Effect of Addition Flowrates of Grafted Polymers on the Flocculation of Kaolinite Suspensions and Oil Sands Mature Fine Tailings
Creators: Sloetjes, Kilian
Publisher: name: University of Alberta Library
Year: 2023

<p>Bitumen extracted from oil sands has been a major source of wealth for Canada, but it comes at a high price because the Clark hot water process generates large volumes of tailings which must be stored in ponds that threaten the environment. These tailing ponds must be treated to meet the land reclamation targets implemented by the government of Alberta. <br>
Tailings are mixtures of clays and sands (~ 30 %), water (~ 70 %) and residual bitumen. Mature fine tailings (MFT) are hard to treat because colloidal interactions stabilize the suspended fine clay particles. The efficiency of the several methods used to treat tailings is low, limiting soil recovery and industry sustainability. One method used for tailings treatment is flocculation. Its aims are to gather tailing particles into large flocs that settle fast (by gravity or helped by mechanical means), recover the process water, and reduce the volume of tailing ponds. Flocculants, such as neutral or negatively-charged polyacrylamides, are typically added to tailings, but the flocs they generate break under shear, retain water, and leave fine solids behind in the supernatant water. <br>
This thesis is dedicated to enhancing oil sands tailings treatment by changing hydrophobicity and cationic charge of natural polymers. Specifically, I grafted cationic polymers onto amylopectin backbones via free radical graft polymerization and tested the performance of the new amylopectin-graft-poly<a href="AP-g-PVBTMAC" rel="noopener noreferrer" target="_blank">(vinylbenzyl)trimethylammonium chloride</a> by flocculating MFT (diluted to 10 wt.%) and measuring the initial settling rate, supernatant turbidity, capillary suction time (CST), and sediment solids content. I also compared different AP-g-PVBTMAC microstructures to find the optimum graft length and frequency, and combined the best AP-g-PVBTMAC with a commercial high molecular weight anionic polyacrylamide (Magnafloc ® 1011, MF1011) to investigate how polymer addition flowrates affected kaolinite suspensions. <br>
Unlike the dosage, the polymer microstructure parameters (graft length and frequency) did not influence much the flocculation, but AP-g-PVBTMAC outperformed the homopolymer PVBTMAC, and the blend of pure AP and PVBTMAC in all flocculation metrics, proving that the amylopectin backbone plays an important role in the flocculation and dewatering. When combined with MF1011, focused beam reflectance measurements (FBRM) showed that addition flowrates determined the size and structure of the flocs as well as fines capture. A minimum addition flowrate of AP-g-PVBTMAC was required to destabilize the suspension and to form primary flocs, which could then grow through combined charge neutralization and bridging mechanism with MF1011. While the addition flowrate of the cationic flocculant affected CST and turbidity, the addition flowrate of the anionic flocculant mattered for flocs solids content based on the central composite design results. </p>