Role of Mixing Energy in the Flocculation of Mature Fine Tailings

Abstract

High-molecular-weight polymer flocculants are used for accelerated dewatering of mature fine tailings (MFTs) to reclaim the land occupied by containment ponds. Two anionic polymers were used to flocculate an MFT sample containing 98% by weight of fines smaller than 44 μm in diameter, with 85% of this fraction being clay minerals. The polymer solutions and polymer-treated MFT followed the Herschel-Bulkley and Bingham equations of state, respectively. The coupling of shear thinning and structural breakdown of the flocculated MFT gave rise to cavern formation during mixing. The mixing energy input for a series of MFT flocculation tests, in which other conditions were held constant, was proportional to the mixing time. The mixing tools used for the flocculation process were a Rushton turbine (RT), a pitched-blade turbine (PBT), a vane, and hydrofoil impellers. The flocculation outcome was evaluated on the basis of the amount of water released and the capillary suction test time (CST). The CST of the treated MFT was inversely proportional to its water release volume in settling columns. There was a clear peak in the rate of water release and a minimum in the CST as a function of mixing time, clearly showing that there is an optimal mixing energy that corresponds to the most rapid dewatering of flocculated MFT.