculants improves flocculation and dewatering (settling, turbidity, capillary suction time and solids content after centrifugation) of mature fine tailings (MFT). In this study, we copolymerized different amounts of polypropylene oxide macromonomers (PPO) with acrylamide to produce PAM-PPO graft copolymers with different hydrophobicities and molecular weights. According to CST, turbidity and centrifugation results, the PAM-PPO copolymers dewatered and densified MFT more efficiently than a reference commercial anionic PAM supposedly because the PPO hydrophobic groups reduced the amount of water trapped inside the polymer floccules. Besides densifying and dewatering tailings more efficiently, the PAM-PPO copolymers had molecular weights ten times smaller than the reference anionic PAM flocculant, which reduced their viscosities and shear-sensitivities. As a result, it is easier to mix these copolymers with tailings under a wider window of operating conditions. We also observed that aged MFT (stored for approximately 10 months) were more easily dewatered, especially at high solids content (20 wt%). This behavior might be attributed to the evaporation of water, hydrocarbons, or other low molecular weight organic compounds. However, further studies are required to understand what and how chemical compositional changes alter the stability of MFT. The information generated in these studies could be used to design polymers that could target the MFT components responsible for its high stability and slow consolidation.